6,311 research outputs found
The imprint of cosmological non-Gaussianities on primordial structure formation
We study via numerical N-body/SPH chemistry simulations the effects of
primordial non-Gaussianities on the formation of the first stars and galaxies,
and investigate the impact of supernova feedback in cosmologies with different
fnl. Density distributions are biased to higher values, so star formation and
the consequent feedback processes take place earlier in high-fnl models and
later in low-fnl ones. Mechanical feedback is responsible for shocking and
evacuating the gas from star forming sites earlier in the highly non-Gaussian
cases, because of the larger bias at high densities. Chemical feedback
translates into high-redshift metal filling factors that are larger by some
orders of magnitude for larger fnl, but that converge within one Gyr, for both
population III and population II-I stellar regimes. The efficient enrichment
process, though, leads to metallicities > 0.01 Zsun by redshift ~9, almost
independently from fnl. The impact of non-Gaussianities on the formation of
dark-matter haloes at high redshift is directly reflected in the properties of
the gas in these haloes, as models with larger fnl show more concentrated gas
profiles at early times. Non-Gaussian signatures in the gas behaviour are lost
after the first feedback takes place and introduces a significant degree of
turbulence and chaotic motions.Comment: 10 pages, 9 figures - accepted for publication in MNRA
Revised rate coefficients for H and H destruction by realistic stellar spectra
Understanding the processes that can destroy H and H species is
quintessential in governing the formation of the first stars, black holes and
galaxies. In this study we compute the reaction rate coefficients for H
photo--dissociation by Lyman--Werner photons ( eV), and H
photo--detachment by 0.76 eV photons emanating from self-consistent stellar
populations that we model using publicly available stellar synthesis codes. So
far studies that include chemical networks for the formation of molecular
hydrogen take these processes into account by assuming that the source spectra
can be approximated by a power-law dependency or a black-body spectrum at
10 or K. We show that using spectra generated from realistic stellar
population models can alter the reaction rates for photo-dissociation, , and photo-detachment, , significantly. In
particular, can be up to orders of magnitude lower
in the case of realistic stellar spectra suggesting that previous calculations
have over-estimated the impact that radiation has on lowering H abundances.
In contrast to burst modes of star formation, we find that models with
continuous star formation predict increasing and , which makes it necessary to include the star formation history of
sources to derive self-consistent reaction rates, and that it is not enough to
just calculate J for the background. For models with constant star
formation rate the change in shape of the spectral energy distribution leads to
a non-negligible late-time contribution to and , and we present self-consistently derived cosmological reaction
rates based on star formation rates consistent with observations of the high
redshift Universe.Comment: Submitted to MNRAS, 9 pages, 7 figures. Comments and communication
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