CHARACTERIZING THE CIRCUMGALACTIC MEDIUM OF NEARBY GALAXIES WITH<i>HST</i>/COS AND<i>HST</i>/STIS ABSORPTION-LINE SPECTROSCOPY

Abstract

The Circumgalactic Medium (CGM) of late-type galaxies is characterized using\nUV spectroscopy of 11 targeted QSO/galaxy pairs at z &lt; 0.02 with the Hubble\nSpace Telescope Cosmic Origins Spectrograph and ~60 serendipitous\nabsorber/galaxy pairs at z &lt; 0.2 with the Space Telescope Imaging Spectrograph.\nCGM warm cloud properties are derived, including volume filling factors of\n3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and\nmetallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5\nvirial radii are metal-bearing and many have velocities consistent with being\nbound, "galactic fountain" clouds. For galaxies with L &gt; 0.1 L*, the total mass\nin these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total\nbaryons in massive spirals and comparable to the baryons in their parent galaxy\ndisks. This leaves &gt;50% of massive spiral-galaxy baryons "missing". Dwarfs\n(&lt;0.1 L*) have smaller area covering factors and warm CGM masses (&lt;5% baryon\nfraction), suggesting that many of their warm clouds escape. Constant warm\ncloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3}\nK) support the inference that previous COS detections of broad, shallow O VI\nand Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K)\nintra-cloud gas which is very massive (&gt;1e11 solar masses). While the warm CGM\nclouds cannot account for all the "missing baryons" in spirals, the hot\nintra-group gas can, and could account for ~20% of the cosmic baryon census at\nz ~ 0 if this hot gas is ubiquitous among spiral groups.\n