[Paper Review] The VIMOS-VLT Deep Survey: Evolution of the galaxy luminosity function up to z=2 in first epoch data

O. Ilbert, L. Tresse+45 more|HAL (Le Centre pour la Communication Scientifique Directe)|Sep 6, 2004

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy35 references182 citations

TL;DR

This paper presents the first comprehensive measurement of the galaxy luminosity function (LF) from z=0.05 to z=2 using the VIMOS-VLT Deep Survey (VVDS), applying the Algorithm for Luminosity Function (ALF) to 11,034 spectroscopic redshifts. It reveals strong evolution in the LF, with the characteristic magnitude M∗ brightening by 1.0–2.5 mag across rest-frame U to I bands, and a steepening faint-end slope by Δα ≈ -0.3 from z=0.05 to z=1, indicating significant evolution in galaxy formation and merging processes.

ABSTRACT

We investigate the evolution of the galaxy luminosity function from the VIMOS-VLT Deep Survey (VVDS) from the present to z=2 in five (U, B, V, R and I) rest-frame band-passes. We use the first epoch VVDS deep sample of 11,034 spectra selected at 17.5 <= I_{AB} <= 24.0, on which we apply the Algorithm for Luminosity Function (ALF), described in this paper. We observe a substantial evolution with redshift of the global luminosity functions in all bands. From z=0.05 to z=2, we measure a brightening of the characteristic magnitude M* included in the magnitude range 1.8-2.5, 1.7-2.4, 1.2-1.9, 1.1-1.8 and 1.0-1.6 in the U, B, V, R and I rest-frame bands, respectively. We confirm this differential evolution of the luminosity function with rest-frame wavelength, from the measurement of the comoving density of bright galaxies (M < M*(z=0.1)). This density increases by a factor of around 2.6, 2.2, 1.8, 1.5, 1.5 between z=0.05 and z=1 in the U, B, V, R, I bands, respectively. We also measure a possible steepening of the faint-end slope of the luminosity functions, with Δα~ -0.3 between z=0.05 and z=1, similar in all bands.

Motivation & Objective

• To measure the evolution of the galaxy luminosity function (LF) from z=0.05 to z=2 across multiple rest-frame bands.
• To investigate how star formation and merging processes shape galaxy luminosity evolution by analyzing wavelength-dependent LF evolution.
• To determine whether the faint-end slope of the LF evolves with redshift, indicating changes in low-mass galaxy formation.
• To use a large, spectroscopically complete sample to provide robust constraints on LF evolution, avoiding biases from photometric redshifts.
• To establish a high-redshift benchmark for the local LF using the VVDS first-epoch data.

Proposed method

• The study uses the VIMOS-VLT Deep Survey (VVDS) first-epoch data, with 11,034 spectroscopic redshifts selected in the IAB magnitude range 17.5 ≤ IAB ≤ 24.0.
• The Algorithm for Luminosity Function (ALF) is applied to compute the Schechter function parameters (M∗, α, φ∗) of the LF in five rest-frame bands: U, B, V, R, and I.
• The 1/Vmax method is used to estimate the comoving number density of galaxies in each redshift and magnitude bin.
• The LF is modeled using the Schechter function: Φ(M) dM = Φ∗ (10^(0.4(M∗−M))) exp(−10^(0.4(M∗−M))) dM, with M∗ as the characteristic magnitude.
• The faint-end slope α is measured via the C+ and SWML methods to cross-validate results.
• The analysis accounts for selection effects and includes error estimation via likelihood contours (2Δlnℒ = 1).

Experimental results

Research questions

• RQ1 How does the characteristic magnitude M∗ of the galaxy luminosity function evolve from z=0.05 to z=2 across rest-frame U to I bands?
• RQ2 Does the faint-end slope α of the luminosity function evolve with redshift, and if so, by how much?
• RQ3 How does the comoving number density of bright galaxies (M ≤ M∗(z=0.1)) change from z=0.05 to z=1 across different rest-frame bands?
• RQ4 Is the evolution of the LF wavelength-dependent, reflecting different contributions from star formation (blue bands) and structure growth (red bands)?
• RQ5 To what extent do the LF parameters derived from spectroscopic redshifts differ from those based on photometric redshifts?

Key findings

• The characteristic magnitude M∗ brightens by 1.8–2.5 magnitudes from z=0.05 to z=2 in the U-band, and by 1.0–1.6 magnitudes in the I-band.
• The comoving density of bright galaxies (M ≤ M∗(z=0.1)) increases by a factor of 2.6 from z=0.05 to z=1 in the U-band, and by 1.5 in the I-band.
• The faint-end slope α of the luminosity function steepens by Δα ≈ -0.3 from z=0.05 to z=1, consistent across all five rest-frame bands.
• The evolution of M∗ is strongest in the blueward bands (U, B), indicating stronger evolution in star formation-driven luminosity growth at shorter wavelengths.
• The LF evolution is consistent with a combination of increasing star formation and merging activity, with the most significant changes occurring at z < 1.
• The ALF method successfully recovers LF parameters with robust error estimates, validating its use in deep spectroscopic surveys.