Speaker
Prof.
John Stocke
(CASA, U. of Colorado)
Description
The Science Team for the Cosmic Origins Spectrograph (COS) has conducted a modest-sized survey of QSOs near very low-z galaxies to characterize gaseous galaxy halos. We have found that high (~100%) covering factors in Lyα absorption extend at least out to the virial radius for L>0.1L* galaxies. Standard photo-ionization modeling of these absorbers finds cloud sizes of 1—30 kpc, masses of 10^(1-8) solar masses and total filling factors of 3—5%. The total mass in warm photo-ionized clouds approaches 10^10 solar masses, comparable to the mass of galaxy disks. This leaves ~50% of spiral galaxy baryons ``missing’’. Dwarfs (L<0.1L*) have smaller covering factors and cloud masses (<5% baryon fraction). Constant cloud pressures as a function of impact parameter and, in a few cases, broad, shallow Lyα absorption suggests the presence of a hot (T≈10^6 K) gas in spiral groups that could account for the remainder of the missing baryons.
