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[2.01] Observational limits to highly ionized absorption systems in the intergalactic medium for z<0.15.

A. Rasmussen, S. M. Kahn, F. Paerels (Columbia U.), JW. den Herder, C. de Vries (S.R.O.N. (Netherlands))

XMM-Newton RGS spectroscopic investigations have yielded the three deepest moderate redshift, high Galactic latitude AGN continuum spectra available for study of discrete absorption by highly ionized intergalactic gas. Absorption is apparently present in all directions, with oxygen column densities of \rm N_i ~10¹⁶\, cm^-2. The bulk of this absorption occurs at near-zero redshift with velocity and temperature limits that appear consistent with the Local Group's virial temperature (\rm T_vir ~2 \times 10⁶\,K), in a mass, conservatively at least twice \rm M_\ast for the Galaxy.

The same data is used to place limits on the presence of hot, intervening systems at discrete redshifts. Particular care is spent in identifying, removing and correcting signatures of the instrument. Likelihood limits for the presence of much weaker systems (e.g., N_i ~ 10^14-15\,cm^-2) systems are expressed, over the available 0.3 units in redshift space. These computed confidence distributions are compared to predictions of hot IGM absorber distributions e.g., of Perna & Loeb (1998) and Cen & Ostriker (1999).

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.