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Steven L. Finkelstein

Publications and source records attributed to Steven L. Finkelstein.

At least 109 records · Page 6Linked to original sources
arXiv2025

The Cosmic Evolution Early Release Science Survey (CEERS)

We present the Cosmic Evolution Early Release Science (CEERS) Survey, a 77.2 hour Director's Discretionary Early Release Science Program. CEERS demonstrates, tests, and validates efficient extragalactic surveys using coordinated, overlapping parallel observations with the JWST instrument suite, including NIRCam and MIRI imaging, NIRSpec low (R~100) and medium (R~1000) resolution spectroscopy, and NIRCam slitless grism (R~1500) spectroscopy. CEERS targets the Hubble Space Telescope-observed region of the Extended Groth Strip (EGS) field, supported by a rich set of multiwavelength data. CEERS facilitated immediate community science in both of the extragalactic core JWST science drivers ``First Light" and ``Galaxy Assembly," including: 1) The discovery and characterization of large samples of galaxies at z >~ 10 from ~90 arcmin^2 of NIRCam imaging, constraining their abundance and physical nature; 2) Deep spectra of >1000 galaxies, including dozens of galaxies at 6 3; and 4) Characterizing galaxy mid-IR emission with MIRI to study dust-obscured star-formation and supermassive black hole growth at z~1-3. As a legacy product for the community, the CEERS team has provided several data releases, accompanied by detailed notes on the data reduction procedures and notebooks to aid in reproducibility. In addition to an overview of the survey and quality of the data, we provide science highlights from the first two years with CEERS data.

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arXiv2024

The Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) Active Galactic Nuclei Catalog: the Fourth Data Release

We present the Active Galactic Nuclei (AGN) catalog from the fourth data release (HDR4) of the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX). HETDEX is an untargeted spectroscopic survey. HDR4 contains 345,874 Integral Field Unit (IFU) observations from January 2017 to August 2023 covering an effective area of 62.9 deg2. With no imaging pre-selection, our spectroscopic confirmed AGN sample includes low-luminosity AGN, narrow-line AGN, and/or red AGN down to g~25. This catalog has 15,940 AGN across the redshifts of z=0.1~4.6, giving a raw AGN number density of 253.4 deg-2. Among them, 10,499 (66%) have redshifts either confirmed by line pairs or matched to the Sloan Digital Sky Survey Quasar Catalog. For the remaining 5,441 AGN, 2,083 are single broad line AGN candidates, while the remaining 3,358 are single intermediate broad line (full width at half maximum, FWHM ~ 1200 km s-1) AGN candidates. A total of 4,060 (39%) of the 10,499 redshift-confirmed AGN have emission-line regions $3σ$ more extended than the image quality which could be strong outflows blowing into the outskirts of the host galaxies or ionized intergalactic medium.

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arXiv2024

Physical Pathways for JWST-Observed Supermassive Black Holes in the Early Universe

Observations with the James Webb Space Telescope (JWST) have revealed active galactic nuclei (AGN) powered by supermassive black holes (SMBHs) with estimated masses of $10^7-10^8$ M$_\odot$ at redshifts $z\sim7-9$. Some reside in overmassive systems with higher AGN to stellar mass ratios than locally. Understanding how massive black holes could form so early in cosmic history and affect their environment to establish the observed relations today are some of the major open questions in astrophysics and cosmology. One model to create these massive objects is through direct collapse black holes (DCBHs) that provide massive seeds ($\sim10^5-10^6$ M$_\odot$), able to reach high masses in the limited time available. We use the cosmological simulation code GIZMO to study the formation and growth of DCBH seeds in the early Universe. To grow the DCBHs, we implement a gas swallowing model set to match the Eddington accretion rate as long as the nearby gaseous environment, affected by stellar and accretion disk feedback, provides sufficient fuel. We find that to create massive AGN in overmassive systems at high redshifts, massive seeds accreting more efficiently than the fiducial Bondi-Hoyle model are needed. We assess whether the conditions for such enhanced accretion rates are realistic by considering limits on plausible transport mechanisms. We also examine various DCBH growth histories and find that mass growth is more sustained in overdense cosmological environments, where high gas densities are achieved locally. We discuss the exciting prospect to directly probe the assembly history of the first SMBHs with upcoming, ultra-deep JWST surveys.

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arXiv2024

A Comprehensive Photometric Selection of `Little Red Dots' in MIRI Fields: An IR-Bright LRD at $z=3.1386$ with Warm Dust Emission

JWST has revealed a population of compact `Little Red Dots' (LRDs) at $z\gtrsim4$, with red rest-frame optical and blue UV colors. These objects are likely compact dusty starbursts or heavily reddened AGNs, playing a pivotal role in early black hole growth, dust production, and stellar assembly. We introduce a new photometric selection to identify LRDs over a broad range in redshifts and rest-frame UV-to-NIR colors enabling a more complete census of the population. This method identifies 248 LRDs with F444W$<27$ mag over 263 arcmin$^2$ in the JADES, PRIMER-COSMOS, and UDS fields with MIRI coverage, increasing the number density by $\times$1.7 compared to previous samples, suggesting that previous census were underestimated. Most LRDs are detected in MIRI/F770W but only 7% (17) are detected in F1800W. We use MIRI-based rest-frame [1$-$3 $μ$m] colors to trace dust emission. F1800W-detected LRDs have a median [1$-$3 $μ$m]$=1.5$ mag, with a broad scatter indicative of diverse dust emission properties. About 20% exhibit [1$-$3 $μ$m]$<1$ mag colors consistent with negligible dust emission, but the majority show significant dust emission at 3 $μ$m (f$^{\rm dust}_{3μm}\lesssim0.8$) from the galaxy ISM or a hot-dust-deficient AGN torus. A correlation between bluer UV-to-NIR colors and stronger IR emission suggests that the bluest LRDs may resemble unobscured QSOs. We report a LRD at $z_{\rm spec}=3.1386$, detected in MIRI, Spitzer/MIPS, and Herschel/PACS. Its IR SED rises steeply at $λ_{\rm rest}>6~μ$m and peaks near $\sim40~μ$m, providing the first direct evidence of warm dust emission (T$=50-100$ K) in a LRD.

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arXiv2024

Exploring the Nature of Little Red Dots: Constraints on AGN and Stellar Contributions from PRIMER MIRI Imaging

JWST has revealed a large population of compact, red galaxies at $z>4$ known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 95 LRDs from the JWST PRIMER survey with complete photometric coverage from $1-18\ μ$m using NIRCam and MIRI imaging, representing the most extensive SED analysis on a large LRD sample with long-wavelength MIRI data. We examine SED models in which either galaxy or active galactic nucleus (AGN) emission dominates the rest-frame UV or optical continuum, extracting physical properties to explore each scenario's implications. In the galaxy-only model, we find massive, dusty stellar populations alongside unobscured, low-mass components, hinting at inhomogeneous obscuration. The AGN-only model indicates dusty, luminous AGNs with low hot dust fractions compared to typical quasars. A hybrid AGN and galaxy model suggests low-mass, unobscured galaxies in the UV, with stellar mass estimates spanning $\sim$2 dex across the different models, underscoring the need for caution in interpreting LRD stellar masses. With MIRI photometry, the galaxy-only model produces stellar masses within cosmological limits, but extremely high stellar mass densities are inferred. The hybrid model infers highly overmassive black holes exceeding those in recently reported high-redshift AGNs, hinting at a partial AGN contribution to the rest-optical continuum or widespread super-Eddington accretion. Our findings highlight the extreme conditions required for both AGN or galaxy dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.

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arXiv2024

Unveiling the Dark Side of UV/Optical Bright Galaxies: Optically Thick Dust Absorption

Over the past decades, a population of galaxies invisible in optical/near-infrared, but bright at longer wavelengths, have been identified through color selections. These so-called optically faint/dark galaxies are considered to be massive quiescent galaxies or highly dust-attenuated galaxies. Having the entire galaxy obscured by dust, however, is likely an extreme case of the much more common occurrence of optically thin and thick absorption coexisting in the same system. With the power of JWST imaging, we are able to spatially resolve massive galaxies at z~3, accurately model their spectral energy distributions, and identify candidate optically thick substructures. We target galaxies with log(M*/Msun)>10.3 and 2.5<z<3.5, and get 486 galaxies in CEERS and PRIMER fields. Based on excess NIR luminosity, we identify 162 galaxies (~33\% of the parent sample) as candidate hosts of optically thick substructures. We then carry out spatially resolved SED modeling to explore the physical properties of those dark substructures and estimate the amount of optically thick obscuration. We find that optically thick dust is ubiquitous in normal massive galaxies with a wide variety of SFR and morphology. 10-20\% of the stellar mass/SFR are unaccounted for in our selected galaxies, and the fraction is insensitive to stellar mass or SFR. The dark substructures are generally dustier than the rest of the galaxies and are irregularly distributed, arguing against an obscured AGN as the source of the NIR excess. A correlation between the obscured luminosity and the presence of a recent starburst in the past <100 Myr is also observed.

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arXiv2024

A luminous and young galaxy at z=12.33 revealed by a JWST/MIRI detection of Hα and [OIII]

The James Webb Space Telescope (JWST) has discovered a surprising population of bright galaxies in the very early universe (<500 Myrs after the Big Bang) that is hard to explain with conventional galaxy formation models and whose physical properties remain to be fully understood. Insight into their internal physics is best captured through nebular lines but, at these early epochs, the brightest of these spectral features are redshifted into the mid-infrared and remain elusive. Using the JWST Mid-Infrared Instrument, MIRI, here we present the first detection of Hα and doubly-ionized oxygen ([OIII]5007AA) at z>10. These detections place the bright galaxy GHZ2/GLASS-z12 at z=12.33+/-0.04, making it the most distant astronomical object with direct spectroscopic detection of these lines. These observations provide key insights into the conditions of this primeval, luminous galaxy, which shows hard ionizing conditions rarely seen in the local Universe likely driven by compact and young (~30Myr) burst of star formation. Its oxygen-to-hydrogen abundance is close to a tenth of the solar value, indicating a rapid metal enrichment. This study confirms the unique conditions of this remarkably bright and distant galaxy and the huge potential of mid-IR observations to characterize these objects.

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arXiv2024

Strong spectral features from asymptotic giant branch stars in distant quiescent galaxies

Dating the ages and weighting the stellar populations in galaxies are essential steps when studying galaxy formation through cosmic times. Evolutionary population synthesis models with different input physics are used for this purpose. Moreover, the contribution from the thermally pulsing asymptotic giant branch (TP-AGB) stellar phase, which peaks for intermediate-age 0.6-2 Gyr, has been debated for decades. Here we report the detection of strong cool-star signatures in the rest-frame near-infrared spectra of three young (~1Gyr), massive (~10^10Msun) quiescent galaxies at large look-back time, z=1-2, using JWST/NIRSpec. The coexistence of oxygen- and carbon-type absorption features, spectral edges and features from rare species, such as vanadium and possibly zirconium, reveal a strong contribution from TP-AGB stars. Population synthesis models with a significant TP-AGB contribution reproduce the observations better than those with a weak TP-AGB, which are commonly used. These findings call for revisions of published stellar population fitting results, as they point to populations with lower masses and younger ages and have further implications for cosmic dust production and chemical enrichment. New generations of improved models are needed, informed by these and future observations.

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arXiv2024

Here There Be (Dusty) Monsters: High Redshift AGN are Dustier Than Their Hosts

JWST spectroscopy has discovered a population of $z \gtrsim 3.5$ galaxies with broad Balmer emission lines, and narrow forbidden lines, that are consistent with hosting active galactic nuclei (AGN). Many of these systems, now known as ``little red dots" (LRDs), are compact and have unique colors that are very red in the optical/near-infrared and blue in the ultraviolet. The relative contribution of galaxy starlight and AGN to these systems remains uncertain, especially for the galaxies with unusual blue+red spectral energy distributions. In this work, we use Balmer decrements to measure the independent dust attenuation of the broad and narrow emission-line components of a sample of 29 broad-line AGN identified from three public JWST spectroscopy surveys: CEERS, JADES, and RUBIES. Stacking the narrow components from the spectra of 25 sources with broad H$\rmα$ and no broad H$\rmβ$ results in a median narrow H$\rmα$/H$\rmβ$ = $2.47^{+0.05}_{-0.05}$ (consistent with $A_{v} = 0$) and broad H$\rmα$/H$\rmβ$ $> 8.85$ ($A_{v} > 3.63$). The narrow and broad Balmer decrements imply little-to-no attenuation of the narrow emission lines, which are consistent with being powered by star formation and located on larger physical scales. Meanwhile, the lower limit in broad H$\rmα$/H$\rmβ$ decrement, with broad H$\rmβ$ undetected in the stacked spectrum of 25 broad-H$\rmα$ AGN, implies significant dust attenuation of the broad-line emitting region that is presumably associated with the central AGN. Our results indicate that these systems, on average, are consistent with heavily dust-attenuated AGN powering the red parts of their SED while their blue UV emission is powered by unattenuated star formation in the host galaxy.

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arXiv2024

Strong rest-UV emission lines in a "little red dot" AGN at $z=7$: Early SMBH growth alongside compact massive star formation?

JWST has now revealed a population of broad-line AGN at $z>4$ characterized by a distinctive SED shape, with very red rest-frame optical and very blue rest-frame UV continuum. While the optical continuum is thought to originate from the accretion disk, the origin of the UV continuum has been largely unclear. We report the detection of the strong rest-frame UV emission lines of CIII]$λλ$1907,1909 and CIV$λλ$1549,1551 in a "little red dot" AGN, COS-66964. Spectroscopically confirmed at $z=7.0371$, COS-66964 exhibits broad H$α$ emission (FWHM $\sim 2000$ km s$^{-1}$), and weak broad H$β$, implying significant dust attenuation to the BLR ($A_V = 3.9^{+1.7}_{-0.9}$). The H$α$ line width implies a central SMBH mass of $M_{\rm BH} = \left(1.9^{+1.6}_{-0.7}\right)\times10^{7}$ M$_\odot$, and an Eddington ratio $λ\sim0.3$-$0.5$. While marginal HeII$\lambda4687$ and [FeX]$\lambda6376$ detections further indicate that the AGN dominates in the rest-frame optical, the non-detection of HeII$\lambda1640$ in the UV despite high EW CIII] and CIV ($\sim 35$ Å) is more consistent with photoionization by massive stars. The non-detection of MgII$λλ$2800 is similarly inconsistent with an AGN scattered light interpretation. Assuming the rest-frame UV is dominated by stellar light, we derive a stellar mass of $\log M_\star/M_\odot\sim8.5$, implying an elevated $M_{\rm BH}/M_\star$ ratio $\sim2$ orders of magnitude above the local relation, but consistent with other high-$z$ AGN discovered by JWST. The source is unresolved in all bands, implying a very compact size $\lesssim200$ pc in the UV. This suggests that the simultaneous buildup of compact stellar populations (i.e., galaxy bulges) and the central SMBH is ongoing even at $z>7$.

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arXiv2024

A Search for $z=5$ H$α$ and H$β+$[O III] Dual-Line Emitting Galaxies in the JWST CEERS Field: Implications for the AGN Abundance

The James Webb Space Telescope (JWST) has enabled us to uncover faint galaxies and active galactic nuclei (AGNs) in the early universe. Taking advantage of the unique filter combination used in the Cosmic Evolution Early Release Science Survey (CEERS) program, we perform an extensive photometric search of galaxies emitting strong H$β+$[O III] and H$α$ lines. The redshift range of the galaxies is limited to $5.03\leq z\leq 5.26$ by requiring photometric excesses in NIRCam's F277W and F410M images. A total of 261 H$β+$[O III] and H$α$ dual-line emitters are found over the absolute UV magnitude $-22\lesssim M_{\mathrm{UV}}\lesssim -17$, with a mean rest-frame equivalent width of 1010 A for H$β+$[O III] and 1040 A for H$α$. This population accounts for $\sim 40\%$ of the Lyman break galaxies at this redshift range. Intriguingly, there are 58 objects (22% of the whole sample) that exhibit compact morphology at the rest-UV or optical wavelength. With an assumption that these compact dual-line emitters are dominated by AGN, their AGN bolometric luminosities are in the range of $2\times 10^{43} \lesssim L_{\rm bol}/({\rm erg~s}^{-1})\lesssim 3\times 10^{44}$. Their number density is two orders of magnitude higher than the extrapolation from the UV-selected luminous quasars, which is in good agreement with previous JWST studies of broad-line AGNs, requiring a $\sim 10\%$ of the AGN duty cycle. Moreover, our dual-line emitter sample reaches the faint end of the H$α$ and [O III] luminosity functions down to $\lesssim 10^{42}~{\rm erg~s}^{-1}$. Spectroscopic follow-up observations are planned in an approved JWST Cycle 3 program, in which we aim to confirm their nature, characterize their black hole activity, and construct their mass distribution at $10^6\lesssim M_{\rm BH}/M_\odot \lesssim 10^8$.

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arXiv2024

A hide-and-seek game: Looking for Population III stars during the Epoch of Reionization through the HeII$λ$1640 line

The gas surrounding first-generation (Pop III) stars is expected to emit a distinct signature in the form of the HeII recombination line at 1640 Å (HeII$λ$1640). Here we explore the challenges and opportunities in identifying this elusive stellar population via the HeII$λ$1640 in $M_\star > 10^{7.5} ~ \mathrm{M_\odot}$ galaxies during the Epoch of Reionization (EoR, $z \simeq 6 - 10$), using JWST/NIRSpec. With this aim in mind, we combine cosmological dustyGadget simulations with analytical modeling of the intrinsic HeII emission. While tentative candidates with bright HeII emission like GN-z11 have been proposed in the literature, the prevalence of such bright systems remains unclear due to significant uncertainties involved in the prediction of the HeII luminosity. In fact, similar Pop III clumps might be almost two orders of magnitude fainter, primarily depending on the assumed Pop III-formation efficiency and initial mass function in star-forming clouds, while the effect of stellar mass loss is responsible for a factor of order unity. Moreover, up to $\sim 90 \%$ of these clumps might be missed with NIRSpec/MOS due to the limited FoV, while this problem appears to be less severe with NIRSpec/IFU. We investigate the potential of deep spectroscopy targeting peripheral Pop III clumps around bright, massive galaxies to achieve a clear detection of the first stars.

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arXiv2024

The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey: 5$σ$ Source Catalog and Redshift Distribution

One of the greatest challenges in galaxy evolution over the last decade has been constraining the prevalence of heavily dust-obscured galaxies in the early Universe. At $z>3$, these galaxies are increasingly rare, and difficult to identify as they are interspersed among the more numerous dust-obscured galaxy population at $z=1-3$, making efforts to secure confident spectroscopic redshifts expensive, and sometimes unsuccessful. In this work, we present the Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey -- a 2mm blank-field survey in the COSMOS-Web field, and the largest ever ALMA blank-field survey to-date covering 577 arcmin$^2$. Ex-MORA is an expansion of the MORA survey designed to identify primarily $z>3$ dusty, star-forming galaxies while simultaneously filtering out the more numerous $z<3$ population by leveraging the very negative $K$-correction at observed-frame 2mm. We identify 37 significant ($>$5$σ$) sources, 33 of which are robust thermal dust emitters. We measure a median redshift of $\langle z \rangle = 3.6^{+0.1}_{-0.2}$, with two-thirds of the sample at $z>3$, and just under half at $z>4$, demonstrating the overall success of the 2mm-selection technique. The integrated $z>3$ volume density of Ex-MORA sources is $\sim1-3\times10^{-5}$ Mpc$^{-3}$, consistent with other surveys of infrared luminous galaxies at similar epochs. We also find that techniques using rest-frame optical emission (or lack thereof) to identify $z>3$ heavily dust-obscured galaxies miss at least half of Ex-MORA galaxies. This supports the idea that the dusty galaxy population is heterogeneous, and that synergies across observatories spanning multiple energy regimes are critical to understanding their formation and evolution at $z>3$.

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arXiv2024

Evidence of extreme ionization conditions and low metallicity in GHZ2/GLASS-z12 from a combined analysis of NIRSpec and MIRI observations

GHZ2/GLASS-z12 has been recently observed by JWST with both NIRSpec and MIRI spectrographs, making it the most distant galaxy ($z_{spec}=12.34$) with complete spectroscopic coverage from rest-frame UV to optical. It is identified as a strong CIV$_{1549}$ emitter with many detected emission lines (NIV], HeII, OIII], NIII], CIII], [OII], [NeIII], [OIII], and H$α$), including a remarkable OIII$_{1333}$ Bowen fluorescence line. We analyze in this paper the joint NIRSpec+MIRI spectral data set. Combining six optical diagnostics (R2, R3, R23, O32, Ne3O2, and Ne3O2Hd), we find extreme ionization conditions, with O32 $=1.39 \pm 0.19$ and Ne3O2 $=0.37 \pm 0.18$ in stark excess compared to typical values in the ISM at lower redshifts. These line properties are compatible either with an AGN or with a compact, dense star-forming environment ($Σ_{\rm SFR}$ $\sim 10^2$-$10^3$ Msun/yr/kpc$^2$), with a high ionization parameter ($\log_{10}$(U) $=-1.75 \pm 0.16$), a high ionizing photon production efficiency $\log(ξ_{\rm ion}) = 25.7_{-0.1}^{+0.2}$, and a low, although not pristine, metal content between $5\%$ and $11\%$ Z$_\odot$ (confirmed by the T$_e$ method), indicating a rapid metal enrichment in the last few Myrs. These properties also suggest that a substantial amount of ionizing photons ($\sim 10\%$) are leaking outside. The general lessons learned from GHZ2 are the following: (i) the UV to optical combined nebular indicators are broadly in agreement with UV-only or optical-only indicators. (ii) UV+optical diagnostics fail to discriminate between an AGN and star-formation in a low metallicity, high density, and extreme ionization environment. (iii) comparing the nebular line ratios with local analogs may be approaching its limits at $z \gtrsim 10$, as this approach is potentially challenged by the unique conditions of star formation experienced by galaxies at these extreme redshifts.

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arXiv2024

The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission

JWST has enabled the detection of the UV continuum of galaxies at z>10, evidencing a population of extremely blue, potentially dust-free galaxies. Interpreting the UV spectra of galaxies as they redden is complicated by the well-known degeneracy between stellar ages, dust, and nebular continuum. The main goal of this paper is to develop a theoretical model for the relationship between galaxy UV slopes, bursty star formation histories, dust evolution, and the contribution from nebular regions. We accomplish this via cosmological zoom-in simulations, and in specific, build a layered model where we simulate the UV slopes of galaxies with increasingly complex physics. Our main results follow. (i) Unattenuated stellar populations with no nebular emission exhibit a diverse range of intrinsic UV slopes, with values ranging from beta ~ -3 --> -2.2 due to long delays between bursts. This is manifested by an inverse correlation between the intrinsic UV slope and sSFR for early galaxies such that higher sSFR corresponds to bluer UV slopes. (ii) When including dust, our model galaxies demonstrate a rapid rise in dust obscuration between z ~ 8-10. This increase in dust mass is due to high grain-grain shattering rates, and enhanced growth per unit dust mass in very small grains, resulting in UV-detected galaxies at z ~ 12 descending into ALMA-detectable galaxies by z ~ 6. The rapid rise in dust content at z ~ 8-10 leads to a systematic reddening of the UV slopes during this redshift range. (iii) The inclusion of nebular continuum reddens the UV slope by a median factor Delta beta ~ 0.2-0.4. However, when including nebular continuum, our highest redshift galaxies (z~12) are insufficiently blue compared to observations; this may imply an evolving escape fraction from HII regions with redshift.

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arXiv2024

Silencing the Giant: Evidence of AGN Feedback and Quenching in a Little Red Dot at z = 4.13

The James Webb Space Telescope (JWST) has uncovered a ubiquitous population of dust-obscured compact sources at $z\gtrsim 4$. Many of these objects exhibit signs of active galactic nucleus (AGN) activity, making their study crucial for understanding the formation of supermassive black holes (SMBHs) and their growth with host galaxies. In this work, we examine low and medium resolution JWST/NIRSpec spectra from the JADES GTO public data release in the GOODS-N field of a red, luminous ($M_{\rm B}\sim-22.2$ mag) and compact ($<500$ pc) source at $z=4.13$. The rest-optical ($λ_{\rm rest} > 4000$ A) continuum of this source is strongly dominated by a massive (log$_{10}$[$M_*/M_\odot] \sim 10.6$), quenched (log$_{10}$[sSFR/yr$^{-1}$] $< -11$) galaxy, as indicated by the clear presence of a Balmer break and stellar absorption lines. Star-formation history modeling reveals a starburst episode followed by rapid quenching about 200 Myr ago. The spectrum shows extremely broad (FWHM $\sim 2500$ km/s) H$α$ emission and elevated optical line ratios, indicating an actively accreting SMBH. Moreover, our work has potentially revealed clear AGN signatures in the rest-UV in LRDs for the first time, via a detection of a strong Ly$α$ emission and a broad MgII, doublet. The derived black hole mass of log$_{10}$($M_{\rm BH}/M_\odot) \sim 7.3$ results in $M_{\rm BH}/M_*\sim 0.04$ %, consistent with the local relations, unlike the elevated ratios in other high-$z$ reddened AGN. Finally, we use JWST data from AGN at $z=4-10$ to explore an evolutionary link between high-$z$ reddened AGN, early quiescent galaxies, and local ellipticals.

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arXiv2024

CEERS Key Paper. IX. Identifying Galaxy Mergers in CEERS NIRCam Images Using Random Forests and Convolutional Neural Networks

A crucial yet challenging task in galaxy evolution studies is the identification of distant merging galaxies, a task which suffers from a variety of issues ranging from telescope sensitivities and limitations to the inherently chaotic morphologies of young galaxies. In this paper, we use random forests and convolutional neural networks to identify high-redshift JWST CEERS galaxy mergers. We train these algorithms on simulated $3<z<5$ CEERS galaxies created from the IllustrisTNG subhalo morphologies and the Santa Cruz SAM lightcone. We apply our models to observed CEERS galaxies at $3<z<5$. We find that our models correctly classify $\sim60-70\%$ of simulated merging and non-merging galaxies; better performance on the merger class comes at the expense of misclassifying more non-mergers. We could achieve more accurate classifications, as well as test for the dependency on physical parameters such as gas fraction, mass ratio, and relative orbits, by curating larger training sets. When applied to real CEERS galaxies using visual classifications as ground truth, the random forests correctly classified $40-60\%$ of mergers and non-mergers at $3<z<4$, but tended to classify most objects as non-mergers at $4<z<5$ (misclassifying $\sim70\%$ of visually-classified mergers). On the other hand, the CNNs tended to classify most objects as mergers across all redshifts (misclassifying $80-90\%$ of visually-classified non-mergers). We investigate what features the models find most useful, as well as characteristics of false positives and false negatives, and also calculate merger rates derived from the identifications made by the models.

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