arXiv subjects

J. Silber

Publications and source records attributed to J. Silber.

At least 109 records · Page 6Linked to original sources

arXiv2025

Model-Independent Measurement of the Matter-Radiation Equality Scale in DESI 2024

The peak of the matter power spectrum, known as the turnover (TO) scale, is determined by the horizon size at the time of matter-radiation equality. This scale can serve as a standard ruler, independent of other features in the matter power spectrum, such as baryon acoustic oscillations (BAO). Here, we present the first detection of the turnover in the galaxy auto-power spectrum, utilising the distribution of quasars (QSO) and luminous red galaxies (LRG) measured by the Dark Energy Spectroscopic Instrument (DESI) during its first year of survey operations in a model-independent manner. To avoid confirmation bias, we first analyse the data using data blinding methods designed for the DESI baryon acoustic oscillation, redshift space distortion and scale-dependent bias signals. We measure the angle-averaged dilation distance $D_V(z = 1.651) = (38.1\pm 2.5)r_H$ from the quasars and $D_{V}(z = 0.733) = (21.8\pm 1.0)r_H$ from the LRG sample in units of the horizon $r_H$ at the matter-radiation-equality epoch. Combining these two constraints and assuming a flat $Λ$CDM model with three standard neutrino species, we can translate this into a constraint of $Ω_{m}h^2 = 0.139^{+0.036}_{-0.046}$. We can break the $Ω_m$-$H_0$ degeneracy with low-redshift distance measurements from type-Ia supernova (SN) data from Pantheon+, we obtain a sound-horizon free estimate of the Hubble-Lemaître parameter of $H_0=65.2^{+4.9}_{-6.2}$ km/s/Mpc, consistent with sound-horizon dependent DESI measurements. On the other hand, combining the DESI BAO and TO, we find a truly DESI-only measurement of $H_0=74.0^{+7.2}_{-3.5}$ km/s/Mpc, in line with DESI-only full-shape results where the sound-horizon scale is marginalised out. This discrepancy in $H_0$ can be reconciled in a $w_0w_a$CDM cosmology, where the combination of DESI BAO and TO data yields $H_0 = 66.5\pm 7.2\;\mathrm{km/s/Mpc}$.

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arXiv2025

The mass of the Milky Way from outer halo stars measured by DESI DR1

As a benchmark for galaxy evolution and dark matter studies, the total mass of the Milky Way is a parameter of cosmological significance, and its value at large radii from the Galactic center remains highly uncertain. Following a hierarchical Bayesian inference approach, we measure the cumulative mass of the Milky Way using full 6D phase-space information of stars from the first data release of the Dark Energy Spectroscopic Instrument (DESI). We employ 330 blue horizontal-branch stars (BHBs) and 110 RR Lyrae stars (RRLs) in DESI covering Galactocentric distances in the range $\sim$50--100 kpc. Within 100 kpc from the Galactic center, we report an enclosed mass of $M(<100\ {\rm kpc}) = 0.57^{+0.08}_{-0.07}\times10^{12}$ M$_\odot$ and $M(<100\ {\rm kpc}) = 0.55^{+0.12}_{-0.10}\times10^{12}$ M$_\odot$ when using BHBs and RRLs, respectively. Extrapolating our mass profiles beyond the extent of our data, we find the virial mass of the Galaxy to be $M_{200}=0.85^{+0.16}_{-0.14}\times10^{12}$ M$_\odot$ and $M_{200}=0.78^{+0.19}_{-0.15}\times10^{12}$ M$_\odot$, respectively. We validate the effectiveness and limitations of our method using mock BHBs and RRLs from two AuriDESI halos. These tests show that the code recovers the enclosed mass of the mock galaxy with high precision and accuracy between 50 and 200 kpc, independent of the stellar tracer used and their spatial distribution. The tests also suggest an underestimation of the galaxy's cumulative mass at a level of up to $\sim20$\% if stars close to the Galactic center are used in the models. Our mass estimates lay the groundwork for future inference of the Galactic mass with upcoming DESI data releases and spectroscopic surveys mapping the halo.

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arXiv2025

Study of the Connected Four-Point Correlation Function of Galaxies from DESI Data Release 1 Luminous Red Galaxy Sample

We present a measurement of the non-Gaussian four-point correlation function (4PCF) from the DESI DR1 Luminous Red Galaxy (LRG) sample. For the gravitationally induced parity-even 4PCF, we detect a signal with a significance of 14.7$σ$ using our fiducial setup. We assess the robustness of this detection through a series of validation tests, including auto- and cross-correlation analyses, sky partitioning across multiple patch combinations, and variations in radial scale cuts. Due to the low completeness of the sample, we find that differences in fiber assignment implementation schemes can significantly impact estimation of the covariance and introduce biases in the data vector. After correcting for these effects, all tests yield consistent results. This is one of the first measurements of the connected 4PCF on the DESI LRG sample: the good agreement between the simulation and the data implies that the amplitude of the density fluctuation inferred from the connected 4PCF is consistent with the Planck $Λ$CDM cosmology. The methodology and diagnostic framework established in this work provide a foundation for interpreting parity-odd 4PCF.

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arXiv2025

Cosmological neutrino mass: a frequentist overview in light of DESI

We derive constraints on the neutrino mass using a variety of recent cosmological datasets, including DESI BAO, the full-shape analysis of the DESI matter power spectrum and the one-dimensional power spectrum of the Lyman-$α$ forest (P1D) from eBOSS quasars as well as the cosmic microwave background (CMB). The constraints are obtained in the frequentist formalism by constructing profile likelihoods and applying the Feldman-Cousins prescription to compute confidence intervals. This method avoids potential prior and volume effects that may arise in a comparable Bayesian analysis. Parabolic fits to the profiles allow one to distinguish changes in the upper limits from variations in the constraining power $σ$ of the different data combinations. We find that all profiles in the $Λ$CDM model are cut off by the $\sum m_ν\geq 0$ bound, meaning that the corresponding parabolas reach their minimum in the unphysical sector. The most stringent 95% C.L. upper limit is obtained by the combination of DESI DR2 BAO, Planck PR4 and CMB lensing at 53 meV, below the minimum of 59 meV set by the normal ordering. Extending $Λ$CDM to non-zero curvature and $w_0w_\mathrm{a}$CDM relaxes the constraints past 59 meV again, but only $w_0w_\mathrm{a}$CDM exhibits profiles with a minimum at a positive value. Using a combination of DESI DR1 full-shape, BBN and eBOSS Lyman-$α$ P1D, we successfully constrain the neutrino mass independently of the CMB. This combination yields $\sum m_ν\leq 285$ meV (95% C.L.). The addition of DESI full-shape or Lyman-$α$ P1D to CMB and DESI BAO results in small but noticeable improvement of the constraining power of the data. Lyman-$α$ free-streaming measurements especially improve the constraint. Since they are based on eBOSS data, this sets a promising precedent for upcoming DESI data.

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arXiv2025

Intrinsic alignment demographics for next-generation lensing: Revealing galaxy property trends with DESI Y1 direct measurements

We present direct measurements of the intrinsic alignments (IA) of over 2 million spectroscopic galaxies using DESI Data Release 1 and imaging from four lensing surveys: DES, HSC, KiDS, and SDSS. In this uniquely data-rich regime, we take initial steps towards a more tailored IA modelling approach by building a library of IA measurements across colour, luminosity, stellar mass, and redshift. We map the dependence between galaxy type -- in terms of rest-frame colour, strength of the 4000 Angstrom break, and specific star formation rate -- and IA amplitude; the bluest galaxies have an alignment consistent with zero, across low ($0.05<z<0.5$) and high ($0.8<z<1.55$) redshifts. In order to construct cosmic shear samples that are minimally impacted by IA but maintain maximum sample size and statistical power, we map the dependence of alignment with colour purity. Red, quenched galaxies are strongly aligned and the amplitude of the signal increases with luminosity, which is tightly correlated with stellar mass in our catalogues. For DESI galaxies between $0<z<1.5$, trends in luminosity and colour alone are sufficient to explain the alignments we measure -- with no need for an explicit redshift dependence. In a companion paper (Jeffrey et al., in prep), we perform detailed modelling of the IA signals with significant detections, including model comparison. Finally, to direct efforts for future IA measurements, we juxtapose the colour-magnitude-redshift coverage of existing IA measurements against modern and future lensing surveys.

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arXiv2025

DESI EDR: Calibrating the Tully-Fisher Relationship with the DESI Peculiar Velocity Survey

We calibrate the Tully-Fisher relation (TFR) with data from the DESI Peculiar Velocity (PV) Survey taken during the Survey Validation (SV) period of the DESI galaxy redshift survey. Placing spectroscopic fibers on the centers and major axes of spatially-extended spiral galaxies identified in the 2020 Siena Galaxy Atlas using the DESI Legacy Surveys, we measure the rotational velocities at 0.33R26 for 1163 (1136 + 27 dwarf) spiral galaxies observed during SV. Using 41 spiral galaxies observed in the Coma Cluster, we find a slope for the TFR of -7.96+/-0.13 AB mag in the r-band, with a scatter about the TFR of 1.07+/-0.02 AB mag. We calibrate the zero-point of the TFR using galaxies with independent distances measured using type Ia supernovae via the cosmological distance ladder. From the SN Ia distances, we measure a zero-point of -19.34(+0.30,-0.29) AB mag in the r-band. We produce a public catalog of the distances to these 1136 spiral galaxies observed during DESI SV as part of the DESI PV Survey with our calibrated TFR. This is, to our knowledge, the first catalog of TFR distances produced with velocities measured at a single point in the disk.

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arXiv2025

Cosmology from Planck CMB Lensing and DESI DR1 Quasar Tomography

We present a measurement of the amplitude of matter fluctuations over the redshift range 0.8 <= z <= 3.5 from the cross correlation of over 1.2 million spectroscopic quasars selected by the Dark Energy Spectroscopic Instrument (DESI) across 7,200 deg$^2$ (approx 170 quasars/deg$^2$) and Planck PR4 (NPIPE) cosmic microwave background (CMB) lensing maps. We perform a tomographic measurement in three bins centered at effective redshifts z=1.44, 2.27 and 2.75, which have ample overlap with the CMB lensing kernel. From a joint fit using the angular clustering of all three redshift bins (auto and cross-spectra), and including an $Ω_m$ prior from DESI DR1 baryon acoustic oscillations to break the $Ω_m-σ_8$ degeneracy, we constrain the amplitude of matter fluctuations in the matter-dominated regime to be $σ_8=0.929^{+0.059}_{-0.074}$ and $S_8\equiv σ_8(Ω_m/0.3)^{0.5} = 0.922^{+0.059}_{-0.073}$. We provide a growth of structure measurement with the largest spectroscopic quasar sample to date at high redshift, which is 1.5$σ$ higher than predictions from $Λ$CDM fits to measurements of the primary CMB from Planck PR4. The cross-correlation between PR4 lensing maps and DESI DR1 quasars is detected with a signal-to-noise ratio of 21.7 and the quasar auto-correlation at 27.2 for the joint analysis of all redshift bins. We combine our measurement with the CMB lensing auto-spectrum from the ground-based Atacama Cosmology Telescope (ACT DR6) and Planck PR4 to perform a sound-horizon-free measurement of the Hubble constant, yielding $H_0=69.1^{+2.2}_{-2.6}\,\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$ through its sensitivity to the matter-radiation equality scale.

astro-ph.CO↗

arXiv2025

Lensing Without Borders: Measurements of galaxy-galaxy lensing and projected galaxy clustering in DESI DR1

We present Galaxy-Galaxy Lensing measurements obtained by cross-correlating spectroscopically observed galaxies from the first data release of the Dark Energy Spectroscopic Instrument (DESI) with source galaxies from the Hyper Suprime-Cam Subaru Strategic Survey, the Kilo-Degree Survey, the Sloan Digital Sky Survey, and the Dark Energy Survey. Specifically, we measure the excess surface mass density $ΔΣ$ and tangential shear $γ_\mathrm{t}$ for the Bright Galaxy Sample and Luminous Red Galaxies measured within the first year of observations with DESI. To ensure robustness, we test the measurements for systematic biases, finding no significant trends related to the properties of the \acrshort{desi} lens galaxies. We identify a significant trend with the average redshift of source galaxies, however, this trend vanishes once we apply shifts to the Hyper Suprime-Cam Subaru Strategic Survey redshift distributions that are also favored by their fiducial cosmology analysis. Additionally, we compare the observed scatter in the measurements with the theoretical covariance and find excess scatter, driven primarily by small-scale measurements of $r\leq 1 \, \mathrm{Mpc}/h$; measurements on larger scales are consistent at the $2\,σ$ level. We further present the projected clustering measurements $w_p$ of the galaxy samples in the the first data release of DESI. These measurements, which will be made publicly available, serve as a foundation for forthcoming cosmological analyses.

astro-ph.CO↗

arXiv2025

Full-Shape analysis of the power spectrum and bispectrum of DESI DR1 LRG and QSO samples

We present the first joint analysis of the power spectrum and bispectrum using the Data Release 1 (DR1) of the Dark Energy Spectroscopic Instrument (DESI), focusing on Luminous Red Galaxies (LRGs) and quasars (QSOs) across a redshift range of $0.4\leq z\leq2.1$. By combining the two- and three-point statistics, we are able to partially break the degeneracy between the logarithmic growth rate, $f(z)$, and the amplitude of dark matter fluctuations, $σ_\textrm{s8}(z)$, which cannot be measured separately in analyses that only involve the power spectrum. In comparison with the (fiducial) Planck $Λ$CDM cosmology we obtain $f/f^\textrm{fid}=\{0.888_{-0.089}^{+0.186},0.977_{-0.220}^{+0.182},1.030_{-0.085}^{+0.368}\}$, $σ_{s8}/σ^\textrm{fid}_\textrm{s8}=\{1.224_{-0.133}^{+0.091},1.071_{-0.163}^{+0.278},1.000_{-0.223}^{+0.088}\}$ respectively for the three LRG redshift bins, corresponding to a cumulative 10.1\% constraint on $f$, and of 8.4\% on $σ_\textrm{s8}$, including the systematic error budget. The cumulative constraints for the ShapeFit compressed parameters from our joint power spectrum-bispectrum analysis are respectively $σ_{α_\textrm{iso}}=0.9\%$ (9\% improvement with respect to our power spectrum-only analysis); $σ_{α_\textrm{AP}}=2.3\%$ (no improvement with respect to power spectrum-only analysis, which is expected given that the bispectrum monopole has no significant anisotropic signal); $σ_{fσ_\textrm{s8}}=5.1\%$ (9\% improvement); $σ_{m+n}=2.3\%$ (11\% improvement). These results are fully consistent with the main DESI power spectrum analysis, demonstrating the robustness of the DESI cosmological constraints, and compatible with Planck $Λ$CDM cosmology.

astro-ph.CO↗

arXiv2025

The Backup Program of the Dark Energy Spectroscopic Instrument's Milky Way Survey

The Milky Way Backup Program (MWBP), a survey currently underway with the Dark Energy Spectroscopic Instrument (DESI) on the Nicholas U. Mayall 4-m Telescope, works at the margins of the DESI Main surveys to obtain spectra of millions of additional stars from the Gaia catalog. Efficiently utilizing twilight times (<18 deg) and poor weather conditions, the MWBP extends the range of stellar sources studied to both brighter magnitudes and lower Galactic latitude and declination than the stars studied in DESI's Main Milky Way Survey. While the MWBP prioritizes candidate giant stars selected from the Gaia catalog (using color and parallax criteria), it also includes an unbiased sample of bright stars (i.e., 11.2 < G < 16 mag) as well as fainter sources (to G < 19 mag). As of March 1, 2025, the survey had obtained spectra of ~7 million stars, approximately 1.2 million of which are included in the DESI Data Release 1. The full survey, when completed, will cover an area of more than 21,000 square degrees and include approximately 10 million Gaia sources, roughly equal to the number of stellar spectra obtained through the DESI Main Survey, while only utilizing <9% of all DESI observing time.

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arXiv2025

Characterization of DESI fiber assignment incompleteness effect on 2-point clustering and mitigation methods for DR1 analysis

We present an in-depth analysis of the fiber assignment incompleteness in the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1). This incompleteness is caused by the restricted mobility of the robotic fiber positioner in the DESI focal plane, which limits the number of galaxies that can be observed at the same time, especially at small angular separations. As a result, the observed clustering amplitude is suppressed in a scale-dependent manner, which, if not addressed, can severely impact the inference of cosmological parameters. We discuss the methods adopted for simulating fiber assignment on mocks and data. In particular, we introduce the fast fiber assignment (FFA) emulator, which was employed to obtain the power spectrum covariance adopted for the DR1 full-shape analysis. We present the mitigation techniques, organised in two classes: measurement stage and model stage. We then use high fidelity mocks as a reference to quantify both the accuracy of the FFA emulator and the effectiveness of the different measurement-stage mitigation techniques. This complements the studies conducted in a parallel paper for the model-stage techniques, namely the $θ$-cut approach. We find that pairwise inverse probability (PIP) weights with angular upweighting recover the "true" clustering in all the cases considered, in both Fourier and configuration space. Notably, we present the first ever power spectrum measurement with PIP weights from real data.

astro-ph.CO↗

arXiv2025

Cosmological implications of DESI DR2 BAO measurements in light of the latest ACT DR6 CMB data

We report cosmological results from the Dark Energy Spectroscopic Instrument (DESI) measurements of baryon acoustic oscillations (BAO) when combined with recent data from the Atacama Cosmology Telescope (ACT). By jointly analyzing ACT and Planck data and applying conservative cuts to overlapping multipole ranges, we assess how different Planck+ACT dataset combinations affect consistency with DESI. While ACT alone exhibits a tension with DESI exceeding 3$σ$ within the $Λ$CDM model, this discrepancy is reduced when ACT is analyzed in combination with Planck. For our baseline DESI DR2 BAO+Planck PR4+ACT likelihood combination, the preference for evolving dark energy over a cosmological constant is about 3$σ$, increasing to over 4$σ$ with the inclusion of Type Ia supernova data. While the dark energy results remain quite consistent across various combinations of Planck and ACT likelihoods with those obtained by the DESI collaboration, the constraints on neutrino mass are more sensitive, ranging from $\sum m_ν< 0.061$ eV in our baseline analysis, to $\sum m_ν< 0.077$ eV (95\% confidence level) in the CMB likelihood combination chosen by ACT when imposing the physical prior $\sum m_ν>0$ eV.

astro-ph.CO↗

arXiv2025

Suppressing the sample variance of DESI-like galaxy clustering with fast simulations

Ongoing and upcoming galaxy redshift surveys, such as the Dark Energy Spectroscopic Instrument (DESI) survey, will observe vast regions of sky and a wide range of redshifts. In order to model the observations and address various systematic uncertainties, N-body simulations are routinely adopted, however, the number of large simulations with sufficiently high mass resolution is usually limited by available computing time. Therefore, achieving a simulation volume with the effective statistical errors significantly smaller than those of the observations becomes prohibitively expensive. In this study, we apply the Convergence Acceleration by Regression and Pooling (CARPool) method to mitigate the sample variance of the DESI-like galaxy clustering in the AbacusSummit simulations, with the assistance of the quasi-N-body simulations FastPM. Based on the halo occupation distribution (HOD) models, we construct different FastPM galaxy catalogs, including the luminous red galaxies (LRGs), emission line galaxies (ELGs), and quasars, with their number densities and two-point clustering statistics well matched to those of AbacusSummit. We also employ the same initial conditions between AbacusSummit and FastPM to achieve high cross-correlation, as it is useful in effectively suppressing the variance. Our method of reducing noise in clustering is equivalent to performing a simulation with volume larger by a factor of 5 and 4 for LRGs and ELGs, respectively. We also mitigate the standard deviation of the LRG bispectrum with the triangular configurations $k_2=2k_1=0.2$ h/Mpc by a factor of 1.6. With smaller sample variance on galaxy clustering, we are able to constrain the baryon acoustic oscillations (BAO) scale parameters to higher precision. The CARPool method will be beneficial to better constrain the theoretical systematics of BAO, redshift space distortions (RSD) and primordial non-Gaussianity (NG).

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arXiv2024

Baryon Acoustic Oscillation Theory and Modelling Systematics for the DESI 2024 results

This paper provides a comprehensive overview of how fitting of Baryon Acoustic Oscillations (BAO) is carried out within the upcoming Dark Energy Spectroscopic Instrument's (DESI) 2024 results using its DR1 dataset, and the associated systematic error budget from theory and modelling of the BAO. We derive new results showing how non-linearities in the clustering of galaxies can cause potential biases in measurements of the isotropic ($α_{\mathrm{iso}}$) and anisotropic ($α_{\mathrm{ap}}$) BAO distance scales, and how these can be effectively removed with an appropriate choice of reconstruction algorithm. We then demonstrate how theory leads to a clear choice for how to model the BAO and develop, implement and validate a new model for the remaining smooth-broadband (i.e., without BAO) component of the galaxy clustering. Finally, we explore the impact of all remaining modelling choices on the BAO constraints from DESI using a suite of high-precision simulations, arriving at a set of best-practices for DESI BAO fits, and an associated theory and modelling systematic error. Overall, our results demonstrate the remarkable robustness of the BAO to all our modelling choices and motivate a combined theory and modelling systematic error contribution to the post-reconstruction DESI BAO measurements of no more than $0.1\%$ ($0.2\%$) for its isotropic (anisotropic) distance measurements. We expect the theory and best-practices laid out to here to be applicable to other BAO experiments in the era of DESI and beyond.

astro-ph.CO↗

arXiv2024

The atomic gas sequence and mass-metallicity relation from dwarfs to massive galaxies

Galaxy scaling relations provide insights into the processes that drive galaxy evolution. The extension of these scaling relations into the dwarf galaxy regime is of particular interest. This is because dwarf galaxies represent a crucial stage in galaxy evolution, and understanding them could also shed light on their role in reionising the early Universe. There is currently no consensus on the processes that dominate the evolution of dwarfs. In this work we constrain the atomic gas sequence (stellar mass vs. atomic gas fraction) and mass-metallicity relation (stellar mass vs. gas phase metallicity) from dwarf ($10^{6.5}$ $\textrm{M}_{\odot}$) to massive ($10^{11.5}$ $\textrm{M}_{\odot}$) galaxies in the local Universe. The combined optical and 21-cm spectroscopic observations of the DESI and ALFALFA surveys allow us to simultaneously constrain both scaling relations. We find a slope change of the atomic gas sequence at a stellar mass of $\sim 10^{9} ~\textrm{M}_{\odot}$. We also find that the shape and scatter of the atomic gas sequence and mass-metallicity relation are strongly linked for both dwarfs and more massive galaxies. Consequently, the low mass slope change of the atomic gas sequence is imprinted onto the mass-metallicity relation of dwarf galaxies. The mass scale of the measured slope change is consistent with a predicted escape velocity threshold below which low mass galaxies experience significant supernova-driven gas loss, as well as with a reduction in cold gas accretion onto more massive galaxies.

astro-ph.GA↗

arXiv2024

Characterization of contaminants in the Lyman-alpha forest auto-correlation with DESI

Baryon Acoustic Oscillations can be measured with sub-percent precision above redshift two with the Lyman-alpha forest auto-correlation and its cross-correlation with quasar positions. This is one of the key goals of the Dark Energy Spectroscopic Instrument (DESI) which started its main survey in May 2021. We present in this paper a study of the contaminants to the lyman-alpha forest which are mainly caused by correlated signals introduced by the spectroscopic data processing pipeline as well as astrophysical contaminants due to foreground absorption in the intergalactic medium. Notably, an excess signal caused by the sky background subtraction noise is present in the lyman-alpha auto-correlation in the first line-of-sight separation bin. We use synthetic data to isolate this contribution, we also characterize the effect of spectro-photometric calibration noise, and propose a simple model to account for both effects in the analysis of the lyman-alpha forest. We then measure the auto-correlation of the quasar flux transmission fraction of low redshift quasars, where there is no lyman-alpha forest absorption but only its contaminants. We demonstrate that we can interpret the data with a two-component model: data processing noise and triply ionized Silicon and Carbon auto-correlations. This result can be used to improve the modeling of the lyman-alpha auto-correlation function measured with DESI.

astro-ph.CO↗

arXiv2024

Systematic Effects in Galaxy-Galaxy Lensing with DESI

The Dark Energy Spectroscopic Instrument (DESI) survey will measure spectroscopic redshifts for millions of galaxies across roughly $14,000 \, \mathrm{deg}^2$ of the sky. Cross-correlating targets in the DESI survey with complementary imaging surveys allows us to measure and analyze shear distortions caused by gravitational lensing in unprecedented detail. In this work, we analyze a series of mock catalogs with ray-traced gravitational lensing and increasing sophistication to estimate systematic effects on galaxy-galaxy lensing estimators such as the tangential shear $γ_{\mathrm{t}}$ and the excess surface density $ΔΣ$. We employ mock catalogs tailored to the specific imaging surveys overlapping with the DESI survey: the Dark Energy Survey (DES), the Hyper Suprime-Cam (HSC) survey, and the Kilo-Degree Survey (KiDS). Among others, we find that fiber incompleteness can have significant effects on galaxy-galaxy lensing estimators but can be corrected effectively by up-weighting DESI targets with fibers by the inverse of the fiber assignment probability. Similarly, we show that intrinsic alignment and lens magnification are expected to be statistically significant given the precision forecasted for the DESI year-1 data set. Our study informs several analysis choices for upcoming cross-correlation studies of DESI with DES, HSC, and KiDS.

astro-ph.CO↗

arXiv2024

Impact of Systematic Redshift Errors on the Cross-correlation of the Lyman-$α$ Forest with Quasars at Small Scales Using DESI Early Data

The Dark Energy Spectroscopic Instrument (DESI) will measure millions of quasar spectra by the end of its 5 year survey. Quasar redshift errors impact the shape of the Lyman-$α$ forest correlation functions, which can affect cosmological analyses and therefore cosmological interpretations. Using data from the DESI Early Data Release and the first two months of the main survey, we measure the systematic redshift error from an offset in the cross-correlation of the Lyman-$α$ forest with quasars. We find evidence for a redshift dependent bias causing redshifts to be underestimated with increasing redshift, stemming from improper modeling of the Lyman-$α$ optical depth in the templates used for redshift estimation. New templates were derived for the DESI Year 1 quasar sample at $z > 1.6$ and we found the redshift dependent bias, $Δr_\parallel$, increased from $-1.94 \pm 0.15$ $h^{-1}$ Mpc to $-0.08 \pm 0.04$ $h^{-1}$ Mpc ($-205 \pm 15~\text{km s}^{-1}$ to $-9.0 \pm 4.0~\text{km s}^{-1}$). These new templates will be used to provide redshifts for the DESI Year 1 quasar sample.

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