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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