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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
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
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
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
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
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
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
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
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
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
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
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
Constraining the lifetime and opening angle of quasars using fluorescent Lyman $α$ emission: the case of Q0420-388Sep 30 2015Jul 08 2016A toy model is developed to understand how the spatial distribution of fluorescent emitters in the vicinity of bright quasars could be affected by the geometry of the quasar bi-conical radiation field and by its lifetime. The model is then applied to ... 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
IGM-Vis: Analyzing Intergalactic and Circumgalactic Medium Absorption Using Quasar Sightlines in a Cosmic Web ContextDec 17 2018Apr 25 2019We introduce IGM-Vis, a novel astrophysics visualization and data analysis application for investigating galaxies and the gas that surrounds them in context with their larger scale environment, the Cosmic Web. Environment is an important factor in the ... More
A cosmic web filament revealed in Lyman-alpha emission around a luminous high-redshift quasarJan 17 2014Simulations of structure formation in the Universe predict that galaxies are embedded in a "cosmic web", where the majority of baryons reside as rarefied and highly ionized gas. This material has been studied for decades in absorption against background ... 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
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
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
Quasar Quartet Embedded in Giant Nebula Reveals Rare Massive Structure in Distant UniverseMay 14 2015All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated by cosmological distances. In a survey for Lyman-alpha ... 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
HI content, metallicities and spin temperatures of damped and sub-damped Lyman alpha systems in the redshift desert (0.6 < z < 1.7)May 06 2012The HI 21cm absorption optical depth and the N(HI) derived from Lya absorption can be combined to yield the spin temperature (Ts) of DLAs. Although Ts measurements exist for samples of DLAs with z <0.6 and z >1.7, the intermediate redshift regime currently ... More
Precious Metals in SDSS Quasar Spectra I: Tracking the Evolution of Strong, 1.5 < z < 4.5 CIV Absorbers with Thousands of SystemsApr 12 2012Jan 07 2013We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey Data-Release 7. We visually verified over 16,000 CIV systems with 1.46 < z < 4.55---a sample size that renders Poisson ... More
Deep HeII and CIV Spectroscopy of a Giant Lyman alpha Nebula: Dense Compact Gas Clumps in the Circumgalactic Medium of a z~2 QuasarApr 14 2015The recent discovery by Cantalupo et al. (2014) of the largest (~500 kpc) and luminous Ly-alpha nebula associated with the quasar UM287 (z=2.279) poses a great challenge to our current understanding of the astrophysics of the halos hosting massive z~2 ... 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
The Evolution of the HeII-Ionizing Background at Redshifts 2.3<z<3.8 Inferred from a Statistical Sample of 24 HST/COS HeII Ly$α$ Absorption SpectraAug 15 2018We present new measurements of the large-scale effective optical depth of HeII Ly$\alpha$ absorption, $\tau_{\rm eff}$, at $2.54<z<3.86$ toward 16 HeII-transparent quasars observed with the Cosmic Origins Spectrograph on the Hubble Space Telescope, to ... More
Dissecting the properties of optically-thick hydrogen at the peak of cosmic star formation historyAug 05 2013Aug 26 2013We present results of a blind survey of Lyman limit systems (LLSs) detected in absorption against 105 quasars at z~3 using the blue sensitive MagE spectrograph at the Magellan Clay telescope. By searching for Lyman limit absorption in the wavelength range ... More
The most metal-rich damped Lyman alpha systems at z>1.5 I: The DataDec 17 2014We present HIRES observations for 30 damped Lyman alpha systems, selected on the basis of their large metal column densities from previous, lower resolution data. The measured metal column densities for Fe, Zn, S, Si, Cr, Mn, and Ni are provided for these ... More
The Stacked Lyman-Alpha Emission Profile from the Circum-Galactic Medium of z~2 QuasarsApr 11 2016In the context of the FLASHLIGHT survey, we obtained deep narrow band images of 15 $z\sim2$ quasars with GMOS on Gemini-South in an effort to measure Ly$\alpha$ emission from circum- and inter-galactic gas on scales of hundreds of kpc from the central ... More
Kinematics of CIV and [OIII] emission in luminous high-redshift quasarsApr 30 2019We characterise ionised gas outflows using a large sample of ~330 high-luminosity (45.5 < log(L_bol/erg s^-1) < 49.0), high-redshift (1.5 < z < 4.0) quasars via their [OIII]4960,5008 emission. The median velocity width of the [OIII] emission line is 1540 ... More
Wavelength Accuracy of the Keck HIRES Spectrograph and Measuring Changes in the Fine Structure ConstantApr 30 2009Nov 17 2009We report on an attempt to accurately wavelength calibrate four nights of data taken with the Keck HIRES spectrograph on QSO PHL957, for the purpose of determining whether the fine structure constant was different in the past. Using new software and techniques, ... 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
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
The Role of Stellar Feedback in the Dynamics of HII RegionsSep 21 2013Sep 15 2014Stellar feedback is often cited as the biggest uncertainty in galaxy formation models today. This uncertainty stems from a dearth of observational constraints as well as the great dynamic range between the small scales (<1 pc) where the feedback occurs ... More
Dissecting the Gaseous Halos of z~2 Damped Ly$α$ Systems with Close Quasar PairsNov 21 2014We use spectroscopy of close pairs of quasars to study diffuse gas in the circumgalactic medium (CGM) surrounding a sample of 40 Damped Lya systems (DLAs). The primary sightline in each quasar pair probes an intervening DLA in the redshift range 1.6 < ... 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
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
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
MApping the Most Massive Overdensities Through Hydrogen (MAMMOTH) I: MethodologyDec 21 2015Modern cosmology predicts that a galaxy overdensity is associated to a large reservoir of the intergalactic gas, which can be traced by the Ly$\alpha$ forest absorption. We have undertaken a systematic study of the relation between Coherently Strong intergalactic ... More
Inspiraling Halo Accretion Mapped in Lyman-$α$ Emission around a $z\sim3$ QuasarSep 24 2017In an effort to search for Ly$\alpha$ emission from circum- and intergalactic gas on scales of hundreds of kpc around $z\sim3$ quasars, and thus characterise the physical properties of the gas in emission, we have initiated an extensive fast-survey with ... More
Witnessing galaxy assembly in an extended z~3 structureJul 21 2017We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the Very Large Telescope in a quasar field that hosts a high column-density damped Ly{\alpha} absorber (DLA) at z~3.25. We detect Ly{\alpha} emission from a ... More
A Deep Search For Faint Galaxies Associated With Very Low-redshift C IV Absorbers: III. The Mass- and Environment-dependent Circumgalactic MediumDec 02 2015Sep 15 2016Using Hubble Space Telescope Cosmic Origins Spectrograph observations of 89 QSO sightlines through the Sloan Digital Sky Survey footprint, we study the relationships between C IV absorption systems and the properties of nearby galaxies as well as large-scale ... More
MAGICC haloes: confronting simulations with observations of the circumgalactic medium at z=0Dec 07 2011Oct 02 2012We explore the circumgalactic medium (CGM) of two simulated star-forming galaxies with luminosities L ~ 0.1 and 1 L* generated using the smooth particle hydrodynamic code GASOLINE. These simulations are part of the Making Galaxies In a Cosmological Context ... 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
Towards the statistical detection of the warm-hot intergalactic medium in inter-cluster filaments of the cosmic webJun 02 2015Oct 13 2015Modern analyses of structure formation predict a universe tangled in a 'cosmic web' of dark matter and diffuse baryons. These theories further predict that at low-z, a significant fraction of the baryons will be shock-heated to $T \sim 10^{5}-10^{7}$K ... 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
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 nature of proximate damped Lyman alpha systemsApr 15 2010We present high resolution echelle spectra of 7 proximate damped Lyman alpha (PDLA) systems whose relative velocity separation from the background quasar is Delta V < 3000 km/s. Combining our sample with a further 9 PDLAs from the literature we compare ... More
Keck telescope constraint on cosmological variation of the proton-to-electron mass ratioJan 22 2010Molecular transitions recently discovered at redshift z_abs=2.059 toward the bright background quasar J2123-0050 are analysed to limit cosmological variation in the proton-to-electron mass ratio, mu=m_p/m_e. Observed with the Keck telescope, the optical ... 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
The Giant Gemini GMOS survey of z>4.4 quasars - I. Measuring the mean free path across cosmic timeFeb 17 2014We have obtained spectra of 163 quasars at $z_\mathrm{em}>4.4$ with the Gemini Multi Object Spectrometers on the Gemini North and South telescopes, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From ... More
Where is the Molecular Hydrogen in Damped Lyman-Alpha Absorbers?Jan 27 2006We show in this paper why molecular millimeter absorption line searches in DLAs have been unsuccessful. We use CO emission line maps of local galaxies to derive the H2 column density distribution function f(N_H2) at z=0. We show that it forms a natural ... More
MASE: A New Data--Reduction Pipeline for the Magellan Echellette SpectrographOct 09 2009We introduce a data reduction package written in Interactive Data Language (IDL) for the Magellan Echellete Spectrograph (MAGE). MAGE is a medium-resolution (R ~4100), cross-dispersed, optical spectrograph, with coverage from ~3000-10000 Angstroms. The ... 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
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
Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a Forest Tomographic Mapping of the COSMOS FieldSep 09 2015Using moderate-resolution optical spectra from 58 background Lyman-break galaxies and quasars at $z\sim 2.3-3$ within a $11.5'\times13.5'$ area of the COSMOS field ($\sim 1200\,\mathrm{deg}^2$ projected area density or $\sim 2.4\,h^{-1}\,\mathrm{Mpc}$ ... 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
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 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
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
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
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
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
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
Multi-Filament Inflows Fueling Young Star Forming GalaxiesApr 25 2019Apr 26 2019Theory suggests that there are two primary modes of accretion through which dark matter halos acquire the gas to form and fuel galaxies, hot and cold mode accretion. In cold mode accretion, gas streams along cosmic web filaments to the center of the halo, ... 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
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 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
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
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
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
The COS Absorption Survey of Baryon Harbors (CASBaH): Warm-hot Circumgalactic Gas Reservoirs Traced by Ne VIII AbsorptionOct 15 2018We present a sample of 30 galaxies at 0.49 < z(gal) < 1.44 probed by Ne VIII absorption to study the highly ionized circumgalactic medium (CGM) based on high-S/N ultraviolet spectra of z > 1 QSOs and the galaxy database from the COS Absorption Survey ... 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
First Data Release of the COSMOS Lyman-Alpha Mapping And Tomography Observations: 3D Lyman-$α$ Forest Tomography at 2.05 < z < 2.55Oct 08 2017Aug 03 2018Faint star-forming galaxies at $z\sim 2-3$ can be used as alternative background sources to probe the Lyman-$\alpha$ forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption ... 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
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
Non cyclic functions in the Hardy space of the bidisc with arbitrary decreaseJan 11 2013We construct an example to show that no condition of slow decrease of the modulus of a function is sufficient to make it cyclic in the Hardy space of the bidisc. This is similar to what is well known in the case of the Hardy space of the disc, but in ... 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
Supermassive Black Hole Binary Environments: Effects on the Scaling Laws and Time to Detection for the Stochastic BackgroundSep 13 2016One of the primary gravitational wave (GW) sources for pulsar timing arrays (PTAs) is the stochastic background formed by supermassive black holes binaries (SMBHBs). In this paper, we investigate how the environments of SMBHBs will effect the sensitivity ... 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
A search for HI 21cm absorption in strong MgII absorbers in the redshift desertMar 25 2009We report results from a deep search for redshifted HI 21cm absorption in 55 strong MgII$\lambda$2796 absorbers (having $W (MgII) > 0.5 \AA$) at intermediate redshifts, $0.58 < z_{\rm abs} < 1.70$, with the Green Bank Telescope (GBT) and the Giant Metrewave ... More
Probing fundamental constant evolution with neutral atomic gas linesMar 01 2010We have detected narrow HI 21cm and CI absorption at $z \sim 1.4 - 1.6$ towards Q0458$-$020 and Q2337$-$011, and use these lines to test for possible changes in the fine structure constant $\alpha$, the proton-electron mass ratio $\mu$, and the proton ... 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
Universal Finite-Size Corrections of the Entanglement Entropy of Quantum Ladders and the Entropic Area LawJun 18 2014Oct 21 2014We investigate the finite-size corrections of the entanglement entropy of critical ladders and propose a conjecture for its scaling behavior. The conjecture is verified for free fermions, Heisenberg and quantum Ising ladders. Our results support that ... More
The N-Leg spin-S Heisenberg ladders: A DMRG studyNov 18 2013Mar 17 2014We investigate the N-leg spin-S Heisenberg Ladders by using the density matrix renormalization group method. We present estimates of the spin gap $\Delta_{s}$ and of the ground state energy per site $e_{\infty}^{N}$ in the thermodynamic limit for ladders ... 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
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
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