From CfA: “Massive Galaxies in the Early Universe”

Harvard Smithsonian Center for Astrophysics

Center For Astrophysics

February 2, 2018

The South Pole Telescope (SPT) is a 10-meter-diameter telescope in the Antarctic that has been operating at millimeter- and submillimeter-waves for a decade; the CfA is an institutional member of the collaboration.

South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the National Institute for Standards and Technology. It is funded by the National Science Foundation.

For the past six years it has been surveying the sky in a search for galaxies in the first few billion years of cosmic history; they are thought to be preferentially detectable at these wavelengths because their dust has been heated by the ultraviolet light of young stars. One of SPT discoveries, the galaxy SPT0311–58, has upon further investigation turned out to date from an epoch a mere 780 million years after the big bang. It is the most distant known case of this postulated but previously undetected population of optically dim but infrared luminous clusters.

CfA astronomers Chris Hayward, Matt Ashby and Tony Stark are members of the SPT team that made the discovery and then followed up with the Spitzer Space Telescope, the ALMA array, the Hubble Space Telescope, and the Gemini optical/infrared telescope.

NASA/Spitzer Infrared Telescope

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

NASA/ESA Hubble Telescope

Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

The scientists were able to determine the cluster’s distance and epoch from the redshift of its spectral features, including a line of ionized carbon, and to characterize the overall emission properties across a wider range of wavelengths. The Spitzer and Hubble images of the source revealed the presence of a foreground galaxy that is acting as a gravitational lens to magnify SPT0311-58 and thus greatly facilitated its detection. The ALMA measurements at high spatial resolution found that the original source is actually two galaxies less than twenty-five thousand light-years apart. The implication is that these two galaxies are in the midst of colliding.

The masses of the two galaxies are nearly one hundred billion and ten billion solar masses, respectively. The larger one is more massive than any other known galaxy at this early time in cosmic evolution, a period during which many galaxies are thought to be just forming, and is very bright, making new stars at a rate of about 2900 solar masses per year (thousands of times faster than the Milky Way). Although current models of cosmic evolution do not preclude such giant systems from existing at such early times, the observation does push the models to its limits. The results also imply that there should be a dark-matter halo present with more than 400 billion solar masses, among the rarest dark-matter haloes that should exist in the early universe.


Galaxy Growth in a Massive Halo in the First Billion Years of Cosmic History, D. P. Marrone, J. S. Spilker, C. C. Hayward, J. D. Vieira, M. Aravena, M. L. N. Ashby, M. B. Bayliss, M. B’ethermin, M. Brodwin, M. S. Bothwell, J. E. Carlstrom, S. C. Chapman, Chian-Chou Chen, T. M. Crawford;, D. J. M. Cunningham, C. De Breuck, C. D. Fassnacht, A. H. Gonzalez, T. R. Greve, Y. D. Hezaveh, K. Lacaille, K. C. Litke, S. Lower, J. Ma, M. Malkan, T. B. Miller, W. R. Morningstar, E. J. Murphy, D. Narayanan, K. A. Phadke, K. M. Rotermund, J. Sreevani, B. Stalder, A. A. Stark, M. L. Strandet, M. Tang, & A. Weiß, Nature, 553, 51, 2018.

a, Emission in the 157.74-μm fine-structure line of ionized carbon ([C ii]) as measured at 240.57 GHz with ALMA, integrated over 1,500 km s−1 of velocity, is shown with the colour scale. The range in flux per synthesized beam (the 0.25″ × 0.30″ beam is shown in the lower left) is provided at right. The rest-frame 160-μm continuum emission that was measured simultaneously is overlaid, with contours at 8, 16, 32 and 64 times the noise level of 34 μJy per beam. SPT0311−58 E and SPT0311−58 W are labelled. b, The continuum-subtracted, source-integrated [C ii] (red) and [O iii] (blue) spectra. The upper spectra are as observed (‘apparent’) with no correction for lensing, whereas the lensing-corrected (‘intrinsic’) [C ii] spectrum is shown at the bottom. SPT0311−58 E and SPT0311−58 W separate almost completely at a velocity of 500 km s−1. c, The source-plane structure after removing the effect of gravitational lensing. The image is coloured according to the flux-weighted mean velocity, showing that the two objects are physically associated but separated by roughly 700 km s−1 in velocity and 8 kpc (projected) in space. The reconstructed 160-μm continuum emission is shown as contours. The scale bar represents the angular size of 5 kpc in the source plane. d, The line-to-continuum ratio at the 158-μm wavelength of [C ii], normalized to the map peak. The [C ii] emission from SPT0311−58 E is much brighter relative to its continuum than for SPT0311−58 W. e, Velocity-integrated emission in the 88.36-μm fine-structure line of doubly ionized oxygen ([O iii]) as measured at 429.49 GHz with ALMA (colour scale). The data have an intrinsic angular resolution of 0.2″ × 0.3″, but have been tapered to 0.5″ owing to the lower signal-to-noise ratio of these data. f, The luminosity ratio between the [O iii] and [C ii] lines. As for the [C ii] line-to-continuum ratio, a large disparity is seen between SPT0311−58 E and SPT0311−58 W. The sky coordinates and contours for rest-frame 160-μm continuum emission in d–f are the same as in a.

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