Browsing by Autor "David H. Brooks"

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Galaxy-multiplet clustering from DESI DR2
(Oxford University Press, 2025) Hanyue Wang; Daniel J. Eisenstein; J. Aguilar; S. P. Ahlen; D. Bianchi; David H. Brooks; T. Claybaugh; Axel de la Macorra; Arjun Dey; Biprateep Dey
ABSTRACT We present an efficient estimator for higher order galaxy clustering using small groups of nearby galaxies, or multiplets. Using the Luminous Red Galaxy sample from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2, we identify galaxy multiplets as discrete objects and measure their cross-correlations with the general galaxy field. Our results show that the multiplets exhibit stronger clustering bias as they trace more massive dark matter haloes than individual galaxies. When comparing the observed clustering statistics with the mock catalogues generated from the N-body simulation AbacusSummit, we find that the mocks underpredict multiplet clustering despite reproducing the galaxy two-point autocorrelation reasonably well. This discrepancy indicates that the standard Halo Occupation Distribution (HOD) model is insufficient to describe the properties of galaxy multiplets, revealing the greater constraining power of this higher order statistic on galaxy–halo connection and the possibility that multiplets are specific to additional assembly bias. We demonstrate that incorporating secondary biases into the HOD model improves agreement with the observed multiplet statistics, specifically by allowing galaxies to preferentially occupy haloes in denser environments. Our results highlight the potential of utilizing multiplet clustering, beyond traditional two-point correlation measurements, to break degeneracies in models describing the galaxy–dark matter connection.
Modelling the impact of quasar redshift errors on the full-shape analysis of correlations in the Lyman-α forest
(Oxford University Press, 2025) C. Gordon; Andrei Cuceu; Andreu Font-Ribera; H. K. Herrera-Alcantar; Jessica Nicole Aguilar Steven Ahlen; D. Bianchi; David H. Brooks; T. Claybaugh; Shaun Cole; Axel de la Macorra
ABSTRACT In preparation for the first cosmological measurements from the full shape of the Lyman-$\alpha$ (Ly $\alpha$) forest from Dark Energy Spectroscopic Instrument (DESI), we must carefully model all relevant systematics that might bias our analysis. It has been shown that random quasar redshift errors produce a smoothing effect on the mean quasar continuum in the Ly $\alpha$ forest region. This, in turn, gives rise to spurious features in the Ly $\alpha$ autocorrelation and its cross-correlation with quasars. Using synthetic data sets based on the DESI survey, we confirm that the impact on baryon acoustic oscillation measurements is small, but that a bias is introduced to parameters which depend on the full shape of our correlations. We combine a model of this contamination in the cross-correlation with a new model we introduce here for the autocorrelation. These are parametrized by three parameters, which, when included in a joint fit to both correlation functions, successfully eliminate any impact of redshift errors on our full-shape constraints. We also present a strategy for removing this contamination from real data, by removing $\sim$0.3 per cent of correlating pairs.
Spectroscopic Characterization of redMaPPer Galaxy Clusters with DESI
(Oxford University Press, 2025) J. Myles; D. Gruen; T Jeltema; Shaojun Fu; S. W. Allen; Shenming Fu; S. P. Ahlen; José Aguilar; David H. Brooks; D. Bianchi
ABSTRACT Optical galaxy cluster identification algorithms such as redMaPPer promise to enable an array of astrophysical and cosmological studies, but suffer from biases whereby galaxies in front of and behind a galaxy cluster are mistakenly associated with the primary cluster halo. These projection effects caused by irreducible photometric redshift uncertainty must be quantified to facilitate the use of optical cluster catalogues. We present measurements of galaxy cluster projection effects and velocity dispersion using spectroscopy from the Dark Energy Spectroscopic Instrument. Our findings are as follows: we confirm that the fraction of redMaPPer putative member galaxies mistakenly associated with cluster haloes is richness dependent, being more than twice as large at low richness than high richness; we present the first spectroscopic evidence of an increase in projection effects with increasing redshift, by as much as 25 per cent from $z\sim 0.1$ to $z\sim 0.2$; moreover, we find qualitative evidence for luminosity dependence in projection effects, with fainter galaxies being more commonly far behind clusters than their bright counterparts; finally, we fit the scaling relation between measured mean spectroscopic richness and velocity dispersion, finding an implied linear scaling between spectroscopic richness and halo mass. We discuss further directions for the application of spectroscopic data sets to improve use of optically selected clusters to test cosmological models.
The rate of extreme coronal line emitting galaxies in the Sloan Digital Sky Survey and their relation to tidal disruption events
(Oxford University Press, 2024) J. A. Callow; Or Graur; P. Clark; A. Palmese; J. Aguilar; S. P. Ahlen; S. BenZvi; David H. Brooks; T. Claybaugh; Axel de la Macorra
ABSTRACT High-ionization iron coronal lines (CLs) are a rare phenomenon observed in galaxy and quasi-stellar object spectra that are thought to be created by high-energy emission from active galactic nuclei and certain types of transients. In cases known as extreme coronal line emitting galaxies (ECLEs), these CLs are strong and fade away on a time-scale of years. The most likely progenitors of these variable CLs are tidal disruption events (TDEs), which produce sufficient high-energy emission to create and sustain the CLs over these time-scales. To test the possible connection between ECLEs and TDEs, we present the most complete variable ECLE rate calculation to date and compare the results to TDE rates from the literature. To achieve this, we search for ECLEs in the Sloan Digital Sky Survey (SDSS). We detect sufficiently strong CLs in 16 galaxies, more than doubling the number previously found in SDSS. Using follow-up spectra from the Dark Energy Spectroscopic Instrument and Gemini Multi-Object Spectrograph, Wide-field Infrared Survey Explorer mid-infrared observations, and Liverpool Telescope optical photometry, we find that none of the nine new ECLEs evolve in a manner consistent with that of the five previously discovered variable ECLEs. Using this sample of five variable ECLEs, we calculate the galaxy-normalized rate of variable ECLEs in SDSS to be $R_\mathrm{G}=3.6~^{+2.6}_{-1.8}~(\mathrm{statistical})~^{+5.1}_{-0.0}~(\mathrm{systematic})\times 10^{-6}~\mathrm{galaxy}^{-1}~\mathrm{yr}^{-1}$. The mass-normalized rate is $R_\mathrm{M}=3.1~^{+2.3}_{-1.5}~(\mathrm{statistical})~^{+4.4}_{-0.0}~(\mathrm{systematic})\times 10^{-17}~\mathrm{M_\odot ^{-1}}~\mathrm{yr}^{-1}$ and the volumetric rate is $R_\mathrm{V}=7~^{+20}_{-5}~(\mathrm{statistical})~^{+10}_{-0.0}~(\mathrm{systematic})\times 10^{-9}~\mathrm{Mpc}^{-3}~\mathrm{yr}^{-1}$. Our rates are one to two orders of magnitude lower than TDE rates from the literature, which suggests that only 10–40 per cent of all TDEs produce variable ECLEs. Additional uncertainties in the rates arising from the structure of the interstellar medium have yet to be included.