Volume 597, January 2017
|Number of page(s)||16|
|Section||Cosmology (including clusters of galaxies)|
|Published online||09 January 2017|
VIMOS Ultra-Deep Survey (VUDS): IGM transmission towards galaxies with 2.5 < z < 5.5 and the colour selection of high-redshift galaxies ⋆
1 Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
2 INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
3 INAF–IASF, via Bassini 15, 20133 Milano, Italy
4 INAF–Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
5 University of Bologna, Department of Physics and Astronomy (DIFA), V. le Berti Pichat 6/2, 40127 Bologna, Italy
6 INAF–IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
7 Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
8 Institut de Recherche en Astrophysique et Planétologie – IRAP, CNRS, Université de Toulouse, UPS-OMP, 14, avenue É. Belin, 31400 Toulouse, France
9 Department of Astronomy, University of Geneva ch. d’cogia 16, 1290 Versoix, Switzerland
10 Geneva Observatory, University of Geneva, ch. des Maillettes 51, 1290 Versoix, Switzerland
11 Centro de Estudios de Física del Cosmos de Aragón, 44001 Teruel, Spain
12 Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249–17, Pasadena, CA 91125, USA
13 Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA
14 Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching bei München, Germany
15 Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho 2-5, 790-8577 Matsuyama, Japan
16 SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK
17 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
18 Instituto de Fisica y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
Received: 14 November 2014
Accepted: 28 June 2016
The observed UV rest-frame spectra of distant galaxies are the result of their intrinsic emission combined with absorption along the line of sight produced by the inter-galactic medium (IGM). Here we analyse the evolution of the mean IGM transmission Tr(Lyα) and its dispersion along the line of sight for 2127 galaxies with 2.5 < z < 5.5 in the VIMOS Ultra Deep Survey (VUDS). We fitted model spectra combined with a range of IGM transmission to the galaxy spectra using the spectral fitting algorithm GOSSIP+. We used these fits to derive the mean IGM transmission towards each galaxy for several redshift slices from z = 2.5 to z = 5.5. We found that the mean IGM transmission defined as Tr(Lyα) = e− τ (with τ as the HI optical depth) is 79%, 69%, 59%, 55%, and 46% at redshifts 2.75, 3.22, 3.70, 4.23, and 4.77, respectively. We compared these results to measurements obtained from quasar lines of sight and found that the IGM transmission towards galaxies is in excellent agreement with quasar values up to redshift z ~ 4. We found tentative evidence for a higher IGM transmission at z ≥ 4 compared to results from QSOs, but a degeneracy between dust extinction and IGM prevents us from firmly concluding whether the internal dust extinction for star-forming galaxies at z > 4 takes a mean value significantly in excess of E(B−V) > 0.15. Most importantly, we found a large dispersion of IGM transmission along the lines of sight towards distant galaxies with 68% of the distribution within 10 to 17% of the median value in δz = 0.5 bins, similar to what is found on the lines of sight towards QSOs. We demonstrate that taking this broad range of IGM transmission into account is important when selecting high-redshift galaxies based on their colour properties (e.g. LBG or photometric redshiftselection) because failing to do so causes a significant incompleteness in selecting high-redshift galaxy populations. We finally discuss the observed IGM properties and speculate that the broad range of observed transmissions might be the result of cosmic variance and clustering along lines of sight. This clearly shows that the sources that cause this extinction need to be more completely modelled.
Key words: Galaxy: evolution / Galaxy: formation / galaxies: high-redshift / cosmology: observations / large-scale structure of Universe
© ESO, 2017
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