[vsnet-alert 11036] Re: re CSS090201:090210-113032 : problematic2MASScolours

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-------- Original Message --------
From: Michael Linnolt <linnolt at hawaii.edu>

> Mine is a valid description of Malmquist effect or error, just as Brian put it too. Its really a simple thing in principle, I don't see the point of your belabored essay on the various alternate descriptions. <

The original Malmquist Bias is not about detection limits per se, it's about seeing only part of a population for limit connected reasons.  In distant galaxy clusters only bright galaxies were seen and galaxy clusters were not truthfully categorised with respect to their actual populations, and wrong conclusions about such clusters and consequently cosmology derived.  There were no error bars involved.  As a selection effect it's got dragged into flux limited instrumentation arguments at times, but in the literature it primarily expresses itself in terms of population samples.

So afore you get shirty, get read the link I googled, not wikipedia.
 
> Thus the seasoned visual observer using proper technique is going to provide better data at the instrumental limit as compared to electronic measurement.<

The seasoned instrumental observer using proper, or more correctly _contextually relevant_, technique is no different to the seasoned visual observer doing so.

2MASS is a dirty great big survey with a pipeline milking every last damn photon.  It can be used and abused however the user and abuser wishes, but carries flags and data for the cautious to be able to work with it in the individual sense, object per object, and what they do with what they get is their responsibility.  Not an inherent limitation of the 2MASS survey.

The quoted limits are somewhat rule of thumb guidelines expressed by the 2MASS people, who then go on to stress use the flags and other provided information.

(The use of the 2MASS data in bulk for statistical assessment of Galactical populations seems to be only just kicking in, going by recent arxivs, in those contexts the trend usually outweighs the outliers for a good quality survey).

Using any survey near its limits is problematic.

The eyeball-brain combination is a connected photon gathering instrument which utilises electromagnetic radiation.  There is no inherent superiority to it.  Tom Droege used to insist CCD was far superior to eye, you insist eye is far superior to CCD.  As long as the measurement being taken is relevant to the context of the object being measured and the result being looked for either system is fine.  If there are many examples of people not doing it right it doesn't mean it's inherently wrong.

You divorce general principles from instrumentation and insist they're only applicable to hominid eye-brain scenarios.

Dunno why.  'seen it 50% of the time it's real' (my paraphrase)... ...what's all that about?

Cheers

John