Discovery of Protoclusters at z~3.7 & 4.9: Embedded in Primordial Superclusters. (arXiv:1912.01625v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Toshikawa_J/0/1/0/all/0/1">Jun Toshikawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Malkan_M/0/1/0/all/0/1">Matthew A. Malkan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kashikawa_N/0/1/0/all/0/1">Nobunari Kashikawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Overzier_R/0/1/0/all/0/1">Roderik Overzier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Uchiyama_H/0/1/0/all/0/1">Hisakazu Uchiyama</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ota_K/0/1/0/all/0/1">Kazuaki Ota</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ishikawa_S/0/1/0/all/0/1">Shogo Ishikawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ito_K/0/1/0/all/0/1">Kei Ito</a>
We have carried out follow-up spectroscopy on three overdense regions of $g$-
and $r$-dropout galaxies in the Canada-France-Hawaii Telescope Legacy Survey
Deep Fields, finding two new protoclusters at $z=4.898$, 3.721 and a possible
protocluster at $z=3.834$. The $z=3.721$ protocluster overlaps with a
previously identified protocluster at $z=3.675$. The redshift separation
between these two protoclusters is $Delta z=0.05$, which is slightly larger
than the size of typical protoclusters. Therefore, if they are not the
progenitors of a $>10^{15},mathrm{M_odot}$ halo, they would grow into
closely-located independent halos like a supercluster. The other protocluster
at $z=4.898$ is also surrounded by smaller galaxy groups. These systems
including protoclusters and neighboring groups are regarded as the early phase
of superclusters. We quantify the spatial distribution of member galaxies of
the protoclusters at $z=3.675$ and 3.721 by fitting triaxial ellipsoids,
finding a tentative difference: one has a pancake-like shape while the other is
filamentary. This could indicate that these two protoclusters are in different
stages of formation. We investigate the relation between redshift and the
velocity dispersion of protoclusters, including other protoclusters from the
literature, in order to compare their dynamical states. Although there is no
significant systematic trend in the velocity dispersions of protoclusters with
redshift, the distribution is skewed to higher velocity dispersion over the
redshift range of $z=2mathrm{-}6$. This could be interpreted as two phases of
cluster formation, one dominated by the steady accretion of galaxies, and the
other by the merging between group-size halos, perhaps depending on the
surrounding large-scale environments.
We have carried out follow-up spectroscopy on three overdense regions of $g$-
and $r$-dropout galaxies in the Canada-France-Hawaii Telescope Legacy Survey
Deep Fields, finding two new protoclusters at $z=4.898$, 3.721 and a possible
protocluster at $z=3.834$. The $z=3.721$ protocluster overlaps with a
previously identified protocluster at $z=3.675$. The redshift separation
between these two protoclusters is $Delta z=0.05$, which is slightly larger
than the size of typical protoclusters. Therefore, if they are not the
progenitors of a $>10^{15},mathrm{M_odot}$ halo, they would grow into
closely-located independent halos like a supercluster. The other protocluster
at $z=4.898$ is also surrounded by smaller galaxy groups. These systems
including protoclusters and neighboring groups are regarded as the early phase
of superclusters. We quantify the spatial distribution of member galaxies of
the protoclusters at $z=3.675$ and 3.721 by fitting triaxial ellipsoids,
finding a tentative difference: one has a pancake-like shape while the other is
filamentary. This could indicate that these two protoclusters are in different
stages of formation. We investigate the relation between redshift and the
velocity dispersion of protoclusters, including other protoclusters from the
literature, in order to compare their dynamical states. Although there is no
significant systematic trend in the velocity dispersions of protoclusters with
redshift, the distribution is skewed to higher velocity dispersion over the
redshift range of $z=2mathrm{-}6$. This could be interpreted as two phases of
cluster formation, one dominated by the steady accretion of galaxies, and the
other by the merging between group-size halos, perhaps depending on the
surrounding large-scale environments.
http://arxiv.org/icons/sfx.gif
