Abstract
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 (G
a
M
or
N
et
) 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+G
a
M
or
N
et
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.
Abstract
We constrain the intrinsic Eddington ratio (
λ
Edd
) distribution function for local active galactic nuclei (AGN) in bins of low and high obscuration
log
(
N
H
/
cm
−
2
)
≤
22
and
22
<
log
...(
N
H
/
cm
−
2
)
<
25
, using the Swift Burst Alert Telescope 70 month/BASS DR2 survey. We interpret the fraction of obscured AGN in terms of circumnuclear geometry and temporal evolution. Specifically, at low Eddington ratios (
log
λ
Edd
<
−2), obscured AGN outnumber unobscured ones by a factor of ∼4, reflecting the covering factor of the circumnuclear material (0.8, or a torus opening angle of ∼34°). At high Eddington ratios (
log
λ
Edd
>
−1), the trend is reversed, with <30% of AGN having
log
(
N
H
/
cm
−
2
)
>
22
, which we suggest is mainly due to the small fraction of time spent in a highly obscured state. Considering the Eddington ratio distribution function of narrow-line and broad-line AGN from our prior work, we see a qualitatively similar picture. To disentangle temporal and geometric effects at high
λ
Edd
, we explore plausible clearing scenarios such that the time-weighted covering factors agree with the observed population ratio. We find that the low fraction of obscured AGN at high
λ
Edd
is primarily due to the fact that the covering factor drops very rapidly, with more than half the time spent with <10% covering factor. We also find that nearly all obscured AGN at high-
λ
Edd
exhibit some broad lines. We suggest that this is because the height of the depleted torus falls below the height of the broad-line region, making the latter visible from all lines of sight.
We present X-ray spectral analysis of XMM-Newton and Chandra observations in the 31.3 deg2 Stripe-82X (S82X) field. Of the 6181 unique X-ray sources in this field, we analyze a sample of 2937 ...candidate active galactic nuclei (AGNs) with solid redshifts and sufficient counts determined by simulations. Our results show an observed population with median values of spectral index Γ=1.94−0.39+0.31, column density logNH/cm−2=20.7−0.5+1.2 and intrinsic, de-absorbed, 2–10 keV luminosity logLX/ergs−1=44.0−1.0+0.7, in the redshift range 0–4. We derive the intrinsic, model-independent, fraction of AGNs that are obscured (22≤logNH/cm−2<24), finding a significant increase in the obscured AGN fraction with redshift and a decline with increasing luminosity. The average obscured AGN fraction is 57% ± 4% for log LX/erg s−1 > 43. This work constrains the AGN obscuration and spectral shape of the still uncertain high-luminosity and high-redshift regimes (log LX/erg s−1 > 45.5, z > 3), where the obscured AGN fraction rises to 64% ± 12%. We report a luminosity and density evolution of the X-ray luminosity function, with obscured AGNs dominating at all luminosities at z > 2, and unobscured sources prevailing at log LX/erg s−1 > 45 at lower redshifts. Our results agree with the evolutionary models in which the bulk of AGN activity is triggered by gas-rich environments and in a downsizing scenario. Moreover, the black hole accretion density (BHAD) is found to evolve similarly to the star formation rate density, confirming the coevolution between AGN and host galaxy, but suggesting different timescales in their growing history. The derived BHAD evolution shows that Compton-thick AGNs contribute to the accretion history of AGNs as much as all other AGN populations combined.
Cold quasars are a rare subpopulation observed to host unobscured, X-ray luminous active galactic nuclei (AGN) while also retaining a cold gas supply fueling high star formation rates. These objects ...are interpreted as AGN early in their evolution. We present new SOFIA HAWC+ far-infrared observations, far-ultraviolet to far-infrared (FUV-FIR) photometry, and optical spectroscopy to characterize the accretion and star formation behavior in a cold quasar at z ∼ 0.405 (CQ 4479). CQ 4479 is a starburst galaxy with a predominantly young stellar population and a high gas mass fraction of ∼50%-70%. The AGN component has yet to become the dominant component of the FIR emission. We also find AGN bolometric luminosity that varies as a function of observation method and AGN region probed. Finally, we identify a candidate outflow feature corroborating the hypothesis that cold quasars have energetic feedback. This object presents an intriguing look into the early stages of AGN feedback and probes the rare phase where an AGN and cold gaseous component coexist.
We present results of a ground-based near-infrared campaign with Palomar TripleSpec, Keck NIRSPEC, and Gemini GNIRS to target two samples of reddened active galactic nucleus (AGN) candidates from the ...31 deg2 Stripe 82 X-ray survey. One sample, which is ∼89% complete to (Vega), consists of eight confirmed AGNs, four of which were identified with our follow-up program, and is selected to have red R − K colors ( , Vega). The fainter sample ( , Vega) represents a pilot program to follow-up four sources from a parent sample of 34 that are not detected in the single-epoch SDSS catalog and have WISE quasar colors. All 12 sources are broad-line AGNs (at least one permitted emission line has an FWHM exceeding 1300 km s−1) and span a redshift range . Half the (R − K)-selected AGNs have features in their spectra suggestive of outflows. When comparing these sources to a matched sample of blue Type 1 AGNs, we find that the reddened AGNs are more distant ( ), and a greater percentage have high X-ray luminosities ( erg s−1). Such outflows and high luminosities may be consistent with the paradigm that reddened broad-line AGNs represent a transitory phase in AGN evolution as described by the major merger model for black hole growth. Results from our pilot program demonstrate proof of concept that our selection technique is successful in discovering reddened quasars at missed by optical surveys.
ABSTRACT
We investigate the relation between active galactic nucleus (AGN) and star formation (SF) activity at 0.5 < z < 3 by analysing 898 galaxies with X-ray luminous AGNs (LX > 1044 erg s−1) and a ...large comparison sample of ∼320 000 galaxies without X-ray luminous AGNs. Our samples are selected from a large (11.8 deg2) area in Stripe 82 that has multiwavelength (X-ray to far-IR) data. The enormous comoving volume (∼0.3 Gpc3) at 0.5 < z < 3 minimizes the effects of cosmic variance and captures a large number of massive galaxies (∼30 000 galaxies with M* > 1011 M⊙) and X-ray luminous AGNs. While many galaxy studies discard AGN hosts, we fit the SED of galaxies with and without X-ray luminous AGNs with Code Investigating GALaxy Emission and include AGN emission templates. We find that without this inclusion, stellar masses and star formation rates (SFRs) in AGN host galaxies can be overestimated, on average, by factors of up to ∼5 and ∼10, respectively. The average SFR of galaxies with X-ray luminous AGNs is higher by a factor of ∼3–10 compared to galaxies without X-ray luminous AGNs at fixed stellar mass and redshift, suggesting that high SFRs and high AGN X-ray luminosities may be fuelled by common mechanisms. The vast majority ($\gt 95 {{\ \rm per\ cent}}$) of galaxies with X-ray luminous AGNs at z = 0.5−3 do not show quenched SF: this suggests that if AGN feedback quenches SF, the associated quenching process takes a significant time to act and the quenched phase sets in after the highly luminous phases of AGN activity.
Quasars are the most luminous of active galactic nuclei, and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog covers 31.3 deg2 of the Stripe 82 field, of ...which the 15.6 deg2 covered with XMM-Newton is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multiwavelength counterparts, and 30% of these are unobscured quasars, with LX > 1044 erg s−1 and MB < −23. We define a new population of quasars that are unobscured, have X-ray luminosities in excess of 1044 erg s−1, have broad emission lines, and yet are also bright in the far-infrared, with a 250 m flux density of S250 > 30 mJy. We refer to these Herschel-detected, unobscured quasars as "cold quasars." A mere 4% (21) of the X-ray- and optically selected unobscured quasars in Stripe 82X are detected at 250 m. These cold quasars lie at z ∼ 1-3, have LIR > 1012 L , and have star formation rates (SFRs) of ∼200-1400 M yr−1. Cold quasars are bluer in the mid-IR than the full quasar population, and 72% of our cold quasars have WISE W3 < 11.5 Vega, while only 19% of the full quasar sample meets this criteria. Crucially, cold quasars have on average ∼nine times as much star formation as the main sequence of star-forming galaxies at similar redshifts. Although dust-rich, unobscured quasars have occasionally been noted in the literature before, we argue that they should be considered as a separate class of quasars due to their high SFRs. This phase is likely short-lived, as the central engine and immense star formation consume the gas reservoir. Cold quasars are type-1 blue quasars that reside in starburst galaxies.
Abstract
We introduce a novel machine-learning framework for estimating the Bayesian posteriors of morphological parameters for arbitrarily large numbers of galaxies. The Galaxy Morphology Posterior ...Estimation Network (GaMPEN) estimates values and uncertainties for a galaxy’s bulge-to-total-light ratio (
L
B
/
L
T
), effective radius (
R
e
), and flux (
F
). To estimate posteriors, GaMPEN uses the Monte Carlo Dropout technique and incorporates the full covariance matrix between the output parameters in its loss function. GaMPEN also uses a spatial transformer network (STN) to automatically crop input galaxy frames to an optimal size before determining their morphology. This will allow it to be applied to new data without prior knowledge of galaxy size. Training and testing GaMPEN on galaxies simulated to match
z
< 0.25 galaxies in Hyper Suprime-Cam Wide
g
-band images, we demonstrate that GaMPEN achieves typical errors of 0.1 in
L
B
/
L
T
, 0.″17 (∼7%) in
R
e
, and 6.3 × 10
4
nJy (∼1%) in
F
. GaMPEN's predicted uncertainties are well calibrated and accurate (<5% deviation)—for regions of the parameter space with high residuals, GaMPEN correctly predicts correspondingly large uncertainties. We also demonstrate that we can apply categorical labels (i.e., classifications such as
highly bulge dominated
) to predictions in regions with high residuals and verify that those labels are ≳97% accurate. To the best of our knowledge, GaMPEN is the first machine-learning framework for determining joint posterior distributions of multiple morphological parameters and is also the first application of an STN to optical imaging in astronomy.
The discovery of Little Red Dots (LRDs) -- a population of compact, high-redshift, dust-reddened galaxies -- is one of the most surprising results from JWST. However, the nature of LRDs is still ...debated: does the near-infrared emission originate from accreting supermassive black holes (SMBHs), or intense star formation? In this work, we utilize ultra-deep Chandra observations and study LRDs residing behind the lensing galaxy cluster, Abell~2744. We probe the X-ray emission from individual galaxies but find that they remain undetected and provide SMBH mass upper limits of \(\lesssim(1.5-16)\times10^{6}~\rm{M_{\odot}}\) assuming Eddington limited accretion. To increase the signal-to-noise ratios, we conduct a stacking analysis of the full sample with a total lensed exposure time of \(\approx87\)~Ms. We also bin the galaxies based on their stellar mass, lensing magnification, and detected broad-line H\(\alpha\) emission. For the LRDs exhibiting broad-line H\(\alpha\) emission, there is a hint of a stacked signal (\(\sim2.6\sigma\)), corresponding to a SMBH mass of \(\sim3.2\times10^{6}~\rm{M_{\odot}}\). Assuming unobscured, Eddington-limited accretion, this BH mass is at least 1.5 orders of magnitude lower than that inferred from virial mass estimates using JWST spectra. Given galaxy-dominated stellar mass estimates, our results imply that LRDs do not host over-massive SMBHs and/or accrete at a few percent of their Eddington limit. However, alternative stellar mass estimates may still support that LRDs host over-massive BHs. The significant discrepancy between the JWST and Chandra data hints that the scaling relations used to infer the SMBH mass from the H\(\alpha\) line and virial relations may not be applicable for high-redshift LRDs.
Recent {\em James Webb Space Telescope (JWST)} observations have revealed a population of compact extragalactic objects at \(z\gtrsim4\) with red near-infrared colors, which have been dubbed as ...``Little Red Dots" (LRDs). The spectroscopically-selected LRDs exhibit broad H\(\alpha\) emission lines, which has led to the conclusion that type-I active galactic nuclei (AGN) are harbored in the galaxies' dust-reddened cores. However, other mechanisms, like strong outflowing winds, could also produce broad H\(\alpha\) emission lines, and thus, the nature of LRDs is still under debate. In this work, we test the AGN hypothesis for LRDs by stacking the archival {\em Chandra} observations of 19 spectroscopically-selected LRDs. We obtain non-detections in both the soft \((0.5-2\text{ keV})\) and the hard \((2-8\text{ keV})\) X-ray band after stacking, and put upper limits on the X-ray luminosities of these LRDs. We find that the soft band upper limit is \(\sim1\) dex lower than the expected level from the \(L_\text{X}-L_{\text{H}\alpha}\) relation, while the hard band upper limit is consistent with this relation. This result suggests that LRDs and typical type-I AGNs have significantly different properties. We consider it unlikely that absorption is the main reason for the observed low \(L_\text{X}/L_{\text{H}\alpha}\) ratios of LRDs. Alternatively, we discuss two plausible hypotheses: (1) LRDs have intrinsically weak X-ray emissions, (2) fast, galactic-scale outflows have a major contribution to the observed broad H\(\alpha\) lines. Our findings indicate that empirical relations (e.g., for black hole mass measurements) established for typical type-I AGNs should be used with caution when analyzing the properties of LRDs.
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