39 research outputs found
The Influence of Streaming Velocities on the Formation of the First Stars
How, when and where the first stars formed are fundamental questions
regarding the epoch of Cosmic Dawn. A second order effect in the fluid
equations was recently found to make a significant contribution: an offset
velocity between gas and dark matter, the so-called streaming velocity.
Previous simulations of a limited number of low-mass dark matter haloes suggest
that this streaming velocity can delay the formation of the first stars and
decrease halo gas fractions and the halo mass function in the low mass regime.
However, a systematic exploration of its effects in a large sample of haloes
has been lacking until now. In this paper, we present results from a set of
cosmological simulations of regions of the Universe with different streaming
velocities performed with the moving mesh code AREPO. Our simulations have very
high mass resolution, enabling us to accurately resolve minihaloes as small as
. We show that in the absence of streaming, the least
massive halo that contains cold gas has a mass , but that cooling only becomes efficient in a
majority of haloes for halo masses greater than . In regions with non-zero streaming velocities,
and both increase significantly, by
around a factor of a few for each one sigma increase in the value of the local
streaming velocity. As a result, in regions with streaming velocities
, cooling of gas in minihaloes is
completely suppressed, implying that the first stars in these regions form
within atomic cooling haloes.Comment: 13 pages, 16 figures, resubmitted to MNRA
Formation of proto-globular cluster candidates in cosmological simulations of dwarf galaxies at
We perform cosmological hydrodynamical simulations to study the formation of
proto-globular cluster candidates in progenitors of present-day dwarf galaxies
at ) as part of the
"Feedback in Realistic Environment" (FIRE) project. Compact ( pc),
relatively massive (), self-bound stellar clusters form at in
progenitors with . Cluster formation
is triggered when at least of dense, turbulent gas
reaches as a
result of the compressive effects of supernova feedback or from cloud-cloud
collisions. The clusters can survive for ; absent numerical
effects, they would likely survive substantially longer, perhaps to . The
longest-lived clusters are those that form at significant distance -- several
hundreds of pc -- from their host galaxy. We therefore predict that globular
clusters forming in progenitors of present-day dwarf galaxies will be offset
from any pre-existing stars within their host dark matter halos as opposed to
deeply embedded within a well-defined galaxy. Properties of the nascent
clusters are consistent with observations of some of the faintest and most
compact high-redshift sources in \textit{Hubble Space Telescope} lensing fields
and are at the edge of what will be detectable as point sources in deep imaging
of non-lensed fields with the \textit{James Webb Space Telescope}. By contrast,
the star clusters' host galaxies will remain undetectable.Comment: 14 pages, 5 figures, submitted to MNRA