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Khusanova, Y.; Le Fèvre, O.; Cassata, P.; Cucciati, O.; Lemaux, B. C.; Tasca, L. A. M.; Thomas, R.; Garilli, B.; Le Brun, V.; Maccagni, D.; Pentericci, L.; Zamorani, G.; Amorín, R.; Bardelli, S.; Castellano, M.; Cassarà, L. P.; Cimatti, A.; Giavalisco, M.; Hathi, N. P.; Ilbert, O.; Koekemoer, A. M.; Marchi, F.; Pforr, J.; Ribeiro, B.; Schaerer, D.; Tresse, L.; Vergani, D.; Zucca, E.
Astronomy and astrophysics (Berlin), 02/2020, Letnik: 634Journal Article
Context. The star formation rate density (SFRD) evolution presents an area of great interest in the studies of galaxy evolution and reionization. The current constraints of SFRD at z > 5 are based on the rest-frame UV luminosity functions with the data from photometric surveys. The VIMOS UltraDeep Survey (VUDS) was designed to observe galaxies at redshifts up to ∼6 and opened a window for measuring SFRD at z > 5 from a spectroscopic sample with a well-controlled selection function. Aims. We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization (5.0 ≤ z ≤ 6.6) from a large sample of 49 galaxies with spectroscopically confirmed redshifts. We determine the rest-frame UV and Ly α luminosity functions and use them to calculate SFRD at the median redshift of our sample z = 5.6. Methods. We selected a sample of galaxies at 5.0 ≤ z spec ≤ 6.6 from the VUDS. We cleaned our sample from low redshift interlopers using ancillary photometric data. We identified galaxies with Ly α either in absorption or in emission, at variance with most spectroscopic samples in the literature where Ly α emitters (LAE) dominate. We determined luminosity functions using the 1/ V max method. Results. The galaxies in this redshift range exhibit a large range in their properties. A fraction of our sample shows strong Ly α emission, while another fraction shows Ly α in absorption. UV-continuum slopes vary with luminosity, with a large dispersion. We find that star-forming galaxies at these redshifts are distributed along the main sequence in the stellar mass vs. SFR plane, described with a slope α = 0.85 ± 0.05. We report a flat evolution of the specific SFR compared to lower redshift measurements. We find that the UV luminosity function is best reproduced by a double power law, while a fit with a Schechter function is only marginally inferior. The Ly α luminosity function is best fitted with a Schechter function. We derive a logSFRD UV ( M ⊙ yr −1 Mpc −3 ) = −1.45 +0.06 −0.08 and logSFRD Ly α ( M ⊙ yr −1 Mpc −3 ) = −1.40 +0.07 −0.08 . The SFRD derived from the Ly α luminosity function is in excellent agreement with the UV-derived SFRD after correcting for IGM absorption. Conclusions. Our new SFRD measurements at a mean redshift of z = 5.6 are ∼0.2 dex above the mean SFRD reported in Madau & Dickinson (2014, ARA&A, 52, 415), but in excellent agreement with results from Bouwens et al. (2015a, ApJ, 803, 34). These measurements confirm the steep decline of the SFRD at z > 2. The bright end of the Ly α luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest LAE at these redshifts. LAE with equivalent width EW > 25 Å contribute to about 75% of the total UV-derived SFRD. While our analysis favors low dust content in 5.0 < z < 6.6, uncertainties on the dust extinction correction and associated degeneracy in spectral fitting will remain an issue, when estimating the total SFRD until future surveys extending spectroscopy to the NIR rest-frame spectral domain, such as with JWST.
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JCR | SNIP | JCR | SNIP | JCR | SNIP | JCR | SNIP |
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