The DESI One-Percent Survey: Constructing Galaxy–Halo Connections for ELGs and LRGs Using Auto and Cross Correlations

Abstract

In the current Dark Energy Spectroscopic Instrument (DESI) survey, emission line galaxies (ELGs) and luminous red galaxies (LRGs) are essential for mapping the dark matter distribution at N M . We measure the auto and cross correlation functions of ELGs and LRGs at 108.0 M ⊙ from the DESI One-Percent survey. Following Gao et al., we construct the galaxy–halo connections for ELGs and LRGs simultaneously. With the stellar–halo mass relation for the whole galaxy population (i.e., normal galaxies), LRGs can be selected directly by stellar mass, while ELGs can also be selected randomly based on the observed number density of each stellar mass, once the probability z ∼ 0.2 of a satellite galaxy becoming an ELG is determined. We demonstrate that the observed small scale clustering prefers a halo mass-dependent z ∼ 0.2 model rather than a constant. With this model, we can well reproduce the auto correlations of LRGs and the cross correlations between LRGs and ELGs at z ∼ 0.7 z ∼ 1. We can also reproduce the auto correlations of ELGs at deg2 z ∼ 1 (0.6 < z < 1.6 z ∼ 1) in real (redshift) space. Although our model has only seven parameters, we show that it can be extended to higher redshifts and reproduces the observed auto correlations of ELGs in the whole range of ∼1012 M ⊙, which enables us to generate a lightcone ELG mock for DESI. With the above model, we further derive halo occupation distributions for ELGs, which can be used to produce ELG mocks in coarse simulations without resolving subhalos.

The DESI One-Percent Survey: A Concise Model for the Galactic Conformity of Emission-line Galaxies

“…Utilizing the highly complete ELG sample in the One-Percent Survey, a series of analyses have shown a strong clustering signal of ELGs within the scale of ∼0.5 Mpc h −1 (Gao et al 2023;Rocher et al 2023). In fact, the prominent clustering of ELGs has also been found in the surveys prior to DESI.…”

“…ELGs are mainly late-type galaxies with significant ongoing star-forming activity, and thus their galaxy-halo connection may differ from that of normal galaxies. Several studies on the halo occupation distribution (HOD; Geach et al 2012;Contreras et al 2013;Alam et al 2020;Avila et al 2020;Okumura et al 2021;Zhai et al 2021;Yuan et al 2022a;Rocher et al 2023), conditional stellar mass function (CSMF; Guo et al 2019), subhalo abundance matching (SHAM; Favole et al 2016Favole et al , 2017Gao et al 2022Gao et al , 2023Lin et al 2023;Prada et al 2023;Yu et al 2024), semi-analytical model (Gonzalez-Perez et al 2018, and hydrodynamical simulation (Hadzhiyska et al 2021(Hadzhiyska et al , 2023a(Hadzhiyska et al , 2023bYuan et al 2022b) suggest that ELGs tend to reside in host halos with masses ∼10 12 M e h −1 and the overall satellite fraction of ELGs is less than 20%. Due to various parameterized assumptions and target selections of ELGs in different surveys with specific color cuts and photometric depths, the ELG-halo connection models vary widely.…”

“…In most previous models of the ELG-halo connection, the central halo and its subhalos are usually assumed to be uncorrelated in forming ELGs. For example, by analyzing the auto and cross correlations of ELGs and luminous red galaxies (LRGs) in the DESI One-Percent Survey (DESI Collaboration et al 2023a), Gao et al (2023) improved the SHAM method (Gao et al 2022) to construct the ELG-halo connection. This method shows an accurate modeling of the auto and cross correlations of ELGs and LRGs, except that it still underestimates the strong one-halo term of the ELG auto correlation at r p < 0.3 Mpc h −1 (s < 1 Mpc h −1 ).…”

“…It is difficult to interpret the high clustering of ELGs on very small scales with the usual SHAM or HOD models. In the SHAM model of Gao et al (2023;hereafter, Paper I), they have found that ELGs can be randomly selected from a general population of galaxies, but the satellite fraction of ELGs in massive halos needs to be reduced (also a kind of galactic conformity). Even though the model has retained the satellite ELGs in the small halos as much as possible, the modeled clustering of ELGs is still not strong enough to match the observed one.…”

The DESI One-Percent survey: exploring the Halo Occupation Distribution of Emission Line Galaxies with AbacusSummit simulations

“…Ref. [19] studies LRGs and ELGs using a stellar-mass-split abundance matching applied on CosmicGrowth [20]. In parallel, there is a series of Subhalo-abundance matching (SHAM) analyses using different simulations, the UNIT [21] simulation in [22] and the Uchuu [23] one in [24].…”