DESI DR2 Galaxy Luminosity Functions

TL;DR

This paper presents detailed galaxy luminosity functions from DESI DR2 data, revealing complex shapes and faint-end upturns, and compares results with previous surveys to refine galaxy formation models.

Contribution

It introduces improved k-corrections, extends LF measurements to very faint magnitudes, and uncovers non-trivial LF shapes and systematic effects in DESI DR2 data.

Findings

LF measurements reach M_r-5log h = -10, showing complex shapes.

Bright end deviates from exponential decline, faint end shows upturn.

North-South survey differences may be due to photometric depth.

Abstract

We present galaxy luminosity functions (LFs) for the Dark Energy Spectroscopic Instrument (DESI) DR2 Bright Galaxy Survey (BGS) in the g,r,z, and w1 bands over 0.002<z<0.6. Our analysis uses updated k-corrections and evolutionary corrections, including new polynomial k-correction fits derived from BGS Year1 data that supersede earlier GAMA-based prescriptions. Exploiting the statistical power of DESI, we measure LFs to very faint magnitudes, reaching M_r-5log h = -10. Independent measurements from the North and South survey regions show excellent agreement around the LF knee, but the very small statistical uncertainties reveal that simple analytic forms fail to capture the full LF shape. The bright end departs from a pure exponential decline, while the faint end exhibits complex, non-power-law behaviour, including a pronounced upturn at M_r-5log h > -15, which is stronger for red galaxies than for blue. We show that our LFs are largely complete for galaxies with surface brightness mu_50<25, and that an apparent steepening fainter than -13 is driven primarily by local overdensity and fragmentation of large galaxies. A systematic North-South offset at the brightest magnitudes is traced to red galaxies and may reflect shallower North photometry underestimating extended early-type profiles, although this remains inconclusive. We therefore also provide LFs based on model-Petrosian magnitudes. Redshift-splitting reveals small but significant residuals, indicating limitations of a simple global evolutionary model. Using the redshift limits of Loveday (2011) we find excellent agreement with GAMA, with substantially reduced statistical errors. These measurements provide a precise reference for studies of environmental and population-dependent LFs and for testing galaxy formation models.