A massive, quiescent galaxy at a redshift of 3.717

• Published in: Nature (London) Vol. 544; no. 7648; pp. 71 - 74
• Main Authors: Glazebrook, Karl, Schreiber, Corentin, Labbé, Ivo, Nanayakkara, Themiya, Kacprzak, Glenn G., Oesch, Pascal A., Papovich, Casey, Spitler, Lee R, Straatman, Caroline M. S., Tran, Kim-Vy H., Yuan, Tiantian
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06-04-2017; Nature Publishing Group
• Subjects: 639/33/34/124; 639/33/34/863; Age; Dark matter; Galaxies; Humanities and Social Sciences; letter; multidisciplinary; Observations; Redshift; Science; Space telescopes; Spectrum analysis; Star & galaxy formation; Stars & galaxies; Universe
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature21680

A massive ancient galaxy with minimal star formation is observed spectroscopically at an epoch when the Universe is less than 2 billion years old, posing a challenge to theories.
Galaxies prematurely aged
Deep astronomical surveys have provided evidence for groups of massive, quiescent galaxies at high redshifts, but this poses a problem: theoretical models do not account for galaxies that stopped forming stars so early in the history of the Universe. Detecting such galaxies is an observational challenge owing to their negligible rest-frame ultraviolet emission and the need for extremely deep near-infrared surveys—the evidence has so far consisted entirely of coarsely sampled photometry. Karl Glazebrook
et al
. report spectroscopic confirmation of one of these galaxies at a redshift of 3.717, with a stellar mass of 1.7 × 10
11
solar masses. The absorption line spectrum shows no current star-formation, and the age of the galaxy is derived to be nearly half that of the Universe. The authors suggest that the galaxy formed its stars in an extreme and short starburst within the first billion years of cosmic history, implying that our picture of galaxy formation may need an update.
Finding massive galaxies that stopped forming stars in the early Universe presents an observational challenge because their rest-frame ultraviolet emission is negligible and they can only be reliably identified by extremely deep near-infrared surveys. These surveys have revealed the presence of massive, quiescent early-type galaxies
1
,
2
,
3
,
4
,
5
,
6
appearing as early as redshift
z
 ≈ 2, an epoch three billion years after the Big Bang. Their age and formation processes have now been explained by an improved generation of galaxy-formation models
7
,
8
,
9
, in which they form rapidly at
z
 ≈ 3–4, consistent with the typical masses and ages derived from their observations. Deeper surveys have reported evidence for populations of massive, quiescent galaxies at even higher redshifts and earlier times, using coarsely sampled photometry. However, these early, massive, quiescent galaxies are not predicted by the latest generation of theoretical models
7
,
8
,
9
,
10
. Here we report the spectroscopic confirmation of one such galaxy at redshift
z
 = 3.717, with a stellar mass of 1.7 × 10
11
solar masses. We derive its age to be nearly half the age of the Universe at this redshift and the absorption line spectrum shows no current star formation. These observations demonstrate that the galaxy must have formed the majority of its stars quickly, within the first billion years of cosmic history in a short, extreme starburst. This ancestral starburst appears similar to those being found by submillimetre-wavelength surveys
11
,
12
,
13
,
14
. The early formation of such massive systems implies that our picture of early galaxy assembly requires substantial revision.