arXiv subjects

Renyue Cen

Publications and source records attributed to Renyue Cen.

At least 73 records · Page 4Linked to original sources

arXiv2020

Absorption line abundances in the SMC-like galaxy UGC 5282: evidence for ISM dilution from inflows on kiloparsec scales

We present an HST Cosmic Origins Spectrograph (COS) spectrum of the QSO SDSS J095109.12+330745.8 ($z_{em} = 0.645$) whose sightline passes through the SMC-like dwarf galaxy UGC 5282 ($M_B = -16.0$, $cz = 1577$ km s$^{-1}$ ), 1.2 kpc in projection from the central HII region of the galaxy. Damped Ly$α$ (DLA) absorption is detected at the redshift of UGC 5282 with $\log$[$N$(HI) cm$^{-2}\:$] = 20.89$^{+0.12}_{-0.21}\:\:$. Analysis of the accompanying SII, PII and OI metal lines yields a neutral gas metallicity, $Z_{HI}$, of [S/H] $\simeq$ [P/H] $= -0.80\pm0.24$. The metallicity of ionized gas from the central HII region, $Z_{HII}\:$, measured from its emission lines is [O/H]$= -0.37\pm0.10$, a difference of $+0.43\pm 0.26$ from $Z_{HI}\:$. This difference $δ$ is consistent with that seen towards HII regions in other star-forming galaxies and supports the idea that ionized gas near star forming regions shows systematically higher metallicities than exist in the rest of a galaxy's neutral interstellar medium (ISM). The positive values of $δ$ found in UGC 5282 (and the other star forming galaxies) is likely due to infalling low metallicity gas from the intergalactic medium that mixes with the galaxy's ISM on kpc scales. This model is also consistent with broad Ly$α$ emission detected at the bottom of the DLA absorption, offset by $\sim 125$ km s$^{-1}$ from the absorption velocity. Models of galaxy evolution that attempt to replicate population characteristics, such as the mass-metallicity relation, may need to start with a galaxy metallicity represented by $Z_{HI}$ rather than that measured traditionally from $Z_{HII}\:$.

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arXiv2020

Evidence for Infalling Gas in a Lyman-$α$ Blob

Lyman-$α$ blobs (LABs) are spatially extended nebulae of emission in the Ly$α$ line of hydrogen, seen at high redshifts$^{1,2}$, and most commonly found in the dense environment of star-forming galaxies$^{3,4}$. The origin of Ly$α$ emission in the LABs is still unclear and under debate$^{5}$. Proposed powering sources generally fall into two categories: (1) photoionization, galactic super-winds/outflows, resonant scattering of Ly$α$ photons from starbursts or active galactic nuclei (AGNs)$^{6,7,8,9,10}$ and (2) cooling radiation from cold streams of gas accreting onto galaxies$^{12}$. Here we analyze the gas kinematics within a LAB providing rare observational evidence for infalling gas. This is consistent with the release of gravitational accretion energy as cold streams radiate Ly$α$ photons. It also provides direct evidence for possible cold streams feeding the central galaxies. The infalling gas is not important by mass but hints at more than one mechanism to explain the origin of the extended Ly$α$ emission around young galaxies. It is also possible that the infalling gas may represent material falling back to the galaxy from where it originated, forming a galactic fountain.

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arXiv2020

The BUFFALO HST Survey

The Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) is a 101 orbit + 101 parallel Cycle 25 Hubble Space Telescope Treasury program taking data from 2018-2020. BUFFALO will expand existing coverage of the Hubble Frontier Fields (HFF) in WFC3/IR F105W, F125W, and F160W and ACS/WFC F606W and F814W around each of the six HFF clusters and flanking fields. This additional area has not been observed by HST but is already covered by deep multi-wavelength datasets, including Spitzer and Chandra. As with the original HFF program, BUFFALO is designed to take advantage of gravitational lensing from massive clusters to simultaneously find high-redshift galaxies which would otherwise lie below HST detection limits and model foreground clusters to study properties of dark matter and galaxy assembly. The expanded area will provide a first opportunity to study both cosmic variance at high redshift and galaxy assembly in the outskirts of the large HFF clusters. Five additional orbits are reserved for transient followup. BUFFALO data including mosaics, value-added catalogs and cluster mass distribution models will be released via MAST on a regular basis, as the observations and analysis are completed for the six individual clusters.

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arXiv2020

Physics of Prodigious Lyman Continuum Leakers

An analysis of the dynamics of a star formation event is performed. It is shown that galaxies able to drive leftover gas to sufficient altitudes in a few million years are characterized by two basic properties: small sizes (<1kpc) and high star formation rate surface densities (Sigma_SFR > 10 Msun/yr/kpc2). For the parameter space of relevance, the outflow is primarily driven by supernovae with radiation pressure being significant but subdominant. Our analysis provides the unifying physical origin for a diverse set of observed LyC leakers, including the green-peas galaxies, [SII]-weak galaxies, Lyman-alpha emitters, with these two characteristics as the common denominator. Among verifiable physical properties of LyC leakers, we predict that (1) the newly formed stellar masses are are typically in the range of 1e8-1e10 Msun, except perhaps ULIRGs, (2) the outflow velocities are typically in the range typically of 100-600km/s, but may exceed 1e3 km/s in ULIRGs, with a strong positive correlation between the stellar masses formed and the outflow velocities, (3) the overall escape fraction of galaxies is expected to increase with increasing redshift, given the cosmological trend that galaxies become denser and more compact with increasing redshift. In addition, two interesting by-product predictions are also borne out. First, ULIRGs appear to be in a parameter region where they should be prodigious LyC leakers, unless there is a large ram-pressure. Second, Lyman break galaxies (LBGs) are not supposed to be prodigious LyC leakers in our model, given their claimed effective radii exceeding 1kpc.

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arXiv2019

On Post-Starburst Galaxies Dominating Tidal Disruption Events

A starburst induced by a galaxy merger may create a relatively thin central stellar disk at radius $\le 100$pc. We calculate the rate of tidal disruption events (TDEs) by the inspiraling secondary supermassive black (SMBH) through the disk. With a small enough stellar velocity dispersion ($σ/v_c \le 0.1$) in the disk, it is shown that $10^5-10^6$ TDEs of solar-type main sequence stars per post-starburst galaxy (PSB) can be produced to explain their dominance in producing observed TDEs. Although the time it takes to bring the secondary SMBH to the disk apparently varies in the range of $\sim 0.1-1$Gyr since the starburst, depending on its landing location and subsequently due to dynamical friction with stars exterior to the central stellar disk in question, the vast majority of TDEs by the secondary SMBH in any individual PSB occurs within a space of time shorter than $\sim 30$Myr. Five unique testable predictions of this model are suggested.

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arXiv2019

Where do quasar hosts lie with respect to the size-mass relation of galaxies?

The evolution of the galaxy size - stellar mass (Mstellar) relation has been a puzzle for over a decade. High redshift galaxies are significantly more compact than galaxies observed today, at an equivalent mass, but how much of this apparent growth is driven by progenitor bias, minor mergers, secular processes, or feedback from AGN is unclear. To help disentangle the physical mechanisms at work by addressing the latter, we study the galaxy size - Mstellar relation of 32 carefully-selected broad-line AGN hosts at 1.2 < z < 1.7 (7.5 < log M_BH < 8.5; L_bol/L_Edd > 0.1). Using HST with multi-band photometry and state-of-the-art modeling techniques, we measure half-light radii while accounting for uncertainties from subtracting bright central point sources. We find AGN hosts to have sizes ranging from 1 to 6 kpc at Mstellar ~ 0.3 - 1 x 10^11 Msun. Thus, many hosts have intermediate sizes as compared to equal-mass star-forming and quiescent galaxies. While inconsistent with the idea that AGN feedback may induce an increase in galaxy sizes, this finding is consistent with hypotheses in which AGNs preferentially occur in systems with prior concentrated gas reservoirs, or are involved in secular compaction processes perhaps responsible for simultaneously building bulges and shutting down star formation. If driven by minor mergers, which do not grow central black holes as fast as they do bulge-like stellar structures, such a process would explain both the galaxy size - mass relation observed here and the evolution in the black hole, bulge mass relation described in a companion paper.

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arXiv2019

The Physical Origins of the Identified and Still Missing Components of the Warm-Hot Intergalactic Medium: Insights from Deep Surveys in the Field of Blazar 1ES1553+113

The relationship between galaxies and the state/chemical enrichment of the warm-hot intergalactic medium (WHIM) expected to dominate the baryon budget at low-z provides sensitive constraints on structure formation and galaxy evolution models. We present a deep redshift survey in the field of 1ES1553+113, a blazar with a unique combination of UV+X-ray spectra for surveys of the circum-/intergalactic medium (CGM/IGM). Nicastro et al. 2018 reported the detection of two O VII WHIM absorbers at $z=0.4339$ and $0.3551$ in its spectrum, suggesting that the WHIM is metal-rich and sufficient to close the missing baryons problem. Our survey indicates that the blazar is a member of a $z=0.433$ group and that the higher-$z$ O VII candidate arises from its intragroup medium. The resulting bias precludes its use in baryon censuses. The $z=0.3551$ candidate occurs in an isolated environment 630 kpc from the nearest galaxy (with stellar mass $\log M_*/M_\odot \approx 9.7$) which we show is unexpected for the WHIM. Finally, we characterize the galactic environments of broad H I Ly$α$ absorbers (Doppler widths of $b=40-80$ \kms; $T\lesssim4\times10^5$ K) which provide metallicity independent WHIM probes. On average, broad Ly$α$, absorbers are ${\approx}2\times$ closer to the nearest luminous ($L>0.25 L_*$) galaxy (700 kpc) than narrow ($b<30$ \kms; $T\lesssim4\times10^5$ K) ones (1300 kpc) but ${\approx}2\times$ further than O\,VI absorbers (350 kpc). These observations suggest that gravitational collapse heats portions of the IGM to form the WHIM but with feedback that does not enrich the IGM far beyond galaxy/group halos to levels currently observable in UV/X-ray metal lines.

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arXiv2019

Ly$α$ view around a z=2.84 hyperluminous QSO at a node of the cosmic web

We report on the results of deep and wide-field (1.1 deg$^2$) narrow-band observations with Subaru/Hyper Suprime-Cam (HSC) of a field around a hyperluminous QSO (HLQSO), HS1549+1919, residing in a protocluster at $z=2.84$, to map the large-scale structure of Ly$α$ emitters (LAEs). One HSC pointing enables us to detect 3490 LAEs and 76 extended Ly$α$ blobs (LABs), probing diverse environments from voids to protoclusters. The HLQSO is found to be near the center of the protocluster, which corresponds to the intersection of $\sim$100 cMpc-scale structures of LAEs. LABs are basically distributed along the large-scale structure, with larger ones particularly clustered around the HLQSO, confirming a previously noted tendency of LABs to prefer denser environments. Moreover, the shapes of LABs near the HLQSO appear to be aligned with the large-scale structure. Finally, a deep Ly$α$ image reveals a diffuse Ly$α$ nebula along a filamentary structure with no luminous UV/sub-mm counterpart. We suggest that the diffuse nebula is due to a cold filament with high clumping factor illuminated by the QSO, with a required high clumpiness provided by unresolved residing halos of mass $\leq 10^{9-10}M_\odot$.

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arXiv2019

CDIM: Cosmic Dawn Intensity Mapper Final Report

The Cosmic Dawn Intensity Mapper (CDIM) will transform our understanding of the era of reionization when the Universe formed the first stars and galaxies, and UV photons ionized the neutral medium. CDIM goes beyond the capabilities of upcoming facilities by carrying out wide area spectro-imaging surveys, providing redshifts of galaxies and quasars during reionization as well as spectral lines that carry crucial information on their physical properties. CDIM will make use of unprecedented sensitivity to surface brightness to measure the intensity fluctuations of reionization on large-scales to provide a valuable and complementary dataset to 21-cm experiments. The baseline mission concept is an 83-cm infrared telescope equipped with a focal plane of 24 \times 20482 detectors capable of R = 300 spectro-imaging observations over the wavelength range of 0.75 to 7.5 μm using Linear Variable Filters (LVFs). CDIM provides a large field of view of 7.8 deg2 allowing efficient wide area surveys, and instead of moving instrumental components, spectroscopic mapping is obtained through a shift-and-stare strategy through spacecraft operations. CDIM design and capabilities focus on the needs of detecting faint galaxies and quasars during reionization and intensity fluctuation measurements of key spectral lines, including Lyman-α and Hα radiation from the first stars and galaxies. The design is low risk, carries significant science and engineering margins, and makes use of technologies with high technical readiness level for space observations.

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arXiv2019

SCORCH. II. Radiation-Hydrodynamic simulations of reionization with varying radiation escape fractions

In the Simulations and Constructions of the Reionization of Cosmic Hydrogen (SCORCH) project, we present new radiation-hydrodynamic simulations with updated high-redshift galaxy populations and varying radiation escape fractions. The simulations are designed to have fixed Thomson optical depth $τ\approx 0.06$, consistent with recent Planck observations, and similar midpoints of reionization $7.5 \lesssim z \lesssim 8.0$, but with different ionization histories. The galaxy luminosity functions and ionizing photon production rates in our model are in good agreement with recent HST observations. Adopting a power-law form for the radiation escape fraction $f_{\text{esc}}(z) = f_8[(1+z)/9]^{a_{8}}$, we simulate the cases for $a_8 = 0$, 1, and 2 and find $a_8 \lesssim 2$ in order to end reionization in the range $5.5 \lesssim z \lesssim 6.5$ to be consistent with Lyman alpha forest observations. At fixed $τ$ and as the power-law slope $a_8$ increases, the reionization process starts earlier but ends later with a longer duration $Δz$ and the decreased redshift asymmetry $Az$. We find a range of durations $3.9 \lesssim Δz \lesssim 4.6$ that is currently in tension with the upper limit $Δz < 2.8$ inferred from a recent joint analysis of Planck and South Pole Telescope observations.

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arXiv2019

On the Assembly Bias of Cool Core Clusters Traced by H$α$ Nebulae

Do cool-core (CC) and noncool-core (NCC) clusters live in different environments? We make novel use of H$α$ emission lines in the central galaxies of redMaPPer clusters as proxies to construct large (1,000's) samples of CC and NCC clusters, and measure their relative assembly bias using both clustering and weak lensing. We increase the statistical significance of the bias measurements from clustering by cross-correlating the clusters with an external galaxy redshift catalog from the Sloan Digital Sky Survey III, the LOWZ sample. Our cross-correlations can constrain assembly bias up to a statistical uncertainty of 6%. Given our H$α$ criteria for CC and NCC, we find no significant differences in their clustering amplitude. Interpreting this difference as the absence of halo assembly bias, our results rule out the possibility of having different large-scale (tens of Mpc) environments as the source of diversity observed in cluster cores. Combined with recent observations of the overall mild evolution of CC and NCC properties, such as central density and CC fraction, this would suggest that either the cooling properties of the cluster core are determined early on solely by the local (<200 kpc) gas properties at formation or that local merging leads to stochastic CC relaxation and disruption in a periodic way, preserving the average population properties over time. Studying the small-scale clustering in clusters at high redshift would help shed light on the exact scenario.

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arXiv2018

Influence of the Void Environment on Chemical Abundances in Dwarf Galaxies and Implications for Connecting Star Formation and Halo Mass

We study how the void environment affects galactic chemical evolution by comparing the oxygen and nitrogen abundances of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from SDSS DR7, we estimate oxygen, nitrogen, and neon abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. A substitute for the [OII] 3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the Direct Te method. We find that void dwarf galaxies have about the same oxygen abundance and Ne/O ratio, slightly higher neon abundances, and slightly lower nitrogen abundance and N/O ratio than dwarf galaxies in denser environments. We conclude that the void environment has a slight influence on dwarf galaxy chemical evolution. Our mass-N/O relationship shows that the secondary production of nitrogen commences at a lower stellar mass in void dwarf galaxies than in dwarf galaxies in denser environments. Our dwarf galaxy sample demonstrates a strong anti-correlation between the sSFR and N/O ratio, providing evidence that oxygen is produced in higher mass stars than those which synthesize nitrogen. The lower N/O ratios and smaller stellar mass for secondary nitrogen production seen in void dwarf galaxies may indicate both delayed star formation and a dependence of cosmic downsizing on the large-scale environment. A shift toward slightly higher oxygen abundances in void dwarf galaxies could be evidence of larger ratios of dark matter halo mass to stellar mass in voids than in denser regions.

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arXiv2017

The most ancient spiral galaxy: a 2.6-Gyr-old disk with a tranquil velocity field

We report an integral-field spectroscopic (IFS) observation of a gravitationally lensed spiral galaxy A1689B11 at redshift $z=2.54$. It is the most ancient spiral galaxy discovered to date and the second kinematically confirmed spiral at $z\gtrsim2$. Thanks to gravitational lensing, this is also by far the deepest IFS observation with the highest spatial resolution ($\sim$ 400 pc) on a spiral galaxy at a cosmic time when the Hubble sequence is about to emerge. After correcting for a lensing magnification of 7.2 $\pm$ 0.8, this primitive spiral disk has an intrinsic star formation rate of 22 $\pm$ 2 $M_{\odot}$ yr$^{-1}$, a stellar mass of 10$^{9.8 \pm 0.3}$$M_{\odot}$ and a half-light radius of $r_{1/2}=2.6 \pm 0.7$ kpc, typical of a main-sequence star-forming (SF) galaxy at $z\sim2$. However, the Hα kinematics show a surprisingly tranquil velocity field with an ordered rotation ($V_{\rm c}$ = 200 $\pm$ 12 km/s) and uniformly small velocity dispersions ($V_{\rm σ, mean}$ = 23 $\pm$ 4 km/s and $V_{\rm σ, outer-disk}$ = 15 $\pm$ 2 km/s). The low gas velocity dispersion is similar to local spiral galaxies and is consistent with the classic density wave theory where spiral arms form in dynamically cold and thin disks. We speculate that A1689B11 belongs to a population of rare spiral galaxies at $z\gtrsim2$ that mark the formation epoch of thin disks. Future observations with JWST will greatly increase the sample of these rare galaxies and unveil the earliest onset of spiral arms.

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arXiv2017

Helium Reionization Simulations. II. Signatures of Quasar Activity on the IGM

We have run a new suite of simulations that solve hydrodynamics and radiative transfer simultaneously to study helium II reionization. Our suite of simulations employs various models for populating quasars inside of dark matter halos, which affect the He II reionization history. In particular, we are able to explore the impact that differences in the timing and duration of reionization have on observables. We examine the thermal signature that reionization leaves on the IGM, and measure the temperature-density relation. As previous studies have shown, we confirm that the photoheating feedback from helium II reionization raises the temperature of the IGM by several thousand kelvin. To compare against observations, we generate synthetic Ly$α$ forest sightlines on-the-fly and match the observed effective optical depth $τ_{\mathrm{eff}}(z)$ of hydrogen to recent observations. We show that when the simulations have been normalized to have the same values of $τ_\mathrm{eff}$, the effect that helium II reionization has on observations of the hydrogen Ly$α$ forest is minimal. Specifically, the flux PDF and the one-dimensional power spectrum are sensitive to the thermal state of the IGM, but do not show direct evidence for the ionization state of helium. We show that the peak temperature of the IGM typically corresponds to the time of 90%-95% helium ionization by volume, and is a relatively robust indicator of the timing of reionization. Future observations of helium reionization from the hydrogen Ly$α$ forest should thus focus on measuring the temperature of the IGM, especially at mean density. Detecting the peak in the IGM temperature would provide valuable information about the timing of the end of helium II reionization.

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arXiv2017

Helium Reionization Simulations. III. The Helium Lyman-$α$ Forest

In La Plante et al. (2017), we presented a new suite of hydrodynamic simulations with the aim of accurately capturing the process of helium II reionization. In this paper, we discuss the observational signatures present in the He II Ly$α$ forest. We show that the effective optical depth of the volume $τ_\mathrm{eff}$ is not sufficient for capturing the ionization state of helium II, due to the large variance inherent in sightlines. However, the He II flux PDF can be used to determine the timing of helium II reionization. The amplitude of the one-dimensional flux power spectrum can also determine the ionization state of helium II. We show that even given the currently limited number of observations ($\sim$50 sightlines), measurements of the flux PDF can yield information about helium II reionization. Further, measurements using the one-dimensional power spectrum can provide clear indications of the timing of reionization, as well as the relative bias of sources of ionizing radiation.

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arXiv2017

Probing the Dependence of the Intergalactic Medium on Large Scale Environment Using the Low Redshift Lyman Alpha Forest

We examine the statistics of the low-redshift Ly-alpha forest in an adaptive mesh refinement hydrodynamic cosmological simulation of sufficient volume to include distinct large-scale environments. We compare our HI column density distribution of absorbers both with recent work and between two highly-refined regions of our simulation: a large-scale overdensity and a large-scale underdensity (on scales of approximately 20 Mpc). We recover the average results presented in Kollmeier et al. (2014) using different simulation methods. We further break down these results as a function of environment to examine the detailed dependence of absorber statistics on large-scale density. We find that the slope of the HI column density distribution in the 10$^{12.5}$ $\le$ N$_{HI}$/cm$^{-2}$ $\le$ 10$^{14.5}$ range depends on environment such that the slope becomes steeper for higher environmental density, and this difference reflects distinct physical conditions of the intergalactic medium on these scales. We track this difference to the different temperature structures of filaments in varying environments. Specifically, filaments in the overdensity are hotter and, correspondingly, are composed of gas with lower HI fractions than those in underdense environments. Our results highlight that in order to understand the physics driving the HI CDD, we need not only improved accounting of the sources of ionizing UV photons, but also of the physical conditions of the IGM and how this may vary as a function of large-scale environment.

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arXiv2017

Quenching Global Star Formation: Dominance of Gravitational Shock Heating at z<2

We systematically study, in the context of the standard cold dark matter model, star-formation suppression effects of two important known physical processes---photoheating due to reionization of the intergalactic medium and gravitational shock heating due to formation of massive halos and large-scale structure---on the global evolution of star formation rate (SFR) density and the so-called cosmic downsizing phenomenon in the redshift range z=0-6. We show that the steep decline of cosmic SFR density from z~2 to z=0 can be primarily explained by gravitational shock heating in two forms: massive halo self-quenching and hot environment. Simultaneously, we show a decreasing trend in the average SFR of star-forming galaxies from z=2 to z=0, reproducing the observed cosmic downsizing at z<2. Nevertheless, the average halo mass of star-forming galaxies is found to continue upsizing from z=2 to z=0. In stark contrast to z<2, both photoheating and gravitational shock heating effects are found to play a minor role in suppressing star formation. Additional negative feedback effects are required to reconcile our model with observations at z>2. Internal feedback from stellar evolution and supermassive black hole growth are the natural candidates for this role, as galaxies at z>2 are more moderate in mass but stronger in star formation and are thus more vulnerable. Our physical model can be used to treat star formation in cosmological N-body simulations.

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arXiv2017

Testing the Large-Scale Environments of Cool-core and Noncool-core Clusters with Clustering Bias

There are well-observed differences between cool-core (CC) and non-cool-core (NCC) clusters, but the origin of this distinction is still largely unknown. Competing theories can be divided into internal (inside-out), in which internal physical processes transform or maintain the NCC phase, and external (outside-in), in which the cluster type is determined by its initial conditions, which in turn lead to different formation histories (i.e., assembly bias). We propose a new method that uses the relative assembly bias of CC to NCC clusters, as determined via the two-point cluster-galaxy cross-correlation function (CCF), to test whether formation history plays a role in determining their nature. We apply our method to 48 ACCEPT clusters, which have well resolved central entropies, and cross-correlate with the SDSS-III/BOSS LOWZ galaxy catalog. We find that the relative bias of NCC over CC clusters is $b = 1.42 \pm 0.35$ ($1.6σ$ different from unity). Our measurement is limited by the small number of clusters with core entropy information within the BOSS footprint, 14 CC and 34 NCC. Future compilations of X-ray cluster samples, combined with deep all-sky redshift surveys, will be able to better constrain the relative assembly bias of CC and NCC clusters and determine the origin of the bimodality.

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