Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy. (arXiv:1212.5658v1 [astro-ph.CO])

Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy. (arXiv:1212.5658v1 [astro-ph.CO]):
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.