%0 Journal Article
%A Costantin, Luca
%A Pérez González, Pablo Guillermo
%A Méndez Abreu, Jairo
%A Huertas Company, Marc
%A Dimauro, Paola
%A Alcalde Pampliega, Belén
%A Buitrago, Fernando
%A Ceverino, Daniel
%A Daddi, Emanuele
%A Domínguez Sánchez, Helena
%A Espino Briones, Néstor
%A Hernán Caballero, Antonio
%A Koekemoer, Anton M.
%A Rodighiero, Giulia
%T A duality in the origin of bulges and spheroidal galaxies
%D 2021
%@ 0004-637X
%U https://hdl.handle.net/20.500.14352/8440
%X Studying the resolved stellar populations of the different structural components which build massive galaxies directly unveils their assembly history. We aim at characterizing the stellar population properties of a representative sample of bulges and pure spheroids in massive galaxies (M* > 10^(10) Mסּ ) in the GOODS-N field. We take advantage of the spectral and spatial information provided by SHARDS and HST data to perform the multi-image spectro-photometrical decoupling of the galaxy light. We derive the spectral energy distribution separately for bulges and disks in the redshift range 0.14 < z ≤1 with spectral resolution R ∼50. Analyzing these SEDs, we find evidences of a bimodal distribution of bulge formation redshifts. We find that 33% of them present old mass-weighted ages, implying a median formation redshift z_(form) = 6.2^(+1.5)_(−1.7). They are relics of the early Universe embedded in disk galaxies. A second wave, dominant in number, accounts for bulges formed at median redshift z_(form) = 1.3^(+0.6)_(−0.6). The oldest (1st-wave) bulges are more compact than the youngest. Virtually all pure spheroids (i.e., those without any disk) are coetaneous with the 2nd-wave bulges, presenting a median redshift of formation z_(form) = 1.1^(+0.3)_(−0.3). The two waves of bulge formation are not only distinguishable in terms of stellar ages, but also in star formation mode. All 1st-wave bulges formed fast at z ∼ 6, with typical timescales around 200 Myr. A significant fraction of the 2nd-wave bulges assembled more slowly, with star formation timescales as long as 1 Gyr. The results of this work suggest that the centers of massive disk-like galaxies actually harbor the oldest spheroids formed in the Universe.
%~