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

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 (COS) and similar to 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 10-10(8)M(circle dot), and metallicities of similar to 0.1-1Z(circle dot). Almost all warm CGM clouds within 0.5 R-vir are metal-bearing and many have velocities consistent with being bound, "galactic fountain" clouds. For galaxies with L greater than or similar to 0.1L*, the total mass in these warm CGM clouds approaches 10(10) M-circle dot, similar to 10%-15% of the total baryons in massive spirals and comparable to the baryons in their parent galaxy disks. This leaves greater than or similar to 50% of massive spiral-galaxy baryons "missing." Dwarfs (<0.1L*) 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 similar to 10 cm(-3) K) support the inference that previous COS detections of broad, shallow O VI and Ly alpha absorptions are of an extensive (similar to 400-600 kpc), hot (T approximate to 106 K), intra-cloud gas which is very massive (>= 10(11) M-circle dot). While the warm CGM clouds cannot account for all the "missing baryons" in spirals, the hot intra-group gas can, and could account for similar to 20% of the cosmic baryon census at z similar to 0 if this hot gas is ubiquitous among spiral groups.