detecting galaxies in Mark III catalog

[Stupendous Man <richmond@a188-l009.rit.edu>]

   Brian Skiff sent me some E-mail recently, describing his
 experience looking for photometry of GALAXIES in the Mark III
 'tenxcat' catalog.  He's given me permission to forward his
 comments here.
 
   Brian writes:
 
>      While doing some browsing, I noticed that the galaxy MCG-01-59-027
> appears in the TASS MkIII 'tenxcat' catalogue.  There are two similar
> entries, but as far as I can tell, the photometry for the galaxy is 
> basically correct.  There is no other proper single-channel or CCD photometry
> for the galaxy, but the MCG magnitude with "French cooking" applied by 
> the Lyon group yields total B magnitude of 14.9.  The MkIII values are
> V = 13.9 +/- 0.3 and I = 12.6 +/- 0.3, which are completely consistent
> with the cooked MCG value, and consistent with the galaxy's appearance
> on plates.
>      The galaxy center is:  23 30 32.29  -02 27 45.0 (2000, Lick NPM1G).
>      ...just for fun, I looked up NGC 3521, also close to the Equator.
> This appears in tenxcat too, but since the galaxy is very large, the
> TASS magnitudes are unsurprisingly too faint, since they probably don't
> take in anything close to the entire galaxy.
>      Based on just these two, the MkIII data is probably okay for smaller,
> fainter galaxies (V > 11.5 or 12), particularly if they are not too
> elongated.

  ...
> 
>      I looked up a bunch more galaxies in 'tenxcat' and found nearly
> everything I looked for---a lot of galaxies in the catalogue!  I made a
> short list of MkIII V and I together with RC3 V-sub-T and B-sub-T as
> available, also looking at galaxy sizes (standard mu25 isophote major axes).
>      In brief the MkIII magnitudes are pretty reliable _if_ the galaxy is
> nearly circular _and_ has a diameter < 1'.1.  If the galaxy is larger, or
> has any sort of faint halo, then the MkIII values are too faint by ~0.75 mag.,
> implying the photometry is missing the outer parts of the galaxy.
>      I found in doing this that for at least one galaxy the RC3 magnitude
> is plain wrong by a whole magnitude, and the MkIII data is clearly correct
> (NGC 1298).
>      It might be an interesting exercise---although I doubt anyone wants
> to look at the data again!---to re-reduce the data centered on specific
> galaxies (all would have good coord now) using fixed apertures (60", 90" etc)
> to get better data.  Most of the galaxies I looked up couldn't be readily 
> compared with the MkIII data because there is no BVRI photometry for them.
> Thus one could argue that the dataset is actually modestly useful for this
> purpose for these intermediate-brightness galaxies.

  Comments?  I suspect we can do similar work with Mark IV images,
though my guess is that they will less uniform backgrounds.  It is,
of course, better to write software specifically to measure 
extended objects from the start than to go back and look at 
measurements made from a fixed aperture ... perhaps someone will
think about how this might best be incoporated into regular 
reductions.

                                                 Michael