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We report on the results of 3--4 $\mu$m spectroscopy of the ultra-luminous infrared galaxy (ULIRG) UGC 5101. It has a cool far-infrared color and a LINER-type optical spectrum, and so, based on a view gaining some currency, would be regarded as dominated by star formation. However, we find that it has strong 3.4 $\mu$m carbonaceous dust absorption, low-equivalent-width 3.3 $\mu$m polycyclic aromatic hydrocarbon (PAH) emission, and a small 3.3 $\mu$m PAH to far-infrared luminosity ratio. This favors an alternative scenario, in which an energetically dominant AGN is present behind obscuring dust. The AGN is plausibly obscured along all lines of sight (a `buried AGN'), rather than merely obscured along our particular line of sight. Such buried AGNs have previously been found in thermal infrared studies of the ULIRGs IRAS 08572+3915 and IRAS F00183$-$7111, both classified optically as LINERs. We argue that buried AGNs can produce LINER-type optical spectra, and that at least some fraction of LINER-type ULIRGs are predominantly powered by buried AGNs.

Thermal infrared photometry in the $L$- and $M'$-band and $L - M'$ colors of type-1 and type-2 active galactic nuclei (AGNs) are presented. After combining our observations with photometric data at similar wavelengths taken from the literature, we find that the excess of $L - M'$ colors of type-2 AGNs (37 sources, 50 data points) relative to type-1 AGNs (27 sources, 36 data points), due to dust extinction, is statistically detectable, but very small. We next investigate the $L - M'$ colors of type-2 AGNs by separating less dust-obscured type-2 AGNs and highly dust-obscured type-2 AGNs. In both cases, the $L - M'$ colors are similar to the intrinsic $L - M'$ color of unobscured AGNs, and the $L - M'$ color excess of the latter highly dust-obscured type-2 AGNs due to dust extinction is much smaller than that expected from the Galactic dust extinction curve. Contamination from starbursts and the time lag of flux variation are unlikely to explain this small $L - M'$ color excess, which is best explained if the dust extinction curve in the close vicinity of AGNs is fairly flat at 3--5 $\mu$m as a result of a size increase of the absorbing dust grains through coagulation., Comment: 24 pages, 4 figures, accepted for publication in AJ

The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed based on their ground-based 3--4 $\mu$m spectra. Both the equivalent width of the 3.3 $\mu$m polycyclic aromatic hydrocarbon (PAH) emission feature and the 3.3 $\mu$m PAH to far-infrared luminosity ratio ($L_{3.3}/L_{\rm FIR}$) are analyzed. Assuming nuclear compact starburst activity in these sources produces the 3.3 $\mu$m PAH emission as strongly as that in starburst galaxies with lower far-infrared luminosities, the followings results are found: For six IRLGs, both the observed equivalent widths and the $L_{3.3}/L_{\rm FIR}$ ratios are too small to explain the bulk of their far-infrared luminosities by compact starburst activity, indicating that active galactic nucleus (AGN) activity is a dominant energy source. For the other three IRLGs, while the 3.3 $\mu$m PAH equivalent widths are within the range of starburst galaxies, the $L_{3.3}/L_{\rm FIR}$ ratios after correction for screen dust extinction are a factor of $\sim$3 smaller. The uncertainty in the dust extinction correction factor and in the scatter of the intrinsic $L_{3.3}/L_{\rm FIR}$ ratios for starburst galaxies do not allow a determination of the ultimate energy sources for these three IRLGs., Comment: 29 pages, 2 figures, Accepted for publication in ApJ

We report the detection of a 9.7 $\mu$m silicate dust absorption feature toward the Cygnus A nucleus. Its optical depth is, however, significantly smaller than that expected from the dust extinction toward the background $L$-band emission region ($A_{\rm V}$ $\sim$ 150 mag). We argue that the most likely explanation for the small optical depth is that the obscuring dust exists so close to the central engine that a temperature gradient occurs. Our calculation confirms that the small optical depth and the spectral energy distribution at 3--30 $\mu$m can be quantitatively reproduced by this explanation. Combining this picture with the huge AGN luminosity, the emission properties of Cygnus A are consistent with those of a type 2 quasar, that is, a highly luminous AGN that is highly obscured ($A_{\rm V}$ $>$ 50 mag) by a dusty torus with an inner radius of $$ a few 100 pc scale dust in the host galaxy., Comment: 17 pages, 2 figures, accepted for publication in ApJ

We have investigated the optical and near-infrared colors of K'-selected galaxies in clusters at z ~ 1.2 near to the radio galaxy 3C 324 using images obtained with the Subaru telescope and archival HST data. The distribution of colors of the galaxies in the cluster region is found to be fairly broad, and it may imply significant scatter in their star-formation histories, although the effect of contamination of field galaxies is uncertain. The red sequence of galaxies whose R-K colors are consistent with passive evolution models for old galaxies is found to be truncated at K' ~ 20 mag, and there are few fainter galaxies with similar red colors in the cluster region. We find that the bulge-dominated galaxies selected by quantitative morphological classification form a broad sequence in the color-magnitude diagram, whose slope is much steeper than that expected from metallicity variations within a passively evolving coeval galaxy population. We argue that the observed color-magnitude sequence can be explained by metallicity and age variations, and the fainter galaxies with K' > 20 mag may be 1-2 Gyr younger than the brighter galaxies. Some spatial segregation of the color and K'-band luminosity is seen in the sky distribution; the redder and the brighter objects tend to be located near 3C 324., 16 pages, 10 figures, accepted for publication in PASJ

We present high spatial resolution images of the gravitational-lens system PG 1115+080 taken with the near-infrared camera (CISCO) on the Subaru telescope. The FWHM of the combined image is $0.''32$ in the $K'$-band, yielding spatial resolution of $0.''14$ after a deconvolution procedure. This is a first detection of an extended emission adjacent to the A1/A2 components, indicating the presence of a fairly bright emission region with a characteristic angular radius of $\sim$ 5 mas (40 pc). The near-infrared image of the Einstein ring was extracted in both the $J$ and $K'$ bands. The $J-K'$ color is found to be significantly redder than that of a synthetic model galaxy with an age of 3 Gyr, the age of the universe at the quasar redshift., 11 pages, 6 figures. Accepted for publication in PASJ(2000)

We compare the luminosities of the hard X-ray and optical/near-infrared broad-line emission from activegalactic nuclei (AGNs) and ultraluminous infrared galaxies (ULIRGs). Both types of emission are thought to be good indicators of activity driven by supermassive black holes. We selected objects for which both X-ray and broad-line data are available, and, additionally, for which we can obtain information about the far-infrared and/or morphological properties. We ®nd that, although the hard X-ray to broad Ha luminosity ratio LX=L…broad Ha† is relatively constant in nearly all of the objects examined, there exist some objects showing a distinctly small LX=L…broad Ha† ratio. These small LX=L…broad Ha† objects are thought to be undergoing a

We present the results of spectroscopic studies of Mrk 231 and NGC 4151 in the 3 /im region. In the spectrum of Mrk 231, the strengths of the 3.3 /im emission feature and the 3.4 /im carbonaceous absorption feature are smaller than expected. The weakness of the 3.3 /im emission feature implies that large fractions of extended H2 emission detected by Krabbe et al. (1997, AAA 67.158.058) are excited by SMBH-driven activities, and/or the 3.3 /im emission carriers in the circumnuclear starburst region are destroyed by being exposed to energetic radiation from SMBH-driven activities. The weakness of the 3.4 /im carbonaceous absorption feature may be due to the destruction of C-H stretching bonds in dust grains and/or lower abundance of C relative to Si, O, and Mg than that in our Galaxy, consistent to the fact that Mrk 231 is now undergoing starburst activities. In the spectrum of NGC 4151, we detect the broad Bra emission line, but do not detect the 3.3 /im emission feature nor the 3.4 /im carbonaceous absorption feature. The nondetection of the 3.3 /im emission feature implies that nuclear starburst activities just outside the obscuring torus are weak (LFIR < 3.7 x 10 9 L@).

We have developed a special grating capable of producing an echellogram (a spectrum arranged in raster form) in the 30th or even higher order in the near-infrared wavelength region. The grating substrate is made of an aluminum alloy that has been carved mechanically with a high-precision shaving machine. The optical efficiency, measured with a special spectrophotometer at about 2 μm, is ~70%. The diffuse light component, possibly attributable to scattering on the grating surface, has been estimated to be at most ~5% when the grating is incorporated in an actual spectrograph system. The measured efficiency of the fabricated grating is compared with that given by a numerical analysis. The comparison shows remarkable agreement in both the optical efficiency and the distribution of energy diffracted to various orders.

We present the 1.2-4.2 fiia spectroscopy of stars found in an objective prism survey of the galactic plane by Stephenson (1992, AAA 55.002.010). These stars were thought by Stephenson to be heavily reddened by interstellar absorption. However, almost all of them have turned out to be late-type stars with clear 2.3 //m CO absorption, which means that they are intrinsically red as well. A few stars have Ay ~ 9, but most of them are only moderately reddened {Ay = 1-5).

We present results from our ALMA Cycle 0 observations, at the frequencies around the HCN, HCO+, and HNC J=4-3 transition lines, of the luminous infrared galaxy IRAS 20551-4250 at z=0.043, which is known to host an energetically important obscured AGN. In addition to the targeted HCN, HCO+, and HNC J=4-3 emission lines, two additional strong emission lines are seen, which we attribute to H2S and CH3CN(+CCH). The HCN-to-HCO+ J=4-3 flux ratio (~0.7) is higher than in the other starburst-dominated galaxy (~0.2) observed in our ALMA Cycle 0 program. We tentatively (~5 sigma) detected the vibrationally excited (v2=1) HCN J=4-3 (l=1f) emission line, which is important for testing an infrared radiative pumping scenario for HCN. This is the second detection of this molecular transition in external galaxies. The most likely reason for this detection is not only the high flux of this emission line, but also the small molecular line widths observed in this galaxy, suggesting that vibrational excitation of HCN may be relatively common in AGN-hosting galaxies., 11 pages, 5 figures, accepted for publication in AJ

We present the results of HCN/HCO+/HNC J=4-3 transition line observations of the nearby starburst galaxy NGC 1614, obtained with ALMA Cycle 0. We find that high density molecular gas, traced with these lines, shows a velocity structure such that the northern (southern) side of the nucleus is redshifted (blueshifted) with respect to the nuclear velocity of this galaxy. The redshifted and blueshifted emission peaks are offset by ~0.6" at the northern and southern sides of the nucleus, respectively. At these offset positions, observations at infrared >3 micron indicate the presence of active dusty starbursts, supporting the picture that high-density molecular gas is the site of active starbursts. The enclosed dynamical mass within the central ~2" in radius, derived from the dynamics of the high-density molecular gas, is ~10^9 Msun, which is similar to previous estimates. Finally, the HCN emission is weaker than HCO+ but stronger than HNC for J=4-3 for all starburst regions of NGC 1614, as seen for J=1-0 transition lines in starburst-dominated galaxies., 19 pages, 9 figures, accepted for publication in AJ

We present a kinematic analysis of the dense molecular gas in the central 200 parsecs of the nearby galaxy NGC1097, based on Cycle 0 observations with the Atacama Large Millimeter/sub-millimeter Array (ALMA). We use the HCN(4-3) line to trace the densest interstellar molecular gas, and quantify its kinematics, and estimate an inflow rate for the molecular gas. We find a striking similarity between the ALMA kinematic data and the analytic spiral inflow model that we have previously constructed based on ionized gas velocity fields on larger scales. We are able to follow dense gas streaming down to 40 pc distance from the supermassive black hole in this Seyfert 1 galaxy. In order to fulfill marginal stability, we deduce that the dense gas is confined to a very thin disc, and we derive a dense gas inflow rate of 0.09 Msun/yr at 40 pc radius. Combined with previous values from the Ha and CO gas, we calculate a combined molecular and ionized gas inflow rate of 0.2 Msun/yr at 40 pc distance from the central supermassive black hole of NGC1097., Accepted for Publication in the ApJ Letters

High resolution (0.4 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 observations of HCO+(4-3) and HCN(4-3) toward a mid-stage infrared bright merger VV114 have revealed compact nuclear (, 5 pages, 4 figures, PASJ Letters accepted

We present the results of our ALMA Cycle 2 high angular resolution (0.1-0.2 arcsec) observations of the nuclear region of the nearby well-studied type-2 active galactic nucleus (AGN), NGC 1068, at HCN J=3-2 and HCO+ J=3-2 emission lines. For the first time, due to a higher angular resolution than previous studies, we clearly detected dense molecular gas emission at the putative AGN location, identified as a ~1.1 mm (~266 GHz) continuum emission peak, by separating this emission from brighter emission located at 0.5-2.0 arcsec on the eastern and western sides of the AGN. The estimated intrinsic molecular emission size and dense molecular mass, which are thought to be associated with the putative dusty molecular torus around an AGN, were ~10 pc and ~several x 10^5 Msun, respectively. HCN-to-HCO+ J=3-2 flux ratios substantially higher than unity were found throughout the nuclear region of NGC 1068. The continuum emission displayed an elongated morphology along the direction of the radio jet located at the northern side of the AGN, as well as a weak spatially resolved component at ~2.0 arcsec on the southwestern side of the AGN. The latter component most likely originated from star formation, with the estimated luminosity more than one order of magnitude lower than the luminosity of the central AGN. No vibrationally excited (v2=1f) J=3-2 emission lines were detected for HCN and HCO+ across the field of view., 7 pages, 4 figures, accepted for publication in ApJ Letters

A mid-infrared (MIR) imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the MIR adaptive optics (AO) system (MIRAO), the instrument will afford ~15 times higher sensitivity and ~4 times better spatial resolution (0.07”) at 10μm compared to 8m-class telescopes. Additionally, through exploiting the large collection area of the TMT, the high-dispersion spectroscopy mode will be unrivaled by other ground- and space-based facilities. These combined capabilities offer the possibility for breakthrough science, as well as ‘workhorse’ observing modes of imaging and low/moderate spectral resolution. In this paper we summarize the primary science drivers that are guiding the instrument design.

WISH, Wide-field Imaging Surveyor for High-redshiftt, is a space mission concept to conduct very deep and widefield surveys at near infrared wavelength at 1-5μm to study the properties of galaxies at very high redshift beyond the epoch of cosmic reionization. The concept has been developed and studied since 2008 to be proposed for future JAXA/ISAS mission. WISH has a 1.5m-diameter primary mirror and a wide-field imager covering 850 arcmin 2 . The pixel scale is 0.155 arcsec for 18μm pitch, which properly samples the diffraction-limited image at 1.5μm. The main program is Ultra Deep Survey (UDS) covering 100 deg 2 down to 28AB mag at least in five broad bands. We expect to detect 4 galaxies at z=8-9, 10 3 -10 4 galaxies at z=11-12, and 50-100 galaxies at z

International audience; We report deep Subaru H alpha 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(circle dot)) 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 H alpha-bright clusters with masses \textgreater 10(3)M(circle dot); and (3) the H alpha-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 (A(V) similar to 0.1 mag) and low metallicity (similar to 0.2Z(circle dot)) 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.

We present the results of a ground-based, high spatial resolution infrared 18 micron imaging study of nearby luminous infrared galaxies (LIRGs), using the Subaru 8.2-m and Gemini South 8.1-m telescopes. The diffraction-limited images routinely achieved with these telescopes in the Q-band (17-23 micron) allow us to investigate the detailed spatial distribution of infrared emission in these LIRGs. We then investigate whether the emission surface brightnesses are modest, as observed in starbursts, or are so high that luminous active galactic nuclei (AGNs; high emission surface brightness energy sources) are indicated. The sample consists of 18 luminous buried AGN candidates and starburst-classified LIRGs identified in earlier infrared spectroscopy. We find that the infrared 18 micron emission from the buried AGN candidates is generally compact, and the estimated emission surface brightnesses are high, sometimes exceeding the maximum value observed in and theoretically predicted for a starburst phenomenon. The starburst-classified LIRGs usually display spatially extended 18 micron emission and the estimated emission surface brightnesses are modest, within the range sustained by a starburst phenomenon. The general agreement between infrared spectroscopic and imaging energy diagnostic methods suggests that both are useful tools for understanding the hidden energy sources of the dusty LIRG population., Comment: 17 pages, 3 figures, accepted for publication in AJ (No. 141, 2011 May issue). Higher resolution version is available at http://optik2.mtk.nao.ac.jp/~imanishi/Paper/20um/20um.pdf

WISH is a new space science mission concept whose primary goal is to study the first galaxies in the early universe. We will launch a 1.5m telescope equipped with 1000 arcmin2 wide-field NIR camera by late 2010's in order to conduct unique ultra-deep and wide-area sky surveys at 1-5 micron. The primary science goal of WISH mission is pushing the high-redshift frontier beyond the epoch of reionization by utilizing its unique imaging capability and the dedicated survey strategy. We expect to detect ~10 4 galaxies at z=8-9, ~3-6x10 3 galaxies at z=11-12, and ~50-100 galaxies at z=14-17 within about 5 years of the planned mission life time. It is worth mentioning that a large fraction of these objects may be bright enough for the spectroscopic observations with the extremely large telescopes. By adopting the optimized strategy for the recurrent observations to reach the depth, we also use the surveys to detect transient objects. Type Ia Supernova cosmology is thus another important primary goal of WISH. A unique optical layout has been developed to achieve the diffraction-limited imaging at 1-5micron over the required large area. Cooling the mirror and telescope to ~100K is needed to achieve the zodiacal light limited imaging and WISH will achieve the required temperature by passive cooling in the stable thermal environment at the orbit near Sun-Earth L2. We are conducting the conceptual studies and development for the important components of WISH including the exchange mechanism for the wide-field filters as well as the primary mirror fixation.

A mid-infrared (MIR) imager and spectrometer is being investigated for possible consideration for construction in the early operation of the Thirty Meter Telescope (TMT). Combined with adaptive optics for the MIR, the instrument will afford 15 times higher sensitivity (0.1mJy as 5 sigma detection in 1hour integration in the N-band imaging) and 4 times better spatial resolution (0.08") at 10μm compared to 8m-class telescopes. In addition, its large light-gathering power allows high-dispersion spectroscopy in the MIR that will be unrivaled by any other facility. We, a collaborating team of Japanese and US MIR astronomers, have carefully considered the science drivers for the TMT MIR instrument. Such an instrument would offer both broad and potentially transformative science. Furthering the science cases for the MIRES1, where high-dispersion spectroscopy was emphasized, we discuss additional capabilities for the instrument drawn from the enlarged science cases. The science cases include broader areas of astronomical fields: star and planet formation, solar system bodies, evolved stars, interstellar medium (ISM), extragalaxies, and cosmology. Based on these science drivers, essential instrument capabilities and key enhancement are discussed (see the companion paper Tokunaga et al. 20102): specifically imaging, lowand high-spectral resolution modes, integral field spectroscopy, and polarimetry.

We present the results of our systematic infrared 2.5–35 μm low‐resolution spectroscopy of nearby ultraluminous infrared galaxies (ULIRGs) at z

We report the results of HCN(J=4-3) and HCO+(J=4-3) observations of two luminous infrared galaxies (LIRGs), NGC 4418 and Arp 220, made using the Atacama Submillimeter Telescope Experiment (ASTE). The ASTE wide-band correlator provided simultaneous observations of HCN(4-3) and HCO+(4-3) lines, and a precise determination of their flux ratios. Both galaxies showed high HCN(4-3) to HCO+(4-3) flux ratios of >2, possibly due to AGN-related phenomena. The J = 4-3 to J = 1-0 transition flux ratios for HCN (HCO+) are similar to those expected for fully thermalized (sub-thermally excited) gas in both sources, in spite of HCN's higher critical density. If we assume collisional excitation and neglect an infrared radiative pumping process, our non-LTE analysis suggests that HCN traces gas with significantly higher density than HCO+. In Arp 220, we separated the double-peaked HCN(4-3) emission into the eastern and western nuclei, based on velocity information. We confirmed that the eastern nucleus showed a higher HCN(4-3) to HCN(1-0) flux ratio, and thus contained a larger amount of highly excited molecular gas than the western nucleus., 21 pages, 4 figures, accepted for publication in PASJ (Vol.62, No.1, 2010 Feb 25 issue)

We present the first detections of the 3um water ice and 3.4um amorphous hydrocarbon (HAC) absorption features in z~2 ULIRGs. These are based on deep rest-frame 2-8um Spitzer IRS spectra of 11 sources selected for their appreciable silicate absorption. The HAC-to-silicate ratio for our z~2 sources is typically higher by a factor of 2-5 than that observed in the Milky Way. This HAC `excess' suggests compact nuclei with steep temperature gradients as opposed to predominantly host obscuration. Beside the above molecular absorption features, we detect the 3.3um PAH emission feature in one of our sources with three more individual spectra showing evidence for it. Stacking analysis suggests that water ice, hydrocarbons, and PAH are likely present in the bulk of this sample even when not individually detected. The most unexpected result of our study is the lack of clear detections of the 4.67um CO gas absorption feature. Only three of the sources show tentative signs of this feature and at significantly lower levels than has been observed in local ULIRGs. Overall, we find that the closest local analogs to our sources, in terms of 3-4um color, HAC-to-silicate and ice-to-silicate ratios, as well as low PAH equivalent widths are sources dominated by deeply obscured nuclei. Such sources form only a small fraction of ULIRGs locally and are commonly believed to be dominated by buried AGN. Our sample suggests that, in absolute number, such buried AGN are at least an order of magnitude more common at z~2 than today. The presence of PAH suggests that significant levels of star-formation are present even if the obscured AGN typically dominate the power budget., 39 pages, 14 figures, accepted for publication in ApJ

Observations at submillimeter wavelengths have revealed a population of sources thought to be at relatively large redshifts. The position of the 850 $\mu$m passband on the Rayleigh-Jeans portion of the Planck function leads to a maximum redshift estimate of $z\sim$4.5 since sources will not retain their redshift independent brightness close to the peak of the Planck function and thus drop out of surveys. Here we review evidence that ice absorption is present in the spectra of local ultraluminous infrared galaxies which are often taken as analogs for the 850 $\mu$m source population. We consider the implication of this absorption for ice induced spectral structure at far infrared wavelengths and present marginal astronomical evidence that amorphous ice may have a feature similar to crystalline ice near 150 $\mu$m. Recent corroborative laboratory evidence is supportive of this conclusion. It is argued that early metal enrichment by pair instability SN may lead to a high ice content relative to refractory dust at high redshift and a fairly robust detection of ice emission in a $z=6.42$ quasar is presented. It is further shown that ice emission is needed to understand the 450 $\mu$m sources observed in the GOODS-N field. We are thus encouraged to apply far infrared ice emission models to the available observations of HDF 850.1, the brightest submillimeter source in the {\it Hubble Deep Field}. We suggest that a redshift as large as 13 may need to be considered for this source, nearly a factor of three above the usual top estimate. Inclusion of the possibility of far infrared ice emission in the spectral energy distributions of model sources generally broadens the range of redshifts to be considered for submillimeter sources compared to models without ice emission., Comment: 37 pages, 8 figures, accepted for publication in the Astrophysical Journal

We report on the results of systematic infrared 3–4 μm spectroscopy of 23 Seyfert 1 and 32 Seyfert 2 galaxies. The putative nuclear starbursts in dusty tori of Seyfert galaxies are investigated through the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature. The 3.3 μm PAH emission is detected in roughly a half of the observed Seyfert galaxies. Since dust extinction is insignificant at infrared 3–4 μm, we can quantitatively estimate the magnitudes of the nuclear starbursts from the observed 3.3 μm PAH emission luminosities. Figure 1 compares the luminosities of nuclear starbursts and AGNs. We find that (1) nuclear starburst to AGN luminosity ratios are similar between Seyfert 1 and 2 galaxies, and that (2) nuclear starburst luminosity positively correlates with AGN power in both types of Seyfert galaxies [1],[2]. Our results suggest that nuclear starbursts are physically closely related to AGNs and control the mass accretion rate onto the central AGNs, through the increased turbulence of molecular gas in the tori and/or increased radiation effects.

We present the results on millimeter interferometric observations of four luminous infrared galaxies (LIRGs), Arp 220, Mrk 231, IRAS 08572+3915, and VV 114, and one Wolf-Rayet galaxy, He 2-10, using the Nobeyama Millimeter Array (NMA). Both the HCN(1-0) and HCO+(1-0) molecular lines were observed simultaneously and their brightness-temperature ratios were derived. High-quality infrared L-band (2.8-4.1 micron) spectra were also obtained for the four LIRGs to better constrain their energy sources deeply buried in dust and molecular gas. When combined with other LIRGs we have previously observed with NMA, the final sample comprised nine LIRGs (12 LIRGs' nuclei) with available interferometric HCN(1-0) and HCO+(1-0) data-sufficient to investigate the overall trend in comparison with known AGNs and starburst galaxies. We found that LIRGs with luminous buried AGN signatures at other wavelengths tend to show high HCN(1-0)/HCO+(1-0) brightness-temperature ratios as seen in AGN-dominated galaxies, while the Wolf-Rayet galaxy He 2-10 displays a small ratio. An enhanced HCN abundance in the interstellar gas surrounding a strongly X-ray-emitting AGN, as predicted by some chemical calculations, is a natural explanation of our results., 43 pages, 11 figures, accepted for publication in Astronomical Journal. Higher resolution version is available at http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN2/HCN2.pdf

We discuss Subaru and Spitzer Space Telescope imaging and spectroscopy of M87 in the mid-infrared from 5-35 um. These observations allow us to investigate mid-IR emission mechanisms in the core of M87 and to establish that the flaring, variable jet component HST-1 is not a major contributor to the mid-IR flux. The Spitzer data include a high signal-to-noise 15-35 $\mu$m spectrum of the knot A/B complex in the jet, which is consistent with synchrotron emission. However, a synchrotron model cannot account for the observed {\it nuclear} spectrum, even when contributions from the jet, necessary due to the degrading of resolution with wavelength, are included. The Spitzer data show a clear excess in the spectrum of the nucleus at wavelengths longer than 25 um, which we model as thermal emission from cool dust at a characteristic temperature of 55 \pm 10 K, with an IR luminosity \sim 10^{39} {\rm ~erg ~s^{-1}}. Given Spitzer's few-arcsecond angular resolution, the dust seen in the nuclear spectrum could be located anywhere within ~5'' (390 pc) of the nucleus. In any case, the ratio of AGN thermal to bolometric luminosity indicates that M87 does not contain the IR-bright torus that classical unified AGN schemes invoke. However, this result is consistent with theoretical predictions for low-luminosity AGNs, Comment: 9 pages, 7 figures, ApJ, in press

We present Spitzer IRS low resolution, mid-IR spectra of a sample of 25 high luminosity QSOs at 2, Comment: accepted for publication in A&A, 17 pages, 9 figures

We present an unprecedented measurement of the disk stability and local instability scales in the luminous infrared Seyfert 1 host, NGC 7469, based on ALMA observations of dense gas tracers and with a synthesized beam of 165 × 132 pc. While we confirm that non-circular motions are not significant in redistributing the dense interstellar gas in this galaxy, we find compelling evidence that the dense gas is a suitable tracer for studying the origin of its intensely high-mass star-forming ringlike structure. Our derived disk stability parameter $\mathcal{Q}$ accounts for a thick disk structure, and its value falls below unity at the radii in which intense star formation is found. Furthermore, we derive the characteristic instability scale ${\lambda }_{c}$ and find a striking agreement between our measured scale of ~180 pc and the typical sizes of individual complexes of young and massive star clusters seen in high-resolution images.

The nearby Sy 1 galaxy NGC 1097 represents an ideal laboratory to explore the molecular chemistry in the presence and surroundings of an active galactic nucleus. Exploring the distribution of different molecular species allows us to understand the physical processes affecting the ISM both in the AGN vicinity as well as in the outer star forming molecular ring. We carried out 3 mm ALMA observations of HCN, HCO+, CCH, CS, HNCO, SiO, HC3N, and SO as well as the 13C isotopologues. All species were imaged over the central 2 kpc (~30") of the galaxy at a resolution of ~2.2"x1.5 (150 pc x 100 pc). HCO+ and CS appear to be slightly enhanced in the star forming ring. CCH, showing the largest variations across NGC 1097, is suggested to be a good tracer of both obscured and early stage star formation. HNCO, SiO and HC3N are significantly enhanced in the inner circumnuclear disk surrounding the AGN. Differences in the molecular abundances are observed between the star forming ring and the inner circumnuclear disk. We conclude that the HCN/HCO+ and HCN/CS differences observed between AGN dominated and starburst galaxies are not due to a HCN enhancement due to X-rays, but rather this enhancement is produced by shocked material at distances of 200 pc from the AGN. Additionally we claim the lower HCN/CS to be a combination of a small under-abundance of CS in AGNs together with excitation effects, where a high dense gas component (~10^6 cm^-3) may be more prominent in SB galaxies. However the most promising are the differences found among the dense gas tracers which, at our modest spatial resolution, seem to outline the physical structure of the molecular disk around the AGN. In this picture, HNCO probes the well shielded gas in the disk, surrounding the dense material moderately exposed to X-ray radiation traced by HC3N. Finally SiO might be the innermost molecule in the disk structure., Comment: 14 pages, 9 figures, A&A Accepted for publication

We present the results of infrared 2.8-4.1 micron (L-band) spectroscopy of nearby infrared luminous galaxies with possible signatures of dust-obscured active galactic nuclei (AGNs) in data at other wavelengths. The samples are chosen to include sources with a radio excess relative to far-infrared emission, strong absorption features in mid-infrared 5-11.5 micron spectra, unusually weak [CII] 158 micron emission relative to the far-infrared continuum, and radio galaxies classified optically as narrow-line objects. Our aim is to investigate whether the signatures of possible obscured AGNs can be detected in our L-band spectra, based on the strengths of emission and absorption features. Six of nine observed sources clearly show 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission features, a good starburst indicator. An absorption feature at 3.1 micron due to ice-covered dust is detected in IRAS 04154+1755 and IRAS 17208-0014. The signature of a bare carbonaceous dust absorption feature at 3.4 micron is seen in NGC 1377. Our L-band spectra reveal strong signatures of obscured AGNs in all three optical Seyfert 2 galaxies (IRAS 04154+1755, Cygnus A, and 3C 234), and two galaxies classified optically as non-Seyferts (NGC 828 and NGC 1377). Among the remaining optical non-Seyferts, IRAS 17208-0014 might also show a buried AGN signature, whereas no explicit AGN evidence is seen in the L-band spectra of the mid-infrared absorption-feature source IRAS 15250+3609, and two weak [CII] emitters IC 860 and CGCG 1510.8+0725., Comment: 14 pages (emulateapj.sty), 3 figures, Accepted for publication in Astronomical Journal Vol. 131 No. 5 (May 2006)

We present interferometric observations of three ultraluminous infrared galaxies (ULIRGs; UGC 5101, Mrk 273, and IRAS 17208-0014) in the 3-mm wavelength range, using the Nobeyama Millimeter Array. Both the HCN (J=1-0) and HCO+ (J=1-0) molecular lines were observed simultaneously. HCN emission was clearly detected at the nuclear positions of these ULIRGs, and HCO+ emission was detected at the nuclear positions of UGC 5101 and IRAS 17208-0014. The HCN to HCO+ brightness-temperature ratios toward the nuclei of the three ULIRGs were derived and compared with those of lower luminosity galaxies known to be dominated by active galactic nuclei (AGNs) or starbursts. In UGC 5101 and Mrk 273, where there is evidence for obscured AGNs from previous observations at other wavelengths, we found high HCN/HCO+ ratios (>1.8) that are in the range found for AGN-dominated galaxies. In IRAS 17208-0014, where the presence of a powerful obscured AGN has been unclear, the ratio (1.7) is in between the observed values for starburst- and AGN-dominated galaxies. The high HCN/HCO+ brightness-temperature ratios in UGC 5101 and Mrk 273 could be the consequence of an HCN abundance enhancement, which is expected from chemical effects of the central X-ray emitting AGN on the surrounding dense molecular gas. Our proposed millimeter interferometric method based on HCN/HCO+ ratios may be an effective tool for unveiling elusive buried AGNs at the cores of ULIRGs, especially because of the negligible dust extinction at these wavelengths., 15 pages (emulateapj.sty), 8 figures (figures 1-5 resolution reduced), Accepted for publication in Astronomical Journal, A PDF file with high resolution is availble at http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN/HCN.pdf

We explore the relationships between the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature and active galactic nucleus (AGN) properties of a sample of 54 hard X-ray selected bright AGNs, including both Seyfert 1 and Seyfert 2 type objects, using the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the 9-month Swift/BAT survey in the 14-195 keV band and all of them have measured X-ray spectra at E ≲ 10 keV. These X-ray spectra provide measurements of the neutral hydrogen column density (NH) towards the AGNs. We use the 3.3 μm PAH luminosity (L3.3μm) as a proxy for star formation activity and hard X-ray luminosity (L14-195keV) as an indicator of the AGN activity. We searched for possible difference of star-formation activity between type 1 (un-absorbed) and type 2 (absorbed) AGNs. Our regression analysis of log L14-195keV versus log L3.3μm shows a positive correlation and the slope seems steeper for type 1/unobscured AGNs than that of type 2/obscured AGNs. The same trend has been found for the log (L14-195keV/MBH) versus log (L3.3μm/MBH) correlation. Our analysis show that the circum-nuclear star-formation is more enhanced in type 2/absorbed AGNs than type 1/un-absorbed AGNs for low X-ray luminosity/low Eddington ratio AGNs.

We present near-infrared and millimeter investigations of the nucleus of the infrared luminous galaxy NGC 4418, which previous observations suggest possesses a powerful buried AGN. We found the following main results: (1) The infrared K-band spectrum shows CO absorption features at 2.3-2.4 micron owing to stars and very strong H2 emission lines. The luminosity ratios of H2 emission lines are suggestive of a thermal origin, and the equivalent width of the H2 1-0 S(1) line is the second largest observed to date in an external galaxy, after the well-studied strong H2-emitting galaxy NGC 6240. (2) The infrared L-band spectrum shows a clear polycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 micron, which is usually found in star-forming galaxies. The estimated star-formation luminosity from the observed PAH emission can account for only a small fraction of the infrared luminosity. (3) Millimeter interferometric observations of the nucleus reveal a high HCN (1-0) to HCO+ (1-0) luminosity ratio of 1.8, as has been previously found in pure AGNs. (4) The measurements of HCN (1-0) luminosity using a single-dish millimeter telescope show that the HCN (1-0) to infrared luminosity ratio is slightly larger than the average, but within the scattered range, for other infrared luminous galaxies. All of these results can be explained by the scenario in which, in addition to energetically-insignificant, weakly-obscured star-formation at the surface of the nucleus, a powerful X-ray emitting AGN deeply buried in dust and high density molecular gas is present., 31 pages, 9 figures, Accepted for publication in Astronomical Journal (2004 November issue)

13 pags., 6 figs., 2 tabs., We present near-infrared K-band slit spectra of the nuclei of 25 Seyfert 2 galaxies in the CfA and 12 μm samples. The strength of the CO absorption features at 2.3-2.4 μm produced by stars is measured in terms of a spectroscopic CO index. A clear anticorrelation between the observed CO index and the nuclear K - L color is present, suggesting that a featureless hot dust continuum heated by an active galactic nucleus (AGN) contributes significantly to the observed K-band fluxes in the nuclei of Seyfert 2 galaxies. After correction for this AGN contribution, we estimate nuclear stellar K-band luminosities for all sources and CO indices for sources with modestly large observed CO indices. The corrected CO indices for 10 (=40%) Seyfert 2 nuclei are found to be as high as those observed in star-forming or elliptical (=spheroidal) galaxies. We combine the K-band data with measurements of the L-band 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature, another powerful indicator for star formation, and find that the 3.3 μm PAH to K-band stellar luminosity ratios are substantially smaller than those of starburst galaxies. Our results suggest that the 3.3 μm PAH emission originates in the putative nuclear starbursts in the dusty tori surrounding the AGNs, because of its high surface brightness, whereas the K-band CO absorption features detected at the nuclei are dominated by old bulge (=spheroid) stars and thus may not be a powerful indicator for the nuclear starbursts. We see no clear difference in the strength of the CO absorption and PAH emission features between the CfA and 12 μm Seyfert 2 galaxies., M. I. is supported by a Grant-in-Aid for Scientific Research (16740117). A. A. H. acknowledges support from the Spanish Programa Nacional de Astronomıa y Astrofısica under grant AYA2002-01055. Some part of the data analysis was made using a computer system operated by the Astronomical Data Analysis Center (ADAC) and the Subaru Telescope of the National Astronomical Observatory, Japan. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and of the NASA/ IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration

We present infrared 2.8-4.1 micron slit spectra of 32 Seyfert 2 galaxies in the CfA and 12 micron samples. The 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission feature was used to estimate the absolute magnitude of a compact nuclear starburst (< a few 100 pc in size) that is presumed to have occurred in the outer region of an obscuring dusty molecular torus around a central supermassive black hole. We detected 3.3 micron PAH emission in 11 of the 32 Seyfert 2 nuclei in our sample, providing evidence for the presence of compact nuclear starbursts in a significant fraction of Seyfert 2 nuclei. However, the rest-frame equivalent widths of the 3.3 micron PAH emission, and the 3.3 micron PAH-to-infrared luminosity ratios measured in this study suggest that compact nuclear starbursts generally do not contribute significantly to the observed 3-4 micron nuclear fluxes or to the infrared luminosities of Seyfert 2 galaxies. Small optical depths of absorption features at 3.4 micron from bare dust and at 3.1 micron from ice-covered dust suggest that dust extinction toward the 3-4 micron continuum-emitting region in the innermost part of the obscuring dusty torus is modest: AV < 50-60 mag. Finally, the 3.3 micron PAH emission luminosities measured in this study were found to be significantly correlated with IRAS 12- and 25-micron, and nuclear N-band (10.6 micron) luminosities. If these three luminosities trace the power of the active galactic nucleus (AGN), then the luminosities of compact nuclear starbursts and AGNs are correlated. This correlation is in agreement with theories predicting that the presence of a compact nuclear starburst in the torus leads to an enhancement of the mass accretion rate onto the central supermassive black hole., 28 pages, 2 figures, Accepted for publication in ApJ

Ground-based 2.8--4.1 $\mu$m slit spectra of the nuclei of seven ultraluminous infrared galaxies (ULIRGs) that are classified optically as LINERs and have cool far-infrared colors are presented. All the nuclei show 3.3 $\mu$m polycyclic aromatic hydrocarbon (PAH) emission, with equivalent widths that are systematically lower than those in starburst galaxies. Strong 3.1 $\mu$m H$_{2}$O ice absorption, with optical depth greater than 0.6, is also detected in five nuclei, and 3.4 $\mu$m carbonaceous dust absorption is detected clearly in one of the five nuclei. It is quantitatively demonstrated that the large optical depths of the H$_{2}$O ice absorption in the five sources, and the 3.4 $\mu$m absorption in one source, are incompatible with a geometry in which the energy sources are spatially mixed with dust and molecular gas, as is expected for a typical starburst, but instead require that a large amount of nuclear dust (including ice-covered grains) and molecular gas be distributed in a screen in front of the 3--4 $\mu$m continuum-emitting sources. This geometrical requirement can naturally be met if the energy sources are more centrally concentrated than the nuclear dust and molecular gas. The low equivalent widths of the PAH emission compared to starbursts and the central concentration of the nuclear energy sources in these five ULIRGs are best explained by the presence of energetically important active galactic nuclei deeply buried in dust and molecular gas., Comment: 27 pages, 3 figures, Accepted for publication in ApJ (2003 v588 May 1 issue)

We have performed a deep optical imaging survey using a narrowband filter ($NB921$) centered at $\lambda =$ 9196 \AA ~ together with $i^\prime$ and $z^\prime$ broadband filters covering an 814 arcmin$^2$ area of the Subaru Deep Field. We obtained a sample of 73 strong $NB921$-excess objects based on the following two color criteria; $z^\prime - NB921 > 1$ and $i^\prime - z^\prime > 1.3$. We then obtained optical spectroscopy of nine objects in our $NB921$-excess sample, and identified at least two Ly$\alpha$ emitters at$z=6.541 \pm 0.002$ and $z=6.578 \pm 0.002$, each of which shows the characteristic sharp cutoff together with the continuum depression at wavelengths shortward of the line peak. The latter object is more distant than HCM-6A at $z=6.56$ and thus this is the most distant known object found so far. These new data allow us to estimate the first meaningful lower limit of the star formation rate density beyond redshift 6; $\rho_{\rm SFR} \sim 5.2 \times 10^{-4} M_\odot$ yr$^{-1}$ Mpc$^{-3}$. Since it is expected that the actual density is higher by a factor of several than this value, our new observation reveals that a moderately high level of star formation activity already occurred at $z \sim$ 6.6., Comment: 13 pages, 3 figures. PASJ (Letters), 55, vol.2, in press

This paper describes a Cooled Infrared Spectrograph and Camera for OHS (CISCO), mounted on the Nasmyth focus of the Subaru telescope. It is primarily designed as a back-end camera of the OH-Airglow Suppressor (OHS), and is also used as an independent, general-purpose near-infrared camera/spectrograph. CISCO is based on a single 1024x1024 format HgCdTe HAWAII array detector, and is capable of either wide-field imaging of 1.8'x1.8' field-of-view or low-resolution spectroscopy from 0.9 to 2.4 um. The limiting magnitudes measured during test observations were found to be J=23.5mag and K'=22.4mag (imaging, 1" aperture, S/N=5, 1 hr exposure)., Comment: 14 pages, 15 figures, accepted by PASJ. Figures with higher resolution are available at http://www.ioa.s.u-tokyo.ac.jp/~kmotohara/CISCO/ciscopap.tar.gz

We present high angular resolution ($\sim$0.5$^\prime$$^\prime$) MIR spectra of the powerful radio galaxy, Cygnus A, obtained with the Subaru telescope. The overall shape of the spectra agree with previous high angular resolution MIR observations, as well as previous Spitzer spectra. Our spectra, both on and off nucleus, show a deep silicate absorption feature. The absorption feature can be modeled with a blackbody obscured by cold dust or a clumpy torus. The deep silicate feature is best fit by a simple model of a screened blackbody, suggesting foreground absorption plays a significant, if not dominant role, in shaping the spectrum of Cygnus A. This foreground absorption prevents a clear view of the central engine and surrounding torus, making it difficult to quantify the extent the torus attributes to the obscuration of the central engine, but does not eliminate the need for a torus in Cygnus A.

We present an atlas of 129 spectral energy distributions for nearby galaxies, with wavelength coverage spanning from the UV to the mid-infrared. Our atlas spans a broad range of galaxy types, including ellipticals, spirals, merging galaxies, blue compact dwarfs and luminous infrared galaxies. We have combined ground-based optical drift-scan spectrophotometry with infrared spectroscopy from Spitzer and Akari, with gaps in spectral coverage being filled using MAGPHYS spectral energy distribution models. The spectroscopy and models were normalized, constrained and verified with matched-aperture photometry measured from Swift, GALEX, SDSS, 2MASS, Spitzer and WISE images. The availability of 26 photometric bands allowed us to identify and mitigate systematic errors present in the data. Comparison of our spectral energy distributions with other template libraries and the observed colors of galaxies indicates that we have smaller systematic errors than existing atlases, while spanning a broader range of galaxy types. Relative to the prior literature, our atlas will provide improved K-corrections, photometric redshifts and star-formation rate calibrations., Comment: 64 pages (inc. 27 pages of appendicies), 18 figures, submitted to The Astrophysical Journal Supplement Series, SEDs and FITS images available from http://dx.doi.org/10.5072/03/529D3551F0117