J. X. Prochaska

University of California, Santa Cruz, Santa Cruz, California, United States

Are you J. X. Prochaska?

Claim your profile

Publications (571)1940.32 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We 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 smaller than the temperature inferred from X-ray spectra (and significantly more precise than previous efforts based on optical and near-UV photometry). Super-imposed on this blue continuum, we detect three classes of features: narrow absorption from the Milky Way (probably a High-Velocity Cloud), and narrow absorption and broad (FWHM $\approx 2000$-8000 km s$^{-1}$) emission lines at/near the systemic host velocity. The absorption lines are blueshifted with respect to the emission lines by $\Delta v = -(250$-400) km s$^{-1}$. Together with the lack of common low-ionization features (Mg II, Fe II), we argue these arise from the same absorbing material responsible for the low-velocity outflow discovered at X-ray wavelengths. The broad nuclear emission lines display a remarkable abundance pattern: N III], N IV], He II are quite prominent, while the common quasar emission lines of C III] and Mg II are weak or entirely absent. Detailed modeling of this spectrum will help elucidate fundamental questions regarding the nature of the emission process(es) at work in TDFs, while future UV spectroscopy of ASASSN-14li would help to confirm (or refute) the previously proposed connection between TDFs and "N-rich" quasars.
    No preview · Article · Jan 2016
  • [Show abstract] [Hide abstract]
    ABSTRACT: We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Ly-alpha absorbers (DLAs) at low redshift (z < 1.6). Our statistical sample includes 463 quasars with spectral coverage spanning a total redshift path, dz = 123.3 or an absorption path, dX = 229.7. Within this survey path, we identify 4 DLAs, defined as absorbers with HI column density N(HI) >= 10^20.3cm-2, which implies an incidence per absorption length, l(X)= 0.017(+0.014-0.008) at a median survey path redshift of z=0.623. While our estimate of l(X) is lower than earlier estimates at z ~ 0 from HI 21cm emission studies, the results are consistent within the measurement uncertainties. Our dataset is too small to properly sample the N(HI) frequency distribution function f(N(HI),X), but the observed distribution agrees with previous estimates at z > 2. Adopting the z > 2 shape of f(N(HI),X), we infer an HI mass density at z ~ 0.6 of rho_HI = 0.25(+0.20-0.12) x 10^8 Msol Mpc-3. This is significantly lower than previous estimates from targeted DLA surveys with the HST, but consistent with results from low-z HI 21cm observations, and suggests that the neutral gas density of the universe has been decreasing over the past 10 Gyrs.
    No preview · Article · Jan 2016
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Modern 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 Ly$\alpha$ Absorption systems (CoSLAs), which have highest optical depth ($\tau$) in $\tau$ distribution, and mass overdensities on the scales of $\sim$ 10 - 20 $h^{-1}$ comoving Mpc. On such large scales, our cosmological simulations show a strong correlation between the effective optical depth ($\tau_{\rm{eff}}$) of the CoSLAs and the 3-D mass overdensities. In moderate signal-to-noise spectra, however, the profiles of CoSLAs can be confused with high column density absorbers. For $z>2.6$, where the corresponding Ly$\beta$ is redshifted to the optical, we have developed the technique to differentiate between these two alternatives. We have applied this technique to SDSS-III quasar survey at $z = 2.6$ - 3.3, and we present a sample of five CoSLA candidates with $\tau_{\rm{eff}}$ on 15 $h^{-1}$ Mpc greater than $4.5\times$ the mean optical depth. At lower redshifts of $z < 2.6$, where the background quasar density is higher, the overdensity can be traced by intergalactic absorption groups using multiple sight lines. Our overdensity searches fully utilize the current and next generation of Ly$\alpha$ forest surveys which cover a survey volume of $> (1\ h^{-1}$ Gpc)$^3$. In addition, systems traced by CoSLAs will build a uniform sample of the most massive overdensities at $z > 2$ to constrain the models of structure formation, and offer a unique laboratory to study the interactions between galaxy overdensities and the intergalactic medium.
    Preview · Article · Dec 2015
  • Bruce Margon · J. Xavier Prochaska · Nicolas Tejos · TalaWanda Monroe
    [Show abstract] [Hide abstract]
    ABSTRACT: An 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 companion. Recent compilations of the photometric behavior strongly suggest that the cool component is a Mira variable. Thus EF Aql appears to be a member of the rare symbiotic Mira subgroup.
    No preview · Article · Dec 2015 · Publications of the Astronomical Society of the Pacific
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We employ a blindly selected sample of low-redshift C IV absorption systems identified in spectra from the Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS), combined with galaxy data from the Sloan Digital Sky Survey (SDSS), to study the metal-enriched circumgalactic medium (CGM) with ~100% completeness for galaxy luminosities L > 0.01 L* at z < 0.015. We find that galaxies are typically found at the C IV absorber redshifts within impact parameters rho < 200 kpc, with the nearest galaxy having L < 0.1 L* for 78% of the absorbers. The ubiquity of faint dwarfs in close proximity to the absorbers suggests that these galaxies affect the enrichment and physical conditions of massive-galaxy halos. However, a fraction of our sample (33%) arise well outside the virial radius of any nearby galaxy brighter than 0.01 L*. The detection rate for C IV absorption within the virial radius is mass dependent and is considerably higher for L >~0.1 L* galaxies (7/8) than for less luminous galaxies (1/10). We also find that the occurrence of C IV absorbers depends strongly on the broader environment: 67% (8/12) of galaxies with rho < 150 kpc in regions of low galaxy density (regions with fewer than ten 0.1 L* galaxies within 1 Mpc) have affiliated C IV absorption while none (0/9) of the galaxies in denser regions show C IV within rho < 150 kpc. The reduced detection rate of C IV in denser environments persists for massive group dark matter halos. In contrast, H I is pervasive in the CGM without regard to mass or environment, although some of these Ly-alpha absorbers could arise in unrelated intergalactic gas.
    Preview · Article · Dec 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a sample of 38 intervening damped Lyman α (DLA) systems identified towards 100 z > 3.5 quasars, observed during the XQ-100 survey. The XQ-100 DLA sample is combined with major DLA surveys in the literature. The final combined sample consists of 742 DLAs over a redshift range approximately 1.6 < zabs < 5.0. We develop a novel technique for computing $\Omega _{\rm H\, {\small I}}^{\rm DLA}$ as a continuous function of redshift, and we thoroughly assess and quantify the sources of error therein, including fitting errors and incomplete sampling of the high column density end of the column density distribution function. There is a statistically significant redshift evolution in $\Omega _{\rm H\,\small {I}}^{\rm DLA}$ (≥3σ) from z ∼ 2 to z ∼ 5. In order to make a complete assessment of the redshift evolution of $\Omega _{\rm H\,\small {I}}$, we combine our high-redshift DLA sample with absorption surveys at intermediate redshift and 21-cm emission line surveys of the local universe. Although $\Omega _{\rm H\,\small {I}}^{\rm DLA}$, and hence its redshift evolution, remains uncertain in the intermediate-redshift regime (0.1 < zabs < 1.6), we find that the combination of high-redshift data with 21-cm surveys of the local universe all yield a statistically significant evolution in $\Omega _{\rm H\,\small {I}}$ from z ∼ 0 to z ∼ 5 (≥3σ). Despite its statistical significance, the magnitude of the evolution is small: a linear regression fit between $\Omega _{\rm H\,\small {I}}$ and z yields a typical slope of ∼0.17 × 10−3, corresponding to a factor of ∼4 decrease in $\Omega _{\rm H\,\small {I}}$ between z = 5 and z = 0.
    Full-text · Article · Nov 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    Michele Fumagalli · John M. O'Meara · J. Xavier Prochaska
    [Show abstract] [Hide abstract]
    ABSTRACT: We 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 ionization models and Bayesian techniques, we derive the posterior probability distribution functions for the density, metallicity, temperature and dust content of the absorbing gas. We find that z > 2 LLSs are highly ionized with ionization parameters between −3 ≲ log U ≲ −2, depending on the H i column density. LLSs are characterized by low temperatures (T < 5 × 104K) and reside in dust-poor environments. Between z ∼ 2.5–3.5, ∼80 per cent of the LLSs have physical densities between nH ∼ 10− 3.5–10− 2 cm− 3 for the assumed UV background, but we caution that a degeneracy between the ionization parameter and the intensity of the radiation field prevents robust inference on the density and sizes of LLSs. Conversely, metallicity estimates are less sensitive to the assumptions behind ionization corrections. LLSs at z > 2 are characterized by a broad unimodal distribution over > 4 orders of magnitude, with a peak at log Z/Z⊙ ∼ −2. LLSs are metal poor, significantly less enriched than DLAs, with ∼70 per cent of the metallicity PDF below log Z/Z⊙ ≤ −1.5. The median metallicity of super LLSs with $\log N_{\rm H\,\small {I}}\ge 19$ rapidly evolves with redshift, with a 10-fold increase between z ∼ 2.1–3.6 (∼1.5 Gyr). Based on this sample, we find that LLSs at z = 2.5–3.5 account for ∼15 per cent of all the metals produced by UV-selected galaxies. The implications for theories of cold gas accretion and metal ejection from galaxies are also discussed.
    Preview · Article · Nov 2015 · Monthly Notices of the Royal Astronomical Society
  • Marie Wingyee Lau · J. Xavier Prochaska · Joseph F. Hennawi
    [Show abstract] [Hide abstract]
    ABSTRACT: We 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 separation < 300 kpc and high dispersion, high S/N spectra, we find extreme kinematics with low metal ion lines typically spanning 500 km s^-1, exceeding any previously studied galactic population. The CGM is significantly enriched, even beyond the virial radius, with a median metallicity [M/H] = -0.6. The alpha/Fe abundance ratio is enhanced, suggesting that halo gas is primarily enriched by Type II supernovae. The total mass of the cool CGM is estimated to be 1.9*10^11 M_sun (R_\perp/160 kpc)^2, accounting for 1/3 of the galaxy halo baryonic budget. The ionization state of CGM gas increases with projected distance from the foreground quasars, contrary to expectation if the quasar dominates the ionizing radiation flux. However, we also found peculiarities not exhibited in the CGM of other galaxy populations. In one absorption system, we may be detecting unresolved fluorescent Ly-alpha emission, and another system shows strong NV lines. Taken together these anomalies suggest that transverse sightlines are at least in some cases possibly illuminated. We also discovered a peculiar case where detection of the CII fine structure line implies an electron density > 100 cm^-3 and subparsec scale gas clumps.
    No preview · Article · Oct 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the evolution of metal-enriched gas over recent cosmic epochs as well as to characterize the diffuse, ionized, metal-enriched circumgalactic medium (CGM), we have conducted a blind survey for C IV absorption systems in 89 QSO sightlines observed with the Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS). We have identified 42 absorbers at z < 0.16, comprising the largest uniform blind sample size to date in this redshift range. Our measurements indicate an increasing C IV absorber number density per comoving path length (dN/dX = 7.5 +/- 1.1) and modestly increasing mass density relative to the critical density of the Universe (Omega(C IV) = 10.0 +/- 1.5 x 10^-8 ) from z ~ 1.5 to the present epoch, consistent with predictions from cosmological hydrodynamical simulations. Furthermore, the data support a functional form for the column density distribution function that deviates from a single power-law, also consistent with independent theoretical predictions. As the data also probe heavy element ions in addition to C IV at the same redshifts, we identify, measure, and search for correlations between column densities of these species where components appear aligned in velocity. Among these ion-ion correlations, we find evidence for tight correlations between C II and Si II, C II and Si III, and C IV and Si IV, suggesting that these pairs of species arise in similar ionization conditions. However, the evidence for correlations decreases as the difference in ionization potential increases. Finally, when controlling for observational bias, we find only marginal evidence for a correlation (86.8% likelihood) between the Doppler line width b(C IV) and column density N(C IV).
    Preview · Article · Oct 2015 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present our extensive observational campaign on the Swift-discovered GRB141121A, al- most ten years after its launch. Our observations covers radio through X-rays, and extends for more than 30 days after discovery. The prompt phase of GRB 141121A lasted 1410 s and, at the derived redshift of z = 1.469, the isotropic energy is E{\gamma},iso = 8.0x10^52 erg. Due to the long prompt duration, GRB141121A falls into the recently discovered class of UL-GRBs. Peculiar features of this burst are a flat early-time optical light curve and a radio-to-X-ray rebrightening around 3 days after the burst. The latter is followed by a steep optical-to-X-ray decay and a much shallower radio fading. We analyze GRB 141121A in the context of the standard forward-reverse shock (FS,RS) scenario and we disentangle the FS and RS contributions. Finally, we comment on the puzzling early-time (t ~3 d) behavior of GRB 141121A, and suggest that its interpretation may require a two-component jet model. Overall, our analysis confirms that the class of UL-GRBs represents our best opportunity to firmly establish the prominent emission mechanisms in action during powerful GRB explosions, and future missions (like SVOM, XTiDE, or ISS-Lobster) will provide many more of such objects.
    Full-text · Article · Oct 2015 · The Astrophysical Journal
  • [Show abstract] [Hide abstract]
    ABSTRACT: A 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 the quasar lifetime. We then compare the predictions of this model to a sample of high equivalent width Ly a emitters (EW0 > 100 A) that were identified in a deep narrow-band 36x36 arcmin2 image centered on the luminous quasar Q0420-388. These are identified to the edge of the field and show some evidence of an azimuthal asymmetry on the sky of the type expected if the quasar is radiating in a bipolar cone. If these sources are being fluorescently illuminated by the quasar, then the two most distant sources require a lifetime of at least 15 Myr for an opening angle of 60 degrees or more, increasing to more than 40 Myr if the opening angle is reduced to a minimum 30 degrees. The overall distribution of all of the sources across the field gives best fit lifetimes in the range 20 < t < 50 Myr for opening angles in the range 90 < alpha < 40 degrees. If these sources are not being fluorescently illuminated by the quasar, then it suggests that a higher equivalent width limit than has been used in the literature to identify fluorescent objects will be required.
    No preview · Article · Sep 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Gamma-ray bursts (GRBs) are the most luminous explosions in the universe, yet the nature and physical properties of their energy sources are far from understood. Very important clues, however, can be inferred by studying the afterglows of these events. We present optical and X-ray observations of GRB 130831A obtained by Swift, Chandra, Skynet, RATIR, Maidanak, ISON, NOT, LT and GTC. This burst shows a steep drop in the X-ray light-curve at $\simeq 10^5$ s after the trigger, with a power-law decay index of $\alpha \sim 6$. Such a rare behaviour cannot be explained by the standard forward shock (FS) model and indicates that the emission, up to the fast decay at $10^5$ s, must be of "internal origin", produced by a dissipation process within an ultrarelativistic outflow. We propose that the source of such an outflow, which must produce the X-ray flux for $\simeq 1$ day in the cosmological rest frame, is a newly born magnetar or black hole. After the drop, the faint X-ray afterglow continues with a much shallower decay. The optical emission, on the other hand, shows no break across the X-ray steep decrease, and the late-time decays of both the X-ray and optical are consistent. Using both the X-ray and optical data, we show that the emission after $\simeq 10^5$ s can be explained well by the FS model. We model our data to derive the kinetic energy of the ejecta and thus measure the efficiency of the central engine of a GRB with emission of internal origin visible for a long time. Furthermore, we break down the energy budget of this GRB into the prompt emission, the late internal dissipation, the kinetic energy of the relativistic ejecta, and compare it with the energy of the associated supernova, SN 2013fu.
    No preview · Article · Sep 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Supernova (SN) Refsdal is the first multiply-imaged, highly-magnified, and spatially-resolved SN ever observed. The SN exploded in a highly-magnified spiral galaxy at z=1.49 behind the Frontier Fields Cluster MACS1149, and provides a unique opportunity to study the environment of SNe at high z. We exploit the time delay between multiple images to determine the properties of the SN and its environment, before, during, and after the SN exploded. We use the integral-field spectrograph MUSE on the VLT to simultaneously target all observed and model-predicted positions of SN Refsdal. We find MgII emission at all positions of SN Refsdal, accompanied by weak FeII* emission at two positions. The measured ratios of [OII] to MgII emission of 10-20 indicate a high degree of ionization with low metallicity. Because the same high degree of ionization is found in all images, it cannot be caused by SN Refsdal, but rather by previous SNe or a young and hot stellar population. We find no variability of the [OII] line over a period of 57 days. This suggests that there is no variation in the [OII] luminosity of the SN over this period, or that the SN contribution to the [OII] emission is too small to distinguish with our observations.
    Full-text · Article · Sep 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Using 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 $\sim 2.4\,h^{-1}\,\mathrm{Mpc}$ mean transverse separation), we reconstruct a 3D tomographic map of the foreground Ly$\alpha$ forest absorption at $2.2<z<2.5$ with an effective smoothing scale of $\sigma_{3d}\approx3.5\,h^{-1}\,\mathrm{Mpc}$ comoving. Comparing with 61 coeval galaxies with spectroscopic redshifts in the same volume, we find that the galaxy positions are clearly biased towards regions with enhanced IGM absorption in the tomographic map. We find an extended IGM overdensity with deep absorption troughs at $z=2.45$ associated with a recently-discovered galaxy protocluster at the same redshift. Based on simulations matched to our data, we estimate the enclosed dark matter mass within this IGM overdensity to be $M_{\rm dm} (z=2.45) = (9\pm4)\times 10^{13}\,h^{-1}\,\mathrm{M_\odot}$, and argue based on this mass and absorption strength that it will form at least one $z\sim0$ galaxy cluster with $M(z=0) = (3\pm 2) \times 10^{14}\,h^{-1}\mathrm{M_\odot}$, although its elongated nature suggests that it will likely collapse into two separate clusters. We also point out a compact overdensity of six MOSDEF galaxies at $z=2.30$ within a $r\sim 1\,h^{-1}\,\mathrm{Mpc}$ radius and $\Delta z\sim 0.006$, which does not appear to have a large associated IGM overdensity. These results demonstrate the potential of Ly$\alpha$ forest tomography on larger volumes to study galaxy properties as a function of environment, as well as revealing the large-scale IGM overdensities associated with protoclusters and other features of large-scale structure.
    Preview · Article · Sep 2015 · The Astrophysical Journal
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the detection of a strong Milky Way-type 2175-Å extinction bump at z = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7 from the Sloan Digital Sky Survey Data Release 10. We conduct follow up observations with the Echelle Spectrograph and Imager on-board the Keck II telescope and the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. This 2175-Å absorber is remarkable in that we simultaneously detect neutral carbon (C i), neutral chlorine (Cl i), and carbon monoxide (CO). It also qualifies as a damped Lyman α system. The J1211+0833 absorber is found to be metal rich and has a dust depletion pattern resembling that of the Milky Way disc clouds. We use the column densities of the C i fine structure states and the C ii/C i ratio (under the assumption of ionization equilibrium) to derive the temperature and volume density in the absorbing gas. A cloudy photoionization model is constructed, which utilizes additional atoms/ions to constrain the physical conditions. The inferred physical conditions are consistent with a canonical cold (T ∼ 100 K) neutral medium with a high density (n(H i) ∼ 100 cm−3) and a slightly higher pressure than the local interstellar medium. Given the simultaneous presence of C i, CO, and the 2175-Å bump, combined with the high metallicity, high dust depletion level, and overall low ionization state of the gas, the absorber towards J1211+0833 supports the scenario that the presence of the bump requires an evolved stellar population.
    No preview · Article · Sep 2015 · Monthly Notices of the Royal Astronomical Society
  • [Show abstract] [Hide abstract]
    ABSTRACT: The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that 'cold accretion flows'-relatively cool (temperatures of the order of 10(4) kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos-are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections. Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging. Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 10(13) solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.
    No preview · Article · Aug 2015 · Nature
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present optical and near-infrared light curves and optical spectra of SN 2013dx, associated with the nearby (redshift 0.145) gamma-ray burst GRB130702A. The prompt isotropic gamma-ray energy released from GRB130702A is measured to be E ;iso = 6:4+1:3
    Full-text · Article · Aug 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Using our sample of the most metal-rich damped Lyman α systems (DLAs) at zabs ∼ 2, 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 Local Group. The metal-rich sample of DLAs at zabs ∼ 2 probes metallicities as high as the Galactic disc and the most metal-rich dwarf spheroidals (dSphs), permitting an analysis of many elements typically observed in DLAs (Fe, Zn, Cr, Mn, Si, and S) in comparison to stellar abundances observed in the Galaxy and its satellites (in particular dSphs). Our main conclusions are: (1) non-solar [Zn/Fe] abundances in metal-poor Galactic stars and in dSphs over the full metallicity range probed by DLAs, suggest that Zn is not a simple proxy for Fe in DLAs and therefore not a suitable indicator of dust depletion. After correcting for dust depletion, the majority of DLAs have subsolar [Zn/Fe] similar to dSphs; (2) at [Fe/H] ∼ −0.5, a constant [Mn/Fe]∼−0.5 and near-solar [α/Fe] (requiring an assumption about dust depletion) are in better agreement with dwarf galaxies than Galactic disc stars; (3) [α/Zn] is usually solar or subsolar in DLAs. However, although low ratios of [α/Fe] are usually considered more ‘dwarf-like’ than ‘Milky Way-like’, subsolar [Zn/Fe] in Local Group dwarfs leads to supersolar [α/Zn] in the dSphs, in contrast with the DLAs. Therefore, whilst DLAs exhibit some similarities with the Local Group dwarf population, there are also notable differences.
    Preview · Article · Jul 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    Rebecca A. Bernstein · Scott M. Burles · J. Xavier Prochaska
    [Show abstract] [Hide abstract]
    ABSTRACT: This 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 the instrument and discuss observational procedures recommended for calibrating the standard data products. We detail the design and implementation of an IDL based data-reduction pipeline for MIKE data (since generalized to other echelle spectrometers, e.g. Keck/HIRES, VLT/UVES). This includes novel techniques for flat-fielding, wavelength calibration, and the extraction of echelle spectroscopy. Sufficient detail is provided in this manuscript to enable inexperienced observers to understand the strengths and weaknesses of the instrument and software package and an assessment of the related systematics.
    Preview · Article · Jun 2015 · Publications of the Astronomical Society of the Pacific
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present an absorption-line survey of optically thick gas clouds -- Lyman Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39 restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3, nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5-10) that may have super-solar abundances. High Si^+/Fe^+ ratios suggest an alpha-enhanced medium whereas the Si^+/C^+ ratios do not exhibit the super-solar enhancement inferred previously for the Lya forest.
    Preview · Article · Jun 2015 · The Astrophysical Journal Supplement Series

Publication Stats

12k Citations
1,940.32 Total Impact Points

Institutions

  • 1925-2015
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States
  • 2014
    • Max Planck Institute for Medical Research
      Heidelburg, Baden-Württemberg, Germany
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, California, United States
  • 2010-2014
    • Saint Michael's College
      Colchester, Vermont, United States
    • University of Florida
      • Department of Astronomy
      Gainesville, Florida, United States
  • 2003-2014
    • University of California Observatories
      Santa Cruz, California, United States
  • 2013
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
    • Princeton University
      Princeton, New Jersey, United States
  • 2012
    • University of Maryland, College Park
      CGS, Maryland, United States
  • 2009
    • University of Leicester
      • Department of Physics and Astronomy
      Leicester, ENG, United Kingdom
    • University of Porto
      Oporto, Porto, Portugal
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States
  • 1996-2009
    • University of California, San Diego
      • • Center for Astrophysics and Space Sciences (CASS)
      • • Department of Physics
      San Diego, California, United States
  • 2006-2008
    • NASA
      Вашингтон, West Virginia, United States
    • Joint Institute for Heavy Ion Research
      Oak Ridge, Tennessee, United States
  • 2000-2008
    • Carnegie Institute
      Pasadena, Texas, United States
    • California Institute of Technology
      Pasadena, California, United States
  • 1998-2008
    • Carnegie Institution for Science
      • Department of Terrestrial Magnetism
      Washington, West Virginia, United States
  • 2002
    • University of Oklahoma
      Norman, Oklahoma, United States