DISCOVERY OF COLD, PRISTINE GAS POSSIBLY ACCRETING ONTO AN OVERDENSITY OF STAR-FORMING GALAXIES AT REDSHIFT z {approx} 1.6
- Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States)
- INAF-Osservatorio Astronomico di Trieste, I-40131 Trieste (Italy)
- National Optical Astronomy Observatories, Tucson, AZ 85719 (United States)
- INAF-Osservatorio Astronomico di Padova, I-35122 Padova (Italy)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- Dipartimento di Astronomia, Universita degli Studi di Bologna, I-40127 Bologna (Italy)
- Max Planck Institut fuer Extraterrestrische Physik, D-85748 Garching (Germany)
- INAF-Osservatorio Astronomico di Bologna, I-40127 Bologna (Italy)
We report the discovery of large amounts of cold (T {approx} 10{sup 4} K), chemically young gas in an overdensity of galaxies at redshift z Almost-Equal-To 1.6 located in the Great Observatories Origins Deep Survey southern field. The gas is identified thanks to the ultra-strong Mg II {lambda}2800 absorption features it imprints onto the rest-frame UV spectra of galaxies in the background of the overdensity. There is no evidence that the optically thick gas is part of any massive galaxy (i.e., M{sub star} > 4 Multiplication-Sign 10{sup 9} M{sub Sun }), but rather is associated with the overdensity; less massive and fainter galaxies (25.5 mag < z < 27.5 mag) have too large an impact parameter to be causing ultra-strong absorption systems, based on our knowledge of such systems. The lack of corresponding Fe II absorption features, not detected even in co-added spectra, suggests that the gas is chemically more pristine than the interstellar medium and outflows of star-forming galaxies at similar redshift, including the galaxies of the overdensity itself, and comparable to the most metal-poor stars in the Milky Way halo. A crude estimate of the projected covering factor of the high-column-density gas (N{sub H} {approx}> 10{sup 20} cm{sup -2}) based on the observed fraction of galaxies with ultra-strong absorbers is C{sub F} Almost-Equal-To 0.04. A broad, continuum absorption profile extending to the red of the interstellar Mg II absorption line by {approx}< 2000 km s{sup -1} is possibly detected in two independent co-added spectra of galaxies belonging to the overdensity, consistent with a large-scale infall motion of the gas onto the overdensity and its galaxies. Overall, these findings provide the first tentative evidence of accretion of cold, chemically young gas onto galaxies at high redshift, possibly feeding their star formation activity. We suggest the fact that the galaxies are members of a large structure, as opposed to field galaxies, might play a significant role in our ability to detect the accreting gas.
- OSTI ID:
- 22004509
- Journal Information:
- Astrophysical Journal, Vol. 743, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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