Global radiation signature from early structure formation. (arXiv:1901.08994v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Liu_B/0/1/0/all/0/1">Boyuan Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jaacks_J/0/1/0/all/0/1">Jason Jaacks</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Finkelstein_S/0/1/0/all/0/1">Steven L. Finkelstein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bromm_V/0/1/0/all/0/1">Volker Bromm</a>
We use cosmological hydrodynamic zoom-in simulations to study early structure
formation in two dark matter (DM) cosmologies, a standard CDM model, and a warm
DM (WDM) model with a particle mass of $m_{chi}c^{2}=3$ keV. We focus on DM
haloes with virial masses $Msim 10^{10} M_{odot}$. We find that the first
star formation activity is delayed by $sim 200$ Myr in the WDM model, with
similar delays for metal enrichment and the formation of the second generation
of stars. However, the differences between the two models in globally-averaged
properties, such as star formation rate density and mean metallicity, decrease
towards lower redshifts ($zlesssim 10$). Metal enrichment in the WDM cosmology
is restricted to dense environments, while low-density gas can also be
significantly enriched in the CDM case. We calculate the free-free contribution
from early structure formation at redshifts $z>6$ to the cosmic radio
background (CRB), and find that it is $3.8_{-1.7}^{+15.8}$%
($10.4_{-4.6}^{+43.3}$%) of the total signal inferred from radio experiments
such as ARCADE 2, in the WDM (CDM) model. We find that the direct detection of
the $mathrm{H_{2}}$ emission from early structure formation ($zgtrsim 7.2$),
originating from the low-mass haloes explored here, will be challenging even
with the next generation of planned far-infrared space telescopes, unless the
signal is magnified by at least a factor of 10 via gravitational lensing.
However, more massive haloes with $Mgtrsim 10^{12} M_{odot}$ may be
observable for $zgtrsim 10$, even without lensing, provided that our
extrapolation from the scale of our simulated haloes is valid.
We use cosmological hydrodynamic zoom-in simulations to study early structure
formation in two dark matter (DM) cosmologies, a standard CDM model, and a warm
DM (WDM) model with a particle mass of $m_{chi}c^{2}=3$ keV. We focus on DM
haloes with virial masses $Msim 10^{10} M_{odot}$. We find that the first
star formation activity is delayed by $sim 200$ Myr in the WDM model, with
similar delays for metal enrichment and the formation of the second generation
of stars. However, the differences between the two models in globally-averaged
properties, such as star formation rate density and mean metallicity, decrease
towards lower redshifts ($zlesssim 10$). Metal enrichment in the WDM cosmology
is restricted to dense environments, while low-density gas can also be
significantly enriched in the CDM case. We calculate the free-free contribution
from early structure formation at redshifts $z>6$ to the cosmic radio
background (CRB), and find that it is $3.8_{-1.7}^{+15.8}$%
($10.4_{-4.6}^{+43.3}$%) of the total signal inferred from radio experiments
such as ARCADE 2, in the WDM (CDM) model. We find that the direct detection of
the $mathrm{H_{2}}$ emission from early structure formation ($zgtrsim 7.2$),
originating from the low-mass haloes explored here, will be challenging even
with the next generation of planned far-infrared space telescopes, unless the
signal is magnified by at least a factor of 10 via gravitational lensing.
However, more massive haloes with $Mgtrsim 10^{12} M_{odot}$ may be
observable for $zgtrsim 10$, even without lensing, provided that our
extrapolation from the scale of our simulated haloes is valid.
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