The red haloes of SDSS low surface brightness disc galaxies

被引:21
作者
Bergvall, Nils [1 ]
Zackrisson, Erik [2 ]
Caldwell, Brady [1 ]
机构
[1] Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden
[2] Stockholm Univ, Dept Astron, Oscar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden
基金
美国国家航空航天局; 美国国家科学基金会; 瑞典研究理事会; 芬兰科学院;
关键词
stars: low-mass; galaxies: haloes; galaxies: photometry; galaxies: stellar content; galaxies: structure; diffuse radiation; INITIAL MASS FUNCTION; STELLAR POPULATION SYNTHESIS; DIGITAL SKY SURVEY; LARGE-MAGELLANIC-CLOUD; GIANT BRANCH STARS; NGC; 5907; MILKY-WAY; SYNTHESIS MODELS; LOCAL UNIVERSE; DATA RELEASE;
D O I
10.1111/j.1365-2966.2010.16650.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
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.
引用
收藏
页码:2697 / 2716
页数:20
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