arXiv subjects

Gwen C. Rudie

Publications and source records attributed to Gwen C. Rudie.

At least 55 records · Page 3Linked to original sources

arXiv2023

LATIS: Constraints on the Galaxy-halo Connection at $z \sim 2.5$ from Galaxy-galaxy and Galaxy-Ly$α$ Clustering

The connection between galaxies and dark matter halos is often quantified using the stellar mass-halo mass (SMHM) relation. Optical and near-infrared imaging surveys have led to a broadly consistent picture of the evolving SMHM relation based on measurements of galaxy abundances and angular correlation functions. Spectroscopic surveys at $z \gtrsim 2$ can also constrain the SMHM relation via the galaxy autocorrelation function and through the cross-correlation between galaxies and Ly$α$ absorption measured in transverse sightlines; however, such studies are very few and have produced some unexpected or inconclusive results. We use $\sim$3000 spectra of $z\sim2.5$ galaxies from the Lyman-alpha Tomography IMACS Survey (LATIS) to measure the galaxy-galaxy and galaxy-Ly$α$ correlation functions in four bins of stellar mass spanning $10^{9.2} \lesssim M_* / M_{\odot} \lesssim 10^{10.5}$. Parallel analyses of the MultiDark N-body and ASTRID hydrodynamic cosmological simulations allow us to model the correlation functions, estimate covariance matrices, and infer halo masses. We find that results of the two methods are mutually consistent and are broadly in accord with standard SMHM relations. This consistency demonstrates that we are able to accurately measure and model Ly$α$ transmission fluctuations $δ_F$ in LATIS. We also show that the galaxy-Ly$α$ cross-correlation, a free byproduct of optical spectroscopic galaxy surveys at these redshifts, can constrain halo masses with similar precision to galaxy-galaxy clustering.

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arXiv2023

The first comprehensive study of a giant nebula around a radio-quiet quasar in the $z < 1$ Universe

We present the first comprehensive study of a giant, $\approx \! \! 70$ kpc-scale nebula around a radio-quiet quasar at $z<1$. The analysis is based on deep integral field spectroscopy with MUSE of the field of HE$\,$0238$-$1904, a luminous quasar at $z=0.6282$. The nebula emits strongly in $\mathrm{[O \, II]}$, $\rm H β$, and $\mathrm{[O \, III]}$, and the quasar resides in an unusually overdense environment for a radio-quiet system. The environment likely consists of two groups which may be merging, and in total have an estimated dynamical mass of $M_{\rm dyn}\approx 4\times 10^{13}$ to $10^{14}\ {\rm M_\odot}$. The nebula exhibits largely quiescent kinematics and irregular morphology. The nebula may arise primarily through interaction-related stripping of circumgalactic and interstellar medium (CGM/ISM) of group members, with some potential contributions from quasar outflows. The simultaneous presence of the giant nebula and a radio-quiet quasar in a rich environment suggests a correlation between such circum-quasar nebulae and environmental effects. This possibility can be tested with larger samples. The upper limits on the electron number density implied by the $\mathrm{[O \, II]}$ doublet ratio range from $\log(n_{\rm e, \, [O \, II]} / \mathrm{cm^{-3}}) < 1.2$ to $2.8$. However, assuming a constant quasar luminosity and negligible projection effects, the densities implied from the measured line ratios between different ions (e.g., $\mathrm{[O\,II]}$, $\mathrm{[O\,III]}$, and $\mathrm{[Ne\,V]}$) and photoionization simulations are often $10{-}400$ times larger. This large discrepancy can be explained by quasar variability on a timescale of $\approx 10^4{-}10^5$ years.

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arXiv2023

LATIS: The Stellar Mass-Metallicity Relation of Star-forming Galaxies at $z\sim 2.5$

We present the stellar mass - stellar metallicity relation for 3491 star-forming galaxies at $2 \lesssim z \lesssim 3$ using rest-frame far-ultraviolet (FUV) spectra from the Ly$α$ Tomography IMACS Survey (LATIS). We fit stellar population synthesis models from the Binary Population And Spectral Synthesis code (BPASS v$2.2.1$) to medium resolution (R $\sim 1000$) and high signal-to-noise ($>30$ per 100 km/s over a wavelength range of 1221 - 1800 Å) composite spectra of galaxies in bins of stellar mass to determine their stellar metallicity, primarily tracing $\rm Fe/H$. We find a strong correlation between stellar mass and stellar metallicity, with stellar metallicity monotonically increasing with stellar mass at low masses and flattening at high masses ($M_* \gtrsim 10^{10.3} M_\odot$). Additionally, we compare our stellar metallicity measurements with the gas-phase oxygen abundance of galaxies at similar redshift and estimate the average $\rm [α/Fe] \sim 0.6$. Such high $α$-enhancement indicates that high-redshift galaxies have not yet undergone significant iron enrichment through Type Ia supernovae. Moreover, we utilize an analytic chemical evolution model to constrain the mass loading parameter of galactic winds as a function of stellar mass. We find that as the stellar mass increases, the mass loading parameter decreases. The parameter then flattens or reaches a turning point at around $M_* \sim 10^{10.5} M_\odot$. Our findings may signal the onset of black hole-driven outflows at $z \sim 2.5$ for galaxies with $M_* \gtrsim 10^{10.5} M_\odot$.

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arXiv2023

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshift z~0.4-1. Through spectrally-resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small as l_cl~1 pc and density lower than nH = 0.001 cm^-3 are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperature T and the non-thermal motions bNT, independent of the ionization models. On average, bNT is found to increase with l_cl following bNT \propto l_cl^0.3 over three decades in spatial scale from l_cl~1 pc to l_cl~1 kpc. Attributing the observed bNT to turbulent motions internal to the clumps, the best-fit bNT-l_cl relation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass of epsilon~0.003 cm^2 s^-3 and a dissipation time scale of <~ 100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferred epsilon is comparable to what is found in CIV absorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.

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arXiv2023

The Cosmic Ultraviolet Baryon Survey (CUBS) VI: Connecting Physical Properties of the Cool Circumgalactic Medium to Galaxies at $z\approx 1$

This paper presents a new sample of 19 unique galaxies and galaxy groups at $z\approx1$ from the CUBS program, which is designated as the CUBSz1 sample. In this CUBSz1 sample, nine galaxies or galaxy groups show absorption features, while ten systems do not have detectable absorption with 2-$σ$ upper limits of log$N$(HeI)/cm$^{-2}\lesssim 13.5$ and log$N$(OV)/cm$^{-2}\lesssim 13.3$. Environmental properties of the galaxies, including galaxy overdensities, the total stellar mass and gravitational potential summed over all nearby neighbors, and the presence of local ionizing sources, are found to have a significant impact on the observed CGM absorption properties. Specifically, massive galaxies and galaxies in overdense regions exhibit a higher rate of incidence of absorption. At the same time, the observed CGM absorption properties in galaxy groups appear to be driven by the galaxy closest to the QSO sightline, rather than by the most massive galaxy or by mass-weighted properties. We introduce a total projected gravitational potential $ψ$, defined as $-ψ/G =\sum M_{\rm halo}/d_{\rm proj}$ summed over all group members, to characterize the overall galaxy environment. This projected gravitational potential correlates linearly with the maximum density detected in each sightline, consistent with higher-pressure gas being confined in deeper gravitational potential wells. In addition, we find that the radial profile of cool gas density exhibits a general decline from the inner regions to the outskirts, being in pressure balance with the hot halo. Finally, we note that the ionizing flux from nearby galaxies can generate an elevated $N$(HI)/$N$(HeI) ratio, which in turn provides a unique diagnostic of possible local sources contributing to the ionizing radiation field.

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arXiv2023

GN-z11 in context: possible signatures of globular cluster precursors at redshift 10

The first JWST spectroscopy of the luminous galaxy GN-z11 simultaneously both established its redshift at $z=10.6$ and revealed a rest-ultraviolet spectrum dominated by signatures of highly-ionized nitrogen, which has so far defied clear interpretation. Here we present a reappraisal of this spectrum in the context of both detailed nebular modeling and nearby metal-poor reference galaxies. The N IV] emission enables the first nebular density measurement in a star-forming galaxy at $z>10$, and reveals evidence for extremely high densities $n_e\gtrsim 10^5$ $\mathrm{cm^{-3}}$. We definitively establish with a suite of photoionization models that regardless of ionization mechanism and accounting for depletion and this density enhancement, an ISM substantially enriched in nitrogen ($[\mathrm{N/O}]=+0.52$) is required to reproduce the observed lines. A search of local UV databases confirms that nearby metal-poor galaxies power N IV] emission, but that this emission is uniformly associated with lower densities than implied in GN-z11. We compare to a unique nearby galaxy, Mrk~996, where a high concentration of Wolf-Rayet stars and their CNO-processed wind ejecta produce a UV spectrum remarkably similar to that of both GN-z11 and the Lyc-leaking super star cluster in the Sunburst Arc. Collating this evidence in the context of Galactic stellar abundances, we suggest that the peculiar nitrogenic features prominent in GN-z11 may be a unique signature of intense and densely clustered star formation in the evolutionary chain of the present-day globular clusters, consistent with in-situ early enrichment with nuclear-processed stellar ejecta on a massive scale. Combined with insight from local galaxies, these and future JWST data open a powerful new window onto the physical conditions of star formation and chemical enrichment at the highest redshifts.

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arXiv2022

Directly tracing cool filamentary accretion over >100 kpc into the interstellar medium of a quasar host at z=1

We report the discovery of giant (50-100 kpc) [O II] emitting nebulae with the Multi-Unit Spectroscopic Explorer (MUSE) in the field of TXS 0206-048, a luminous quasar at z=1.13. Down-the-barrel UV spectra of the quasar show absorption at velocities coincident with those of the extended nebulae, enabling new insights into inflows and outflows around the quasar host. One nebula exhibits a filamentary morphology extending over 120 kpc from the halo toward the quasar and intersecting with another nebula surrounding the quasar host with a radius of 50 kpc. This is the longest cool filament observed to-date and arises at higher redshift and in a less massive system than those in cool-core clusters. The filamentary nebula has line-of-sight velocities >300 km/s from nearby galaxies but matches that of the nebula surrounding the quasar host where they intersect, consistent with accretion of cool inter- or circum-galactic medium or cooling hot halo gas. The kinematics of the nebulae surrounding the quasar host are unusual and complex, with redshifted and blueshifted spiral-like structures. The emission velocities at 5-10 kpc from the quasar match those of inflowing absorbing gas observed in UV spectra of the quasar. Together, the extended nebulae and associated redshifted absorption represent a compelling case of cool, filamentary gas accretion from halo scales into the extended interstellar medium and toward the nucleus of a massive quasar host. The inflow rate implied by the combined emission and absorption constraints is well below levels required to sustain the quasar's radiative luminosity, suggesting anisotropic or variable accretion.

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arXiv2022

Empirical constraints on the turbulence in QSO host nebulae from velocity structure function measurements

We present the first empirical constraints on the turbulent velocity field of the diffuse circumgalactic medium around four luminous QSOs at $z\!\approx\!0.5$--1.1. Spatially extended nebulae of $\approx\!50$--100 physical kpc in diameter centered on the QSOs are revealed in [OII]$λλ\,3727,3729$ and/or [OIII]$λ\,5008$ emission lines in integral field spectroscopic observations obtained using MUSE on the VLT. We measure the second- and third-order velocity structure functions (VSFs) over a range of scales, from $\lesssim\!5$ kpc to $\approx\!20$--50 kpc, to quantify the turbulent energy transfer between different scales in these nebulae. While no constraints on the energy injection and dissipation scales can be obtained from the current data, we show that robust constraints on the power-law slope of the VSFs can be determined after accounting for the effects of atmospheric seeing, spatial smoothing, and large-scale bulk flows. Out of the four QSO nebulae studied, one exhibits VSFs in spectacular agreement with the Kolmogorov law, expected for isotropic, homogeneous, and incompressible turbulent flows. The other three fields exhibit a shallower decline in the VSFs from large to small scales. However, with a limited dynamic range in the spatial scales in seeing-limited data, no constraints can be obtained for the VSF slopes of these three nebulae. For the QSO nebula consistent with the Kolmogorov law, we determine a turbulence energy cascade rate of $\approx\!0.2$ cm$^{2}$ s$^{-3}$. We discuss the implication of the observed VSFs in the context of QSO feeding and feedback in the circumgalactic medium.

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arXiv2022

The connection between the escape of ionizing radiation and galaxy properties at z~3 in the Keck Lyman Continuum Spectroscopic Survey

The connection between the escape fraction of ionizing radiation ($f_{esc}$) and the properties of galaxies, such as stellar mass (M*), age, star-formation rate (SFR), and dust content, are key inputs for reionization models, but many of these relationships remain untested at high redshift. We present an analysis of a sample of 96 z~3 galaxies from the Keck Lyman Continuum Spectroscopic Survey (KLCS). These galaxies have both sensitive Keck/LRIS spectroscopic measurements of the Lyman continuum (LyC) region, and multi-band photometry that places constraints on stellar population parameters. We construct composite spectra from subsamples binned as a function of galaxy property and quantify the ionizing-photon escape for each composite. We find a significant anti-correlation between $f_{esc}$ and M*, consistent with predictions from cosmological zoom-in simulations. We also find significant anti-correlation between $f_{esc}$ and E(B-V), encoding the underlying physics of LyC escape in our sample. We also find no significant correlation between $f_{esc}$ and either stellar age or specific SFR (=SFR/M*), challenging interpretations that synchronize recent star formation and favorable conditions for ionizing escape. The galaxy properties now shown to correlate with $f_{esc}$ in the KLCS are Ly$α$ equivalent width, UV Luminosity, M*, SFR, and E(B-V), but not age or sSFR. To date, this is the most comprehensive analysis of galaxy properties and LyC escape at high redshift, and will be used to guide future models and observations of the reionization epoch.

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arXiv2022

The Cosmic Ultraviolet Baryon Survey (CUBS) V: On the Thermodynamic Properties of the Cool Circumgalactic Medium at $z < 1$

This paper presents a systematic study of the photoionization and thermodynamic properties of the cool circumgalactic medium (CGM) as traced by rest-frame ultraviolet absorption lines around 26 galaxies at redshift $z\lesssim1$. The study utilizes both high-quality far-ultraviolet and optical spectra of background QSOs and deep galaxy redshift surveys to characterize the gas density, temperature, and pressure of individual absorbing components and to resolve their internal non-thermal motions. The derived gas density spans more than three decades, from $\log (n_{\rm H}/{\rm cm^{-3}}) \approx -4$ to $-1$, while the temperature of the gas is confined in a narrow range of $\log (T/{\rm K})\approx 4.3\pm 0.3$. In addition, a weak anti-correlation between gas density and temperature is observed, consistent with the expectation of the gas being in photoionization equilibrium. Furthermore, decomposing the observed line widths into thermal and non-thermal contributions reveals that more than 30% of the components at $z\lesssim 1$ exhibit line widths driven by non-thermal motions, in comparison to $<20$% found at $z\approx 2$-3. Attributing the observed non-thermal line widths to intra-clump turbulence, we find that massive quenched galaxies on average exhibit higher non-thermal broadening/turbulent energy in their CGM compared to star-forming galaxies at $z\lesssim 1$. Finally, strong absorption features from multiple ions covering a wide range of ionization energy (e.g., from Mg II to O IV) can be present simultaneously in a single absorption system with kinematically aligned component structure, but the inferred pressure in different phases may differ by a factor of $\approx 10$.

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arXiv2022

A population of ultraviolet-dim protoclusters detected in absorption

Galaxy protoclusters, which will eventually grow into the massive clusters we see in the local universe, are usually traced by locating overdensities of galaxies. Large spectroscopic surveys of distant galaxies now exist, but their sensitivity depends mainly on a galaxy's star formation activity and dust content rather than its mass. Tracers of massive protoclusters that do not rely on their galaxy constituents are therefore needed. Here we report observations of Lyman-$α$ absorption in the spectra of a dense grid of background galaxies, which we use to locate a substantial number of candidate protoclusters at redshifts 2.2-2.8 via their intergalactic gas. We find that the structures producing the most absorption, most of which were previously unknown, contain surprisingly few galaxies compared to the dark matter content of their analogs in cosmological simulations. Nearly all are expected to be protoclusters, and we infer that half of their expected galaxy members are missing from our survey because they are unusually dim at rest-frame ultraviolet wavelengths. We attribute this to an unexpectedly strong and early influence of the protocluster environment on the evolution of these galaxies that reduced their star formation or increased their dust content.

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arXiv2022

Reconciling the Results of the z~2 MOSDEF and KBSS-MOSFIRE Surveys

The combination of the MOSDEF and KBSS-MOSFIRE surveys represents the largest joint investment of Keck/MOSFIRE time to date, with ~3000 galaxies at 1.4<=z<=3.8, roughly half of which are at z~2. MOSDEF is photometric- and spectroscopic-redshift selected with a rest-optical magnitude limit, while KBSS-MOSFIRE is primarily selected based on rest-UV colors and a rest-UV magnitude limit. Analyzing both surveys in a uniform manner with consistent spectral-energy-distribution (SED) models, we find that the MOSDEF z~2 targeted sample has a higher median M_* and redder rest U-V color than the KBSS-MOSFIRE z~2 targeted sample, and a smaller median SED-based SFR and sSFR (SFR(SED) and sSFR(SED)). Specifically, MOSDEF targeted a larger population of red galaxies with U-V and V-J >=1.25, while KBSS-MOSFIRE contains more young galaxies with intense star formation. Despite these differences in the z~2 targeted samples, the subsets of the surveys with multiple emission lines detected and analyzed in previously published work are much more similar. All median host-galaxy properties with the exception of stellar population age -- i.e., M_*, SFR(SED), sSFR(SED), A_V, and UVJ colors -- agree within the uncertainties. Additionally, when uniform emission-line fitting and stellar Balmer absorption correction techniques are applied, there is no significant offset between the two samples in the [OIII]$λ$5008/H$β$ vs. [NII]$λ$6585/H$α$ diagnostic diagram, in contrast to previously-reported discrepancies. We can now combine the MOSDEF and KBSS-MOSFIRE surveys to form the largest z~2 sample with moderate-resolution rest-optical spectra and construct the fundamental scaling relations of star-forming galaxies during this important epoch.

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arXiv2022

Characterizing Protoclusters and Protogroups at z $\sim$ 2.5 Using Ly$α$ Tomography

Ly-$α$ tomography surveys have begun to produce three-dimensional (3D) maps of the intergalactic medium (IGM) opacity at $z \sim 2.5$ with Mpc resolution. These surveys provide an exciting new way to discover and characterize high-redshift overdensities, including the progenitors of today's massive groups and clusters of galaxies, known as protogroups and protoclusters. We use the IllustrisTNG-$300$ hydrodynamical simulation to build mock maps that realistically mimic those observed in the Ly-$α$ Tomographic IMACS Survey (LATIS). We introduce a novel method for delineating the boundaries of structures detected in 3D Ly-$α$ flux maps by applying the watershed algorithm. We provide estimators for the dark matter masses of these structures (at $z\sim2.5$), their descendant halo masses at $z=0$, and the corresponding uncertainties. We also investigate the completeness of this method for the detection of protogroups and protoclusters. Compared to earlier work, we apply and characterize our method over a wider mass range that extends to massive protogroups. We also assess the widely used fluctuating Gunn-Peterson approximation (FGPA) applied to dark-matter-only simulations; we conclude while it is adequate for estimating the Ly-$α$ absorption signal from moderate-to-massive protoclusters ($ \gtrsim 10^{14.2} M_{\odot}$), it artificially merges a minority of lower-mass structures with more massive neighbors. Our methods will be applied to current and future Ly-$α$~tomography surveys to create catalogs of overdensities and study environment-dependent galaxy evolution in the Cosmic~Noon~era.

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arXiv2022

Discovery of a damped Ly$α$ absorber originating in a spectacular interacting dwarf galaxy pair at $z = 0.026$

We present the discovery of neutral gas detected in both damped Ly$α$ absorption (DLA) and HI 21-cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an HI bridge connecting two interacting dwarf galaxies (log$(M_{\text{star}}/\text{M}_{\odot}) = 8.5 \pm 0.2$) that host a $z = 0.026$ DLA with log[$N$(HI)/cm$^{-2}$]$ = 20.60 \pm 0.05$ toward the QSO J2339-5523 ($z_{\text{QSO}} = 1.35$). At impact parameters of $d = 6$ and $33$ kpc, the dwarf galaxies have no companions more luminous than $\approx 0.05L_{*}$ within at least $Δv = \pm 300$ km s$^{-1}$ and $d \approx 350$ kpc. HI 21-cm emission is spatially coincident with the DLA at the 2-3$σ$ level per spectral channel over several adjacent beams. However, HI 21-cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with spin temperature to covering factor ratio $T_{s}/f_{c} > 1880$ K). VLT-MUSE observations demonstrate that the $α$-element abundance of the ionized ISM is consistent with the DLA ($\approx 10$% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf-dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and HI 21-cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

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arXiv2021

Direct Constraints on the Extremely Metal-Poor Massive Stars Underlying Nebular C IV Emission from Ultra-Deep HST/COS Ultraviolet Spectroscopy

Metal-poor nearby galaxies hosting massive stars have a fundamental role to play in our understanding of both high-redshift galaxies and low metallicity stellar populations. But while much attention has been focused on their bright nebular gas emission, the massive stars that power it remain challenging to constrain. Here we present exceptionally deep Hubble Space Telescope ultraviolet spectra targeting six galaxies that power strong nebular C IV emission approaching that encountered at $z>6$. We find that the strength and spectral profile of the nebular C IV in these new spectra follow a sequence evocative of resonant scattering models, indicating that the hot circumgalactic medium likely plays a key role in regulating C IV escape locally. We constrain the metallicity of the massive stars in each galaxy by fitting the forest of photospheric absorption lines, reporting measurements driven by iron that lie uniformly below 10% solar. Comparison with the gas-phase oxygen abundances reveals evidence for enhancement in O/Fe above solar across the sample, robust to assumptions about the absolute gas-phase metallicity scale. This supports the idea that these local systems are more chemically-similar to their primordial high-redshift counterparts than to the bulk of nearby galaxies. Finally, we find significant tension between the strong stellar wind profiles observed and our population synthesis models constrained by the photospheric forest in our highest-quality spectra. This reinforces the need for caution in interpreting wind lines in isolation at high-redshift, but also suggests a unique path towards validating fundamental massive star physics at extremely low metallicity with integrated ultraviolet spectra.

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arXiv2021

Chemical abundance scaling relations for multiple elements in z~2-3 star-forming galaxies

The chemical abundance patterns of gas and stars in galaxies are powerful probes of galaxies' star formation histories and the astrophysics of galaxy assembly but are challenging to measure with confidence in distant galaxies. In this paper, we report the first measurements of the correlation between stellar mass and multiple tracers of chemical enrichment (including O, N, and Fe) in individual z~2-3 galaxies, using a sample of 195 star-forming galaxies from the Keck Baryonic Structure Survey (KBSS). The galaxies' chemical abundances are inferred using photoionization models capable of reconciling high-redshift galaxies' observed extreme rest-UV and rest-optical spectroscopic properties. We find that the stellar mass-O/H relation for our sample is relatively shallow, with moderately large scatter, and is offset ~0.35 dex higher than the corresponding stellar mass-Fe/H relation. The two relations have very similar slopes, indicating a high level of alpha-enhancement -- with O/Fe approximately 2.2 times higher than solar O/Fe -- across two decades in stellar mass. The stellar mass-N/H relation has the steepest slope and largest intrinsic scatter, which likely results from the fact that many z~2 galaxies are observed near or past the transition from "primary" to "secondary" N production and may reflect uncertainties in the astrophysical origin of N. Together, these results suggest that z~2 galaxies are old enough to have seen substantial enrichment from intermediate mass stars, but are still young enough that Type Ia supernovae have not had time to contribute significantly to their enrichment.

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arXiv2021

The Cosmic Ultraviolet Baryon Survey (CUBS) IV: The Complex Multiphase Circumgalactic Medium as Revealed by Partial Lyman Limit Systems

We present a detailed study of two partial Lyman limit systems (pLLSs) of neutral hydrogen column density $N_\mathrm{H\,I}\approx(1-3)\times10^{16}\,\mathrm{cm}^{-2}$ discovered at $z=0.5$ in the Cosmic Ultraviolet Baryon Survey (CUBS). Available far-ultraviolet spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and optical echelle spectra from MIKE on the Magellan Telescopes enable a comprehensive ionization analysis of diffuse circumgalactic gas based on resolved kinematics and abundance ratios of atomic species spanning five different ionization stages. These data provide unambiguous evidence of kinematically aligned multi-phase gas that masquerades as a single-phase structure and can only be resolved by simultaneous accounting of the full range of observed ionic species. Both systems are resolved into multiple components with inferred $α$-element abundance varying from $[α/\text{H}]\approx\!{-0.8}$ to near solar and densities spanning over two decades from $\log n_\mathrm{H}\mathrm{cm}^{-3}\approx\!-2.2$ to $<-4.3$. Available deep galaxy survey data from the CUBS program taken with VLT/MUSE, Magellan/LDSS3-C and Magellan/IMACS reveal that the $z=0.47$ system is located 55 kpc from a star-forming galaxy with prominent Balmer absorption of stellar mass $M_\star\approx2\times10^{10}M_\odot$, while the $z=0.54$ system resides in an over-dense environment of 11 galaxies within 750 kpc in projected distance, with the most massive being a luminous red galaxy of $M_\star\approx2\times10^{11}M_\odot$ at 375 kpc. The study of these two pLLSs adds to an emerging picture of the complex, multiphase circumgalactic gas that varies in chemical abundances and density on small spatial scales in diverse galaxy environments. The inhomogeneous nature of metal enrichment and density revealed in observations must be taken into account in theoretical models of diffuse halo gas.

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arXiv2021

The KBSS-KCWI Survey: The connection between extended Ly$α$ halos and galaxy azimuthal angle at $z\sim 2-3$

We present the first statistical analysis of kinematically-resolved, spatially-extended Ly$α$ emission around $z = 2-3$ galaxies in the Keck Baryonic Structure Survey (KBSS) using the Keck Cosmic Web Imager (KCWI). Our sample of 59 star-forming galaxies ($z_\mathrm{med} = 2.29$) comprises the subset with typical KCWI integration times of ~5 hours and with existing imaging data from the Hubble Space Telescope and/or adaptive optics-assisted integral field spectroscopy. The high resolution images were used to evaluate the azimuthal dependence of the diffuse Ly$α$ emission with respect to the stellar continuum within projected galactocentric distances of $\lesssim 30$ proper kpc. We introduce cylindrically-projected 2D spectra (CP2D) that map the averaged Ly$α$ spectral profile over a specified range of azimuthal angle, as a function of impact parameter around galaxies. The averaged CP2D spectrum of all galaxies shows clear signatures of Ly$α$ resonant scattering by outflowing gas. We stacked the CP2D spectra of individual galaxies over ranges of azimuthal angle with respect to their major axes. The extended Ly$α$ emission along the galaxy principal axes are statistically indistinguishable, with residual asymmetry of $\le$ 2% ($\sim 2 σ$) of the integrated Ly$α$ emission. The symmetry implies that the Ly$α$ scattering medium is dominated by outflows in all directions within 30 kpc. Meanwhile, we find that the blueshifted component of Ly$α$ emission is marginally stronger along galaxy minor axes for galaxies with relatively weak Ly$α$ emission. We speculate that this weak directional dependence of Ly$α$ emission becomes discernible only when the Ly$α$ escape fraction is low. These discoveries highlight the need for similar analyses in simulations with Ly$α$ radiative transfer modeling.

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