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Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6

Authors :
Decarli, Roberto
Walter, Fabian
Venemans, Bram P.
Bañados, Eduardo
Bertoldi, Frank
Carilli, Chris
Fan, Xiaohui
Farina, Emanuele Paolo
Mazzucchelli, Chiara
Riechers, Dominik
Rix, Hans-Walter
Strauss, Michael
Wang, Ran
Yang, Yujin
Publication Year :
2017

Abstract

The existence of massive ($10^{11}$ solar masses) elliptical galaxies by redshift z~4 (when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z>6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower. The only known galaxies with very high star-formation rates at z>6 are, with only one exception, the host galaxies of quasars, but these galaxies also host accreting supermassive (more than $10^9$ solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([CII] at a wavelength of 158 micrometres) in four galaxies at z>6 that are companions of quasars, with velocity offsets of less than 600 kilometers per second and linear offsets of less than 600 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [CII] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [CII] brightness, linewidth and implied dynamical masses, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift. We find such close companions in four out of twenty-five z>6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [CII] luminosity function, then they can account for the population of massive elliptical galaxies at z~4 in terms of cosmic space density.<br />Comment: Nature, in press

Details

Database :
arXiv
Publication Type :
Report
Accession number :
edsarx.1705.08662
Document Type :
Working Paper
Full Text :
https://doi.org/10.1038/nature22358