Angular clustering properties of the DESI QSO target selection using DR9 Legacy Imaging Surveys

Chaussidon, Edmond; Yèche, Ch; Palanque-Delabrouille, N.; Mattia, Arnaud de; Myers, Adam D.; Rezaie, Mehdi; Ross, Ashley J.; Seo, Hee-Jong; Gaztañaga, E.; Kehoe, R.; Levi, Michael; Newman, Jeffrey A.; Tarlè, G.; Zhang, Kai

doi:10.1093/mnras/stab3252

Cited by 17 publications

(34 citation statements)

References 56 publications

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“…We process every brick with the desitarget code 3 . The catalog making step already includes a sophisticated masking of bad pixels or objects near bright stars or extended galaxies, which has been refined over the years (Kitanidis et al 2020;Rezaie et al 2020;Chaussidon et al 2021;Zarrouk et al 2021).…”

Section: Galaxy Catalogsmentioning

confidence: 99%

“…We consider four samples of galaxies: Luminous red galaxies (LRGs), Emission line galaxies (ELGs), Quasars (QSOs), and g -dropout Lyman Break Galaxies (GLBGs). The colour cut for the first three galaxy types can be found in the desitarget pipeline as well as in Kitanidis et al (2020); Rezaie et al (2020); Chaussidon et al (2021), for example. We only needed to define cuts for the GLBGs (analogous to that of quasars): signal-to-noise ratios smaller than 3 in the r band (i.e., a non-detection) and greater than 4 in the r, z, and W 1 bands, and greater than 3 or 2 for the W 2 band (in the South or North, respectively).…”

Section: Galaxy Catalogsmentioning

confidence: 99%

“…Two maps ('GAIA12' and 'GAIA') are based on the Gaia data (Gaia Collaboration et al 2018): the density of point sources in the magnitude ranges phot_G_mean_mag < 12 and 12 < phot_G_mean_mag < 17. We also follow the procedure of Chaussidon et al (2021) to make a map of the Sagitarius stream from the catalogs of Antoja et al (2020). Finally, we make an additional stellar map generated by counting point-source objects from the bricks, following Kitanidis et al (2020).…”

Section: External Maps Of Contaminants (Sky-level Systematics)mentioning

confidence: 99%

“…The most common form of model is linear in the inputs, and predicts the galaxy number counts or the overdensity field. More complex models (e.g., based on neural networks) can provide significant improvements for some galaxy samples (see e.g., Rezaie et al 2020;Chaussidon et al 2021). Omitting inputs or adopting an overly simplistic model will lead to an incomplete subtraction of the spurious non-cosmological correlations.…”

Section: Introductionmentioning

confidence: 99%

“…We analyse four types of galaxies (luminous red galaxies, emission line galaxies, quasars, and Lyman break galaxies) extracted from DESI Legacy Surveys (DLS) data, and illustrate the effect of the new technique on clustering measurements and cross-correlations with potential contaminants. This allows us to follow several previous works that have analysed DLS galaxy samples, e.g., Rezaie et al (2020); Kitanidis et al (2020); Chaussidon et al (2021); Zarrouk et al (2021). However we do not extract cosmological parameters from those measurements since they require more thorough tests (as well as realistic mocks) which must be different for each galaxy sample.…”

Section: Introductionmentioning

confidence: 99%

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Spurious correlations between galaxies and multi-epoch image stacks in the DESI Legacy Surveys

Eggert¹,

Leistedt²

2022

Preprint

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A non-negligible source of systematic bias in cosmological analyses of galaxy surveys is the on-sky modulation caused by foregrounds and variable image characteristics such as observing conditions. Standard mitigation techniques perform a regression between the observed galaxy density field and sky maps of the potential contaminants. Such maps are ad-hoc, lossy summaries of the heterogeneous sets of co-added exposures that contribute to the survey. We present a methodology to address this limitation, and extract the spurious correlations between the observed distribution of galaxies and arbitrary stacks of single-epoch exposures. We study four types of galaxies (LRGs, ELGs, QSOs, LBGs) in the three regions of the DESI Legacy Surveys (North, South, DES), which results in twelve samples with varying levels and type of contamination. We find that the new technique outperforms the traditional ones in all cases, and is able to remove higher levels of contamination. This paves the way for new methods that extract more information from multi-epoch galaxy survey data and mitigate large-scale biases more effectively.

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Section: Galaxy Catalogsmentioning

confidence: 99%

Section: Galaxy Catalogsmentioning

confidence: 99%

Section: External Maps Of Contaminants (Sky-level Systematics)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spurious correlations between galaxies and multi-epoch image stacks in the DESI Legacy Surveys

Eggert¹,

Leistedt²

2022

Preprint

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Constraining primordial non-Gaussianity from DESI quasar targets and Planck CMB lensing

Krolewski,

Percival,

Ferraro

et al. 2024

J. Cosmol. Astropart. Phys.

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We detect the cross-correlation between 2.7 million DESI quasar targets across 14,700 deg2 (180 quasars deg-2) and Planck 2018 CMB lensing at ∼30σ. We use the cross-correlation on very large scales to constrain local primordial non-Gaussianity via the scale dependence of quasar bias. The DESI quasar targets lie at an effective redshift of 1.51 and are separated into four imaging regions of varying depth and image quality. We select quasar targets from Legacy Survey DR9 imaging, apply additional flux and photometric redshift cuts to improve the purity and reduce the fraction of unclassified redshifts, and use early DESI spectroscopy of 194,000 quasar targets to determine their redshift distribution and stellar contamination fraction (2.6%). Due to significant excess large-scale power in the quasar autocorrelation, we apply weights to mitigate contamination from imaging systematics such as depth, extinction, and stellar density. We use realistic contaminated mocks to determine the greatest number of systematic modes that we can fit, before we are biased by overfitting and spuriously remove real power. We find that linear regression with one to seven imaging templates removed per region accurately recovers the input cross-power, f NL and linear bias. As in previous analyses, our f NL constraint depends on the linear primordial non-Gaussianity bias parameter, bϕ = 2(b - p)δc assuming universality of the halo mass function. We measure f NL = -26+45 -40 with p = 1.6 (f NL = -18+29 -27 with p = 1.0), and find that this result is robust under several systematics tests. Future spectroscopic quasar cross-correlations with Planck lensing can tighten the f NL constraints by a factor of 2 if they can remove the excess power on large scales in the quasar auto power spectrum.

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Using angular two-point correlations to self-calibrate the photometric redshift distributions of DECaLS DR9

Zhang

Peng

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Calibrating the redshift distributions of photometric galaxy samples is essential in weak lensing studies. The self-calibration method combines angular auto- and cross-correlations between galaxies in multiple photometric redshift (photo-z) bins to reconstruct the scattering rates matrix between redshift bins. In this paper, we test a recently proposed self-calibration algorithm using the DECaLS Data Release 9 and investigate to what extent the scattering rates are determined. We first mitigate the spurious angular correlations due to imaging systematics by a machine learning based method. We then improve the algorithm for χ2 minimization and error estimation. Finally, we solve for the scattering matrices, carry out a series of consistency tests and find reasonable agreements: (1) finer photo-z bins return a high-resolution scattering matrix, and it is broadly consistent with the low-resolution matrix from wider bins; (2) the scattering matrix from the Northern Galactic Cap is almost identical to that from Southern Galactic Cap; (3) the scattering matrices are in reasonable agreement with those constructed from the power spectrum and the weighted spectroscopic subsample. We also evaluate the impact of cosmic magnification. Although it changes little the diagonal elements of the scattering matrix, it affects the off-diagonals significantly. The scattering matrix also shows some dependence on scale cut of input correlations, which may be related to a known numerical degeneracy between certain scattering pairs. This work demonstrates the feasibility of the self-calibration method in real data and provides a practical alternative to calibrate the redshift distributions of photometric samples.

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Angular clustering properties of the DESI QSO target selection using DR9 Legacy Imaging Surveys

Cited by 17 publications

References 56 publications

Spurious correlations between galaxies and multi-epoch image stacks in the DESI Legacy Surveys

Spurious correlations between galaxies and multi-epoch image stacks in the DESI Legacy Surveys

Constraining primordial non-Gaussianity from DESI quasar targets and Planck CMB lensing

Using angular two-point correlations to self-calibrate the photometric redshift distributions of DECaLS DR9

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