arXiv subjects

Mauro Giavalisco

Publications and source records attributed to Mauro Giavalisco.

At least 37 records · Page 2Linked to original sources

arXiv2026

A Bending in the Size-mass Relation of Star-forming Galaxies across $0.5 < z < 6.0$ at a Critical Stellar Mass of $10^{10}M_\odot$ Revealed by JWST

We investigate the rest-frame optical size-stellar mass relation of galaxies at $0.5 M_{\rm p}$, an increasing fraction of SFGs decouple from halo growth and become compact, likely associated with rapid bulge (and black hole) growth in $M_{\rm h} \gtrsim 10^{12} M_{\odot}$ halos. These compact SFGs are promising progenitors of massive QGs, as evidenced by their similar masses, surface brightness profiles, and morphologies. Their high number densities can account for the observed buildup of massive QGs at $z > 2$, suggesting that the compaction pathway, rather than major mergers of extended SFGs, dominates the formation of high-z massive QGs.

astro-ph.GA↗

arXiv2026

Massive Galaxies Form Early and Gray: Stellar Assembly and Dust Attenuation at $\mathbf{z>3.5}$ from CAPERS

The stellar mass assembly of massive galaxies in the first few billion years of cosmic history remains a central challenge in galaxy formation. Galaxies with $M_\star \gtrsim 10^{10}M_\odot$ observed at $z \gtrsim 4$ must grow rapidly under conditions of intense gas accretion, feedback, and dust production. Observationally, their star-formation histories (SFHs) have been poorly constrained due to degeneracies inherent to broadband photometry. The advent of JWST enables direct spectroscopic access to detailed continuum shapes and rest-frame optical diagnostics at high redshift, providing a critical opportunity to reconstruct formation timescales of massive early galaxies. Here, we investigate massive galaxies using joint spectro-photometric SED fitting of JWST/NIRSpec prism spectroscopy from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS). Our sample comprises 148 galaxies selected photometrically with log $(M_\star/M_\odot) > 9.5$ at $z > 3.5$. We find that the most massive galaxies (log $(M_\star/M_\odot) > 10.5$) preferentially exhibit shallow, gray dust attenuation curves, consistent with higher dust optical depths and large grain sizes. We also find significant diversity in the time at which galaxies form 25% of their stellar mass. While formation timescales converge toward later cosmic times, galaxies with lower sSFR ($\lesssim -9$) at the observation epoch formed significantly earlier than systems with higher sSFRs. Across the full mass range, inferred assembly times are systematically earlier than model predictions, suggesting more rapid early growth than currently captured theoretically. These results underscore the importance of spectroscopic constraints and flexible SFH and dust models for reconstructing high-redshift massive galaxy formation histories.

astro-ph.GA↗

arXiv2026

Using Ly$α$ Transmitted Spectrum to Probe IGM Transmission and Identify Ionized Structures in Cosmic Reionization

We present a study of intergalactic medium (IGM) transmission at $4.5 < z < 6.5$ using high-signal-to-noise JWST/NIRSpec prism spectroscopy of 143 galaxies at $5<z<7$ from the CAPERS and JADES surveys. By comparing the observed flux blueward of Ly$α$ emission line to the prediction of spectral energy distribution modeling, we directly measure the IGM transmission along the individual galaxy sightlines. The average transmission measured from these galaxy sightlines is consistent with previous measurements based on luminous quasars. Current NIRSpec spectroscopy is sufficiently deep to probe IGM transmission on single sightlines. We find evidence for a highly ionized structure, \bubble, at $z\sim 5.75-6$ in the GOODS-S field based on the analysis of a high-S/N spectrum of one galaxy, GS-18846, at $z=6.335$. The IGM transmission of GS-z6IS is $0.17\pm0.02$, an order of magnitude higher than the average of previous measurements at this redshift. This structure has a line-of-sight scale of $\sim110$ cMpc and spatially extends over at least $21\times17$ cMpc$^2$. GS-z6IS is associated with a known large-scale galaxy overdensity at the same redshift, whose member galaxies show enhanced Ly$α$ visibility and a broader Ly$α$ equivalent width distribution compared to field galaxies at similar redshift. This result supports the interpretation that Ly$α$ overdensity can trace bubbles of increased IGM transmission, although environmental effects on galaxy properties may also contribute. Our study demonstrates that high-S/N galaxy spectra offer a powerful new approach to tracing ionized structures during the epoch of reionization.

astro-ph.GA↗

arXiv2026

Near-infrared emission line diagnostics for AGN from the local Universe to redshift 3

Optical rest-frame spectroscopic diagnostics are usually employed to distinguish between star formation and AGN-powered emission. However, this method is biased against dusty sources, hampering a complete census of the AGN population across cosmic epochs. To mitigate this effect, it is crucial to observe at longer wavelengths in the rest-frame near-infrared (near-IR), which is less affected by dust attenuation and can thus provide a better description of the intrinsic properties of galaxies. AGN diagnostics in this regime have not been fully exploited so far, due to the scarcity of near-IR observations of both AGNs and star-forming galaxies, especially at redshifts higher than 0.5. Using Cloudy photoionization models, we identify new AGN - star formation diagnostics based on the ratio of bright near-infrared emission lines, namely [SIII] 9530 Angstrom, [CI] 9850 Angstrom, [PII] 1.188 $μm$, [FeII] $1.257 μm$, and [FeII] $1.64 μm$ to Paschen lines (either Pa$γ$ or Pa$β$), providing simple, analytical classification criteria. We apply these diagnostics to a sample of 64 star-forming galaxies and AGNs at 0 < z < 1, and 65 sources at 1 < z < 3 recently observed with JWST-NIRSpec in CEERS. We find that the classification inferred from the near-infrared is broadly consistent with the optical one based on the BPT and the [SII]/H$α$ ratio. However, in the near-infrared, we find $\sim 60 \%$ more AGNs than in the optical (13 instead of 8), with 5 sources classified as 'hidden' AGNs, showing a larger AGN contribution at longer wavelengths, possibly due to the presence of optically thick dust. The diagnostics we present provide a promising tool to find and characterize AGNs from z=0 to z=3 with low and medium-resolution near-IR spectrographs in future surveys.

astro-ph.GA↗

arXiv2026

Reconstructing the Assembly of Massive Galaxies. III: Quiescent Galaxies Loose Angular Momentum as They Evolve in a Mass-dependent Fashion

We study the evolution of stellar kinematics of a sample of 952 massive quiescent galaxies with $M_*>10^{10.5}M_\odot$ at $0.6 10^{11.3}M_\odot$, the relationship between $σ^\prime_{star}$ and $q$ becomes significantly flattened with increasing stellar age. This indicates that, as the very massive galaxy populations continue to evolve after quenching, angular momentum gradually reduces, which eventually transforms them into velocity-dispersion supported systems. We suggest that incoherent, continuous merging and accretion events onto the galaxies are the main drivers of the observed mass-dependent, posting-quenching dynamical evolution, because more massive galaxies are more likely to undergo such interactions. We are witnessing the early formation epoch of fast and slow rotators at $z \sim 0.8$, when the Universe was only half of its age nowadays.

astro-ph.GA↗

arXiv2026

From "The Cliff" to "Virgil": Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec

One of JWST's most unexpected discoveries is the emergence of "Little Red Dots'' (LRDs): compact sources at $z \gtrsim 3$ with blue rest-frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest a population of early, unusual active galactic nuclei (AGNs). Using a comprehensive photometric selection and public NIRSpec/PRISM spectroscopy across six JWST deep fields, we identify a large sample of 118 LRDs with high-S/N spectra, enabling a population-wide analysis of their UV-optical continuum and emission lines. We find clear correlations between rest-frame color ([0.3-0.9\,$μ$m]) and slopes: bluer LRDs have blue UV slopes ($β_{ν,\mathrm{UV}} \sim 0.3$) and red optical slopes, while redder LRDs exhibit redder UV slopes ($β_{ν,\mathrm{UV}} \sim 1.1$). The continuum shape shows a similar trend: redder LRDs display prominent Balmer breaks and curvature, while bluer LRDs follow power-law-like optical SEDs. From literature compilations, $\sim$60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission-line diagnostics reveal a shift from high H$_α$/H$_β$ and low [OIII]$\lambda5007$/H$_β$ in redder LRDs to the opposite in bluer ones, along with stronger narrow-line equivalent widths, suggesting a transition from AGN- to host-dominated emission. We fit the spectra with a two-component model combining a gas-enshrouded black hole (BH) and a galaxy host. Redder LRDs require higher-luminosity, unreddened BHs and modestly reddened hosts; bluer LRDs require lower-luminosity, reddened BHs and dust-free galaxies. This framework reproduces the diversity in colors and spectral shape by varying BH luminosity, obscuration, and host-to-BH luminosity ratio.

astro-ph.GA↗

arXiv2025

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Cosmology and High-z Universe

Full sky coverage with 30-40 meter-class telescopes is essential to answer fundamental questions in Astrophysics, Cosmology, and Physics, such as the composition of the Universe and the formation of the first stars and supermassive black holes. An ELT/TMT-like telescope in the Northern Hemisphere is a fundamental and necessary facility to provide multiplexing of observing power, diversity of instrumentation, rapid response, and statistical power required to address the questions and the problems, current and future, unveiled by full sky observatories such as JWST, Euclid, or Roman space telescopes. The Northern ELT/TMT will expedite the study of unique, extreme, rare, transient, and/or high-energy events which will give the most information about fundamental Physics problems in the era of multi-messenger and time-domain Astronomy.

astro-ph.IM↗

arXiv2025

Testing Photometric Techniques for Measuring the Rest-Frame UV Spectral Slope Against JWST PRISM Spectroscopy

We present a sample of 53 galaxy spectra at z_spec ~ 5-12 from the JWST CEERS and RUBIES surveys, combining NIRSpec PRISM spectroscopy with NIRCam photometry. We aim to use these data to establish best practices for measuring the UV spectral slope ($β$) in the era of JWST. We adopt power-law fits to the rest-frame UV continuum from the spectroscopic data as our fiducial, or `true', $β$ values, and compare them to photometric estimates derived through four methods: (1) photometric power-law fitting, (2) power-law fitting to an SED model fitted to the photometry, (3) single-color fitting near the Lyman break, and (4) single-color fitting at fixed rest-frame wavelengths. We find that photometric power-law fitting most closely recovers the spectroscopic slopes, with minimal bias and scatter. SED fitting performs moderately well, and can be preferable in cases of low signal-to-noise where photometric power-law fitting may become unreliable. Single-color estimates, while commonly used in past studies, show the most significant deviations and are not recommended when more than a single color is available. Our results highlight the limitations and strengths of each approach and provide practical guidance for measuring $β$ from photometry when spectra are unavailable or are of insufficient quality.

astro-ph.GA↗

arXiv2025

Beyond the Monsters: A More Complete Census of Black Hole Activity at Cosmic Dawn

JWST has revealed an abundance of low-luminosity active galactic nuclei (AGN) at high redshifts ($z > 3$), pushing the limits of black hole (BH) science in the early Universe. Results have claimed that these BHs are significantly more massive than expected from the BH mass-host galaxy stellar mass relation derived from the local Universe. We present a comprehensive census of the BH populations in the early Universe through a detailed stacking analysis of galaxy populations, binned by luminosity and redshift, using JWST spectroscopy from the CEERS, JADES, RUBIES, and GLASS extragalactic deep field surveys. Broad H$α$ detections in $31\%$ of the stacked spectra (5/16 bins) imply median BH masses of $10^{5.21} - 10^{6.13}~ \rm{M_{\odot}}$ and the stacked SEDs of these bins indicate median stellar masses of $10^{7.84} - 10^{8.56} ~\rm{M_{\odot}}$. This suggests that the median galaxy hosts a BH that is at most a factor of 10 times over-massive compared to its host galaxy and lies closer to the locally derived $M_{BH}-M_*$ relation. We investigate the seeding properties of the inferred BHs and find that they can be well-explained by a light stellar remnant seed undergoing moderate Eddington accretion. Our results indicate that individual detections of AGN are more likely to sample the upper envelope of the $M_{BH}-M_*$ distribution, while stacking on ``normal" galaxies and searching for AGN signatures can overcome the selection bias of individual detections.

astro-ph.GA↗

arXiv2025

Investigating the Growth of Little Red Dot Descendants at z<4 with the JWST

One of JWST's most remarkable discoveries is a population of compact red galaxies known as Little Red Dots (LRDs). Their existence raises many questions about their nature, origin, and evolution. These galaxies show a steep decline in number density-nearly two orders of magnitude-from $z=6$ to $z=3$. In this study, we explore their potential evolution by identifying candidate descendants in CEERS, assuming a single evolutionary path: the development of a blue star-forming outskirt around the red compact core. Our color-magnitude selection identifies galaxies as red as LRDs at $z<4$, surrounded by young, blue stellar outskirts. Morphological parameters were derived from single Sérsic profile fits; physical properties were obtained from SED fitting using a stellar-only model. These "post-LRD" candidates show LRD-like features with $M_\ast \sim 10^{10} \ M_\odot $, central densities ($ Σ_\ast \sim 10^{11} \ M_\odot \ \text{kpc}^{-2}$ ), compact sizes, and red rest-frame colors, but with an added extended component. Their number density at $z = 3 \pm 0.5$ ( $ \sim 10^{-4.15} \, \text{Mpc}^{-3} $) matches that of LRDs at $5 < z < 7$ , supporting a possible evolutionary link. We observe a redshift-dependent increase in outskirts mass fraction and galaxy size-from $\sim 250$ pc at $ z = 5 $ to $\sim 600$ pc at $ z = 3 $-suggesting global stellar growth. Meanwhile, the core remains red and compact, but the V-shaped SED fades as the outskirts grow. These findings support an evolutionary scenario in which LRDs gradually acquire an extended stellar component over cosmic time by cold accretion. This may explain the apparent decline in their observed number density at lower redshift.

astro-ph.GA↗

arXiv2025

The $M_{\rm BH}-M_{*}$ Relationship at $3<z<7$: Big Black Holes in Little Red Dots

JWST has identified a large population of faint, broad-line active galactic nuclei (AGN) in the early universe that are powered by black holes (BHs) that often appear overmassive relative to their host galaxies. In this study, we examine the relationship between BH mass and galaxy stellar mass at $3 3σ$ above the relationship measured for local broad-line AGN. We derive an intrinsic scatter in this relationship of $0.9$ dex, which does not vary over the redshift range of our sample. We also find that the $M_{\rm BH}/M_{\star}$ ratio increases by $2.3$ dex from $z = 3.5$ and $z = 6.5$ with a confidence level of $ > 3σ$. We attribute this trend with the increasing fraction of LRDs in our sample at $z>4$ as their host masses are $\sim1$ dex lower than the non-LRD AGN in our sample. These results support a picture in which the BHs powering JWST's broad-line AGN are genuinely overmassive and become increasingly so with redshift. We discuss the implications of our findings on early BH growth relative to that of their host galaxies and the constraints it places on BH seeding models.

astro-ph.GA↗

arXiv2025

The rise of the galactic empire: luminosity functions at $z\sim17$ and $z\sim25$ estimated with the MIDIS$+$NGDEEP ultra-deep JWST/NIRCam dataset

We present a sample of six F200W and three F277W dropout sources identified as $16 16$ candidates present mass-weighted ages around 30 Myr, and attenuations $\mathrm{A(V)}<0.1$ mag. Their average stellar mass is $\mathrm{M}_\bigstar\sim10^{7}\,\mathrm{M}_\odot$, implying a stellar-to-baryon mass fraction around 10% if the emissivity increases with redshift, or significantly higher otherwise. Three candidates present very blue UV spectral slopes ($β\sim-3$) compatible with Pop III young ($\lesssim10$ Myr) stars and/or high escape fractions of ionizing photons; the rest have $β\sim-2.5$ similar to $z=10-12$ samples.

astro-ph.GA↗

arXiv2025

Power-law Emission-line Wings and Radiation-Driven Superwinds in Local Lyman Continuum Emitters

We investigate broad emission-line wings, reaching $\leq 800\rm~km~s^{-1}$, observed in 26 galaxies with Lyman continuum (LyC) observations, primarily from the Low-redshift Lyman Continuum Survey (LzLCS). Using Magellan/MIKE, VLT/X-shooter, and WHT/ISIS high-resolution spectroscopy, we show that this fast gas appears to probe the dominant feedback mechanisms linked to LyC escape. We find that in 14 galaxies, the wings are best fit with power laws of slope $α\sim -3.5 \text{ to } -1.6$, with four others best fit by Gaussians of width $σ_{\rm BW} \sim 300~\rm km~s^{-1}$; the remaining eight show ambiguous wing morphologies. Gaussian wings are found only at low $O_{32}$ = $[\rm O~III]\lambda5007/[O~II]\lambda3726,3729$ and high metallicity, while power-law wings span the full range of these parameters. The general evidence suggests a dual-mode paradigm for LyC escape: radiation-driven superwinds traced by power-law wings and supernova-driven feedback traced by Gaussian wings. For the former, the $<3$ Myr-old, pre-supernova stellar population correlates with more luminous, faster winds. The data also show that radiation-driven wind parameters like wind luminosity and power-law slope $α$ depend on the UV luminosity more than the optically thick covering fraction, consistent with ``picket-fence" radiative transfer. Observed $α$ values flatten with both escaping LyC luminosity and higher extinction, while still preserving the anticorrelation between these two quantities. Additionally, the differential between red and blue slopes implies that extinction and dense gas are centrally concentrated relative to the wind emission. Overall, our results show that power-law emission-line wings probe LyC-driven winds and LyC escape in metal-poor starbursts.

astro-ph.GA↗

arXiv2025

Very bright, very blue, and very red: JWST CAPERS analysis of highly luminous galaxies with extreme UV slopes at $\mathbf{z = 10}$

We present JWST/NIRSpec PRISM observations of three luminous ($M_{\rm UV}<-20$) galaxies at $z\sim10$ observed with the CAPERS Cycle 3 program. These galaxies exhibit extreme UV slopes compared to typical galaxies at $z=10$. Of the three sources, two of them are a close pair (0.22 - arcsec) of blue galaxies at $z=9.800\pm0.003$ and $z=9.808\pm0.002$ with UV slopes of $β=-2.87\pm0.15$ and $β=-2.46\pm0.10$ respectively, selected from PRIMER COSMOS NIRCam imaging. We perform spectrophotometric modeling of the galaxies which suggests extremely young stellar ages and a lack of dust attenuation. For the bluest galaxy, its UV slope also suggests significant Lyman continuum escape. In contrast, the third source (selected from CEERS NIRCam imaging) at $z=9.942\pm0.002$ exhibits a red UV slope with $β=-1.51\pm0.08$. We rule out the possibility of a strong nebular continuum due to the lack of a Balmer jump and find no evidence to support the presence of active galactic nucleus continuum due to a lack of strong UV emission lines and no broad component to H$γ$ or H$β$. Instead, it is most likely that the red UV slope is due to dust-reddening ($A_{\rm V}\simeq0.9$) implying a significant level of dust-obscured star-formation only $\simeq480\, \rm Myr$ after the Big Bang. Under standard assumptions for dust attenuation, EGS-25297 would be the most intrinsically UV-luminous galaxy ($M_{\mathrm{UV,corr}}\simeq -22.4^{+0.7}_{-1.1}$) yet spectroscopically confirmed at $z \sim 10$. This work highlights that luminous galaxies at $z\gtrsim10$ have a diversity of dust properties and that spectroscopy of these galaxies is essential to fully understand star-formation at $z\gtrsim10$.

astro-ph.GA↗

arXiv2025

The Lyman-alpha and Continuum Origins Survey. I. Survey description and Ly$α$ imaging

Understanding the mechanisms driving the escape of ionizing or Lyman continuum (LyC) emission from the interstellar medium of galaxies is necessary to constrain the evolution of reionization, and the sources responsible for it. While progress has been made into identifying the global galaxy properties linked to the escape fraction of ionizing radiation, $f_{esc}^{LyC}$, little is currently known about how spatially resolved galaxy properties impact this parameter. We present Hubble Space Telescope (HST) imaging data obtained as part of the Lyman $α$ and Continuum Origins Survey (LaCOS). LaCOS consists of HST imaging in 5 filters covering rest-frame optical and UV bands for a subsample of 42 galaxies in the Low redshift Lyman Continuum Survey, 22 being Lyman continuum emitters ($f_{esc}^{LyC}=0.01-0.49$). Here, we describe the sample, observations and data reduction, and investigate connections between global and sub-kpc Lyman $α$ (Ly$α$) emission, and $f_{esc}^{LyC}$. We confirm the correlation between $f_{esc}^{LyC}$ and EW$_{Lyα}$ , and the anticorrelation with $r_{50}$, when using values obtained via global photometry. We also find correlations previously found with spectroscopy with global photometric $L_{Lyα}$, $f_{esc}^{Lyα}$, $Σ_{SFR}$ , and $f_{esc}^{LyC}$, but with a smaller degree of correlation ($\overline{|Δτ|}\sim0.1$). We find correlations are strongest between $Lyα$ observables ($L_{\rm Lyα}$, EW$_{\rm Lyα}$) and $f_{\rm esc}^{\rm LyC}$ when measured in a small aperture around the brightest UV source in each galaxy. We interpret these results as evidence that LyC photons escaping on the line-of-sight are contributed by a small number of UV-bright compact regions in most galaxies in LaCOS.

astro-ph.GA↗

arXiv2025

The Importance of Dust Distribution in Ionizing-photon Escape: NIRCam and MIRI Imaging of a Lyman Continuum-emitting Galaxy at z ~ 3.8

We present deep JWST/NIRCam and MIRI imaging of Ion1, a previously confirmed Lyman Continuum (LyC)-emitting galaxy at $z_{spec}=3.794$. Together with existing HST imaging, these new observations from the JADES program enable a joint analysis of Ion1's LyC, rest-frame UV, stellar, and dust emission with unprecedented detail. We report the first detection of dust emission at rest-frame $\sim3 μ$m in a high-redshift LyC-emitting galaxy using MIRI/F1500W. Our analysis suggests a porous distribution of dust in Ion1, with regions exhibiting evidence of dust deficit coinciding both with LyC-emitting regions and with the peak of H$α$ emission. Furthermore, multi-band NIRCam imaging reveals a strong FUV-to-optical color gradient, where LyC-emitting regions appear significantly bluer than the rest of Ion1. Spatially resolved SED fitting confirms that this color gradient is primarily driven by spatially varying dust attenuation. Together, these findings suggest that Ion1's LyC emission originates from a compact star-forming complex near its stellar-light centroid, where stellar feedback carves out low HI column density channels, facilitating LyC escape. However, only a fraction of these LyC photons - specifically those along sightlines with minimal HI obscuration - ultimately escape and reach observers. This work underscores the critical role of dust and neutral gas geometry in shaping LyC escape in galaxies at high redshifts. Anisotropic LyC escape may be a common feature in the early Universe, which must be properly incorporated to constrain the Epoch of Reionization.

astro-ph.GA↗

arXiv2025

CAPERS-LRD-z9: A Gas Enshrouded Little Red Dot Hosting a Broad-line AGN at z=9.288

We present CAPERS-LRD-z9, a little red dot (LRD) which we confirm to be a $z=9.288$ broad-line AGN (BLAGN). First identified as a high-redshift LRD candidate from PRIMER NIRCam photometry, follow-up NIRSpec/PRISM spectroscopy of CAPERS-LRD-z9 from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS) has revealed a broad $3500$ km s$^{-1}$ H$β$ emission line and narrow [O III]$λ\lambda4959,5007$ lines, indicative of a BLAGN. Based on the broad H$β$ line, we compute a canonical black-hole mass of $\log(M_{\textrm{BH}}/M_{\odot})=7.58\pm0.15$, although full consideration of systematic uncertainties yields a conservative range of $6.65<\log(M_{\textrm{BH}}/M_{\odot})<8.50$. These observations suggest that either a massive black hole seed, or a lighter stellar remnant seed undergoing periods of super-Eddington accretion, is necessary to grow such a massive black hole in $\lesssim500$ Myr of cosmic time. CAPERS-LRD-z9 exhibits a strong Balmer break, consistent with a central AGN surrounded by dense ($\sim 10^{10}\textrm{ cm}^{-3}$) neutral gas. We model CAPERS-LRD-z9 using CLOUDY to fit the emission red-ward of the Balmer break with a dense gas-enshrouded AGN, and bagpipes to fit the rest-ultraviolet emission as a host-galaxy stellar population. This upper limit on the stellar mass of the host galaxy ($<10^9\,{\rm M_\odot}$) implies that the black-hole to stellar mass ratio may be extremely large, possibly $>5\%$ (although systematic uncertainties on the black-hole mass prevent strong conclusions). However, the shape of the UV continuum differs from typical high-redshift star-forming galaxies, indicating that this UV emission may also be of AGN origin, and hence the true stellar mass of the host may be still lower.

astro-ph.GA↗

arXiv2025

Broad-Line AGN at 3.5<z<6: The Black Hole Mass Function and a Connection with Little Red Dots

We present a sample of 50 H-alpha detected broad-line active galactic nuclei (BLAGN) at redshifts 3.5 0), independent of the contributions of emission lines to the broadband photometry. We construct the black hole (BH) mass function at 3.5<z<6 after computing robust observational and line detection completeness corrections. This BH mass function shows broad agreement with both recent JWST/NIRSpec and JWST/NIRCam WFSS based BH mass functions, though we extend these earlier results to log(M(BH)/M(sun)) < 7. The derived BH mass function is consistent with a variety of theoretical models, indicating that the observed abundance of black holes in the early universe is not discrepant with physically-motivated predictions. The BH mass function shape resembles a largely featureless power-law, suggesting that any signature from black-hole seeding has been lost by redshift z~5-6. Finally, we compute the BLAGN UV luminosity function and find good agreement with JWST-detected BLAGN samples from recent works, finding that BLAGN hosts constitute <10% of the total observed UV luminosity at all but the brightest luminosities.

astro-ph.GA↗