%0 Generic %1 werk2016coshalos %A Werk, Jessica K. %A Prochaska, J. Xavier %A Cantalupo, Sebastiano %A Fox, Andrew J. %A Oppenheimer, Benjamin %A Tumlinson, Jason %A Tripp, Todd M. %A Lehner, Nicolas %A McQuinn, Matthew %D 2016 %K cgm cos halo highly ionised sfr %T The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies %U http://arxiv.org/abs/1609.00012 %X 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$_OVI$ 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$50 km/s and is found only in halos with M$_halo$ $<$ 10$^12$ M$_ødot$. 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.

@misc{werk2016coshalos, 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$_{\rm OVI}$ 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$50 km/s and is found only in halos with M$_{\rm 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.}, added-at = {2016-09-02T09:54:26.000+0200}, author = {Werk, Jessica K. and Prochaska, J. Xavier and Cantalupo, Sebastiano and Fox, Andrew J. and Oppenheimer, Benjamin and Tumlinson, Jason and Tripp, Todd M. and Lehner, Nicolas and McQuinn, Matthew}, biburl = {https://www.bibsonomy.org/bibtex/2a77aabbb00d52c8b09e8930125d5e409/miki}, description = {[1609.00012] The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies}, interhash = {eff9d8ab1a66679f024c32d117d97656}, intrahash = {a77aabbb00d52c8b09e8930125d5e409}, keywords = {cgm cos halo highly ionised sfr}, note = {cite arxiv:1609.00012Comment: 24 pages, 12 figures. Originally submitted to ApJ July 2015; this version is extensively revised and was re-submitted 8/30/16. Comments welcome}, timestamp = {2016-09-02T09:54:26.000+0200}, title = {The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies}, url = {http://arxiv.org/abs/1609.00012}, year = 2016 }