arXiv subjects

Kathy L. Cooksey

Publications and source records attributed to Kathy L. Cooksey.

At least 19 recordsLinked to original sources

arXiv2023

Machine Learning Uncovers the Universe's Hidden Gems: A Comprehensive Catalogue of CIV Absorption Lines in SDSS DR12

We assemble the largest CIV absorption line catalogue to date, leveraging machine learning, specifically Gaussian processes, to remove the need for visual inspection for detecting CIV absorbers. The catalogue contains probabilities classifying the reliability of the absorption system within a quasar spectrum. Our training set was a sub-sample of DR7 spectra that had no detectable CIV absorption in a large visually inspected catalogue. We used Bayesian model selection to decide between our continuum model and our absorption-line models. Using a random hold-out sample of 1301 spectra from all of the 26,030 investigated spectra in DR7 CIV catalogue, we validated our pipeline and obtained an 87% classification performance score. We found good purity and completeness values, both ~80%, when a probability of ~95% is used as the threshold. Our pipeline obtained similar CIV redshifts and rest equivalent widths to our training set. Applying our algorithm to 185,425 selected quasar spectra from SDSS DR12, we produce a catalogue of 113,775 CIV doublets with at least 95% confidence. Our catalogue provides maximum a posteriori values and credible intervals for CIV redshift, column density, and Doppler velocity dispersion. We detect CIV absorption systems with a redshift range of 1.37 $\!-\!$ 5.1, including 33 systems with a redshift larger than 5 and 549 absorbers systems with a rest equivalent width greater than 2 A at more than 95% confidence. Our catalogue can be used to investigate the physical properties of the circumgalactic and intergalactic media.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2023

The Bimodal Absorption System Imaging Campaign (BASIC) I. A Dual Population of Low-metallicity Absorbers at z $<1$

The bimodal absorption system imaging campaign (BASIC) aims to characterize the galaxy environments of a sample of 36 HI-selected partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) in 23 QSO fields at $z \lesssim 1$. These pLLSs/LLSs provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (CGM) at $z<1$. Here we present Keck/KCWI and VLT/MUSE observations of 11 of these QSO fields (19 pLLSs) that we combine with HST/ACS imaging to identify and characterize the absorber-associated galaxies. We find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. For seven absorbers, all with $<10\%$ solar metallicities, we find no associated galaxies with $\log M_\star \gtrsim 9.0$ within $ρ/R_{vir}$ and $|Δv|/v_{esc} \le$ 1.5 with respect to the absorber. We do not find any strong correlations between the metallicities or HI column densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([X/H] $\le -1.4$) systems have a probability of $0.39^{+0.16}_{-0.15}$ for having a host galaxy with $\log M_\star \ge 9.0$ within $ρ/R_{vir} \le 1.5$, while the higher metallicity absorbers have a probability of $0.78^{+0.10}_{-0.13}$. This implies metal-enriched pLLSs/LLSs at $z<1$ are typically associated with the CGM of galaxies with $\log M_\star > 9.0$, whereas low-metallicity pLLSs/LLSs are found in more diverse locations, with one population arising in the CGM of galaxies and another more broadly distributed in overdense regions of the universe. Using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [X/H] $\lesssim -2.1$ at $z<1$, which is lower than previously estimated.

astro-ph.GA↗

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

Galaxy-Classification Activity for All Ages

Classification is a general tool of science; it is used to sort and categorize biological organisms, chemical elements, astronomical objects, and many other things. In scientific classification, taxonomy often reflects shared physical properties that, in turn, may indicate shared origins and/or evolution. A "hands-on" galaxy-classification activity developed and implemented by Professional Development Program (PDP) participants, for a high-school summer STEM enrichment program, has been adopted for various age groups and venues, from young (K-3) to college students. We detail the basic tools required, outline the general activity, and describe the modifications to the activity based on learners' ages and learning objectives. We describe the facilitation strategies learned through PDP training and used when implementing the activity, including prompts to motivate the students. We also discuss how we connected the classification process to astronomy and science more broadly during the concluding remarks.

physics.ed-ph↗

arXiv2022

Using Pre-/Post-Quizzes Intentionally in Curriculum Development and Evaluation

Developing the final summative assessment of a course at the start of curriculum development is an implementation of "backward design," whereby learning objectives are identified first and the curriculum is engineered end-to-beginning to achieve them. We trained in backward design through the Professional Development Program (PDP) and adapted PDP assessment ideas for evaluation of curriculum designs and teaching efficacy. A pre-/post-quiz is an assessment administered the first and last day of a course; a learner's scores are used to measure normalized gain: the ratio of what a student learned during a course relative to what they knew entering it. The intentional process of developing a pre-/post-quiz for every course focuses the educator on the essential understanding desired of the learners exiting the course. The normalized-gain statistics for the course can then be used to evaluate the course's efficacy, and improvements to the curriculum can be monitored by tracking the normalized gains over time, using the same pre-/post-quiz. Moreover, an individual instructor may self-evaluate their teaching efficacy by tracking normalized gains from all courses over time. Here we discuss applying the practice of backward curriculum design starting with a custom pre-/post-quiz and utilizing it for immediate and longitudinal evaluation, focusing primarily on designing an entire undergraduate science course.

physics.ed-ph↗

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 $\approx 10$.

astro-ph.GA↗

arXiv2022

On the Kinematics of Cold, Metal-enriched Galactic Fountain Flows in Nearby Star-forming Galaxies

We use medium-resolution Keck/Echellette Spectrograph and Imager spectroscopy of bright quasars to study cool gas traced by CaII 3934,3969 and NaI 5891,5897 absorption in the interstellar/circumgalactic media of 21 foreground star-forming galaxies at redshifts 0.03 < z < 0.20 with stellar masses 7.4 < log M_*/M_sun < 10.6. The quasar-galaxy pairs were drawn from a unique sample of Sloan Digital Sky Survey quasar spectra with intervening nebular emission, and thus have exceptionally close impact parameters (R_perp < 13 kpc). The strength of this line emission implies that the galaxies' star formation rates (SFRs) span a broad range, with several lying well above the star-forming sequence. We use Voigt profile modeling to derive column densities and component velocities for each absorber, finding that column densities N(CaII) > 10^12.5 cm^-2 (N(NaI) > 10^12.0 cm^-2) occur with an incidence f_C(CaII) = 0.63^+0.10_-0.11 (f_C(NaI) = 0.57^+0.10_-0.11). We find no evidence for a dependence of f_C or the rest-frame equivalent widths W_r(CaII K) or W_r(NaI 5891) on R_perp or M_*. Instead, W_r(CaII K) is correlated with local SFR at >3sigma significance, suggesting that CaII traces star formation-driven outflows. While most of the absorbers have velocities within +/-50 km/s of the host redshift, their velocity widths (characterized by Delta v_90) are universally 30-177 km/s larger than that implied by tilted-ring modeling of the velocities of interstellar material. These kinematics must trace galactic fountain flows and demonstrate that they persist at R_perp > 5 kpc. Finally, we assess the relationship between dust reddening and W_r(CaII K) (W_r(NaI 5891)), finding that 33% (24%) of the absorbers are inconsistent with the best-fit Milky Way E(B-V)-W_r relations at >3sigma significance.

astro-ph.GA↗

arXiv2022

The COS CGM Compendium. IV. Effects of Varying Ionization Backgrounds on Metallicity Determinations in the z < 1 Circumgalactic Medium

Metallicity estimates of circumgalactic gas based on absorption line measurements typically require photoionization modeling to account for unseen ionization states. We explore the impact of uncertainties in the extreme ultraviolet background (EUVB) radiation on such metallicity determinations for the z < 1 circumgalactic medium (CGM). In particular, we study how uncertainties in the power-law slope of the EUV radiation, $\mathrm{α_{EUVB}}$, from active galactic nuclei affect metallicity estimates in a sample of 34 absorbers with HI column densities between 15.25 < log ($\mathrm{N_{HI}}$ / $\mathrm{cm^{-2}}$) < 17.25 and measured metal ion column densities. We demonstrate the sensitivity of metallicity estimates to changes in the EUV power-law slope of active galactic nuclei, $\mathrm{α_{EUVB}}$, at low redshift (z < 1), showing derived absorber metallicities increase on average by approximately 0.3 dex as the EUV slope is hardened from $\mathrm{α_{EUVB}}$ = -2.0 to -1.4. We use Markov Chain Monte Carlo sampling of photoionization models with $\mathrm{α_{EUVB}}$ as a free parameter to derive metallicities for these absorbers. The current sample of absorbers does not provide a robust constraint on the slope, $\mathrm{α_{EUVB}}$, itself; we discuss how future analyses may provide stronger constraints. Marginalizing over the uncertainty in the slope of the background, we find the average uncertainties in the metallicity determinations increase from 0.08 dex to 0.14 dex when switching from a fixed EUVB slope to one that freely varies. Thus, we demonstrate that EUVB uncertainties can be included in ionization models while still allowing for robust metallicity inferences.

astro-ph.GA↗

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.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2021

The Cosmic Ultraviolet Baryon Survey (CUBS) -- III. Physical properties and elemental abundances of Lyman limit systems at $z<1$

(Abridged) We present a systematic investigation of physical conditions and elemental abundances in four optically thick Lyman-limit systems (LLSs) at $z=0.36-0.6$ discovered within the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS LLSs exhibit multi-component kinematic structure and a complex mix of multiphase gas, with associated metal transitions from multiple ionization states that span several hundred km/s in line-of-sight velocity. Specifically, higher column density components (log N(HI)>16) in all four absorbers comprise dynamically cool gas with $\langle T \rangle =(2\pm1) \times10^4\,$K and modest non-thermal broadening of $5\pm3\,$ km/s. The high quality of the QSO absorption spectra allows us to infer the physical conditions of the gas, using a detailed ionization modeling that takes into account the resolved component structures of HI and metal transitions. The range of inferred gas densities indicates that these absorbers consist of spatially compact clouds with a median line-of-sight thickness of $160^{+140}_{-50}$ pc. While obtaining robust metallicity constraints for the low-density, highly ionized phase remains challenging due to the uncertain N(HI), we demonstrate that the cool-phase gas in LLSs has a median metallicity of $\mathrm{[α/H]_{1/2}}=-0.7^{+0.1}_{-0.2}$, with a 16-84 percentile range of $\mathrm{[α/H]}=(-1.3,-0.1)$. Furthermore, the wide range of inferred elemental abundance ratios ($\mathrm{[C/α]}$, $\mathrm{[N/α]}$, and $\mathrm{[Fe/α]}$) indicate a diversity of chemical enrichment histories. Combining the absorption data with deep galaxy survey data characterizing the galaxy environment of these absorbers, we discuss the physical connection between star-forming regions in galaxies and diffuse gas associated with optically thick absorption systems in the $z<1$ circumgalactic medium.

astro-ph.GA↗

arXiv2021

The Cosmic Ultraviolet Baryon Survey (CUBS) II: Discovery of an H$_{2}$-Bearing DLA in the Vicinity of an Early-Type Galaxy at z = 0.576

We report the serendipitous detection of an H$_{2}$-bearing damped Lyman-$α$ absorber at z = 0.576 in the spectrum of the QSO J0111-0316 in the Cosmic Ultraviolet Baryon Survey. Spectroscopic observations from HST-COS in the far-ultraviolet reveal a damped absorber with log[N(HI)/cm^-2] = 20.1 +/- 0.2 and log[N(H$_{2}$)/cm^-2] = 18.97 (-0.06, +0.05). The diffuse molecular gas is found in two velocity components separated by dv = 60 km/s, with >99.9% of the total H$_{2}$ column density concentrated in one component. At a metallicity of $\approx$ 50% of solar, there is evidence for Fe enhancement and dust depletion, with a dust-to-gas ratio $κ_{\text{O}} \approx$ 0.4. A galaxy redshift survey conducted with IMACS and LDSS-3C on Magellan reveals an overdensity of nine galaxies at projected distance d <= 600 proper kpc (pkpc) and line-of-sight velocity offset dv$_{g}$ <= 300 km/s from the absorber. The closest is a massive, early-type galaxy at d = 41 pkpc which contains $\approx$ 70% of the total stellar mass identified at d <= 310 pkpc of the H$_{2}$ absorber. The close proximity of the H$_{2}$-bearing gas to the quiescent galaxy and the Fe-enhanced chemical abundance pattern of the absorber suggest a physical connection, in contrast to a picture in which DLAs are primarily associated with gas-rich dwarfs. This case study illustrates that deep galaxy redshift surveys are needed to gain insight into the diverse environments that host dense and potentially star-forming gas.

astro-ph.GA↗

arXiv2020

The Cosmic Ultraviolet Baryon Survey (CUBS) I. Overview and the diverse environments of Lyman limit systems at z<1

We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z<~1 using absorption-line spectroscopy of 15 UV-bright QSOs with matching deep galaxy survey data. CUBS QSOs are selected based on their NUV brightness to avoid biases against the presence of intervening Lyman Limit Systems (LLSs) at zabs<1. We report five new LLSs of log N(HI)/cm^-2 >~ 17.2 over a total redshift survey pathlength of dz=9.3, and a number density of n(z)=0.43 (-0.18, +0.26). Considering all absorbers with log N(HI)/cm^-2 > 16.5 leads to n(z)=1.08 (-0.25, +0.31) at z<1. All LLSs exhibit a multi-component structure and associated metal transitions from multiple ionization states such as CII, CIII, MgII, SiII, SiIII, and OVI absorption. Differential chemical enrichment levels as well as ionization states are directly observed across individual components in three LLSs. We present deep galaxy survey data obtained using the VLT-MUSE integral field spectrograph and the Magellan Telescopes, reaching sensitivities necessary for detecting galaxies fainter than 0.1L* at d<~300 physical kpc (pkpc) in all five fields. A diverse range of galaxy properties is seen around these LLSs, from a low-mass dwarf galaxy pair, a co-rotating gaseous halo/disk, a star-forming galaxy, a massive quiescent galaxy, to a galaxy group. The closest galaxies have projected distances ranging from d=15 to 72 pkpc and intrinsic luminosities from ~0.01L* to ~3L*. Our study shows that LLSs originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities.

astro-ph.GA↗

arXiv2019

The COS CGM Compendium. III: Metallicity and Physical Properties of the Cool Circumgalactic Medium at z<1

We characterize the metallicities and physical properties of cool, photoionized gas in a sample of 152 z<1 strong Lya forest systems (SLFSs, absorbers with 15<log N(HI)<16.2). The sample is drawn from our COS circumgalactic medium (CGM) compendium (CCC), an ultraviolet survey of HI-selected circumgalactic gas around z<1 galaxies that targets 262 absorbers with 15<log N(HI)<19. We show that the metallicity probability distribution function of the SLFSs at z<1 is unimodal, skewed to low metallicities with a mean and median of [X/H]=-1.47$ and -1.18 dex. Very metal-poor gas with [X/H]<-1.4 represents about half of the population of absorbers with 15<log N(HI)<18. Thus, there are important reservoirs of primitive (though not pristine) gas around z<1 galaxies. The photoionized gas around z<1 galaxies is highly inhomogeneous based on the wide range of metallicities observed (-3<[X/H]<+0.4) and that there are large metallicity variations (factors of 2 to 25) for most of the closely-spaced absorbers (Dv<300 km/s) along the same sightlines. These absorbers show a complex evolution with redshift and HI column density, and we identify subtle cosmic evolution effects that affect the interpretation of metallicity distributions and comparison with other of absorbers samples. We discuss the physical conditions and cosmic baryon and metal budgets of the CCC absorbers. Finally, we compare the CCC results to recent cosmological zoom simulations and explore the origins of the 15<log N(HI)<19 absorbers within the EAGLE high-resolution simulations.

astro-ph.GA↗

arXiv2019

A Giant Intragroup Nebula Hosting a Damped Lya Absorber at z=0.313

This paper reports the discovery of spatially-extended line-emitting nebula, reaching to ~100 physical kpc (pkpc) from a damped Lyα absorber (DLA) at z_DLA=0.313 along the sightline toward QSO PKS1127-145 (z_QSO=1.188). This DLA was known to be associated with a galaxy group of dynamical mass M_group ~3e12 M_sun, but its physical origin remained ambiguous. New wide-field integral field observations revealed a giant nebula detected in [OII], Hβ, [OIII], Hα, and [NII] emission, with the line-emitting gas following closely the motions of group galaxies. One of the denser streams passes directly in front of the QSO with kinematics consistent with the absorption profiles recorded in the QSO echelle spectra. The emission morphology, kinematics, and line ratios of the nebula suggest that shocks and turbulent mixing layers, produced as a result of stripped gaseous streams moving at supersonic speed across the ambient hot medium, contribute significantly to the ionization of the gas. While the DLA may not be associated with any specific detected member of the group, both the kinematic and dust properties are consistent with the DLA originating in streams of gas stripped from sub-L* group members at <~25 pkpc from the QSO sightline. This study demonstrates that gas stripping in low-mass galaxy groups is effective in releasing metal-enriched gas from star-forming regions, producing absorption systems in QSO spectra, and that combining absorption and emission-line observations provides an exciting new opportunity for studying gas and galaxy co-evolution.

astro-ph.GA↗

arXiv2018

The COS CGM Compendium. II: Metallicities of the Partial and Lyman Limit Systems at z<1

We present the results from our COS circumgalactic medium (CGM) compendium (CCC), a survey of the CGM at z<1 using HI-selected absorbers with 15 19 have mostly -1<[X/H]<0 at z<1. The metal-enriched gas probed by pLLSs and LLSs confirms that galaxies that have been enriching their CGM over billions of years. Surprisingly, despite this enrichment, there is also abundant metal-poor CGM gas (41-59% of the pLLSs have [X/H]<-1.4), representing a reservoir of near-pristine gas around z<1 galaxies. We compare our empirical results to recent cosmological zoom simulations, finding some discrepancies, including an overabundance of metal-enriched CGM gas in simulations.

astro-ph.GA↗

arXiv2018

The COS CGM Compendium (CCC). I: Survey Design and Initial Results

We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15 2 orders of magnitude at any given N(HI), indicating a wide range of metallicities (from solar to <1/100 solar). In the range 16.2<log N(HI)<17, there is a gap in the N(MgII) distribution corresponding to gas with ~10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. Less than 3% of the absorbers in our sample show no detectable metal absorption, implying truly-pristine gas at z<1 is uncommon. We find [FeII/MgII] = -0.4+/-0.3, and since alpha-enhancement can affect this ratio, dust depletion is extremely mild.

astro-ph.GA↗