Monday, November 09, 2015 at 4:00 PM

JILA Auditorium

Todd Tripp, Univ. Massachusetts

"Whodunnit? A Deep Study of the Origin and Nature of Circumgalactic QSO absorbers"

Abstract:

The Cosmic Origins Spectrograph (COS), developed and built at UC-Boulder, has broken open an important aspect of galaxy evolution: the so-called circumgalactic medium (CGM), the gaseous intermediary between the stellar component of galaxies and the intergalactic medium. The CGM regulates galaxy evolution by affecting inflows and outflows (e.g., by stalling outflowing galactic winds or inflowing accretion streams), but it also provides a wealth of empirical data that can provide insight on a variety of physical processes. But, as the best scientific tools tend to do, COS studies have yielded more questions than answers. For example, the COS-Halos survey has shown that the gaseous halos of blue, star-forming galaxies are pervasively filled with O VI out to at least 150 kpc, and while red/passive galaxies show affiliated OVI significantly less frequently, the cool gases traced by H I and low ions in the gaseous envelopes of blue and red galaxies are also ubiquitous and appear to be quite similar in red and blue galaxies. Standard ionization models indicate that the CGM traced by OVI and low ions is a massive baryon reservoir. But, do we really understand the physics and origins of these gases? This talk will present results from new COS studies to probe the nature of the CGM including (1) a deep search for very faint galaxies associated with low-redshift CGM absorption systems, and (2) a Bayesian approach to analysis of QSO absorbers that provide rich diagnostics of physical conditions and metallicities, and (3) some musings about the physical picture of the CGM. These studies suggest that systematic uncertainties are considerably larger than the literature indicates, and COS has a lot more work to do in its final years.

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