arXiv subjects

Xiaohui Fan

Publications and source records attributed to Xiaohui Fan.

At least 199 records · Page 11Linked to original sources

arXiv2022

First Census of Gas-phase Metallicity Gradients of Star-forming Galaxies in Overdense Environments at Cosmic Noon

We report the first spatially resolved measurements of gas-phase metallicity radial gradients in star-forming galaxies in overdense environments at $z\gtrsim2$. The spectroscopic data are acquired by the \mg\ survey, a Hubble Space Telescope (HST) cycle-28 medium program. This program is obtaining 45 orbits of WFC3/IR grism spectroscopy in the density peak regions of three massive galaxy protoclusters (BOSS 1244, BOSS 1542 and BOSS 1441) at $z=2-3$. Our sample in the BOSS 1244 field consists of 20 galaxies with stellar-mass ranging from $10^{9.0}$ to $10^{10.3}$ \Msun\ , star formation rate (SFR) from 10 to 240 \Msun\,yr$^{-1}$, and global gas-phase metallicity (\oh) from 8.2 to 8.6. At $1σ$ confidence level, 2/20 galaxies in our sample show positive (inverted) gradients -- the relative abundance of oxygen increasing with galactocentric radius, opposite the usual trend. Furthermore, 1/20 shows negative gradients and 17/20 are consistent with flat gradients. This high fraction of flat/inverted gradients is uncommon in simulations and previous observations conducted in blank fields at similar redshifts. To understand this, we investigate the correlations among various observed properties of our sample galaxies. We find an anticorrelation between metallicity gradient and global metallicity of our galaxies residing in extreme overdensities, and a marked deficiency of metallicity in our massive galaxies as compared to their coeval field counterparts. We conclude that the cold-mode gas accretion plays an active role in shaping the chemical evolution of galaxies in the protocluster environments, diluting their central chemical abundance, and flattening/inverting their metallicity gradients.

astro-ph.GA↗

arXiv2022

Submillimetre galaxies in two massive protoclusters at z = 2.24: witnessing the enrichment of extreme starbursts in the outskirts of HAE density peaks

Submillimetre galaxies represent a rapid growth phase of both star formation and massive galaxies. Mapping SMGs in galaxy protoclusters provides key insights into where and how these extreme starbursts take place in connections with the assembly of the large-scale structure in the early Universe. We search for SMGs at 850$\,μm$ using JCMT/SCUBA-2 in two massive protoclusters at $z=2.24$, BOSS1244 and BOSS1542, and detect 43 and 54 sources with $S_{850}>4\,$mJy at the $4σ$ level within an effective area of 264$\,$arcmin$^2$, respectively. We construct the intrinsic number counts and find that the abundance of SMGs is $2.0\pm0.3$ and $2.1\pm0.2$ times that of the general fields, confirming that BOSS1244 and BOSS1542 contain a higher fraction of dusty galaxies with strongly enhanced star formation. The volume densities of the SMGs are estimated to be $\sim15-$30 times the average, significantly higher than the overdensity factor ($\sim 6$) traced by H$α$ emission-line galaxies (HAEs). More importantly, we discover a prominent offset between the spatial distributions of the two populations in these two protoclusters -- SMGs are mostly located around the high-density regions of HAEs, and few are seen inside these regions. This finding may have revealed for the first time the occurrence of violent star formation enhancement in the outskirts of the HAE density peaks, likely driven by the boosting of gas supplies and/or starburst triggering events. Meanwhile, the lack of SMGs inside the most overdense regions at $z\sim2$ implies a transition to the environment disfavouring extreme starbursts.

astro-ph.GA↗

arXiv2022

Radio and Far-IR Emission Associated with a Massive Star-forming Galaxy Candidate at z$\simeq$6.8: A Radio-Loud AGN in the Reionization Era?

We report the identification of radio (0.144-3 GHz), mid-IR, far-IR, and sub-mm (24-850$μ$m) emission at the position of one of 41 UV-bright (M$_\mathrm{UV}^{}\lesssim-21.25$) $z\simeq6.6-6.9$ Lyman-break galaxy candidates in the 1.5 deg$^2$ COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor $>$3) between two narrow/intermediate bands at 9450 and 9700 Angstroms and is undetected in all nine bands blueward of 9600 Angstroms, as expected from a Lyman-alpha break at $z\simeq6.8$. The full multi-wavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M$_{\ast}=10^{10.8}$ M$_{\odot}$) and extremely red (rest-UV slope $β=-0.59$) $z\simeq6.8$ galaxy with hyperluminous infrared emission (L$_{\mathrm{IR}}=10^{13.6}$ L$_{\odot}$) powered by both an intense burst of highly-obscured star formation (SFR$\approx$1800 M$_{\odot}$ yr$^{-1}$) and an obscured ($τ_{\mathrm{9.7μm}}=7.7\pm2.5$) radio-loud (L$_{\mathrm{1.4\ GHz}}\approx10^{25.4}$ W Hz$^{-1}$) AGN. The radio emission is compact (1.04$\pm$0.12 arcsec) and exhibits an ultra-steep spectrum between 1.32-3 GHz ($α=-1.57^{+0.22}_{-0.21}$) that flattens at lower frequencies ($α=-0.86^{+0.22}_{-0.16}$ between 0.144-1.32 GHz), consistent with known $z>4$ radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11$\times$) galaxy overdensity at $z\simeq6.6-6.9$, as common for systems hosting radio-loud AGN. Nonetheless, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 as we cannot yet completely rule out low-redshift solutions. If confirmed to lie at $z\simeq6.8$, the properties of COS-87259 would be consistent with a picture wherein AGN and highly-obscured star formation activity are fairly common among very massive (M$_{\ast}>10^{10}$ M$_{\odot}$) reionization-era galaxies.

astro-ph.GA↗

arXiv2022

Molecular Contrastive Learning with Chemical Element Knowledge Graph

Molecular representation learning contributes to multiple downstream tasks such as molecular property prediction and drug design. To properly represent molecules, graph contrastive learning is a promising paradigm as it utilizes self-supervision signals and has no requirements for human annotations. However, prior works fail to incorporate fundamental domain knowledge into graph semantics and thus ignore the correlations between atoms that have common attributes but are not directly connected by bonds. To address these issues, we construct a Chemical Element Knowledge Graph (KG) to summarize microscopic associations between elements and propose a novel Knowledge-enhanced Contrastive Learning (KCL) framework for molecular representation learning. KCL framework consists of three modules. The first module, knowledge-guided graph augmentation, augments the original molecular graph based on the Chemical Element KG. The second module, knowledge-aware graph representation, extracts molecular representations with a common graph encoder for the original molecular graph and a Knowledge-aware Message Passing Neural Network (KMPNN) to encode complex information in the augmented molecular graph. The final module is a contrastive objective, where we maximize agreement between these two views of molecular graphs. Extensive experiments demonstrated that KCL obtained superior performances against state-of-the-art baselines on eight molecular datasets. Visualization experiments properly interpret what KCL has learned from atoms and attributes in the augmented molecular graphs. Our codes and data are available at https://github.com/ZJU-Fangyin/KCL.

cs.LG↗

arXiv2022

Connecting Low- and High-Redshift Weak Emission-Line Quasars via HST Spectroscopy of Ly$α$ Emission

We present ultraviolet spectroscopy covering the Ly$α$ + N V complex of six candidate low-redshift ($0.9 < z < 1.5$) weak emission-line quasars (WLQs) based on observations with the Hubble Space Telescope. The original systematic searches for these puzzling Type 1 quasars with intrinsically weak broad emission lines revealed an $N \approx 100$ WLQ population from optical spectroscopy of high-redshift ($z > 3$) quasars, defined by a Ly$α$ + N V rest-frame equivalent width (EW) threshold $< 15.4$ Å. Identification of lower-redshift ($z < 3$) WLQ candidates, however, has relied primarily on optical spectroscopy of weak broad emission lines at longer rest-frame wavelengths. With these new observations expanding existing optical coverage into the ultraviolet, we explore unifying the low- and high-$z$ WLQ populations via EW[Ly$α$+NV]. Two objects in the sample unify with high-$z$ WLQs, three others appear consistent with the intermediate portion of the population connecting WLQs and normal quasars, and the final object is consistent with typical quasars. The expanded wavelength coverage improves the number of available line diagnostics for our individual targets, allowing a better understanding of the shapes of their ionizing continua. The ratio of EW[Ly$α$+NV] to EW[MgII] in our sample is generally small but varied, favoring a soft ionizing continuum scenario for WLQs, and we find a lack of correlation between EW[Ly$α$+NV] and the X-ray properties of our targets, consistent with a "slim-disk" shielding gas model. We also find indications that weak absorption may be a more significant contaminant in low-$z$ WLQ populations than previously thought.

astro-ph.GA↗

arXiv2022

Molecular gas in z~6 quasar host galaxies

We investigate the molecular gas content of z~6 quasar host galaxies using the IRAM / Northern Extended Millimeter Array. We target the 3mm dust continuum, and the line emission from CO(6-5), CO(7-6), [CI]2-1 in 10 infra-red-luminous quasars that have been previously studied in their 1mm dust continuum and [CII] line emission. We detect CO(7-6) at various degrees of significance in all the targeted sources, thus doubling the number of such detections in z~6 quasars. The 3mm to 1mm flux density ratios are consistent with a modified black body spectrum with a dust temperature $T_{dust}$~47 K and an optical depth $τ_ν$=0.2 at the [CII] frequency. Our study provides us with four independent ways to estimate the molecular gas mass, $M_{H2}$, in the targeted quasars. This allows us to set constraints on various parameters used in the derivation of molecular gas mass estimates, such as the mass per luminosity ratios $α_{CO}$ and $α_{[CII]}$, the gas-to-dust ratio $δ_{g/d}$, and the carbon abundance [C]/H2. Leveraging either on the dust, CO, [CI], or [CII] emission yields mass estimates of the entire sample in the range $M_{H2}$~$10^{10}$ to $10^{11}$ M$_{\odot}$. We compare the observed luminosities of dust, [CII], [CI], and CO(7-6) with predictions from photo-dissociation and X-ray dominated regions. We find that the former provide better model fits to our data, assuming that the bulk of the emission arises from dense ($n_H>10^4$ cm$^{-3}$) clouds with a column density $N_{H}$~$10^{23}$ cm$^{-2}$, exposed to a radiation field with intensity $G_0$~$10^3$ (in Habing units). Our analysis reiterates the presence of massive reservoirs of molecular gas fueling star formation and nuclear accretion in $z$~6 quasar host galaxies. It also highlights the power of combined 3mm and 1mm observations for quantitative studies of the dense gas content in massive galaxies at cosmic dawn.

astro-ph.GA↗

arXiv2022

Exploring the radio spectral energy distribution of the ultraluminous radio-quiet quasar SDSS J0100+2802 at redshift 6.3

We report deep Karl G. Jansky Very Large Array (VLA) observations of the optically ultraluminous and radio-quiet quasar SDSS J010013.02 + 280225.8 (hereafter J0100+2802) at redshift $z=$6.3. We detected the radio continuum emission at 1.5 GHz, 6 GHz, and 10 GHz. This leads to a radio power-law spectral index of $α= -0.52\pm0.18$ ($S \propto ν^α$). The radio source is unresolved in all VLA bands with an upper limit to the size of $0.2^{\prime \prime}$ (i.e., $\sim$ 1.1 kpc) at 10 GHz. We find variability in the flux density (increase by $\sim 33\%$) and the spectral index (steepened) between observations in 2016 and 2017. We also find that the VLA 1.5 GHz flux density observed in the same year is 1.5 times that detected with the Very Long Baseline Array (VLBA) in 2016 at the same frequency. This difference suggests that half of the radio emission from J0100+2802 comes from a compact core within 40 pc, and the rest comes from the surrounding few kpc area which is diffuse and resolved out in the VLBA observations. The diffuse emission is four times brighter than that would be expected if driven by star formation. We conclude that the central active galactic nucleus is the dominant power engine of the radio emission in J0100+2802.

astro-ph.GA↗

arXiv2022

A Mock Catalog of Gravitationally Lensed Quasars for the LSST Survey

We present a mock catalog of gravitationally lensed quasars at $z_\text{qso}<7.5$ with simulated images for the Rubin Observatory Legacy Survey of Space and Time (LSST). We adopt recent measurements of quasar luminosity functions to model the quasar population, and use the CosmoDC2 mock galaxy catalog to model the deflector galaxies, which successfully reproduces the observed galaxy velocity dispersion functions up to $z_d\sim1.5$. The mock catalog is highly complete for lensed quasars with Einstein radius $θ_E>0\farcs07$ and quasar absolute magnitude $M_{i}<-20$. We estimate that there are $\sim10^3$ lensed quasars discoverable in current imaging surveys, and LSST will increase this number to $\sim2.4\times10^3$. Most of the lensed quasars have image separation $Δθ>0\farcs5$, which will at least be marginally resolved in LSST images with seeing of $\sim0\farcs7$. There will be $\sim200$ quadruply-lensed quasars discoverable in the LSST. The fraction of quad lenses among all discoverable lensed quasars is about $\sim10\%-15\%$, and this fraction decreases with survey depth. This mock catalog shows a large diversity in the observational features of lensed quasars, in terms of lensing separation and quasar-to-deflector flux ratio. We discuss possible strategies for a complete search of lensed quasars in the LSST era.

astro-ph.GA↗

arXiv2022

ALMA 200 pc imaging of a z~7 quasar reveals a compact, disk-like host galaxy

We present 0".035 resolution (~200 pc) imaging of the 158 um [CII] line and the underlying dust continuum of the z=6.9 quasar J234833.34-305410.0. The 18 h ALMA observations reveal extremely compact emission (diameter ~1 kpc) that is consistent with a simple, almost face-on, rotation-supported disk with a significant velocity dispersion of ~160 km/s. The gas mass in just the central 200 pc is ~4x10^9 M_sun, about a factor two higher than that of the central supermassive black hole. Consequently we do not resolve the black hole's sphere of influence, and find no kinematic signature of the central supermassive black hole. Kinematic modeling of the [CII] line shows that the dynamical mass at large radii is consistent with the gas mass, leaving little room for a significant mass contribution by stars and/or dark matter. The Toomre-Q parameter is less than unity throughout the disk, and thus is conducive to star formation, consistent with the high infrared luminosity of the system. The dust in the central region is optically thick, at a temperature >132 K. Using standard scaling relations of dust heating by star formation, this implies an unprecedented high star formation rate density of >10^4 M_sun / yr / kpc^2. Such a high number can still be explained with the Eddington limit for star formation under certain assumptions, but could also imply that the central supermassive black hole contributes to the heating of the dust in the central 110 pc.

astro-ph.GA↗

arXiv2022

The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar and APOGEE-2 Data

This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library (MaStar) accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) survey which publicly releases infra-red spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the sub-survey Time Domain Spectroscopic Survey (TDSS) data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey (SPIDERS) sub-survey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated Value Added Catalogs (VACs). This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper (MWM), Local Volume Mapper (LVM) and Black Hole Mapper (BHM) surveys.

astro-ph.GA↗

arXiv2021

Deep XMM-Newton Observations of an X-ray Weak, Broad Absorption Line Quasar at $z=6.5$

We report X-ray observations of the most distant known gravitationally lensed quasar, J0439+1634 at $z=6.52$, which is also a broad absorption line (BAL) quasar, using the XMM-Newton Observatory. With a 130 ks exposure, the quasar is significantly detected as a point source at the optical position with a total of 358$^{+19}_{-19}$ net counts using the EPIC instrument. By fitting a power-law plus Galactic absorption model to the observed spectra, we obtain a spectral slope of $Γ=1.45^{+0.10}_{-0.09}$. The derived optical-to-X-ray spectral slope $α_{\rm{ox}}$ is $-2.07^{+0.01}_{-0.01}$, suggesting that the X-ray emission of J0439+1634 is weaker by a factor of 18 than the expectation based on its 2500 Angstrom luminosity and the average $α_{\rm{ox}}$ vs. luminosity relationship. This is the first time that an X-ray weak BAL quasar at $z>6$ has been observed spectroscopically. Its X-ray weakness is consistent with the properties of BAL quasars at lower redshift. By fitting a model including an intrinsic absorption component, we obtain intrinsic column densities of $N_{\rm{H}}=2.8^{+0.7}_{-0.6}\times10^{23}\,\rm{cm}^{-2}$ and $N_{\rm{H}}= 4.3^{+1.8}_{-1.5}\times10^{23}\,\rm{cm}^{-2}$, assuming a fixed $Γ$ of 1.9 and a free $Γ$, respectively. The intrinsic rest-frame 2--10 keV luminosity is derived as $(9.4-15.1)\times10^{43}\,\rm{erg\,s}^{-1}$, after correcting for lensing magnification ($μ=51.3$). The absorbed power-law model fitting indicates that J0439+1634 is the highest redshift obscured quasar with a direct measurement of the absorbing column density. The intrinsic high column density absorption can reduce the X-ray luminosity by a factor of $3-7$, which also indicates that this quasar could be a candidate of intrinsically X-ray weak quasar.

astro-ph.GA↗

arXiv2021

Quasar UV Luminosity Function at $3.5<z<5.0$ from SDSS Deep Imaging Data

We present a well-designed sample of more than 1000 type 1 quasars at $3.5 0.5$. The evolution of the QLFs from $z\sim5$ to $3.5$ can be described by a pure density evolution model ($\propto10^{kz}$) and the parameter $k$ is similar to that at $5<z<7$, suggesting a nearly uniform evolution of the quasar density at $z=3.5-7$.

astro-ph.GA↗

arXiv2021

Metallicity in Quasar Broad Line Regions at Redshift $\sim$ 6

Broad line regions (BLRs) in high-redshift quasars provide crucial information of chemical enrichment in the early universe. Here we present a study of BLR metallicities in 33 quasars at redshift $5.7<z<6.4$. Using the near-IR spectra of the quasars obtained from the Gemini telescope, we measure their rest-frame UV emission line flux and calculate flux ratios. We then estimate BLR metallicities with empirical calibrations based on photoionization models. The inferred median metallicity of our sample is a few times the solar value, indicating that the BLR gas had been highly metal-enriched at $z\sim6$. We compare our sample with a low-redshift quasar sample with similar luminosities and find no evidence of redshift evolution in quasar BLR metallicities. This is consistent with previous studies. The Fe II$/$Mg II flux ratio, a proxy for the Fe$/α$ element abundance ratio, shows no redshift evolution as well, further supporting rapid nuclear star formation at $z\sim6$. We also find that the black hole mass-BLR metallicity relation at $z\sim6$ is consistent with the relation measured at $2<z<5$, suggesting that our results are not biased by a selection effect due to this relation.

astro-ph.GA↗

arXiv2021

Ultra-luminous high-redshift quasars from SkyMapper -- II. New quasars and the bright end of the luminosity function

We search for ultra-luminous Quasi-Stellar Objects (QSOs) at high redshift using photometry from the SkyMapper Southern Survey Data Release 3 (DR3), in combination with 2MASS, VHS DR6, VIKING DR5, AllWISE, and CatWISE2020, as well as parallaxes and proper motions from Gaia DR2 and eDR3. We report 142 newly discovered Southern QSOs at $3.8 80$ per cent complete for $M_{145}<-27.33$ ABmag at $z=4.7$ and for $M_{145}<-27.73$ ABmag at $z=5.4$. We derive the bright end of the QSO luminosity function at restframe 145 nm for $z=4.7-5.4$ and measure its slope to be $β= -3.60\pm0.37$ and $β= -3.38\pm0.32$ for two different estimates of the faint-end QSO density adopted from the literature. We also present the first $z\sim 5$ QSO luminosity function at restframe 300 nm.

astro-ph.CO↗

arXiv2021

Revisiting the Lensed Fraction of High-Redshift Quasars

The observed lensed fraction of high-redshift quasars $(\sim0.2\%)$ is significantly lower than previous theoretical predictions $(\gtrsim4\%)$. We revisit the lensed fraction of high-redshift quasars predicted by theoretical models, where we adopt recent measurements of galaxy velocity dispersion functions (VDFs) and explore a wide range of quasar luminosity function (QLF) parameters. We use both analytical methods and mock catalogs which give consistent results. For ordinary QLF parameters and the depth of current high-redshift quasar surveys $(m_z\lesssim22)$, our model suggests a multiply-imaged fraction of $F_\text{multi}\sim 0.4\%-0.8\%$. The predicted lensed fraction is $\sim1\%-6\%$ for the brightest $z_s\sim6$ quasars $(m_z\lesssim19)$, depending on the QLF. The systematic uncertainties of the predicted lensed fraction in previous models can be as large as $2-4$ times and are dominated by the VDF. Applying VDFs from recent measurements decreases the predicted lensed fraction and relieves the tension between observations and theoretical models. Given the depth of current imaging surveys, there are $\sim15$ lensed quasars at $z_s>5.5$ detectable over the sky. Upcoming sky surveys like the LSST survey and the {\em Euclid} survey will find several tens of lensed quasars at this redshift range.

astro-ph.GA↗

arXiv2021

The mass-metallicity relation at cosmic noon in overdense environments: first results from the MAMMOTH-Grism HST slitless spectroscopic survey

The MAMMOTH-Grism slitless spectroscopic survey is a Hubble Space Telescope (HST) cycle-28 medium program, which is obtaining 45 orbits of WFC3/IR grism spectroscopy in the density peak regions of three massive galaxy protoclusters at $z=2-3$ discovered using the MAMMOTH technique. We introduce this survey by presenting the first measurement of the mass-metallicity relation (MZR) at high redshift in overdense environments via grism spectroscopy. From the completed MAMMOTH-Grism observations in the field of the BOSS1244 protocluster at $z=2.24\pm0.02$, We secure a sample of 36 protocluster member galaxies at $z\sim2.24$, showing strong nebular emission lines ([O III], H$β$ and [O II]) in their G141 spectra. Using the multi-wavelength broad-band deep imaging from HST and ground-based telescopes, we measure their stellar masses in the range of $[10^{9},10^{10.4}]M_\odot$, instantaneous star formation rates (SFR) from 10 to 240$M_\odot yr^{-1}$, and global gas-phase metallicities [$\frac{1}{3}$,1] of solar. Compared with similarly selected field galaxy sample at the same redshift, our galaxies show on average increased SFRs by $\sim$0.06dex and $\sim$0.18dex at $\sim$10$^{10.1}M_\odot$ and $\sim$10$^{9.8}M_\odot$, respectively. Using the stacked spectra of our sample galaxies, we derive the MZR in the BOSS1244 protocluster core as $12+\log({\rm O/H})=(0.136\pm0.018)\times\log(M_\ast/M_\odot)+(7.082\pm0.175)$, showing significantly shallower slope than that in the field. This shallow MZR slope is likely caused by the combined effects of efficient recycling of feedback-driven winds and cold-mode gas accretion in protocluster environments. The former effect helps low-mass galaxies residing in overdensities retain their metal production, whereas the latter effect dilutes the metal content of high-mass galaxies, making them more metal poor than their coeval field counterparts.

astro-ph.GA↗

arXiv2021

Paving the Way for Euclid and JWST via Optimal Selection of High-z Quasars

We introduce a probabilistic approach to select 6 75% and an efficiency of >15% for selecting quasars at 6 7 from the entire sky, we select 5/6 or a completeness of ~80%.The failure to select the majority of 6<z<7 quasars arises because our model of quasar SEDs underestimates the scatter in the distribution of fluxes. This new optimal approach to quasar selection paves the way for efficient spectroscopic follow-up of Euclid quasar candidates with ground based telescopes and JWST.

astro-ph.GA↗

arXiv2021

Discovery of a protocluster core associated with an enormous Ly$α$ Nebula at $z = 2.3$

The MAMMOTH-1 nebula at $z=2.317$ is an enormous Ly$α$ nebula (ELAN) extending to a $\sim$440 kpc scale at the center of the extreme galaxy overdensity BOSS 1441. In this paper, we present observations of the $\rm CO(3-2)$ and 250 GHz dust-continuum emission from the MAMMOTH-1 using the IRAM NOrthern Extended Millimeter Array. Our observations show that $\rm CO(3-2)$ emission in this ELAN has not extended widespread emission into the circum- and inter-galactic media. We also find a remarkable concentration of six massive galaxies in $\rm CO(3-2)$ emission in the central $\sim$100 kpc region of the ELAN. Their velocity dispersions suggest a total halo mass of $M_{200c} \sim 10^{13.1} M_{\odot}$, marking a possible protocluster core associated with the ELAN. The peak position of the $\rm CO(3-2)$ line emission from the obscured AGN is consistent with the location of the intensity peak of MAMMOTH-1 in the rest-frame UV band. Its luminosity line ratio between the $\rm CO(3-2)$ and $\rm CO(1-0)$ $r_{3,1}$ is 0.61$\pm$0.17. The other five galaxies have $\rm CO(3-2)$ luminosities in the range of (2.1-7.1)$\times 10^9$ K $\rm km\,s^{-1}$ pc$^2$, with the star-formation rates derived from the 250GHz continuum of ($<$36)-224 $M_{\odot}$yr$^{-1}$. Follow-up spectroscopic observations will further confirm more member galaxies and improve the accuracy of the halo mass estimation.

astro-ph.GA↗