* Astronomy

Blobrana · L

RE: Submillimetre-bright Galaxies

Blobrana · L

Using a special camera known as AzTEC developed by a research team led by Grant Wilson, astronomy professor at the University of Massachusetts Amherst, an international research group has imaged a set of ultra-massive galaxies that are thought to form the backbone of a super large structure, or collection of galaxies congregated together, in the very early universe.
The cluster of galaxies about 11.5 billion light years away is described in a recent issue of the journal, Nature, by lead investigator Yoichi Tamura of the University of Tokyo and Japans National Astronomy Observatory (NAOJ), with colleagues at UMass Amherst and other universities in Mexico and the United States. Their findings are very valuable for understanding how galaxies formed in the early universe, when it was less than 2 billion years old, and at a time when clusters of galaxies were just beginning to be formed, the researchers say. The universe is estimated to be about 13.7 billion years old.
For this study, astronomer Min Yun at UMass Amherst, with Wilson and graduate students Jason Austermann, Kimberly Scott and others, pointed the telescope and the AzTEC camera toward the constellation Aquarius, an area known since the 1990s for hosting hundreds of small yet optically bright galaxies called Lyman alpha emitters in the remote Universe.

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Title: Spitzer IRAC Infrared Colours of Submillimetre-bright Galaxies
Authors: Min S. Yun, I. Aretxaga, M. L. N. Ashby, J. Austermann, G. G. Fazio, M. Giavalisco, J.-S. Huang, D. H. Hughes, S. Kim, J. D. Lowenthal, T. Perera, K. Scott, G. W. Wilson, J. D. Younger

High-redshift submillimetre-bright galaxies identified by blank field surveys at millimetre and submillimetre wavelengths appear in the region of the IRAC colour-colour diagrams previously identified as the domain of luminous active galactic nuclei (AGNs). Our analysis using a set of empirical and theoretical dusty starburst spectral energy distribution (SED) models shows that power-law continuum sources associated with hot dust heated by young (<100 Myr old), extreme starbursts at z>2 also occupy the same general area as AGNs in the IRAC colour-colour plots. A detailed comparison of the IRAC colours and SEDs demonstrates that the two populations are distinct from each other, with submillimetre-bright galaxies having a systematically flatter IRAC spectrum (>1 mag bluer in the observed [4.5]-[8.0] colour). Only about 20% of the objects overlap in the colour-colour plots, and this low fraction suggests that submillimetre galaxies powered by a dust-obscured AGN are not common. The red IR colours of the submillimetre galaxies are distinct from those of the ubiquitous foreground IRAC sources, and we propose a set of IR colour selection criteria for identifying SMG counterparts that can be used even in the absence of radio or Spitzer MIPS 24 micron data.

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