Blue stuff in the cores of rich clusters: what is it?
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JeanTate
Here's an example, SDSS J155006.65+341945.8 (ignore the zph, it's almost certainly wrong), in the heart of a z ~0.43 rich cluster:
Back in the original Galaxy Zoo, I often noticed such things, but failed to take notes. And every now and then, Dolorous_Edd posts something similar, e.g. in this Discussion thread, and here (this latter one is a confirmed EELR 😃).
Is there a collection of such objects somewhere here in GZ Talk, or a Discussion thread devoted to them (I tried to find such, using Search, but came up blank)? Have you come across these sorts of things? How (and where) did you note them?
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mlpeck
Maybe just a galaxy? The "Butcher-Oemler effect" was at one time at least one of the great mysteries of extragalactic astrophysics. Also, the first K+A galaxies were found in cluster environments at redshifts comparable to this one: https://ui.adsabs.harvard.edu/#abs/1983ApJ...270....7D/abstract.
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JeanTate
in response to mlpeck's comment.
Thanks mlpeck.
It would be quite surprising if all these blue objects are an astrophysically homogeneous class. Some are surely foreground galaxies (i.e. chance alignments with much lower z galaxies); some may be EELRs (if at z>~0.3, they could be very interesting, not least because they could be very big); some may be AGN-dominated galaxies in the cluster (AGN with blue continua); some ...
Perhaps a fun mini-project? 😃
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