We use high-quality, medium-resolution Hubble Space Telescope/Cosmic Origins Spectrograph (HST/COS) observations of 82 UV-bright active galactic nuclei (AGNs) at redshifts zAGN < 0.85 to construct ...the largest survey of the low-redshift intergalactic medium (IGM) to date: 5138 individual extragalactic absorption lines in H i and 25 different metal-ion species grouped into 2611 distinct redshift systems at zabs < 0.75 covering total redshift pathlengths ?zH i = 21.7 and zO vi = 14.5. Our semi-automated line-finding and measurement technique renders the catalog as objectively defined as possible. We find substantial clustering of H i absorbers on scales of v = 50-300 km s-1 with no significant clustering at v gsim 1000 km s-1. Splitting the sample into strong and weak absorbers, we see that most of the clustering occurs in strong, NH i gsim 1013.5 cm-2, metal-bearing IGM systems.
The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. Ultraviolet photons influence the atmospheric ...temperature profiles and production of potential bio-markers on Earth-like planets around these stars. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both far-UV (FUV) and near-UV (NUV) wavelengths. Additional modeling work is needed to differentiate between a stellar photospheric or possible exoplanetary origin for the hot molecular gas observed in the objects.
Using the new Cosmic Origins Spectrograph on the Hubble Space Telescope, we obtained moderate-resolution, high signal/noise ultraviolet spectra of HD 209458 and its exoplanet HD 209458b during ...transit, both orbital quadratures, and secondary eclipse. We compare transit spectra with spectra obtained at non-transit phases to identify spectral features due to the exoplanet's expanding atmosphere. We find that the mean flux decreased by 7.8% {+-} 1.3% for the C II 1334.5323 A and 1335.6854 A lines and by 8.2% {+-} 1.4% for the Si III 1206.500 A line during transit compared to non-transit times in the velocity interval -50 to +50 km s{sup -1}. Comparison of the C II and Si III line depths and transit/non-transit line ratios shows deeper absorption features near -10 and +15 km s{sup -1} and less certain features near -40 and +30-70 km s{sup -1}, but future observations are needed to verify this first detection of velocity structure in the expanding atmosphere of an exoplanet. Our results for the C II lines and the non-detection of Si IV 1394.76 A absorption are in agreement with Vidal-Madjar et al., but we find absorption during transit in the Si III line contrary to the earlier result. The 8% {+-} 1% obscuration of the star during transit is far larger than the 1.5% obscuration by the exoplanet's disk. Absorption during transit at velocities between -50 and +50 km s{sup -1} in the C II and Si III lines requires high-velocity ion absorbers. Assuming hydrodynamic model values for the gas temperature and outflow velocity at the limb of the outflow as seen in the C II lines, we find mass-loss rates in the range (8-40)x10{sup 10} g s{sup -1}. These rates assume that the carbon abundance is solar, which is not the case for the giant planets in the solar system. Our mass-loss rate estimate is consistent with theoretical hydrodynamic models that include metals in the outflowing gas.
We present the results of a large search for intrinsic H i 21 cm and OH 18 cm absorption in 145 compact radio sources in the redshift range 0.02 < z < 3.8 with the Green Bank Telescope. We redetect H ...i 21 cm absorption toward six known absorption systems, but detect no new H i or OH absorption in 102 interference-free sources. Seventy-nine sources have not previously been observed for H i 21 cm absorption. We recover a mean optical depth limit of τ3 < 0.023 for all the nondetections in the survey. Our results do not support the high intrinsic absorption rates found by previous studies in compact radio sources at low redshift. Our results do, however, support the hypothesis proposed by Curran et al. that high ultraviolet (UV) luminosity active galactic nuclei do not show intrinsic H i 21 cm absorption, confirming a threshold of LUV = 1023 W Hz−1, above which our intrinsic absorption fraction is zero (54 sources). The exact nature of the UV luminosity effect on H i absorption systems remains ambiguous. We additionally find no statistical correlation between the 1.4 GHz radio luminosity or the source size and the 21 cm absorption detection rate. We attribute the lack of intrinsic absorption in our survey to the UV luminosity effect caused by an optical selection bias and a decreased column density sensitivity with increasing redshift due to lower radio continuum flux densities, high radio frequency interference, and higher telescope system temperatures at low frequencies.
Abstract
We present basic data and modeling for a survey of the cool, photoionized circumgalactic medium (CGM) of low-redshift galaxies using far-UV QSO absorption-line probes. This survey consists ...of “targeted” and “serendipitous” CGM subsamples, originally described in Stocke et al. (Paper I). The targeted subsample probes low-luminosity, late-type galaxies at
z
<
0.02
with small impact parameters (
〈
ρ
〉
=
71
kpc), and the serendipitous subsample probes higher luminosity galaxies at
z
≲
0.2
with larger impact parameters (
〈
ρ
〉
=
222
kpc).
Hubble Space Telescope
and
FUSE
UV spectroscopy of the absorbers and basic data for the associated galaxies, derived from ground-based imaging and spectroscopy, are presented. We find broad agreement with the COS-Halos results, but our sample shows no evidence for changing ionization parameter or hydrogen density with distance from the CGM host galaxy, probably because the COS-Halos survey probes the CGM at smaller impact parameters. We find at least two passive galaxies with H
i
and metal-line absorption, confirming the intriguing COS-Halos result that galaxies sometimes have cool gas halos despite no on-going star formation. Using a new methodology for fitting H
i
absorption complexes, we confirm the CGM cool gas mass of Paper I, but this value is significantly smaller than that found by the COS-Halos survey. We trace much of this difference to the specific values of the low-
z
metagalactic ionization rate assumed. After accounting for this difference, a best-value for the CGM cool gas mass is found by combining the results of both surveys to obtain
log
(
M
/
M
⊙
)
=
10.5
±
0.3
, or ∼30% of the total baryon reservoir of an
L
≥
L
*
, star-forming galaxy.
The circumgalactic medium (CGM) of late-type galaxies is characterized using UV spectroscopy of 11 targeted QSO/galaxy pairs at z < or =, slant 0.02 with the Hubble Space Telescope Cosmic Origins ...Spectrograph (COS) and ~60 serendipitous absorber/galaxy pairs at z < or =, slant 0.2 with the Space Telescope Imaging Spectrograph. CGM warm cloud properties are derived, including volume filling factors of 3%-5%, cloud sizes of 0.1-30 kpc, masses of 10-10 super(8) M sub(middot in circle), and metallicities of ~0.1-1 Z sub(middot in circle). Almost all warm CGM clouds within 0.5 R sub(vir) are metal-bearing and many have velocities consistent with being bound, "galactic fountain" clouds. For galaxies with L > ~0.1 L*, the total mass in these warm CGM clouds approaches 10 super(10) M sub(middot in circle), ~10%-15% of the total baryons in massive spirals and comparable to the baryons in their parent galaxy disks. This leaves > ~50% of massive spiral-galaxy baryons "missing." Dwarfs (<0.1 L*) have smaller area covering factors and warm CGM masses (< or =, slant5% baryon fraction), suggesting that many of their warm clouds escape. Constant warm cloud internal pressures as a function of impact parameter (P/k ~ 10 cm super(-3) K) support the inference that previous COS detections of broad, shallow O VI and Ly alpha absorptions are of an extensive (~400-600 kpc), hot (T asymptotically = 10 super(6) K), intra-cloud gas which is very massive (> or =, slanted10 super(11) M sub(middot in circle)). While the warm CGM clouds cannot account for all the "missing baryons" in spirals, the hot intra-group gas can, and could account for ~20% of the cosmic baryon census at z ~ 0 if this hot gas is ubiquitous among spiral groups.
ABSTRACT This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for ...obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Paper I. In this paper, we present both high-resolution radio continuum images for all of these sources and H i 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size <0 5 and flux densities >0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ∼three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H i 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral "window" (i.e., the percentage of H i 21 cm absorption-line detections could be as high as ∼90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H i detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H i absorption may well be present but is masked by the RFI. Future searches for highly redshifted H i and molecular absorption can easily find more distant CSOs among bright, "blank field" radio sources, but will be severely hampered by an inability to determine accurate spectroscopic redshifts due to their lack of rest-frame UV continuum.
To establish the connection between galaxies and UV-detected absorption systems in the local universe, a deep (g ≤ 20) and wide (∼20′ radius) galaxy redshift survey is presented around 47 sight lines ...to UV-bright AGNs observed by the Cosmic Origins Spectrograph (COS). Specific COS science team papers have used this survey to connect absorbers to galaxies, groups of galaxies, and large-scale structures, including voids. Here we present the technical details of the survey and the basic measurements required for its use, including redshifts for individual galaxies and uncertainties determined collectively by spectral class (emission-line, absorption-line, and composite spectra) and completeness for each sight line as a function of impact parameter and magnitude. For most of these sight lines, the design criteria of >90% completeness over a >1 Mpc region down to 0.1 L* luminosities at z ≤ 0.1 allows a plausible association between low-z absorbers and individual galaxies. Ly covering fractions are computed to approximate the star-forming and passive galaxy populations using the spectral classes above. In agreement with previous results, the covering fraction of star-forming galaxies with L ≥ 0.3 L* is consistent with unity inside one virial radius and declines slowly to >50% at four virial radii. On the other hand, passive galaxies have lower covering fractions (∼60%) and a shallower decline with impact parameter, suggesting that their gaseous halos are patchy but have a larger scale-length than star-forming galaxies. All spectra obtained by this project are made available electronically for individual measurement and use.
We investigate the association between galaxies and metal-enriched and metal-deficient absorbers in the local universe (z < 0.16) using a large compilation of far-ultraviolet spectra of bright active ...galactic nuclei targets observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. In this homogeneous sample of 18 O vi detections at and 18 nondetections at using absorbers with , the maximum distance O vi extends from galaxies of various luminosities is ∼0.6 Mpc, or ∼5 virial radii, confirming and refining earlier results. This is an important value that must be matched by numerical simulations, which input the strength of galactic winds at the sub-grid level. We present evidence that the primary contributors to the spread of metals into the circum- and intergalactic media are sub-L* galaxies ( ). The maximum distances that metals are transported from these galaxies is comparable to, or less than, the size of a group of galaxies. These results suggest that, where groups are present, the metals produced by the group galaxies do not leave the group. Since many O vi nondetections in our sample occur at comparably close impact parameters as those of the metal-bearing absorbers, some more pristine intergalactic material appears to be accreting onto groups where it can mix with metal-bearing clouds.
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