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Evolution of neutral gas at high redshift: implications for the epoch of galaxy formation

Storrie-Lombardi, L. J. and McMahon, R. G. and Irwin, M. J. (1996) Evolution of neutral gas at high redshift: implications for the epoch of galaxy formation. Monthly Notices of the Royal Astronomical Society, 283 (3). L79-L83. ISSN 0035-8711. doi:10.1093/mnras/283.3.L79.

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Although observationally rare, damped Lyα absorption systems dominate the mass density of neutral gas in the Universe. 11 high-redshift damped Lyα systems covering 2.8 ≤z ≤ 4.4 were discovered in 26 QSOs from the APM z > 4 QSO survey, extending these absorption system surveys to the highest redshifts currently possible. Combining our new data set with previous surveys, we find that the cosmological mass density in neutral gas, Ωg, does not rise as steeply prior to z ∼ 2 as indicated by previous studies. There is evidence in the observed Ωg for a flattening at z ∼ 2 and a possible turnover at z ∼ 3. When combined with the decline at z > 3.5 in number density per unit redshift of damped systems with column densities log NHI ≥ 21 atom cm^(−2), these results point to an epoch at z ≳ 3 prior to which the highest column density damped systems are still forming. We find that, over the redshift range 2 < z < 4, the total mass in neutral gas is marginally comparable to the total visible mass in stars in present-day galaxies. However, if one considers the total mass visible in stellar discs alone, i.e. excluding galactic bulges, the two values are comparable. We are observing a mass of neutral gas that is comparable to the mass of visible disc stars. Lanzetta, Wolfe & Turnshek found that Ω(z ≈ 3.5) was twice Ω(z ≈ 2), implying that a much larger amount of star formation must have taken place between z = 3.5 and 2 than is indicated by metallicity studies. This created a ‘cosmic G-dwarf problem’. The more gradual evolution of Ωg that we find alleviates this. These results have profound implications for theories of galaxy formation.

Item Type:Article
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Storrie-Lombardi, L. J.0000-0002-5987-5210
Additional Information:© 1996 Royal Astronomical Society. Accepted 1996 September 10. Received 1996 August 28; in original form 1996 March 25. We acknowledge fruitful discussions with Art Wolfe, Max Pettini and Mike Fall. RGM thanks the Royal Society for support. USL acknowledges support from an Isaac Newton Studentship, the Cambridge Overseas Trust, and a University of California President’s Postdoctoral Fellowship. We thank the PATT for time awarded to carry out the observations with the William Herschel Telescope that made this work possible. We thank the referee, Ken Lanzetta, for his comments.
Funding AgencyGrant Number
Isaac Newton StudentshipUNSPECIFIED
Cambridge Overseas TrustUNSPECIFIED
University of CaliforniaUNSPECIFIED
Subject Keywords:galaxies: evolution, galaxies: formation, quasars: absortion lines, cosmology: miscellaneous
Issue or Number:3
Record Number:CaltechAUTHORS:20170322-131945695
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75320
Deposited By: Ruth Sustaita
Deposited On:22 Mar 2017 21:31
Last Modified:15 Nov 2021 16:32

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