Active Galactic Nuclei Host Galaxies Research Articles

The M•–σe relation for local type 1 AGNs and quasars

We analyzed Multi Unit Spectroscopic Explorer observations of 42 local z ≲ 0.1 type 1 active galactic nucleus (AGN) host galaxies taken from the Palomar-Green quasar sample and the close AGN reference survey. Our goal was to study the relation between the black hole mass (M•) and bulge stellar velocity dispersion (σe) for type 1 active galaxies. The sample spans black hole masses of 106.0 − 109.2 M⊙, bolometric luminosities of 1042.9 − 1046.0 erg s−1, and Eddington ratios of 0.006 − 1.2. We avoided AGN emission by extracting the spectra over annular apertures. We modeled the calcium triplet stellar features and measured stellar velocity dispersions of σ* = 60 − 230 km s−1 for the host galaxies. We find stellar velocity dispersion values in agreement with previous measurements for local (z ≲ 0.1) AGN host galaxies, but slightly lower compared with those reported for nearby X-ray-selected type 2 quasars. Using a novel annular aperture correction recipe to estimate σe from σ* that considers the bulge morphology and observation beam-smearing, we estimate flux-weighted σe = 60 − 250 km s−1. If we consider the bulge type when estimating M•, we find no statistical difference between the distributions of AGN hosts and the inactive galaxies on the M•–σe plane for M• ≲ 108 M⊙. Conversely, if we do not consider the bulge type when computing M•, we find that both distributions disagree. We find no correlation between the degree of offset from the M•–σe relation and Eddington ratio for M• ≲ 108 M⊙. The current statistics preclude firm conclusions from being drawn for the high-mass range. We argue these observations support notions that a significant fraction of the local type 1 AGNs and quasars have undermassive black holes compared with their host galaxy bulge properties.

Active Galactic Nuclei in the Green Valley at z ∼ 0.7

We present near-infrared (NIR) spectroscopy using the MMT and Magellan infrared spectrograph for a sample of 29 massive galaxies ( logM*/M⊙≳10 ) at z ∼ 0.7 with optical spectroscopy from the Large Early Galaxy Astrophysics Census (LEGA-C) survey. Having both optical and NIR spectroscopy at this redshift allows us to measure the full suite of rest-optical strong emission lines, enabling the study of ionization sources and the rest-optical selection of active galactic nuclei (AGN), as well as the measurement of dust-corrected Hα-based star formation rates (SFRs). We find that 11 out of 29 galaxies host AGN. We infer the nonparametric star formation histories with the spectral energy distribution fitting code Prospector and classify galaxies as star-forming, green valley, or quiescent based on their most recent specific SFRs. We explore the connection between AGN activity and suppressed star formation, and find that 89% ± 15% of galaxies in the green valley or below host AGN, while only 15% ± 8% of galaxies above the green valley host AGN. We construct the star-forming main sequence (SFMS) and find that the AGN host galaxies are 0.37 dex below the SFMS, while galaxies without detectable AGN are consistent with being on the SFMS. However, when compared to a bootstrapped mass-matched sample, the SFRs of our sample of AGN host galaxies are consistent with the full LEGA-C sample. Based on this mass-matched analysis, we cannot rule out that this suppression of star formation is driven by other processes associated with the higher mass of the AGN sample. We therefore cannot link the presence of AGN activity to the quenching of star formation.

An ALMA CO(1-0) survey of the 2Jy sample: large and massive molecular discs in radio AGN host galaxies

ABSTRACT The jets of radio AGN provide one of the most important forms of active galactic nuclei (AGN) feedback, yet considerable uncertainties remain about how they are triggered. Since the molecular gas reservoirs of the host galaxies can supply key information about the dominant triggering mechanism(s), here we present Atacama Large Millimeter/sub-millimeter Array CO(1-0) observations of a complete sample of 29 powerful radio AGN ($P_{1.4\,{\rm GHz}} \gt 10^{25}$ W Hz$^{-1}$ and $0.05 \lt z \lt 0.3$) with an angular resolution of about 2–3 arcsec (corresponding to 2–8 kpc). We detect molecular gas with masses in the range $10^{8.9} \lt M_{{\rm H}_2} \lt 10^{10.2}$ M$_\odot$ in the early-type host galaxies of ten targets, while for the other 19 sources, we derive upper limits. The detection rate of objects with such large molecular masses – $34\pm 9$ per cent – is higher than in the general population of non-active early-type galaxies (ETGs: $\lt $10 per cent). The kinematics of the molecular gas are dominated in most cases by rotating disc-like structures, with diameters up to 25 kpc. Compared with the results for samples of quiescent ETG in the literature, we find a larger fraction of more massive, more extended and less settled molecular gas structures. In most of the CO-detected sources, the results are consistent with triggering of the AGN as the gas settles following a merger or close encounter with a gas-rich companion. However, in a minority of objects at the centres of rich clusters of galaxies, the accretion of gas cooling from the hot X-ray haloes is a plausible alternative to galaxy interactions as a triggering mechanism.

The miniJPAS Survey: The radial distribution of star formation rates in faint X-ray active galactic nuclei

We study the impact of black hole nuclear activity on both the global and radial star formation rate (SFR) profiles in X-ray-selected active galactic nuclei (AGN) in the field of miniJPAS, the precursor of the much wider J-PAS project. Our sample includes 32 AGN with z < 0.3 detected via the XMM-Newton and Chandra surveys. For comparison, we assembled a control sample of 71 star-forming (SF) galaxies with similar magnitudes, sizes, and redshifts. To derive the global properties of both the AGN and the control SF sample, we used CIGALE to fit the spectral energy distributions derived from the 56 narrowband and 4 broadband filters from miniJPAS. We find that AGN tend to reside in more massive galaxies than their SF counterparts. After matching samples based on stellar mass and comparing their SFRs and specific SFRs (sSFRs), no significant differences appear. This suggests that the presence of AGN does not strongly influence overall star formation. However, when we used miniJPAS as an integral field unit (IFU) to dissect galaxies along their position angle, a different picture emerges. We find that AGN tend to be more centrally concentrated in mass with respect to SF galaxies. Moreover, we find a suppression of the sSFR up to 1Re and then an enhancement beyond 1Re, strongly contrasting with the decreasing radial profile of sSFRs in SF galaxies. This could point to an inside-out quenching of AGN host galaxies. Additionally, we examined how the radial profiles of the sSFRs in AGN and SF galaxies depend on galaxy morphology, by dividing our sample into disk-dominated (DD), pseudo-bulge (PB), and bulge-dominated (BD) systems. In DD systems, AGN exhibit a flat sSFR profile in the central regions and enhanced star formation beyond 1Re, contrasting with SF galaxies. In PB systems, SF galaxies show a decreasing sSFR profile, while AGN hosts exhibit an inside-out quenching scenario. In BD systems, both populations demonstrate consistent flat sSFR profiles. These findings suggest that the reason we do not see differences on a global scale is because star formation is suppressed in the central regions and enhanced in the outer regions of AGN host galaxies. While limited in terms of sample size, this work highlights the potential of the upcoming J-PAS as a wide-field low-resolution IFU for thousands of nearby galaxies and AGN.

The Contribution of Host Galaxy Properties in X-Ray Active Galactic Nuclei Clusters

In this study, the influence of host galaxy properties on X-ray active galactic nuclei (AGN) clusters was investigated using multiwavelength data. X-ray data from the eFEDS main catalog, optical and near-infrared data from the fourth data release of KiDS/VIKING, and mid-infrared data from WISE were utilized. By integrating these datasets and employing the CIGALE code, the star formation rate, luminosity, and stellar mass of the host galaxies were estimated. The analysis reveals significant associations between luminosity, stellar mass, and star formation rate, providing valuable insights into AGN activity. Furthermore, AGN clusters were compared with non-AGN clusters to uncover distinctive characteristics. AGN clusters exhibit differences in their population across various luminosity levels. Interestingly, a significant proportion of AGN clusters is concentrated in the middle range of luminosity (45-46 measured in logL<sub>(0.5-2.0 keV)</sub>) for both low and high redshift classifications. Additionally, galaxies hosting AGNs detected in X-ray emission tend to fall within a specific range of stellar mass (10-11 measured in log(M<sub>⋆</sub>(M<sub>⊚</sub>)). This stellar mass range is populated by a substantial number of AGN galaxies, irrespective of their redshift classification. Moreover, a significant population of X-ray AGN is concentrated within the star formation rate range of 1.5-2.5 (expressed in log(M<sub>⊚</sub> yr<sup>-1</sup>)) in both low and high redshift regions. By analyzing the dependencies on luminosity, stellar mass, and star formation rate, this study provides valuable insights into the correlation and relationship between AGN clusters and their host galaxies. The comparison with non-AGN clusters and the integration of multiwavelength data from eFEDS, KiDS/VIKING, and WISE enhance the depth of analysis, contributing to a comprehensive evaluation of AGN clusters. These findings advance our understanding of the complex relationship between AGN clusters and host galaxy properties in the field of astrophysics.

The Role of Active Galactic Nucleus Winds in Galaxy Formation: Connecting AGN Outflows at Low Redshifts to the Formation/Evolution of Their Host Galaxies

Using Sloan Digital Sky Survey (SDSS) spectra, we applied an automatic method to search for outflows (OFs) in three large samples of narrow-line active galactic nuclei (AGN) at low redshifts (z < 0.4), separated into three spectral activity classes: radio-loud galaxies (RGs), 15,793; radio-quiet Seyfert 2 AGN (Sy2), 18,585; and LINERs, 25,656. In general, the probability of detecting an OF decreases along the sequence Sy1→Sy2→LINER/RG and independently of the AGN class, the wind velocity, traced by W80, increases with the AGN luminosity. Moreover W80 is systematically higher in RGs or any of the other AGN classes when detected in radio. These results support the idea that there are two main modes of production of OF, the radiative mode dominant in radio-quiet AGN and the jet mode dominant in RGs, although both modes could also happen simultaneously at different levels. From the spectra and SDSS photometry, the characteristics of the AGN host galaxies and their supermassive black holes (SMBHs) were also retrieved using the stellar population synthesis code STARLIGHT. This revealed that, independently of the AGN spectral class, (1) galaxy hosts with OFs have systematically later morphological types and higher star formation rates (SFRs) than their counterparts without OF, (2) the AGN occupy different positions in the specific diagnostic diagram (specific black hole accretion rate (sBHAR) versus specific SFR), which suggests they follow different evolutionary paths congruent with the morphology of their galaxy hosts, and (3) they show no evidence of AGN quenching or triggering of star formation. These results are consistent with a scenario explaining the different AGN classes as consequences of different formation processes of galaxies: early-type galaxies (LINERs and RGs) formed bigger bulges and more massive SMBHs, exhausting their reservoir of gas more rapidly than late-type galaxies (Sy2 and Sy1), and thereby quenching their star formation and starving their SMBHs.

Chromatically modeling the parsec-scale dusty structure in the center of NGC 1068

Context. The Very Large Telescope Interferometer (VLTI) has been providing breakthrough images of the dust in the central parsecs of active galactic nuclei (AGNs), which is thought to be a key component of the AGN unification scheme and AGN host galaxy interaction. In single infrared bands, these images can enjoin multiple interpretations, some of which could challenge the unification scheme. This is the case for the archetypal type 2 AGN of NGC 1068, whereby the degeneracy is reduced by multi-band temperature maps that are hindered by an ambiguity in the alignment between different single-band images. Aims. We aim to solve this problem by creating a chromatic model capable of simultaneously explaining the VLTI GRAVITY+MATISSE 2 μm–13 μm observations of AGNs hosted by NGC 1068. Methods. We employed a simple disk and wind geometry populated by spherical black-body emitters and dust obscuration to create a versatile multi-wavelength modelling method for chromatic IR interferometric data of dusty objects. Results. This simple geometry is capable of reproducing the spectro-interferometric data of NGC 1068 from the K through N bands. It explains the complex single band images with obscuration and inclination effects, and it solves the alignment problem between bands. We find that the resulting model disk and wind geometry is consistent with previous studies of comparable and larger scales. For example, compared to molecular gas emission, our model wind position angle (PA) of 2322° is close to the mas-scale outflowing CO(6–5) PA of ∼33° seen with ALMA. The equivalent 90° offset model disk PA is also consistent with the CO(6–5) disk axis of 112° as well as the mas-scale disk axis from CO(2–1), CO(3–2), and HCO+(4–3) of 115 ± 5°. Furthermore, the resulting model images visually resemble the multiple achromatic image reconstructions of the same data when evaluated at the same wavelengths. We conclude that the IR emitting structure surrounding the AGN within NGC 1068 can indeed be explained by the clumpy disk+wind iteration of the AGN unification scheme. Within the scheme, we find that it is best explained as a type 2 AGN and the obscuring dust chemistry can be explained by a mix of olivine silicates and 16 ± 1% amorphous carbon.

Exploring Low-mass Black Holes through Tidal Disruption Events in the Early Universe: Perspectives in the Era of the JWST, Roman Space Telescope, and LSST Surveys

The James Webb Space Telescope (JWST) has recently uncovered the presence of low-luminosity active galactic nuclei (AGNs) at z = 4–11. Spectroscopic observations have provided estimates of the nuclear black hole (BH) masses for these sources, extending the low-mass boundary down to M • ∼ 106–7 M ⊙. Despite this breakthrough, the observed lowest mass of BHs is still ≳1–2 orders of magnitude heavier than the predicted mass range of their seed population, thereby leaving the initial mass distribution of massive BHs poorly constrained. In this paper, we focus on UV-to-optical (in the rest frame) flares of stellar tidal disruption events (TDEs) embedded in low-luminosity AGNs as a tool for exploring low-mass BH populations with ≲104–6 M ⊙. We provide an estimate of the TDE rate over z = 4–11, associated with the properties of JWST-detected AGN host galaxies, and we find that deep and wide survey programs with JWST and the Roman Space Telescope (RST) can detect and identify TDEs up to z ≃ 4–7. The predicted detection numbers of TDEs at z > 4 in 1 yr are NTDE∼2–10(0.2–2) for the JADES-Medium (and COSMOS-Web) survey with JWST and NTDE∼2–10(8–50) for the deep (and wide) tiers of the High Latitude Time Domain Survey with RST. We further discuss survey strategies for hunting for transient high-redshift TDEs in wide-field surveys with RST, as well as a joint observation campaign with the Vera C. Rubin Observatory for enhancing the detection number. The high-redshift TDE search will give us a unique opportunity to probe the mass distribution of early BH populations.

Alignments in the orientation of radio jets from AGN and their host galaxies

It is well established that active galactic nuclei (AGNs) play an important role in the evolution of galaxies. These AGNs can be linked to the accretion processes onto massive black holes and past merger events in their host galaxies, which may lead to different alignments of the jets with respect to the host galaxies. This paper presents a study of the position angle (PA) differences between radio and optical images of radio-AGNs based on the second data release (DR2) of the Low Frequency Array (LOFAR) Two-Meter Sky Survey (LoTSS), the Karl G. Jansky Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters Survey (FIRST), the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, and the Sloan Digital Sky Survey (SDSS). We assessed PA measurement biases in the data and classified the radio-AGNs based on the radio luminosity and infrared colour from the Wide-field Infrared Survey Explorer (WISE). This resulted in the largest sample of radio AGNs with reliable radio and optical PA measurements published to date, with a total of 3682 AGNs. The PA difference (dPA) distributions for the radio-AGN sample show a prominent minor-axis alignment tendency. Based on some simple assumptions, we simulated the projection effect to estimate the intrinsic jet--galaxy alignment. The observed dPA distribution can be well described by a two-component jet-alignment model in which one component is more aligned with the minor axis of the host galaxy than the other. The fitting results indicate that the jet alignment is dependent on radio luminosity and the shape of the host galaxies, with the jets being more likely to be aligned with the minor axis of the galaxy for lower radio luminosity and for optically more elongated radio-AGNs. The minor-axis alignment of the entire sample may suggest a coherent accretion model present in most AGN host galaxies, while a considerable number of luminous radio-AGNs with massive host galaxies might have undergone accretion ---according to the chaotic model--- or past merger events.

Investigating the Star Formation Rates of Active Galactic Nucleus Hosts Relative to the Star-forming Main Sequence

A fundamental question in galaxy and black hole evolution remains how galaxies and their supermassive black holes have evolved together over cosmic time. Specifically, it is still unclear how the position of X-ray active galactic nucleus (AGN) host galaxies with respect to the star-forming main sequence (MS) may change with the X-ray luminosity (L X) of the AGN or the stellar mass (M ⋆) of the host galaxy. We use data from the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) to probe this issue. XMM-SERVS is covered by the largest medium-depth X-ray survey (with superb supporting multiwavelength data) and thus contains the largest sample to date for study. To ensure consistency, we locally derive the MS from a large reference galaxy sample. In our analysis, we demonstrate that the turnover of the galaxy MS does not allow reliable conclusions to be drawn for high-mass AGNs, and we establish a robust safe regime where the results do not depend upon the choice of MS definition. Under this framework, our results indicate that less massive AGN host galaxies ( logM⋆∼9.5–10.5M⊙ ) generally possess enhanced star formation rates compared to their normal-galaxy counterparts while the more massive AGN host galaxies ( logM⋆∼10.5–11.5M⊙ ) lie on or below the star-forming MS. Further, we propose an empirical model for how the placement of an AGN with respect to the MS (SFRnorm) evolves as a function of both M ⋆ and L X.

Deep Chandra Observation of the Remarkable Ionization Cones of NGC 5252

Seyfert galaxy NGC 5252 harbors enormously extended ionization cones that have been previously detected in the optical and X-ray band, offering a unique opportunity to investigate the interaction between the central active galactic nucleus (AGN) and the surrounding gas in the AGN host galaxy. We present deep Chandra imaging spectroscopy of NGC 5252 with a total exposure time of 230 ks. The morphology in the soft X-rays shows resolved extended structure from the nucleus to a large radial distance, and for the first time we detect the outermost X-ray arc at ∼20 kpc. The X-ray cone mostly follows the direction of the optical ionization cones in the southeast and northwest directions, about 20° misaligned with the major axis of the galactic disk of NGC 5252. Fitting the spectra extracted from radial sectors with photoionization models supports that extended emission is mainly photoionized by the central AGN. We also examine the variation of the photoionization parameter along the radial extension and infer a decreasing ionizing continuum of the central engine by a factor of ∼50 over the past 64,000 yr. These findings are consistent with previous suggestions that NGC 5252 resembles a quasar relic with an M ∼ 109 M ⊙ supermassive black hole that went through a minor merger event and switched to a low accretion rate state.

An Extended Lyα Outflow from a Radio Galaxy at z = 3.7?

Spatially resolved observations of active galactic nuclei (AGN) host galaxies undergoing feedback processes are one of the most relevant avenues through which galactic evolution can be studied, given the long-lasting effects AGN feedback has on gas reservoirs, star formation, and AGN environments at all scales. Within this context, we report results from Very Large Telescope/MUSE integral field optical spectroscopy of TN J1049-1258, one of the most powerful radio sources known, at a redshift of 3.7. We detected extended (∼18 kpc) Lyα emission, spatially aligned with the radio axis, redshifted by 2250 ± 60 km s−1 with respect to the host galaxy systemic velocity, and cospatial with UV continuum emission. This Lyα emission could arise from a companion galaxy, although there are arguments against this interpretation. Alternatively, it might correspond to an outflow of ionized gas stemming from the radio galaxy. The outflow would be the highest redshift spatially resolved ionized outflow to date. The enormous amount of energy injected, however, appears to be unable to quench the host galaxy’s prodigious star formation, occurring at a rate of ∼4500 M ⊙yr−1, estimated using its far-infrared luminosity. Within the field, we also found two companion galaxies at projected distances of ∼25 and ∼60 kpc from the host, which suggests the host galaxy is harbored within a protocluster.

A complete catalogue of broad-line AGNs and double-peaked emission lines from MaNGA integral-field spectroscopy of 10K galaxies: stellar population of AGNs, supermassive black holes, and dual AGNs

ABSTRACT We analyse the integral field spectroscopy data for the ≈10 000 galaxies in final data release of the MaNGA survey. We identify 188 galaxies for which the emission lines cannot be described by single Gaussian components. These galaxies can be classified into (1) 38 galaxies with broad $\rm H\alpha$ and [O iii] $\rm \lambda$5007 lines, (2) 101 galaxies with broad $\rm H\alpha$ lines but no broad [O iii] $\rm \lambda$5007 lines, and (3) 49 galaxies with double-peaked narrow emission lines. Most of the broad-line galaxies are classified as active galactic nuclei (AGNs) from their line ratios. The catalogue helps us further understand the AGN-galaxy coevolution through the stellar population of broad-line region host galaxies and the relation between broad lines’ properties and the host galaxies’ dynamical properties. The stellar population properties (including mass, age, and metallicity) of broad-line host galaxies suggest there is no significant difference between narrow-line Seyfert-2 galaxies and Type-1 AGNs with broad $\rm H\alpha$ lines. We use the broad-$\rm H\alpha$ line width and luminosity to estimate masses of black hole in these galaxies, and test the MBH–σe relation in Type-1 AGN host galaxies. Furthermore, we find three dual AGN candidates supported by radio images from the VLA FIRST survey. This sample may be useful for further studies on AGN activities and feedback processes.

Mapping the stellar population and gas excitation of MaNGA galaxies with megacubes. Results for AGN versus control sample

ABSTRACT We present spaxel-by-spaxel stellar population fits for the ∼10 000 MaNGA data cubes. We provide multiple extension fits files, nominated as megacubes, with maps of several properties as well as emission-line profiles that are provided for each spaxel. All the megacubes are available through a web interface (https://manga.linea.org.br/ or http://www.if.ufrgs.br/~riffel/software/megacubes/). We also defined a final Active Galactic Nuclei (AGN) sample, as well as a control sample matching the AGN host galaxy properties. We have analysed the stellar populations and spatially resolved emission-line diagnostic diagrams of these AGNs and compared them with the control galaxies sample. We find that the relative fractions of young (t ≤56 Myr) and intermediate-age (100 Myr ≤t ≤ 2 Gyr) show predominantly a positive gradient for both AGNs and controls. The relative fraction of intermediate-age stellar population is higher in AGN hosts when compared to the control sample, and this difference becomes larger for higher [O iii] luminosity AGNs. We attribute this to the fact that extra gas is available in these more luminous sources and that it most likely originates from mass-loss from the intermediate-age stars. The spatially resolved diagnostic diagrams reveal that the AGN emission is concentrated in the inner 0.5 Re (effective radius) region of the galaxies, showing that the AGN classification is aperture dependent and that emission-line ratios have to be taken together with the H α equivalent width for proper activity classification. We present a composite ‘BPT+WHAN’ diagram that produces a more comprehensive mapping of the gas excitation.

The Most Obscured AGNs in the XMM-SERVS Fields

We perform X-ray spectral analyses to derive the characteristics (e.g., column density, X-ray luminosity) of ≈10,200 active galactic nuclei (AGNs) in the XMM-Spitzer Extragalactic Representative Volume Survey, which was designed to investigate the growth of supermassive black holes across a wide dynamic range of cosmic environments. Using physical torus models (e.g., Borus02) and a Bayesian approach, we uncover 22 representative Compton-thick (CT; N H > 1.5 × 1024 cm−2) AGN candidates with good signal-to-noise ratios as well as a large sample of 136 heavily obscured AGNs. We also find an increasing CT fraction (f CT) from low (z < 0.75) to high (z > 0.75) redshift. Our CT candidates tend to show hard X-ray spectral shapes and dust extinction in their spectral energy distribution fits, which may shed light on the connection between AGN obscuration and host-galaxy evolution.

Environmental Dependence of Different Colors of Active Galactic Nucleus (AGN) Host Galaxies

Environmental Dependence of Different Colors of Active Galactic Nucleus (AGN) Host Galaxies

An empirical relation to estimate host galaxy stellar light from AGN spectra

ABSTRACT Measurement of black hole mass for low-z (z≤ 0.8) Active Galactic Nuclei (AGNs) is difficult due to the strong contribution from host galaxy stellar light necessitating detailed spectral decomposition to estimate the AGN luminosity. Here, we present an empirical relation to estimate host galaxy stellar luminosity from the optical spectra of AGNs at z ≤ 0.8. The spectral data were selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalogue having a signal-to-noise ratio at 5100 Å (SNR5100) &amp;gt;10 containing 11 415 quasars. The median total luminosity (log (Ltotal/[erg s−1])), stellar luminosity (log (Lstar/[erg s−1])), and AGN continuum luminosity ((log Lcont/[erg s−1])) in our sample are 44.52, 44.06, and 44.30, respectively. We fit the AGN power-law continuum, host galaxy, and iron blend contribution, simultaneously over the entire available spectrum. We found the host galaxy fraction to anticorrelate with continuum luminosity and can be well-represented by a polynomial function, which can be used to correct the stellar light contribution from AGN spectra. We also found anticorrelation between host galaxy fraction and iron strength, Eddington ratio, and redshift. The empirical relation gives comparable results of host-fraction with the image decomposition method.

Using Machine Learning to Determine Morphologies of z < 1 AGN Host Galaxies in the Hyper Suprime-Cam Wide Survey

We present a machine-learning framework to accurately characterize the morphologies of active galactic nucleus (AGN) host galaxies within z < 1. We first use PSFGAN to decouple host galaxy light from the central point source, then we invoke the Galaxy Morphology Network (GaMorNet) to estimate whether the host galaxy is disk-dominated, bulge-dominated, or indeterminate. Using optical images from five bands of the HSC Wide Survey, we build models independently in three redshift bins: low (0 < z < 0.25), mid (0.25 < z < 0.5), and high (0.5 < z < 1.0). By first training on a large number of simulated galaxies, then fine-tuning using far fewer classified real galaxies, our framework predicts the actual morphology for ∼60%–70% of the host galaxies from test sets, with a classification precision of ∼80%–95%, depending on the redshift bin. Specifically, our models achieve a disk precision of 96%/82%/79% and bulge precision of 90%/90%/80% (for the three redshift bins) at thresholds corresponding to indeterminate fractions of 30%/43%/42%. The classification precision of our models has a noticeable dependency on host galaxy radius and magnitude. No strong dependency is observed on contrast ratio. Comparing classifications of real AGNs, our models agree well with traditional 2D fitting with GALFIT. The PSFGAN+GaMorNet framework does not depend on the choice of fitting functions or galaxy-related input parameters, runs orders of magnitude faster than GALFIT, and is easily generalizable via transfer learning, making it an ideal tool for studying AGN host galaxy morphology in forthcoming large imaging surveys.

Deep Herschel observations of the 2 Jy sample: assessing the non-thermal and AGN contributions to the far-IR continuum

ABSTRACT The far-IR/sub-mm wavelength range contains a wealth of diagnostic information that is important for understanding the role of active galactic nuclei (AGN) in galaxy evolution. Here we present the results of Herschel PACS and SPIRE observations of a complete sample of 46 powerful 2 Jy radio AGN at intermediate redshifts (0.05 &amp;lt; z &amp;lt; 0.7), which represent the deepest pointed observations of a major sample of radio AGN undertaken by Herschel. In order to assess the importance of non-thermal synchrotron emission at far-IR wavelengths, we also present new APEX sub-mm and ALMA mm data. We find that the overall incidence of non-thermal contamination in the PACS bands (&amp;lt;200 μm) is in the range 28–43 per cent; however, this rises to 30–72 per cent for wavelengths (&amp;gt;200 μm) sampled by the SPIRE instrument. Non-thermal contamination is strongest in objects with compact CSS/GPS or extended FRI radio morphologies, and in those with type 1 optical spectra. Considering thermal dust emission, we find strong correlations between the 100 and 160 μm monochromatic luminosities and AGN power indicators, providing further evidence that radiation from the AGN may be an important heating source for the far-IR emitting dust. Clearly, AGN contamination – whether by the direct emission from synchrotron-emitting lobes and cores, or via radiative heating of the cool dust – needs to be carefully considered when using the far-IR continuum to measure the star formation rates in the host galaxies of radio AGN.

The molecular gas main sequence and Schmidt–Kennicutt relation are fundamental, the star-forming main sequence is a (useful) byproduct

ABSTRACT We investigate the relationship between the star formation rate (SFR), stellar mass (M*), and molecular gas mass ($M_{\mathrm{ H}_2}$) for local star-forming galaxies. We further investigate these relationships for high-z (z = 1–3) galaxies and for the hosts of a local sample of active galactic nuclei (AGN). We explore which of these dependencies are intrinsic and which are an indirect byproduct by employing partial correlation coefficients and random forest regression. We find that for local star-forming galaxies, high-z galaxies, and AGN host galaxies, the Schmidt–Kennicutt (SK) relation (between $M_{\mathrm{ H}_2}$ and SFR) and the molecular gas main sequence (MGMS; between $M_{\mathrm{ H}_2}$ and M*) are intrinsic primary relations, while the relationship between M* and SFR, i.e. the star-forming main sequence (SFMS), is an indirect byproduct of the former two. Hence the SFMS is not a fundamental scaling relation for local or high-z galaxies. We find evidence for both the evolution of the MGMS and SK relation over cosmic time, where, at a given stellar mass, the higher the redshift, the greater the molecular gas mass and the star formation efficiency. We offer a parametrization of both the MGMS and SK relation’s evolution with redshift, showing how they combine to form the observed evolution of the SFMS. In addition, we find that the local AGN host galaxies follow an AGN–MGMS relation (as well as an AGN–SK relation), where the MGMS is offset to lower $M_{\mathrm{ H}_2}$ for a given M* compared to local star-forming galaxies.