The COS-Halos survey: origins of the highly ionized circumgalactic medium of star-forming galaxies
- University of Washington, Department of Astronomy, Seattle, WA (United States)
- UCO/Lick Observatory, University of California, Santa Cruz, CA (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD (United States)
- CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)
- Department of Astronomy, University of Massachusetts, Amherst, MA (United States)
- Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)
The total contribution of diffuse halo gas to the galaxy baryon budget strongly depends on its dominant ionization state. In this paper, we address the physical conditions in the highly ionized circumgalactic medium (CGM) traced by O VI absorption lines observed in COS-Halos spectra. We analyze the observed ionic column densities, absorption-line widths and relative velocities, along with the ratios of N V/O VI for 39 fitted Voigt profile components of O vi. We compare these quantities with the predictions given by a wide range of ionization models. Photoionization models that include only extragalactic UV background radiation are ruled out; conservatively, the upper limits to N V/O VI and measurements of N{sub OVI} imply unphysically large path lengths ≳100 kpc. Furthermore, very broad O VI absorption (b > 40 km s{sup −1}) is a defining characteristic of the CGM of star-forming L* galaxies. We highlight two possible origins for the bulk of the observed O VI: (1) highly structured gas clouds photoionized primarily by local high-energy sources or (2) gas radiatively cooling on large scales behind a supersonic wind. Approximately 20% of circumgalactic O vi does not align with any low-ionization state gas within ±50 km s{sup −1} and is found only in halos with M{sub halo} < 10{sup 12} M{sub ⊙}. We suggest that this type of unmatched O vi absorption traces the hot corona itself at a characteristic temperature of 10{sup 5.5} K. We discuss the implications of these very distinct physical origins for the dynamical state, gas cooling rates, and total baryonic content of L* gaseous halos.
- OSTI ID:
- 22868370
- Journal Information:
- Astrophysical Journal, Vol. 833, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
THE CIRCUMGALACTIC MEDIUM OF MASSIVE GALAXIES AT z {approx} 3: A TEST FOR STELLAR FEEDBACK, GALACTIC OUTFLOWS, AND COLD STREAMS
THE BARYON CENSUS IN A MULTIPHASE INTERGALACTIC MEDIUM: 30% OF THE BARYONS MAY STILL BE MISSING