Strange Hosts of Blue Compact Galaxies

DOI: 10.1007/10995020_58

ABSTRACT Luminous Blue Compact Galaxies (BCGs) have low metallicities, high gas consumption rates and are frequently involved in mergers.
These are properties characteristic of young galaxies in the hierarchical formation scenario. Local BCGs can therefore be
used as a complement to high redshift studies provided that the evolution of BCGs can be understood in more detail and be
applied to early galaxy formation. Although much is known about the central starburst, few studies discuss the relation between
the starburst and the progenitor, or the “host galaxy” of the starburst. Here we report of an effort to derive information
about the host from the colours of the faint halo.

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    ABSTRACT: The stellar haloes of galaxies can currently be studied either through observations of resolved halo stars or through surface photometry. Curiously, the two methods appear to give conflicting results, as a number of surface photometry measurements have revealed integrated colours that are too red to be reconciled with the halo properties inferred from the study of resolved stars. Several explanations for this anomaly have been proposed - including dust photoluminescence, extinction of extragalactic background light and a bottom-heavy stellar initial mass function. A decisive test is, however, still lacking. Here, we explain how observations of the halo of a nearby galaxy, involving a combination of both surface photometry and bright star counts, can be used to distinguish between the proposed explanations. We derive the observational requirements for this endeavour and find that star counts in filters VI and surface photometry in filters VIJ appears to be the optimal strategy. Since the required halo star counts are already available for many nearby galaxies, the most challenging part of this test is likely to be the optical surface photometry, which requires several nights of exposure time on a 4-8 m telescope, and the near-IR surface photometry, which is most readily carried out using the upcoming James Webb Space Telescope.
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    ABSTRACT: Aims: We present deep surface photometry of a volume-limited sample of 21 UM emission line galaxies in broadband optical UBVRI and near infrared (NIR) HKs filters. The sample comprises 19 blue compact galaxies (BCGs) and two spirals. Methods: We separated the burst and host populations for each galaxy and compared them to stellar evolutionary models with and without nebular emission contribution. We measured and analyzed the A180 asymmetry in all filters, the concentration index C, the scale length, and the central surface brightness of the host galaxy. Results: A shift in the average A180 asymmetry is detected from optical to NIR. This shift seems correlated with the morphological class of the BCGs. Using the color-asymmetry relation, we identify five BCGs in the sample as mergers, which is confirmed by their morphological class. Though clearly separated from normal galaxies in the concentration-asymmetry parameter space, we find that it is not possible to distinguish luminous starbursting BCGs from the merely star forming low luminosity BCGs. Reduced images (FITS files) are only available at the CDS via anonymous ftp to ( or via
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    ABSTRACT: 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 μr∼ 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.
    Monthly Notices of the Royal Astronomical Society 07/2010; 405(4):2697 - 2716. · 5.52 Impact Factor