ABSTRACT Long-duration gamma-ray bursts (GRBs) allow us to pinpoint and study star-forming galaxies in the early universe, thanks to their orders of magnitude brighter peak luminosities compared to ...other astrophysical sources, and their association with the deaths of massive stars. We present Hubble Space Telescope Wide Field Camera 3 detections of three Swift GRB host galaxies lying at redshifts z = 5.913 (GRB 130606A), z = 6.295 (GRB 050904), and z = 6.327 (GRB 140515A) in the F140W (wide-JH band, ) filter. The hosts have magnitudes (corrected for Galactic extinction) of and , respectively. In all three cases, the probability of chance coincidence of lower redshift galaxies is , indicating that the detected galaxies are most likely the GRB hosts. These are the first detections of high-redshift ( ) GRB host galaxies in emission. The galaxies have luminosities in the range 0.1-0.6 (with ) and half-light radii in the range 0.6-0.9 . Both their half-light radii and luminosities are consistent with existing samples of Lyman-break galaxies at . Spectroscopic analysis of the GRB afterglows indicate low metallicities ( ) and low dust extinction ( ) along the line of sight. Using stellar population synthesis models, we explore the implications of each galaxy's luminosity for its possible star-formation history and consider the potential for emission line metallicity determination with the upcoming James Webb Space Telescope.
We report on the observed properties of the plasma revealed through high signal-to-noise observations of 54 intervening Ovi absorption systems containing 85 Ovi and 133 Hi components in a blind ...survey of 14 QSOs observed at ~18 km s super(-1) resolution with the Cosmic Origins Spectrograph over a redshift path of 3.52 at z < 0.5. Simple systems with one or two Hi components and one Ovi component comprise 50% of the systems. For a sample of 45 well-aligned absorption components where the temperature can be estimated, we find evidence for cool photoionized gas in 31 (69%) and warm gas (6 > log T > 5) in 14 (31%) of the components. The total hydrogen content of the 14 warm components can be estimated from the temperature and the measured value of log N(HI). The very large implied values of log N(H) range from 18.38 to 20.38 with a median of 19.35. The metallicity, O/H, in the 6 warm components with log T > 5.45 ranges from -1.93 to 0.03 with a median value of -1.0 dex. Ground-based galaxy redshift studies reveal that most of the absorbers we detect sample gas in the intergalactic medium extending 200 to 600 kpc beyond the closest associated galaxy. For the warm aligned O VI absorbers, we estimate Omega sub(b)(O VI) sub(Warm) = 0.0019 + or - 0.0005 which corresponds to (4.1 + or - 1.1)% of the baryons at low z. The warm plasma traced by the aligned Ovi and Hi absorption contains nearly as many baryons as are found in galaxies.
High signal-to-noise observations of the QSO PKS 0405-123 (z {sub em} = 0.572) with the Cosmic Origins Spectrograph from 1134 to 1796 A with a resolution of {approx}17 km s{sup -1} are used to study ...the multi-phase partial Lyman limit system (LLS) at z = 0.16716, which has previously been studied using relatively low signal-to-noise spectra from STIS and FUSE. The LLS and an associated H I-free broad O VI absorber likely originate in the circumgalactic gas associated with a pair of galaxies at z = 0.1688 and 0.1670 with impact parameters of 116 h {sup -1} {sub 70} and 99 h {sup -1} {sub 70}. The broad and symmetric O VI absorption is detected in the z = 0.16716 rest frame with v = -278 {+-} 3 km s{sup -1}, log N(O VI) = 13.90 {+-} 0.03, and b = 52 {+-} 2 km s{sup -1}. This absorber is not detected in H I or other species with the possible exception of N V. The broad, symmetric O VI profile and the absence of corresponding H I absorption indicate that the circumgalactic gas in which the collisionally ionized O VI arises is hot (log T {approx} 5.8-6.2). The absorber may represent a rare but important new class of low-z intergalactic medium absorbers. The LLS has strong asymmetrical O VI absorption with log N(O VI) = 14.72 {+-} 0.02 spanning a velocity range from -200 to +100 km s{sup -1}. The high and low ions in the LLS have properties resembling those found for Galactic highly ionized high-velocity clouds where the O VI is likely produced in the conductive and turbulent interfaces between cool and hot gas.
We present H i 21 cm emission observations of the z ∼ 0.006 32 subdamped Lyman-α absorber (sub-DLA) towards PG 1216+069 made using the Arecibo Telescope and the Very Large Array (VLA). The Arecibo H ...i 21cm spectrum corresponds to an H i mass of ∼3.2 × 107 M⊙, two orders of magnitude smaller than that of a typical spiral galaxy. This is surprising since in the local Universe the cross-section for absorption at high H i column densities is expected to be dominated by spirals. The H i 21cm emission detected in the VLA spectral cube has a low signal-to-noise ratio, and represents only half the total flux seen at Arecibo. Emission from three other sources is detected in the VLA observations, with only one of these sources having an optical counterpart. This group of H i sources appears to be part of complex ‘W’, believed to lie in the background of the Virgo cluster. While several H i cloud complexes have been found in and around the Virgo cluster, it is unclear whether the ram pressure and galaxy harassment processes that are believed to be responsible for the creation of such clouds in a cluster environment are relevant at the location of this cloud complex. The extremely low metallicity of the gas, ∼1/40 solar, also makes it unlikely that the sub-DLA consists of material that has been stripped from a galaxy. Thus, while our results have significantly improved our understanding of the host of this sub-DLA, the origin of the gas cloud remains a mystery.
The circumgalactic medium (CGM) around galaxies is believed to record various forms of galaxy feedback and contain a significant portion of the 'missing baryons' of individual dark matter halos. ...However, clear observational evidence for the existence of the hot CGM is still absent. We use intervening galaxies along 12 background active galactic nuclei (AGNs) as tracers to search for X-ray absorption lines produced in the corresponding CGM. Stacking Chandra grating observations with respect to galaxy groups and different luminosities of these intervening galaxies, we obtain spectra with signal-to-noise ratios of 46-72 per 20 mA spectral bin at the expected O VII K{alpha} line. We find no detectable absorption lines of C VI, N VII, O VII, O VIII, or Ne IX. The high spectral quality allows us to tightly constrain upper limits to the corresponding ionic column densities. These nondetections are inconsistent with the Local Group hypothesis of the X-ray absorption lines at z {approx_equal} 0 commonly observed in the spectra of AGNs. These results indicate that the putative CGM in the temperature range of 10{sup 5.5}-10{sup 6.3} K may not be able to account for the missing baryons unless the metallicity is less than 10% solar.
We present the methodology for "blind" millimeter-wave surveys for redshifted molecular absorption in the CO/HCO super(+) rotational lines. The frequency range 30-50 GHz appears optimal for such ...surveys, providing sensitivity to absorbers at z gap 0.85. It is critical that the survey is "blind," i.e., based on a radio-selected sample, including sources without known redshifts. We also report results from the first large survey of this kind, using the Q-band receiver on the Green Bank Telescope (GBT) to search for molecular absorption toward 36 sources, 3 without known redshifts, over the frequency range 39.6-49.5 GHz. The GBT survey has a total redshift path of Delta z approximately 24, mostly at 0.81 < z < 1.91, and a sensitivity sufficient to detect equivalent H sub(2) column densities gap3 x 10 super(21) cm super(-2) in absorption at 5sigma significance (using CO-to-H sub(2) and HCO super(+)-to-H sub(2) conversion factors of the Milky Way). The survey yielded no confirmed detections of molecular absorption, yielding the 2sigma upper limit n(z = 1.2) < 0.15 on the redshift number density of molecular gas at column densities N(H sub(2)) gap 3 x 10 super(21) cm super(-2).
We report results from XMM-Newton observations of 13 X-ray bright BL Lacertae objects, selected from the Einstein Slew Survey sample (SSS). The survey was designed to look for evidence of departures ...of the X-ray spectra from a simple power-law shape (i.e., curvature and/or line features) and to find objects worthy of deeper study. Our data are generally well fit by power-law models, with three cases having hard ( < 2; dN/dE 8 E super(-)) spectra that indicate synchrotron peaks at E 5 keV. Previous data had suggested a presence of absorption features in the X-ray spectra of some BL Lac objects. In contrast, none of these spectra show convincing examples of line features in either absorption or emission, suggesting that such features are rare among BL Lac objects, or, more likely, are artifacts caused by instrumental effects. We find significant evidence for intrinsic curvature steepening by d/d(log E) = 0.4 c 0.15 in 14 of the 17 X-ray spectra. This cannot be explained satisfactorily via excess absorption, since the curvature is essentially constant from 0.5-6 keV, an observation that is inconsistent with the modest amounts of absorption that would be required. We use the XMM-Newton Optical Monitor data with concurrent radio monitoring to derive broadband spectral energy distributions and peak frequency estimates. From these, we examine models of synchrotron emission and model the spectral curvature we see as the result of episodic particle acceleration.
We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) and Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of the QSO PG 1211+143 (z sub(em) = 0.081) and a galaxy ...survey of the surrounding field. This sight line shows two strong intergalactic absorption systems at cz 15,300 and 19,300 km s super(-1). This sight line addresses the nature and origin of the O VI absorbers and their connection to galaxies. We explore the relationship of these absorbers to the nearby galaxies and compare them to other O VI-bearing absorbers in diverse environments. At 15,300 km s super(-1), we find four distinct H I components and associated C II, C III, C IV, Si II, Si III, Si IV, N V, and O VI, lying near a spiral-dominated galaxy group with a bright member galaxy 137 h super(-) sub(7) super(1) sub(0) kpc from the sight line. The observed ions of C, Si, and N are likely to be photoionized, but the O VI is more consistent with collisional ionization. The ion ratios in this absorber resemble the highly ionized Galactic high-velocity clouds (HVCs); it may also trace the hot intragroup medium gas or the unbound wind of an undiscovered dwarf galaxy. At 19,300 km s super(-1), we find five H I components and associated C III, Si III, and collisionally ionized O VI lying 146 h super(-) sub(7) super(1) sub(0) kpc from an isolated galaxy. The properties of the O VI-bearing gas are consistent with an origin in strong shocks between low-metallicity gas (.2%-6% solar) and one or more of the warm photoionized components. It is likely that these absorbers are related to the nearby galaxies, perhaps by outflows or gas stripped from unseen satellite galaxies by interactions. However, we cannot reject completely the hypothesis that they reside in the same large-scale structure in which the galaxies are embedded but are otherwise not directly related.
We present new optical emission-line images of the young SNR 1E 0102-7219 in the SMC obtained with the ACS on HST. This object is a member of the oxygen-rich class of SNRs showing strong oxygen, ...neon, and other metal-line emissions in its optical and X-ray spectra, and an absence of hydrogen and helium. The progenitor of 1E 0102-7219 may have been a Wolf-Rayet star that underwent considerable mass loss prior to exploding as a Type Ib/c or IIL/b supernova. The ejecta in this SNR are generally fast-moving (V > 1000 km s super(-1)) and emit as they are compressed and heated in the reverse shock. In 2003 we obtained optical O III, Ha, and continuum images with the ACS Wide Field Camera. The O III image through the F475W filter captures the full velocity range of the ejecta and shows considerable high-velocity emission projected in the middle of the SNR that was Doppler-shifted out of the narrow F502N bandpass of a previous WFPC2 image from 1995. Using these two epochs separated by 68.5 yr, we measure the transverse expansion of the ejecta around the outer rim in this SNR for the first time at visible wavelengths. From proper-motion measurements of 12 ejecta filaments, we estimate a mean expansion velocity for the bright ejecta of 62000 km s super(-1) and an inferred kinematic age for the SNR of 62050 c 600 yr. The age we derive from HST data is about twice that inferred by Hughes et al. from X-ray data, although our 1 s error bars overlap. Our proper-motion age is consistent with an independent optical kinematic age derived by Eriksen et al. in 2003 using spatially resolved O III radial-velocity data. We derive an expansion center that lies very close to conspicuous X-ray and radio hot spots, which could indicate the presence of a compact remnant (neutron star or black hole).
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