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Journal Articles The Astrophysical Journal Year : 2021

A Duality in the Origin of Bulges and Spheroidal Galaxies

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Luca Costantin
  • Function : Author
Pablo G. Pérez-González
  • Function : Author
Jairo Méndez-Abreu
  • Function : Author
Paola Dimauro
  • Function : Author
Belén Alcalde-Pampliega
  • Function : Author
Fernando Buitrago
  • Function : Author
Daniel Ceverino
  • Function : Author
Emanuele Daddi
  • Function : Author
Helena Domínguez-Sánchez
  • Function : Author
Néstor Espino-Briones
  • Function : Author
Antonio Hernán-Caballero
  • Function : Author
Anton M. Koekemoer
  • Function : Author
Giulia Rodighiero
  • Function : Author

Abstract

Studying the resolved stellar populations of the different structural components that 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 > 1010 M) in the GOODS-N field. We take advantage of the spectral and spatial information provided by SHARDS and Hubble Space Telescope data to perform the multi-image spectrophotometric 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 spectral energy distributions, we find evidence of a bimodal distribution of bulge formation redshifts. We find that 33% of them present old mass-weighted ages, implying a median formation redshift ${z}_{\mathrm{form}}={6.2}_{-1.7}^{+1.5}$ . They are relics of the early universe embedded in disk galaxies. A second wave, dominant in number, accounts for bulges formed at median redshift ${z}_{\mathrm{form}}={1.3}_{-0.6}^{+0.6}$ . The oldest (first-wave) bulges are more compact than the youngest. Virtually all pure spheroids (i.e., those without any disk) are coetaneous with the second-wave bulges, presenting a median redshift of formation ${z}_{\mathrm{form}}={1.1}_{-0.3}^{+0.3}$ . The two waves of bulge formation are distinguishable not only in terms of stellar ages but also in star formation mode. All first-wave bulges formed fast at z ∼ 6, with typical timescales around 200 Myr. A significant fraction of the second-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.

Dates and versions

insu-03717926 , version 1 (08-07-2022)

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Luca Costantin, Pablo G. Pérez-González, Jairo Méndez-Abreu, Marc Huertas-Company, Paola Dimauro, et al.. A Duality in the Origin of Bulges and Spheroidal Galaxies. The Astrophysical Journal, 2021, 913, ⟨10.3847/1538-4357/abef72⟩. ⟨insu-03717926⟩
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