Photometry

We have used a preliminary galaxy pipeline (Mamon et al. 1997b, 1998), based upon the SExtractor package (Bertin & Arnouts 1996) to obtain I_c, J and K_s Kron photometry from the DENIS images at the location of MB galaxies.  Although many of the galaxies have a considerable number of stars superimposed on their images, magnitudes derived from this automated algorithm agree well with independent measurements.

Figure 5 shows the dependence of the colour J-K on foreground extinction A_B. Included are data from the low-latitude (

,

), rich cluster Abell 3627 (cf. Paper II), where the foreground extinction is less than . The group of MB galaxies with

shows a similar scatter but is offset in colour with respect to the galaxies in A3627. Also, the galaxy at

is considerably redder than all the other galaxies.

Figure 5: NIR colour as a dependence on foreground extinction.

In Paper I we discussed the NIR colour-colour diagram I-J versus J-K of galaxies in the A3627 cluster in detail. We found that the extinction-corrected colours of the cluster galaxies do match the colours of galaxies in unobscured high latitude regions (Mamon et al. 1997b, 1998), suggesting that our preliminary photometry is reasonably accurate.  The shift in colour can be fully explained by the foreground extinction. Hence, the NIR colours of obscured galaxies (in particular of elliptical galaxies) provide an independent way of mapping the extinction in the ZOA (see also Mamon et al. 1997a) and calibrating the DIRBE maps at low Galactic latitudes (see also Mamon et al. 1997a).

© Copyright Astronomical Society of Australia 1997