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

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.

To appear in Nature

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• Stellar populations from spectroscopy of a large sample of quiescent galaxies at z > 1: Measuring the contribution of progenitor bias to early size growth
• Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z$\gtrsim$2: High velocity dispersions in progenitors of compact quiescent galaxies
• CANDELS: Elevated Black Hole Growth in the Progenitors of Compact Quiescent Galaxies at z~2
• Spectroscopic Confirmation of an Ultra Massive and Compact Galaxy at z=3.35: A Detailed Look at an Early Progenitor of Local Most Massive Ellipticals
• Low Gas Fractions Connect Compact Star-Forming Galaxies to their z ~ 2 Quiescent Descendants
• From Diversity to Dichotomy, and Quenching: Milky-Way-Like and Massive-Galaxy Progenitors at 0.5<z<3.0
• One Plane for All: Massive Star-Forming and Quiescent Galaxies Lie on the Same Mass Fundamental Plane at z~0 and z~0.7
• The interstellar medium and feedback in the progenitors of the compact passive galaxies at z~2
• A controlled study of cold dust content in galaxies from $z=0-2$
• Evidence for Reduced Specific Star Formation Rates in the Centers of Massive Galaxies at z = 4
• Fluctuation Spectroscopy: A New Probe of Old Stellar Populations
• Unravelling the Origin of the Counter-Rotating Core in IC 1459 with KMOS and MUSE