Volume 626, June 2019
|Number of page(s)||11|
|Published online||10 June 2019|
UV slope of z ∼ 3 bright (L > L*) Lyman-break galaxies in the COSMOS field
INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (RM), Italy
2 Carnegie Observatories, Las Campanas Observatory, Casilla 601, La Serena, Chile
Accepted: 23 January 2019
Context. The analysis of the UV slope β of Lyman-break galaxies (LBG) at different luminosities and redshifts is fundamental for understanding their physical properties, and in particular, their dust extinction.
Aims. We analyse a unique sample of 517 bright (L > L*) LBGs at redshift z ∼ 3 in order to characterise the distribution of their UV slopes β and infer their dust extinction under standard assumptions.
Methods. We exploited multi-band observations over 750 arcmin2 of the COSMOS field that were acquired with three different ground-based facilities: the Large Binocular Camera (LBC) on the Large Binocular Telescope (LBT), the Suprime-Cam on the SUBARU telescope, and the VIRCAM on the VISTA telescope (ULTRAVISTA DR2). Our multi-band photometric catalogue is based on a new method that is designed to maximise the signal-to-noise ratio in the estimate of accurate galaxy colours from images with different point spread functions (PSF). We adopted an improved selection criterion based on deep Y-band data to isolate a sample of galaxies at z ∼ 3 to minimise selection biases. We measured the UV slopes (β) of the objects in our sample and then recovered the intrinsic probability density function of β values (PDF(β)), taking into account the effect of observational uncertainties through detailed simulations.
Results. The galaxies in our sample are characterised by mildly red UV slopes with ⟨β⟩≃ − 1.70 throughout the enitre luminosity range that is probed by our data (−24 ≲ M1600 ≲ −21). The resulting dust-corrected star formation rate density (SFRD) is log(SFRD)≃ − 1.6 M⊙ yr−1 Mpc−3, corresponding to a contribution of about 25% to the total SFRD at z ∼ 3 under standard assumptions.
Conclusions. Ultra-bright LBGs at z ∼ 3 match the known trends, with UV slopes being redder at decreasing redshifts, and brighter galaxies being more highly dust extinct and more frequently star-forming than fainter galaxies.
Key words: catalogs / galaxies: high-redshift / galaxies: evolution
© ESO 2019
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