Brian A. Keeney

University of Colorado at Boulder, Boulder, Colorado, United States

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Publications (73)196.44 Total impact


  • No preview · Article · Jan 2016 · The Astrophysical Journal
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    ABSTRACT: 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.
    No preview · Article · Oct 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present HI 21cm emission observations of the z ~ 0.00632 sub-damped Lyman-alpha absorber (sub-DLA) towards PG1216+069 made using the Arecibo Telescope and the Very Large Array (VLA). The Arecibo 21cm spectrum corresponds to an HI mass of ~ 3.2x10^7 solar masses, 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 HI column densities is expected to be dominated by spirals. The 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 HI sources appears to be part of complex "W", believed to lie in the background of the Virgo cluster. While several HI 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
    Preview · Article · Aug 2015
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    ABSTRACT: The size and mass of two circum-galactic medium (CGM) clouds in the halo (impact parameter = 65 kpc) of a nearby late-type galaxy, MGC-01-04-005 ($cz = 1865$ km/s), are investigated using a close triplet of QSO sight lines (the "LBQS Triplet"; Crighton et al. 2010). Far ultraviolet spectra obtained with the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST) find two velocity components in Lyman $\alpha$ at $\sim1830$ and 1900 km/s in two of these sight lines, requiring minimum transverse cloud sizes of $\geq10$ kpc. A plausible, but not conclusive, detection of CIV 1548 \AA\ absorption at the higher velocity in the third sight line suggests an even larger lower limit of $\geq23$ kpc for that cloud. Using various combinations of constraints, including photo-ionization modeling for one absorber, lower limits on masses of these two clouds of $\geq10^6$ M_Sun are obtained. Ground-based imaging and long-slit spectroscopy of MCG -01-04-005 obtained at the Apache Point Observatory (APO) 3.5m telescope find it to be a relatively normal late-type galaxy with a current star formation rate (SFR) of $\sim0.01$ M_Sun per year. Galaxy Evolution Explorer (GALEX) photometry finds an SFR only a few times higher over the last $10^8$ yrs. We conclude that the CGM clouds probed by these spectra are typical in being at impact parameters of 0.4-0.5 R_vir from a rather typical, non-starbursting late-type galaxy so that these size and mass results should be generic for this class. Therefore, at least some CGM clouds are exceptionally large and massive.
    Preview · Article · Jun 2015 · The Astrophysical Journal
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    ABSTRACT: Detailed studies of stellar populations in the halos of the Milky Way and the Andromeda (M 31) galaxies have shown increasing numbers of tidal streams and dwarf galaxies, attesting to a complicated and on-going process of hierarchical structure formation. The most prominent feature in the halo of M 31 is the Giant Stellar Stream, a structure ~4.5 degrees in extent along the sky, which is close to, but not coincident with the galaxy's minor axis. The stars that make up this stream are kinematically and chemically distinct from the other stars in the halo. Here, we present HST/COS high-resolution ultraviolet absorption spectra of three Active Galactic Nuclei sight lines which probe the M 31 halo, including one that samples gas in the main southwestern portion of the Giant Stream. We see two clear absorption components in many metal species at velocities typical of the M 31 halo and a third, blue-shifted component which arises in the stream. Photoionization modeling of the column density ratios in the different components shows gas in an ionization state typical of that seen in other galaxy halo environments and suggests solar to slightly super-solar metallicity, consistent with previous findings from stellar spectroscopy.
    Preview · Article · Jun 2015 · The Astrophysical Journal
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    ABSTRACT: We present new GALEX images and optical spectroscopy of J1229+02, a dwarf post-starburst galaxy located 81 kpc from the 1585 km/s absorber in the 3C 273 sight line. The absence of H\alpha\ emission and the faint GALEX UV fluxes confirm that the galaxy's recent star formation rate is $<10^{-3} M_{\odot}$/yr. Absorption-line strengths and the UV-optical SED give similar estimates of the acceptable model parameters for its youngest stellar population where $f_m$ < 60% of its total stars (by mass) formed in a burst $t_sb$ = 0.7-3.4 Gyr ago with a stellar metallicity of -1.7 < [Fe/H] < +0.2; we also estimate the stellar mass of J1229+02 to be 7.3 < log($M_*/M_{\odot}$) < 7.8. Our previous study of J1229+02 found that a supernova-driven wind was capable of expelling all of the gas from the galaxy (none is observed today) and could by itself plausibly create the nearby absorber. But, using new data, we find a significantly higher galaxy/absorber velocity difference, a younger starburst age, and a smaller starburst mass than previously reported. Simple energy-conserving wind models for J1229+02 using fiducial values of $f_m$ ~ 0.1, $t_sb$ ~ 2 Gyr, and log(M$_*/M_{\odot}$) ~ 7.5 allow us to conclude that the galaxy alone cannot produce the observed QSO absorber; i.e., any putative ejecta must interact with ambient gas from outside J1229+02. Because J1229+02 is located in the southern extension of the Virgo cluster ample potential sources of this ambient gas exist. Based on the two nearest examples of strong metal-line absorbers discovered serendipitously (the current one and the 1700 km/s metal-line absorber in the nearby Q1230+0115 sight line), we conclude that absorbers with $10^{14} < N_{HI} < 10^{16}$ cm$^{-2}$ at impact parameters >1$R_{vir}$ are likely intergalactic systems and cannot be identified unambiguously as the circumgalactic material of any one individual galaxy.
    Preview · Article · Sep 2014 · The Astronomical Journal
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    ABSTRACT: Since the discovery of the large (2 × 109M ☉) intergalactic cloud known as the Leo Ring in the 1980s, the origin of this object has been the center of a lively debate. Determining the origin of this object is still important as we develop a deeper understanding of the accretion and feedback processes that shape galaxy evolution. We present Hubble Space Telescope/Cosmic Origins Spectrograph observations of three sightlines near the ring, two of which penetrate the high column density neutral hydrogen gas visible in 21 cm observations of the object. These observations provide the first direct measurement of the metallicity of the gas in the ring, an important clue to its origin. Our best estimate of the metallicity of the ring is ~10% Z ☉, higher than expected for primordial gas but lower than expected from an interaction. We discuss possible modifications to the interaction and primordial gas scenarios that would be consistent with this metallicity measurement.
    Full-text · Article · Jun 2014 · The Astrophysical Journal
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    ABSTRACT: Using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) the COS Science Team has conducted a high signal-to-noise survey of 14 bright QSOs. In a previous paper (Savage et al. 2014) these far-UV spectra were used to discover 14 "warm" ($T > 10^5$ K) absorbers using a combination of broad Ly\alpha\ and O VI absorptions. A reanalysis of a few of this new class of absorbers using slightly relaxed fitting criteria finds as many as 20 warm absorbers can be present in this sample. A shallow, wide spectroscopic galaxy redshift survey has been conducted around these sight lines to investigate the warm absorber environment, which is found to be spiral-rich galaxy groups or cluster outskirts with radial velocity dispersions of \sigma_v = 250-750 km/s. While 2\sigma\ evidence is presented favoring the hypothesis that these absorptions are associated with the galaxy groups and not with the individual nearest galaxies, this evidence has considerable systematic uncertainties and so is not conclusive. However, if the associations are with galaxy groups, the observed frequency of warm absorbers dN/dz = 3.5-5 per unit redshift plus the local density of galaxy groups require these warm absorbers to be very large (~1 Mpc in radius at high covering factor) and, if diffuse (i.e., high filling factor), very massive (> $10^{11} M_{\odot}$). However, with only single probes through each group in this small sample, the conclusion that these "warm absorbers" are detections of a massive intra-group medium in spiral galaxy groups is tentative.
    Full-text · Article · May 2014 · The Astrophysical Journal
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    ABSTRACT: We report on the observed properties of the plasma revealed through high signal-to-noise (S/N) observations of 54 intervening O VI absorption systems containing 85 O VI and 133 H I components in a blind survey of 14 QSOs observed at ~18 km s-1 resolution with the Cosmic Origins Spectrograph (COS) over a redshift path of 3.52 at z < 0.5. Simple systems with one or two H I components and one O VI 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(H I). 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 IGM extending 200 to 600 kpc beyond the closest associated galaxy. We estimate the warm aligned O VI absorbers contain (4.1+/-1.1)% of the baryons at low z. The warm plasma traced by the aligned O VI and H I absorption contains nearly as many baryons as are found in galaxies.
    Preview · Article · Mar 2014 · The Astrophysical Journal Supplement Series
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    ABSTRACT: We use high-quality, medium-resolution HST/COS observations of 75 UV-bright AGN at redshifts $z_{\rm AGN}< 0.85$ to construct the largest survey of the low-redshift IGM to date. The catalog is comprised of 4369 individual extragalactic absorption lines of HI and 20 different metal ions grouped together into 2508 distinct redshift systems at $z_{\rm abs}<0.75$ and represents a significant improvement in total redshift pathlength and weak line sensitivity over previous studies. The column-density distribution of HI systems is seen to evolve both in amplitude and slope at $z< 0.47$. We observe 985 metal lines in 354 systems, and find that the fraction of absorbers detected in metals is strongly dependent on HI column density. OVI absorbers appear to evolve in the same sense as the Ly$\alpha$ forest. A velocity-space two-point correlation function shows substantial clustering of HI absorbers on scales of $\Delta v=50-300\rm~km~s^{-1}$ with no significant clustering at larger $\Delta v$. Most of the clustering signal comes from the stronger ($N_{\rm HI}>10^{13.5}~\rm cm^{-2}$) absorbers particularly those with metal absorption. The full catalog of absorption lines and fully-reduced spectra is available via MAST as a high-level science product at http://archive.stsci.edu/prepds/igm/.
    Full-text · Article · Feb 2014
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    ABSTRACT: We have detected and characterized the circumgalactic medium (CGM) of nearby late-type galaxies using both targeted and serendipitous QSO/galaxy pairs at z < 0.2. Photoionization modeling of warm CGM clouds finds volume filling factors of ~5%, cloud sizes of 0.1-30 kpc, cloud masses of 10-108 M⊙, and metallicities of ~0.1-1 Z⊙. The total mass of these warm clouds surrounding L > 0.1 L* galaxies approaches 1010 M⊙, comparable to the total baryons in massive galaxy disks. We also find evidence for an extensive (>500 kpc), hot (105 - 106 K) intracloud medium that is very massive (> 1011 M⊙). We interpret this hot, massive baryon reservoir as the intragroup medium of spiral-rich galaxy groups and find that its inclusion can solve the missing baryon problem in spiral galaxies.
    No preview · Article · Jan 2014
  • Julie Davis · C. Danforth · B. A. Keeney · J. T. Stocke
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    ABSTRACT: The standard model for propagation of gamma rays from very high energy (VHE, E>100 GeV) blazars through the universe requires an understanding of the diffuse extragalactic background light (EBL). Due to photon-photon collision and pair production from gamma ray/infrared photon interaction in the intergalactic medium, we expect to see a redshift “horizon” beyond which gamma rays from these sources are no longer observable. Three TeV-bright blazars examined in this project pose a problem to the horizon hypothesis due to their substantial redshifts, requiring reevaluation of either the gamma-ray propagation model or the EBL model. This project establishes a minimum density of infrared photons and a potential lower limit on the EBL flux toward these high-z blazars by integrating and summing flux contributions from intervening galaxies within reasonable impact parameters of the blazar sight lines. Galaxies along the lines of sight and their flux contributions are inferred from from measured HI (Lyman alpha forest) and metal-ion absorbers seen in far-UV spectra of PKS1424+240 and 3C66A (HST/COS) and 3C279 (HST/FOS).
    No preview · Article · Jan 2014
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    ABSTRACT: The unprecedented far-UV throughput of the Cosmic Origins Spectrograph (COS) is revolutionizing studies of the local intergalactic medium (IGM). In particular, COS is allowing us to refine estimates of the baryon content and metallicity of the IGM, as well as the relationship of IGM absorbers to galaxies. For the past several years we have been using WIYN/HYDRA to obtain spectra of all galaxies brighter than g=20 that are within 20 arcminutes of the ~25 AGN targeted by the COS Science Team that are accessible from the northern hemisphere. When combined with the COS spectra of these AGN, this galaxy redshift survey is enhancing our understanding of the composition and topology of the nearby Universe in both gas and galaxies, allowing us to assess the extent of metal transport away from galaxies, the filling factor of gas and metal-enriched gas in galaxy filaments, and the metallicity of gas in galaxy voids. Here we present estimates of the completeness of our survey along these sight lines and examples of close galaxy-absorber associations discovered by our survey.
    No preview · Article · Jun 2013
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    ABSTRACT: We have used the Cosmic Origins Spectrograph (COS) to obtain far-UV spectra of three closely-spaced QSO sight lines that probe the circumgalactic medium (CGM) of an edge-on spiral galaxy, ESO 157-49, at impact parameters of 74 and 93 kpc near its major axis and 172 kpc along its minor axis. H I Ly\alpha\ absorption is detected at the galaxy redshift in the spectra of all three QSOs, and metal lines of Si III, Si IV, and C IV are detected along the two major-axis sight lines. Photoionization models of these clouds suggest metallicities close to the galaxy metallicity, cloud sizes of ~1 kpc, and gas masses of ~10^4 solar masses. Given the high covering factor of these clouds, ESO 157-49 could harbor ~2x10^9 solar masses of warm CGM gas. We detect no metals in the sight line that probes the galaxy along its minor axis, but gas at the galaxy metallicity would not have detectable metal absorption with ionization conditions similar to the major-axis clouds. The kinematics of the major-axis clouds favor these being portions of a "galactic fountain" of recycled gas, while two of the three minor-axis clouds are constrained geometrically to be outflowing gas. In addition, one of our QSO sight lines probes a second more distant spiral, ESO 157-50, along its major axis at an impact parameter of 88 kpc. Strong H I Ly\alpha\ and C IV absorption only are detected in the QSO spectrum at the redshift of ESO 157-50.
    Full-text · Article · Jan 2013 · The Astrophysical Journal
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    ABSTRACT: In three years of science operations onboard HST, the Cosmic OriginsSpectrograph has generated an archive of far-ultraviolet AGN spectra of unprecedented breadth, depth, and quality. COS was designed to be sensitive to many important diagnostic lines in the far-UV (1135-1800A) in the low-redshift, "local" universe: Lya (z<0.47), Lyb (0.1<z<0.7), OVI (0.1<z<0.7), SiIII (z<0.5), CIV (z<0.17), NeVIII (0.45<z<1.3), etc. We report on our ongoing survey of extragalactic absorption systems toward ~200 low- to moderate-redshift (z<1.5), UV-bright AGN. When complete mid-2013), the COS IGM absorber catalog will provide an unbiased, statistical sampling of local intergalactic absorption along ~200 extragalactic sight lines. This significant cornerstone of the scientific legacy of COS is at least an order-of-magnitude improvement over previous low-z IGM surveys in total observed pathlength and number of absorbers as well as substantial improvements in sensitivity and uniformity. Of particular interest is the sensitivity of COS to weak and broad absorption. We discuss the scope of and methodology behind the catalog, several initial discoveries, and the overall statistical findings of the survey. Finally, we discuss the new areas of cosmology enabled by this expanded study.
    No preview · Article · Jan 2013
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    ABSTRACT: The Circumgalactic Medium (CGM) of late-type galaxies is characterized using UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous absorber/galaxy pairs at z < 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 10-1e8 solar masses and metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5 virial radii 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 1e10 solar masses, ~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 (<5% 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^{-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 ~ 1e6 K) intra-cloud gas which is very massive (>1e11 solar masses). 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.
    Preview · Article · Dec 2012 · The Astrophysical Journal
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    ABSTRACT: We present optical and near-IR spectroscopic observations of the luminous blue variable SN 2009ip during its remarkable photometric evolution of 2012. The spectra sample three key points in the SN 2009ip lightcurve, corresponding to its initial brightening in August (2012-A) and its dramatic rebrightening in early October (2012-B). Based on line fluxes and velocities measured in our spectra, we find a surprisingly low I(H-alpha)/I(H-beta) ratio (~1.5) in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where H-alpha, but not H-beta, is optically thick, or an extremely high density for the circumstellar material of n_e > 10^(13) cm^(-3). The H-alpha line intensity yields a minimum radiating surface area of >~20,000 AU^2 in H-alpha at the peak of SN 2009ip's photometric evolution. Combined with the nature of this object's spectral evolution in 2012, a high circumstellar density and large radiating surface area imply the presence of a thin disk geometry around the central star (and, consequently, a possible binary companion), suggesting that the observed 2012-B rebrightening of SN 2009ip can be attributed to the illumination of the disk's inner rim by fast-moving ejecta produced by the underlying events of 2012-A.
    Full-text · Article · Nov 2012 · The Astronomical Journal
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    ABSTRACT: The BL Lacertae object S5 0716+714 is one of the most studied blazars on the sky due to its active variability and brightness in many bands, including very-high-energy gamma rays. We present here two serendipitous results from recent far-ultraviolet spectroscopic observations by the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (HST). First, during the course of our 7.3 hr HST observations, the blazar increased in flux rapidly by ~40% (–0.45 mag hr–1) followed by a slower decline (+0.36 mag hr–1) to previous FUV flux levels. We model this flare using asymmetric flare templates and constrain the physical size and energetics of the emitting region. Furthermore, the spectral index of the object softens considerably during the course of the flare from αν ≈ –1.0 to αν ≈ –1.4. Second, we constrain the source redshift directly using the ~30 intervening absorption systems. A system at z = 0.2315 is detected in Lyα, Lyβ, O VI, and N V and defines the lower bound on the source redshift. No absorbers are seen in the remaining spectral coverage (0.2315 < z Lyα 0.47) and we set a statistical upper bound of z < 0.322 (95% confidence) on the blazar. This is the first direct redshift limit for this object and is consistent with literature estimates of z = 0.31 ± 0.08 based on the detection of a host galaxy.
    Preview · Article · Sep 2012 · The Astrophysical Journal
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    ABSTRACT: We present empirical scaling relations for the significance of absorption features detected in medium resolution, far-UV spectra obtained with the Cosmic Origins Spectrograph (COS). These relations properly account for both the extended wings of the COS line spread function and the non-Poissonian noise properties of the data, which we characterize for the first time, and predict limiting equivalent widths that deviate from the empirical behavior by \leq 5% when the wavelength and Doppler parameter are in the ranges \lambda = 1150-1750 A and b > 10 km/s. We have tested a number of coaddition algorithms and find the noise properties of individual exposures to be closer to the Poissonian ideal than coadded data in all cases. For unresolved absorption lines, limiting equivalent widths for coadded data are 6% larger than limiting equivalent widths derived from individual exposures with the same signal-to-noise. This ratio scales with b-value for resolved absorption lines, with coadded data having a limiting equivalent width that is 25% larger than individual exposures when b \approx 150 km/s.
    Preview · Article · Jun 2012 · Publications of the Astronomical Society of the Pacific
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    ABSTRACT: Ultraviolet observations of the QSO 3C 263 (zem = 0.652) with COS and FUSE reveal O VI absorption systems at z = 0.06342 and 0.14072 . WIYN multi-object spectrograph observations provide information about the galaxies associated with the absorbers. The multi-phase system at z = 0.06342 traces cool photoionized gas and warm collisionally ionized gas associated with a L ~ 0.31L* compact spiral emission line galaxy with an impact parameter of 63 kpc. The cool photoionized gas in the absorber is well modeled with log U ~ -2.6, log N(H) ~17.8, log n(H) ~ -3.3 and [Si/H] = -0.14\pm0.23. The collisionally ionized gas containing C IV and O VI probably arises in cooling shock heated transition temperature gas with log T ~ 5.5. The absorber is likely tracing circumgalactic gas enriched by gas ejected from the spiral emission line galaxy. The simple system at z = 0.14072 only contains O VI and broad and narrow H I. The O VI with b = 33.4\pm11.9 km s-1 is likely associated with the broad H I {\lambda}1215 absorption with b = 86.7\pm15.4 km s-1. The difference in Doppler parameters implies the detection of a very large column of warm gas with log T = 5.61(+0.16, -0.25), log N(H) = 19.54(+0.26, -0.44) and [O/H] = -1.48 (+0.46, -0.26). This absorber is possibly associated with a 1.6L* absorption line galaxy with an impact parameter of 617 kpc although an origin in warm filament gas or in the halo of a fainter galaxy is more likely.
    Preview · Article · May 2012 · The Astrophysical Journal

Publication Stats

716 Citations
196.44 Total Impact Points

Institutions

  • 2004-2015
    • University of Colorado at Boulder
      • • Department of Astrophysical and Planetary Sciences
      • • Center for Astrophysics and Space Astronomy
      Boulder, Colorado, United States
  • 2014
    • East Tennessee State University
      • Department of Physics and Astronomy
      Johnson City, Tennessee, United States
  • 2011
    • University of Colorado
      Denver, Colorado, United States