arXiv subjects

Regina A. Jorgenson

Publications and source records attributed to Regina A. Jorgenson.

At least 19 recordsLinked to original sources

arXiv2026

The KAGG survey: KCWI Analysis of Gas around Galaxies at z~3-5

We present the KCWI Analysis of Gas around Galaxies (KAGG) survey of Ly$α$ emission around Damped Ly$α$ Absorbers (DLAs) at z~3-5 with the Keck Cosmic Web Imager (KCWI) integral-field spectrograph. The KAGG survey is characterized by the sample of 36 DLAs spanning a wide metallicity range, the wide search area for associated Ly$α$ emission (impact parameter b$~\lesssim 120~$kpc), and the high emission sensitivity, reaching Ly$α$ luminosities $\lesssim10^{42}$ erg s$^{-1}$. We identify 7 DLA Ly$α$ emitters that are likely DLA galaxy candidates due to the good match between the Ly$α$ emission and DLA redshifts. Based on a composite sample of 11 DLA Ly$α$ emitters from KAGG and MAGG (MUSE Analysis of Gas around Galaxies), we find that the impact parameters of DLA Ly$α$ emitters decrease with DLA metallicity, from b$~>50~$kpc at [M/H]~-2 to b$~<50~$kpc at [M/H]~-1. Including Ly$α$ emitters at larger velocity offsets and at larger impact parameters from the DLAs, we construct samples of 35 "Group" Ly$α$ emitters and 17 "Large-scale" Ly$α$ emitters. We find that their impact parameters and incidence rates also depend on DLA metallicity. Based on simulations of our survey and comparisons with models of galaxy formation, we conclude that higher DLA metallicities are associated with higher halo masses. The low Ly$α$ emission detection rate at low impact parameters suggests that most DLA galaxies either have low stellar masses (M$~\lesssim10^{8}M_{\odot}$) or have their Ly$α$ emission suppressed due to HI resonant scattering and/or dust absorption.

astro-ph.GA↗

arXiv2026

The Low-mass Dwarf Host Galaxy of Nonrepeating FRB 20230708A

We present Very Large Telescope/X-Shooter spectroscopy for the host galaxies of 12 fast radio bursts (FRBs) detected by the Australian SKA Pathfinder observed through the ``Fast and Unbiased FRB Host Galaxy (FURBY)" Large Programme at the European Southern Observatory, which imposes strict selection criteria on the included FRBs and their host galaxies to produce a homogeneous and well-defined sample. We describe the data reduction and analysis of these spectra and report their redshifts, line-emission fluxes, and derived host properties. From the present sample, this paper focuses on the faint host of FRB ($m_R = 22.53 \pm 0.02$) identified at low redshift ($z=0.1050$). This indicates an intrinsically very low-luminosity galaxy ($L \approx 10^8 L_\odot$), making it the lowest-luminosity nonrepeating FRB host to date by a factor of $\sim 3$, and slightly dimmer than the lowest-luminosity host for repeating FRBs. Our SED fitting analysis reveals a low stellar mass ($M_* \approx 10^{8.0} M_\odot$), low star formation rate (${\rm SFR} \approx 0.04 M_\odot \rm yr^{-1}$), and very low metallicity ($12+\log(\text{O}/\text{H})\sim(8.0-8.3)$), distinct from the more massive galaxies ($\log(M/M_\odot) \sim 10$) that are commonly identified for non-repeating FRBs. Its discovery demonstrates that FRBs can arise in among the faintest, metal-poor galaxies of the universe. In turn, this suggests that at least one FRB progenitor channel must include stars (or their remnants) created in very low metallicity environments. This indicates better prospects for detecting FRBs from the high-$z$ universe where young, low-mass galaxies proliferate.

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arXiv2025

The Qz5 Survey (I): How the HI Mass Density of the Universe Evolves With Cosmic Time

We report that the neutral hydrogen (HI) mass density of the Universe ($ρ_{HI}$) increases with cosmic time since $z \sim 5$, peaks at $z \sim 3$, and then decreases toward $z \sim 0$. This is the first result of Qz5, our spectroscopic survey of 63 quasars at $z \gtrsim 5$ with VLT/X-SHOOTER and Keck/ESI aimed at characterizing intervening HI gas absorbers at $z \sim 5$. The main feature of Qz5 is the high resolution ($R \sim 7000 - 9000$) of the spectra, which allows us to (1) accurately detect high column density HI gas absorbers in an increasingly neutral intergalactic medium at $z \sim 5$ and (2) determine the reliability of previous $ρ_{HI}$ measurements derived with lower resolution spectroscopy. We find 5 intervening Damped Ly$α$ absorbers (DLAs) at $z > 4.5$, which corresponds to the lowest DLA incidence rate ($0.034^{0.05}_{0.02}$) at $z \gtrsim 2$. We also measure the lowest $ρ_{HI}$ at $z \gtrsim 2$ from our sample of DLAs and subDLAs, corresponding to $ρ_{HI} = 0.56^{0.82}_{0.31} \times 10^8~$M$_{\odot}~$Mpc$^{-3}$ at $z \sim 5$. Taking into account our measurements at $z \sim 5$ and systematic biases in the DLA detection rate at lower spectral resolutions, we conclude that $ρ_{HI}$ doubles from $z \sim 5$ to $z \sim 3$. From these results emerges a qualitative agreement between how the cosmic densities of HI gas mass, molecular gas mass, and star-formation rate build up with cosmic time.

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arXiv2024

The Environments of Fast Radio Bursts Viewed Using Adaptive Optics

We present GeMS/GSAOI observations of five fast radio burst (FRB) host galaxies with sub-arcsecond localizations. We examine and quantify their spatial distributions and locations with respect to their host galaxy light distributions, finding a median host-normalized offset of 2.09 r_e and in fainter regions of the host. When combined with the FRB sample from Mannings et al. (2021), we find that FRBs are statistically distinct from Ca-rich transients in terms of light and from SGRBs and LGRBs in terms of host-normalized offset. We further find that most FRBs are in regions of elevated local stellar mass surface densities in comparison to the mean global values of their hosts. This, in combination with the combined FRB sample trace the distribution of stellar mass, points towards a possible similarity of the environments of CC-SNe and FRBs. We also find that 4/5 FRB hosts exhibit distinct spiral arm features, and the bursts originating from such hosts tend to appear on or close to the spiral structure of their hosts, with a median distance of 0.53 kpc. With many well-localized FRB detections looming on the horizon, we will be able to better characterize the properties of FRB environments relative to their host galaxies and other transient classes.

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arXiv2024

A survey of Ly$α$ emission around Damped Ly$α$ absorbers at $z \approx 2$ with the Keck Cosmic Web Imager

We present Keck Cosmic Web Imager (KCWI) Ly$α$ integral field spectroscopy of the fields surrounding 14 Damped Ly$α$ absorbers (DLAs) at $z \approx 2$. Of these 14 DLAs, 9 have high metallicities ([M/H]$~> -0.3$), and 4 of those 9 feature a CO-emitting galaxy at an impact parameter $\lesssim 30$ kpc. Our search reaches median Ly$α$ line flux sensitivities of $\sim 2 \times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$ over apertures of $\sim6$ kpc and out to impact parameters of $\sim50$ kpc. We recover the Ly$α$ flux of three known Ly$α$-emitting H I-selected galaxies in our sample. In addition, we find two Ly$α$ emitters at impact parameters of $\approx 50-70$ kpc from the high metallicity DLA at $z \approx 1.96$ toward QSO B0551-366. This field also contains a massive CO-emitting galaxy at an impact parameter of $\approx 15$ kpc. Apart from the field with QSO B0551-366, we do not detect significant Ly$α$ emission in any of the remaining 8 high-metallicity DLA fields. Considering the depth of our observations and our ability to recover previously known Ly$α$ emitters, we conclude that H I-selected galaxies associated with high-metallicity DLAs at $z \approx 2$ are dusty, and therefore might feature low Ly$α$ escape fractions. Our results indicate that complementary approaches -- using Ly$α$, CO, H$α$, and [C II] 158$μ$m emission -- are necessary to identify the wide range of galaxy types associated with $z \approx 2$ DLAs.

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arXiv2023

Constraining the Molecular Gas Content of Fast Radio Burst (FRB) Host Galaxies

We used Bands 6 and 7 of the Atacama Large Millimeter/submillimeter Array (ALMA) in Cycles 7 and 8 to search for $\mathrm{CO}\,(3-2)$ emission from a sample of five fast radio burst (FRB) host galaxies discovered by the Commensal Real-time ASKAP Fast Transients (CRAFT) survey and the Fast and Fortunate for FRB Follow-up (F$^4$) team. These galaxies have redshifts $z \approx 0.16-0.48$, masses log$(M_{\rm star}/M_{\odot})\approx 9.30-10.4$ characteristic of field galaxies, and emission lines indicative of ongoing star formation. We detected three of the five galaxies with luminosities $L'(3-2)\approx0.2-4\times10^8\,\rm K\,km \, s^{-1}\,pc^2$ and set upper limits for the other two. Adopting standard metallicity-dependent CO-to-H$_2$ conversion factors, we estimate molecular gas masses $M_{\rm gas}\approx 0.2-3\times 10^9 \, M_{\odot}$. As a population, FRB host galaxies track the main $M_{\rm star}-M_{\rm gas}$ locus of star-forming galaxies in the present-day universe, with gas fractions of $μ_{\rm gas}\approx0.1$ and gas depletion times $t_{\rm dep} \gtrapprox 1\,$Gyr. We employ the Kaplan-Meier estimator to compare the redshift-corrected $μ_{\rm gas}$ and $t_{\rm dep}$ for all known FRB hosts with measurements or upper limits with those from the xCOLD GASS survey and find statistically different gas fractions. The difference is not statistically significant when we consider only the five hosts studied here with consistently determined properties, suggesting more FRB hosts with measured molecular gas masses are needed to robustly study the population. Lastly, we present a multi-wavelength analysis of one host (HG20180924B) combining high-spatial resolution imaging and integral field spectroscopy to demonstrate that future high-resolution observations will allow us to study the host galaxy environments local to the FRBs.

astro-ph.GA↗

arXiv2022

Constraining the Size of the Circumgalactic Medium Using the Transverse Autocorrelation Function of C IV Absorbers in Paired Quasar Spectra

The circumgalactic medium (CGM) plays a vital role in the formation and evolution of galaxies, acting as a lifeline between galaxies and the surrounding intergalactic medium (IGM). In this study we leverage a unique sample of quasar pairs to investigate the properties of the CGM with absorption line tomography. We present a new sample of medium resolution Keck/ESI, Magellan/MagE, and VLT/XSHOOTER spectra of 29 quasar pairs at redshift $2 < z < 3$. We supplement the sample with additional spectra of 32 pairs from the literature, creating a catalog of 61 quasar pairs with angular separations between 1.7" and 132.9" and projected physical separations ($r_\perp$) between 14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption doublets of C IV ($λλ1548, 1550$) with equivalent widths ranging from 6 mÅ $\leq W_{r, 1550} \leq 2053$ mÅ. The best fit linear model to the log-space equivalent width frequency distribution ($\log f(W_r) = m\log(W_{r}) + b$) of the sample yields coefficients of $m=-1.44\pm0.16$ and $b=-0.43\pm0.16$. To constrain the projected extent of C IV, we calculate the transverse autocorrelation function. The flattening of the autocorrelation function at low $r_\perp$ provides a lower limit for the coherence length of the metal enriched CGM - on the order of 200 $h^{-1}$ comoving kpc. This physical size constraint allows us to refine our understanding of the metals in the CGM, where the extent of C IV in the CGM depends on gas flows, feedback, timescale of metal injection and mixing, and the mass of the host galaxies.

astro-ph.GA↗

arXiv2021

Dissecting the Local Environment of FRB 190608 in the Spiral Arm of its Host Galaxy

We present a high-resolution analysis of the host galaxy of fast radio burst (FRB)~190608, an SB(r)c galaxy at $z=0.11778$ (hereafter HG 190608), to dissect its local environment and its contributions to the FRB properties. Our Hubble Space Telescope Wide Field Camera 3 ultraviolet and visible light image reveals that the subarcsecond localization of FRB~190608 is coincident with a knot of star-formation ($Σ_{\rm SFR} = 1.5 \times 10^{-2}~ M_{\odot} \, \rm \, yr^{-1} \, kpc^{-2}$) in the northwest spiral arm of HG~190608. Using H$β$ emission present in our Keck Cosmic Web Imager integral field spectrum of the galaxy with a surface brightness of $μ_{\rm Hβ}= \mathrm{(3.36\pm0.21)\times10^{-17}\;erg\;s^{-1}\;cm^{-2}\;arcsec^{-2}}$, we infer an extinction-corrected H$α$ surface brightness and compute a dispersion measure (DM) from the interstellar medium of HG 190608 of $\rm DM_{\rm Host,ISM} = 94 \pm 38~ \;pc\;cm^{-3}$. The galaxy rotates with a circular velocity $v_{\rm circ} = \rm 141 \pm 8~ km\;s^{-1}$ at an inclination $i_{\mathrm{gas}} = 37 \pm 3^\circ$, giving a dynamical mass $M_{\rm halo}^{\rm dyn} \approx 10^{11.96 \pm 0.08}~M_{\odot}$. This implies a halo contribution to the DM of $\rm DM_{\rm Host,Halo}= \rm 55\pm25 \;pc\;cm^{-3}$ subject to assumptions on the density profile and fraction of baryons retained. From the galaxy rotation curve, we infer a bar-induced pattern speed of $Ω_p=34\pm 6\;\mathrm{km\;s^{-1}\;kpc^{-1}}$ using linear resonance theory. We then calculate the maximum time since star-formation for a progenitor using the furthest distance to the arm's leading edge within the localization, and find $t_{\mathrm{enc}} = 21_{-6}^{+25}$ Myr. Unlike previous high-resolution studies of FRB environments, we find no evidence of disturbed morphology, emission, or kinematics for FRB 190608.

astro-ph.GA↗

arXiv2021

Deciphering the Origin of Ionized Gas in IC 1459 with VLT/MUSE

IC 1459 is an early-type galaxy (ETG) with a rapidly counter-rotating stellar core, and is the central galaxy in a gas-rich group of spirals. In this work, we investigate the abundant ionized gas in IC 1459 and present new stellar orbital models to connect its complex array of observed properties and build a more complete picture of its evolution. Using the Multi-Unit Spectroscopic Explorer (MUSE), the optical integral field unit (IFU) on the Very Large Telescope (VLT), we examine the gas and stellar properties of IC 1459 to decipher the origin and powering mechanism of the galaxy's ionized gas. We detect ionized gas in a non-disk-like structure rotating in the opposite sense to the central stars. Using emission-line flux ratios and velocity dispersion from full-spectral fitting, we find two kinematically distinct regions of shocked emission-line gas in IC 1459, which we distinguished using narrow ($σ$ $\leq$ 155 km s$^{-1}$) and broad ($σ$ $>$ 155 km s$^{-1}$) profiles. Our results imply that the emission-line gas in IC 1459 has a different origin than that of its counter-rotating stellar component. We propose that the ionized gas is from late-stage accretion of gas from the group environment, which occurred long after the formation of the central stellar component. We find that shock heating and AGN activity are both ionizing mechanisms in IC 1459 but that the dominant excitation mechanism is by post-asymptotic giant branch stars from its old stellar population.

astro-ph.GA↗

arXiv2019

Keck/OSIRIS IFU Detection of a z $\sim$ 3 Damped Lyman Alpha Host Galaxy

We present Keck/OSIRIS infrared IFU observations of the $z = $ 3.153 sub-DLA DLA2233+131, previously detected in absorption to a background quasar and studied with single slit spectroscopy and PMAS integral field spectroscopy (IFU). We used the Laser Guide Star Adaptive Optics (LGSAO) and OSIRIS IFU to reduce the point-spread function of the background quasar to FWHM$\sim$0.15 arcseconds and marginally resolve extended, foreground DLA emission. We detect [OIII]$λ$5007 emission with a flux F$^{[OIII]\lambda5007}$ = $(2.4\pm0.5)\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$, as well as unresolved [OIII]$λ$4959 and H$βλ$4861 emission. Using a composite spectrum over the emission region, we measure dynamical mass $\sim$ $3.1\times10^9$ M$_{\odot}$. We make several estimates of star formation rate using [OIII]$λ$5007 and H$βλ$4861 emission, and measure a star formation rate of $\sim$ $7.1- 13.6$ M$_{\odot}$ yr$^{-1}$. We map [OIII]$λ$5007 and H$βλ$4861 emission and the corresponding velocity fields to search for signs of kinematic structure. These maps allow for a more detailed kinematic analysis than previously possible for this galaxy. While some regions show slightly red and blue-shifted emission indicative of potential edge-on disk rotation, the data are insufficient to support this interpretation.

astro-ph.GA↗

arXiv2018

Probing the Southern Fermi Bubble in Ultraviolet Absorption using Distant AGNs

The Fermi Bubbles are two giant gamma-ray emitting lobes extending 55$^{\circ}$ above and below the Galactic Center. While the Northern Bubble has been extensively studied in ultraviolet (UV) absorption, little is known about the gas kinematics of the southern Bubble. We use UV absorption-line spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to probe the southern Fermi Bubble using a sample of 17 background AGN projected behind or near the Bubble. We measure the incidence of high-velocity clouds (HVC), finding that four out of six sightlines passing through the Bubble show HVC absorption, versus six out of eleven passing outside. We find strong evidence that the maximum absolute LSR velocity of the HVC components decreases as a function of galactic latitude within the Bubble, for both blueshifted and redshifted components, as expected for a decelerating outflow. We explore whether the column-density ratios SiIV/SiIII, SiIV/SiII and SiIII/SiII correlate with the absolute galactic latitude within the Bubble. These results demonstrate the use of UV absorption-line spectroscopy to characterize the kinematics and ionization conditions of embedded clouds in the Galactic Center outflow.

astro-ph.GA↗

arXiv2015

The most metal-poor damped Lyman alpha systems: An insight into dwarf galaxies at high redshift

In this paper we analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyman-alpha systems (DLAs), to uncover their links to modern-day galaxies. We present evidence that the DLA population as a whole exhibits a `knee' in the relative abundances of the alpha-capture and Fe-peak elements when the metallicity is [Fe/H] ~ -2.0, assuming that Zn traces the build-up of Fe-peak elements. In this respect, the chemical evolution of DLAs is clearly different from that experienced by Milky Way halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. We also find a close correspondence between the kinematics of Local Group dwarf galaxies and of high redshift metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, we propose that the most metal-poor DLAs provide us with a unique opportunity to directly study the dwarf galaxy population more than ten billion years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, we have measured some of the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence. We find that metal-poor DLAs contain a warm neutral medium with T_gas ~ 9600 K predominantly held up by thermal pressure. Furthermore, all of the DLAs in our sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth. These results are among the first empirical descriptions of the environments where the first few generations of stars may have formed in the Universe.

astro-ph.GA↗

arXiv2014

The Magellan Uniform Survey of Damped Lyman alpha Systems II: Paucity of Strong Molecular Hydrogen Absorption

We present the first large, blind and uniformly selected survey for molecular hydrogen (H_2) in damped Lyman alpha systems (DLAs) with moderate-to-high resolution spectra. 86 DLAs were searched for absorption in the many Lyman and Werner H_2 transitions, with approximately 79% completeness for H_2 column densities above N(H_2)=10^17.5 cm^-2 for an assumed Doppler broadening parameter b=2 km s^-1. Only a single strong H_2 absorber was found -- a system detected previously in VLT/UVES spectra. Given our distribution of N(H_2) upper limits, this ~1% detection rate is smaller than expected from previous surveys at 99.8% confidence. Assuming the N(H_2) distribution shape from previous surveys, our detection rate implies a covering factor of ~1% for N(H_2) >= 10^17.5 cm^-2 gas in DLAs (<6% at 95% confidence). We obtained new Magellan/MagE spectra for 53 DLAs; 8 km s^-1 -resolution spectra were available for 27 DLAs. MagE's moderate resolution (~71 km s^-1) yields weaker N(H_2) upper limits and makes them dependent on the assumed Doppler parameter. For example, half the (relevant) previous H_2 detections have N(H_2) >= 10^18.1 cm^-2, a factor of just 3 higher than our median upper limit. Nevertheless, several tests suggest our upper limits are accurate, and they would need to be increased by 1.8 dex to bring our detection rate within 95% confidence of previous surveys.

astro-ph.GA↗

arXiv2013

Precision measures of the primordial abundance of deuterium

We report the discovery of deuterium absorption in the very metal-poor ([Fe/H] = -2.88) damped Lyman-alpha system at z_abs = 3.06726 toward the QSO SDSS J1358+6522. On the basis of 13 resolved D I absorption lines and the damping wings of the H I Lyman alpha transition, we have obtained a new, precise measure of the primordial abundance of deuterium. Furthermore, to bolster the present statistics of precision D/H measures, we have reanalyzed all of the known deuterium absorption-line systems that satisfy a set of strict criteria. We have adopted a blind analysis strategy (to remove human bias), and developed a software package that is specifically designed for precision D/H abundance measurements. For this reanalyzed sample of systems, we obtain a weighted mean of (D/H)_p = (2.53 +/- 0.04) x 10^-5, corresponding to a Universal baryon density100 Omega_b h^2 = 2.202 +/- 0.046 for the standard model of Big Bang Nucleosynthesis. By combining our measure of (D/H)_p with observations of the cosmic microwave background, we derive the effective number of light fermion species, N_eff = 3.28 +/- 0.28. We therefore rule out the existence of an additional (sterile) neutrino (i.e. N_eff = 4.046) at 99.3 percent confidence (2.7 sigma), provided that N_eff and the baryon-to-photon ratio (eta_10) did not change between BBN and recombination. We also place a strong bound on the neutrino degeneracy parameter, xi_D = +0.05 +/- 0.13 based only on the CMB+(D/H)_p observations. Combining xi_D with the current best literature measure of Y_p, we find |xi| <= +0.062. In future, improved measurements of several key reaction rates, in particular d(p,gamma)3He, and further measures of (D/H)_p with a precision comparable to those considered here, should allow even more stringent limits to be placed on new physics beyond the standard model.

astro-ph.CO↗

arXiv2013

Spatially Resolved Emission of a High Redshift DLA Galaxy with the Keck/OSIRIS IFU

We present the first Keck/OSIRIS infrared IFU observations of a high redshift damped Lyman-alpha (DLA) galaxy detected in the line of sight to a background quasar. By utilizing the Laser Guide Star Adaptive Optics (LGSAO) to reduce the quasar PSF to FWHM~0.15 arcsec, we were able to search for and map the foreground DLA emission free from the quasar contamination. We present maps of the H-alpha and [OIII] $λλ$ 5007, 4959 emission of DLA 2222-0946 at a redshift of z ~ 2.35. From the composite spectrum over the H-alpha emission region we measure a star formation rate of 9.5 $\pm$ 1.0 M$_{\odot}$ year$^{-1}$ and a dynamical mass, M$_{dyn}$ = 6.1 x 10$^9$ M$_{\odot}$. The average star formation rate surface density is < Σ_{SFR} > = 0.55 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$, with a central peak of 1.7 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$. Using the standard Kennicutt-Schmidt relation, this corresponds to a gas mass surface density of $Σ_{gas}$ = 243 M$_{\odot}$ pc$^{-2}$. Integrating over the size of the galaxy we find a total gas mass of M$_{gas}$ = 4.2 x 10$^9$ M$_{\odot}$. We estimate the gas fraction of DLA 2222-0946 to be $f_{gas}$ ~ 40%. We detect [NII]$λ$6583 emission at 2.5 sigma significance with a flux corresponding to a metallicity of 75% solar. Comparing this metallicity with that derived from the low-ion absorption gas ~6 kpc away, ~30% solar, indicates possible evidence for a metallicity gradient or enriched in/outflow of gas. Kinematically, both H-alpha and [OIII] emission show relatively constant velocity fields over the central galactic region. While we detect some red and blueshifted clumps of emission, they do not correspond with rotational signatures that support an edge-on disk interpretation.

astro-ph.CO↗

arXiv2013

The Magellan Uniform Survey of Damped Lyman alpha Systems I: Cosmic Metallicity Evolution

We present the chemical abundance measurements of the first large, medium-resolution, uniformly selected damped Lyman alpha system (DLA) survey. The sample contains 99 DLAs towards 89 quasars selected from the SDSS DR5 DLA sample in a uniform way. We analyze the metallicities and kinematic diagnostics, including the velocity width of 90% of the optical depth, Δv_{90}, and the equivalent widths of the SiII 1526, CIV 1548 and MgII 2796 transitions. To avoid strong line-saturation effects on the metallicities measured in medium-resolution spectra (FWHM~71 km/s), we derived metallicities from metal transitions which absorbed at most 35% of the quasar continuum flux. We find the evolution in cosmic mean metallicity of the sample, = (-0.04 +- 0.013)z -(1.06 +- 0.36), consistent with no evolution over the redshift range z ~ [2.2, 4.4], but note that the majority of our sample falls at z ~ [2.2, 3.5]. The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median Δv_{90} and SiII 1526 equivalent width values. While this result may seem to conflict with other large surveys that have detected significant metallicity evolution, such as Rafelski et al. 2012 who found = (-0.22 +- 0.03)z - (0.65 +- 0.09) over z ~ [0, 5], several tests show that these surveys are not inconsistent with our new result. However, over the smaller redshift range covered by our uniformly-selected sample, the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the Rafelski et al. 2012 estimate.

astro-ph.CO↗

arXiv2013

The explosion energy of early stellar populations: The Fe-peak element ratios in low metallicity damped Lyman-alpha systems

The relative abundances of the Fe-peak elements (Ti-Zn) at the lowest metallicities are intimately linked to the physics of core-collapse supernova explosions. With a sample of 25 very metal-poor damped Lyman-alpha systems, we investigate the trends of the Fe-peak element ratios with metallicity. For nine of the 25 DLAs, a direct measurement (or useful upper limit) of one or more of the Ti,Cr,Co,Ni,Zn/Fe abundance ratios could be determined from detected absorption lines. For the remaining systems (without detections), we devised a new form of spectral stacking to estimate the typical Fe-peak element ratios of the DLA population in this metallicity regime. We compare these data to analogous measurements in metal-poor stars of the Galactic halo and to detailed calculations of explosive nucleosynthesis in metal-free stars. We conclude that most of the DLAs in our sample were enriched by stars that released an energy of < 1.2 x 10^51 erg when they exploded as core-collapse supernovae. Finally, we discuss the exciting prospect of measuring Fe-peak element ratios in damped Lyman-alpha systems with Fe/H < 1/1000 of solar when 30-m class telescopes become available. Only then will we be able to pin down the energy that was released by the supernovae of the first stars.

astro-ph.CO↗

arXiv2011

Spectral Polarization of the Redshifted 21 cm Absorption Line Toward 3C 286

A re-analysis of the Stokes-parameter spectra obtained of the z=0.692 21 cm absorption line toward 3C 286 shows that our original claimed detection of Zeeman splitting by a line-of-sight magnetic field, B_los = 87 microgauss is incorrect. Because of an insidious software error, what we reported as Stokes V is actually Stokes U: the revised Stokes V spectrum indicates a 3-sigma upper limit of B_los < 17 microgauss. The correct analysis reveals an absorption feature in fractional polarization that is offset in velocity from the Stokes I spectrum by -1.9 km/s. The polarization position-angle spectrum shows a dip that is also significantly offset from the Stokes I feature, but at a velocity that differs slightly from the absorption feature in fractional polarization. We model the absorption feature with 3 velocity components against the core-jet structure of 3C 286. Our chisquare minimization fitting results in components with differing (1) ratios of H I column density to spin temperature, (2) velocity centroids, and (3) velocity dispersions. The change in polarization position angle with frequency implies incomplete coverage of the background jet source by the absorber. It also implies a spatial variation of the polarization position angle across the jet source, which is observed at frequencies higher than the 839.4 MHz absorption frequency. The multi-component structure of the gas is best understood in terms of components with spatial scales of ~100 pc comprised of hundreds of low-temperature (T < 200 K) clouds with linear dimensions of about 1 pc.

astro-ph.CO↗