A Kiloparsec-Scale Hyper-Starburst in a Quasar Host Less than 1 Gigayear after the Big Bang

TL;DR

This paper presents a high-resolution observation of a quasar host galaxy at redshift 6.42, revealing a large, intense starburst region of about 750pc, indicating early formation of massive spheroidal structures less than a billion years after the Big Bang.

Contribution

It provides the first spatially resolved imaging of star-forming gas in an early Universe galaxy, showing a large-scale hyper-starburst in a quasar host less than 1 Gyr after the Big Bang.

Findings

Star formation occurs over a ~750pc region.

Surface density of star formation rate is ~1000 M_sun/yr/kpc^2.

Starburst likely leads to formation of a massive spheroid.

Abstract

The host galaxy of the quasar SDSS J114816.64+525150.3 (at redshift z=6.42, when the Universe was <1 billion years old) has an infrared luminosity of 2.2x10^13 L_sun, presumably significantly powered by a massive burst of star formation. In local examples of extremely luminous galaxies such as Arp220, the burst of star formation is concentrated in the relatively small central region of <100pc radius. It is unknown on which scales stars are forming in active galaxies in the early Universe, which are likely undergoing their initial burst of star formation. We do know that at some early point structures comparable to the spheroidal bulge of the Milky Way must have formed. Here we report a spatially resolved image of [CII] emission of the host galaxy of J114816.64+525150.3 that demonstrates that its star forming gas is distributed over a radius of ~750pc around the centre. The surface density of the star formation rate averaged over this region is ~1000 M_sun/yr/kpc^2. This surface density is comparable to the peak in Arp220, though ~2 orders of magnitudes larger in area. This vigorous star forming event will likely give rise to a massive spheroidal component in this system.