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Results for "J. Xavier Prochaska"

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The igmspec Database of Public Spectra Probing the Intergalactic MediumMar 14 2017We describe v02 of igmspec, a database of publically available ultraviolet, optical, and near-infrared spectra that probe the intergalactic medium (IGM). This database, a child of the specdb repository in the specdb github organization, comprises 403277 ... More
An Explanation for the Different X-ray to Optical Column Densities in the Environments of Gamma Ray Bursts: A Progenitor Embedded in a Dense MediumJul 27 2013We study the > 10 ratios in the X-ray to optical column densities inferred from afterglow spectra of Gamma Ray Bursts due to gas surrounding their progenitors. We present time-evolving photoionization calculations for these afterglows and explore different ... More
Circumgalactic Oxygen Absorption and FeedbackAug 23 2017OVI absorption in quasar spectra caused by intervening circumgalactic atmospheres suggests a downturn in the atmospheric column density in sightlines passing beyond about 100 kpc from central star-forming galaxies. This turnover supports the hypothesis ... More
Constraints on the gas masses of low-z damped Lyman-$α$ systemsJun 04 2014Jun 06 2014We report a deep search for redshifted HI 21 cm emission from three damped and sub-damped Lyman-$\alpha$ absorbers (DLAs) at $z \approx 0.1$ with the Green Bank Telescope (GBT). No evidence for a redshifted HI 21 cm emission signal was obtained in the ... More
The Little Cub: Discovery of an Extremely Metal-Poor Star-Forming Galaxy in the Local UniverseAug 03 2017We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local Universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its ... More
Quasars Probing Quasars IX. The Kinematics of the Circumgalactic Medium Surrounding z ~ 2 QuasarsMay 09 2017Mar 22 2018We examine the kinematics of the gas in the environments of galaxies hosting quasars at $z\sim2$. We employ 148 projected quasar pairs to study the circumgalactic gas of the foreground quasars in absorption. The sample selects foreground quasars with ... More
An Empirical Relation between Sodium Absorption and Dust ExtinctionJun 26 2012Aug 02 2012Dust extinction and reddening are ubiquitous in astronomical observations and are often a major source of systematic uncertainty. We present here a study of the correlation between extinction in the Milky Way and the equivalent width of the NaI D absorption ... More
A z = 3 Lyman Alpha Blob Associated with a Damped Lyman Alpha System Proximate to its Background QuasarJul 14 2008We report on the discovery of a bright Lyman alpha blob associated with the z=3 quasar SDSSJ124020.91+145535.6 which is also coincident with strong damped Lyman alpha absorption from a foreground galaxy (a so-called proximate damped Lyman alpha system; ... More
Deep Learning of Quasar Spectra to Discover and Characterize Damped Lya SystemsSep 14 2017We have designed, developed, and applied a convolutional neural network (CNN) architecture using multi-task learning to search for and characterize strong HI Lya absorption in quasar spectra. Without any explicit modeling of the quasar continuum nor application ... More
Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha SystemsMay 07 2009Jun 23 2009We continue our recent work to characterize the plasma content of high-redshift damped and sub-damped Lyman-alpha systems (DLAs/sub-DLAs), which represent multi-phase gaseous (proto)galactic disks and halos seen toward a background source. We survey N ... More
Keck ESI Observations of Metal-Poor Damped Lyman-α SystemsJun 21 2010We present the first results from a survey of SDSS quasars selected for strong H I damped Lyman-{\alpha} (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g. C II {\lambda}1334 and Si II {\lambda}1260). ... More
The Cosmic Evolution of the Metallicity Distribution of Ionized Gas Traced by Lyman Limit SystemsAug 08 2016We present the first results from our KODIAQ Z survey aimed to determine the metallicity distribution and physical properties of the partial and full Lyman limit systems (pLLSs and LLSs; 16.2<log N(HI)<19) at z>2, which probe gas in the interface regions ... More
Revealing the host galaxy of a quasar 2175 Å$ $ dust absorber at z = 2.12Apr 06 2018We report the first detection of the host galaxy of a strong 2175 \AA$ $ dust absorber at z = 2.12 towards the background quasar SDSS J121143.42+083349.7 using HST/WFC3 IR F140W direct imaging and G141 grism spectroscopy. The spectroscopically confirmed ... More
Spectral Polarization of the Redshifted 21 cm Absorption Line Toward 3C 286Mar 21 2011A 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 ... More
On the CGM Fundamental Plane: The Halo Mass Dependency of Circumgalactic HIDec 06 2017Aug 07 2018We analyze the equivalent widths of HI Ly-$\alpha$ ($W_{Ly\alpha}$) absorption from the inner (R < 160 kpc) circumgalactic medium (CGM) of 85 galaxies at $z \sim 0$ with stellar masses $M*$ ranging $\rm{8 \leq log M* / M_{\odot} \leq 11.6}$. Across three ... More
Evidence of ongoing AGN-driven feedback in a quiescent post starburst E+A galaxyMay 10 2017Post starburst E+A galaxies are thought to have experienced a significant starburst that was quenched abruptly. Their disturbed, bulge-dominated morphologies suggest that they are merger remnants. We present ESI/Keck observations of SDSS J132401.63+454620.6, ... More
Identification of variability in recent star formation histories of local galaxies based on H$α$/UV ratioMay 02 2017Sep 24 2018Because the timescale of H$\alpha$ emission (several tens of Myr) following star formation is significantly shorter than that of UV radiation (a few hundred Myr), the H$\alpha$/UV flux ratio provides insight on the star formation histories (SFHs) of galaxies ... More
The Circumgalactic Medium of Submillimeter Galaxies. II. Unobscured QSOs within Dusty Starbursts and QSO Sightlines with Impact Parameters below 100 KiloparsecMay 24 2017Jun 26 2017We present Atacama Large Millimeter/submillimeter Array (ALMA) 870um observations of 29 bright Herschel sources near high-redshift QSOs. The observations confirm that 20 of the Herschel sources are submillimeter-bright galaxies (SMGs) and identify 16 ... More
The chemistry of the most metal-rich damped Lyman $α$ systems at z$\sim2$ II. Context with the Local GroupJul 29 2015Using our sample of the most metal-rich damped Lyman $\alpha$ systems (DLAs) at z$\sim2$, and two literature compilations of chemical abundances in 341 DLAs and 2818 stars, we present an analysis of the chemical composition of DLAs in the context of the ... More
Quasar 2175 Å dust absorbers I: metallicity, depletion pattern, and kinematicsAug 14 2017We present 13 new 2175 {\AA} dust absorbers at z_abs = 1.0 - 2.2 towards background quasars from the Sloan Digital Sky Survey. These absorbers are examined in detail using data from the Echelle Spectrograph and Imager (ESI) on the Keck II telescope. Many ... More
High Dust Depletion in Two Intervening Quasar Absorption Line Systems with the 2175-Å Extinction Bump at $z\sim1.4$Sep 28 2010We present the column densities of heavy-elements and dust depletion studies in twostrong Mg~II absorption systems at $z\sim1.4$ displaying the 2175-{\AA} dust extinction feature. Column densities are measured from low-ionization absorption lines using ... More
Statistical Detection of the HeII Transverse Proximity Effect: Evidence for Sustained Quasar Activity for $>$25 Million YearsJan 30 2017The HeII transverse proximity effect -- enhanced HeII Ly$\alpha$~transmission in a background sightline caused by the ionizing radiation of a foreground quasar -- offers a unique opportunity to probe the morphology of quasar-driven HeII reionization. ... More
Implications of $z \sim 6$ Quasar Proximity Zones for the Epoch of Reionization and Quasar LifetimesMar 07 2017May 10 2017We study quasar proximity zones in the redshift range $5.77 \leq z \leq 6.54$ by homogeneously analyzing $34$ medium resolution spectra, encompassing both archival and newly obtained data, and exploiting recently updated systemic redshift and magnitude ... More
A VLT/FORS2 Narrowband Imaging Search for MgII Emission Around z ~ 0.7 GalaxiesMay 14 2019We perform a Very Large Telescope FOcal Reducer and low dispersion Spectrograph 2 (VLT/FORS2) narrowband imaging search around 5 star-forming galaxies at redshift z=0.67-0.69 in the Great Observatories Origins Deep Survey South (GOODS-S) field to constrain ... More
Reconciling the Metallicity Distributions of Gamma-ray Burst, Damped Lyman-alpha, and Lyman-break Galaxies at z=3Jan 22 2008Apr 13 2008We test the hypothesis that the host galaxies of long-duration gamma-ray bursts (GRBs) as well as quasar-selected damped Lyman-alpha (DLA) systems are drawn from the population of UV-selected star-forming, high-z galaxies (generally referred to as Lyman-break ... More
Galactic and Circumgalactic OVI and its Impact on the Cosmological Metal and Baryon Budgets at 2<z<3.5Jan 08 2014Apr 28 2014We present the first results from our NASA Keck Observatory Database of Ionized Absorbers toward Quasars (KODIAQ) survey which aims to characterize the properties of the highly ionized gas of high redshift galaxies and their circumgalactic medium (CGM) ... More
On the limitations of statistical absorption studies with the Sloan Digital Sky Surveys I--IIIFeb 06 2018Apr 04 2018We investigate the limitations of statistical absorption measurements with the SDSS optical spectroscopic surveys. We show that changes in the data reduction strategy throughout different data releases have led to a better accuracy at long wavelengths, ... More
Imprints of the first billion years: Lyman limit systems at $z \sim 5$Oct 23 2018Lyman Limit systems (LLSs) trace the low-density circumgalactic medium and the most dense regions of the intergalactic medium, so their number density and evolution at high redshift, just after reionisation, are important to constrain. We present a survey ... More
A Deep Narrowband Imaging Search for CIV and He II Emission from Ly$α$ BlobsJul 10 2014We conduct a deep narrow-band imaging survey of 13 Ly$\alpha$ blobs (LABs) located in the SSA22 proto-cluster at z~3.1 in the CIV and HeII emission lines in an effort to constrain the physical process powering the Ly$\alpha$ emission in LABs. Our observations ... More
The Optical Variability of SDSS Quasars from Multi-epoch Spectroscopy. III. A Sudden UV Cutoff in Quasar SDSS J2317+0005May 24 2016We have collected near-infrared to X-ray data of 20 multi-epoch heavily reddened SDSS quasars to investigate the physical mechanism of reddening. Of these, J2317+0005 is found to be a UV cutoff quasar. Its continuum, which usually appears normal, decreases ... More
MUSE searches for galaxies near very metal-poor gas clouds at z~3: new constraints for cold accretion modelsJul 13 2016Aug 03 2016We report on the search for galaxies in the proximity of two very metal-poor gas clouds at z~3 towards the quasar Q0956+122. With a 5-hour MUSE integration in a ~500x500 kpc^2 region centred at the quasar position, we achieve a >80% complete spectroscopic ... More
Evidence for Ubiquitous Collimated Galactic-Scale Outflows along the Star-Forming Sequence at z~0.5Jul 04 2013We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption line profiles in individual spectra of 105 galaxies at 0.3<z<1.4. The galaxies, drawn from redshift surveys of the GOODS fields and the Extended Groth Strip, fully sample the ... More
The UV-bright Quasar Survey (UVQS): DR1Feb 19 2016We present the first data release (DR1) from our UV-bright Quasar Survey (UVQS) for new $z \sim 1$ active galactic nuclei (AGN) across the sky. Using simple GALEX UV and WISE near-IR color selection criteria, we generated a list of 1450 primary candidates ... More
The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming GalaxiesAug 31 2016Nov 15 2016The total contribution of diffuse halo gas to the galaxy baryon budget strongly depends on its dominant ionization state. In this paper, we address the physical conditions in the highly ionized circumgalactic medium (CGM) traced by OVI absorption lines ... More
Discovery of a Lya emitting dark-cloud within z ~ 2.8 SMMJ02399-0136 systemMar 07 2019We present Keck/KCWI integral field spectrograph observations of the complex system surrounding SMM J02399$-$0136 (a lensed $z=2.8$ sub-mm galaxy), including an associated Ly$\rm \alpha$ nebula, a dust-obscured, broad-absorption-line quasar, and neighboring ... More
The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming GalaxiesAug 31 2016The total contribution of diffuse halo gas to the galaxy baryon budget strongly depends on its dominant ionization state. In this paper, we address the physical conditions in the highly-ionized circumgalactic medium (CGM) traced by OVI absorption lines ... More
Direct evidence of AGN-feedback: a post starburst galaxy stripped of its gas by AGN-driven windsApr 09 2018Post starburst E+A galaxies show indications of a powerful starburst that was quenched abruptly. Their disturbed, bulge-dominated morphologies suggest that they are merger remnants. The more massive E+A galaxies are suggested to be quenched by AGN feedback, ... More
Cold gas and a Milky Way-type 2175 Å bump in a metal-rich and highly depleted absorption systemSep 04 2015We report the detection of a strong Milky Way-type 2175 \AA$ $ extinction bump at $z$ = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7 from the Sloan Digital Sky Survey (SDSS) Data Release 10. We conduct follow up observations with the ... More
MApping the Most Massive Overdensities (MAMMOTH) II -- Discovery of an Extremely Massive Overdensity BOSS1441 at $z=2.32$Sep 09 2016Cosmological simulations suggest a strong correlation between high optical-depth Ly$\alpha$ absorbers, which arise from the intergalactic medium (IGM), and 3-D mass overdensities on scales of $10-30$ $h^{-1}$ comoving Mpc. By examining the absorption ... More
The End of Helium Reionization at z~2.7 Inferred from Cosmic Variance in HST/COS HeII Lyman Alpha Absorption SpectraMar 29 2011May 11 2011We report on the detection of strongly varying intergalactic HeII absorption in HST/COS spectra of two z~3 quasars. From our homogeneous analysis of the HeII absorption in these and three archival sightlines, we find a marked increase in the mean HeII ... More
The Power Spectrum of the Lyman-$α$ Forest at z < 0.5Aug 16 2018Apr 09 2019We present new measurements of the flux power-spectrum P(k) of the $z<0.5$ HI Lyman-$\alpha$ forest spanning scales k ~ 0.001-0.1 s/km. These results were derived from 65 far ultraviolet quasar spectra (resolution R~18000) observed with the Cosmic Origin ... More
A VLT/MUSE galaxy survey towards QSO Q1410: looking for a WHIM traced by BLAs in inter-cluster filamentsMar 26 2018May 25 2018Cosmological simulations predict that a significant fraction of the low-$z$ baryon budget resides in large-scale filaments in the form of a diffuse plasma at temperatures $T \sim 10^{5} - 10^{7}$ K. However, direct observation of this so-called warm-hot ... More
Molecular Emission from a Galaxy Associated with a z~2.2 Damped Lyman-alpha AbsorberMar 15 2018Using the Atacama Large Millimeter/sub-millimeter Array, we have detected CO(3-2) line and far-infrared continuum emission from a galaxy associated with a high-metallicity ([M/H] = -0.27) damped Ly-alpha absorber (DLA) at z =2.19289. The galaxy is located ... More
The large and small scale properties of the intergalactic gas in the Slug Ly-alpha nebula revealed by MUSE HeII emission observationsNov 28 2018Dec 20 2018With a projected size of about 450 kpc at z~2.3, the Slug Ly-alpha nebula is a rare laboratory to study, in emission, the properties of the intergalactic gas in the Cosmic Web. Since its discovery, the Slug has been the subject of several spectroscopic ... More
The COS Absorption Survey of Baryon Harbors: The Galaxy Database and Cross-Correlation Analysis of OVI SystemsAug 21 2019We describe the survey for galaxies in the fields surrounding 9 sightlines to far-UV bright, z~1 quasars that define the COS Absorption Survey of Baryon Harbors (CASBaH) program. The photometry and spectroscopy that comprise the dataset come from a mixture ... More
Linking gas and galaxies at high redshift: MUSE surveys the environments of six damped Lyman alpha galaxies at z~3Apr 15 2019We present results from a survey of galaxies in the fields of six z>3 Damped Lyman alpha systems (DLAs) using the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). We report a high detection rate of up to ~80% of galaxies within ... More
Detailed Design of a Deployable Tertiary Mirror for the Keck I TelescopeSep 07 2016Motivated by the ever increasing pursuit of science with the transient sky (dubbed Time Domain Astronomy or TDA), we are fabricating and will commission a new deployable tertiary mirror for the Keck I telescope (K1DM3) at the W.M. Keck Observatory. This ... More
A metal-poor damped Ly-alpha system at redshift 6.4Mar 14 2019We identify a strong Ly-alpha damping wing profile in the spectrum of the quasar P183+05 at z=6.4386. Given the detection of several narrow metal absorption lines at z=6.40392, the most likely explanation for the absorption profile is that it is due to ... More
Extreme circumgalactic HI and CIII absorption around the most massive, quenched galaxiesSep 26 2018Luminous red galaxies (LRGs) are the most massive galaxies at $z\sim 0.5$ and, by selection, have negligible star formation. These objects have halo masses between those of $L_{*}$ galaxies, whose circumgalactic media (CGM) are observed to have large ... More
Quasars Probing Quasars VI. Excess HI Absorption Within One Proper Mpc of z~2 QuasarsAug 28 2013With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the HI Lya absorption transverse to luminous, ... More
Fast Radio Burst Tomography of the Unseen UniverseMar 12 2019The discovery of Fast Radio Bursts (FRBs) at cosmological distances has opened a powerful window on otherwise unseen matter in the Universe. In the 2020s, observations of $>10^{4}$ FRBs will assess the baryon contents and physical conditions in the hot/diffuse ... More
Keck/Palomar Cosmic Web Imagers (KCWI/PCWI) Reveal an Enormous Ly$α$ Nebula in an Extremely Overdense QSO Pair Field at $z=2.45$Mar 28 2018Enormous Ly$\alpha$ nebulae (ELANe) represent the extrema of Ly$\alpha$ nebulosities. They have detected extents of $>200$ kpc in Ly$\alpha$ and Ly$\alpha$ luminosities $>10^{44}$ erg s$^{-1}$. The ELAN population is an ideal laboratory to study the interactions ... More
A search for the host galaxy of FRB171020Oct 10 2018We report on a search for the host galaxy of FRB171020, the fast radio burst with the smallest recorded dispersion measure (DM $=114$ pc cm$^{-3}$) of our on-ongoing ASKAP survey. The low DM confines the burst location within a sufficiently small volume ... More
Discovery of an Enormous Ly$α$ nebula in a massive galaxy overdensity at $z=2.3$Sep 13 2016Jan 02 2019Enormous Ly$\alpha$ Nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys, or ... More
Nature and statistical properties of quasar associated absorption systems in the XQ-100 Legacy SurveyMay 15 2016We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. ... More
The Neutral Hydrogen Cosmological Mass Density at z=5Jun 05 2015We present the largest homogeneous survey of $z>4.4$ damped Lyman-$\alpha$ systems (DLAs) using the spectra of 163 QSOs that comprise the Giant Gemini GMOS (GGG) survey. With this survey we make the most precise high-redshift measurement of the cosmological ... More
GALEX far-UV color selection of UV-bright high-redshift quasarsApr 20 2010Dec 15 2010We study the small population of z>2.7 quasars detected by GALEX, whose far-UV emission is not extinguished by intervening HI Lyman limit systems. These quasars are of particular importance to detect intergalactic HeII absorption along their sightlines. ... More
Probing Galactic Halos with Fast Radio BurstsJan 30 2019The precise localization (<1'') of multiple fast radio bursts (FRBs) to z>0.1 galaxies has confirmed that the dispersion measures (DMs) of these enigmatic sources afford a new opportunity to probe the diffuse ionized gas around and in between galaxies. ... More
The SPectral Image Typer (SPIT)Jul 04 2018We present the Spectral Image Typer (SPIT), a convolutional neural network (CNN) built to classify spectral images. In contrast to traditional, rules-based algorithms which rely on meta data provided with the image (e.g. header cards), SPIT is trained ... More
The Astrophysical Consequences of Intervening Galaxy Gas on Fast Radio BurstsNov 01 2017We adopt and analyze results on the incidence and physical properties of damped Ly$\alpha$ systems (DLAs) to predict the astrophysical impact of gas in galaxies on observations of Fast Radio Bursts (FRBs). Three DLA measures form the basis of this analysis: ... More
The spin and charge gaps of the half-filled N-leg Kondo laddersMay 17 2004In this work, we study N-leg Kondo ladders at half-filling through the density matrix renormalization group. We found non-zero spin and charge gaps for any finite number of legs and Kondo coupling $J>0$. We also show evidence of the existence of a quantum ... More
Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas Around the Andromeda GalaxyJun 06 2017Aug 22 2017We present a deep search for HI 21-cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large program Hubble Space Telescope program to study the circumgalactic medium of the Andromeda galaxy. Our observations with the Robert C. ... More
The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational Wave SourceOct 16 2017We discovered Swope Supernova Survey 2017a (SSS17a) in the LIGO/Virgo Collaboration (LVC) localization volume of GW170817, the first detected binary neutron star (BNS) merger, only 10.9 hours after the trigger. No object was present at the location of ... More
An Ultraviolet Spectrum of the Tidal Disruption Flare ASASSN-14liJan 13 2016Feb 02 2016We present a Hubble Space Telescope STIS spectrum of ASASSN-14li, the first rest-frame UV spectrum of a tidal disruption flare (TDF). The underlying continuum is well fit by a blackbody with $T_{\mathrm{UV}} = 3.5 \times 10^{4}$ K, an order of magnitude ... More
Lyman-alpha Forest Tomography from Background Galaxies: The First Megaparsec-Resolution Large-Scale Structure Map at z>2Sep 19 2014We present the first observations of foreground Lyman-$\alpha$ forest absorption from high-redshift galaxies, targeting 24 star-forming galaxies (SFGs) with $z\sim 2.3-2.8$ within a $5' \times 15'$ region of the COSMOS field. The transverse sightline ... More
GRB 090426: The Environment of a Rest-Frame 0.35-second Gamma-Ray Burst at Redshift z=2.609Jul 09 2009We present the discovery of an absorption-line redshift of z = 2.609 for GRB 090426, establishing the first firm lower limit to a redshift for a gamma-ray burst with an observed duration of <2 s. With a rest-frame burst duration of T_90z = 0.35 s and ... More
Quasars Probing Quasars IV: Joint Constraints on the Circumgalactic Medium from Absorption and EmissionMar 11 2013We have constructed a sample of 29 close projected quasar pairs where the background quasar spectrum reveals absorption from optically thick HI gas associated with the foreground quasar. These unique sightlines allow us to study the quasar circumgalactic ... More
On the Analysis of DLA KinematicsSep 20 2010We discuss two mistreatments of damped Lya (DLA) kinematic analysis that were first performed by Haehnelt, Steinmetz, & Rauch (1998; hereafter HSR98) and have recently been repeated by Hong et al. (2010; arXiv:1008.4242v1, arXiv:1008.4242v2; hereafter ... More
Simple Models of Metal-Line Absorption and Emission from Cool Gas OutflowsFeb 16 2011We analyze the absorption and emission-line profiles produced by a set of simple, cool gas wind models motivated by galactic-scale outflow observations. We implement monte carlo radiative transfer techniques that track the propagation of scattered and ... More
Quasars Probing Quasars III: New Clues to Feedback, Quenching, and the Physics of Massive Galaxy FormationJun 04 2008Sep 15 2008Galaxies hosting z~2 quasars are the high-$z$ progenitors of today's massive `red-and-dead' galaxies. With close pairs of quasars at different redshifts, a background quasar can be used to study a foreground quasar's halo gas in absorption, providing ... More
ALMA and RATIR observations of GRB131030ADec 20 2016We report on the first open-use based Atacama Large Millimeter/submm Array (ALMA) 345-GHz observation for the late afterglow phase of GRB131030A. The ALMA observation constrained a deep limit at 17.1 d for the afterglow and host galaxy. We also identified ... More
On the (Non)Evolution of HI Disks over Cosmic TimeNov 12 2008We present new results on the frequency distribution of projected HI column densities f(N,X), total comoving covering fraction, and integrated mass densities rho_HI of high redshift, HI `disks' from a survey of damped Lya systems (DLAs) in the Sloan Digital ... More
Interpolation and peak functions for the Nevanlinna and Smirnov classesDec 26 2012It is known (implicit in [HMNT]) that when $\Lambda$ is an interpolating sequence for the Nevanlinna or the Smirnov class then there exist functions $f_\lambda$ in these spaces, with uniform control of their growth and attaining values 1 on $\lambda$ ... More
A Metal-Strong and Dust-Rich Damped \lya Absorption System toward the Quasar SDSS J115705.52+615521.7Oct 03 2012Nov 03 2012(Abridged for arXiv) We report the discovery of an unusual, extremely dust-rich and metal-strong damped \lya absorption system (DLA) at a redshift $z_{a}=2.4596$ toward the quasar SDSS J115705.52+615521.7 (hereafter J1157+6155) with an emission-line redshift ... More
A Dusty Mg~II absorber Associated with the Quasar SDSS J003545.13+011441.2Sep 28 2010We report on a dusty Mg~II absorber associated with the quasar SDSSJ003545.13+011441.2 (hereafter J0035+0114) at $z$=1.5501, which is the strongest one among the three Mg~II absorbers along the sight line of quasar. The two low redshift intervening absorbers ... More
Constraining Sub-Parsec Binary Supermassive Black Holes in Quasars with Multi-Epoch Spectroscopy. III. Candidates from Continued Radial Velocity TestsSep 12 2018Oct 26 2018Quasars whose broad emission lines show temporal, bulk radial velocity (RV) shifts have been proposed as candidate sub-parsec (sub-pc), binary supermassive black holes (BSBHs). We identified a sample of 16 BSBH candidates based on two-epoch spectroscopy ... More
Searching for the Lowest Metallicity GalaxiesJul 11 2018We report a method of identifying candidate low-metallicity blue compact dwarf galaxies (BCDs) from the Sloan Digital Sky Survey (SDSS) imaging data and present 3-m Lick Observatory and 10-m W.M. Keck Observatory optical spectroscopic observations of ... More
Metallicities and dust content of proximate damped Lyman alpha systems in the Sloan Digital Sky SurveyOct 25 2010Composite spectra of 85 proximate absorbers (log N(HI)>20 and velocity difference between the absorption and emission redshift, dv<10,000 km/s) in the SDSS are used to investigate the trends of metal line strengths with velocity separation from the QSO. ... More
A comprehensive set of elemental abundances in damped Ly-alpha systems: revealing the nature of these high-redshift galaxiesDec 08 2003By combining our UVES-VLT spectra of a sample of four damped Ly-alpha systems (DLAs) toward the quasars Q0100+13, Q1331+17, Q2231-00 and Q2343+12 with the existing HIRES-Keck spectra, we covered the total spectral range from 3150 to 10000 A for the four ... More
Compilation of extended recursion in call-by-value functional languagesFeb 07 2009This paper formalizes and proves correct a compilation scheme for mutually-recursive definitions in call-by-value functional languages. This scheme supports a wider range of recursive definitions than previous methods. We formalize our technique as a ... More
Detection of Pristine Gas Two Billion Years after the Big BangNov 09 2011In the current cosmological model, only the three lightest elements were created in the first few minutes after the Big Bang; all other elements were produced later in stars. To date, however, heavy elements have been observed in all astrophysical environments. ... More
Probing the Physical Conditions of Atomic Gas at High RedshiftNov 18 2014Nov 30 2014A new method is used to measure the physical conditions of the gas in damped Lyman-alpha systems (DLAs). Using high resolution absorption spectra of a sample of 80 DLAs, we are able to measure the ratio of the upper to lower fine-structure levels of the ... More
The Fundamental Plane of Damped Lyman Alpha SystemsMar 28 2013May 06 2013Using a sample of 100 H I - selected damped Lyman alpha (DLA) systems, observed with the High Resolution Echelle Spectrometer on the Keck I telescope, we present evidence that the scatter in the well-studied correlation between the redshift and metallicity ... More
Precise limits on cosmological variability of the fine-structure constant with zinc and chromium quasar absorption linesJun 20 2016Oct 02 2016The strongest transitions of Zn and CrII are the most sensitive to relative variations in the fine-structure constant ($\Delta\alpha/\alpha$) among the transitions commonly observed in quasar absorption spectra. They also lie within just 40\AA\ of each ... More
The Bright Symbiotic Mira EF AquilaeDec 13 2015An incidental spectrum of the poorly studied long period variable EF Aquilae shows [O III] emission indicative of a symbiotic star. Strong GALEX detections in the UV reinforce this classification, providing overt evidence for the presence of the hot subluminous ... More
Understanding Physical Conditions in High Redshift Galaxies through C I Fine Structure Lines: Data and MethodologyAug 27 2010We probe the physical conditions in high redshift galaxies, specifically, the Damped Lyman-alpha Systems (DLAs) using neutral carbon (CI) fine structure lines and molecular hydrogen (H2). We report five new detections of CI and analyze the CI in an additional ... More
A Direct Measurement of the IGM Opacity to HI Ionizing PhotonsSep 30 2009We present a new method to directly measure the opacity from HI Lyman limit (LL) absorption k_LL along quasar sightlines by the intergalactic medium (IGM). The approach analyzes the average (``stacked'') spectrum of an ensemble of quasars at a common ... More
Quasars Probing Quasars VIII. The Physical Properties of the Cool Circumgalactic Medium Surrounding z ~ 2-3 Massive Galaxies Hosting QuasarsOct 20 2015Aug 12 2016We characterize the physical properties of the cool T ~10^4 K circumgalactic medium surrounding z ~2-3 quasar host galaxies, which are predicted to evolve into present day massive ellipticals. Using a statistical sample of 14 quasar pairs with projected ... More
The gas and stellar mass of low-redshift damped Lyman-$α$ absorbersOct 02 2017We report Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet and Arecibo Telescope H{\sc i} 21cm spectroscopic studies of six damped and sub-damped Lyman-$\alpha$ absorbers (DLAs and sub-DLAs, respectively) at $z \lesssim 0.1$, that have ... More
Metal-Poor, Cool Gas in the Circumgalactic Medium of a z = 2.4 Star-Forming Galaxy: Direct Evidence for Cold Accretion?Jul 24 2013Aug 22 2013In our current galaxy formation paradigm, high-redshift galaxies are predominantly fuelled by accretion of cool, metal-poor gas from the intergalactic medium. Hydrodynamical simulations predict that this material should be observable in absorption against ... More
A Substantial Mass of Cool, Metal-Enriched Gas Surrounding the Progenitors of Modern-Day EllipticalsNov 26 2012The hosts of luminous z~2 quasars evolve into today's massive elliptical galaxies. Current theories predict that the circum-galactic medium (CGM) of these massive, dark-matter halos (M~10^12.5 Msun) should be dominated by a T~10^7 K virialized plasma. ... More
Ionization corrections in a multi-phase interstellar medium: Lessons from a z~2 sub-DLAJun 30 2010We present a high resolution (FWHM=2.7 km/s), high S/N echelle spectrum for the z = 2.26 QSO J2123-0050 and determine elemental abundances for the z = 2.06 sub-DLA in its line of sight. This high redshift sub-DLA has a complex kinematic structure and ... More
Quasars Probing Quasars VII. The Pinnacle of the Cool Circumgalactic Medium Surrounds Massive z~2 GalaxiesSep 22 2014We survey the incidence and absorption strength of the metal-line transitions CII 1334 and CIV from the circumgalactic medium (CGM) surrounding z~2 quasars, which act as signposts for massive dark matter halos M_halo~10^12.5 Msun. On scales of the virial ... More
A search for H$α$ emission in high-metallicity damped Lyman-$α$ systems at $z \sim 2.4$Jan 23 2015We report on a sensitive search for redshifted H$\alpha$ line-emission from three high-metallicity damped Ly$\alpha$ absorbers (DLAs) at $z \approx 2.4$ with the Near-infrared Integral Field Spectrometer (NIFS) on the Gemini-North telescope, assisted ... More
A Definitive Survey for Lyman Limit Systems at z~3.5 with the Sloan Digital Sky SurveyDec 01 2009We perform a semi-automated survey for tau>=2 Lyman Limit systems (LLSs) in quasar spectra from the Sloan Digital Sky Survey, Data Release 7. From a starting sample of 2473 quasars with zem=3.6-4.4, we analyze 469 spectra meeting strict seletion criteria ... More
The physical properties of z>2 Lyman limit systems: new constraints for feedback and accretion modelsNov 05 2015We study the physical properties of a homogeneous sample of 157 optically-thick absorption line systems at redshifts ~1.8-4.4, selected from a high-dispersion spectroscopic survey of Lyman limit systems (LLSs). By means of multiple ionisation models and ... More
Early and Extended Helium Reionization Over More Than 600 Million Years of Cosmic TimeMay 28 2014Jun 01 2016We measure the effective optical depth of HeII Ly\alpha\ absorption \tau$_\mathsf{eff,HeII}$ at 2.3<z<3.5 in 17 UV-transmitting quasars observed with UV spectrographs on the Hubble Space Telescope (HST). The median \tau$_\mathsf{eff,HeII}$ values increase ... More
Data Reduction with the MIKE SpectrometerJun 29 2015Jul 01 2015This manuscript describes the design, usage, and data-reduction pipeline developed for the Magellan Inamori Kyocera Echelle (MIKE) spectrometer used with the Magellan telescope at the Las Campanas Observatory. We summarize the basic characteristics of ... More
Small Fermi surface in the one-dimensional Kondo lattice modelSep 26 2002We study the one-dimensional Kondo lattice model through the density matrix renormalization group (DMRG). Our results for the spin correlation function indicate the presence of a small Fermi surface in large portions of the phase diagram, in contrast ... More
Deep Learning Based Cryptographic Primitive ClassificationSep 25 2017Cryptovirological augmentations present an immediate, incomparable threat. Over the last decade, the substantial proliferation of crypto-ransomware has had widespread consequences for consumers and organisations alike. Established preventive measures ... More