paper

Downsizing of Star-Forming Galaxies by Gravitational Processes

arXiv:astro-ph/0601042 · doi:10.1051/0004-6361:20065604

Abstract

There is observed a trend that a lower mass galaxy forms stars at a later epoch. This downsizing of star-forming galaxies has been attributed to hydrodynamical or radiative feedback processes that regulate star formation. However, here we explain the downsizing by gravitational processes alone, in the bottom-up scenario where galaxies evolve from subgalactic-scale objects. Within a region of the initial density field that is to evolve into a lower mass galaxy, subgalactic-scale fluctuation is of a smaller amplitude. The formation of subgalactic-scale objects, i.e., gravitational collapse of the subgalactic-scale fluctuation, and the subsequent onset of star formation accordingly occur at a later epoch for a lower mass galaxy. As a function of galaxy mass, we calculate the peak epoch of formation of subgalactic-scale objects. The peak epoch is consistent with the peak epoch of star formation derived from observations. [abridged]

4 pages, to appear in Astronomy and Astrophysics (Research Note)

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