A High-Resolution Survey of Low-Redshift QSO Absorption Lines: Statistics and Physical Conditions of O VI Absorbers

By T. Tripp, K. Sembach, D. Bowen, B. Savage, E. Jenkins, N. Lehner, P. Richter. 2007

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Using high-resolution ultraviolet spectra of 16 low-z QSOs obtained with the E140M echelle mode of the Space Telescope Imaging Spectrograph, we study the physical conditions and statistics of O VI absorption in the intergalactic medium (IGM) at z < 0.5. We identify 51 intervening (zabs≪ zQSO) O VI systems comprising 77 individual components, and we find 14 “proximate” systems (zabs ≈ zQSO) containing 34 components. For intervening systems (components) with rest-frame equivalent width Wr > 30 mÅ, the number of O VI absorbers per unit redshift dN/dz = 15.6−2.4+2.9 (21.0−2.8+3.2) , and this decreases to dN/dz = 0.9−0.5+1.0 (0.3−0.3+0.7) for Wr > 300 mÅ. The number per redshift increases steeply as zabs approaches zQSO; we find that dN/dz is ≈3-10 times higher within 2500 km s−1 of zQSO. The most striking difference between intervening and proximate systems is that some proximate absorbers have substantially lower H I/O VI ratios. The lower ratios in proximate systems could be partially due to ionization effects, but these proximate absorbers must also have significantly higher metallicities. We find that 37% of the intervening O VI absorbers have velocity centroids that are well aligned with corresponding H I absorption. If the O VI and the H I trace the same gas, the relatively small differences in line widths imply that the absorbers are cool, with T < 105 K. Most of these well-aligned absorbers have the characteristics of metal-enriched photoionized gas. However, the O VI in the apparently simple and cold systems could be associated with a hot phase with T ≈ 105.5 K if the metallicity is high enough to cause the associated broad Lyα absorption to be too weak to detect. We show that 53% of the intervening O VI systems are complex multiphase absorbers that can accommodate both lower metallicity collisionally ionized gas with T > 105 K and cold photoionzed gas.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/59dbaadad154a9cf91327e289b53ab6ec2d2f9fc

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In Atomic and Molecular Physics, and Optics

In Condensed Matter Physics

Simon D. M. White

Citations in the corpus

PROBING THE INTERGALACTIC MEDIUM/GALAXY CONNECTION. V. ON THE ORIGIN OF Lyα AND O vi ABSORPTION AT z < 0.2 (2011, methodology): “…NSF Astronomy & Astrophysics Postdoctoral Fellow, MIT Kavli Institute for Astrophysics & Space Research, 77 Massachusetts Avenue, 37-611, Cambridge, MA 02139, USA; kcooksey@space.mit.edu Prochaska et al. 2006; Thom & Chen 2008b; Tripp et al. 2008; Danforth & Shull 2008; Cooksey et al. 2010).”
The physics of the intergalactic medium (2007, background): “…Kirkman and Tytler, 1997b), at low redshifts they are associated with a warm-hot intergalactic medium (WHIM) (Danforth and Shull, 2005, 2008; Richter et al., 2004; Savage et al., 2002; Tripp and Savage, 2000; Tripp et al., 2008), that is most likely collisionally ionized rather than photoionized.”
The Circumgalactic Medium (2017, background): “…the relationship exhibits considerable scatter, is impacted significantly by blending of multiple unresolved components (at least at the moderate R ∼ 20, 000 resolution of COS), and may arise from other physical scenarios such as turbulent mixing (e.g. Tripp et al. 2008; Lehner et al. 2014).”
THE COS-HALOS SURVEY: RATIONALE, DESIGN, AND A CENSUS OF CIRCUMGALACTIC NEUTRAL HYDROGEN (2013, methodology): “To do this, we compare the line-profile fits from COS-Halos to the “blind” samples of Tripp et al. (2008), Thom & Chen (2008), and Tilton et al. (2012).”
THE COS-HALOS SURVEY: ORIGINS OF THE HIGHLY IONIZED CIRCUMGALACTIC MEDIUM OF STAR-FORMING GALAXIES (2016, methodology): “…is 55 km s−1, a value that is considerably broader than the O VI absorption in general absorption-line centric surveys (discussed in Section 3.3.2; Tripp et al. 2008; Muzahid et al. 2012; Savage et al. 2014; Danforth et al. 2016) Turning to the lower panel of Figure 6, we directly examine the…”
The Low-z Intergalactic Medium. III. H I and Metal Absorbers at z < 0.4 (2007, methodology): “Our counting statistics are intermediate between the “component” and “system” nomenclature of Tripp et al. (2008), but generally closer to the latter classification.”
THE BARYON CENSUS IN A MULTIPHASE INTERGALACTIC MEDIUM: 30% OF THE BARYONS MAY STILL BE MISSING (2011, background): “Ultraviolet spectroscopic surveys of Lyα and O VI have identified substantial numbers of absorbers (Danforth & Shull 2008; Tripp et al. 2008; Thom & Chen 2008), but claimed detections of hotter in X-ray absorption by O VII (Nicastro et al. 2005) remain controversial (Kaastra et al. 2006; Yao et al.…”
Bimodality of low-redshift circumgalactic O VI in non-equilibrium EAGLE zoom simulations (2016, methodology): “The study of the metal enrichment of the low-z intergalactic medium (IGM) relied on surveys of metal lines in serendipitous sight lines providing a cross section-weighted sampling (e.g. Thom & Chen 2008; Tripp et al. 2008; Wakker & Savage 2009; Tilton et al. 2012; Danforth et al. 2014).”
CHARACTERIZING THE CIRCUMGALACTIC MEDIUM OF NEARBY GALAXIES WITH HST/COS AND HST/STIS ABSORPTION-LINE SPECTROSCOPY (2012, background): “However, the ionization mechanism for this transition remains controversial, as both photo-ionization (Davé & Oppenheimer 2007; Tripp et al. 2008) and collisional ionization due to shocks (Cen & Ostriker 1999; Shull, Smith, & Danforth 2012) have been proposed.”
The EAGLE project: Simulating the evolution and assembly of galaxies and their environments (2014, result): “Particularly for Ovi, the analysis of COS spectra by Danforth et al. (2014) yields systematically more absorbers than the earlier analyses of STIS/FUSE/GHRS data by Danforth & Shull (2008), Thom & Chen (2008), and Tripp et al. (2008).”
THE COS-HALOS SURVEY: PHYSICAL CONDITIONS AND BARYONIC MASS IN THE LOW-REDSHIFT CIRCUMGALACTIC MEDIUM (2014, methodology): “As a final note, we point out that group environments significantly complicate any interpretation on the origin of the CGM since absorption profiles are typically kinematically very complex (Aracil et al. 2006; Tripp et al. 2008; Burchett et al. 2013).”
THE COS-HALOS SURVEY: AN EMPIRICAL DESCRIPTION OF METAL-LINE ABSORPTION IN THE LOW-REDSHIFT CIRCUMGALACTIC MEDIUM (2012, background): “…UV absorber surveys selected targets based on QSO properties such as brightness or redshift and not based on the properties of foreground galaxies (e.g., Shull et al. 1996; Penton et al. 2000; Davé & Tripp 2001; Tripp et al. 2008; Thom & Chen 2008a, 2008b; Cooksey et al. 2010; Tilton et al. 2012).”