Formation of the First Generation of Galaxies and the Cosmological Implications

Details Formation of the First Generation of Galaxies and the Cosmological Implications Formation of the First Generation of Galaxies and the Cosmological Implications

Feb 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sgyu.conf...73k&link_type=abstract

Studies of Galaxies in the Young Universe with New Generation Telescope, Proceedings of Japan-German Seminar, held in Sendai, Ja

Computer Science

Scientific paper

The existence of an intense ultraviolet background (UVB) radiation, inferred from observations of QSO absorption spectra, is likely to have prominent impacts on early galaxy formation. We study the consequences of such radiative feedback, solving explicitly radiative transfer of photons, non-equilibrium H2 chemistry, and one-dimensional hydrodynamics. While the formation of low-mass galaxies are greatly suppressed by the external UVB, the cut-off scale of collapse is shown to drop significantly compared to previous optically thin predictions, owing to both self-shielding of the gas and H2 cooling. Objects above this cut-off undergo run-away collapse and do not settle into hydrostatic equilibrium. For plausible values of radiation intensity, the cloud center is shielded against external photons and the gas cools efficiently to temperatures well below 104 K by H2 before rotationally supported. Our results imply that star formation can take place in low mass objects collapsing in the UVB. The threshold baryon mass for star formation is about 109 solar mass for clouds collapsing at redshifts z < 3, but drops significantly at higher redshifts. In a conventional cold dark matter universe, the latter coincides roughly with that of the 1 σ density fluctuations. Objects near and above this threshold can thus constitute `building blocks' of luminous structures, and we discuss their links to dwarf spheroidal/elliptical galaxies and faint blue objects.

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