arXiv subjects

Hyunsung D. Jun

Publications and source records attributed to Hyunsung D. Jun.

At least 37 records · Page 2Linked to original sources

arXiv2025

Searching for Low-Redshift Hot Dust-Obscured Galaxies

Hot Dust-Obscured Galaxies (Hot DOGs), discovered by the "W1W2 dropout" selection at high redshifts ($z\sim$ 2-4), are a rare population of hyper-luminous obscured quasars. Their number density is comparable to similarly luminous type 1 quasars in the same redshift range, potentially representing a short, yet critical stage in galaxy evolution. The evolution in their number density towards low redshift, however, remains unclear as their selection function is heavily biased against objects at $z\lesssim2$. We combine data from the WISE and Herschel archives to search for Hot DOGs at $z<0.5$ based on their unique spectral energy distributions. We find 68 candidates, and spectroscopic observations confirm that 3 of them are at $z<0.5$. For those 3 we find their black hole accretion is close to the Eddington limit, with lower bolometric luminosities and black hole masses than those of higher-$z$ Hot DOGs. Compared to high-$z$ systems, these low-$z$ systems are closer to the local relation between host galaxy stellar mass and black hole mass but still lie above it, and we discuss several possible scenarios for it. Finally, we also find the surface number density of $z<$0.5 Hot DOGs is $\rm 2.4 \times 10^{-3}$ deg$^{-2}$, about an order of magnitude lower than high-$z$ Hot DOGs but comparable to hyper-luminous unobscured quasars in the same redshift range. These results further support the idea that Hot DOGs may be a transitional phase of galaxy evolution.

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arXiv2025

A Quasar-Anchored Protocluster at z=6.6 in the ASPIRE Survey: I. Properties of [OIII] Emitters in a 10 Mpc Overdensity Structure

ASPIRE (A SPectroscopic survey of bIased halos in the Reionization Era) is a quasar legacy survey primarily using \textit{JWST} to target a sample of 25 $z>6$ quasars with NIRCam slitless spectroscopy and imaging. The first study in this series found evidence of a strong overdensity of galaxies around J0305$-$3150, a luminous quasar at $z=6.61$, within a single NIRCam pointing obtained in JWST Cycle 1. Here, we present the first results of a JWST Cycle 2 mosaic that covers 35 arcmin$^2$ with NIRCam imaging/WFSS of the same field to investigate the spatial extent of the putative protocluster. The F356W grism data targets [OIII]+H$β$ at $5.3 10$ cMpc.

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arXiv2025

A Quasar-Anchored Protocluster at z=6.6 in the ASPIRE Survey: II. An Environmental Analysis of Galaxy Properties in an Overdense Structure

We present paper II comprising a 35 arcmin$^2$ \textit{JWST}/NIRCam imaging and wide-field slitless spectroscopy mosaic centered on J0305$-$3150, a luminous quasar at $z=6.61$. The F356W grism data reveals 124 [OIII]+H$β$ emitters at $5.3<z<7$, 53 of which constitute a protocluster spanning (10 cMpc)$^2$ across $6.5<z<6.8$. We find no evidence of any broad-line AGN in individual galaxies or stacking, reporting a median H$β$ FWHM of 585 $\pm$ 152 km s$^{-1}$; however, the mass-excitation diagram and ``little red dot" color and compactness criteria suggest that there are a few AGN candidates on the outskirts of the protocluster. We fit the spectral energy distributions (SEDs) of the [OIII] emitters with \texttt{Prospector} and \texttt{Bagpipes}, and find that none of the SED-derived properties (stellar mass, age, or star formation rate) correlates with proximity to the quasar. While there is no correlation between galaxy age and local galaxy density, we find modest correlations between local galaxy density with increasing stellar mass, decreasing 10-to-100 Myr star formation rate ratios and decreasing nebular line equivalent widths. We further find that the protocluster galaxies are consistent with being more massive, older, and hosting higher star formation rates than the field sample at the 3$σ$ level, distributed in a filamentary structure which supports inside-out formation of the protocluster. There is modest evidence that galaxy evolution proceeds differently as a function of the density of local environment within protoclusters during the epoch of reionization, and the central quasar has little effect on the galaxy properties of the surrounding structure.

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arXiv2025

Spatially resolved dust properties over 50 kpc in a hyperluminous galaxy merger at $z = 4.6$

We present spatially resolved dust-continuum ALMA observations from rest-frame $\sim$60 to $\sim$600 $μ$m (bands 3-10) of the hyperluminous hot dust-obscured galaxy (hot DOG) WISE J224607.6-052634.9 (W2246-0526), at redshift $z=4.6$. W2246-0526 is interacting with at least three companion galaxies, forming a system connected by tidal streams. We model the multiwavelength ALMA observations of the dust continuum using a modified blackbody, from which we derive the dust properties (mass, emissivity index, area of the emitting region, and temperature) in the hot DOG and resolved structures across a region of nearly $\sim$50 kpc. The peak temperature at the location of the hot DOG, $\sim$110 K, is likely the consequence of heating by the central quasar. The dust temperature drops to $\sim$40 K at a radius of $\sim$8 kpc, suggesting that heating by the quasar beyond that distance is nondominant. The dust in the connecting streams between the host and companion galaxies is at temperatures between 30-40 K, typical of starburst galaxies, suggesting it is most likely heated by recent, in-situ star formation. This is the first time dust properties are spatially resolved over several tens of kpc in a galaxy system beyond Cosmic Noon --this is more than six times the scales previously probed in galaxies at those redshifts.

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arXiv2025

Constraints on the variation of the fine-structure constant at 3<z<10 with JWST emission-line galaxies

We present constraints on the spacetime variation of the fine-structure constant $α$ at redshifts $2.5\le z<9.5$ using JWST emission-line galaxies. The galaxy sample consists of 621 high-quality spectra with strong and narrow [O III] $λλ$4959,5007 doublet emission lines from 578 galaxies, including 232 spectra at $z>5$. The [O III] doublet lines are arguably the best emission lines to probe the variation in $α$. We divide our sample into six subsamples based on redshift and calculate the relative variation $Δα/α$ for the individual subsamples. The calculated $Δα/α$ values are consistent with zero within $1σ$ at all redshifts, suggesting no time variation in $α$ above a level of $(1-2) \times10^{-4}$ ($1σ$) in the past 13.2 billion years. When the whole sample is combined, the constraint is improved to be $Δα/α= (0.2\pm0.7) \times10^{-4}$. We further test the spatial variation in $α$ using four subsamples of galaxies in four different directions on the sky. The measured $Δα/α$ values are consistent with zero at a $1σ$ level of $\sim 2\times10^{-4}$. While the constraints in this work are not as stringent as those from lower-redshift quasar absorption lines in previous studies, this work uses an independent tracer and provides the first constraints on $Δα/α$ at the highest redshifts. With the growing number of emission-line galaxies from JWST, we expect to achieve stronger constraints in the future.

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arXiv2024

A unique window into the Epoch of Reionisation: A double-peaked Lyman-$α$ emitter in the proximity zone of a quasar at $z\sim 6.6$

We present a study of a double-peaked Ly$α$ emitter, named LAE-11, found in the proximity zone of QSO J0910-0414 at $z\sim6.6$. We use a combination of deep photometric data from Subaru Telescope, HST, and JWST with spectroscopic data from Keck/DEIMOS, NIRCam WFSS and NIRSpec MSA to characterise the ionising and general properties of the galaxy, as well as the quasar environment surrounding it. We detect Ly$α$, H$β$, [OIII] doublet, and H$α$ emission lines in the various spectral datasets. The presence of a double-peaked Ly$α$ line in the spectrum allows us to characterise the opening angle and lifetime of the QSO as $θ_Q>49.62$° and $t_Q > 3.8\times10^5$ years. LAE-11 is a fairly bright (M$_\rm{UV} = -19.84^{+0.14}_{-0.16}$), blue galaxy with a UV slope of $β= -2.61^{+0.06}_{-0.08}$. Since the galaxy is located in a quasar-ionised region, we have a unique opportunity to measure the escape fraction of Lyman Continuum photons using the un-attenuated double-peaked Ly$α$ emission profile and its equivalent width at such high redshift. We employ diagnostics which do not rely on the detection of Ly$α$ for comparison, and find that all tracers of ionising photon leakage agree within 1$σ$ uncertainty. We measure a moderate escape of Lyman Continuum photons from LAE-11 of $f_\rm{esc}^\rm{LyC} = (8 - 33)\%$. Detections of both H$α$ and H$β$ emission lines allow for separate measurements of the ionising photon production efficiency, resulting with $\log(ξ_\rm{ion}/\rm{Hz~erg^{-1}}) = 25.59\pm0.08$ and $25.65\pm0.09$, for H$α$ and H$β$, respectively. The total ionising output of LAE-11, $\log(f_\rm{esc}^\rm{LyC}ξ_\rm{ion, Hα}/\rm{Hz~erg^{-1}}) = 24.85^{+0.24}_{-0.34}$, is higher than the value of $24.3 - 24.8$ which is traditionally assumed as needed to drive Reionisation forward.

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arXiv2024

A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Spectroscopically Complete Census of Obscured Cosmic Star Formation Rate Density at $z=4-6$

We present a stringent measurement of the dust-obscured star-formation rate density (SFRD) at $z=4-6$ from the ASPIRE JWST Cycle-1 medium and ALMA Cycle-9 large program. We obtained JWST/NIRCam grism spectroscopy and ALMA 1.2-mm continuum map along 25 independent quasar sightlines, covering a total survey area of $\sim$35 arcmin$^2$ where we search for dusty star-forming galaxies (DSFGs) at $z = 0 - 7$. We identify eight DSFGs in seven fields at $z=4-6$ through the detection of H$α$ or [O III] $λ$5008 lines, including fainter lines such as H$β$, [O III] $λ$4960, [N II] $λ$6585, [S II] $λλ$6718,6733 for six sources. With this spectroscopically complete DSFG sample at $z=4-6$ and negligible impact from cosmic variance (shot noise), we measure the infrared luminosity function (IRLF) down to $L_\mathrm{IR} \sim 2\times10^{11}$ $L_\odot$. We find flattening of IRLF at $z=4-6$ towards the faint end (power-law slope $α= 0.59_{-0.45}^{+0.39}$). We determine the dust-obscured cosmic SFRD at this epoch as $\log[ρ_\mathrm{SFR,IR} / (\mathrm{M}_\odot\,\mathrm{yr}^{-1}\,\mathrm{Mpc}^{-3})] = -1.52_{-0.13}^{+0.14}$. This is significantly higher than previous determination using ALMA data in the Hubble Ultra Deep Field, which is void of DSFGs at $z=4-6$ because of strong cosmic variance (shot noise). We conclude that the majority ($66\pm7$%) of cosmic star formation at $z \sim 5$ is still obscured by dust. We also discuss the uncertainty of SFRD propagated from far-IR spectral energy distribution and IRLF at the bright end, which will need to be resolved with future ALMA and JWST observations.

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arXiv2024

Overdensity of Lyman-Break Galaxy Candidates Around Hot Dust-Obscured Galaxies

Hot dust-obscured galaxies (Hot DOGs), are a family of hyper-luminous, heavily obscured quasars. A number of studies have shown that these objects reside in significantly overdense regions of the Universe based on the identification of companions at optical through far-IR wavelengths. Here we present further characterization of their environments by studying the surface density of Lyman break galaxy (LBG) candidates in the vicinity of three Hot DOGs. For two of them, WISE J041010.60-091305.2 at z=3.631 and WISE J083153.25+014010.8 at z=3.912, we identify the candidate LBG companions using deep observations obtained with Baade/IMACS. For the third, WISE J224607.56-052634.9 at z=4.601, we re-analyse previously published data obtained with Gemini-S/GMOS-S. We optimise the LBG photometric selection criteria at the redshift of each target using the COSMOS2020 catalog. When comparing the density of LBG candidates found in the vicinity of these Hot DOGs with that in the COSMOS2020 catalog, we find overdensities of $δ=1.83\pm 0.08$ ($δ' = 7.49\pm 0.68$), $δ=4.67\pm 0.21$ ($δ' = 29.17\pm 2.21$), and $δ= 2.36\pm 0.25$ ($δ' = 11.60\pm 1.96$) around W0410-0913, W0831+0140, and W2246-0526, respectively, without (with) contamination correction. Additionally, we find that the overdensities are centrally concentrated around each Hot DOG. Our analysis also reveals that the overdensity of the fields surrounding W0410-0913 and W0831+0140 declines steeply beyond physical scales of $\sim$2 Mpc. If these overdensities evolve to clusters by z=0, these results suggest that the Hot DOG may correspond to the early formation stages of the brightest cluster galaxy. We were unable to determine if this is also the case for W2246-0526 due to the smaller field of view of the GMOS-S observations. Our results imply that Hot DOGs may be excellent tracers of protoclusters.

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arXiv2024

A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): JWST Supports Earlier Reionization around [OIII] Emitters

Understanding when and how reionization happened is crucial for studying the early structure formation and the properties of first galaxies in the Universe. At $z>5.5$, the observed IGM optical depth shows a significant scatter, indicating an inhomogeneous reionization process. However, the nature of the inhomogeneous reionization remains debated. ASPIRE is a JWST Cycle 1 program that has spectroscopically identified $>400$ [OIII] emitters in 25 quasar fields at $z>6.5$. Combined with deep ground-based optical spectroscopy of ASPIRE quasars, ASPIRE program provides the current largest sample for IGM-galaxy connection studies during cosmic reionization. We present the first results of IGM effective optical depth measurements around [OIII] emitters using 14 ASPIRE quasar fields. We find the IGM transmission is tightly related with reionization-era galaxies to the extent that significant excess of Ly$α$ transmission exists around [OIII] emitters. We measure the stacked IGM effective optical depth of IGM patches associated with [OIII] emitters and find they reach the same IGM effective optical depth at least dz~0.1 ahead of those IGM patches where no [OIII] emitters are detected, supporting earlier reionization around [OIII] emitters. Our results indicate an enhancement in IGM Ly$α$ transmission around [OIII] emitters at scales beyond 25 $h^{-1}$ cMpc, consistent with the predicted topology of reionization from fluctuating UV background (UVB) models.

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arXiv2024

Fast Outflow in the Host Galaxy of the Luminous z $=$ 7.5 Quasar J1007$+$2115

James Webb Space Telescope opens a new window to directly probe luminous quasars powered by billion solar mass black holes in the epoch of reionization and their co-evolution with massive galaxies with unprecedented details. In this paper, we report the first results from the deep NIRSpec integral field spectroscopy study of a quasar at $z = 7.5$. We obtain a bolometric luminosity of $\sim$$1.8\times10^{47}$ erg s$^{-1}$ and a black hole mass of $\sim$0.7--2.5$\times10^{9}$ M$_{\odot}$ based on H$β$ emission line from the quasar spectrum. We discover $\sim$2 kpc scale, highly blueshifted ($\sim$$-$870 km/s) and broad ($\sim$1400 km/s) [O III] line emission after the quasar PSF has been subtracted. Such line emission most likely originates from a fast, quasar-driven outflow, the earliest one on galactic-scale known so far. The dynamical properties of this outflow fall within the typical ranges of quasar-driven outflows at lower redshift, and the outflow may be fast enough to reach the circumgalactic medium. Combining both the extended and nuclear outflow together, the mass outflow rate, $\sim$300 M$_{\odot}$yr, is $\sim$60%--380% of the star formation rate of the quasar host galaxy, suggesting that the outflow may expel a significant amount of gas from the inner region of the galaxy. The kinetic energy outflow rate, $\sim$3.6$\times10^{44}$ erg s$^{-1}$, is $\sim$0.2% of the quasar bolometric luminosity, which is comparable to the minimum value required for negative feedback based on simulation predictions. The dynamical timescale of the extended outflow is $\sim$1.7 Myr, consistent with the typical quasar lifetime in this era.

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arXiv2024

CO spectra of the ISM in the Host Galaxies of the Most Luminous WISE-Selected AGNs

We present observations of mid-J J=4-3 or J=5-4 carbon monoxide (CO) emission lines and continuum emission from a sample of ten of the most luminous log(L/L_solar)~14 Hot Dust-Obscured Galaxies (Hot DOGs) discovered by the Wide-field Infrared Survey Explorer (WISE) with redshifts up to 4.6. We uncover broad spectral lines (FWHM~400 km/s) in these objects, suggesting a turbulent molecular interstellar medium (ISM) may be ubiquitous in Hot DOGs. A halo of molecular gas, extending out to a radius of 5 kpc is observed in W2305-0039, likely supplied by 940 km/s molecular outflows. W0831+0140 is plausibly the host of a merger between at least two galaxies, consistent with observations made using ionized gas. These CO(4-3) observations contrast with previous CO(1-0) studies of the same sources: the CO(4-3) to CO(1-0) luminosity ratios exceed 300 in each source, suggesting that the lowest excited states of CO are underluminous. These findings show that the molecular gas in Hot DOGs is consistently turbulent, plausibly a consequence of AGN feedback, triggered by galactic mergers.

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arXiv2024

A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Broad-line AGN at $z=4-5$ revealed by JWST/NIRCam WFSS

Low-luminosity AGNs with low-mass black holes (BHs) in the early universe are fundamental to understanding the BH growth and their co-evolution with the host galaxies. Utilizing JWST NIRCam Wide Field Slitless Spectroscopy (WFSS), we perform a systematic search for broad-line ${\rm Hα}$ emitters (BHAEs) at $z\approx 4-5$ in 25 fields of the ASPIRE (A SPectroscopic survey of biased halos In the Reionization Era) project, covering a total area of 275 arcmin$^2$. We identify 16 BHAEs with FWHM of the broad components spanning from $\sim$ 1000 km s$^{-1}$ to 3000 km s$^{-1}$. Assuming the broad linewidths arise due to Doppler broadening around BHs, the implied BH masses range from $10^7$ to $10^{8}~M_\odot$, with broad ${\rm Hα}$-converted bolometric luminosity of $10^{44.5}-10^{45.5}$ erg s$^{-1}$ and Eddington ratios of $0.07-0.47$. The spatially extended structure of the F200W stacked image may trace the stellar light from the host galaxies. The ${\rm Hα}$ luminosity function indicates an increasing AGN fraction towards the higher ${\rm Hα}$ luminosities. We find possible evidence for clustering of BHAEs: two sources are at the same redshift with a projected separation of 519 kpc; one BHAE appears as a composite system residing in an overdense region with three close companion ${\rm Hα}$ emitters. Three BHAEs exhibit blueshifted absorption troughs indicative of the presence of high-column-density gas. We find the broad-line and photometrically selected BHAE samples exhibit different distributions in the optical continuum slopes, which can be attributed to their different selection methods. The ASPIRE broad-line ${\rm Hα}$ sample provides a good database for future studies of faint AGN populations at high redshift.

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arXiv2024

A quasar-galaxy merger at $z\sim 6.2$: rapid host growth via accretion of two massive satellite galaxies

We present JWST/NIRSpec Integral Field Spectroscopy in the rest-frame optical bands of the system PJ308-21, a quasar at $z=6.2342$ caught as its host galaxy interacts with companion galaxies. We detect spatially extended emission of several emission lines (H$α$, H$β$, [OIII], [NII], [SII], HeII), which we use to study the properties of the ionized phase of the interstellar medium: the source and hardness of the photoionizing radiation field, metallicity, dust reddening, electron density and temperature, and star formation. We also marginally detect continuum starlight emission associated with the companion sources. We find that at least two independent satellite galaxies are part of the system. While the quasar host appears highly enriched and obscured, with AGN-like photoionization conditions, the western companion shows minimal dust extinction, low metallicity ($Z\sim0.4$ Z$_\odot$), and star-formation driven photoionization. The eastern companion shows higher extinction and metallicity ($Z\sim0.8$ Z$_\odot$) compared to the western companion, and it is at least partially photoionized by the nearby quasar. We do not find any indication of AGN in the companion sources. Our study shows that while the quasar host galaxy is already very massive ($M_{\rm dyn}>10^{11}$ M$_\odot$), it is still rapidly building up by accreting two relatively massive ($M_{\rm star}\sim 10^{10}$ M$_\odot$) companion sources. This dataset showcases the power of JWST in exposing the build-up of massive galaxies in the first Gyr of the Universe.

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arXiv2024

Black Hole Mass and Eddington Ratio Distribution of Hot Dust-Obscured Galaxies

Hot Dust-Obscured Galaxies (Hot DOGs) are a rare population of hyper-luminous infrared galaxies discovered by the WISE mission. Despite the significant obscuration of the AGN by dust in these systems, pronounced broad and blue-shifted emission lines are often observed. Previous work has shown that 8 Hot DOGs, referred to as Blue-excess Hot DOGs (BHDs), present a blue excess consistent with type 1 quasar emission in their UV-optical SEDs, which has been shown to originate from the light of the obscured central engine scattered into the line of sight. We present an analysis of the rest-frame optical emission characteristics for 172 Hot DOGs through UV-MIR SED modeling and spectroscopic details, with a particular focus on the identification of BHDs. We find that while the optical emission observed in Hot DOGs is in most cases dominated by a young stellar population, 26% of Hot DOGs show a significant enough blue excess emission to be classified as BHDs. Based on their broad CIV and MgII lines, we find that the $M_{\rm BH}$ in BHDs range from $10^{8.7}$ to $10^{10} \ M_{\odot}$. When using the same emission lines in regular Hot DOGs, we find the $M_{\rm BH}$ estimates cover the entire range found for BHDs while also extending to somewhat lower values. This agreement may imply that the broad lines in regular Hot DOGs also originate from scattered light from the central engine, just as in BHDs, although a more detailed study would be needed to rule out an outflow-driven nature. Similar to $z\sim 6$ quasars, we find that Hot DOGs sit above the local relation between stellar and black hole mass, suggesting either that AGN feedback has not yet significantly suppressed the stellar mass growth in the host galaxies, or that they will be outliers of the relation when reaching $z$=0.

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arXiv2024

NuSTAR Observations of Candidate Subparsec Binary Supermassive Black Holes

We present analysis of NuSTAR X-ray observations of three AGN that were identified as candidate subparsec binary supermassive black hole (SMBH) systems in the Catalina Real-Time Transient Survey based on apparent periodicity in their optical light curves. Simulations predict that close-separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs. We previously observed these AGN with Chandra and found no differences between their low energy X-ray properties and the larger AGN population. However some models predict differences to be more prominent at energies higher than probed by Chandra. We find that even at the higher energies probed by NuSTAR, the spectra of these AGN are indistinguishable from the larger AGN population. This could rule out models predicting large differences in the X-ray spectra in the NuSTAR bands. Alternatively, it might mean that these three AGN are not binary SMBHs.

astro-ph.HE↗

arXiv2024

A quasar-galaxy merger at $z\sim6.2$: black hole mass and quasar properties from the NIRSpec spectrum

We present JWST/NIRSpec integral field data of the quasar PJ308-21 at $z=6.2342$. As shown by previous ALMA and HST imaging, the quasar has two companion sources, interacting with the quasar host galaxy. The high-resolution G395H/290LP NIRSpec spectrum covers the $2.87-5.27\ \rm μm$ wavelength range and shows the rest-frame optical emission of the quasar with exquisite quality ($S/N\sim 100-400$ per spectral element). Based on the H$β$ line from the broad line region, we obtain an estimate of the black hole mass $M_{\rm BH,Hβ}\sim 2.7\times 10^{9}\ \rm M_{\odot}$. This value is within a factor $\lesssim 1.5$ of the H$α$-based black hole mass from the same spectrum ($M_{\rm BH, Hα}\sim 1.93\times 10^{9}\ \rm M_{\odot}$) and is consistent with a previous estimate relying on the MgII $λ2799$ ($M_{\rm BH, MgII}\sim 2.65\times 10^{9}\ \rm M_{\odot}$). All these $M_{\rm BH}$ are within the $\sim 0.5$ dex intrinsic scatter of the adopted mass calibrations. The high Eddington ratio of PJ308-21 $λ_{\rm Edd,Hβ}\sim 0.67$ ($λ_{\rm Edd,Hα}\sim 0.96$) is in line with the overall quasar population at $z \gtrsim 6$. The relative strengths of the [OIII], FeII and H$β$ lines are consistent with the empirical "Eigenvector 1" correlations as observed for low redshift quasars. We find evidence for blueshifted [OIII] $λ5007$ emission with a velocity offset $Δv_{\rm [OIII]}=-1922\pm 39$ km s$^{-1}$ from the systemic velocity and a $\rm FWHM([OIII])=2776^{+75}_{-74}$ km s$^{-1}$. This may be the signature of an outflow from the nuclear region, despite the true values of $Δv_{\rm [OIII]}$ and $\rm FWHM([OIII])$ are likely more uncertain due to the blending with H$β$ and FeII lines. Our study demonstrates the unique capabilities of NIRSpec in capturing quasar spectra at cosmic dawn and studying their properties in unprecedented detail.

astro-ph.GA↗

arXiv2024

A benchmark for extreme conditions of the multiphase interstellar medium in the most luminous hot dust-obscured galaxy at z = 4.6

WISE J224607.6-052634.9 (W2246-0526) is a hot dust-obscured galaxy at $z$ = 4.601, and the most luminous obscured quasar known to date. W2246-0526 harbors a heavily obscured supermassive black hole that is most likely accreting above the Eddington limit. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in seven bands, including band 10, of the brightest far-infrared (FIR) fine-structure emission lines of this galaxy: [OI]$_{63μm}$, [OIII]$_{88μm}$, [NII]$_{122μm}$, [OI]$_{145μm}$, [CII]$_{158μm}$, [NII]$_{205μm}$, [CI]$_{370μm}$, and [CI]$_{609μm}$. A comparison of the data to a large grid of Cloudy radiative transfer models reveals that a high hydrogen density ($n_{H}\sim3\times10^3$ cm$^{-3}$) and extinction ($A_{V}\sim300$ mag), together with extreme ionization ($log(U)=-0.5$) and a high X-ray to UV ratio ($α_{ox}\geq-0.8$) are required to reproduce the observed nuclear line ratios. The values of $α_{ox}$ and $U$ are among the largest found in the literature and imply the existence of an X-ray-dominated region (XDR). In fact, this component explains the a priori very surprising non-detection of the [OIII]$_{88μm}$ emission line, which is actually suppressed, instead of boosted, in XDR environments. Interestingly, the best-fitted model implies higher X-ray emission and lower CO content than what is detected observationally, suggesting the presence of a molecular gas component that should be further obscuring the X-ray emission over larger spatial scales than the central region that is being modeled. These results highlight the need for multiline infrared observations to characterize the multiphase gas in high redshift quasars and, in particular, W2246-0526 serves as an extreme benchmark for comparisons of interstellar medium conditions with other quasar populations at cosmic noon and beyond.

astro-ph.GA↗

arXiv2023

Discovery of a Low-Redshift Hot Dust-Obscured Galaxy

We report the discovery of the hyperluminous, highly obscured AGN WISE J190445.04+485308.9 (W1904+4853 hereafter, $L_{bol} = 1.1 \times 10^{13} \ L_{\odot}$) at z=0.415. Its well-sampled spectral energy distribution (SED) is dominated by infrared dust emission, though broad emission lines are detected in the optical spectra. These features suggest that W1904+4853 contains an actively accreting supermassive black hole hidden in its dusty cocoon, resembling the observed properties of Hot Dust-Obscured Galaxies (Hot DOGs), a population previously only identified at z>1.0. Using the broad component of the MgII emission line, we estimate a black hole mass of $log \ (M_{BH}/M_{\odot}) = 8.4 \pm 0.4$. The corresponding Eddington ratio of 1.4 implies that the central black hole accretion is at the theoretical limit of isotropic accretion. The rest-frame UV-optical SED also indicates that the host galaxy of W1904+4853 harbors strong star formation activity at the rate of $6-84 \ M_{\odot} \ \rm{yr^{-1}}$ with an independent estimate of SFR up to $\sim 45 \ M_{\odot} \ \rm{yr^{-1}}$ using the [O II] emission line. With an estimated stellar mass of $3 \times 10^{10} \ M_{\odot}$, the host galaxy appears to be a starburst system with respect to the main sequence of the star-forming galaxies at the same redshift. Although blueshifted and asymmetric [O III] emission provides evidence of an outflow, we estimate it to be an order of magnitude smaller than the star formation rate, indicating that the current obscured AGN activity at the center has not yet produced significant feedback on the host galaxy star formation activity. W1904+4853 supports the interpretation that Hot DOGs are a rare transitional phase of AGN accretion in galaxy evolution, a phase that can persist into the present-day Universe.

astro-ph.GA↗