Mid-infrared Luminosity Research Articles

Evidence for Intrinsic X-Ray Weakness among Red Quasars at Cosmic Noon

Quasar feedback is a key ingredient in shaping galaxy evolution. A rare population of extremely red quasars (ERQs) at z = 2−3 are often associated with high-velocity [O iii]λ5008 outflows and may represent sites of strong feedback. In this paper, we present an X-ray study of 50 ERQs to investigate the link between the X-ray and outflow properties of these intriguing objects. Using hardness ratio analysis, we confirm that the ERQs are heavily obscured systems with gas column density reaching N H = 1023−24 cm−2. We identify 20 X-ray-nondetected ERQs at high mid-infrared (MIR) luminosities of ν L ν,6 μm ≳ 3 × 1046 erg s−1. By stacking the X-ray observations, we find that the nondetected ERQs are on average underluminous in X-rays by a factor of ∼10 for their MIR luminosities. We consider such X-ray weakness to be due to both heavy gas absorption and intrinsic factors. Moreover, we find that the X-ray-weak sources also display higher-velocity outflows. One option to explain this trend is that weaker X-rays facilitate more vigorous line-driven winds, which then accelerate the [O iii]-emitting gas to kiloparsec scales. Alternatively, super-Eddington accretion could also lead to intrinsic X-ray weakness and more powerful continuum-driven outflow.

Exploring the faintest end of mid-infrared luminosity functions up to z ≃ 5 with the JWST CEERS survey

ABSTRACT Mid-infrared (MIR) light from galaxies is sensitive to dust-obscured star formation activities because it traces the characteristic emission of dust heated by young, massive stars. By constructing the MIR luminosity functions (LFs), we are able to quantify the overall dusty star formation history and the evolution of galaxies over cosmic time. In this work, we report the first rest-frame MIR LFs at 7.7, 10, 12.8, 15, 18, and 21 μm as well as the total IR LF from the JWST Cosmic Evolution Early Release Science (CEERS) survey. We identify 506 galaxies at z = 0–5.1 in the CEERS survey that also have optical photometry from the Hubble Space Telescope. With the unprecedented sensitivity of the JWST, we probe the faintest end of the LFs at z = 0–1 down to L* ∼ 107L⊙, ∼2 orders of magnitude fainter than those from the previous generation of IR space telescopes. Our findings connect well with and continue the faint end of the MIR LFs from the deepest observations in past works. As a proxy of star formation history, we present the MIR-based luminosity density up to z ≃ 4.0, marking the first probe of the early Universe by JWST Mid-Infrared Instrument.

Estimators of Bolometric Luminosity and Black Hole Mass with Mid-infrared Continuum Luminosities for Dust-obscured Quasars: Prevalence of Dust-obscured SDSS Quasars

We present bolometric luminosity (L bol) and black hole (BH) mass (M BH) estimators based on mid-infrared (MIR) continuum luminosity (hereafter, L MIR) that are measured from infrared (IR) photometric data. The L MIR-based estimators are relatively immune from dust extinction effects, hence they can be used for dust-obscured quasars. To derive the L bol and M BH estimators, we use unobscured quasars selected from the Sloan Digital Sky Survey (SDSS) quasar catalog, which have wide ranges of L bol (1044.62–1046.16 erg s−1) and M BH (107.14–109.69 M ⊙). We find empirical relations between (i) continuum luminosity at 5100 Å (hereafter, L5100) and L MIR; (ii) L bol and L MIR. Using these relations, we derive the L MIR-based L bol and M BH estimators. We find that our estimators allow the determination of L bol and M BH at an accuracy of ∼0.2 dex against the fiducial estimates based on the optical properties of the unobscured quasars. We apply the L MIR-based estimators to SDSS quasars at z ≲ 0.5 including obscured ones. The ratios of L bol from the L MIR-based estimators to those from the optical luminosity-based estimators become larger with the amount of the dust extinction, and a non-negligible fraction (∼15%) of the SDSS quasars exhibits ratios greater than 1.5. This result suggests that dust extinction can significantly affect physical parameter derivations even for SDSS quasars, and that dust extinction needs to be carefully taken into account when deriving quasar properties.

The Fifth Catalogue of Nearby Stars (CNS5)

Context. We present the compilation of the Fifth Catalogue of Nearby Stars (CNS5), based on astrometric and photometric data from Gaia EDR3 and HIPPARCOS and supplemented with parallaxes from ground-based astrometric surveys carried out in the infrared. Aims. The aim of the CNS5 is to provide the most complete sample of objects in the solar neighbourhood. For all known stars and brown dwarfs in the 25 pc sphere around the Sun, basic astrometric and photometric parameters are given. Furthermore, we provide the colour-magnitude diagram (CMD) and various luminosity functions of the stellar content in the solar neighbourhood, and characterise the completeness of the CNS5 catalogue. Methods. We compiled a sample of stars and brown dwarfs that are most likely located within 25 pc of the Sun, taking space-based parallaxes from Gaia EDR3 and HIPPARCOS as well as ground-based parallaxes from Best et al. (2021, AJ, 161, 42), Kirkpatrick et al. (2021, ApJS, 253, 7), and from the CNS4 into account. We developed a set of selection criteria to clean the sample from spurious sources. Furthermore, we show that effects of blending in the Gaia photometry, which mainly affect the faint and red sources in Gaia, can be mitigated to reliably place those objects in a CMD. We also assessed the completeness of the CNS5 using a Kolmogorov-Smirnov test and derive observational optical and mid-infrared (MIR) luminosity functions for the main-sequence stars and white dwarfs (WDs) in the solar neighbourhood. Results. The CNS5 contains 5931 objects, including 5230 stars (4946 main-sequence stars, 20 red giants and 264 white dwarfs) and 701 brown dwarfs. We find that the CNS5 catalogue is statistically complete down to 19.7 mag in the G-band and 11.8 mag in W1-band absolute magnitudes, corresponding to a spectral type of L8. The stellar number density in the solar neighbourhood is (7.99 ± 0.11) × 10−2 stars pc−3, and about 72% of stars in the solar neighbourhood are M dwarfs. Furthermore, we show that the WD sample in CNS5 is statistically complete within 25 pc. The derived number density of WDs is (4.03 ± 0.25) × 10−3 stars pc−3. The ratio between stars and brown dwarfs within 15 pc is 4.6 ± 0.4, whereas within 25 pc it is 7.5 ± 0.3. Thus, we estimate that about one third of brown dwarfs are still missing within 25 pc, particularly those with spectral types later than L8 and distances close to the 25 pc limit.

The demographics of obscured AGN from X-ray spectroscopy guided by multiwavelength information

ABSTRACT A complete census of active galactic nuclei (AGNs) is a prerequisite for understanding the growth of supermassive black holes across cosmic time. A significant challenge towards this goal is the whereabouts of heavily obscured AGN that remain uncertain. This paper sets new constraints on the demographics of this population by developing a methodology that combines X-ray spectral information with priors derived from multiwavelength observations. We select X-ray AGN in the Chandra COSMOS Legacy survey and fit their $2.2\!-\!500\, \mu \mathrm{m}$ spectral energy distributions with galaxy and AGN templates to determine the mid-infrared ($6\, \mu \mathrm{m}$) luminosity of the AGN component. Empirical correlations between X-ray and $6\, \mu \mathrm{m}$ luminosities are then adopted to infer the intrinsic accretion luminosity at X-rays for individual AGN. This is used as prior information in our Bayesian X-ray spectral analysis to estimate physical properties, such as line-of-sight obscuration. Our approach breaks the degeneracies between accretion luminosity and obscuration that affect X-ray spectral analysis, particularly for the most heavily obscured (Compton-Thick) AGN with low photon counts X-ray spectra. The X-ray spectral results are then combined with the selection function of the Chandra COSMOS Legacy survey to derive the AGN space density and a Compton-Thick fraction of $21.0^{+16.1}_{-9.9}{{\ \rm per\ cent}}$ at redshifts z < 0.5. At higher redshift, our analysis suggests upper limits to the Compton-Thick AGN fraction of $\lesssim 40{{\ \rm per\ cent}}$. These estimates are at the low end of the range of values determined in the literature and underline the importance of multiwavelength approaches for tackling the challenge of heavily obscured AGN demographics.

Star Formation Activity beyond the Outer Arm. II. Distribution and Properties of Star Formation

The outer Galaxy beyond the Outer Arm represents a promising opportunity to study star formation in an environment vastly different from the solar neighborhood. In our previous study, we identified 788 candidate star-forming regions in the outer Galaxy (at galactocentric radii R G ≥ 13.5 kpc) based on the Wide-field Infrared Survey Explorer (WISE) mid-infrared (MIR) all-sky survey. In this paper, we investigate the statistical properties of the candidates and their parental molecular clouds derived from the Five College Radio Astronomy Observatory (FCRAO) CO survey. We show that the molecular clouds with candidates have cloud mass functions with shallower slopes, larger fractions of clouds bound by self-gravity, and a greater density than the molecular clouds without candidates. To investigate the star formation efficiency (SFE) at different R G, we used two parameters: (1) the fraction of molecular clouds with candidates and (2) the monochromatic MIR luminosities of candidates per parental molecular cloud mass. We did not find any clear correlation between SFE parameters and R G at R G of 13.5–20.0 kpc, suggesting that the SFE is independent of environmental parameters such as metallicity and gas surface density, which vary considerably with R G. Previous studies reported that the SFE per year (SFE/yr) derived from the star formation rate surface density per total gas surface density, H i plus H2, decreases with increased R G. Our results might suggest that the decreasing trend is due to a decrease in the conversion of H i gas to H2 gas.

The statistical properties of 28 IR-bright dust-obscured galaxies and SED modelling using CIGALE

AbstractThe aim of this study is to characterize the physical and statistical properties of a sample of infrared-bright dust-obscured galaxies (DOGs) by fitting their spectral energy distributions (SEDs). We examined 28 DOGs at redshifts 0.47 ≤ z ≤ 1.63 discovered by combining images of the Subaru Hyper Suprime-Cam (HSC) survey, the VISTA Kilo-degree Infrared Galaxy (VIKING) survey, and the Wide-field Infrared Survey Explorer (WISE) all-sky survey, and detected at Herschel Spectral and Photometric Imaging Receiver (SPIRE) bands. We have detected a significant active galactic nucleus (AGN) contribution to the mid-infrared luminosity for $71\%$ of DOGs. Our DOGs contain several types of AGNs; the majority of AGN emission originates from Type 2 AGNs. Our DOG sample shows very high values of stellar mass [log (M*/M${}_\odot $) = 11.49 ± 1.61] compared with other samples of DOGs selected at infrared wavelengths. Our study is promising to identify a new type of DOGs called “overweight” DOGs (ODOGs). ODOGs may indicate the end of the DOG phase, and then they become visible quasars. Principal component (PC) analysis is applied to reduce the number of dimensions of our sample, removing the dependency on the observed variables. There are two significant PCs describing $72.7\%$ of the total variance. The first PC strongly correlates with redshift, dust luminosity, dust mass, and stellar mass, while far-ultraviolet (FUV) attenuation strongly correlates with the second PC, which is orthogonal to the first one. The partial correlation between the resulted physical parameters is tested, supporting the reliability of the correlations.

Consistent Analysis of the AGN LF in X-Ray and MIR in the XMM-LSS Field

Abstract The luminosity function of active galactic nuclei (AGN) probes the history of supermassive black hole assembly and growth across cosmic time. To mitigate selection biases, we present a consistent analysis of the AGN luminosity functions (LFs) derived for both X-ray and mid-infrared (MIR) selected AGN in the XMM-Large Scale Structure field. There are 4268 AGN used to construct the MIR luminosity function (IRLF) and 3427 AGN used to construct the X-ray luminosity function (XLF), providing the largest census of the AGN population out to z = 4 in both bands with significant reduction in uncertainties. We are able for the first time to see the knee of the IRLF at z > 2 and observe a flattening of the faint-end slope as redshift increases. The bolometric luminosity density, a proxy for the cosmic black hole accretion history, computed from our LFs, shows a peak at z ≈ 2.25, consistent with recent estimates of the peak in the star formation rate density (SFRD). However, at earlier epochs, the AGN luminosity density is flatter than the SFRD. If confirmed, this result suggests that the build up of black hole mass outpaces the growth of stellar mass in high-mass systems at z ≳ 2.5. This is consistent with observations of redshift z ∼ 6 quasars that lie above the local M − σ relationship. The luminosity density derived from the IRLF is higher than that from the XLF at all redshifts. This is consistent with the dominant role of obscured AGN activity in the cosmic growth of supermassive black holes.

Influence of Comptonization region over the ambiance of accretion disc in active galactic nucleus

ABSTRACT Understanding the radiative and physical structures of inner region of a few 100 pc of active galactic nucleus (AGNs) is important to constrain the causes of their activities. Although the X-ray emission from the Comptonization region/corona and the accretion disc regulates the broad-line emission regions and torus structures, the exact mutual dependency is not understood well. We performed correlation studies for X-ray, mid-infrared, and different components of Balmer emission lines for the selected sample of AGNs. Almost 10 different parameters and their interdependencies were explored in order to understand the underlying astrophysics. We found that the X-ray luminosity has a linear dependency on the various components of broad Balmer emission lines (e.g. L$_{\text{2-10 keV}}\, \propto$ L$^{0.78}_{\text{H}\beta ^{\text{B}}}$) and found a strong dependency on the optical continuum luminosity (L$_{\text{2-10 keV}}\, \propto$ L$^{0.86}_{5100\, \mathring{\rm A}}$). For a selected sample, we also observed a linear dependency between X-ray and mid-infrared luminosity (L$_{\text{2-10 keV}}\, \propto$ L$^{0.74}_{6\, \mu \text{m}}$). A break point was observed in our correlation studies for X-ray power-law index, Γ, and mass of black hole at ∼ log (M/M⊙) = 8.95. Similarly, the relations between Γ and full width at half-maximum (FWHM) of H α and H β broad components show breaks at FWHMH α = 7642 ± 657 km s−1 and FWHMH β = 7336 ± 650 km s−1. However, more data are required to confine the breaks locations exactly. We noted that Γ and Eddington ratios are negatively correlated to Balmer decrements in our selected sample. We analysed and discussed about the implications of new findings in terms of interaction AGN structures.

Discovery of new changing-look quasar 3C 332 and constraints for a double-peaked emission line scenario

Abstract Recently, a new class of quasars, called changing-look quasars (CLQs), has been reported. CLQs exhibit significant changes in optical and mid-infrared luminosity, accompanied by the appearance or disappearance of broad emission lines. We performed spectroscopic observations at the Nishi-Harima Astronomical Observatory in 2018 May to identify objects that show long-term (∼10 yr) continuous optical luminosity variations as candidates for CLQs. We discovered significant fluctuations in the Hβ emission line of 3C 332. This source has previously been reported to have a characteristic double-peaked Hα emission line. To explain the shape of the emission lines, a ring disk model has been proposed, and the possibility of a binary black hole has also been suggested. To further investigate the characteristics of 3C 332, we performed nine spectroscopic observations at Okayama Observatory (Kyoto University) from 2020 February to June. Based on the change in the velocity offset of the emission lines and the negative correlation between the line intensity and the velocity difference between the two peaks, we conclude that the double-peaked origin of this source is consistent with the ring disk model. In addition, the timescale of the changing look (of the optical and mid-infrared luminosities) is consistent with the thermal timescale or the propagation timescale of the heating/cooling front.

Mid-infrared Outbursts in Nearby Galaxies (MIRONG). I. Sample Selection and Characterization

Abstract Optical time-domain astronomy has grown rapidly in the past decade, but the dynamic infrared sky is rarely explored. Aiming to construct a sample of mid-infrared outbursts in nearby galaxies (MIRONG), we have conducted a systematical search of low-redshift (z < 0.35) Sloan Digital Sky Survey spectroscopic galaxies that have experienced recent mid-infrared (MIR) flares using their Wide-field Infrared Survey Explorer (WISE) light curves. A total of 137 galaxies have been selected by requiring a brightening amplitude of 0.5 mag in at least one WISE band with respect to their quiescent phases. Only a small fraction (10.9%) has corresponding optical flares. Except for the four supernovae (SNe) in our sample, the MIR luminosities of the remaining sources (L 4.6 μm > 1042 erg s−1) are markedly brighter than known SNe, and their physical locations are very close to the galactic center (median <0.″1). Only four galaxies are radio-loud, indicating that synchrotron radiation from relativistic jets could contribute to MIR variability. We propose that these MIR outbursts are dominated by the dust echoes of transient accretion onto supermassive black holes, such as tidal disruption events (TDEs) and turn-on (changing-look) active galactic nuclei. Moreover, the inferred peak MIR luminosity function is generally consistent with the X-ray and optical TDEs at the high end, albeit with large uncertainties. Our results suggest that a large population of transients has been overlooked by optical surveys, probably due to dust obscuration or intrinsically optical weakness. Thus, a search in the infrared band is crucial for us to obtain a panoramic picture of nuclear outburst. The multiwavelength follow-up observations of the MIRONG sample are in progress and will be presented in a series of subsequent papers.

Active Galactic Nucleus Ghosts: A Systematic Search for Faded Nuclei

Abstract Physical processes such as reignition, enhancement, and fading of active galactic nuclei (AGN) are not entirely understood because the timeline of these events is expected to last many years. However, it is well known that the differences in the energy budget between AGN components, like the optical ionizing region and the mid-infrared (MIR) dust echoes, can be interpreted as a hint of AGN evolution. Here we present a catalog of 88 AGN candidates showing hints of the fading and rising of their activity in the nearby universe. We use AGN scaling relations to select them from an initial sample of 877 candidates using publicly available optical, X-ray, and MIR luminosities. We then use the multiwavelength information to discard sources contaminated with extranuclear emission and those with an X-ray luminosity not well corrected for absorption. We find that 96% of our candidates are fading sources. This result suggests a scenario where the universe had its peak of AGN activity somewhere in the past and is dominated by a fading phase at the present time. Alternatively, the fading phase is longer than the rising phase, which is consistent with galaxy merger simulations. Around 50% of these fading candidates are associated with merging or interacting systems. Finally, we also find the existence of jets in ∼30% of these candidates and that the preferred AGN dust geometry is torus-like instead of wind-like. Our results are compatible with the fading of nuclear activity, expected if they are in an inefficient state.

The Carnegie Supernova Project II

We present optical and near-infrared photometry and spectroscopy of the Type IIn supernova, (SN) 2014ab, obtained by the Carnegie Supernova Project II and initiated immediately after its optical discovery. We also study public mid-infrared photometry obtained by the Wide-field Infrared Survey Explorer satellite extending from 56 days prior to the optical discovery to over 1600 days. The light curve of SN 2014ab evolves slowly, while the spectra exhibit strong emission features produced from the interaction between rapidly expanding ejecta and dense circumstellar matter. The light curve and spectral properties are very similar to those of SN 2010jl. The estimated mass-loss rate of the progenitor of SN 2014ab is of the order of 0.1 M⊙ yr−1 under the assumption of spherically symmetric circumstellar matter and steady mass loss. Although the mid-infrared luminosity increases due to emission from dust, which is characterized by a blackbody temperature close to the dust evaporation temperature (∼2000 K), there were no clear signatures of in situ dust formation observed within the cold dense shell located behind the forward shock in SN 2014ab in the early phases. Mid-infrared emission of SN 2014ab may originate from pre-existing dust located within dense circumstellar matter that is heated by the SN shock or shock-driven radiation. Finally, for the benefit of the community, we also present five near-infrared spectra of SN 2010jl obtained between 450 to 1300 days post-discovery in the appendix.

Mid-infrared Diagnostics of the Circumnuclear Environments of the Youngest Radio Galaxies

Abstract We present a systematic analysis of the mid-infrared (MIR) properties of the youngest radio galaxies, based on low-resolution data provided by the Wide-field Infrared Survey Explorer and IRAS satellites. We restrict our analysis to sources with available X-ray data that constitute the earliest phase of radio galaxy evolution, i.e., those classified as gigahertz-peaked spectrum and/or compact symmetric objects. In our sample of 29 objects, we find that the host galaxies are predominantly red/yellow ellipticals, with some of them displaying distorted morphology. We find a variety of MIR colors and observe that the sources in which the MIR emission is dominated by the ISM component uniformly populate the region occupied by galaxies with a wide range of pronounced (≥0.5M ⊙ yr−1) star formation activity. We compare the MIR color distribution in our sample to that in the general population of local active galactic nuclei (AGNs), in the population of evolved FR II radio galaxies, and also in the population of radio galaxies with recurrent jet activity. We conclude that the triggering of radio jets in AGNs does not differentiate between elliptical hosts with substantially different fractions of young stars; instead, there is a relationship between the jet duty cycle and the ongoing star formation. The distribution of the subsample of our sources with z < 0.4 on the low-resolution MIR versus absorption-corrected X-ray luminosity plane is consistent with the distribution of a sample of local AGNs. Finally, we comment on the star formation rates of the two γ-ray-detected sources in our sample, 1146+596 and 1718–649.

A Redshift for the First Einstein Ring, MG 1131+0456

Abstract MG 1131+0456 is a radio-selected gravitational lens, and is the first known Einstein ring. Discovered in 1988, the system consists of a bright (S 74 MHz = 3.7 Jy) radio source imaged into a ring and two compact, flat-spectrum components separated by 2.″1. The ring is optically faint (R = 23.3), rising steeply into the near- and mid-infrared (K = 17.8; W2 = 13.4). The system has been intensively studied in the intervening years, including high-resolution radio imaging, radio monitoring, and near-infrared imaging with Hubble and Keck. The lensing galaxy is at z l = 0.844. However, to date, no spectroscopic redshift had been reported for the lensed source. Using archival Keck data from 1997, we report the robust detection of a single narrow emission line at 5438 Å, which we associate with C iii] λ1909 Å from a type-2 quasar at z s = 1.849. Support for this redshift identification comes from weaker emission associated with C iv λ1549 Å and He ii λ1640 Å, typical of type-2 quasars, as well as the lack of emission lines in archival near-infrared Keck spectroscopy. We also present, for the first time, Cycle 1 Chandra observations of MG 1131+0456, which clearly resolves into two point sources with a combined flux of ∼10−13 erg cm−2 s−1 and a best-fit column density of ∼3 × 1022 cm−2. We suggest a new method to identify candidate lensed active galactic nuclei from low-resolution X-ray surveys such as eROSITA by targeting sources that have anomalously high X-ray luminosity given their mid-infrared luminosity.

Multiwavelength Observations of SDSS J105621.45+313822.1, a Broad-line, Low-metallicity AGN

Abstract In contrast to massive galaxies with solar or super-solar gas phase metallicities, very few active galactic nuclei (AGNs) are found in low-metallicity dwarf galaxies. Such a population could provide insight into the origins of supermassive black holes. Here we report near-IR spectroscopic and X-ray observations of SDSS J105621.45+313822.1, a low-mass, low-metallicity galaxy with optical narrow line ratios consistent with star-forming galaxies but a broad Hα line and mid-infrared colors consistent with an AGN. We detect the [Si vi] 1.96 μm coronal line and a broad Paα line with an FWHM of 850 ± 25 km s−1. Together with the optical broad lines and coronal lines seen in the Sloan Digital Sky Survey (SDSS) spectrum, we confirm the presence of a highly accreting black hole with mass (2.2 ± 1.3) × 106 M ⊙, with a bolometric luminosity of ≈1044 erg s−1 based on the coronal line luminosity, implying a highly accreting AGN. Chandra observations reveal a weak nuclear point source with erg s−1, ∼2 orders of magnitude lower than that predicted by the mid-infrared luminosity, suggesting that the AGN is highly obscured despite showing broad lines in the optical spectrum. The low X-ray luminosity and optical narrow line ratios of J1056+3138 highlight the limitations of commonly employed diagnostics in the hunt for AGNs in the low-metallicity, low-mass regime.

Estimating the Molecular Gas Mass of Low-redshift Galaxies from a Combination of Mid-infrared Luminosity and Optical Properties

Abstract We present CO (J = 1−0) and/or CO (J = 2−1) spectroscopy for 31 galaxies selected from the ongoing Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, obtained with multiple telescopes. This sample is combined with CO observations from the literature to study the correlation of the CO luminosities ( ) with the mid-infrared luminosities at 12 ( ) and 22 μm ( ), as well as the dependence of the residuals on a variety of galaxy properties. The correlation with is tighter and more linear, but galaxies with relatively low stellar masses ( M ⊙) and blue colors ( and/or NUV − r ≲ 3) fall significantly below the mean – relation. We propose a new estimator of the CO (1−0) luminosity (and thus the total molecular gas mass M mol) that is a linear combination of three parameters: , , and g − r. We show that, with a scatter of only 0.18 dex in log , this estimator provides unbiased estimates for galaxies of different properties and types. An immediate application of this estimator to a compiled sample of galaxies with only CO (J = 2−1) observations yields a distribution of the CO (J = 2−1) to CO (J = 1−0) luminosity ratios (R21) that agrees well with the distribution of real observations, in terms of both the median and the shape. Application of our estimator to the current MaNGA sample reveals a gas-poor population of galaxies that are predominantly early-type and show no correlation between molecular gas-to-stellar mass ratio and star formation rate, in contrast to gas-rich galaxies. We also provide alternative estimators with similar scatters, based on r- and/or z-band luminosities instead of . These estimators serve as cheap and convenient M mol proxies to be potentially applied to large samples of galaxies, thus allowing statistical studies of gas-related processes of galaxies.

Reverberation Measurements of the Inner Radii of the Dust Tori in Quasars

Abstract We present the results of a dust-reverberation survey of quasars at redshifts z < 0.6. We found a delayed response of the K-band flux variation after the optical flux variation in 25 out of 31 targets, and obtained the lag time between them for 22 targets. Combined with the results for nearby Seyfert galaxies, we provide the largest homogeneous collection of K-band dust-reverberation data for 36 type 1 active galactic nuclei (AGNs). This doubles the sample and includes the most distant AGN and the largest lag so far measured. We estimated the optical luminosity of the AGN component of each target using three different methods: spectral decomposition, the flux-variation-gradient method, and image decomposition. We found a strong correlation between the reverberation radius for the innermost dust torus and the optical luminosity over a range of approximately four orders of magnitude in luminosity, as is already known for Seyfert galaxies. We estimated the luminosity distances of the AGNs based on their dust-reverberation lags, and found that the data in the redshift–distance diagram are consistent with the current standard estimates of the cosmological parameters. We also present the radius–luminosity relations for isotropic luminosity indicators such as the hard X-ray (14–195 keV), [O IV] 25.89 μm, and mid-infrared (12 μm) continuum luminosities, which are applicable to obscured AGNs.

Variation of the Mid-infrared versus Hα Luminosity Correlation with Increasing Redshift for Galaxies in the Local Universe

Abstract The correlation between mid-infrared (MIR) and Hα luminosity (hereafter referred to as the MIR versus Hα correlation) has been investigated for years, and these approximate linear correlations have been applied to many studies to derive the ongoing star formation rate (SFR) for galaxies near and far. We present and analyze the correlations between rest-frame 12 and 22 μm and Hα luminosities for a large sample of star-forming galaxies with redshift ranging from 0.03 to 0.15 selected in the cross-matched SDSS DR7 and ALLWISE survey. For the galaxies located in a relatively narrow redshift bin (Δz ∼ 0.01), we find that the fitting slope of the MIR versus Hα correlation is always less than 1, and less than the slope derived for all the star-forming galaxies covering a broad redshift range (0.03 < z < 0.15). Additionally, the fitting intercept increases with redshift. We check the influence on the L[MIR] versus L[Hα] correlation from K- and aperture correction, the variation of either star formation history or morphology, and find their influence is not large enough to account for the inconsistency of the MIR versus Hα correlation individually. We also find that there is possible evolution for the SFR versus M* (stellar mass) correlation within the redshift coverage from 0.03 to 0.15. Finally, we warn that an unwanted error might be brought in if the MIR versus Hα correlation derived from the sample covering a large redshift interval has been applied, and indicate an explicit study is needed to establish an accurate, redshift-independent MIR versus Hα correlation.

Does the mid-infrared–hard X-ray luminosity relation for active galactic nuclei depend on Eddington ratio?

We revisit the correlation between the mid-infrared (6 $\mu$m) and hard X-ray (2--10 keV) luminosities of active galactic nuclei (AGNs) to understand the physics behind it. We construct an X-ray flux-limited sample of 571 type 1 AGNs with $f_{0.5-2.0 \,{\rm keV}} > 2.4 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$, drawn from the ROSAT Bright Survey catalog. Cross-matching the sample with infrared data taken from Wide-field Infrared Survey Explorer, we investigate the relation between the rest-frame 6 $\mu$m luminosity ($L_{\rm 6}$) and the rest-frame 2--10 keV luminosity ($L_{\rm X}$), where $L_{\rm 6}$ is corrected for the contamination of host galaxies by using the spectral energy distribution fitting technique. We confirm that $L_{\rm 6}$ and $L_{\rm X}$ are correlated over four orders of magnitude, in the range of $L_{\rm X} = 10^{42-46}$ erg s$^{-1}$. We investigate what kinds of physical parameters regulate this correlation. We find that $L_{\rm X}$/$L_{\rm 6}$ clearly depends on the Eddington ratio ($\lambda_{\rm Edd}$) as $\log \lambda_{\rm Edd} = -(0.56 \pm 0.10) \log \, (L_{\rm X}/L_{\rm 6}) - (1.07 \pm 0.05)$, even taking into account quasars that are undetected by ROSAT as well as those detected by XMM-Newton in the literature. We also add hyper-luminous quasars with $L_{\rm 6}$ $>$ 10$^{46}$ erg s$^{-1}$ in the literature and perform a correlation analysis. The resultant correlation coefficient is $-0.41 \pm 0.07$, indicating a moderately tight correlation between $L_{\rm X}$/$L_{\rm 6}$ and $\lambda_{\rm Edd}$. This means that AGNs with high Eddington ratios tend to have lower X-ray luminosities with respect to the mid-infrared luminosities. This dependence can be interpreted as a change in the structure of the accretion flow.