Probing the assembly of dwarf galaxies through cosmic time with damped
Lyman-$\alpha$ absorption spectroscopy
M. Jeon, G. Besla, and V. Bromm. (2019)cite arxiv:1905.05409Comment: 13 pages, 14 figures, Accepted for Publication in ApJ.
We investigate the absorption features associated with a gas-rich dwarf
galaxy using cosmological hydrodynamics simulations. Our goal is to explore
whether the progenitors of the lowest mass dwarf galaxies known to harbor
neutral hydrogen today (M_star~10^6 solar mass, M_halo=4x10^9 solar mass) could
possibly be detected as Damped Lyman-alpha Absorbers (DLAs) over cosmic time.
We trace the evolution of a single dwarf galaxy, pre-selected to contain DLAs,
from the era of the first metal-free, so-called Population~III (Pop~III),
stars, down to z=0, thus allowing us to study the metal enrichment history of
DLAs associated with the simulated galaxy. We find that the progenitors of the
simulated dwarf are expected to be seen for most of their evolution as DLAs
that are contaminated by normal, Population~II, stars. The time period during
which DLAs are only metal-enriched by Pop~III stars, on the other hand, is
likely very brief, confined to high redshifts, z~6. The susceptibility of the
dwarfs to the external UV radiation background allows them to preserve neutral
gas only at the centre (a few ~100 pc). This results in a small probability
that the simulated dwarf would be observed as a DLA. This study suggests that
DLAs are unlikely to be hosted in the lowest mass dwarfs that can harbor
neutral gas (M_halo~ 4x10^9 solar mass), below which neutral gas is unlikely to
exist. However, this study does illustrate that, when detected, absorption
lines provide a powerful method for probing ISM conditions inside the smallest
dwarf galaxies at intermediate to high redshifts.