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The red haloes of SDSS low surface brightness disc galaxies
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
2010 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 405, no 4, 2697-2716 p.Article in journal (Refereed) Published
Abstract [en]

The faint stellar haloes of galaxies contain key information about the oldest stars and the process of galaxy formation. A previous study of stacked SDSS images of disc galaxies has revealed a halo with an abnormally red r - i colour, seemingly inconsistent with our current understanding of the stellar populations inhabiting stellar haloes. Measurements of this type are, however, plagued by large uncertainties which calls for follow-up studies. Here, we investigate the statistical properties of the faint envelopes of low surface brightness disc galaxies to look for further support for a red excess. A total of 1510 nearly edge-on, bulgeless low surface brightness galaxies were selected from the SDSS Data Release 5, rescaled to the same apparent size, aligned and stacked. This procedure allows us to reach a surface brightness of mu(r) similar to 31 mag arcsec-2. After a careful assessment of instrumental light scattering effects in the stacked images, we derive median and average radial surface brightness and colour profiles in g, r and i. The sample is then divided into three subsamples according to g - r colour. All three samples exhibit a red colour excess in r - i in the thick disc/halo region. The halo colours of the full sample, g - r = 0.60 +/- 0.15 and r - i = 0.80 +/- 0.15, are found to be incompatible with the colours of any normal type of stellar population. The fact that no similar colour anomaly is seen at comparable surface brightness levels along the disc rules out a sky subtraction residual as the source of the extreme colours. A number of possible explanations for these abnormally red haloes are discussed. We find that two different scenarios - dust extinction of extragalactic background light and a stellar population with a very bottom-heavy initial mass function - appear to be broadly consistent with our observations and with similar red excesses reported in the haloes of other types of galaxies.

Place, publisher, year, edition, pages
2010. Vol. 405, no 4, 2697-2716 p.
Keyword [en]
stars: low-mass, galaxies: haloes, galaxies: photometry, galaxies: stellar content, galaxies: structure, diffuse radiation
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-49901DOI: 10.1111/j.1365-2966.2010.16650.xISI: 000279450900046OAI: diva2:380429
authorCount :3Available from: 2010-12-21 Created: 2010-12-20 Last updated: 2011-05-09Bibliographically approved

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Zackrisson, Erik
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Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)
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