The galaxy-halo connection of emission-line galaxies in IllustrisTNG. (arXiv:2011.05331v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hadzhiyska_B/0/1/0/all/0/1">Boryana Hadzhiyska</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tacchella_S/0/1/0/all/0/1">Sandro Tacchella</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bose_S/0/1/0/all/0/1">Sownak Bose</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Eisenstein_D/0/1/0/all/0/1">Daniel J. Eisenstein</a>

We employ the hydrodynamical simulation IllustrisTNG-300-1 to explore the
halo occupation distribution (HOD) and environmental dependence of luminous
star-forming emission-line galaxies (ELGs) at $z sim 1$. Such galaxies are key
targets for current and upcoming cosmological surveys. We select model galaxies
through cuts in color-color space allowing for a direct comparison with the
Extended Baryon Oscillation Spectroscopic Survey and the Dark Energy
Spectroscopic Instrument (DESI) surveys and then compare them with galaxies
selected based on star-formation rate (SFR) and stellar mass. We demonstrate
that the ELG populations are twice more likely to reside in lower-density
regions (sheets) compared with the mass-selected populations and twice less
likely to occupy the densest regions of the cosmic web (knots). We also show
that the color-selected and SFR-selected ELGs exhibit very similar occupation
and clustering statistics, finding that the agreement is best for lower
redshifts. In contrast with the mass-selected sample, the occupation of halos
by a central ELG peaks at $sim$20%. We furthermore explore the dependence of
the HOD and the auto-correlation on environment, noticing that at fixed halo
mass, galaxies in high-density regions cluster about 10 times more strongly
than low-density ones. This result suggests that we should model carefully the
galaxy-halo relation and implement assembly bias effects into our models
(estimated at $sim$4% of the clustering of the DESI color-selected sample at
$z = 0.8$). Finally, we apply a simple mock recipe to recover the clustering on
large scales ($r gtrsim 1 {rm Mpc}/h$) to within 1% by augmenting the HOD
model with an environment dependence, demonstrating the power of adopting
flexible population models.

We employ the hydrodynamical simulation IllustrisTNG-300-1 to explore the
halo occupation distribution (HOD) and environmental dependence of luminous
star-forming emission-line galaxies (ELGs) at $z sim 1$. Such galaxies are key
targets for current and upcoming cosmological surveys. We select model galaxies
through cuts in color-color space allowing for a direct comparison with the
Extended Baryon Oscillation Spectroscopic Survey and the Dark Energy
Spectroscopic Instrument (DESI) surveys and then compare them with galaxies
selected based on star-formation rate (SFR) and stellar mass. We demonstrate
that the ELG populations are twice more likely to reside in lower-density
regions (sheets) compared with the mass-selected populations and twice less
likely to occupy the densest regions of the cosmic web (knots). We also show
that the color-selected and SFR-selected ELGs exhibit very similar occupation
and clustering statistics, finding that the agreement is best for lower
redshifts. In contrast with the mass-selected sample, the occupation of halos
by a central ELG peaks at $sim$20%. We furthermore explore the dependence of
the HOD and the auto-correlation on environment, noticing that at fixed halo
mass, galaxies in high-density regions cluster about 10 times more strongly
than low-density ones. This result suggests that we should model carefully the
galaxy-halo relation and implement assembly bias effects into our models
(estimated at $sim$4% of the clustering of the DESI color-selected sample at
$z = 0.8$). Finally, we apply a simple mock recipe to recover the clustering on
large scales ($r gtrsim 1 {rm Mpc}/h$) to within 1% by augmenting the HOD
model with an environment dependence, demonstrating the power of adopting
flexible population models.

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