Tracing the cosmic velocity field at z ~ 0.1 from galaxy luminosities in the SDSS DR7

TL;DR

This study uses galaxy luminosity modulations from SDSS DR7 to map the cosmic velocity field at z ~ 0.1, confirming consistency with ΛCDM predictions and estimating the matter power spectrum amplitude.

Contribution

It introduces a method to probe the cosmic velocity field through luminosity modulations, accounting for luminosity evolution and comparing results with ΛCDM simulations.

Findings

Bulk flows agree with ΛCDM predictions.

Estimated σ₈ ≈ 1.1 ± 0.4, limited by galaxy sample size.

Luminosity function well modeled by a Schechter form.

Abstract

Spatial modulations in the distribution of observed luminosities (computed using redshifts) of ~ 5 $\times$ 10$^5$ galaxies from the SDSS Data Release 7, probe the cosmic peculiar velocity field out to z ~ 0.1. Allowing for luminosity evolution, the r-band luminosity function, determined via a spline-based estimator, is well represented by a Schechter form with M$^{\star}$(z) - 5log$_{10}$h = -20.52 - 1.6(z - 0.1) $\pm$ 0.05 and $\alpha^{\star}$ = -1.1 $\pm$ 0.03. Bulk flows and higher velocity moments in two redshift bins, 0.02 < z < 0.07 and 0.07 < z < 0.22, agree with the predictions of the $\Lambda$CDM model, as obtained from mock galaxy catalogs designed to match the observations. Assuming a $\Lambda$CDM model, we estimate $\sigma_{8}$ $\approx$ 1.1 $\pm$ 0.4 for the amplitude of the linear matter power spectrum, where the low accuracy is due to the limited number of galaxies. While the low-z bin is robust against coherent photometric uncertainties, the bias of results from the second bin is consistent with the ~ 1% magnitude tilt reported by the SDSS collaboration. The systematics are expected to have a significantly lower impact in future datasets with larger sky coverage and better photometric calibration.