[Paper Review] The VIMOS VLT Deep Survey - Evolution of the luminosity functions by galaxy type up to z=1.5 from first epoch data

E. Zucca, O. Ilbert+48 more|ArXiv.org|Jun 16, 2005

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy55 references79 citations

TL;DR

This study presents the first comprehensive analysis of luminosity function evolution by galaxy type using a purely magnitude-selected, spectroscopic sample from the VIMOS VLT Deep Survey (VVDS), covering redshifts up to z=1.5. It reveals that late-type (irregular) galaxies drive most of the observed evolution, with strong brightening of M* and steepening of the faint-end slope, while early-type galaxies evolve passively with minimal change in luminosity function shape.

ABSTRACT

From the first epoch observations of the VVDS up to z=1.5 we have derived luminosity functions (LF) of different spectral type galaxies. The VVDS data, covering ~70% of the life of the Universe, allow for the first time to study from the same sample and with good statistical accuracy the evolution of the LFs by galaxy type in several rest frame bands from a purely magnitude selected sample. The magnitude limit of the VVDS allows the determination of the faint end slope of the LF with unprecedented accuracy. Galaxies have been classified in four spectral classes, using their colours and redshift, and LFs have been derived in the U, B, V, R and I rest frame bands from z=0.05 to z=1.5. We find a significant steepening of the LF going from early to late types. The M* parameter is significantly fainter for late type galaxies and this difference increases in the redder bands. Within each of the galaxy spectral types we find a brightening of M* with increasing redshift, ranging from =< 0.5 mag for early type galaxies to ~1 mag for the latest type galaxies, while the slope of the LF of each spectral type is consistent with being constant with redshift. The LF of early type galaxies is consistent with passive evolution up to z~1.1, while the number of bright early type galaxies has decreased by ~40% from z~0.3 to z~1.1. We also find a strong evolution in the normalization of the LF of latest type galaxies, with an increase of more than a factor 2 from z~0.3 to z~1.3: the density of bright late type galaxies in the same redshift range increases of a factor ~6.6. These results indicate a strong type-dependent evolution and identifies the latest spectral types as responsible for most of the evolution of the UV-optical luminosity function out to z=1.5.

Motivation & Objective

• To measure the evolution of galaxy luminosity functions by spectral type from z=0.05 to z=1.5 using a single, deep, spectroscopic survey.
• To determine how the Schechter function parameters (M*, α, φ*) vary with redshift and galaxy type.
• To identify which galaxy types dominate the observed evolution in the global UV-optical luminosity function.
• To assess the role of passive evolution versus star formation in shaping the luminosity function across cosmic time.
• To improve constraints on the faint-end slope of the luminosity function using a faint magnitude limit (I_AB=24) and spectroscopic redshifts.

Proposed method

• Utilized first-epoch VVDS data with I_AB ≤ 24 magnitude limit, providing a purely magnitude-selected spectroscopic sample of 7,713 galaxies.
• Classified galaxies into four spectral types (1: early, 2: S0, 3: S, 4: irregular) using rest-frame U-B and B-I colours and redshift.
• Derived luminosity functions in rest-frame U, B, V, R, and I bands for each galaxy type in redshift bins from z=0.05 to z=1.5.
• Fitted the luminosity functions with the Schechter function: Φ(M)dM = Φ* (10^(0.4(M*-M))) exp(-10^(0.4(M*-M))) dM.
• Compared results with photometric redshift surveys (e.g., COMBO-17) and previous studies (e.g., 2dFGRS, SDSS) to validate findings.
• Used spectroscopic redshifts to minimize classification degeneracy and ensure accurate sampling of rare, bright populations.

Experimental results

Research questions

• RQ1 How does the luminosity function evolve with redshift for different galaxy spectral types?
• RQ2 What is the role of early-type versus late-type galaxies in driving the evolution of the global luminosity function up to z=1.5?
• RQ3 How do the Schechter function parameters (M*, α, φ*) vary with redshift and galaxy type?
• RQ4 To what extent do the observed luminosity function evolutions reflect passive evolution or ongoing star formation?
• RQ5 What is the contribution of faint and bright galaxies of each type to the total UV-optical luminosity density at high redshift?

Key findings

• The faint-end slope α of the luminosity function steepens significantly from early (type 1) to late (type 4) galaxies, by Δα ≈ 1.3–1.5 across all rest-frame bands.
• The characteristic magnitude M* is significantly fainter for late-type galaxies, with a difference of up to 1.4 mag in the I band compared to early types.
• M* brightens by up to ~1 mag from z≈0.3 to z≈1.3 for the latest-type (type 4) galaxies, while the slope α remains constant with redshift.
• The normalization φ* of the luminosity function for type 4 galaxies increases by more than a factor of 2 from z≈0.3 to z≈1.3.
• The number density of bright (M_B_AB < -20) late-type galaxies increases by a factor of ~6.6 from z≈0.3 to z≈1.3, indicating strong evolution in star-forming populations.
• Early-type galaxies show only mild evolution: M* brightens by ≤0.5 mag and the number density of bright early types decreases by ~40% from z≈0.3 to z≈1.1, consistent with passive evolution.