Non-Universal Stellar Initial Mass Functions: Large Uncertainties in Star Formation Rates at $zapprox 2-4$ and Other Astrophysical Probes. (arXiv:2205.07845v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ziegler_J/0/1/0/all/0/1">Joshua J. Ziegler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Edwards_T/0/1/0/all/0/1">Thomas D. P. Edwards</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Suliga_A/0/1/0/all/0/1">Anna M. Suliga</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tamborra_I/0/1/0/all/0/1">Irene Tamborra</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Horiuchi_S/0/1/0/all/0/1">Shunsaku Horiuchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ando_S/0/1/0/all/0/1">Shin&#x27;ichiro Ando</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Freese_K/0/1/0/all/0/1">Katherine Freese</a>

We explore the assumption, widely used in many astrophysical calculations,
that the stellar initial mass function (IMF) is universal across all galaxies.
By considering both a canonical Salpeter-like IMF and a non-universal IMF, we
are able to compare the effect of different IMFs on multiple observables and
derived quantities in astrophysics. Specifically, we consider a non-universal
IMF which varies as a function of the local star formation rate, and explore
the effects on the star formation rate density (SFRD), the extragalactic
background light, the supernova (both core-collapse and thermonuclear) rates,
and the diffuse supernova neutrino background. Our most interesting result is
that our adopted varying IMF leads to much greater uncertainty on the SFRD at
$z approx 2-4$ than is usually assumed. Indeed, we find a SFRD (inferred using
observed galaxy luminosity distributions) that is a factor of $gtrsim 3$ lower
than canonical results obtained using a universal Salpeter-like IMF. Secondly,
the non-universal IMF we explore implies a reduction in the supernova
core-collapse rate of a factor of $sim2$, compared against a universal IMF.
The other potential tracers are only slightly affected by changes to the
properties of the IMF. We find that currently available data do not provide a
clear preference for universal or non-universal IMF. However, improvements to
measurements of the star formation rate and core-collapse supernova rate at
redshifts $z gtrsim 2$ may offer the best prospects for discernment.

We explore the assumption, widely used in many astrophysical calculations,
that the stellar initial mass function (IMF) is universal across all galaxies.
By considering both a canonical Salpeter-like IMF and a non-universal IMF, we
are able to compare the effect of different IMFs on multiple observables and
derived quantities in astrophysics. Specifically, we consider a non-universal
IMF which varies as a function of the local star formation rate, and explore
the effects on the star formation rate density (SFRD), the extragalactic
background light, the supernova (both core-collapse and thermonuclear) rates,
and the diffuse supernova neutrino background. Our most interesting result is
that our adopted varying IMF leads to much greater uncertainty on the SFRD at
$z approx 2-4$ than is usually assumed. Indeed, we find a SFRD (inferred using
observed galaxy luminosity distributions) that is a factor of $gtrsim 3$ lower
than canonical results obtained using a universal Salpeter-like IMF. Secondly,
the non-universal IMF we explore implies a reduction in the supernova
core-collapse rate of a factor of $sim2$, compared against a universal IMF.
The other potential tracers are only slightly affected by changes to the
properties of the IMF. We find that currently available data do not provide a
clear preference for universal or non-universal IMF. However, improvements to
measurements of the star formation rate and core-collapse supernova rate at
redshifts $z gtrsim 2$ may offer the best prospects for discernment.

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