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We have developed an efficient active galactic nucleus (AGN) selection method using 18-band spectral energy distribution (SED) fitting in mid-infrared (mid-IR). AGNs are often obscured by gas and dust, and those obscured AGNs tend to be missed in optical, UV and soft X-ray observations. Mid-IR light can help us to recover them in an obscuration-free way using their thermal emission. On the other hand, star-forming galaxies (SFGs) also have strong polycyclic aromatic hydrocarbon emission features in mid-IR. Hence, establishing an accurate method to separate populations of AGNs and SFGs is important. However, in previous mid-IR surveys, only three or four filters were available, and thus the selection was limited. We combined AKARI's continuous nine mid-IR bands with Wide field Infrared Survey Explorer (WISE) and Spitzer data to create 18 mid-IR bands for AGN selection. Among 4682 galaxies in the AKARI north ecliptic pole deep field, 1388 are selected to be AGN hosts, which implies an AGN fraction of 29.6 ± 0.8 per cent (among them 47 per cent are Seyfert 1.8 and 2). Comparing the result from SED fitting into WISE and Spitzer colour-colour diagram reveals that Seyferts are often missed by previous studies. Our result has been tested by stacking median magnitude for each sample. Using X-ray data from Chandra, we compared the result of our SED fitting with WISE's colour box selection. We recovered more X-ray detected AGNs than previous methods by 20 per cent. [ABSTRACT FROM AUTHOR]

The mass, metallicity, and star formation rate (SFR) of a galaxy are crucial parameters in understanding galaxy formation and evolution. However, the relation between these parameters, (i.e., the fundamental relation) is still amatter of debate for luminous infrared (IR) galaxies, which carry a bulk of the SFR budget of the universe at z ~ 1. We have investigated the relation among stellar mass, gas-phase oxygen abundance, and SFR of the Japanese infrared satellite AKARI-detected mid-IR galaxies at z ~ 0.88 in the AKARI north ecliptic pole deep field.We observed ~350 AKARI sources with Subaru/Fiber Multi Object Spectrograph near-IR spectrograph, and detected confirmed Hα emission lines from 25 galaxies and expected Hα emission lines from 44 galaxies. The SFRHα, IR of our sample is almost constant (〈SFRHα,IR〉 =~25M⊙ yr-1) over the stellar mass range of our sample. Compared with main-sequence (MS) galaxies at a similar redshift range (z ~ 0.78), the average SFR of our detected sample is comparable for massive galaxies (~1010.58 M⊙), while higher by ~0.6 dex for less massive galaxies (~1010.05 M⊙). We measure metallicities from the [N II]/Hα emission line ratio. We find that the mass-metallicity relation of our individually measured sources agrees with that for optically-selected star-forming galaxies at z ~ 0.1, while metallicities of stacked spectra agree with that of MS galaxies at z ~ 0.78. Considering the high SFR of individually measured sources, the fundamental metallicity relation (FMR) of the IR galaxies is different from that at z ~ 0.1. However, on the mass-metallicity plane, they are consistent with the MS galaxies, highlighting the higher SFR of the IR galaxies. This suggests that the evolutionary path of our infrared galaxies is different from that of MS galaxies. A possible physical interpretation includes that the star-formation activities of IR galaxies at z ~ 0.88 in our sample are enhanced by interactions and/or mergers of galaxies, but the inflow of metal-poor gas is not yet induced, keeping the metallicity intact. [ABSTRACT FROM AUTHOR]

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 tgrow 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]

Using star-forming galaxies sample in the nearby Universe (0.02 < z < 0.10) selected from the Sloan Digital Sky Survey (DR7) and Galaxy Evolution Explorer all-sky survey (GR5), we present a new empirical calibration for predicting dust extinction of galaxies from the Hα-to-FUV flux ratio. We find that the Hα dust extinction (AHα) derived with Hα/Hβ ratio (Balmer decrement) increases with increasing Hα/UV ratio as expected, but there remains a considerable scatter around the relation, which is largely dependent on stellar mass and/or Hα equivalent width (EWHα). At fixed Hα/UV ratio, galaxies with higher stellar mass (or galaxies with lower EWHα) tend to be more highly obscured by dust. We quantify this trend and establish an empirical calibration for predicting AHα with a combination of Hα/UV ratio, stellar mass, and EWHα, with which we can successfully reduce the systematic uncertainties accompanying the simple Hα/UV approach by ~15–30 percent. The new recipes proposed in this study will provide a convenient tool for predicting dust extinction level of galaxies particularly when Balmer decrement is not available. By comparing AHα (derived with Balmer decrement) and AUV (derived with IR/UV luminosity ratio) for a subsample of galaxies for which AKARI far-infrared photometry is available, we demonstrate that more massive galaxies tend to have higher extra extinction towards the nebular regions compared to the stellar continuum light. Considering recent studies reporting smaller extra extinction towards nebular regions for high-redshift galaxies, we argue that the dust geometry within high-redshift galaxies resembles low-mass galaxies in the nearby Universe. [ABSTRACT FROM AUTHOR]

We present infrared (IR) galaxy luminosity functions (LFs) in the AKARI North Ecliptic Pole (NEP) deep field using recently-obtained, wider Canada–France–Hawaii Telescope (CFHT) optical/near-IR images. AKARI has obtained deep images in the mid-infrared (IR), covering 0.6 deg² of the NEP deep field. However, our previous work was limited to the central area of 0.25 deg² due to the lack of optical coverage of the full AKARI NEP survey. To rectify the situation, we recently obtained CFHT optical and near-IR images over the entire AKARI NEP deep field. These new CFHT images are used to derive accurate photometric redshifts, allowing us to fully exploit the whole AKARI NEP deep field. AKARI's deep, continuous filter coverage in the mid-IR wavelengths (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24 μm) exists nowhere else, due to filter gaps of other space telescopes. It allows us to estimate rest-frame 8 and 12 μm luminosities without using a large extrapolation based on spectral energy distribution fitting, which was the largest uncertainty in previous studies. Total infrared (TIR) luminosity is also obtained more reliably due to the superior filter coverage. The resulting rest-frame 8 and 12 μm, and TIR LFs at 0.15 < z < 2.2 are consistent with previous works, but with reduced uncertainties, especially at the high-luminosity end, thanks to the wide-field coverage. In terms of cosmic infrared luminosity density (ΩIR), we found that the ΩIR evolves as  ∝ (1 + z)4.2 ± 0.4. [ABSTRACT FROM AUTHOR]

Aims. We present an 8-band (u*, g', r', i', z', Y, J, Ks) optical to near-infrared deep photometric catalog based on the observations made with MegaCam and WIRCam at the CFHT, and compute photometric redshifts, zp in the north ecliptic pole (NEP) region. AKARI infrared satellite carried out a deep survey in the NEP region at near- to mid-infrared wavelengths. Our optical to near-infrared catalog allows us to identify the counterparts and zp for the AKARI sources. Methods. We obtained seven-band (g', r', i', z', Y, J, Ks) imaging data, and we crossmatched them with existing u*-band data (limiting magnitude = 24.6 mag [5σ; AB]) to design the band-merged catalog. We included all z'-band sources with counterparts in at least one of the other bands in the catalog. We used a template-fitting methods to compute zp for all the cataloged sources. Results. The estimated 4σ detection limits within a 1 arcsec aperture radius are 26.7, 25.9, 25.1, and 24.1 mag [AB] for the optical g', r', i', and z'-bands and 23.4, 23.0, and 22.7 mag for the near-infrared Y, J, and Ks-bands, respectively. There are a total of 85 797 sources in the band-merged catalog. An astrometric accuracy of this catalog determined by examining coordinate offsets with regard to 2MASS is 0.013 arcsec with a root mean square offset of 0.32 arcsec. We distinguish 5441 secure stars from extended sources using the u* − J versus g' − Ks colours, combined with the SExtractor stellarity index of the images. Comparing with galaxy spectroscopic redshifts, we find a photometric redshift dispersion, σΔz/(1 + z), of 0.032 and catastrophic failure rate, Δz/(1 + z) > 0.15, of 5.8% at z< 1, while a dispersion of 0.117 and a catastrophic failure rate of 16.6% at z> 1. We extend the estimate of the zp uncertainty over the full magnitude/redshift space with a redshift probability distribution function and find that our redshifts are highly accurate with z' < 22 at zp< 2.5 and for fainter sources with z' < 24 at zp< 1. From the investigation of photometric properties of AKARI infrared sources (23 354 sources) using the g'z'Ks diagram, < 5% of AKARI sources with optical counterparts are classified as high-z (1.4

We report high-resolution 12CO(J = 2-1), 13CO(7 = 2-1), and 12CO(J = 3-2) imaging of the Seyfert 1 /starburst ring galaxy NGC 1097 with the Submillimeter Array for the purpose of studying the physical and kinematic properties of the 1 kpc circumnuclear starburst ring. Individual star clusters as detected in the Hubble Space Telescope map of Paα line emission have been used to determine the star formation rate (SFR), and are compared with the properties of the molecular gas. The molecular ring has been resolved into individual clumps at the giant molecular cloud association (GMA) scale of 200-300 pc in all three CO lines. The intersection between the dust lanes and the starburst ring, which is associated with the orbit-crowding region, is resolved into two physically/kinematically distinct features in the 1".5 x 1".0 (105 x 70 pc) 12CO(J = 2-1) map. The clumps associated with the dust lanes have broader line widths, higher surface gas densities, and lower SFRs, while the narrow line clumps associated with the starburst ring have opposite characteristics. A Toomre-Q value lower than unity at the radius of the ring suggests that the molecular ring is gravitationally unstable to fragmentation at GMA scale. The line widths and surface density of the gas mass of the clumps show an azimuthal variation related to the large-scale dynamics. The SFR, on the other hand, is not significantly affected by the dynamics, but has a correlation with the intensity ratio of 12CO (J = 3-2) and 12CO(J = 2-1), which traces the denser gas associated with star formation. Our resolved CO map, especially in the orbit-crowding region, observationally demonstrates for the first time that the physical/kinematic properties of GMAs are affected by the large-scale bar-potential dynamics in NGC 1097. [ABSTRACT FROM AUTHOR]

We performed near-diffraction-limited ( FWHM) N-band imaging of one of the nearest active galactic nuclei (AGNs) in M51 with the 8.2 m Subaru Telescope to study the nuclear structure and spectral energy distribution (SED) at 8–13 μm. We found that the nucleus is composed of an unresolved core (at pc resolution, orintrinsic size corrected for the instrumental effect of pc) and an extended halo (at a few tens of parsec scale), and each of their SEDs is almost flat. We examined the SED by comparing with the archival Spitzer IRS spectrum processed to mimic our chopping observation of the nucleus and the published radiative transfer model SEDs of the AGN clumpy dusty torus. The halo SED is likely due to circumnuclear star formation showing deficient polycyclic aromatic hydrocarbon emission due to the AGN. The core SED is likely dominated by the AGN because of the following two reasons. First, the clumpy torus model SEDs can reproduce the red mid-infrared continuum with apparently moderate silicate 9.7 μm absorption. Second, the core 12 μm luminosity and the absorption-corrected X-ray luminosity at 2–10 keV in the literature follow the mid-infrared–X-ray luminosity correlation known for the nearby AGNs, including the Compton-thick ones. [ABSTRACT FROM AUTHOR]