arXiv subjects

Glenn G. Kacprzak

Publications and source records attributed to Glenn G. Kacprzak.

At least 73 records · Page 4Linked to original sources

arXiv2021

ZFIRE: The Beginning of the End for Massive Galaxies at z ~ 2 and Why Environment Matters

We use ZFIRE and ZFOURGE observations with the Spectral Energy Distribution (SED) fitting tool Prospector to reconstruct the star formation histories (SFHs) of proto-cluster and field galaxies at $z\sim 2 $ and compare our results to the TNG100 run of the IllustrisTNG cosmological simulation suite. In the observations, we find that massive proto-cluster galaxies ($\log[{\rm M}_{\ast}/{\rm M}_{\odot}]>$10.5) form $45 \pm 8 \%$ of their total stellar mass in the first $2$ Gyr of the Universe compared to $31 \pm 2 \%$ formed in the field galaxies. In both observations and simulations, massive proto-cluster galaxies have a flat/declining SFH with decreasing redshift compared to rising SFH in their field counterparts. Using IllustrisTNG, we find that massive galaxies ($\log[{\rm M}_{\ast}/{\rm M}_{\odot}] \geq 10.5$) in both environments are on average $\approx190$ Myr older than low mass galaxies ($\log[{\rm M}_{\ast}/{\rm M}_{\odot}]= 9-9.5$). However, the difference in mean stellar ages of cluster and field galaxies is minimal when considering the full range in stellar mass ($\log[{\rm M}_{\ast}/{\rm M}_{\odot}] \geq 9$). We explore the role of mergers in driving the SFH in IllustrisTNG and find that massive cluster galaxies consistently experience mergers with low gas fraction compared to other galaxies after 1 Gyr from the Big Bang. We hypothesize that the low gas fraction in the progenitors of massive cluster galaxies is responsible for the reduced star formation.

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arXiv2021

Consistent dynamical and stellar masses with potential light IMF in massive quiescent galaxies at $3 < z < 4$ using velocity dispersions measurements with MOSFIRE

We present the velocity dispersion measurements of four massive $\sim10^{11}M_\odot$ quiescent galaxies at $3.2 < z < 3.7$ based on deep H and K$-$band spectra using the Keck/MOSFIRE near-infrared spectrograph. We find high velocity dispersions of order $σ_e\sim250$ km/s based on strong Balmer absorption lines and combine these with size measurements based on HST/WFC3 F160W imaging to infer dynamical masses. The velocity dispersion are broadly consistent with the high stellar masses and small sizes. Together with evidence for quiescent stellar populations, the spectra confirm the existence of a population of massive galaxies that formed rapidly and quenched in the early universe $z>4$. Investigating the evolution at constant velocity dispersion between $z\sim3.5$ and $z\sim2$, we find a large increase in effective radius $0.35\pm0.12$ dex and in dynamical-to-stellar mass ratio $<$log(M$_{\textrm{dyn}}$/M*)$>$ of 0.33$\pm0.08$ dex, with low expected contribution from dark matter. The dynamical masses for our $z\sim3.5$ sample are consistent with the stellar masses for a Chabrier initial mass function (IMF), with the ratio $<$log(M$_{\textrm{dyn}}$/M$^*_{\textrm{Ch}})>$ = -0.13$\pm$0.10 dex suggesting an IMF lighter than Salpeter may be common for massive quiescent galaxies at $z>3$. This is surprising in light of the Salpeter or heavier IMFs found for high velocity dispersion galaxies at $z\sim2$ and cores of present-day ellipticals, which these galaxies are thought to evolve into. Future imaging and spectroscopic observations with resolved kinematics using the upcoming James Webb Space Telescope could rule out potential systematics from rotation, and confirm these results.

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arXiv2020

Spatial Distribution of OVI Covering Fractions in the Simulated Circumgalactic Medium

We use adaptive mesh refinement cosmological simulations to study the spatial distribution and covering fraction of OVI absorption in the circumgalactic medium (CGM) as a function of projected virial radius and azimuthal angle. We compare these simulations to an observed sample of 53 galaxies from the Multiphase Galaxy Halos Survey. Using Mockspec, an absorption line analysis pipeline, we generate synthetic quasar absorption line observations of the simulated CGM. To best emulate observations, we studied the averaged properties of 15,000 "mock samples" each of 53 sightlines having a distribution of $D/R_{vir}$ and sightline orientation statistically consistent with the observations. We find that the OVI covering fraction obtained for the simulated galaxies agrees well with the observed value for the inner halo ($D/R_{vir} \leq 0.375$) and is within $1.1σ$ in the outer halo ($D/R_{vir} > 0.75$), but is underproduced within $0.375 < D/R_{vir} \leq 0.75$. The observed bimodal distribution of OVI covering fraction with azimuthal angle, showing higher frequency of absorption along the projected major and minor axes of galaxies, is not reproduced in the simulations. Further analysis reveals the spatial-kinematic distribution of OVI absorbing gas is dominated by outflows in the inner halo mixed with a inflowing gas that originates from further out in the halo. Though the CGM of the individual simulated galaxies exhibit spatial structure, the flat azimuthal distribution occurs because the individual simulated galaxies do not develop a CGM structure that is universal from galaxy to galaxy.

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arXiv2020

Disentangling the multi-phase circumgalactic medium shared between a dwarf and a massive star-forming galaxy at z~0.4

The multi-phase circumgalactic medium (CGM) arises within the complex environment around a galaxy, or collection of galaxies, and possibly originates from a wide range of physical mechanisms. In this paper, we attempt to disentangle the origins of these multi-phase structures and present a detailed analysis of the quasar field Q0122-003 field using Keck/KCWI galaxy observations and HST/COS spectra probing the CGM. Our re-analysis of this field shows that there are two galaxies associated with the absorption. We have discovered a dwarf galaxy, G_27kpc ($M_{\star}=10^{8.7}$ M$_{\odot}$), at z=0.39863 that is 27 kpc from the quasar sightline. G_27kpc is only +21 km/s from a more massive ($M_{\star}=10^{10.5}$ M$_{\odot}$) star-forming galaxy, G_163kpc, at an impact parameter of 163 kpc. While G_163kpc is actively forming stars (SFR=6.9 M$_{\odot}$ yr$^{-1}$), G_27kpc has a low star-formation rate (SFR=$0.08\pm0.03$ M$_{\odot}$ yr$^{-1}$) and star formation surface density ($Σ_{SFR}=0.006$ M$_{\odot}$ kpc$^{-2}$ yr$^{-1}$), implying no active outflows. By comparing galaxy SFRs, kinematics, masses and distances from the quasar sightline to the absorption kinematics, column densities and metallicities, we have inferred the following: (1) Part of the low-ionization phase has a metallicity and kinematics consistent with being accreted onto G_27kpc. (2) The remainder of the low ionization phase has metallicities and kinematics consistent with being intragroup gas being transferred from G_27kpc to G_163kpc. (3) The high ionization phase is consistent with being produced solely by outflows originating from the massive halo of G_163kpc. Our results demonstrate the complex nature of the multi-phase CGM, especially around galaxy groups, and that detailed case-by-case studies are critical for disentangling its origins.

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arXiv2020

Evidence for galaxy quenching in the green valley caused by a lack of a circumgalactic medium

The relationship between a galaxy's properties and its circumgalactic medium (CGM) provides a unique view of how galaxies evolve. We present an interesting edge-on (i=86 degrees) disk galaxy (G1547) where the CGM is probed by a background quasar at a distance of 84 kpc and within 10 degrees of the galaxy major axis. G1547 does not have any detectable CGM absorption down to stringent limits, covering HI (EW$_r$<0.02A, log(N(HI)/cm$^{-2}$)<12.6) and a range of low and high ionisation absorption lines (OI, CII, NII, SiII, CIII, NIII, SiIII, CIV, SiIV, NV and OVI). This system is rare, given the covering fraction of $1.00_{-0.04}^{+0.00}$ for sub-L* galaxies within 50-100 kpc of quasar sightlines. G1547 has a low SFR (1.1 M$_{\odot}$yr$^{-1}$), SSFR ($1.5\times10^{-10}$yr$^{-1}$) and $Σ_{\rm SFR}$ (0.06 M$_{\odot}$yr$^{-1}$kpc$^{-2}$) and does not exhibit AGN or star-formation driven outflows. Compared to the general population of galaxies, G1547 is in the green valley and has an above average metallicity with a negative gradient. When compared to other HI absorption-selected galaxies, we find that quiescent galaxies with log(SSFR/yr$^{-1})<-11$ have a low probability (4/12) of possessing detectable HI in their CGM, while all galaxies (40/40) with log(SSFR/yr$^{-1})>-11$ have HI absorption. We conclude that SSFR is a good indicator of the presence of HI CGM. Interestingly however, G1547 is the only galaxy with log(SSFR/yr$^{-1})>-11$ that has no detectable CGM. Given the properties of G1547, and its absent CGM, it is plausible that G1547 is undergoing quenching due to a lack of accreting fuel for star-formation, with an estimated quenching timescale of $4\pm1$ Gyr. G1547 provides a unique perspective into the external mechanisms that could explain the migration of galaxies into the green valley.

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arXiv2020

The CGM at Cosmic Noon with KCWI: Outflows from a Star-forming Galaxy at z=2.071

We present the first results from our CGM at Cosmic Noon with KCWI program to study gas flows in the circumgalactic medium (CGM) at $z=2-3$. Combining the power of a high-resolution VLT/UVES quasar spectrum, an HST/ACS image, and integral field spectroscopy with Keck/KCWI, we detected Lya emission from a $1.7L_{\ast}$ galaxy at $z_{\rm gal}=2.0711$ associated with a Lyman limit system with weak MgII ($W_r(2796)=0.24$ Ang) in quasar field J143040$+$014939. The galaxy is star-forming (${\rm SFR}_{\rm FUV}=37.8$ M$_{\odot}$ yr$^{-1}$) and clumpy: either an edge-on disk ($i=85^{\circ}$) or, less likely, a major merger. The background quasar probes the galaxy at an impact parameter of $D=66$ kpc along the projected galaxy minor axis ($Φ=89^{\circ}$). From photoionization modeling of the absorption system, we infer a total line-of-sight CGM metallicity of ${\rm [Si/H]}=-1.5^{+0.4}_{-0.3}$. The absorption system is roughly kinematically symmetric about $z_{\rm gal}$, with a full MgII velocity spread of $\sim210$ km s$^{-1}$. Given the galaxy-quasar orientation, CGM metallicity, and gas kinematics, we interpret this gas as an outflow that has likely swept-up additional material. By modeling the absorption as a polar outflow cone, we find the gas is decelerating with average radial velocity $V_{\rm out}=109-588$ km s$^{-1}$ for half opening angles of $θ_0=14^{\circ}-75^{\circ}$. Assuming a constant $V_{\rm out}$, it would take on average $t_{\rm out}\sim111-597$ Myr for the gas to reach 66 kpc. The outflow is energetic, with a mass outflow rate of $\dot{M}_{\rm out}<52{\pm37}$ M$_{\odot}$ yr$^{-1}$ and mass loading factor of $η<1.4{\pm1.0}$. We aim to build a sample of $\sim50$ MgII absorber--galaxy pairs at this epoch to better understand gas flows when they are most actively building galaxies.

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arXiv2020

Evolution of CIV Absorbers I. The Cosmic Incidence

We present a large high-resolution study of the distribution and evolution of CIV absorbers, including the weakest population with equivalent widths $W_r<0.3$~Å. By searching 369 high-resolution, high signal-to-noise spectra of quasars at $1.1\leq z_{em} \leq5.3$ from Keck/HIRES and VLT/UVES, we find $1268$ CIV absorbers with $W_r \geq 0.05$~Å (our $\sim50\%$ completeness limit) at redshifts $1\leq z \leq4.75$. A Schechter function describes the observed equivalent width distribution with a transition from power-law to exponential decline at $W_r \gtrsim 0.5$~Å. The power-law slope $α$ rises by $\sim7\%$ and transition equivalent width $W_{\star}$ falls by $\sim\!20\%$ from $\langle z \rangle=1.7$ to $\langle z \rangle=3.6$. We find that the co-moving redshift path density, $dN/dX$, of $W_r \geq 0.05$~Å absorbers rises by $\sim1.8$ times from $z\simeq 4.0$ to $z\simeq 1.3$, while the $W_r \geq 0.6$~Å $dN/dX$ rises by a factor of $\sim8.5$. We quantify the observed evolution by a model in which $dN/dX$ decreases linearly with redshift. The model suggests that populations with larger $W_r$ thresholds evolve faster with redshift and appear later in the universe. The cosmological Technicolor Dawn simulations at $z=3-5$ over-produce the observed abundance of absorbers with $W_r<0.3$~Å, while yielding better agreement at higher $W_r$. Our empirical linear model successfully describes {CIV evolution in the simulations and the observed evolution of $W_r \geq 0.6$~Å CIV for the past $\sim12$ Gyr. Combining our measurements with the literature gives us a picture of CIV-absorbing structures becoming more numerous and/or larger in physical size over the last $\approx13$ Gyr of cosmic time ($z\sim6$ to $z\sim0$).

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arXiv2020

MgII Absorbers in High Resolution Quasar Spectra. I. Voigt Profile Models

We present the Voigt profile (VP) models, column densities, Doppler b parameters, kinematics, and distribution of components for 422 MgII absorbers found in a survey of 249 HIRES and UVES quasar spectra. The equivalent width range of the sample is 0.006 < W_r(2796) < 6.23 angstroms (A) and the redshift range is 0.19 < z < 2.55, with a mean of = 1.18. Based on historical precedent, we classified 180 absorbers as weak systems (W_r(2796) < 0.3 A) and 242 as strong systems (W_r(2796) >= 0.3 A). Assuming a minimum number of significant components per system, the VP fitting, yielded a total of 2,989 components, with an average of 2.7 and 10.3 components found for the weak and strong MgII subsamples, respectively. The VP component line density for the full sample is 8.62 +/- 0.23 clouds/A. The distribution of VP component column density over the range 12.4 < log[N(MgII)] < 17.0 [ions cm^-2] is well modeled with a power-law slope of -1.45 +/- 0.01. The median Doppler b parameters are 4.5 +/- 3.5 km/s, 6.0 +/- 4.5 km/s and 5.7 +/- 4.4 km/s for the weak, strong, and full samples. We modeled the probability of component velocity splitting (the two-point velocity correlation function, TPCF) of our full sample using a three-component composite Gaussian function. Our resulting velocity dispersions are 25.4, 68.7, and 207.1 km/s, respectively. These data provide an excellent database for studying the cosmic evolution of MgII absorber kinematic evolution.

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arXiv2020

A giant galaxy in the young Universe with a massive ring

In the local (redshift z~0) Universe, collisional ring galaxies make up only ~0.01% of galaxies and are formed by head-on galactic collisions that trigger radially propagating density waves. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe. However, not much is known about distant (z>0.1) collisional rings. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z=2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5-2.2 times larger and is forming stars 50 times faster. The large, diffuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved, the implied large bar in a giant disk would be inconsistent with the current understanding of the earliest formation of barred spirals. Contrary to previous predictions, this work suggests that massive collisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.

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arXiv2020

Low Mass Group Environments have no Substantial Impact on the Circumgalactic Medium Metallicity

We explore how environment affects the metallicity of the circumgalactic medium (CGM) using 13 low mass galaxy groups (2-5 galaxies) at $\langle z_{abs}\rangle=0.25$ identified near background quasars. Using quasar spectra from HST/COS and from Keck/HIRES or VLT/UVES we measure column densities of, or determine limits on, CGM absorption lines. We use a Markov chain Monte Carlo approach with Cloudy to estimate metallicities of cool ($T\sim10^4$K) CGM gas within groups and compare them to CGM metallicities of 47 isolated galaxies. Both group and isolated CGM metallicities span a wide range ($-2<$[Si/H]$<0$), where the mean group ($-0.54\pm0.22$) and isolated ($-0.77\pm0.14$) CGM metallicities are similar. Group and isolated environments have similar distributions of {\HI} column densities as a function of impact parameter. However, contrary to isolated galaxies, we do not find an anti-correlation between {\HI} column density and the nearest group galaxy impact parameter. We additionally divided the groups by member luminosity ratios (i.e., galaxy-galaxy and galaxy-dwarf groups). While there was no significant difference in their mean metallicities, a modest increase in sample size should allow one to statistically identify a higher CGM metallicity in galaxy-dwarf groups compared to galaxy-galaxy groups. We conclude that either environmental effects have not played an important role in the metallicity of the CGM at this stage and expect that this may only occur when galaxies are strongly interacting or merging, or that some isolated galaxies have higher CGM metallicities due to past interactions. Thus, environment does not seem to be the cause of the CGM metallicity bimodality.

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arXiv2020

MOSEL: Strong [OIII]5007 Å Emitting Galaxies at (3<z<4) from the ZFOURGE Survey

To understand how strong emission line galaxies (ELGs) contribute to the overall growth of galaxies and star formation history of the universe, we target Strong ELGs (SELGs) from the ZFOURGE imaging survey that have blended (Hb+[OIII]) rest-frame equivalent widths of >230A and 2.5 60%, i.e. the inferred gas masses can easily fuel a starburst to double stellar masses within ~10-100 Myr. Combined with recent results using ZFOURGE, our analysis indicates that 1) strong [OIII]5007A emission signals an early episode of intense stellar growth in low mass (Mstar<0.1M*) galaxies and 2) many, if not most, galaxies at z>3 go through this starburst phase. If true, low-mass galaxies with strong [OIII]5007A emission (EW_rest>200A) may be an increasingly important source of ionizing UV radiation at z>3.

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arXiv2020

MOSEL Survey: Tracking the Growth of Massive Galaxies at 2<z<4 using Kinematics and the IllustrisTNG Simulation

We use K-band spectroscopic data from the Multi-Object Spectroscopic Emission Line (MOSEL) survey to analyze the kinematic properties of galaxies at z>3. Our sample consists of 34 galaxies at 3.0 10.2 at z > 3 have 56 +/- 21 km/s lower integrated velocity dispersion compared to galaxies at z ~ 2 of similar stellar mass. Massive galaxies at z > 3 have either a flat or declining star formation history (SFH), whereas similar stellar mass galaxies at z~2.0 exhibit a slight peak in the past 500 Myrs. Comparing with the IllustrisTNG cosmological simulation, we find that (i) the dynamical mass of massive galaxies in simulations (log(M_star) > 10.0) increases by ~0.1 dex at a fixed stellar mass between z=2.0-3.0, and (ii) dynamical mass growth is coupled with a rapid rise in the ex-situ stellar mass fraction (stars accreted from other galaxies) for massive galaxies at z < 3.5. We speculate that the rising contribution of ex-situ stellar mass to the total stellar mass growth of massive galaxies is driving the higher integrated velocity dispersion and rising SFHs of massive galaxies at z~2.0 compared to galaxies of similar stellar masses at z > 3.

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arXiv2020

ZFIRE: Measuring Electron Density with [OII] as a function of environment at z = 1.62

The global star formation rates (SFR) of galaxies at fixed stellar masses increase with redshift and are known to vary with environment unto z~2. We explore here whether the changes in the star formation rates can also apply to the electron densities of the inter-stellar medium (ISM) by measuring the [OII] (3727A/3729A) ratio for cluster and field galaxies at z~2. We measure a median electron density of ne = 366+/-84 cm-3 for six galaxies (with 1-sigma scatter = 163 cm-3) in the UDS proton-cluster at z=1.62. We find that the median electron density of galaxies in the UDS photo-cluster environment is three times higher compared to the median electron density of field galaxies (ne = 113+/- 63 cm-3 and 1-sigma scatter = 79 cm-3) at comparable redshifts, stellar mass and SFR. However, we note that a sample of six photo-cluster galaxies is insufficient to reliably measure the electron density in the average porto-cluster environment at z~2. We conclude that the electron density increases with redshift in both cluster and field environments up to z~2 (ne = 30 +/- 1 cm-3 for z ~ 0 to ne =254+/- 76 cm-3 for z~1.5). We find tentative evidence (~2.6 sigma ) for a possible dependence of electron density on environment, but the results require confirmation with larger sample sizes.

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arXiv2020

Reconstructing the observed ionizing photon production efficiency at z~2 using stellar population models

The ionizing photon production efficiency, $ξ_{ion}$, is a critical parameter that provides a number of physical constraints to the nature of the early Universe, including the contribution of galaxies to the timely completion of the reionization of the Universe. Here we use KECK/MOSFIRE and ZFOURGE multi-band photometric data to explore the $ξ_{ion}$ of a population of galaxies at $z\sim2$ with $log_{10}(M_*/M_\odot)\sim9.0-11.5$. Our 130 \Halpha\ detections show a median $log_{10}(ξ_{ion}[Hz/erg])$ of $24.8\pm0.5$ when dust corrected using a Calzetti et al. (2000) dust prescription. Our values are typical of mass/magnitude selected $ξ_{ion}$ values observed in the $z\sim2$ Universe. Using BPASSv2.2.1 and Starburst99 stellar population models with simple parametric star-formation-histories (SFH), we find that even with models that account for effects of stellar evolution with binaries/stellar rotation, model galaxies at $log_{10}(ξ_{ion}[Hz/erg])\lesssim25.0$ have low H$α$ equivalent widths (EW) and redder colors compared to our $z\sim2$ observed sample. We find that introducing star-bursts to the SFHs resolve the tension with the models, however, due to the rapid time evolution of $ξ_{ion}$, H$α$ EWs, and rest-frame optical colors, our Monte Carlo simulations of star-bursts show that random distribution of star-bursts in evolutionary time of galaxies are unlikely to explain the observed distribution. Thus, either our observed sample is specially selected based on their past SFH or stellar models require additional mechanisms to reproduce the observed high UV luminosity of galaxies for a given production rate of hydrogen ionizing photons.

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arXiv2019

The Relationship Between Galaxy ISM and Circumgalactic Gas Metallicities

We present ISM and CGM metallicities for 25 absorption systems associated with isolated star-forming galaxies ( =0.28) with 9.4 17.2) reside along the minor axis. This suggest N(HI) could be a useful indicator of accretion/outflows. We conclude that CGM is not well mixed, given the range of galaxy-CGM metallicities, and that metallicity at low redshift might not be a good tracer of CGM processes. Furthermore we should replace integrated line-of-sight, single phase, metallicities with multi-phase, cloud-cloud metallicities, which could be more indicative of the physical processes within the CGM.

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arXiv2019

Kinematics of the OVI Circumgalactic Medium: Halo Mass Dependence and Outflow Signatures

We probe the high-ionization circumgalactic medium by examining absorber kinematics, absorber-galaxy kinematics, and average absorption profiles of 31 OVI absorbers from the "Multiphase Galaxy Halos" Survey as a function of halo mass, redshift, inclination, and azimuthal angle. The galaxies are isolated at $0.12<z_{\rm gal}<0.66$ and are probed by a background quasar within $D\approx 200$ kpc. Each absorber-galaxy pair has Hubble Space Telescope images and COS quasar spectra, and most galaxy redshifts have been accurately measured from Keck/ESI spectra. Using the pixel-velocity two-point correlation function (TPCF) method, we find that OVI absorber kinematics have a strong halo mass dependence. Absorbers hosted by $\sim L^{\ast}$ galaxies have the largest velocity dispersions, which we interpret to be that the halo virial temperature closely matches the temperature at which the collisionally ionized OVI fraction peaks. Lower mass galaxies and group environments have smaller velocity dispersions. Total column densities follow the same behavior, consistent with theoretical findings. After normalizing out the observed mass dependence, we studied absorber-galaxy kinematics with a modified TPCF and found non-virialized motions due to outflowing gas. Edge-on minor axis gas has large optical depths concentrated near the galaxy systemic velocity as expected for bipolar outflows, while face-on minor axis gas has a smoothly decreasing optical depth distribution out to large normalized absorber-galaxy velocities, suggestive of decelerating outflowing gas. Accreting gas signatures are not observed due to "kinematic blurring" in which multiple line-of-sight structures are observed. These results indicate that galaxy mass dominates OVI properties over baryon cycle processes.

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arXiv2019

A Tale of Two Clusters: An Analysis of Gas-Phase Metallicity and Nebular Gas Conditions in Proto-cluster Galaxies at z~2

The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck 1: one at z=2.095 in COSMOS and another at z=1.62 in UDS. Here we use an updated ZFIRE dataset to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines H$β$ 4861Å, [OIII] 5007Å, H$α$ 6563Å, [NII] 6585Å, and [SII] 6716,6731Å. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass-Metallicity Relation with both metallicity indicators. We compare our results to recent IllustrisTNG results, which reports no significant gas-phase metallicity offset between proto-cluster and field galaxies until z=1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that UDS high mass proto-cluster and field galaxies have differing [OIII]/H$β$ ratios, however these results are dependent on the sample size of the high mass stacks.

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arXiv2019

Relationship between the Metallicity of the Circumgalactic Medium and Galaxy Orientation

We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around $47$, $z<0.7$ galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar spectra from HST/COS and from Keck/HIRES or VLT/UVES we measure column densities of, or determine limits on, CGM absorption lines. We then use a Monte-Carlo Markov chain approach with Cloudy to estimate the metallicity of cool (T$\sim$$10^4$K) CGM gas. We also use HST images to determine host galaxy inclination and quasar--galaxy azimuthal angles. Our sample spans a HI column density range of $13.8$ cm s$^{-1}<{\log N_{HI}}<19.9$ cm s$^{-1}$. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution ($0.4σ$). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of HI column density, impact parameter and galaxy color. (4) Ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at $z<0.7$. The presence of low metallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low metallicity gas in integrated line-of-sight CGM metallicities.

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