Fast Outflows Identified in Early Star-Forming Galaxies at $z = 5-6$. (arXiv:1904.03106v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Sugahara_Y/0/1/0/all/0/1">Yuma Sugahara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ouchi_M/0/1/0/all/0/1">Masami Ouchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harikane_Y/0/1/0/all/0/1">Yuichi Harikane</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bouche_N/0/1/0/all/0/1">Nicolas Bouché</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mitchell_P/0/1/0/all/0/1">Peter D. Mitchell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blaizot_J/0/1/0/all/0/1">Jérémy Blaizot</a>
We present velocities of galactic outflows in seven star-forming galaxies at
$z=$5-6 with a stellar mass of $M_* sim10^{10.1} rm{M_odot}$. Although it
is challenging to observationally determine the outflow velocities, we overcome
this challenge by making use of the ALMA [CII]158 $mu$m emission lines for
systemic velocities and the deep Keck spectra with metal absorption lines for
velocity profiles available to date. We construct a composite Keck spectrum of
the galaxies at $z=$5-6 with the [CII]-systemic velocities, and fit
outflow-line profiles to the SiII1260, CII1335, and SiIV1394,1403 absorption
lines in the composite spectrum. We measure the maximum (90%) outflow velocity
$v_rm{max}$ and the central outflow velocity $v_rm{out}$ to be
$v_rm{max}=810^{+140}_{-160} rm{km s^{-1}}$ and $v_rm{out} =
440^{+110}_{-140} rm{km s^{-1}}$ on average, respectively. For $M_*
sim10^{10.1} rm{M_odot}$, we find the redshift evolution that the
$v_rm{max}$ value of our $z=$5-6 galaxies is higher than those of $z=0$
galaxies by a factor of 3.5 and comparable to the one of $z=2$ galaxies.
Estimating the halo circular velocity $v_rm{cir}$ from the stellar masses and
the abundance matching results, we investigate a $v_rm{max}$-$v_rm{cir}$
relation. Interestingly, $v_rm{max}$ for galaxies with $M_*=10^{10.0-10.8}
rm{M_odot}$ shows a clear positive correlation with $v_rm{cir}$ (as well as
the star-formation rate) over $z=$0-6 with small scatters of $simeq pm 0.1$
dex, which is in good agreement with the theoretical predictions (Muratov et
al. 2015). This positive correlation suggests that the outflow velocity is
physically related to the halo circular velocity corresponding to the depth of
the gravitational potential, and that the redshift evolution of $v_rm{max}$ is
explained by the increase of $v_rm{cir}$ toward high redshift.
We present velocities of galactic outflows in seven star-forming galaxies at
$z=$5-6 with a stellar mass of $M_* sim10^{10.1} rm{M_odot}$. Although it
is challenging to observationally determine the outflow velocities, we overcome
this challenge by making use of the ALMA [CII]158 $mu$m emission lines for
systemic velocities and the deep Keck spectra with metal absorption lines for
velocity profiles available to date. We construct a composite Keck spectrum of
the galaxies at $z=$5-6 with the [CII]-systemic velocities, and fit
outflow-line profiles to the SiII1260, CII1335, and SiIV1394,1403 absorption
lines in the composite spectrum. We measure the maximum (90%) outflow velocity
$v_rm{max}$ and the central outflow velocity $v_rm{out}$ to be
$v_rm{max}=810^{+140}_{-160} rm{km s^{-1}}$ and $v_rm{out} =
440^{+110}_{-140} rm{km s^{-1}}$ on average, respectively. For $M_*
sim10^{10.1} rm{M_odot}$, we find the redshift evolution that the
$v_rm{max}$ value of our $z=$5-6 galaxies is higher than those of $z=0$
galaxies by a factor of 3.5 and comparable to the one of $z=2$ galaxies.
Estimating the halo circular velocity $v_rm{cir}$ from the stellar masses and
the abundance matching results, we investigate a $v_rm{max}$-$v_rm{cir}$
relation. Interestingly, $v_rm{max}$ for galaxies with $M_*=10^{10.0-10.8}
rm{M_odot}$ shows a clear positive correlation with $v_rm{cir}$ (as well as
the star-formation rate) over $z=$0-6 with small scatters of $simeq pm 0.1$
dex, which is in good agreement with the theoretical predictions (Muratov et
al. 2015). This positive correlation suggests that the outflow velocity is
physically related to the halo circular velocity corresponding to the depth of
the gravitational potential, and that the redshift evolution of $v_rm{max}$ is
explained by the increase of $v_rm{cir}$ toward high redshift.
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