The talks are in the same order as the Program Schedule.
Irwin, Jimmy - The Low Metallicity ISM of X-ray Faint Elliptical Galaxies
Yao, Yangsen - Limits on Hot Galactic Halo Gas from X-ray Absorption Lines
Ann Hornschemeier (NASA GSFC) , Andrew Ptak (JHU), Timothy Heckman (JHU), John Grimes (JHU), Samir Salim (NOAO), John Sheets (Boston Univ.), David Strickland (JHU)
We discuss X-ray constraints on GALEX-selected Ultraviolet-Luminous Galaxies (UVLGs). An interesting subset of these UVLGs appear to be analogs to the distant (3 < z < 4) Lyman Break Galaxies (LBGs). The 2-10 keV X-ray emission of LBGs appear to be broadly similar to that of galaxies in the local Universe, possibly indicating similarity in the production of accreting binaries over large evolutionary timescales in the Universe. Given the very large distances to the LBGs, we have elected to use the the UVLGs as possible local-Universe comparison sample. This technique is showing promise; we have detected luminous X-ray emission from one UVLG that permits basic X-ray spectroscopic analysis, and have direct X-ray constraints on a total of 6 UVLGs (including two previously studied by Chandra). The luminous X-ray emitting galaxy is perhaps very interesting as it demonstrates a lack of emission from hot gas even though the inferred star formation rate is very high.
Jimmy Irwin (University of Michigan)
Since the hot interstellar medium (ISM) of early-type galaxies is believed to originate primarily from stellar mass loss and supernovae, the metallicity of the ISM should reflect that of the stars contributing the mass to the ISM. This has been confirmed for gas-rich X-ray bright ellipticals, as both the X-ray-determined ISM abundances and optically-determined stellar abundances are approximately solar. However, this does not seem to be the case for gas-poor, X-ray faint ellipticals, for which very sub-solar abundances have been reported, although poor statistics and significant X-ray binary contamination have been listed as the cause of these (erroneously) low abundance measurements. We present Chandra + XMM-Newton spectra of one of the best-observed X-ray faint ellipticals, NGC4697, and confirm that O, Ne, Mg, Si, Fe, and Ni are all significantly subsolar, and are not the result of poor spectral fitting or poor statistics. We speculate that the low metal abundances are the result of dilution from the accretion over time of pristine metal-free gas that surrounds the galaxy. The implications of this accretion in the context of galaxy formation will be discussed.
Yangsen Yao (MIT) , M. Nowak (MIT), Q. D. Wang (UMass), N. Schulz (MIT), C. Canizares (MIT)
Many theoretical calculations and numerical calculations for galaxy formation predict the existence of large-scale (>20 kpc) hot gaseous halos around individual galaxies. However, such halos are yet to be discovered observationally. We here present a differential study of searching for such a halo around our Galaxy. We compared the highly ionized X-ray absorption lines observed in sight-line of a Galactic source 4U 1957+11 (distance D>10 kpc) with those observed toward extragalactic sources LMC X-3 (D 50 kpc) and Mrk 421. We found that all the line absorptions observed in the extragalactic sources can be attributed to the hot gas in a thick Galactic disk, as traced by the absorption lines in the spectra of 4U 1957+11. We then obtained a firm upper limit of the absorption due to the putative Galactic halo and estimated the halo mass and metallicity. These results provide a direct observational test of galaxy formation theories.