A SUBSTANTIAL MASS OF COOL, METAL-ENRICHED GAS SURROUNDING THE PROGENITORS OF MODERN-DAY ELLIPTICALS
- Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
- Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69115 Heidelberg (Germany)
- MIT-Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
The hosts of luminous z {approx} 2 quasars evolve into today's massive elliptical galaxies. Current theories predict that the circumgalactic medium (CGM) of these massive, dark matter halos (M{sub DM} {approx} 10{sup 12.5} M{sub Sun }) should be dominated by a T {approx} 10{sup 7} K virialized plasma. We test this hypothesis with observations of 74 close-projected quasar pairs, using spectra of the background QSO to characterize the CGM of the foreground one. Surprisingly, our measurements reveal a cool (T Almost-Equal-To 10{sup 4} K), massive (M{sub CGM} > 10{sup 10} M{sub Sun }), and metal-enriched (Z {approx}> 0.1 Z{sub Sun }) medium extending to at least the expected virial radius (r{sub vir} = 160 kpc). The average equivalent widths of H I Ly{alpha} (W-bar{sub Ly{alpha}}= 2.1{+-}0.15 A for impact parameters R < 200 kpc) and C II 1334 (W-bar{sub 1334}= 0.7{+-}0.1) exceed the corresponding CGM measurements of these transitions from all galaxy populations studied previously. Furthermore, we conservatively estimate that the quasar CGM has a 64{sup +6}{sub -7}% covering fraction of optically thick gas (N{sub HI} > 10{sup 17.2} cm{sup -2}) within r{sub vir}; this covering factor is twice that of the contemporaneous Lyman break galaxy population. This unexpected reservoir of cool gas is rarely detected 'down-the-barrel' to quasars, and hence it is likely that our background sight lines intercept gas that is shadowed from the quasar ionizing radiation by the same obscuring medium often invoked in models of active galactic nucleus unification. Because the high-z halos inhabited by quasars predate modern groups and clusters, these observations are also relevant to the formation and enrichment history of the intragroup/intracluster medium.
- OSTI ID:
- 22078347
- Journal Information:
- Astrophysical Journal Letters, Vol. 762, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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