Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-line Spectroscopy
The Astrophysical Journal, Volume 763, Issue 2, article id. 148, 30 pp. (2013).
Published in Feb 2013
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 ~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 10-108 M ☉, and metallicities of ~0.1-1 Z ☉. 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 〉~ 0.1 L*, the total mass in these warm CGM clouds approaches 1010 M ☉, ~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 Lyα absorptions are of an extensive (~400-600 kpc), hot (T ≈ 106 K), intra-cloud gas which is very massive (〉=1011 M ☉). 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.Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
galaxies: dwarf; galaxies: groups: general; galaxies: halos; galaxies: spiral; intergalactic medium; quasars: absorption lines