Dwarf Galaxies in Voids: Dark Matter Halos and Gas Cooling

TL;DR

This paper uses hydrodynamical simulations to explore why voids, despite hosting dark matter halos, lack dwarf galaxies, highlighting the role of UV background radiation in suppressing baryon accretion in low-mass halos.

Contribution

It identifies the characteristic mass threshold for baryon deficiency in dwarf galaxies due to UV photo-heating, linking gas heating processes to galaxy formation in voids.

Findings

Baryon accretion is suppressed below a circular velocity of ~40 km/s.

UV background radiation causes photo-heating that reduces baryon content in low-mass halos.

Heating processes increase the characteristic mass, decreasing observable dwarf galaxies.

Abstract

Galaxy surveys have shown that luminous galaxies are mainly distributed in large filaments and galaxy clusters. The remaining large volumes are virtually devoid of luminous galaxies. This is in concordance with the formation of the large-scale structure in Universe as derived from cosmological simulations. However, the numerical results indicate that cosmological voids are abundantly populated with dark matter haloes which may in principle host dwarf galaxies. Observational efforts have in contrast revealed, that voids are apparently devoid of dwarf galaxies. We investigate the formation of dwarf galaxies in voids by hydrodynamical cosmological simulations. Due to the cosmic ultra-violet background radiation low-mass haloes show generally are reduced baryon fraction. We determine the characteristic mass below which dwarf galaxies are baryon deficient. We show that the circular velocity below which the accretion of baryons is suppressed is approximately 40 km/s. The suppressed baryon accretion is caused by the photo-heating due to the UV-background. We set up a spherical halo model and show that the effective equation of state of the gas in the periphery of dwarf galaxies determines the characteristic mass. This implies that any process which heats the gas around dwarf galaxies increases the characteristic mass and thus reduces the number of observable dwarf galaxies.