Astrophysics Paper Published :-)

20 July 2010

Well everybody,

It has been a few years work, many revisions and peer reviewing, that has finally paid off.  Our Low Surface Bightness Galaxy (LSBG) scientific article has finally been published: LSBG paper, in a world class astrophysical journal, the British MNRAS (Monthly Notices of the Royal Astronomical Society).


An example of an edge-on LSBG, of the type that we worked on. These images are from the SDSS (Sloan Digital Sky Survey). Beautiful! 🙂

Here is what LSBGs look like face on …

You can see that LSBGs are very dim, blueish (lots of big blue stars just forming), little or no dust in the arms and almost no central brigh ball-like bulge. In short, a galaxy just forming. 

Compare the above LSBGs with …

the more developed and normal Whirlpool spiral galaxy (a “grand design” spiral: easy to trace out its arms, which seen here is interacting with a smaller elliptical galaxy). Notice too, all the darker brown-orange dust lanes and brighter central core.

Here is the abstract:

Monthly Notices of the Royal Astronomical Society

“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.”

Well, a great big THANKS to Nils and Erik, wonderful astronomers both.  And now we wait to see if our paper is quoted, neglected or starts a controversy (the last option is best 🙂 )

Best regards,



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