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The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies | | Jessica K. Werk
; J. Xavier Prochaska
; Sebastiano Cantalupo
; Andrew J. Fox
; Benjamin Oppenheimer
; Jason Tumlinson
; Todd M. Tripp
; Nicolas Lehner
; Matthew McQuinn
; | | Date: |
31 Aug 2016 | | Abstract: | 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 OVI 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 NV/OVI for 39 fitted Voigt profile
components of OVI. 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 NV/OVI and measurements of N$_{
m OVI}$ imply unphysically large
path lengths $gtrsim$ 100 kpc. Furthermore, very broad OVI absorption (b $>$
40 km/s) is a defining characteristic of the CGM of star-forming L$^{*}$
galaxies. We highlight two possible origins for the bulk of the observed OVI:
(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 OVI does not align with any
low-ionization state gas within $pm$50 km/s and is found only in halos with
M$_{
m halo}$ $<$ 10$^{12}$ M$_{odot}$. We suggest that this type of
unmatched OVI absorption traces the hot corona itself at a characteristic
temperature of 10$^{5.5}$ 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. | | Source: | arXiv, 1609.0012 | | Services: | Forum | Review | PDF | Favorites | |
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