The observed UV rest-frame spectra of distant galaxies are the result of their intrinsic emission combined with absorption along theline 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 fittedmodel spectra combined with a range of IGM transmission to the galaxy spectra using the spectral fitting algorithm GOSSIP+. Weused these fits to derive the mean IGM transmission towards each galaxy for several redshift slices from z = 2:5 to z = 5:5. Wefound 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% atredshifts 2.75, 3.22, 3.70, 4.23, and 4.77, respectively.We compared these results to measurements obtained from quasar lines of sightand found that the IGM transmission towards galaxies is in excellent agreement with quasar values up to redshift z∼ 4. We foundtentative evidence for a higher IGM transmission at z ≥ 4 compared to results from QSOs, but a degeneracy between dust extinctionand IGM prevents us from firmly concluding whether the internal dust extinction for star-forming galaxies at z >4 takes a mean valuesignificantly in excess of E(B-V) > 0:15. Most importantly, we found a large dispersion of IGM transmission along the lines of sighttowards distant galaxies with 68% of the distribution within 10 to 17% of the median value in δ z = 0:5 bins, similar to what is foundon the lines of sight towards QSOs. We demonstrate that taking this broad range of IGM transmission into account is important whenselecting high-redshift galaxies based on their colour properties (e.g. LBG or photometric redshift selection) because failing to do socauses a significant incompleteness in selecting high-redshift galaxy populations.We finally discuss the observed IGM properties andspeculate 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.
VIMOS Ultra-Deep Survey (VUDS): IGM transmission towards galaxies with 2.5 < z < 5.5 and the colour selection of high-redshift galaxies / Thomas, R.; Le Fèvre, O.; Le Brun, V.; Cassata, P.; Garilli, B.; Lemaux, B.C.; Maccagni, D.; Pentericci, L.; Tasca, L.A.M.; Zamorani, G.; Zucca, E.; Amorin, R.; Bardelli, S.; Cassarà, L.; Castellano, M.; Cimatti, A.; Cucciati, O.; Durkalec, A.; Fontana, A.; Giavalisco, M.; Grazian, A.; Hathi, N.P.; Ilbert, O.; Paltani, S.; Pforr, J.; Ribeiro, B.; Schaerer, D.; Scodeggio, M.; Sommariva, V.; Talia, M.; Tresse, L.; Vanzella, E.; Vergani, D.; Capak, P.; Charlot, S.; Contini, T.; Cuby, J.G.; De La Torre, S.; Dunlop, J.; Fotopoulou, S.; Koekemoer, A.; López-Sanjuan, C.; Mellier, Y.; Salvato, M.; Scoville, N.; Taniguchi, Y.; Wang, P.W.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - STAMPA. - 597:(2017), pp. A88.A88-A88.A104. [10.1051/0004-6361/201425342]
VIMOS Ultra-Deep Survey (VUDS): IGM transmission towards galaxies with 2.5 < z < 5.5 and the colour selection of high-redshift galaxies
CIMATTI, ANDREA;TALIA, MARGHERITA;
2017
Abstract
The observed UV rest-frame spectra of distant galaxies are the result of their intrinsic emission combined with absorption along theline 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 fittedmodel spectra combined with a range of IGM transmission to the galaxy spectra using the spectral fitting algorithm GOSSIP+. Weused these fits to derive the mean IGM transmission towards each galaxy for several redshift slices from z = 2:5 to z = 5:5. Wefound 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% atredshifts 2.75, 3.22, 3.70, 4.23, and 4.77, respectively.We compared these results to measurements obtained from quasar lines of sightand found that the IGM transmission towards galaxies is in excellent agreement with quasar values up to redshift z∼ 4. We foundtentative evidence for a higher IGM transmission at z ≥ 4 compared to results from QSOs, but a degeneracy between dust extinctionand IGM prevents us from firmly concluding whether the internal dust extinction for star-forming galaxies at z >4 takes a mean valuesignificantly in excess of E(B-V) > 0:15. Most importantly, we found a large dispersion of IGM transmission along the lines of sighttowards distant galaxies with 68% of the distribution within 10 to 17% of the median value in δ z = 0:5 bins, similar to what is foundon the lines of sight towards QSOs. We demonstrate that taking this broad range of IGM transmission into account is important whenselecting high-redshift galaxies based on their colour properties (e.g. LBG or photometric redshift selection) because failing to do socauses a significant incompleteness in selecting high-redshift galaxy populations.We finally discuss the observed IGM properties andspeculate 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
