The existence of massive (1011 solar masses) elliptical galaxies by redshift z ≈ 4 (refs 1, 2, 3; 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 lower4. The only known galaxies with very high star-formation rates at z > 6 are, with one exception5, the host galaxies of quasars6, 7, 8, 9, but these galaxies also host accreting supermassive (more than 109 solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([C ii] at a wavelength of 158 micrometres) in four galaxies at z > 6 that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 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 [C ii] 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 [C ii] brightness, linewidth and implied dynamical mass, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift10, 11, 12. We find such close companions in four out of the twenty-five z > 6 quasars surveyed, a fraction that needs to be accounted for in simulations13, 14. If they are representative of the bright end of the [C ii] luminosity function, then they can account for the population of massive elliptical galaxies at z ≈ 4 in terms of the density of cosmic space.
At a glance
- A substantial population of massive quiescent galaxies at z ~ 4 from ZFOURGE. Astrophys. J. 783, L14 (2014) et al.
- A study of massive and evolved galaxies at high redshift. Astrophys. J. 794, 68 (2014) et al.
- Quiescent galaxies in the 3D-HST survey: spectroscopic confirmation of a large number of galaxies with relatively old stellar populations at z ~ 2. Astrophys. J. 770, L39 (2013) et al.
- UV luminosity functions at redshifts z ~ 4 to z ~ 10: 10,000 galaxies from HST legacy fields. Astrophys. J. 803, 34 (2015) et al.
- A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34. Nature 496, 329–333 (2013) et al.
- Dust emission from the most distant quasars. Astron. Astrophys. 406, L55–L58 (2003) et al.
- A kiloparsec-scale hyper-starburst in a quasar host less than 1 gigayear after the Big Bang. Nature 457, 699–701 (2009) et al.
- Star formation and gas kinematics of quasar host galaxies at z ~ 6: new insights from ALMA. Astrophys. J. 773, 44 (2013) et al.
- Cool gas in high-redshift galaxies. Annu. Rev. Astron. Astrophys. 51, 105–161 (2013) &
- Molecular gas and dust around a radio-quiet quasar at redshift 4.69. Nature 382, 428–431 (1996) et al.
- ALMA observations show major mergers among the host galaxies of fast-growing, high-redshift supermassive black holes. Astrophys. J. 836, 8 (2017) et al.
- ALMA imaging of gas and dust in a galaxy protocluster at redshift 5.3: [C ii] emission in “typical” galaxies and dusty starbursts ≈1 billion years after the Big Bang. Astrophys. J. 796, 84 (2014) et al.
- The formation of submillimetre-bright galaxies from gas infall over a billion years. Nature 525, 496–499 (2015) et al.
- On the number density of ‘direct collapse’ black hole seeds. Mon. Not. R. Astron. Soc. 463, 529–540 (2016) , , , &
- [C ii] 158 μm emission as a star formation tracer. Astrophys. J. 800, 1 (2015) et al.
- The applicability of far-infrared fine-structure lines as star formation rate tracers over wide ranges of metallicities and galaxy types. Astron. Astrophys. 568, A62 (2014) et al.
- The Pan-STARRS1 distant z > 5.6 quasar survey: more than 100 quasars within the first Gyr of the universe. Astrophys. J. Suppl. Ser. 227, 11 (2016) et al.
- ALMA spectroscopic survey in the Hubble Ultra Deep Field: survey description. Astrophys. J. 833, 67 (2016) et al.
- A survey of molecular gas in luminous sub-millimetre galaxies. Mon. Not. R. Astron. Soc. 429, 3047–3067 (2013) et al.
- 350 μm dust emission from high-redshift quasars. Astrophys. J. 642, 694–694 (2006) et al.
- Submillimeter spectrum and dust mass of the primeval galaxy IRAS 10214+4724. Astrophys. J. 398, L25–L27 (1992) et al.
- Measures of galaxy dust and gas mass with Herschel photometry and prospects for ALMA. Astron. Astrophys. 587, A73 (2016) , , , &
- Far-infrared fine-structure line diagnostics of ultraluminous infrared galaxies. Astrophys. J. 776, 38 (2013) et al.
- Far-infrared spectroscopy of normal galaxies: physical conditions in the interstellar medium. Astrophys. J. 561, 766–786 (2001) et al.
- The ALMA spectroscopic survey in the Hubble Ultra Deep Field: search for [C ii] line and dust emission in 6 < z < 8 galaxies. Astrophys. J. 833, 71 (2016) et al.
- An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field-South: detection of [C ii] at z = 4.4. Mon. Not. R. Astron. Soc. 427, 1066–1074 (2012) et al.
- https://arxiv.org/abs/1701.01114 (2017) , , & Strong clustering of Lyman break galaxies around luminous quasars at z~4. Preprint at
- ALMA spectroscopic survey in the Hubble Ultra Deep Field: the infrared excess of UV-selected z = 2–10 galaxies as a function of UV-continuum slope and stellar mass. Astrophys. J. 833, 72 (2016) et al.
- Galaxies at redshifts 5 to 6 with systematically low dust content and high [C ii] emission. Nature 522, 455–458 (2015) et al.
- Star formation in the Milky Way and nearby galaxies. Annu. Rev. Astron. Astrophys. 50, 531–608 (2012) &