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

2013; IOP Publishing; Volume: 763; Issue: 2 Linguagem: Inglês

10.1088/0004-637x/763/2/148

1538-4357

John T. Stocke, Brian A. Keeney, Charles Danforth, J. Michael Shull, Cynthia S. Froning, James C. Green, Steven V. Penton, Blair D. Savage,

Astronomy and Astrophysical Research

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 Rvir 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.