arXiv subjects
Publications and source records attributed to Gwen C. Rudie.
We present a spectroscopic survey of 318 faint $(R\sim 27$, $L\sim0.1L_*)$, Lyα-emission-selected galaxies (LAEs) at 2.5 v_{esc}$.
We use quasar absorption lines to study the physical conditions in the circumgalactic medium of redshift $z\approx 2.3$ star-forming galaxies taken from the Keck Baryonic Structure Survey (KBSS). In Turner et al. 2014 we used the pixel optical depth technique to show that absorption by HI and the metal ions OVI, NV, CIV, CIII and SiIV is strongly enhanced within $|Δv|\lesssim170$ km/s and projected distances $|d|\lesssim180$ proper kpc from sightlines to the background quasars. Here we demonstrate that the OVI absorption is also strongly enhanced at fixed HI, CIV, and SiIV optical depths, and that this enhancement extends out to $\sim350$ km/s. At fixed HI the increase in the median OVI optical depth near galaxies is 0.3-0.7 dex and is detected at 2--3-$σ$ confidence for all seven HI bins that have $\log_{10}τ_{\rm HI}\ge-1.5$. We use ionization models to show that the observed strength of OVI as a function of HI is consistent with enriched, photoionized gas for pixels with $τ_{\rm HI}\gtrsim10$. However, for pixels with $τ_{\rm HI} \lesssim 1$ this would lead to implausibly high metallicities at low densities if the gas were photoionized by the background radiation. This indicates that the galaxies are surrounded by gas that is sufficiently hot to be collisionally ionized ($T > 10^5\,$K) and that a substantial fraction of the hot gas has a metallicity $\gtrsim 10^{-1}$ of solar. Given the high metallicity and large velocity extent (out to $\sim1.5\times v_{\rm circ}$) of this gas, we conclude that we have detected hot, metal enriched outflows arising from star-forming galaxies.
(Abridged) We study metal absorption around 854 $z\approx$2.4 star-forming galaxies taken from the Keck Baryonic Structure Survey (KBSS). The galaxies examined in this work lie in the fields of 15 hyper-luminous background QSOs, with galaxy impact parameters ranging from 35 proper kpc (pkpc) to 2 proper Mpc (pMpc). Using the pixel optical depth technique, we present the first galaxy-centred 2-D maps of the median absorption by OVI, NV, CIV, CIII, and SIV, as well as updated results for HI. At small galactocentric radii we detect a strong enhancement of the absorption relative to randomly located regions that extend out to at least 180 pkpc in the transverse direction, and $\pm$240 km/s along the line-of-sight (LOS, ~1 pMpc in the case of pure Hubble flow) for all ions except NV. For CIV (and HI) we detect a significant enhancement of the absorption signal out to 2 pMpc in the transverse direction, corresponding to the maximum impact parameter in our sample. After normalising the median absorption profiles to account for variations in line strengths and detection limits, in the transverse direction we find no evidence for a sharp drop-off in metals distinct from that of HI. We argue instead that non-detection of some metal line species in the extended circumgalactic medium is consistent with differences in the detection sensitivity. We also present measurements of covering fractions and equivalent widths as a function of projected galaxy distance. Limiting the sample to the 340 galaxies with redshifts measured from nebular emission lines does not decrease the extent of the enhancement along the LOS compared to that in the transverse direction. This rules out redshift errors as the source of the observed redshift-space anisotropy and thus implies that we have detected the signature of gas peculiar velocities from infall, outflows, or virial motions for HI, OVI, CIV, CIII, and CIV.
We study the Lya profiles of 36 spectroscopically-detected Lya-emitters (LAEs) at z2-3, using Keck MOSFIRE to measure systemic redshifts and velocity dispersions from rest-frame optical nebular emission lines. The sample has a median optical magnitude R=26.0, and ranges from R23 to R>27, corresponding to rest-frame UV absolute magnitudes M_UV-22 to M_UV>-18.2. Dynamical masses range from M_dyn<1.3e8 Msun to M_dyn=6.8e9 Msun, with a median value of M_dyn=6.3e8 Msun. Thirty of the 36 Lya emission lines are redshifted with respect to the systemic velocity with at least 1 sigma significance, and the velocity offset with respect to systemic dv_Lya is correlated with R-band magnitude, M_UV, and the velocity dispersion measured from nebular emission lines with >3 sigma significance: brighter galaxies with larger velocity dispersions tend to have larger values of dv_Lya. We also make use of a comparison sample of 122 UV-color-selected R<25.5 galaxies at z2, all with Lya emission and systemic redshifts measured from nebular emission lines. Using the combined LAE and comparison samples for a total of 158 individual galaxies, we find that dv_Lya is anti-correlated with the Lya equivalent width with 7 sigma significance. Our results are consistent with a scenario in which the Lya profile is determined primarily by the properties of the gas near the systemic redshift; in such a scenario, the opacity to Lya photons in lower mass galaxies may be reduced if large gaseous disks have not yet developed and if the gas is ionized by the harder spectrum of young, low metallicity stars.
We present Keck/MOSFIRE observations of the role of environment in the formation of galaxies at z~2. Using K-band spectroscopy of H-alpha and [N II] emission lines, we have analyzed the metallicities of galaxies within and around a z=2.3 protocluster discovered in the HS1700+643 field. Our main sample consists of 23 protocluster and 20 field galaxies with estimates of stellar masses and gas-phase metallicities based on the N2 strong-line metallicity indicator. With these data we have examined the mass-metallicity relation (MZR) with respect to environment at z~2. We find that field galaxies follow the well-established trend between stellar mass and metallicity, such that more massive galaxies have larger metallicities. The protocluster galaxies, however, do not exhibit a dependence of metallicity on mass, with the low-mass protocluster galaxies showing an enhancement in metallicity compared to field galaxies spanning the same mass range. A comparison with galaxy formation models suggests that the mass-dependent environmental trend we observed can be qualitatively explained in the context of the recycling of "momentum-driven" galaxy wind material. Accordingly, winds are recycled on a shorter timescale in denser environments, leading to an enhancement in metallicity at fixed mass for all but the most massive galaxies. Future hydrodynamical simulations of z~2 overdensities matching the one in the HS1700 field will be crucial for understanding the origin of the observed environmental trend in detail.
We measure the dark matter halo masses of z~2.36 UV color-selected star-forming galaxies by matching the observed median HI 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 pMpc and line of sight separations 154-616 km/s, we find a minimum halo mass of log10(Mmin/Msun)=11.6(+0.2)(-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 (WMAP1 vs. WMAP3) 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 x 30 arcseconds. In addition, we find that the observed anisotropy in the 2-D HI 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.
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(NHI) < 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-NHI absorbers than low-NHI 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(NHI) < 17.2. Reproducing the opacity measured in our data as well as the incidence of absorbers with log(NHI) > 17.2 requires a broken power law parameterization of the frequency distribution with a break near log(NHI) ~ 15. We compute new estimates of the mean free path (mfp) to hydrogen-ionizing photons at z=2.4, finding 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 mfp = 121 +- 15 Mpc. These 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.
The relative abundances of the Fe-peak elements (Ti-Zn) at the lowest metallicities are intimately linked to the physics of core-collapse supernova explosions. With a sample of 25 very metal-poor damped Lyman-alpha systems, we investigate the trends of the Fe-peak element ratios with metallicity. For nine of the 25 DLAs, a direct measurement (or useful upper limit) of one or more of the Ti,Cr,Co,Ni,Zn/Fe abundance ratios could be determined from detected absorption lines. For the remaining systems (without detections), we devised a new form of spectral stacking to estimate the typical Fe-peak element ratios of the DLA population in this metallicity regime. We compare these data to analogous measurements in metal-poor stars of the Galactic halo and to detailed calculations of explosive nucleosynthesis in metal-free stars. We conclude that most of the DLAs in our sample were enriched by stars that released an energy of < 1.2 x 10^51 erg when they exploded as core-collapse supernovae. Finally, we discuss the exciting prospect of measuring Fe-peak element ratios in damped Lyman-alpha systems with Fe/H < 1/1000 of solar when 30-m class telescopes become available. Only then will we be able to pin down the energy that was released by the supernovae of the first stars.
We present new measurements of the temperature-density (T-rho) relation for neutral hydrogen in the 2.0 < z < 2.8 intergalactic medium (IGM) using a sample of ~6000 individual HI absorbers fitted with Voigt profiles constrained in all cases by multiple Lyman series transitions. We find model independent evidence for a positive correlation between the column density of HI (NHI) and the minimum observed velocity width of absorbers (bmin). With minimal interpretation, this implies that the temperature-density relation in the IGM is not "inverted", contrary to many recent studies. Fitting bmin as a function of NHI results in line width - column density dependence of the form bdmin = b_0 [NHI/N_(HI,0)]^(Gamma-1) with a minimum line width at mean density rhobar [N_(HI, 0) = 10^13.6 cm^-2] of b_0 = 17.9 +- 0.2 km/s and a power-law index of (Gamma-1) = 0.15 +- 0.02. Using analytic arguments, these measurements imply an "equation of state" for the IGM at = 2.4 of the form T = T_0 (rho/rhobar)^(gamma-1) with a temperature at mean density of T_0 = (1.94 +- 0.05) x 10^4 K and a power-law index (gamma -1) = 0.46 +- 0.05.
[Abridged] 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 < 2 (proper) Mpc to the line of sight of one of 15 bright, background QSOs. We present the first 2-D maps of the absorption around galaxies, plotting the median Ly-a pixel optical depth as a function of transverse and line of sight, LOS, separation from galaxies. The median optical depth, and hence the median density of atomic hydrogen, drops by more than an order of magnitude around 100 kpc, which is similar to the virial radius of the halos thought to host the galaxies. The median remains enhanced (>3 sigma level) out to at least 2.8 Mpc (i.e. > 9 comoving Mpc). Within 100 (200) kpc, and over \pm 165 km/s, the covering fraction of gas with Ly-a optical depth greater than unity is 100(+0)(-32)% (86(+14)(-18)%). Absorbers with tau(Ly-a)> 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 tau(Ly-a)~1 reside in regions where the galaxy number density is close to the cosmic mean on scales > 0.25 Mpc. We detect two types of redshift space anisotropies. On scales < 200 km/s, or < 1 Mpc, the absorption is stronger along the LOS than in the transverse direction. This "finger of God" effect may be partly due to redshift errors, but is probably dominated by gas motions within or very close to the halos. On the other hand, on scales of 1.4 - 2.0 Mpc the absorption is compressed along the LOS (>3 sigma significance), which we attribute to large-scale infall (i.e. the Kaiser effect).
We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey designed to explore the connection between galaxies and intergalactic baryons. The KBSS is optimized for the redshift range z ~ 2-3, combining S/N ~ 100 Keck/HIRES spectra of 15 hyperluminous QSOs with densely sampled galaxy redshift surveys surrounding each QSO sightline. We perform Voigt profile decomposition of all 6000 HI absorbers within the full Lya forest in the QSO spectra. Here we present the distribution, column density, kinematics, and absorber line widths of HI surrounding 886 star-forming galaxies with 2.0 < z < 2.8 and within 3 Mpc of a QSO sightline. We find that N_HI and the multiplicity of HI components increase rapidly near galaxies. The strongest HI absorbers within ~ 100 physical kpc of galaxies have N_HI ~ 3 dex higher than those near random locations in the IGM. The circumgalactic zone of most enhanced HI absorption (CGM) is found within 300 kpc and 300 km/s of galaxies. Nearly half of absorbers with log(N_HI) > 15.5 are found within the CGM of galaxies meeting our photometric selection, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic N_HI remain elevated to transverse distances of 2 physical Mpc. Absorbers with log(N_HI) > 14.5 are tightly correlated with the positions of galaxies, while absorbers with lower N_HI are correlated only on Mpc scales. Redshift anisotropies on Mpc scales indicate coherent infall toward galaxies, while on scales of ~100 physical kpc peculiar velocities of 260 km/s are indicated. The median Doppler widths of absorbers within 1-3 virial radii of galaxies are ~50% larger than randomly chosen absorbers of the same N_HI, suggesting higher gas temperatures and/or increased turbulence likely caused by accretion shocks and/or galactic winds.
We present a high spectral resolution survey of the most metal-poor damped Lyman-alpha 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 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 very metal-poor (VMP) DLAs is essentially constant, and shows very little dispersion, with a mean [ ] = +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] 6300 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 very metal-poor 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.
Rest-frame UV spectral lines of star-forming galaxies are systematically offset from the galaxies' systemic redshifts, probably because of large-scale outflows. We calibrate galaxy redshifts measured from rest-frame UV lines by utilizing the fact that the mean HI Ly-alpha absorption profiles around the galaxies, as seen in spectra of background objects, must be symmetric with respect to the true galaxy redshifts if the galaxies are oriented randomly with respect to the lines of sight to the background objects. We use 15 QSOs at z~2.5-3 and more than 600 foreground galaxies with spectroscopic redshifts at z~1.9-2.5. All galaxies are within 2 Mpc proper from the lines of sight to the background QSOs. We find that LyA emission and ISM absorption redshifts require systematic shifts of v_LyA=-295(+35)(-35) km/s and v_ISM=145(+70)(-35) km/s. Assuming a Gaussian distribution, we put 1-sigma upper limits on possible random redshift offsets of <220 km/s for LyA and <420 km/s for ISM redshifts. For the small subset (<10%) of galaxies for which near-IR spectra have been obtained, we can compare our results to direct measurements based on nebular emission lines which we confirm to mark the systemic redshifts. While our v_ISM agrees with the direct measurements, our v_LyA is significantly smaller. However, when we apply our method to the near-IR subsample which is characterized by slightly different selection effects, the best-fit velocity offset comes into agreement with the direct measurement. This confirms the validity of our approach, and implies that no single number appropriately describes the whole population of galaxies, in line with the observation that the line offset depends on galaxy spectral morphology. This method provides accurate redshift calibrations and will enable studies of circumgalactic matter around galaxies for which rest-frame optical observations are not available.
We present high resolution observations of an extremely metal-poor damped Lyman-alpha system, at z_abs = 2.3400972 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] = -3.04, shows a clear `odd-even' effect, and is C-rich with [C/Fe] = +1.53, a factor of about 20 greater than reported in any other damped Lyman-alpha system. In analogy to the carbon-enhanced metal-poor stars in the Galactic halo (with [C/Fe] > +1.0), this is the first reported case of a carbon-enhanced damped Lyman-alpha system. We determine an upper limit to the mass of 12C, M(12C) < 200 solar masses, which depends on the unknown gas density n(H); if n(H) > 1 atom per cubic cm (which is quite likely for this DLA given its low velocity dispersion), then M(12C) < 2 solar masses, consistent with pollution by only a few prior supernovae. We speculate that DLAs such as the one reported here may represent the `missing link' between the yields of Pop 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 sightline to the brighter member of the gravitationally lensed quasar pair UM 673A,B intersects a damped Lyman-alpha system (DLA) at z = 1.62650 which, because of its low redshift, has not been recognised 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 B, indicating that the DLA's extent in this direction is much less than the 2.7 kpc separation between the two sightlines at z = 1.62650. By reassessing 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) kpc, smaller than previously realised. 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 Ly-alpha emission line which we attribute to star formation activity at a rate SFR >~ 0.2 M_solar/yr. The DLA in UM 673A is metal-poor, with an overall metallicity Z_DLA ~ 1/30 Z_solar, 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.
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 (SBC) on Hubble Space Telescope. We report the detection of leaking Lyman continuum (LyC) radiation from an AGN-starburst composite. While we find no direct detections of LyC emission in the remainder of our sample, we achieve individual lower limits (3 sigma) of the observed non-ionizing UV to LyC flux density ratios, f_{nu}(1500A)/f_{nu}(830A) 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 (IGM) 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 3 sigma 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 escape fractions 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 which could affect the escape of LyC photons.
We discuss the findings of a comprehensive imaging and spectroscopic survey of the optical emission associated with the supernova remnant 3C 58 (Fesen et al. 2007) as they relate to the topic of pre-SN mass loss. Spectroscopically measured radial velocities of ~450 emission knots within the remnant show two distinct kinematic populations of optical knots: a high-velocity group with radial velocities in the range of 700 - 1100 km/s and a lower velocity group exhibiting radial expansion velocities below ~250 km/s. We interpret the high-velocity knots as ejecta from the SN explosion and the low-velocity knots as shocked circumstellar material likely resulting from pre-SN mass loss. The chemical signatures of the two populations also show marked differences. The high velocity group includes a substantial number of knots with notably higher [N II]/H-alpha ratios not seen in the lower velocity population, suggesting greater nitrogen enrichment in the SN ejecta than in the CSM. These results are compared with evidence for pre-SN mass loss in the Crab Nebula, perhaps the SNR most similar to 3C 58. These SNRs may comprise two case studies of pre-SN mass loss in relatively low mass (~8 - 10 solar masses) core-collapse SN progenitors.
II Zwicky 23 (UGC 3179) is a luminous, nearby compact narrow emission line starburst galaxy with blue optical colors and strong emission lines. We present a photometric and morphological study of II Zw 23 and its interacting companions using data obtained with the WIYN 3.5-m telescope in Kitt Peak, Arizona. II Zwicky 23 has a highly disturbed outer structure with long trails of debris that may be feeding tidal dwarfs. Its central regions appear disky, a structure that is consistent with the overall rotation pattern observed in the H-alpha velocity field measured from Densepak observations obtained with WIYN. We discuss the structure of II Zwicky 23 and its set of companions and possible scenarios of debris formation in this system.