Spectroscopic confirmation of an ultramassive and compact galaxy at Z = 3.35: A detailed look at an early progenitor of local giant ellipticals

Z. Cemile Marsan, Danilo Marchesini, Gabriel B. Brammer, Mauro Stefanon, Adam Muzzin, Alberto Fernández-Soto, Stefan Geier, Kevin N. Hainline, Huib Intema, Alexander Karim, Ivo Labbé, Sune Toft, Pieter G.Van Dokkum

Research output: Contribution to journalArticlepeer-review

44 Scopus citations

Abstract

We present the first spectroscopic confirmation of an ultramassive galaxy at redshift z > 3 using data from Keck- NIRSPEC, VLT-X-shooter, and GTC-Osiris. We detect strong [O III] and Lyα emission, and weak [O II], C IV, and He II, placing C1-23152 at a spectroscopic redshift of zspec = 3.351. The modeling of the emission-line-corrected spectral energy distribution (SED) results in a best-fit stellar mass of M = 3.1-0.7+0.6 × 1011 M, a star formation rate of <7 Myr-1, and negligible dust extinction. The stars appear to have formed in a short intense burst ∼300-500 Myr prior to the observation epoch, setting the formation redshift of this galaxy at z ∼ 4.1. From the analysis of the line ratios and widths and the observed flux at 24 μm, we confirm the presence of a luminous hidden active galactic nucleus (AGN), with bolometric luminosity of ∼1046 erg s-1. Potential contamination of the observed SED from the AGN continuum is constrained, placing a lower limit on the stellar mass of 2 × 1011 M. HST/WFC3 H160 and ACS I814 images are modeled, resulting in an effective radius of re ∼ 1 kpc in the H160 band and a -Sti-eŕrsic index n ∼ 4.4. This object may be a prototype of the progenitors of local most massive elliptical galaxies in the first 2 Gyr of cosmic history, having formed most of its stars at z > 4 in a highly dissipative, intense, and short burst of star formation. C1-23152 is completing its transition to a post-starburst phase while hosting a powerful AGN, potentially responsible for the quenching of the star formation activity.

Original languageEnglish (US)
Article number133
JournalAstrophysical Journal
Volume801
Issue number2
DOIs
StatePublished - Mar 10 2015
Externally publishedYes

Keywords

  • galaxies: active
  • galaxies: evolution
  • galaxies: general
  • galaxies: high-redshift
  • galaxies: stellar content
  • galaxies: structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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