Cosmology-independent estimate of the fraction of baryon mass in the IGM from fast radio burst observations. (arXiv:1904.08927v1 [astro-ph.CO])

Cosmology-independent estimate of the fraction of baryon mass in the IGM from fast radio burst observations. (arXiv:1904.08927v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Li_Z/0/1/0/all/0/1">Zhengxiang Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gao_H/0/1/0/all/0/1">He Gao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wei_J/0/1/0/all/0/1">Jun-Jie Wei</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_Y/0/1/0/all/0/1">Yuan-Pei Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_B/0/1/0/all/0/1">Bing Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhu_Z/0/1/0/all/0/1">Zong-Hong Zhu</a>

The excessive dispersion measure (DM) of fast radio bursts (FRBs) has been
proposed to be a powerful tool to study intergalactic medium (IGM) and to
perform cosmography. One issue is that the fraction of baryons in the IGM,
$f_{rm IGM}$, is not properly constrained. Here we propose a method of
estimating $f_{rm IGM}$ using a putative sample of FRBs with the measurements
of both DM and luminosity distance $d_{rm L}$. The latter can be obtained if
the FRB is associated with a distance indicator (e.g. a gamma-ray burst or a
gravitational wave event), or the redshift $z$ of the FRB is measured and
$d_{rm L}$ at the corresponding $z$ is available from other distance
indicators (e.g. type Ia supernovae) at the same redshift. Since $d_{rm
L}/{rm DM}$ essentially does not depend on cosmological parameters, our method
can determine $f_{rm IGM}$ independent of cosmological parameters. We
parameterize $f_{rm IGM}$ as a function of redshift and model the DM
contribution from a host galaxy as a function of star formation rate. Assuming
$f_{rm IGM}$ has a mild evolution with redshift with a functional form and by
means of Monte Carlo simulations, we show that an unbiased and
cosmology-independent estimate of the present value of $f_{rm IGM}$ with a
$sim 12%$ uncertainty can be obtained with 50 joint measurements of $d_{rm
L}$ and DM. In addition, such a method can also lead to a measurement of the
mean value of DM contributed from the local host galaxy.

The excessive dispersion measure (DM) of fast radio bursts (FRBs) has been
proposed to be a powerful tool to study intergalactic medium (IGM) and to
perform cosmography. One issue is that the fraction of baryons in the IGM,
$f_{rm IGM}$, is not properly constrained. Here we propose a method of
estimating $f_{rm IGM}$ using a putative sample of FRBs with the measurements
of both DM and luminosity distance $d_{rm L}$. The latter can be obtained if
the FRB is associated with a distance indicator (e.g. a gamma-ray burst or a
gravitational wave event), or the redshift $z$ of the FRB is measured and
$d_{rm L}$ at the corresponding $z$ is available from other distance
indicators (e.g. type Ia supernovae) at the same redshift. Since $d_{rm
L}/{rm DM}$ essentially does not depend on cosmological parameters, our method
can determine $f_{rm IGM}$ independent of cosmological parameters. We
parameterize $f_{rm IGM}$ as a function of redshift and model the DM
contribution from a host galaxy as a function of star formation rate. Assuming
$f_{rm IGM}$ has a mild evolution with redshift with a functional form and by
means of Monte Carlo simulations, we show that an unbiased and
cosmology-independent estimate of the present value of $f_{rm IGM}$ with a
$sim 12%$ uncertainty can be obtained with 50 joint measurements of $d_{rm
L}$ and DM. In addition, such a method can also lead to a measurement of the
mean value of DM contributed from the local host galaxy.

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