Gwen C. Rudie

THE GASEOUS ENVIRONMENT OF HIGH-z GALAXIES: PRECISION MEASUREMENTS OF NEUTRAL HYDROGEN IN THE CIRCUMGALACTIC MEDIUM OF z ∼ 2-3 GALAXIES IN THE KECK BARYONIC STRUCTURE SURVEY*

We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and intergalactic baryons within the same survey volumes, focusing particularly on scales from ∼ 50 kpc to a few Mpc. The KBSS is optimized for the redshift range z ∼ 2-3, combining S/N ∼ 100 Keck/HIRES spectra of 15 of the brightest QSOs in the sky at z ≃ 2.5-2.9 with very densely sampled galaxy redshift surveys within a few arcmin of each QSO sightline. In this paper, we present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen (H_I) surrounding a subset of 886 KBSS star-forming galaxies with 2.0 ≾ z ≾ 2.8 and with projected distances ≤ 3 physical Mpc from a QSO sightline. Using Voigt profile decompositions of the full Lyα forest region of all 15 QSO spectra, we compiled a catalog of ∼6000 individual absorbers in the redshift range of interest, with 12 ≤ log(N_(HI)) ≤ 21. These are used to measure H I absorption statistics near the redshifts of foreground galaxies as a function of projected galactocentric distance from the QSO sightline and for randomly chosen locations in the intergalacticmedium (IGM) within the survey volume. We find that NHI and the multiplicity of velocity-associated H I components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest H_I absorbers within ≃ 100 physical kpc of galaxies have N_(HI) ∼ 3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced H_I absorption is found within transverse distances of ≾ 300 kpc and within ±300 km s^(-1) of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), nearly half of absorbers with log(N_(HI)) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic NHI remain significantly elevated to transverse distances of ∼2 physical Mpc from galaxies in our sample. Absorbers with N_(HI) > 10^(14.5) cm^(-2) are tightly correlated with the positions of galaxies, while absorbers with lower N_(HI) are correlated with galaxy positions only on ≳ Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of ∼ 100 physical kpc peculiar velocities of Δv ≃ ±260 km s^(-1) with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1-3 r_(vir) of galaxies are larger by ≃ 50% than randomly chosen absorbers of the same NHI, suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with M_(halo) ≃ 10^(12) M_⊙ at z ∼ 2-3.

The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime★

We present a high spectral resolution survey of the most metal-poor damped Lyα absorption systems (DLAs) aimed at probing the nature and nucleosynthesis of the earliest generations of stars. Our survey comprises 22 systems with iron abundance less than 1/100 solar; observations of seven of these are reported here for the first time. Together with recent measures of the abundances of C and O in Galactic metal-poor stars, we reinvestigate the trend of C/O in the very metal-poor (VMP) regime and we compare, for the first time, the O/Fe ratios in the most metal-poor DLAs and in halo stars. We confirm the near-solar values of C/O in DLAs at the lowest metallicities probed, and find that their distribution is in agreement with that seen in Galactic halo stars. We find that the O/Fe ratio in VMP DLAs is essentially constant, and shows very little dispersion, with a mean [〈O/Fe〉]=+0.39 ± 0.12, in good agreement with the values measured in Galactic halo stars when the oxygen abundance is measured from the [O i] λ6300 line. We speculate that such good agreement in the observed abundance trends points to a universal origin for these metals. In view of this agreement, we construct the abundance pattern for a typical VMP DLA and compare it to model calculations of Population II and Population III nucleosynthesis to determine the origin of the metals in VMP DLAs. Our results suggest that the most metal-poor DLAs may have been enriched by a generation of metal-free stars; however, given that abundance measurements are currently available for only a few elements, we cannot yet rule out an additional contribution from Population II stars.

A carbon-enhanced metal-poor damped Lyα system: probing gas from Population III nucleosynthesis?

We present high-resolution observations of an extremely metal-poor damped Lyα system (DLA), at z_(abs) = 2.340 0972 in the spectrum of the QSO J0035−0918, exhibiting an abundance pattern consistent with model predictions for the supernova yields of Population III stars. Specifically, this DLA has [Fe/H]≃−3, shows a clear ‘odd–even’ effect, and is C-rich with [C/Fe]=+1.53, a factor of ∼20 greater than reported in any other DLA. In analogy to the carbon-enhanced metal-poor stars in the Galactic halo (with [C/Fe] > +1.0), this is the first known case of a carbon-enhanced DLA. We determine an upper limit to the mass of ^(12)C, M(^(12)C) ≤ 200 M_⊙, which depends on the unknown gas density n(H); if n(H) > 1 cm^(−3) (which is quite likely for this DLA given its low velocity dispersion), then M(^(12)C) ≤ 2 M_⊙, consistent with pollution by only a few prior supernovae. We speculate that DLAs such as the one discovered here may represent the ‘missing link’ between the yields of Population III stars and their later incorporation in the class of carbon-enhanced metal-poor stars which show no enhancement of neutron-capture elements (CEMP-no stars).

The Column Density Distribution and Continuum Opacity of the Intergalactic and Circumgalactic Medium at Redshift z = 2.4

We present new high-precision measurements of the opacity of the intergalactic and circumgalactic medium (IGM, CGM) at =2.4. Using Voigt profile fits to the full Lyman alpha and Lyman beta forests in 15 high-resolution high-S/N spectra of hyperluminous QSOs, we make the first statistically robust measurement of the frequency of absorbers with HI column densities 14≾log(N_(HI))≾ 17.2. We also present the first measurements of the frequency distribution of HI absorbers in the volume surrounding high-z galaxies (the CGM, 300 pkpc), finding that the incidence of absorbers in the CGM is much higher than in the IGM. In agreement with Rudie et al. (2012), we find that there are fractionally more high-N_(HI) absorbers than low-N_(HI) absorbers in the CGM compared to the IGM, leading to a shallower power law fit to the CGM frequency distribution. We use these new measurements to calculate the total opacity of the IGM and CGM to hydrogen-ionizing photons, finding significantly higher opacity than most previous studies, especially from absorbers with log(N_(HI)) 17.2 requires a broken power law parameterization of the frequency distribution with a break near log(N^(HI))≈10^(15)cm^(-2). We compute new estimates of the mean free path λ_(mfp) to hydrogen-ionizing photons at Z_(em)=2.4, finding λ_(mfp) = 147 + 15 Mpc when considering only IGM opacity. If instead, we consider photons emanating from a high-z star-forming galaxy and account for the local excess opacity due to the surrounding CGM of the galaxy itself, the mean free path is reduced to λ_(mfp) = 121 + 15 Mpc. These λ_(mfp) measurements are smaller than recent estimates and should inform future studies of the metagalactic UV background and of ionizing sources at z≈2-3.

A SPECTROSCOPIC SEARCH FOR LEAKING LYMAN CONTINUUM AT z ∼ 0.7*

We present the results of rest-frame, UV slitless spectroscopic observations of a sample of 32 z ~ 0.7 Lyman break galaxy (LBG) analogs in the COSMOS field. The spectroscopic search was performed with the Solar Blind Channel on the Hubble Space Telescope. We report the detection of leaking Lyman continuum (LyC) radiation from an active galactic nucleus-starburst composite. While we find no direct detections of LyC emission in the remainder of our sample, we achieve individual lower limits (3σ) of the observed non-ionizing UV-to-LyC flux density ratios, f -ν (1500 A)/f _ν(830 A) of 20 to 204 (median of 73.5) and 378.7 for the stack. Assuming an intrinsic Lyman break of 3.4 and an intergalactic medium transmission of LyC photons along the line of sight to the galaxy of 85%, we report an upper limit for the relative escape fraction in individual galaxies of 0.02-0.19 and a stacked 3σ upper limit of 0.01. We find no indication of a relative escape fraction near unity as seen in some LBGs at z ~ 3. Our UV spectra achieve the deepest limits to date at any redshift for the escape fraction in individual sources. The contrast between these z ~ 0.7 low escape fraction LBG analogs with z ~ 3 LBGs suggests that either the processes conducive to high f esc are not being selected for in the z 1 samples or the average escape fraction is decreasing from z ~ 3 to z ~ 1. We discuss possible mechanisms that could affect the escape of LyC photons

NEUTRAL HYDROGEN OPTICAL DEPTH NEAR STAR-FORMING GALAXIES AT z ≈ 2.4 IN THE KECK BARYONIC STRUCTURE SURVEY*

We study the interface between galaxies and the intergalactic medium by measuring the absorption by neutral hydrogen in the vicinity of star-forming galaxies at z ≈ 2.4. Our sample consists of 679 rest-frame UV-selected galaxies with spectroscopic redshifts that have impact parameters 3σ level, out to at least 2.8 Mpc (i.e., >9 comoving Mpc), but the scatter at a given distance is large compared with the median excess optical depth, suggesting that the gas is clumpy. Within 100 (200) kpc, and over ±165 km s^(–1), the covering fraction of gas with Lyα optical depth greater than unity is 100^(+0)_(–32%) (66% ± 16%). Absorbers with τ_(Lyα) > 0.1 are typically closer to galaxies than random. The mean galaxy overdensity around absorbers increases with the optical depth and also as the length scale over which the galaxy overdensity is evaluated is decreased. Absorbers with τ_(Lyα) ~ 1 reside in regions where the galaxy number density is close to the cosmic mean on scales ≥0.25 Mpc. We clearly detect two types of redshift space anisotropies. On scales 3σ significance), an effect that we attribute to large-scale infall (i.e., the Kaiser effect).

A newly discovered DLA and associated Lyα emission in the spectra of the gravitationally lensed quasar UM 673A,B

The sightline to the brighter member of the gravitationally lensed quasar pair UM 673A,B intersects a damped Lyα system (DLA) at z = 1.62650 which, because of its low redshift, has not been recognized before. Our high-quality echelle spectra of the pair, obtained with HIRES on the Keck I telescope, show a drop in neutral hydrogen column density N(H i) by a factor of at least 400 between UM 673A and UM 673B, indicating that the DLA’s extent in this direction is much less than the 2.7 h^(−1)_(70) kpc separation between the two sightlines at z = 1.62650. By re-assessing this new case together with published data on other quasar pairs, we conclude that the typical size (radius) of DLAs at these redshifts is R ≃ (5 ± 3) h^(−1)_(70) kpc, smaller than previously realized. Highly ionized gas associated with the DLA is more extended, as we find only small differences in the C iv absorption profiles between the two sightlines. Coincident with UM 673B, we detect a weak and narrow Lyα emission line which we attribute to star formation activity at a rate SFR ≳ 0.2 M_⊙ yr^(−1). The DLA in UM 673A is metal poor, with an overall metallicity Z_(DLA) ≃ 1/30 Z_⊙, and has a very low internal velocity dispersion. It exhibits some apparent peculiarities in its detailed chemical composition, with the elements Ti, Ni and Zn being deficient relative to Fe by factors of 2–3. The [Zn/Fe] ratio is lower than those measured in any other DLA or Galactic halo star, presumably reflecting somewhat unusual previous enrichment by stellar nucleosynthesis. We discuss the implications of these results for the nature of the galaxy hosting the DLA.

A measurement of galaxy halo mass from the surrounding H i Lyα absorption

We measure the dark matter halo masses of 〈z〉 ≈ 2.36 UV colour-selected star-forming galaxies by matching the observed median H I Lyα absorption around them, as observed in the spectra of background QSOs, to the absorption around haloes above a given mass in cosmological simulations. Focusing on transverse separations 0–2 proper Mpc (pMpc) and line-of-sight separations 154–616 km s^(−1), we find a minimum halo mass of log_(10)M_(min)/M⊙ = 11.6 ± 0.2, which is in good agreement with published halo mass estimates from clustering analyses. We verified that the measured halo mass is insensitive to a change in the cosmological parameters (Wilkinson Microwave Anisotropy Probe 1 versus Wilkinson Microwave Anisotropy Probe 3) and to the inclusion of strong AGN feedback. One unique strength of this method is that it can be used in narrow field galaxy–QSO surveys, i.e. ≈30 × 30 arcsec. In addition, we find that the observed anisotropy in the 2D H I Lyα absorption distribution on scales of 1.5–2 pMpc is consistent with being a consequence of large-scale gas infall into the potential wells occupied by galaxies.

The Crab Nebula's dynamical age as measured from its northern filamentary jet

We present a deep [O III] λλ4959,5007 image of the northern filamentary jet in the Crab Nebula taken with the 8.2-m Subaru telescope. Using this image and an image taken with the Kitt Peak National Observatory (KPNO) 4-m in 1988, we have computed proper motions for 35 locations in the jet. The results suggest that when compared to the main body of the remnant, the jet experienced less outward acceleration from the central pulsar’s rapidly expanding synchrotron nebula. The jet’s apparent expansion rate yields an undecelerated explosion date for the Crab Nebula of 1055 ± 24 CE, a date much closer to the appearance of the historic 1054 CE guest star than the 1120–1140 CE dates estimated in previous studies using filaments located within the remnant’s main nebula. Our proper motion measurements suggest the jet likely formed during the 1054 supernova explosion and represents the remnant’s highest velocity knots possibly associated with a suspected N–S bipolar outflow from the supernova explosion.

Late-Time X-Ray, UV, and Optical Monitoring of Supernova 1979C

We present results from observations of supernova (SN) 1979C with the Newton X-Ray Multi-Mirror (XMM-Newton) mission in X-rays and in UV, archival X-ray, and Hubble Space Telescope (HST) data, and follow-up ground-based optical imaging. The XMM-Newton MOS spectrum shows the best-fit two-temperature thermal plasma emission characteristics of both the forward (kT(high) = 4:1(-2.4)(+76) keV) and reverse shock (kT(low) = 0.79(-0.17)(+0.24) keV) with no intrinsic absorption. The long-term X-ray light curve, constructed from all X-ray data available, reveals that SN 1979C is still radiating at a flux level similar to that detected by ROSAT in 1995, showing no sign of a decline over the last 6 years, some 16-23 yr after its outburst. The high inferred X-ray luminosity (L(0.3-2) = 8 x 10(38) ergs s(-1)) is caused by the interaction of the SN shock with dense circumstellar matter, likely deposited by a strong stellar wind from the progenitor with a high mass- loss rate of. M approximate to 1.5 x 10(-4) M(circle dot) yr(-1) (v(w)/10 km s(-1)). The X-ray data support a strongly decelerated shock and show a mass-loss rate history that is consistent with a constant progenitor mass-loss rate and wind velocity over the past greater than or similar to 16,000 yr in the stellar evolution of the progenitor. We find a best-fit circumstellar medium (CSM) density profile of rho(CSM) proportional to r(-s) with index s less than or similar to 1.7 and high CSM densities (greater than or similar to 10(4) cm(-3)) out to large radii from the site of the explosion (r greater than or similar to 4 x 10(17) cm). Using XMM-Newton Optical Monitor data, we further detect a pointlike optical/UV source consistent with the position of SN 1979C, with B-, U-, and UVW1-band luminosities of 5, 7, and 9 x 10(36) ergs s(-1), respectively. The young stellar cluster in the vicinity of the SN, as imaged by the HSTand follow- up ground- based optical imaging, can only provide a fraction of the total observed flux, so that a significant contribution to the output likely arises from the strong interaction of SN 1979C with dense CSM.