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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--Ks >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]

We present far-infrared (FIR) properties of an extremely luminous infrared galaxy (ELIRG) at zspec = 3.703, WISE J101326.25+611220.1 (WISE 1013+6112). This ELIRG is selected as an IR-bright dust-obscured galaxy based on the photometry from the Sloan Digital Sky Survey and the Wide-field Infrared Survey Explorer (WISE). In order to derive its accurate IR luminosity, we perform follow-up observations at 89 and 154 μm using the High-resolution Airborne Wideband Camera-plus (HAWC+) on board the 2.7 m Stratospheric Observatory For Infrared Astronomy (SOFIA) telescope. We conduct spectral energy distribution (SED) fitting with CIGALE using 15 photometric data (0.4–1300 μm). We successfully pin down FIR SED of WISE 1013+6112 and its IR luminosity is estimated to be LIR = (1.62 ± 0.08) × 1014L☉, making it one of the most luminous IR galaxies in the universe. We determine the dust temperature of WISE 1013+6112 is Tdust = 89 ± 3 K, which is significantly higher than that of other populations such as submillimeter galaxies and FIR-selected galaxies at similar IR luminosities. The resultant dust mass is Mdust = (2.2 ± 0.1) × 108M☉. This indicates that WISE 1013+6112 has a significant active galactic nucleus and star-forming activity behind a large amount of dust. [ABSTRACT FROM AUTHOR]

We report the discovery of a Compton-thick (CT), dust-obscured galaxy at z = 0.89, WISE J082501.48+300257.2 (WISE 0825+3002), observed by the Nuclear Spectroscopic Telescope Array. X-ray analysis with the XCLUMPY model revealed that hard X-ray luminosity in the rest-frame 2–10 keV band of WISE 0825+3002 is LX (2–10 keV) = erg s−1 while its hydrogen column density is NH = cm−2, indicating that WISE 0825+3002 is a mildly CT active galactic nucleus (AGN). We performed spectral energy distribution (SED) fitting with CIGALE to derive its stellar mass, star formation rate, and infrared luminosity. The estimated Eddington ratio based on stellar mass and integration of the best-fit SED of the AGN component is λEdd = 0.70, which suggests that WISE 0825+3002 harbors an actively growing black hole behind a large amount of gas and dust. We found that the relationship between the luminosity ratio of X-ray and 6 μm, and Eddington ratio, follows an empirical relation for AGNs reported by Toba et al. [ABSTRACT FROM AUTHOR]

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 zspec = 0.493, we performed follow-up observations using ALMA to investigate their CO molecular gas properties. As a result, we successfully detected 12CO(J = 2–1) and 12CO(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]

We investigate the star-forming activity of a sample of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme red color in the optical and IR regime, . Combining an IR-bright DOG sample with the flux at 22 μm > 3.8 mJy discovered by Toba & Nagao with the IRAS faint source catalog version 2 and AKARI far-IR (FIR) all-sky survey bright source catalog version 2, we selected 109 DOGs with FIR data. For a subsample of seven IR-bright DOGs with spectroscopic redshifts () that were obtained from the literature, we estimated their IR luminosity, star formation rate (SFR), and stellar mass based on the spectral energy distribution fitting. We found that (1) the WISE 22 μm luminosity at the observed frame is a good indicator of IR luminosity for IR-bright DOGs and (2) the contribution of the active galactic nucleus to IR luminosity increases with IR luminosity. By comparing the stellar mass and SFR relation for our DOG sample and the literature, we found that most of the IR-bright DOGs lie significantly above the main sequence of star-forming galaxies at similar redshift, indicating that the majority of IRAS- or AKARI-detected IR-bright DOGs are starburst galaxies. [ABSTRACT FROM AUTHOR]

We present measurements of the clustering properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining 125 deg2 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]

We report on the optical properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that are defined as . Because supermassive black holes (SMBHs) in IR-bright DOGs are expected to be rapidly growing in the major-merger scenario, they provide useful clues for understanding the coevolution of SMBHs and their host galaxies. However, the optical properties of IR-bright DOGs remain unclear because the optical emission of a DOG is very faint. By combining ∼105 deg2 images of the optical, near-IR, and mid-IR data obtained from the Subaru Hyper Suprime-Cam (HSC) survey, the VISTA VIKING survey, and the Wide-field Infrared Survey Explorer all-sky survey, respectively, 571 IR-bright DOGs were selected. We found that IR-bright DOGs show a redder (g − z)AB color than do other populations of dusty galaxies, such as ultraluminous IR galaxies (ULIRGs) at a similar redshift, with a significantly large dispersion. Among the selected DOGs, star formation (SF)-dominated DOGs show a relatively red color, while active galactic nucleus (AGN)-dominated DOGs show a rather blue color in optical. This result is consistent with the idea that the relative AGN contribution in the optical emission becomes more significant at a later stage in the major-merger scenario. We discovered eight IR-bright DOGs showing a significant blue excess in blue HSC bands. This blue excess can be interpreted as a leaked AGN emission that is either a directly leaking or a scattered AGN emission, as proposed for some blue-excess Hot DOGs in earlier studies. [ABSTRACT FROM AUTHOR]

We present the discovery of an extremely luminous dust-obscured galaxy (DOG) at zspec = 3.703, WISE J101326.25+611220.1. This DOG is selected as a candidate of extremely luminous infrared (IR) galaxies based on the photometry from the Sloan Digital Sky Survey and Wide-field Infrared Survey Explorer. In order to derive its accurate IR luminosity, we perform follow-up observations at 450 and 850 μm using the Submillimetre Common User Bolometer Array 2 on the James Clerk Maxwell Telescope, and at 870 and 1300 μm using the Submillimeter Array, which enable us to pin down its IR Spectral Energy Distribution (SED). We perform SED fitting using 14 photometric data (0.4–1300 μm) and estimate its IR luminosity, LIR (8–1000 μm), to be ×1014L☉, making it one of the most luminous IR galaxies in the universe. The energy contribution from an active galactic nucleus (AGN) to the IR luminosity is %, which indicates that it is an AGN-dominated DOG. On the other hand, its stellar mass (M*) and star formation rate (SFR) are = and ) = , respectively, which means that this DOG can be considered a starburst galaxy in the M*–SFR plane. This extremely luminous DOG shows significant AGN and star-forming activity that provides us with an important laboratory to probe the maximum phase of the coevolution of galaxies and supermassive black holes. [ABSTRACT FROM AUTHOR]

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 (M1450 > -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]

We have measured the clustering of galaxies around active galactic nuclei (AGNs) for which single-epoch virial masses of the super-massive black hole (SMBH) are available to investigate the relation between the large-scale environment of AGNs and the evolution of SMBHs. The AGN samples used in this work were derived from the Sloan Digital Sky Survey (SDSS) observations and the galaxy samples were from the 240 deg2 S15b data of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). The investigated redshift range is 0.6-3.0, and the masses of the SMBHs lie in the range 107.5-1010 M⊙. The absolute magnitude of the galaxy samples reaches to Mλ310 ~ -18 at rest-frame wavelength 310 nm for the low-redshift end of the samples. More than 70% of the galaxies in the analysis are blue. We found a significant dependence of the cross-correlation length on redshift, which primarily reflects the brightness-dependence of the galaxy clustering. At the lowest redshifts the cross-correlation length increases from 7 h-1 Mpc around Mλ310 = -19 mag to >10 h-1 Mpc beyond Mλ310 = -20 mag. No significant dependence of the cross-correlation length on BH mass was found for whole galaxy samples dominated by blue galaxies, while there was an indication of BH mass dependence in the cross-correlation with red galaxies. These results provides a picture of the environment of AGNs studied in this paper being enriched with blue star-forming galaxies, and a fraction of the galaxies are evolving into red galaxies along with the evolution of SMBHs in that system. [ABSTRACT FROM AUTHOR]

We present the ionized gas properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme optical/IR color, , selected with the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). For 36 IR-bright DOGs that show [O iii]λ5007 emission in the SDSS spectra, we performed a detailed spectral analysis to investigate their ionized gas properties. In particular, we measured the velocity offset (the velocity with respect to the systemic velocity measured from the stellar absorption lines) and the velocity dispersion of the [O iii] line. We found that the derived velocity offset and dispersion of most IR-bright DOGs are larger than those of Seyfert 2 galaxies (Sy2s) at , meaning that the IR-bright DOGs show relatively strong outflows compared to Sy2s. This can be explained by the difference in IR luminosity contributed from active galactic nuclei, (AGN), because we found that (i) (AGN) correlates with the velocity offset and dispersion of [O iii] and (ii) our IR-bright DOG sample has larger (AGN) than Sy2s. Nevertheless, the fact that about 75% IR-bright DOGs have a large (>300 km s−1) velocity dispersion, which is a larger fraction compared to other AGN populations, suggests that IR-bright DOGs are good laboratories to investigate AGN feedback. The velocity offset and dispersion of [O iii] and [Ne iii]λ3869 are larger than those of [O ii]λ3727, which indicates that the highly ionized gas tends to show stronger outflows. [ABSTRACT FROM AUTHOR]

Low-metallicity active galactic nuclei (AGNs) are interesting to study for the early phase of AGN evolution. However, most AGNs are chemically matured, and accordingly, low-metallicity AGNs are extremely rare. One approach to search for low-metallicity AGNs systematically is utilizing the so-called BPT diagram that consists of the [O iii]λ5007/Hβ and [N ii]/Hα flux ratios. Specifically, photoionization models predict that low-metallicity AGNs show a high [O iii]λ5007/Hβλ4861 ratio and a relatively low [N ii]λ6584/Hαλ6563 ratio that corresponds to the location between the sequence of star-forming galaxies and that of usual AGNs on the BPT diagram (hereafter “the BPT valley”). However, other populations of galaxies such as star-forming galaxies and AGNs with a high electron density or a high-ionization parameter could be also located in the BPT valley, not only low-metallicity AGNs. In this paper, we examine whether most of the emission-line galaxies at the BPT valley are low-metallicity AGNs or not. We select 70 BPT-valley objects from 212,866 emission-line galaxies obtained by the Sloan Digital Sky Survey. Among the 70 BPT-valley objects, 43 objects show firm evidence of the AGN activity, i.e., the He ii λ4686 emission and/or weak but significant broad Hα emission. Our analysis shows that those 43 BPT-valley AGNs are not characterized by a very high gas density nor ionization parameter, inferring that at least 43 among 70 BPT-valley objects (i.e., %) are low-metallicity AGNs. This suggests that the BPT diagram is an efficient tool to search for low-metallicity AGNs. [ABSTRACT FROM AUTHOR]

In order to investigate the physical relationship between strong Ly α absorbers (log NHI ≥ 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]

Recent studies have derived quasar luminosity functions (QLFs) at various redshifts. However, the faint side of the QLF at high redshifts is still too uncertain. An accurate estimate of the survey completeness is essential to derive an accurate QLF for use in studying the luminosity-dependent density evolution (LDDE) of the quasar population. Here we investigate how the luminosity dependence of quasar spectra (the Baldwin effect) and the attenuation model for the intergalactic medium (IGM) affect the completeness estimates. For this purpose, we specifically revisit the completeness of quasar surveys at , using the COSMOS images observed with Subaru/Suprime-Cam. As a result, we find that the completeness estimates are sensitive to the luminosity dependence of the quasar spectrum and to different the IGM attenuation models. At , the number density of quasars when we adopt the latest IGM model and take the luminosity dependence of spectra into account is Mpc−3 mag−1 for and Mpc−3 mag−1 for , which are ∼24% lower than that estimated by the conventional method. On the other hand, at , the confidence upper limit of the number density at in our new estimates is ∼43% higher than that estimated previously. The results suggest that the luminosity dependence of the quasar spectrum and the IGM model are important for deriving the accurate number density of high-z quasars. Even taking these effects into account, the inferred LDDE of quasars is consistent with the AGN downsizing evolutionary picture. [ABSTRACT FROM AUTHOR]

Nearby active galactic nuclei were diagnosed in the X-ray and mid-to-far infrared wavelengths with Monitor of All-sky X-ray Image (MAXI) and the Japanese infrared observatory AKARI, respectively. One hundred of the X-ray sources listed in the second release of the MAXI all-sky X-ray source catalog are currently identified as non-blazar-type active galactic nuclei. These include 95 Seyfert galaxies and 5 quasars, and they are composed of 73 type-1 and 27 type-2 objects. The AKARI all-sky survey point source catalog was searched for their mid- and far-infrared counterparts at 9, 18, and 90 μm. As a result, 69 Seyfert galaxies in the MAXI catalog (48 type-1 and 21 type-2) were found to be detected with AKARI. The X-ray (3-4 keV and 4-10 keV) and infrared luminosities of these objects were investigated, together with their color information. Adopting the canonical photon index, G = 1.9, of the intrinsic X-ray spectrum of the Seyfert galaxies, the X-ray hardness ratio between the 3-4 and 4-10 keV ranges derived with MAXI was roughly converted into the absorption column density. After the X-ray luminosity was corrected for absorption from the estimated column density, the well-known X-ray-to-infrared luminosity correlation was confirmed, at least in the Compton-thin regime. In contrast, NGC 1365, the only Compton-thick object in the MAXI catalog, was found to deviate from the correlation toward a significantly lower X-ray luminosity by nearly an order of magnitude. It was verified that the relation between the X-ray hardness below 10 keV and X-ray-to-infrared color acts as an effective tool to pick up Compton-thick objects. The difference in the infrared colors between the type-1 and type-2 Seyfert galaxies and its physical implication on the classification and unification of active galactic nuclei are briefly discussed. [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]

We construct a SCUBA-2 450 μm map in the COSMOS field that covers an area of 300 arcmin2 and reaches a 1σ noise level of 0.65 mJy in the deepest region. We extract 256 sources detected at 450 μm with signal-to-noise ratios >4.0 and analyze the physical properties of their multiwavelength counterparts. We find that most of the sources are at z ≲ 3, with a median of . About of our sources are classified as starburst galaxies based on their total star formation rates (SFRs) and stellar masses (M*). By fitting the far-infrared spectral energy distributions, we find that our 450 μm selected sample has a wide range of dust temperatures (20 K ≲ Td ≲ 60 K), with a median of K. We do not find a redshift evolution in dust temperature for sources with at z < 3. However, we find a moderate correlation where the dust temperature increases with the deviation from the SFR–M* relation. The increase in dust temperature also correlates with optical morphology, which is consistent with merger-triggered starbursts in submillimeter galaxies. Our galaxies do not show the tight IRX–βUV correlation that has been observed in the local universe. We construct the infrared luminosity functions of our 450 μm sources and measure their comoving SFR densities (SFRDs). The contribution of the population to the SFRD rises dramatically from z = 0 to 2 (∝(1 + z)3.9±1.1) and dominates the total SFRD at z ≳ 2. [ABSTRACT FROM AUTHOR]

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 ≤ M1450 ≤ −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 109.3M⊙. The Eddington ratios Lbol/LEdd range from 0.16 to 1.1, but the majority of the HSC quasars are powered by MBH ∼ 109M⊙ 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 ∼ 109M⊙ 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]

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]

Arp 187 is one of the fading active galactic nuclei (AGNs), whose AGN activity is currently decreasing in luminosity. We investigate the observational signatures of AGN in Arp 187, which trace various physical scales from less than 0.1 pc to the nearly 10 kpc, to estimate the long-term luminosity change over 104 yr. The Very Large Array 5 GHz and 8 GHz images and the ALMA 133 GHz images reveal bimodal jet lobes with ∼5 kpc size and the absence of the central radio core. The 6dF optical spectrum shows that Arp 187 hosts a narrow line region with the estimated size of ∼1 kpc, and the line strengths give the AGN luminosity of Lbol = 1.5 × 1046 erg s−1. On the other hand, the current AGN activity estimated from the AGN torus emission gives the upper bound of Lbol < 2.2 × 1043 erg s−1. The absence of the radio core gives the more strict upper bound of the current AGN luminosity of Lbol < 8.0 × 1040 erg s−1, suggesting that the central engine is already quenched. These multiwavelength signatures indicate that Arp 187 hosts a “dying” AGN: the central engine is already dead, but the large-scale AGN indicators are still observable as the remnant of the past AGN activity. The central engine has experienced the drastic luminosity decline by a factor of ∼103–5 fainter within ∼104 yr, which is roughly consistent with the viscous timescale of the inner part of the accretion disk within ∼500 yr. [ABSTRACT FROM AUTHOR]

We report the result of optical identifications of FIRST radio sources with the Hyper Suprime-Cam Subaru Strategic Program survey (HSC-SSP). The positional cross-match within 1″ between the FIRST and HSC-SSP catalogs (i ≲ 26) produced more than 3600 optical counterparts in the 156 deg2 of the HSC-SSP field. The matched counterparts account for more than 50% of the FIRST sources in the search field, which substantially exceed previously reported fractions of SDSS counterparts (i ≲ 22) of ∼30%. Among the matched sample, 9% are optically unresolved sources such as radio-loud quasars. The optically faint (i > 21) radio galaxies (RGs) show that the fitting linear function of the 1.4 GHz source counts has a slope that is flatter than that of the bright RGs, while optically faint radio quasars show a slope steeper than that of bright radio quasars. The optically faint RGs show a flat slope in the i-band number counts down to 24 mag, implying either less massive or distant radio-active galactic nuclei (AGNs) beyond 24 mag. The photometric redshift and the comparison of colors with the galaxy models show that most of the matched RGs are distributed at redshifts from 0 to 1.5. The optically faint sample includes the high radio-loudness sources that are not seen in the optically bright sample. Such sources are located at redshift z > 1. This study gives ∼1500 radio AGNs lying at the optically faint end and high-redshift regime not probed by previous searches. [ABSTRACT FROM AUTHOR]

We present structural parameters and morphological properties of faint 450 μm selected submillimeter galaxies (SMGs) from the JCMT Large Program, STUDIES, in the COSMOS-CANDELS region. Their properties are compared to an 850 μm selected and a matched star-forming samples. We investigate stellar structures of 169 faint 450 μm sources (S450 = 2.8–29.6 mJy; S/N > 4) at z < 3 using HST near-infrared observations. Based on our spectral energy distribution fitting, half of such faint SMGs (LIR = 1011.65±0.98L⊙) lie above the star formation rate (SFR)/stellar mass plane. The size–mass relation shows that these SMGs are generally similar to less-luminous star-forming galaxies selected by NUV − r versus r − J colors. Because of the intrinsic luminosity of the sample, their rest-frame optical emission is less extended than the 850 μm sources (S850 > 2 mJy) and more extended than the star-forming galaxies in the same redshift range. For the stellar mass and SFR-matched sample at z ≃ 1 and z ≃ 2, the size differences are marginal between faint SMGs and the matched galaxies. Moreover, faint SMGs have similar Sérsic indices and projected axis ratios as star-forming galaxies with the same stellar mass and SFR. Both SMGs and the matched galaxies show high fractions (∼70%) of disturbed features at z ≃ 2, and the fractions depend on the SFRs. These suggest that their star formation activity is related to galaxy merging and the stellar structures of SMGs are similar to those of star-forming galaxies. We show that the depths of submillimeter surveys are approaching the lower luminosity end of star-forming galaxies, allowing us to detect galaxies on the main sequence. [ABSTRACT FROM AUTHOR]

We systematically investigate the near- to far-infrared (FIR) photometric properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky ultra-hard X-ray (14–195 keV) survey. Out of 606 non-blazar AGNs in the Swift/BAT 70 month catalog at high galactic latitudes of , we obtain IR photometric data of 604 objects by cross-matching the AGN positions with catalogs from the WISE, AKARI, IRAS, and Herschel infrared observatories. We find a good correlation between the ultra-hard X-ray and mid-IR luminosities over five orders of magnitude (). Informed by previous measurements of the intrinsic spectral energy distribution of AGNs, we find FIR pure-AGN candidates whose FIR emission is thought to be AGN-dominated with low star-formation activity. We demonstrate that the dust covering factor decreases with the bolometric AGN luminosity, confirming the luminosity-dependent unified scheme. We also show that the completeness of the WISE color–color cut in selecting Swift/BAT AGNs increases strongly with 14–195 keV luminosity. [ABSTRACT FROM AUTHOR]

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 deg2 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]

We report a new sample of obscured active galactic nuclei (AGNs) selected from the XMM-Newton serendipitous source and AKARI point-source catalogs. We match X-ray sources with infrared (18 and 90 μm) sources located at to create a sample consisting of 173 objects. Their optical classifications and absorption column densities measured by X-ray spectra are compiled and study efficient selection criteria to find obscured AGNs. We apply the criteria (1) X-ray hardness ratio defined by using the 2–4.5 keV and 4.5–12 keV bands > −0.1 and (2) EPIC-PN count rate (CR) in the 0.2–12 keV to infrared flux ratio CR/ or CR/ where F18 and F90 are infrared fluxes at 18 and 90 μm in Jy, respectively, to search for obscured AGNs. X-ray spectra of 48 candidates, for which no X-ray results have been published, are analyzed and X-ray evidence for the presence of obscured AGNs such as a convex shape X-ray spectrum indicative of absorption of ∼ 1022–24 cm−2, a very flat continuum, or a strong Fe–K emission line with an equivalent width of is found in 26 objects. Six of them are classified as Compton-thick AGNs, and four are represented by either Compton-thin or Compton-thick spectral models. The success rate of finding obscured AGNs combining our analysis and the literature is 92% if the 18 μm condition is used. Of the 26 objects, 4 are optically classified as an H ii nucleus and are new “elusive AGNs” in which star formation activity likely overwhelms AGN emission in the optical and infrared bands. [ABSTRACT FROM AUTHOR]