47 results on '"Masatoshi Imanishi"'
Search Results
2. eROSITA Final Equatorial-Depth Survey (eFEDS): eFEDS X-ray view of WERGS radio galaxies selected by the Subaru/HSC and VLA/FIRST survey.
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Kohei Ichikawa, Takuji Yamashita, Merloni, Andrea, Junyao Li, Teng Liu, Salvato, Mara, Masayuki Akiyama, Arcodia, Riccardo, Dwelly, Tom, Xiaoyang Chen, Masatoshi Imanishi, Kohei Inayoshi, Toshihiro Kawaguchi, Taiki Kawamuro, Mitsuru Kokubo, Yoshiki Matsuoka, Nagao, Tohru, Schramm, Malte, Hyewon Suh, and Masayuki Tanaka
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RADIO jets (Astrophysics) ,RADIO galaxies ,X-rays ,ACTIVE galactic nuclei ,STELLAR mass ,RADIO programs - Abstract
We constructed the eROSITA X-ray catalog of radio galaxies discovered by the WERGS survey, made by cross-matching the wide area Subaru/Hyper Suprime-Cam (HSC) optical survey and VLA/FIRST 1.4 GHz radio survey. We report finding 393 eROSITA detected radio galaxies in the 0.52 keV band in the eFEDS field covering 140 deg2. Thanks to the wide and medium depth eFEDS X-ray survey down to f0:52 keV = 6:5 = 1015 erg s1 cm2, the sample contains the rare and most X-ray luminous radio galaxies above the knee of the X-ray luminosity function, spanning 44 < log(L(abs;corr) 0:52 keV=erg s1) < 46:5 at 1 < z < 4. The sample also contains the sources around and below the knee for the sources 41 < log(L(abs;corr) 0:52 keV=erg s1) < 45 at z < 1. Based on the X-ray properties obtained by the spectral fitting, 37 sources show obscured active galactic nucleus (AGN) signatures with log(NH=cm2) > 22. These obscured and radio AGN reside in 0:4 < z < 3:2, indicating that they are obscured counterparts of the radio-loud quasar, which were missed in the previous optical quasar surveys. By combining radio and X-ray luminosities, we also investigated the jet production effciency jet = radPjet=LAGN;bol by utilizing the jet power of Pjet. We find that there are 14 sources with extremely high jet production effciency at et 1. This high jet value might be a result of the decreased radiation effciency of rad < 0:1, due to the low accretion rate for those sources, and/or of the boosting due to the decline of LAGN;bol by a factor of 10100 by keeping Pjet constant in the previous Myr, indicating the experience of the AGN feedback. Finally, inferring the BH masses from the stellar mass, we find that X-ray luminous sources show the excess of the radio emission with respect to the value estimated from the fundamental plane. This radio emission excess cannot be explained by the Doppler boosting alone, and therefore the disk-jet connection of X-ray luminous eFEDS-WERGS is fundamentally diffrent from the conventional fundamental plane which mainly covers the low-accretion regime. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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3. The Key Science Drivers for MICHI: a thermal-infrared instrument for the TMT.
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Packham, Chris, Mitsuhiko Honda, Chun, Mark, Itsuki Sakon, Richter, Matthew, Okamoto, Yoshiko, Hirokazu Kataza, Marois, Christian, Meyer, Michael, Puravankara, Manoj, Birkby, Jayne, Crossfield, Ian, Currie, Thayne, Greathouse, Thomas, Herczeg, Gregory, Ichikawa, Kohei, Inami, Hanae, Masatoshi Imanishi, and Lopez-Rodriguez, Enrique
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- 2018
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4. Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). III. Star formation properties of the host galaxies at z ≳ 6 studied with ALMA.
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Takuma IZUMI, Masafusa ONOUE, Hikari SHIRAKATA, Tohru NAGAO, Kotaro KOHNO, Yoshiki MATSUOKA, Masatoshi IMANISHI, STRAUSS, Michael A., KASHIKAWA, Nobunari, SCHULZE, Andreas, SILVERMAN, John D., Seiji FUJIMOTO, Yuichi HARIKANE, Yoshiki TOBA, Hideki UMEHATA, Kouichiro NAKANISHI, GREENE, Jenny E., Yoichi TAMURA, Akio TANIGUCHI, and Yuki YAMAGUCHI
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LUMINOSITY ,STAR formation ,QUASARS ,GALAXIES ,STELLAR atmospheres - Abstract
We present our ALMA Cycle 4 measurements of the [C II] emission line and the underlying far-infrared (FIR) continuum emission from four optically low-luminosity (M
1450 > -25) quasars at z ≳ 6 discovered by the Subaru Hyper Suprime Cam (HSC) survey. The [C II] line and FIR continuum luminosities lie in the ranges L[C II] = (3.8-10.2) x 108 L⊙ and LFIR = (1.2-2.0) x 1011 L⊙ , which are at least one order of magnitude smaller than those of optically-luminous quasars at z ≳ 6. We estimate the star formation rates (SFRs) of our targets as ≃ 23-40 M⊙ yr-1 . Their line and continuum-emitting regions are marginally resolved, and found to be comparable in size to those of optically-luminous quasars, indicating that their SFR or likely gas mass surface densities (key controlling parameter of mass accretion) are accordingly different. The L[C II] /LFIR ratios of the hosts, ≃ (2.2-8.7) x 10-3, are fully consistent with local star-forming galaxies. Using the [C II] dynamics, we derived their dynamical masses within a radius of 1.5-2.5 kpc as ≃ (1.4-8.2) x 1010 M⊙ . By interpreting these masses as stellar ones, we suggest that these faint quasar hosts are on or even below the star-forming main sequence at z ~ 6, i.e., they appear to be transforming into quiescent galaxies. This is in contrast to the optically-luminous quasars at those redshifts, which show starburst-like properties. Finally, we find that the ratios of black hole mass to host galaxy dynamical mass of most of the low-luminosity quasars, including the HSC ones, are consistent with the local value. The mass ratios of the HSC quasars can be reproduced by a semi-analytical model that assumes merger-induced black hole host galaxy evolution. [ABSTRACT FROM AUTHOR]- Published
- 2018
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5. Luminous quasars do not live in the most overdense regions of galaxies at z ~ 4.
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Hisakazu UCHIYAMA, Jun TOSHIKAWA, Nobunari KASHIKAWA, Roderik OVERZIER, Yi-Kuan CHIANG, Murilo MARINELLO, Masayuki TANAKA, Yuu NIINO, Shogo ISHIKAWA, Masafusa ONOUE, Kohei ICHIKAWA, Masayuki AKIYAMA, Jean COUPON, Yuichi HARIKANE, Masatoshi IMANISHI, Tadayuki KODAMA, Yutaka KOMIYAMA, Chien-Hsiu LEE, Yen-Ting LIN, and Satoshi MIYAZAKI
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QUASARS ,STELLAR luminosity function ,LUMINOSITY ,GALAXY clusters ,GALAXIES ,STAR formation - Abstract
We present the cross-correlation between 151 luminous quasars (M
UV < -26) and 179 protocluster candidates at z ~ 3.8, extracted from the Wide imaging survey (~121 deg2 ) performed as part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at >4 σ. The distributions of the distances between quasars and the nearest protoclusters and the significance of the overdensity at the positions of quasars are statistically identical to those found for g-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of g-dropout galaxies around quasars is slightly higher than that around g-dropout galaxies on 1.0-2.5 pMpc scales, while at <0.5 pMpc that around quasars tends to be lower. We also find that quasars with higher UV luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near-zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which luminous quasars at z ~ 4 reside in structures that are less massive than those expected for the progenitors of today's rich clusters of galaxies, and possibly that luminous quasarsmay be suppressing star formation in their close vicinity. [ABSTRACT FROM AUTHOR]- Published
- 2018
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6. The quasar luminosity function at redshift 4 with the Hyper Suprime-Cam Wide Survey.
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Masayuki AKIYAMA, Wanqiu HE, Hiroyuki IKEDA, Mana NIIDA, Tohru NAGAO, James BOSCH, Jean COUPON, Motohiro ENOKI, Masatoshi IMANISHI, Nobunari KASHIKAWA, Toshihiro KAWAGUCHI, Yutaka KOMIYAMA, Chien-Hsiu LEE, Yoshiki MATSUOKA, Satoshi MIYAZAKI, NISHIZAWA, Atsushi J., Masamune OGURI, Yoshiaki ONO, Masafusa ONOUE, and Masami OUCHI
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LUMINOSITY ,QUASARS ,ASTRONOMICAL surveys ,REDSHIFT ,IMAGING systems in astronomy - Abstract
We present the luminosity function of z ~ 4 quasars based on the Hyper Suprime-Cam Subaru Strategic Program Wide layer imaging data in the g, r, i, z, and y bands covering 339.8 deg
2 . From stellar objects, 1666 z ~ 4 quasar candidates are selected via the g-dropout selection down to i = 24.0mag. Their photometric redshifts cover the redshift range between 3.6 and 4.3, with an average of 3.9. In combination with the quasar sample from the Sloan Digital Sky Survey in the same redshift range, a quasar luminosity function covering the wide luminosity range of M1450 = -22 to -29mag is constructed. The quasar luminosity function is well described by a double power-law model with a knee at M1450 = -25.36±0.13mag and a flat faint-end slope with a power-law index of -1.30±0.05. The knee and faint-end slope show no clear evidence of redshift evolution from those seen at z ~ 2. The flat slope implies that the UV luminosity density of the quasar population is dominated by the quasars around the knee, and does not support the steeper faint-end slope at higher redshifts reported at z > 5. If we convert the M1450 luminosity function to the hard X-ray 2-10 keV luminosity function using the relation between the UV and X-ray luminosity of quasars and its scatter, the number density of UV-selected quasars matches well with that of the X-ray-selected active galactic nuclei (AGNs) above the knee of the luminosity function. Below the knee, the UV-selected quasars show a deficiency compared to the hard X-ray luminosity function. The deficiency can be explained by the lack of obscured AGNs among the UV-selected quasars. [ABSTRACT FROM AUTHOR]- Published
- 2018
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7. Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 quasars and luminous galaxies at 5.7 < z ≤ 6.8.
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Yoshiki MATSUOKA, Masafusa ONOUE, Nobunari KASHIKAWA, Kazushi IWASAWA, STRAUSS, Michael A., Tohru NAGAO, Masatoshi IMANISHI, Chien-Hsiu LEE, Masayuki AKIYAMA, Naoko ASAMI, James BOSCH, Sébastien FOUCAUD, Hisanori FURUSAWA, Tomotsugu GOTO, GUNN, James E., Yuichi HARIKANE, Hiroyuki IKEDA, Takuma IZUMI, Toshihiro KAWAGUCHI, and Satoshi KIKUTA
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QUASARS ,GALAXIES ,RADIO sources (Astronomy) ,TELESCOPES ,BAYESIAN analysis ,PROBABILITY theory - Abstract
We present spectroscopic identification of 32 new quasars and luminous galaxies discovered at 5.7 < z ≤ 6.8. This is the second in a series of papers presenting the results of the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multi-band imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The photometric candidates were selected by a Bayesian probabilistic algorithm, and then observed with spectrographs on the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous paper of this series, we have now identified 64 HSC sources over about 430 deg2, which include 33 high-z quasars, 14 high-z luminous galaxies, two [O III] emitters at z ∼ 0.8, and 15 Galactic brown dwarfs. The new quasars have considerably lower luminosity (M1450 ∼ −25 to −22 mag) than most of the previously known high-z quasars. Several of these quasars have luminous (>1043 erg s−1) and narrow (< 500 km s−1) Lyα lines, and also a possible mini broad-absorption-line system of N V λ1240 in the composite spectrum, which clearly separate them from typical quasars. On the other hand, the high-z galaxies have extremely high luminosities (M1450 ∼ −24 to −22 mag) compared to other galaxies found at similar redshifts. With the discovery of these new classes of objects, we are opening up new parameter spaces in the high-z Universe. Further survey observations and follow-up studies of the identified objects, including the construction of the quasar luminosity function at z ∼ 6, are ongoing. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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8. A search for Ly a emitters around a concentrated region of strong Ly α absorbers at z = 2.3*.
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Kazuyuki OGURA, Tohru NAGAO, Masatoshi IMANISHI, Nobunari KASHIKAWA, Yoshiaki TANIGUCHI, Masaru KAJISAWA, KOBAYASHI, Masakazu A. R., Yoshiki TOBA, and Kodai NOBUHARA
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ABSORPTION ,NARROW gap semiconductors ,NEUTRON absorbers ,STELLAR luminosity function ,DISTRIBUTION (Probability theory) - Abstract
In order to investigate the physical relationship between strong Ly α absorbers (log N
HI ≥ 20.0 cm-2 ) such as damped Ly α absorption systems (DLAs) and young star-forming galaxies at high redshift, we have conducted narrow-band observations of Ly α emitters (LAEs) in a concentrated region of strong Ly α absorbers at z = 2.3, the J1230+34 field. Using a catalog of Ly α absorbers with log NHI ≥ 20.0 cm-2 based on the Baryon Oscillation Spectroscopic Survey, we found six fields where three or more absorbers are concentrated within a (50 Mpc)3 cubic box in the comoving scale. Among them, we focus on the J1230+34 field, where two DLAs and two sub-DLAs are present. Our narrow-band imaging observations with Subaru/Suprime-Cam using a custom-made filter, NB400 (λc = 4003 A and FWHM = 92A) yield a sample of 149 LAEs in this field. In the large scale (~50 Mpc), we have found no differences between the obtained Ly α luminosity function and those in the blank fields at similar redshifts. We also compare the frequency distribution of the Ly α rest-frame equivalent width (EW0) in the target field and other fields including both overdensity region and blank field, but find no differences. On the other hand, in the small scale (~10 Mpc), we have found a possible overdensity of LAEs around a DLA with the highest HI column density (NHI = 21.08 cm-2 ) in the target field while there are no density excesses around the other absorbers with a lower NHI . [ABSTRACT FROM AUTHOR]- Published
- 2017
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9. ALMA observations of the submillimetre hydrogen recombination line from the type 2 active nucleus of NGC 1068.
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Takuma Izumi, Kouichiro Nakanishi, Masatoshi Imanishi, and Kotaro Kohno
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ASTRONOMICAL observations ,MOLECULAR clouds ,ACTIVE galactic nuclei ,ELECTRON density ,HYDROGEN ,IONIZED gases ,SUBMILLIMETER astronomy - Abstract
Hydrogen recombination lines at the submillimetre band (submm-RLs) can serve as probes of ionized gas without dust extinction. One therefore expects to probe the broad-line region (BLR) of an obscured (type 2) active galactic nucleus (AGN) with those lines. However, admitting the large uncertainty in the continuum level, here we report on the non-detection of both broad and narrow H26 a emission line (rest frequency = 353.62 GHz) towards the prototypical type 2 AGN of NGC 1068 with the Atacama Large Millimeter/submillimeter Array (ALMA). We also investigate the nature of BLR clouds that can potentially emit submm-RLs with model calculations. As a result, we suggest that clouds with an electron density (N
e ) of ~109 cm-3 can mainly contribute to broad submm-RLs in terms of the line flux. On the other hand, line flux from other density clouds would be insignificant considering their too large or too small line optical depths. However, even for the case of Ne ~ 109 cm-3 clouds, we also suggest that the expected line flux is extremely low, which is impractical to detect even with ALMA. [ABSTRACT FROM AUTHOR]- Published
- 2016
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10. Near-infrared spectroscopy of quasars at z ~ 3 and estimates of their supermassive black hole masses.
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Yuriko SAITO, Masatoshi IMANISHI, Yosuke MINOWA, Tomoki MOROKUMA, Toshihiro KAWAGUCHI, Hiroaki SAMESHIMA, Takeo MINEZAKI, Nagisa OI, Tohru NAGAO, Nozomu KAWATATU, and Kenta MATSUOKA
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QUASARS ,NEAR infrared spectroscopy ,SUPERMASSIVE black holes ,GALACTIC redshift ,EDDINGTON mass limit ,ACTIVE galactic nuclei - Abstract
We present the results of new infrared spectroscopic observations of 37 quasars at z ∼ 3, selected based on the optical r'-band magnitude and the availability of nearby bright stars for future imaging follow-up with an adaptive optics system. The supermassive black hole (SMBH) masses (MBH) were successfully estimated in 28 out of 37 observed objects from the combination of the Hβ emission linewidth and continuum luminosity at rest-frame 5100Å. Comparing these results with those fromprevious studies of quasars with similar redshift, our sample exhibited slightly lower Eddington ratios (∼−0.11 dex in median), and the SMBH masses are slightly higher (∼0.38 dex in median). The SMBH growth time, tgrow, was calculated by dividing the estimated SMBH mass by the mass accretion rate measured using optical luminosity. We found, given reasonable assumptions, that t
grow was smaller than the age of the universe at the redshift of individual quasars for a large fraction of observed sources, suggesting that the SMBHs in many of our observed quasars are in the growing phase with high accretion rates. A comparison of the SMBH masses derived from our Hβ data and archived CIV data indicated considerable scattering, as indicated in previous studies. All quasars with measured SMBH masses have at least one nearby bright star, such that they are suitable targets for adaptive optics observations to study the mass relationship between SMBHs and host galaxies' stellar components at high redshift. [ABSTRACT FROM AUTHOR]- Published
- 2016
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11. The Subaru FMOS Galaxy Redshift Survey (FastSound). III. The mass-metallicity relation and the fundamental metallicity relation at z~1.4.
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Kiyoto YABE, Kouji OHTA, Masayuki AKIYAMA, BUNKER, Andrew, DALTON, Gavin, ELLIS, Richard, GLAZEBROOK, Karl, Tomotsugu GOTO, Masatoshi IMANISHI, Fumihide IWAMURO, Hiroyuki OKADA, Ikkoh SHIMIZU, Naruhisa TAKATO, Naoyuki TAMURA, Motonari TONEGAWA, and Tomonori TOTANI
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GALAXIES ,GALACTIC evolution ,GALACTIC redshift ,NEAR infrared spectroscopy ,STELLAR evolution ,STELLAR mass - Abstract
We present the results from a large near-infrared spectroscopic survey made with Subaru/FMOS (FastSound) consisting of ~4000 galaxies at z~1.4 with significant Ha detection. We measure the gas-phase metallicity from the [N II]λ6583/Hα emission line ratio of the composite spectra in various stellar mass and star-formation rate bins. The resulting mass-metallicity relation generally agrees with previous studies obtained in a similar redshift range to that of our sample. No clear dependence of the mass-metallicity relation on star-formation rate is found. Our result at z~1.4 is roughly in agreement with the fundamental metallicity relation at z~0.1 with a fiber aperture corrected starformation rate. We detect significant [S II]λλ6716,6731 emission lines from the composite spectra. The electron density estimated from the [S II]λλ6716,6731 line ratio ranges from 10-500 cm-3, which generally agrees with that of local galaxies. On the other hand, the distribution of our sample on [N II]λ6583/Hα vs. [S II]λλ6716,6731/Hα is different to that found locally. We estimate the nitrogen-to-oxygen abundance ratio (N/O) from the N2S2 index, and find that the N/O in galaxies at z~1.4 is significantly higher than the local values at a fixed metallicity and stellar mass. The metallicity at z~1.4 recalculated with this N/O enhancement taken into account decreases by 0.1-0.2 dex. The resulting metallicity is lower than the local fundamental metallicity relation. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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12. Hyper-luminous dust-obscured galaxies discovered by the Hyper Suprime-Cam on Subaru and WISE.
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Yoshiki TOBA, Tohru NAGAO, STRAUSS, Michael A., Kentaro AOKI, Tomotsugu GOTO, Masatoshi IMANISHI, Toshihiro KAWAGUCHI, Yuichi TERASHIMA, Yoshihiro UEDA, James BOSCH, Kevin BUNDY, Yoshiyuki DOI, Hanae INAMI, Yutaka KOMIYAMA, LUPTON, Robert H., Hideo MATSUHARA, Yoshiki MATSUOKA, Satoshi MIYAZAKI, Tomoki MOROKUMA, and Fumiaki NAKATA
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INTERSTELLAR medium ,GALAXIES ,INFRARED astronomy ,STELLAR luminosity function ,ASTRONOMICAL photometry - Abstract
We present the photometric properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining wide and deep optical images obtained with the Hyper Suprime-Cam on the Subaru Telescope and all-skymid-IR (MIR) images taken withWide- Field Infrared Survey Explorer, we discovered 48 DOGs with i--K
s >1.2 and i--[22]>7.0, where i, Ks , and [22] represent AB magnitude in the i-band, Ks -band, and 22μm, respectively, in the GAMA 14 hr field (~9deg2). Among these objects, 31 (~65%) show powerlaw spectral energy distributions (SEDs) in the near-IR (NIR) and MIR regime, while the remainder show an NIR bump in their SEDs. Assuming that the redshift distribution for our DOGs sample is Gaussian, with mean and sigma z=1.99±0.45, we calculated their total IR luminosity using an empirical relation between 22μm luminosity and total IR luminosity. The average value of the total IR luminosity is (3.5±1.1)×1013 L, which classifies them as hyper-luminous infrared galaxies. We also derived the total IR luminosity function (LF) and IR luminosity density (LD) for a flux-limited subsample of 18 DOGs with 22μm flux greater than 3.0mJy and with i-band magnitude brighter than 24 AB magnitude. The derived space density for this subsample is log Φ=--6.59±0.11 [Mpc--3]. The IR LF for DOGs including data obtained from the literature is fitted well by a double-power law. The derived lower limit for the IR LD for our sample is ρIR ~3.8×107 [LMpc-3 ] and its contributions to the total IR LD, IR LD of all ultraluminous infrared galaxies, and that of all DOGs are >3%, >9%, and >15%, respectively. [ABSTRACT FROM AUTHOR]- Published
- 2015
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13. Near- to mid-infrared imaging and spectroscopy of two buried AGNs of the nearby merging galaxy NGC6240 with Subaru/IRCS+AO and GTC/CanariCam.
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MORI, Tamami I., Masatoshi IMANISHI, Almudena ALONSO-HERRERO, PACKHAM, Chris, RAMOS ALMEIDA, Cristina, NIKUTTA, Robert, GONZÁLEZ-MARTÍN, Omaira, PERLMAN, Eric, SAITO, Yuriko, and LEVENSON, Nancy A.
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INFRARED imaging ,ACTIVE galactic nuclei ,LUMINOSITY ,SPECTRAL energy distribution ,GALAXY mergers ,STARBURSTS - Abstract
We report near-infrared K', L', and M' band imaging observations of the nearby merging galaxy NGC6240 with the Infrared Camera and Spectrograph on the Subaru telescope. The observations were performed with the assistance of the Subaru Adaptive Optics System, and the achieved spatial resolutions were around 0. "10-0. "20. We also obtained new mid-infrared imaging in the Si-2 filter band (8.7μm) and N-band (7.5-13μm) spectroscopy of this galaxy with the CanariCam on the Gran Telescopio Canarias with a spatial resolution of 0."4-0."5. In the K' band image the two nuclei of the galaxy each show a double peak suggesting the complex geometry of the source, while the L', M', and Si-2 band images show single compact structures in each of the two nuclei. Assuming that the center core observed at wavelengths longer than 3.8μm is associated with dust heated by the buried AGN, we re-evaluated the spectral energy distributions (SEDs) of the southern nucleus from 2 to 30μm with additional literature values, and performed the SED+spectroscopy fit using the clumpy torus models of Nenkova et al. (2008a, ApJ, 685, 145; 2008b, ApJ, 685, 160) and a Bayesian fitting approach. The model fit suggests that the high covering factor torus emission in the southern nucleus is also obscured by foreground dust in the host galaxy. The estimated AGN bolometric luminosity of the southern nucleus, L
bol (AGN) ∼ 1×1045 erg s-1 , accounts for approximately 40% of the whole luminosity of the system. [ABSTRACT FROM AUTHOR]- Published
- 2014
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14. THE UNIVERSAL INITIAL MASS FUNCTION IN THE EXTENDED ULTRAVIOLET DISK OF M83.
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JIN KODA, MASAFUMI YAGI, BOISSIER, SAMUEL, DE PAZ, ARMANDO GIL, MASATOSHI IMANISHI, MEYER, JENNIFER DONOVAN, MADORE, BARRY F., and THILKER, DAVID A.
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ULTRAVIOLET radiation ,STELLAR initial mass function ,CAMERAS ,SPECTRAL energy distribution ,STAR clusters - Abstract
We report deep Subaru Hα observations of the extended ultraviolet (XUV) disk of M83. These new observations enable the first complete census of very young stellar clusters over the entire XUV disk. Combining Subaru and Galaxy Evolution Explorer data with a stellar population synthesis model, we find that (1) the standard, but stochastically sampled, initial mass function (IMF) is preferred over the truncated IMF because there are low-mass stellar clusters (10
2-3 M⊙ ) that host massive O-type stars; (2) the standard Salpeter IMF and a simple aging effect explain the counts of far-UV (FUV)-bright and Hα-bright clusters with masses >10³ M⊙ ; and (3) the Hα-to-FUV flux ratio over the XUV disk supports the standard IMF. To reach conclusion (2), we assumed instantaneous cluster formation and a constant cluster formation rate over the XUV disk. The Subaru Prime Focus Camera covers a large area even outside the XUV disk--far beyond the detection limit of the H I gas. This enables us to statistically separate the stellar clusters in the disk from background contamination. The new data, model, and previous spectroscopic studies provide overall consistent results with respect to the internal dust extinction (AV ~ 0.1 mag) and low metallicity (~0.2 Z⊙ ) using the dust extinction curve of the Small Magellanic Cloud. The minimum cluster mass for avoiding the upper IMF incompleteness due to stochastic sampling and the spectral energy distributions of O, B, and A stars are discussed in the Appendices. [ABSTRACT FROM AUTHOR]- Published
- 2012
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15. ALMA Polarimetry Measures Magnetically Aligned Dust Grains in the Torus of NGC 1068.
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Enrique Lopez-Rodriguez, Almudena Alonso-Herrero, Santiago García-Burillo, Michael S. Gordon, Kohei Ichikawa, Masatoshi Imanishi, Seiji Kameno, Nancy A. Levenson, Robert Nikutta, and Chris Packham
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TORUS ,DUST ,SPECTRAL energy distribution ,ACTIVE galactic nuclei ,POLARIMETRY ,SEYFERT galaxies ,SUPERMASSIVE black holes - Abstract
The obscuring structure surrounding active galactic nuclei (AGN) can be explained as a dust and gas flow cycle that fundamentally connects the AGN with their host galaxies. This structure is believed to be associated with dusty winds driven by radiation pressure. However, the role of magnetic fields, which are invoked in almost all models for accretion onto a supermassive black hole and outflows, has not been thoroughly studied. Here we report the first detection of polarized thermal emission by means of magnetically aligned dust grains in the dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum observations (0.″07, 4.2 pc; 348.5 GHz, 860 μm). The polarized torus has an asymmetric variation across the equatorial axis with a peak polarization of 3.7% ± 0.5% and position angle of 109° ± 2° (B-vector) at ∼8 pc east from the core. We compute synthetic polarimetric observations of magnetically aligned dust grains assuming a toroidal magnetic field and homogeneous grain alignment. We conclude that the measured 860 μm continuum polarization arises from magnetically aligned dust grains in an optically thin region of the torus. The asymmetric polarization across the equatorial axis of the torus arises from (1) an inhomogeneous optical depth and (2) a variation of the velocity dispersion, i.e., a variation of the magnetic field turbulence at subparsec scales, from the eastern to the western region of the torus. These observations and modeling constrain the torus properties beyond spectral energy distribution results. This study strongly supports that magnetic fields up to a few parsecs contribute to the accretion flow onto the active nuclei. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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16. The MBHBM⋆ Project. I. Measurement of the Central Black Hole Mass in Spiral Galaxy NGC 3504 Using Molecular Gas Kinematics.
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Dieu D. Nguyen, Mark den Brok, Anil C. Seth, Timothy A. Davis, Jenny E. Greene, Michelle Cappellari, Joseph B. Jensen, Sabine Thater, Satoru Iguchi, Masatoshi Imanishi, Takuma Izumi, Kristina Nyland, Nadine Neumayer, Kouichiro Nakanishi, Phuong M. Nguyen, Takafumi Tsukui, Martin Bureau, Kyoko Onishi, Quang L. Nguyen, and Ngan M. Le
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SPIRAL galaxies ,BLACK holes ,SUPERMASSIVE black holes ,MILKY Way ,KINEMATICS ,MASS measurement - Abstract
We present a dynamical mass measurement of the supermassive black hole (SMBH) in the nearby double-barred spiral galaxy NGC 3504 as part of the Measuring Black Holes in below Milky Way (M
⋆ ) Mass Galaxies Project. Our analysis is based on Atacama Large Millimeter/submillimeter Array cycle 5 observations of the emission line. These observations probe NGC 3504's circumnuclear gas disk (CND). Our dynamical model of the CND simultaneously constrains a black hole (BH) mass of M⊙ , which is consistent with the empirical BH–galaxy scaling relations and a mass-to-light ratio in the H band of 0.44 ± 0.12 (M⊙ /). This measurement also relies on our new estimation of the distance to the galaxy of 32.4 ± 2.1 Mpc using the surface brightness fluctuation method, which is much further than the existing distance estimates. Additionally, our observations detect a central deficit in the integrated intensity map with a diameter of 6.3 pc at the putative position of the SMBH. However, we find that a dense gas tracer CS(5 − 4) peaks at the galaxy center, filling in the12 CO(2 − 1)-attenuated hole. Holes like this one are observed in other galaxies, and our observations suggest these may be caused by changing excitation conditions rather than a true absence of molecular gas around the nucleus. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
17. Subaru Infrared Adaptive Optics-assisted High-spatial-resolution Imaging Search for Luminous Dual Active Galactic Nuclei in Nearby Ultraluminous Infrared Galaxies.
- Author
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Masatoshi Imanishi, Taiki Kawamuro, Satoshi Kikuta, Suzuka Nakano, and Yuriko Saito
- Subjects
GALAXY mergers ,ACTIVE galactic nuclei ,SUPERMASSIVE black holes ,GALAXIES ,ADAPTIVE optics - Abstract
We present infrared K′-band (2.1 μm) and L′-band (3.8 μm) high-spatial-resolution (<0.″3) imaging observations of 17 nearby (z < 0.17) ultraluminous infrared galaxies (ULIRGs) assisted with the adaptive optics of the Subaru Telescope. We search for compact red K′ − L′ color emission as the indicator of luminous active galactic nuclei (AGNs) due to AGN-heated hot dust emission. Two luminous dual AGN candidates are revealed. Combining these results with those of our previous study, we can state that the detected fraction of luminous dual AGNs in nearby ULIRGs is much less than unity (<20%), even when infrared wavelengths >2 μm are used that should be sensitive to buried AGNs due to small dust extinction effects. For ULIRGs with resolved multiple nuclear K′-band emission, we estimate the activation of supermassive black holes (SMBHs) in individual galaxy nuclei in the form of AGN luminosity normalized by SMBH mass inferred from the stellar luminosity of the host galaxy. We confirm a trend that more massive SMBHs in K′-band brighter primary galaxy nuclei are generally more active, with higher SMBH-mass-normalized AGN luminosity, than less massive SMBHs in K′-band fainter secondary galaxy nuclei, as predicted by numerical simulations of gas-rich major galaxy mergers. In two sources, the presence of even infrared-elusive extremely deeply buried AGNs is indicated by comparisons with available (sub)millimeter data. Non-synchronous SMBH activation (i.e., less activation of less massive SMBHs) and the possible presence of such infrared-elusive AGNs may be responsible for the small fraction of infrared-detected luminous dual AGNs in nearby merging ULIRGs. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
18. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 7.0.
- Author
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Yoshiki Matsuoka, Kazushi Iwasawa, Masafusa Onoue, Nobunari Kashikawa, Michael A. Strauss, Chien-Hsiu Lee, Masatoshi Imanishi, Tohru Nagao, Masayuki Akiyama, Naoko Asami, James Bosch, Hisanori Furusawa, Tomotsugu Goto, James E. Gunn, Yuichi Harikane, Hiroyuki Ikeda, Takuma Izumi, Toshihiro Kawaguchi, Nanako Kato, and Satoshi Kikuta
- Subjects
QUASARS ,GALAXIES ,DWARF stars - Abstract
We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 [O iii] emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg
2 , surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Lyα emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ1240 emission and resembles that of lower-z narrow-line quasars, the small Lyα width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies. [ABSTRACT FROM AUTHOR]- Published
- 2019
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19. A NuSTAR and XMM-Newton Study of the Two Most Actively Star-forming Green Pea Galaxies (SDSS J0749+3337 and SDSS J0822+2241).
- Author
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Taiki Kawamuro, Yoshihiro Ueda, Kohei Ichikawa, Masatoshi Imanishi, Takuma Izumi, Atsushi Tanimoto, and Kenta Matsuoka
- Subjects
SPECTRAL energy distribution ,ACTIVE galactic nuclei ,PEAS ,GALAXIES ,HARD X-rays ,SEYFERT galaxies ,X-ray binaries - Abstract
We explore X-ray evidence for the presence of active galactic nuclei (AGNs) in the two most actively star-forming Green Pea galaxies (GPs), SDSS J0749+3337 and SDSS J0822+2241, which have star formation rates (SFRs) of 123 M
⊙ yr−1 and 78 M⊙ yr−1 , respectively. The GPs have red mid-infrared (MIR) spectral energy distributions and higher 22 μm luminosities than expected from a proxy of the SFR (Hα luminosity), consistent with hosting AGNs with 2–10 keV luminosities of ∼1044 erg s−1 . We thus obtain and analyze the first hard (>10 keV) X-ray data observed with NuSTAR and archival XMM-Newton data below 10 keV. From the NuSTAR ≈20 ks data, however, we find no significant hard X-ray emission. By contrast, soft X-ray emission with 0.5–8 keV luminosities of ≈1042 erg s−1 is significantly detected in both targets, which can be explained only by star formation (SF). A possible reason for the lack of clear evidence is that a putative AGN torus absorbs most of the X-ray emission. Applying a smooth-density AGN torus model, we determine minimum hydrogen column densities along the equatorial plane () consistent with the nondetection. The results indicate cm−2 for SDSS J0749+3337 and cm−2 for SDSS J0822+2241. Therefore, the GPs may host such heavily obscured AGNs. Otherwise, no AGN exists and the MIR emission is ascribed to SF. Active SF in low-mass galaxies is indeed suggested to reproduce red MIR colors. This would imply that diagnostics based on MIR photometry data alone may misidentify such galaxies as AGNs. [ABSTRACT FROM AUTHOR]- Published
- 2019
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20. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). VI. Black Hole Mass Measurements of Six Quasars at 6.1 ≤ z ≤ 6.7.
- Author
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Masafusa Onoue, Nobunari Kashikawa, Yoshiki Matsuoka, Nanako Kato, Takuma Izumi, Tohru Nagao, Michael A. Strauss, Yuichi Harikane, Masatoshi Imanishi, Kei Ito, Kazushi Iwasawa, Toshihiro Kawaguchi, Chien-Hsiu Lee, Akatoki Noboriguchi, Hyewon Suh, Masayuki Tanaka, and Yoshiki Toba
- Subjects
QUASARS ,BLACK holes ,MASS measurement ,SUPERMASSIVE black holes ,COMPACT objects (Astronomy) - Abstract
We present deep near-infrared spectroscopy of six quasars at 6.1 ≤ z ≤ 6.7 with Very Large Telescope/X-Shooter and Gemini-N/GNIRS. Our objects, originally discovered through a wide-field optical survey with the Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP), have the lowest luminosities (−25.5 mag ≤ M
1450 ≤ −23.1 mag) of the z > 5.8 quasars with measured black hole (BH) masses. From single-epoch mass measurements based on Mg ii λ2798, we find a wide range in BH masses, from MBH = 107.6 to 109.3 M⊙ . The Eddington ratios Lbol /LEdd range from 0.16 to 1.1, but the majority of the HSC quasars are powered by MBH ∼ 109 M⊙ supermassive black holes (SMBHs) accreting at sub-Eddington rates. The Eddington ratio distribution of the HSC quasars is inclined to lower accretion rates than those of Willott et al., who measured the BH masses for similarly faint z ∼ 6 quasars. This suggests that the global Eddington ratio distribution is wider than has previously been thought. The presence of MBH ∼ 109 M⊙ SMBHs at z ∼ 6 cannot be explained with constant sub-Eddington accretion from stellar remnant seed BHs. Therefore, we may be witnessing the first buildup of the most massive BHs in the first billion years of the universe, the accretion activity of which is transforming from active growth to a quiescent phase. Measurements of a larger complete sample of z ≳ 6 low-luminosity quasars, as well as deeper observations with future facilities, will enable us to better understand the early SMBH growth in the reionization epoch. [ABSTRACT FROM AUTHOR]- Published
- 2019
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21. Luminosity Ratio between [O iv] 25.89 μm Line and Nuclear Continuum 12 μm as a Diagnostic for “Buried” AGNs.
- Author
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Satoshi Yamada, Yoshihiro Ueda, Atsushi Tanimoto, Taiki Kawamuro, Masatoshi Imanishi, and Yoshiki Toba
- Subjects
SEYFERT galaxies ,ACTIVE galactic nuclei ,LUMINOSITY - Abstract
We propose new diagnostics that utilize the [O iv] 25.89 μm and nuclear (subarcsecond scale) 12 μm luminosity ratios for identifying whether an active galactic nucleus (AGN) is deeply “buried” in their surrounding materials. Utilizing a sample of 16 absorbed AGNs at redshifts lower than 0.03 in the Swift/BAT catalog observed with Suzaku, we find that AGNs with small scattering fractions (<0.5%) tend to show weaker [O iv]-to-12 μm luminosity ratios than the average of Seyfert 2 galaxies. This suggests that this ratio is a good indicator for identifying buried AGNs. Then, we apply this criterion to 23 local luminous and ultraluminous infrared galaxies (U/LIRGs) in various merger stages hosting AGNs. We find that AGNs in most mid- to late-stage mergers are buried, while those in earlier-stage ones (including nonmerger) are not. This result suggests that the fraction of buried AGNs in U/LIRGs increases as the galaxy–galaxy interaction becomes more significant. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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- View/download PDF
22. ALMA Spatially Resolved Dense Molecular Gas Survey of Nearby Ultraluminous Infrared Galaxies.
- Author
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Masatoshi Imanishi, Kouichiro Nakanishi, and Takuma Izumi
- Published
- 2019
- Full Text
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23. Discovery of the First Low-luminosity Quasar at z > 7.
- Author
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Yoshiki Matsuoka, Masafusa Onoue, Nobunari Kashikawa, Michael A Strauss, Kazushi Iwasawa, Chien-Hsiu Lee, Masatoshi Imanishi, Tohru Nagao, Masayuki Akiyama, Naoko Asami, James Bosch, Hisanori Furusawa, Tomotsugu Goto, James E Gunn, Yuichi Harikane, Hiroyuki Ikeda, Takuma Izumi, Toshihiro Kawaguchi, Nanako Kato, and Satoshi Kikuta
- Published
- 2019
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- View/download PDF
24. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6.
- Author
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Yoshiki Matsuoka, Michael A. Strauss, Nobunari Kashikawa, Masafusa Onoue, Kazushi Iwasawa, Ji-Jia Tang, Chien-Hsiu Lee, Masatoshi Imanishi, Tohru Nagao, Masayuki Akiyama, Naoko Asami, James Bosch, Hisanori Furusawa, Tomotsugu Goto, James E. Gunn, Yuichi Harikane, Hiroyuki Ikeda, Takuma Izumi, Toshihiro Kawaguchi, and Nanako Kato
- Subjects
LUMINOSITY ,LUMINESCENCE ,QUASARS ,RADIO sources (Astronomy) ,METAPHYSICAL cosmology ,STELLAR luminosity function ,STELLAR magnitudes - Abstract
We present new measurements of the quasar luminosity function (LF) at z ∼ 6 over an unprecedentedly wide range of the rest-frame ultraviolet luminosity M
1450 from −30 to −22 mag. This is the fifth in a series of publications from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam Subaru Strategic Program survey. The LF was calculated with a complete sample of 110 quasars at 5.7 ≤ z ≤ 6.5, which includes 48 SHELLQs quasars discovered over 650 deg2 and 63 brighter quasars discovered by the Sloan Digital Sky Survey and the Canada–France–Hawaii Quasar Survey (including one overlapping object). This is the largest sample of z ∼ 6 quasars with a well-defined selection function constructed to date, which has allowed us to detect significant flattening of the LF at its faint end. A double power-law function fit to the sample yields a faint-end slope , a bright-end slope , a break magnitude , and a characteristic space density Gpc−3 mag−1 . Integrating this best-fit model over the range −18 < M1450 < −30 mag, quasars emit ionizing photons at the rate of s−1 Mpc−3 at z = 6.0. This is less than 10% of the critical rate necessary to keep the intergalactic medium ionized, which indicates that quasars are not a major contributor to cosmic reionization. [ABSTRACT FROM AUTHOR]- Published
- 2018
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- View/download PDF
25. Spatially Resolved Dense Molecular Gas Excitation in the Nearby LIRG VV 114.
- Author
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Toshiki Saito, Daisuke Iono, Daniel Espada, Kouichiro Nakanishi, Junko Ueda, Hajime Sugai, Min S. Yun, Shuro Takano, Masatoshi Imanishi, Tomonari Michiyama, Satoshi Ohashi, Minju Lee, Yoshiaki Hagiwara, Kentaro Motohara, Takuji Yamashita, Misaki Ando, and Ryohei Kawabe
- Subjects
GAS tracers (Chemistry) ,EXCITED states ,GALAXIES ,STAR formation ,TURBULENCE - Abstract
We present high-resolution observations (0.″2–1.″5) of multiple dense gas tracers, HCN and HCO
+ (J = 1–0, 3–2, and 4–3), HNC (J = 1–0), and CS (J = 7–6) lines, toward the nearby luminous infrared galaxy VV 114 with the Atacama Large Millimeter/submillimeter Array. All lines are robustly detected at the central gaseous filamentary structure, including the eastern nucleus and the overlap region, the collision interface of the progenitors. We found that there is no correlation between star formation efficiency and dense gas fraction, indicating that the amount of dense gas does not simply control star formation in VV 114. We predict the presence of more turbulent and diffuse molecular gas clouds around the overlap region compared to those at the nuclear region, assuming a turbulence-regulated star formation model. The intracloud turbulence at the overlap region might be excited by galaxy-merger-induced shocks, which also explains the enhancement of gas-phase CH3 OH abundance previously found there. We also present spatially resolved spectral line energy distributions of HCN and HCO+ for the first time, and derive excitation parameters by assuming optically thin and local thermodynamic equilibrium (LTE) conditions. The LTE model revealed that warmer, HCO+ -poorer molecular gas medium is dominated around the eastern nucleus, harboring an active galactic nucleus (AGN). The HCN abundance is remarkably flat (∼3.5 × 10−9 ) independently of the various environments within the filament of VV 114 (i.e., AGN, star formation, and shock). [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
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26. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). IV. Discovery of 41 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 6.9.
- Author
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Yoshiki Matsuoka, Kazushi Iwasawa, Masafusa Onoue, Nobunari Kashikawa, Michael A. Strauss, Chien-Hsiu Lee, Masatoshi Imanishi, Tohru Nagao, Masayuki Akiyama, Naoko Asami, James Bosch, Hisanori Furusawa, Tomotsugu Goto, James E. Gunn, Yuichi Harikane, Hiroyuki Ikeda, Takuma Izumi, Toshihiro Kawaguchi, Nanako Kato, and Satoshi Kikuta
- Published
- 2018
- Full Text
- View/download PDF
27. The MALATANG Survey: The L GAS–L IR Correlation on Sub-kiloparsec Scale in Six Nearby Star-forming Galaxies as Traced by HCN J = 4 → 3 and HCO+ J = 4 → 3.
- Author
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Qing-Hua Tan, Yu Gao, Zhi-Yu Zhang, Thomas R. Greve, Xue-Jian Jiang, Christine D. Wilson, Chen-Tao Yang, Ashley Bemis, Aeree Chung, Satoki Matsushita, Yong Shi, Yi-Ping Ao, Elias Brinks, Malcolm J. Currie, Timothy A. Davis, Richard de Grijs, Luis C. Ho, Masatoshi Imanishi, Kotaro Kohno, and Bumhyun Lee
- Subjects
QUASARS ,GALAXIES ,LUMINOSITY ,STAR formation ,STATISTICAL correlation - Abstract
We present and maps of six nearby star-forming galaxies, NGC 253, NGC 1068, IC 342, M82, M83, and NGC 6946, obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey. All galaxies were mapped in the central 2′ × 2′ region at 14″ (FWHM) resolution (corresponding to linear scales of ∼0.2–1.0 kpc). The L
IR –L′dense relation, where the dense gas is traced by the and the emission, measured in our sample of spatially resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. We find that the luminosity ratio, LIR /L′dense , shows systematic variations with LIR within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. A rising trend is also found between LIR /L′dense ratio and the warm-dust temperature gauged by the 70 μm/100 μm flux ratio. We find that the luminosity ratios of IR/HCN (4–3) and IR/HCO+ (4–3), which can be taken as a proxy for the star formation efficiency (SFE) in the dense molecular gas (SFEdense ), appear to be nearly independent of the dense gas fraction (fdense ) for our sample of galaxies. The SFE of the total molecular gas (SFEmol ) is found to increase substantially with fdense when combining our data with those on local (ultra)luminous infrared galaxies and high-z quasars. The mean line ratio measured for the six targeted galaxies is 0.9 ± 0.6. No significant correlation is found for the ratio with the star formation rate as traced by LIR , nor with the warm-dust temperature, for the different populations of galaxies. [ABSTRACT FROM AUTHOR]- Published
- 2018
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28. Broadband X-Ray Spectral Analysis of the Double-nucleus Luminous Infrared Galaxy Mrk 463.
- Author
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Satoshi Yamada, Yoshihiro Ueda, Saeko Oda, Atsushi Tanimoto, Masatoshi Imanishi, Yuichi Terashima, and Claudio Ricci
- Subjects
GALAXIES ,STELLAR luminosity function ,LUMINOSITY ,X-ray diffraction ,NUCLEAR spectroscopic factors - Abstract
We present a broadband (0.4–70 keV) X-ray spectral analysis of the luminous infrared galaxy (LIRG) system Mrk 463 observed with Nuclear Spectroscopic Telescope Array (NuSTAR), Chandra, and XMM-Newton, which contains double active galactic nuclei (AGNs; Mrk 463E and Mrk 463W) with a separation of ∼3.8 kpc. Detecting their transmitted hard X-ray >10 keV continua with NuSTAR, we confirm that Mrk 463E and Mrk 463W have AGNs with intrinsic luminosities of (1.6–2.2) × 10
43 and (0.5–0.6) × 1043 erg s−1 (2–10 keV) obscured by hydrogen column densities of 8 × 1023 and 3 × 1023 cm−2 , respectively. Both nuclei show strong reflection components from cold matter. The luminosity ratio between X-ray (2–10 keV) and [O iv] 25.89 μm of Mrk 463E is ∼5 times smaller than those of normal Seyfert galaxies, suggesting that the intrinsic SED is X-ray weak relative to the UV luminosity. In fact, the bolometric AGN luminosity of Mrk 463E estimated from L′-band (3.8 μm), [O iv] 25.89 μm, and [Ne v] 14.32 μm lines indicate a large bolometric-to-X-ray luminosity ratio, κ2–10 keV ≈ 110–410, and a high Eddington ratio, λEdd ∼ 0.4–0.8. We suggest that the merger triggered a rapid growth of the black hole in Mrk 463E, which is not yet deeply “buried” by circumnuclear dust. By contrast, the L′-band luminosity of Mrk 463W is unusually small relative to the X-ray luminosity, suggesting that the Eddington ratio is low (<10−3 ) and it might be still in an early phase of merger-driven AGN activity. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
29. ALMA Multiple-transition Observations of High-density Molecular Tracers in Ultraluminous Infrared Galaxies.
- Author
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Masatoshi Imanishi, Kouichiro Nakanishi, and Takuma Izumi
- Subjects
GALAXIES ,LUMINOSITY ,STARBURSTS ,INFRARED spectroscopy ,SUPERGIANT stars - Abstract
We present the results of our ALMA observations of 11 (ultra)luminous infrared galaxies ((U)LIRGs) at J = 4–3 of HCN, HCO
+ , and HNC and J = 3–2 of HNC. This is an extension of our previously published HCN and HCO+ J = 3–2 observations to multiple rotational J-transitions of multiple molecules, to investigate how molecular emission line flux ratios vary at different J-transitions. We confirm that ultraluminous infrared galaxies (ULIRGs) that contain or may contain luminous obscured active galactic nuclei (AGNs) tend to show higher HCN-to-HCO+ flux ratios than starburst galaxies, both at J = 4–3 and J = 3–2. For selected HCN-flux-enhanced AGN-important ULIRGs, our isotopologue H13 CN, H13 CO+ , and HN13 C J = 3–2 line observations suggest a higher abundance of HCN than HCO+ and HNC, which is interpreted to be primarily responsible for the elevated HCN flux in AGN-important galaxies. For such sources, the intrinsic HCN-to-HCO+ flux ratios after line opacity correction will be higher than the observed ratios, making the separation between AGNs and starbursts even larger. The signature of the vibrationally excited (v2 = 1f) HCN J = 4–3 emission line is seen in one ULIRG, IRAS 12112−0305 NE. P Cygni profiles are detected in the HCO+ J = 4–3 and J = 3–2 lines toward IRAS 15250+3609, with an estimated molecular outflow rate of ∼250–750 M⊙ yr−1 . The SiO J = 6–5 line also exhibits a P Cygni profile in IRAS 12112+0305 NE, suggesting the presence of shocked outflow activity. Shock tracers are detected in many sources, suggesting ubiquitous shock activity in the nearby ULIRG population. [ABSTRACT FROM AUTHOR]- Published
- 2018
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30. ALMA Reveals an Inhomogeneous Compact Rotating Dense Molecular Torus at the NGC 1068 Nucleus.
- Author
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Masatoshi Imanishi, Kouichiro Nakanishi, Takuma Izumi, and Keiichi Wada
- Published
- 2018
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- View/download PDF
31. No Sign of Strong Molecular Gas Outflow in an Infrared-bright Dust-obscured Galaxy with Strong Ionized-gas Outflow.
- Author
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Yoshiki Toba, Shinya Komugi, Tohru Nagao, Takuji Yamashita, Wei-Hao Wang, Masatoshi Imanishi, and Ai-Lei Sun
- Subjects
COSMIC dust ,MOLECULAR gas lasers ,IONIZED gases ,GAS flow ,ASTRONOMICAL observations - Abstract
We report the discovery of an infrared (IR)-bright dust-obscured galaxy (DOG) that shows a strong ionized-gas outflow but no significant molecular gas outflow. Based on detailed analysis of their optical spectra, we found some peculiar IR-bright DOGs that show strong ionized-gas outflow ([O iii] λ5007) from the central active galactic nucleus (AGN). For one of these DOGs (WISE J102905.90+050132.4) at z
spec = 0.493, we performed follow-up observations using ALMA to investigate their CO molecular gas properties. As a result, we successfully detected12 CO(J = 2–1) and12 CO(J = 4–3) lines and the continuum of this DOG. The intensity-weighted velocity map of both lines shows a gradient, and the line profile of those CO lines is well-fitted by a single narrow Gaussian, meaning that this DOG has no sign of strong molecular gas outflow. The IR luminosity of this object is log (LIR /L☉ ) = 12.40, which is classified as an ultraluminous IR galaxy (ULIRG). We found that (i) the stellar mass and star formation rate relation and (ii) the CO luminosity and far-IR luminosity relation are consistent with those of typical ULIRGs at similar redshifts. These results indicate that the molecular gas properties of this DOG are normal despite the fact that its optical spectrum shows a powerful AGN outflow. We conclude that a powerful ionized-gas outflow caused by the AGN does not necessarily affect the cold interstellar medium in the host galaxy, at least for this DOG. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
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32. ALMA Multiple-transition Molecular Line Observations of the Ultraluminous Infrared Galaxy IRAS 20551–4250: Different HCN, HCO+, and HNC Excitation, and Implications for Infrared Radiative Pumping.
- Author
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Masatoshi Imanishi, Kouichiro Nakanishi, and Takuma Izumi
- Subjects
GALAXIES ,STARBURSTS ,QUASARS ,SUPERMASSIVE black holes ,ASTROPHYSICS - Abstract
We present our ALMA multi-transition molecular line observational results for the ultraluminous infrared galaxy IRAS 20551−4250, which is known to contain a luminous buried active galactic nucleus and shows detectable vibrationally excited (v
2 = 1f) HCN and HNC emission lines. The rotational J = 1–0, 4–3, and 8–7 of HCN, , and HNC emission lines were clearly detected at a vibrational ground level (v = 0). Vibrationally excited (v2 = 1f) J = 4–3 emission lines were detected for HCN and HNC, but not for . Their observed flux ratios further support our previously obtained suggestion, based on J = 3–2 data, that (1) infrared radiative pumping plays a role in rotational excitation at v = 0, at least for HCN and HNC, and (2) HCN abundance is higher than and HNC. The flux measurements of the isotopologue H13 CN, , and HN13 C J = 3–2 emission lines support the higher HCN abundance scenario. Based on modeling with collisional excitation, we constrain the physical properties of these line-emitting molecular gases, but find that higher HNC rotational excitation than HCN and is difficult to explain, due to the higher effective critical density of HNC. We consider the effects of infrared radiative pumping using the available 5–30 μm infrared spectrum and find that our observational results are well-explained if the radiation source is located at 30–100 pc from the molecular gas. The simultaneously covered very bright CO J = 3–2 emission line displays a broad emission wing, which we interpret as being due to molecular outflow activity with the estimated rate of . [ABSTRACT FROM AUTHOR]- Published
- 2017
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- View/download PDF
33. Minor Contribution of Quasars to Ionizing Photon Budget at z ∼ 6: Update on Quasar Luminosity Function at the Faint End with Subaru/Suprime-Cam.
- Author
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Masafusa Onoue, Nobunari Kashikawa, Chris J. Willott, Pascale Hibon, Myungshin Im, Hisanori Furusawa, Yuichi Harikane, Masatoshi Imanishi, Shogo Ishikawa, Satoshi Kikuta, Yoshiki Matsuoka, Tohru Nagao, Yuu Niino, Yoshiaki Ono, Masami Ouchi, Masayuki Tanaka, Ji-Jia Tang, Jun Toshikawa, and Hisakazu Uchiyama
- Published
- 2017
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- View/download PDF
34. Calibration of Ultraviolet, Mid-infrared, and Radio Star Formation Rate Indicators.
- Author
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Michael J. I. Brown, John Moustakas, Robert C. Kennicutt, Nicolas J. Bonne, Huib T. Intema, Francesco de Gasperin, Mederic Boquien, T. H. Jarrett, Michelle E. Cluver, J.-D. T. Smith, Elisabete da Cunha, Masatoshi Imanishi, Lee Armus, Bernhard R. Brandl, and J. E. G. Peek
- Subjects
STAR formation ,ULTRAVIOLET radiation ,SPECTROPHOTOMETRY ,GALAXIES ,LUMINOSITY - Abstract
We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radio-continuum bands, including one of the first direct calibrations of 150 MHz as an SFR indicator. Our calibrations utilize 66 nearby star-forming galaxies with Balmer-decrement-corrected luminosities, which span five orders of magnitude in SFR and have absolute magnitudes of . Most of our photometry and spectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has been validated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seen in SFR indicator calibrations. We find that the Wide-field Infrared Space Explorer W4 (22.8 μm), Spitzer 24 μm, and 1.4 GHz bands have tight correlations with the Balmer-decrement-corrected Hα luminosity, with a scatter of only 0.2 dex. Our calibrations are comparable to those from the prior literature for L
∗ galaxies, but for dwarf galaxies, our calibrations can give SFRs that are far greater than those derived from most previous literature. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
35. Active Galactic Nucleus Environments and Feedback to Neighboring Galaxies at z ∼ 5 Probed by Lyα Emitters.
- Author
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Satoshi Kikuta, Masatoshi Imanishi, Yoshiki Matsuoka, Yuichi Matsuda, Kazuhiro Shimasaku, and Fumiaki Nakata
- Subjects
ACTIVE galactic nuclei ,GALACTIC redshift ,GALACTIC dynamics ,GALAXY formation ,RADIO galaxies - Abstract
Active galactic nuclei (AGNs) in the high-redshift universe are thought to reside in overdense environments. However, recent works provide controversial results, partly due to the use of different techniques and possible suppression of nearby galaxy formation by AGN feedback. We conducted deep and wide-field imaging observations with the Suprime-Cam on the Subaru Telescope and searched for Lyα emitters (LAEs) around two quasi-stellar objects (QSOs) at z ∼ 4.9 and a radio galaxy at z ∼ 4.5 by using narrowband filters to address these issues more robustly. In the QSO fields, we obtained additional broadband images to select Lyman break galaxies (LBGs) at z ∼ 5 for comparison. We constructed a photometric sample of 301 LAEs and 170 LBGs in total. A wide field of view (34′ × 27′, corresponding to 80 × 60 comoving Mpc
2 ) of the Suprime-Cam enabled us to probe galaxies in the immediate vicinities of the AGNs and in the blank fields simultaneously and compare various properties of them in a consistent manner. The two QSOs are located near local density peaks (<2σ), and one of the QSOs has a close companion LAE with projected separation of 80 physical kpc. The radio galaxy is found to be near a void of LAEs. The number densities of LAEs/LGBs in a larger spatial scale around the AGNs are not significantly different from those in blank fields. No sign of feedback is found down to . Our results suggest that high-redshift AGNs are not associated with extreme galaxy overdensity and that this cannot be attributed to the effect of AGN feedback. [ABSTRACT FROM AUTHOR]- Published
- 2017
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36. Shedding Light on the Compton-thick Active Galactic Nucleus in the Ultraluminous Infrared Galaxy UGC 5101 with Broadband X-Ray Spectroscopy.
- Author
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Saeko Oda, Atsushi Tanimoto, Yoshihiro Ueda, Masatoshi Imanishi, Yuichi Terashima, and Claudio Ricci
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ACTIVE galactic nuclei ,X-ray spectroscopy ,STELLAR luminosity function ,INFRARED radiation ,SEYFERT galaxies - Abstract
We report the broadband X-ray spectra of the ultraluminous infrared galaxy (ULIRG) UGC 5101 in the 0.25–100 keV band observed with the Swift/Burst Alert Telescope (BAT), Nuclear Spectroscopic Telescope Array (NuSTAR), Suzaku, XMM-Newton, and Chandra. A Compton-thick active galactic nucleus (AGN) obscured with a hydrogen column density of cm
−2 is detected above 10 keV. A spectral fit with a numerical torus model favors a large half-opening angle of the torus, °, suggesting that the covering fraction of material heavily obscuring the X-ray source is moderate. The intrinsic 2–10 keV luminosity is determined to be erg s−1 , which is times larger than the previous estimate using only data below 10 keV with a simple spectral model. We find that UGC 5101 shows the ratio between the [O iv] 26 μm line and 2–10 keV luminosities similar to those of normal Seyfert galaxies, along with other ULIRGs observed with NuSTAR, indicating that a significant portion of local ULIRGs are not really “X-ray faint” with respect to the flux of forbidden lines originating from the narrow-line region. We propose a possible scenario that (1) the AGN in UGC 5101 is surrounded not only by Compton-thick matter located close to the equatorial plane but also by Compton-thin ( cm−2 ) matter in the torus-hole region and (2) it is accreting at a high Eddington rate with a steep UV to X-ray spectral energy distribution. Nevertheless, we argue that AGNs in many ULIRGs do not look extraordinary (i.e., extremely X-ray faint), as suggested by recent works, compared with normal Seyferts. [ABSTRACT FROM AUTHOR]- Published
- 2017
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37. CLUSTERING OF INFRARED-BRIGHT DUST-OBSCURED GALAXIES REVEALED BY THE HYPER SUPRIME-CAM AND WISE.
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Yoshiki Toba, Tohru Nagao, Masaru Kajisawa, Taira Oogi, Masayuki Akiyama, Hiroyuki Ikeda, Jean Coupon, Michael A. Strauss, Wei-Hao Wang, Masayuki Tanaka, Mana Niida, Masatoshi Imanishi, Chien-Hsiu Lee, Hideo Matsuhara, Yoshiki Matsuoka, Masafusa Onoue, Yuichi Terashima, Yoshihiro Ueda, Yuichi Harikane, and Yutaka Komiyama
- Subjects
GALAXIES ,CLASSIFICATION of galaxies ,TIDAL stripping (Astrophysics) ,INFRARED absorption ,ACTINIC flux ,AUTOCORRELATION (Statistics) - Abstract
We present measurements of the clustering properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining 125 deg
2 of wide and deep optical images obtained with the Hyper Suprime-Cam on the Subaru Telescope and all-sky mid-IR images taken with Wide-Field Infrared Survey Explorer, we have discovered 4367 IR-bright DOGs with and flux density at 22 mJy. We calculate the angular autocorrelation function (ACF) for a uniform subsample of 1411 DOGs with 3.0 mJy < flux (22 ) < 5.0 mJy and < 24.0. The ACF of our DOG subsample is well-fit with a single power law, = (0.010 ± 0.003) , where θ is in degrees. The correlation amplitude of IR-bright DOGs is larger than that of IR-faint DOGs, which reflects a flux dependence of the DOG clustering, as suggested by Brodwin et al. We assume that the redshift distribution for our DOG sample is Gaussian, and consider two cases: (1) the redshift distribution is the same as IR-faint DOGs with flux at 22 < 1.0 mJy, mean and sigma z = 1.99 ± 0.45, and (2) z = 1.19 ± 0.30, as inferred from their photometric redshifts. The inferred correlation length of IR-bright DOGs is r0 = 12.0 ± 2.0 and 10.3 ± 1.7 Mpc, respectively. IR-bright DOGs reside in massive dark matter halos with a mass of and in the two cases, respectively. [ABSTRACT FROM AUTHOR]- Published
- 2017
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38. MERGER-INDUCED SHOCKS IN THE NEARBY LIRG VV 114 THROUGH METHANOL OBSERVATIONS WITH ALMA.
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Toshiki Saito, Satoshi Ohashi, Minju Lee, Ryohei Kawabe, Kentaro Motohara, Daisuke Iono, Daniel Espada, Kouichiro Nakanishi, Junko Ueda, Hajime Sugai, Shuro Takano, Min S. Yun, Masatoshi Imanishi, and Yoshiaki Hagiwara
- Subjects
METHANOL ,GALAXIES ,RADIO lines ,EMISSIONS (Air pollution) - Abstract
We report the detection of two CH
3 OH lines (JK = 2K –1K and 3K –2K ) between the progenitor’s disks (“Overlap”) of the mid-stage merging galaxy VV 114 obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 and Band 4. The detected CH3 OH emission shows an extended filamentary structure (∼3 kpc) across the progenitor’s disks with relatively large velocity width (FWZI ∼ 150 km s−1 ). The emission is only significant in the “overlap” and not detected in the two merging nuclei. Assuming optically thin emission and local thermodynamic equilibrium, we found the CH3 OH column density relative to H2 () peaks at the “Overlap” (∼8 × 10−9 ), which is almost an order of magnitude larger than that at the eastern nucleus. We suggest that kpc-scale shocks driven by galaxy–galaxy collision may play an important role to enhance the CH3 OH abundance at the “Overlap.” This scenario is consistent with shock-induced large velocity dispersion components of ionized gas that have been detected in optical wavelength at the same region. Conversely, low at the nuclear regions might be attributed to the strong photodissociation by nuclear starbursts and/or a putative active galactic nucleus, or inefficient production of CH3 OH on dust grains due to initial high-temperature conditions (i.e., desorption of the precursor molecule, CO, into gas phase before forming CH3 OH on dust grains). These ALMA observations demonstrate that CH3 OH is a unique tool to address kpc-scale shock-induced gas dynamics and star formation in merging galaxies. [ABSTRACT FROM AUTHOR]- Published
- 2017
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39. SUBARU HIGH-z EXPLORATION OF LOW-LUMINOSITY QUASARS (SHELLQs). I. DISCOVERY OF 15 QUASARS AND BRIGHT GALAXIES AT 5.7 < z < 6.9.
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Yoshiki Matsuoka, Masafusa Onoue, Nobunari Kashikawa, Kazushi Iwasawa, Michael A. Strauss, Tohru Nagao, Masatoshi Imanishi, Mana Niida, Yoshiki Toba, Masayuki Akiyama, Naoko Asami, James Bosch, Sébastien Foucaud, Hisanori Furusawa, Tomotsugu Goto, James E. Gunn, Yuichi Harikane, Hiroyuki Ikeda, Toshihiro Kawaguchi, and Satoshi Kikuta
- Subjects
QUASARS ,RADIO sources (Astronomy) ,LUMINOSITY ,STELLAR luminosity function ,BAYESIAN analysis - Abstract
We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High-z Exploration of Low-Luminosity Quasars project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg
2 of the survey footprint. The success rate of our photometric selection is quite high, approaching 100% at the brighter magnitudes (zAB < 23.5 mag). Our selection also recovered all the known high-z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Lyα lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of z ≥ 6 galaxies, compared with that of quasars, at magnitudes fainter than M1450 ∼ −22 mag or zAB ∼ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing. [ABSTRACT FROM AUTHOR]- Published
- 2016
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40. ALMA INVESTIGATION OF VIBRATIONALLY EXCITED HCN/HCO+/HNC EMISSION LINES IN THE AGN-HOSTING ULTRALUMINOUS INFRARED GALAXY IRAS 20551−4250.
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Masatoshi Imanishi (今西昌俊), Kouichiro Nakanishi (中西康一郎), and Takuma Izumi (泉拓磨)
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GALAXIES ,VIBRATIONAL spectra ,GALACTIC nuclei ,STARBURSTS ,INFRARED spectra - Abstract
We present the results of ALMA Cycle 2 observations of the ultraluminous infrared galaxy IRAS 20551−4250 at HCN/HCO
+ /HNC J = 3–2 lines at both vibrational ground (v = 0) and vibrationally excited (v2 = 1) levels. This galaxy contains a luminous buried active galactic nucleus (AGN), in addition to starburst activity, and our ALMA Cycle 0 data revealed a tentatively detected vibrationally excited HCN v2 = 1f J = 4–3 emission line. In our ALMA Cycle 2 data, the HCN/HCO+ /HNC J = 3–2 emission lines at v = 0 are clearly detected. The HCN and HNC v2 = 1f J = 3–2 emission lines are also detected, but the HCO+ v2 = 1f J = 3–2 emission line is not. Given the high energy level of v2 = 1 and the resulting difficulty of collisional excitation, we compared these results with those of the calculation of infrared radiative pumping, using the available infrared 5–35 μm spectrum. We found that all of the observational results were reproduced if the HCN abundance was significantly higher than that of HCO+ and HNC. The flux ratio and excitation temperature between v2 = 1f and v = 0, after correction for possible line opacity, suggests that infrared radiative pumping affects rotational (J-level) excitation at v = 0 at least for HCN and HNC. The HCN-to-HCO+ v = 0 flux ratio is higher than those of starburst-dominated regions, and will increase even more when the derived high HCN opacity is corrected. The enhanced HCN-to-HCO+ flux ratio in this AGN-hosting galaxy can be explained by the high HCN-to-HCO+ abundance ratio and sufficient HCN excitation at up to J = 4, rather than the significantly higher efficiency of infrared radiative pumping for HCN than HCO+ . [ABSTRACT FROM AUTHOR]- Published
- 2016
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41. ALMA 0.1–0.2 arcsec RESOLUTION IMAGING OF THE NGC 1068 NUCLEUS: COMPACT DENSE MOLECULAR GAS EMISSION AT THE PUTATIVE AGN LOCATION.
- Author
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Masatoshi Imanishi (今 西 昌 俊), Kouichiro Nakanishi (中 西 康 一 郎), and Takuma Izumi (泉 拓 磨)
- Published
- 2016
- Full Text
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42. SUBMILLIMETER-HCN DIAGRAM FOR ENERGY DIAGNOSTICS IN THE CENTERS OF GALAXIES.
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Takuma Izumi, Kotaro Kohno, Susanne Aalto, Daniel Espada, Kambiz Fathi, Nanase Harada, Bunyo Hatsukade, Pei-Ying Hsieh, Masatoshi Imanishi, Melanie Krips, Sergio Martín, Satoki Matsushita, David S. Meier, Naomasa Nakai, Kouichiro Nakanishi, Eva Schinnerer, Kartik Sheth, Yuichi Terashima, and Jean L. Turner
- Subjects
HYDROCYANIC acid ,ACTIVE galactic nuclei ,STARBURSTS ,RADIATIVE transfer ,GAS phase reactions - Abstract
Compiling data from literature and the Atacama Large Millimeter/submillimeter Array archive, we show enhanced HCN(4–3)/HCO
+ (4–3) and/or HCN(4–3)/CS(7–6) integrated intensity ratios in circumnuclear molecular gas around active galactic nuclei (AGNs) compared to those in starburst (SB) galaxies (submillimeter HCN enhancement). The number of sample galaxies is significantly increased from our previous work. We expect that this feature could potentially be an extinction-free energy diagnostic tool of nuclear regions of galaxies. Non-LTE radiative transfer modelings of the above molecular emission lines involving both collisional and radiative excitation, as well as a photon trapping effect, were conducted to investigate the cause of the high line ratios in AGNs. As a result, we found that enhanced abundance ratios of HCN to HCO+ and HCN to CS in AGNs as compared to SB galaxies by a factor of a few to even ≳10 are a plausible explanation for the submillimeter HCN enhancement. However, a counterargument of a systematically higher gas density in AGNs than in SB galaxies can also be a plausible scenario. Although we cannot fully distinguish these two scenarios at this moment owing to an insufficient amount of multi-transition, multi-species data, the former scenario is indicative of abnormal chemical composition in AGNs. Regarding the actual mechanism to realize the composition, we suggest that it is difficult with conventional gas-phase X-ray-dominated region ionization models to reproduce the observed high line ratios. We might have to take into account other mechanisms such as neutral–neutral reactions that are efficiently activated in high-temperature environments and/or mechanically heated regions to further understand the high line ratios in AGNs. [ABSTRACT FROM AUTHOR]- Published
- 2016
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43. ALMA OBSERVATIONS OF THE SUBMILLIMETER DENSE MOLECULAR GAS TRACERS IN THE LUMINOUS TYPE-1 ACTIVE NUCLEUS OF NGC 7469.
- Author
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Takuma Izumi, Kotaro Kohno, Susanne Aalto, Akihiro Doi, Daniel Espada, Kambiz Fathi, Nanase Harada, Bunyo Hatsukade, Takashi Hattori, Pei-Ying Hsieh, Soh Ikarashi, Masatoshi Imanishi, Daisuke Iono, Sumio Ishizuki, Melanie Krips, Sergio Martín, Satoki Matsushita, David S. Meier, Hiroshi Nagai, and Naomasa Nakai
- Subjects
STELLAR evolution ,LUMINOSITY ,X-ray spectra ,SPECTROMETRY ,ASTROPHYSICS - Abstract
We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 1 observations of the central kiloparsec region of the luminous type 1 Seyfert galaxy NGC 7469 with unprecedented high resolution (0.″5 ×0.″4 = 165 × 132 pc) at submillimeter wavelengths. Utilizing the wide bandwidth of ALMA, we simultaneously obtained HCN(4–3), HCO
+ (4–3), CS(7–6), and partially CO(3–2) line maps, as well as the 860 μm continuum. The region consists of the central ∼1″ component and the surrounding starburst ring with a radius of ∼1.″5–2.″5. Several structures connect these components. Except for CO(3–2), these dense gas tracers are significantly concentrated toward the central ∼1″, suggesting their suitability to probe the nuclear regions of galaxies. Their spatial distribution resembles well those of centimeter and mid-infrared continuum emissions, but it is anticorrelated with the optical one, indicating the existence of dust-obscured star formation. The integrated intensity ratios of HCN(4–3)/HCO+ (4–3) and HCN(4–3)/CS(7–6) are higher at the active galactic nucleus (AGN) position than at the starburst ring, which is consistent with our previous findings (submillimeter-HCN enhancement). However, the HCN(4–3)/HCO+ (4–3) ratio at the AGN position of NGC 7469 (1.11 ± 0.06) is almost half of the corresponding value of the low-luminosity type 1 Seyfert galaxy NGC 1097 (2.0 ± 0.2), despite the more than two orders of magnitude higher X-ray luminosity of NGC 7469. But the ratio is comparable to that of the close vicinity of the AGN of NGC 1068 (∼1.5). Based on these results, we speculate that some heating mechanisms other than X-ray (e.g., mechanical heating due to an AGN jet) can contribute significantly for shaping the chemical composition in NGC 1097. [ABSTRACT FROM AUTHOR]- Published
- 2015
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44. LOCAL INSTABILITY SIGNATURES IN ALMA OBSERVATIONS OF DENSE GAS IN NGC 7469.
- Author
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Kambiz Fathi, Takuma Izumi, Alessandro B. Romeo, Sergio Martín, Masatoshi Imanishi, Evanthia Hatziminaoglou, Susanne Aalto, Daniel Espada, Kotaro Kohno, Melanie Krips, Satoki Matsushita, David S. Meier, Naomasa Nakai, and Yuichi Terashima
- Published
- 2015
- Full Text
- View/download PDF
45. ALMA MULTI-LINE OBSERVATIONS OF THE IR-BRIGHT MERGER VV 114.
- Author
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Toshiki Saito, Daisuke Iono, Min S. Yun, Junko Ueda, Kouichiro Nakanishi, Hajime Sugai, Daniel Espada, Masatoshi Imanishi, Kentaro Motohara, Yosiaki Hagiwara, Ken Tateuchi, Minju Lee, and Ryohei Kawabe
- Subjects
MOLECULAR gas lasers ,KINEMATICS ,SPATIAL variation ,GALAXIES ,RADIATIVE transfer - Abstract
We present Atacama Large Millimeter/submillimeter Array cycle 0 observations of the molecular gas and dust in the IR-bright mid-stage merger VV 114 obtained at 160–800 pc resolution. The main aim of this study is to investigate the distribution and kinematics of the cold/warm gas and to quantify the spatial variation of the excitation conditions across the two merging disks. The data contain 10 molecular lines, including the first detection of extranuclear CH
3 OH emission in interacting galaxies, as well as continuum emission. We map the12 CO(3–2)/12 CO(1–0) and the12 CO(1–0)/13 CO(1–0) line ratio at 800 pc resolution (in the units of K km s−1 ), and find that these ratios vary from 0.2–0.8 and 5–50, respectively. Conversely, the 200 pc resolution HCN(4–3)/HCO+ (4–3) line ratio shows low values (<0.5) at a filament across the disks except for the unresolved eastern nucleus which is three times higher (1.34 ± 0.09). We conclude from our observations and a radiative transfer analysis that the molecular gas in the VV 114 system consists of five components with different physical and chemical conditions, i.e., (1) dust-enshrouded nuclear starbursts and/or active galactic nuclei, (2) widespread star-forming dense gas, (3) merger-induced shocked gas, (4) quiescent tenuous gas arms without star formation, and (5) H2 gas mass of (3.8 ± 0.7) × 107 (assuming a conversion factor of αCO = 0.8 ) at the tip of the southern tidal arm, as a potential site of tidal dwarf galaxy formation. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
46. THE DIFFERENCES IN THE TORUS GEOMETRY BETWEEN HIDDEN AND NON-HIDDEN BROAD LINE ACTIVE GALACTIC NUCLEI.
- Author
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Kohei Ichikawa, Christopher Packham, Cristina Ramos Almeida, Andrés Asensio Ramos, Almudena Alonso-Herrero, Omaira González-Martín, Enrique Lopez-Rodriguez, Yoshihiro Ueda, Tanio Díaz-Santos, Moshe Elitzur, Sebastian F. Hönig, Masatoshi Imanishi, Nancy A. Levenson, Rachel E. Mason, Eric S. Perlman, and Crystal D. Alsip
- Subjects
ACTIVE galactic nuclei ,ACTIVE galaxies ,GALAXIES ,ASTROPHYSICS ,PHOTOMETRY - Abstract
We present results from the fitting of infrared (IR) spectral energy distributions of 21 active galactic nuclei (AGNs) with clumpy torus models. We compiled high spatial resolution (∼0.3–0.7 arcsec) mid-IR (MIR) N-band spectroscopy, Q-band imaging, and nuclear near- and MIR photometry from the literature. Combining these nuclear near- and MIR observations, far-IR photometry, and clumpy torus models enables us to put constraints on the torus properties and geometry. We divide the sample into three types according to the broad line region (BLR) properties: type-1s, type-2s with scattered or hidden broad line region (HBLR) previously observed, and type-2s without any published HBLR signature (NHBLR). Comparing the torus model parameters gives us the first quantitative torus geometrical view for each subgroup. We find that NHBLR AGNs have smaller torus opening angles and larger covering factors than HBLR AGNs. This suggests that the chance to observe scattered (polarized) flux from the BLR in NHBLR could be reduced by the dual effects of (a) less scattering medium due to the reduced scattering volume given the small torus opening angle and (b) the increased torus obscuration between the observer and the scattering region. These effects give a reasonable explanation for the lack of observed HBLR in some type-2 AGNs. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
47. DISCOVERY OF NEW DWARF GALAXY NEAR THE ISOLATED SPIRAL GALAXY NGC 6503.
- Author
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Jin Koda, Masafumi Yagi, Yutaka Komiyama, Samuel Boissier, Alessandro Boselli, Alexandre Y. K. Bouquin, Jennifer Donovan Meyer, Armando Gil de Paz, Masatoshi Imanishi, Barry F. Madore, and David A. Thilker
- Published
- 2015
- Full Text
- View/download PDF
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