2017A&A...602A..35T


Query : 2017A&A...602A..35T

2017A&A...602A..35T - Astronomy and Astrophysics, volume 602A, 35-35 (2017/6-1)

The extended epoch of galaxy formation: Age dating of ∼3600 galaxies with 2 <z < 6.5 in the VIMOS Ultra-Deep Survey.

THOMAS R., LE FEVRE O., SCODEGGIO M., CASSATA P., GARILLI B., LE BRUN V., LEMAUX B.C., MACCAGNI D., PFORR J., TASCA L.A.M., ZAMORANI G., BARDELLI S., HATHI N.P., TRESSE L., ZUCCA E. and KOEKEMOER A.M.

Abstract (from CDS):

In this paper we aim at improving constraints on the epoch of galaxy formation by measuring the ages of 3597 galaxies with reliable spectroscopic redshifts 2≤z≤6.5 in the VIMOS Ultra Deep Survey (VUDS). We derive ages and other physical parameters from the simultaneous fitting with the GOSSIP+ software of observed UV rest-frame spectra and photometric data from the u band up to 4.5µm using model spectra from composite stellar populations. We perform extensive simulations and conclude that at z≥2 the joint analysis of spectroscopy and photometry, combined with restricted age possibilities when taking the age of the Universe into account, substantially reduces systematic uncertainties and degeneracies in the age derivation; we find that age measurements from this process are reliable. We find that galaxy ages range from very young with a few tens of million years to substantially evolved with ages up to 1.5Gyr or more. This large age spread is similar for different age definitions including ages corresponding to the last major star formation event, stellar mass-weighted ages, and ages corresponding to the time since the formation of 25% of the stellar mass. We derive the formation redshift zf from the measured ages and find galaxies that may have started forming stars as early as zf∼15. We produce the formation redshift function (FzF), the number of galaxies per unit volume formed at a redshift zf, and compare the FzF in increasing observed redshift bins finding a remarkably constant FzF. The FzF is parametrized with (1+z)ζ, where ζ~=0.58±0.06, indicating a smooth increase of about 2dex from the earliest redshifts, z∼15, to the lowest redshifts of our sample at z∼2. Remarkably, this observed increase in the number of forming galaxies is of the same order as the observed rise in the star formation rate density (SFRD). The ratio of the comoving SFRD with the FzF gives an average SFR per galaxy of ∼7-17M/yr at z∼4-6, in agreement with the measured SFR for galaxies at these redshifts. From the smooth rise in the FzF we infer that the period of galaxy formation extends all the way from the highest possible formation redshifts that we can probe at z∼15 down to redshifts z∼2. This indicates that galaxy formation is a continuous process over cosmic time, with a higher number of galaxies forming at the peak in SFRD at z∼2 than at earlier epochs.

Abstract Copyright: © ESO, 2017

Journal keyword(s): galaxies: evolution - Galaxy: formation - galaxies: high-redshift - galaxies: star formation - galaxies: star formation

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10456 1
2 NAME Extended Chandra Deep Field South reg 03 32 30.0 -27 48 20           ~ 726 0
3 NAME COSMOS Field reg 10 00 28.60 +02 12 21.0           ~ 2628 0

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2022.11.28-13:06:37

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