A Massive Galaxy in its Core Formation Phase Three Billion Years After the Big Bang

TL;DR

This paper reports the discovery of a galaxy in the process of forming a dense stellar core 11 billion years ago, providing rare observational evidence of early core formation in massive galaxies.

Contribution

It presents the first candidate galaxy with both stellar structure and gas dynamics indicative of a forming core at high redshift.

Findings

Galaxy GOODS-N-774 has a stellar mass of 10^11 Msun.

It exhibits high gas velocity dispersion of 317 km/s.

The galaxy's properties suggest many forming cores are obscured and missed in surveys.

Abstract

Most massive galaxies are thought to have formed their dense stellar cores at early cosmic epochs. However, cores in their formation phase have not yet been observed. Previous studies have found galaxies with high gas velocity dispersions or small apparent sizes but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we present a candidate core in formation 11 billion years ago, at z=2.3. GOODS-N-774 has a stellar mass of 1.0x10^11 Msun, a half-light radius of 1.0 kpc, and a star formation rate of 90[+45-20]Msun/yr. The star forming gas has a velocity dispersion 317+-30 km/s, amongst the highest ever measured. It is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, compact quiescent galaxies at z~2 and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 appear to be rare; however, from the star formation rate and size of the galaxy we infer that many star forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.