Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...505..148y&link_type=abstract
The Astrophysical Journal, Volume 505, Issue 1, pp. 148-158.
Astronomy and Astrophysics
Astronomy
27
Galaxies: Formation, Instabilities, Shock Waves
Scientific paper
We estimate the fragment mass scale of a primordial gas sheet compressed by steady state shock waves with a wide variety of initial parameters. We estimate the perturbation growth timescale tau_MGR(~tau_ff) and consider that fragmentation occurs when tau_cool = tau_MGR, then calculate the Jeans mass at the fragmentation. It is shown that there are two fragment mass scales depending on the values of shock velocity and preshock density because of the trough of the cooling coefficient at T ~ 8000 K. As an application, we consider the disklike collapse of the protocloud just after the turnaround. We assume the standard cold dark matter model with h = 0.8 and Omega_bh^2 = 0.01 and estimate the typical shock velocity and preshock density for each mass scale at the collapse. Compared with our steady state shock results, there is found to be a critical mass ~10^8 M_&sun; which assorts the subsequent evolution of protoclouds. We suggest that this critical mass scale provides the observed minimum mass of the bright galaxy sequence and the mass scale of the first luminous objects.
Nishi Ryoichi
Yamada Masako
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