The evolution of galaxy intrinsic alignments in the MassiveBlack II universe. (arXiv:1905.00906v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bhowmick_A/0/1/0/all/0/1">Aklant K Bhowmick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_Y/0/1/0/all/0/1">Yingzhang Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tenneti_A/0/1/0/all/0/1">Ananth Tenneti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matteo_T/0/1/0/all/0/1">Tiziana Di Matteo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mandelbaum_R/0/1/0/all/0/1">Rachel Mandelbaum</a>
We investigate the redshift evolution of the intrinsic alignments (IA) of
galaxies in the texttt{MassiveBlackII} (MBII) simulation. We select galaxy
samples above fixed subhalo mass cuts ($M_h>10^{11,12,13}~M_{odot}/h$) at
$z=0.6$ and trace their progenitors to $z=3$ along their merger trees. Dark
matter components of $z=0.6$ galaxies are more spherical than their progenitors
while stellar matter components tend to be less spherical than their
progenitors. The distribution of the galaxy-subhalo misalignment angle peaks at
$sim10~mathrm{deg}$ with a mild increase with time. The evolution of the
ellipticity-direction~(ED) correlation amplitude $omega(r)$ of galaxies (which
quantifies the tendency of galaxies to preferentially point towards surrounding
matter overdensities) is governed by the evolution in the alignment of
underlying dark matter~(DM) subhaloes to the matter density of field, as well
as the alignment between galaxies and their DM subhaloes. At scales
$sim1~mathrm{cMpc}/h$, the alignment between DM subhaloes and matter
overdensity gets suppressed with time, whereas the alignment between galaxies
and DM subhaloes is enhanced. These competing tendencies lead to a complex
redshift evolution of $omega(r)$ for galaxies at $sim1~mathrm{cMpc}/h$. At
scales $>1~mathrm{cMpc}/h$, alignment between DM subhaloes and matter
overdensity does not evolve significantly; the evolution of the galaxy-subhalo
misalignment therefore leads to an increase in $omega(r)$ for galaxies by a
factor of $sim4$ from $z=3$ to $0.6$ at scales $>1~mathrm{cMpc}/h$. The
balance between competing physical effects is scale dependant, leading to
different conclusions at much smaller scales($sim0.1~mathrm{Mpc}/h$).
We investigate the redshift evolution of the intrinsic alignments (IA) of
galaxies in the texttt{MassiveBlackII} (MBII) simulation. We select galaxy
samples above fixed subhalo mass cuts ($M_h>10^{11,12,13}~M_{odot}/h$) at
$z=0.6$ and trace their progenitors to $z=3$ along their merger trees. Dark
matter components of $z=0.6$ galaxies are more spherical than their progenitors
while stellar matter components tend to be less spherical than their
progenitors. The distribution of the galaxy-subhalo misalignment angle peaks at
$sim10~mathrm{deg}$ with a mild increase with time. The evolution of the
ellipticity-direction~(ED) correlation amplitude $omega(r)$ of galaxies (which
quantifies the tendency of galaxies to preferentially point towards surrounding
matter overdensities) is governed by the evolution in the alignment of
underlying dark matter~(DM) subhaloes to the matter density of field, as well
as the alignment between galaxies and their DM subhaloes. At scales
$sim1~mathrm{cMpc}/h$, the alignment between DM subhaloes and matter
overdensity gets suppressed with time, whereas the alignment between galaxies
and DM subhaloes is enhanced. These competing tendencies lead to a complex
redshift evolution of $omega(r)$ for galaxies at $sim1~mathrm{cMpc}/h$. At
scales $>1~mathrm{cMpc}/h$, alignment between DM subhaloes and matter
overdensity does not evolve significantly; the evolution of the galaxy-subhalo
misalignment therefore leads to an increase in $omega(r)$ for galaxies by a
factor of $sim4$ from $z=3$ to $0.6$ at scales $>1~mathrm{cMpc}/h$. The
balance between competing physical effects is scale dependant, leading to
different conclusions at much smaller scales($sim0.1~mathrm{Mpc}/h$).
http://arxiv.org/icons/sfx.gif
