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Bulgeless galaxies in the COSMOS field: environment and star formation evolution at z < 1

M. Grossi, C. A. C Fernandes, D. Sobral, J. Afonso, E. Telles, L. Bizzocchi, A. Paulino-Afonso, I. Matute

Abstract
Combining the catalogue of galaxy morphologies in the COSMOS field and the sample of H α emitters at redshifts z = 0.4 and z = 0.84 of the HiZELS survey, we selected ∼ 220 star-forming bulgeless systems (Sérsic index n ≤ 1.5) at both epochs. We present their star formation properties and we investigate their contribution to the star formation rate function (SFRF) and global star formation rate density (SFRD) at z < 1. For comparison, we also analyse H α emitters with more structurally evolved morphologies that we split into two classes according to their Sérsic index n: intermediate (1.5 < n ≤ 3) and bulge-dominated (n > 3). At both redshifts, the SFRF is dominated by the contribution of bulgeless galaxies and we show that they account for more than 60 per cent of the cosmic SFRD at z < 1. The decrease of the SFRD with redshift is common to the three morphological types, but it is stronger for bulge-dominated systems. Star-forming bulgeless systems are mostly located in regions of low to intermediate galaxy densities (Σ ∼ 1–4 Mpc−2) typical of field-like and filament-like environments and their specific star formation rates (sSFRs) do not appear to vary strongly with local galaxy density. Only few bulgeless galaxies in our sample have high (sSFR > 10−9 yr−1) and these are mainly low-mass systems. Above M* ∼ 1010 M bulgeless are evolving at a ‘normal’ rate (10−9 yr−1 < sSFR < 10−10 yr−1) and in the absence of an external trigger (i.e. mergers/strong interactions) they might not be able to develop a central classical bulge.

Keywords
galaxies: bulges; galaxies: evolution; galaxies: star formation; galaxies: structure; galaxies: luminosity function; mass function

Monthly Notices of the Royal Astronomical Society
Volume 475, Issue 1, Page 735
2018 March

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia