Construction of a Self-consistent Reference Dataset
Spanning 8th to 18th mag.
Christopher Ke-shih Young
, PASA, 18 (2), in press.
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Title/Abstract Page: Total Magnitudes of Virgo
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The scope of this dataset
Although no new observations have been presented in this paper, 13 new Bt values have been derived for VPC objects of intermediate apparent brightnesses but previously lacking Bt estimates. Also, 48 new Bt values have been derived for bright Virgo galaxies through the re-analysis of existing photometry. Combining these 61 new Bt values (as tabulated in Tables 2 and 3) with the VPC enables us to define a reliable dataset covering a subset of Virgo galaxies spanning a range in apparent luminosity of 10,000 (or 10 mag.). Interestingly we find that the brightest Virgo galaxy is NGC 4472 (=M49) (8.93 mag.) followed by NGC 4406 (=M86) (9.15 mag.). This leaves NGC 4486 (=M87) (9.43 mag.) in third place. Of course, should there be significant spatial depth in the distribution of these objects, their relative rankings in terms of absolute magnitude may be quite different. Recent distance estimates are available for two of these giants from Gavazzi et al. (1999), who find NGC 4472 to be 0.24 mag. closer to us in distance-modulus space than NGC 4486. This would suggest that in terms of intrinsic luminosity NGC 4472 is only 0.26 mag. brighter than NGC 4486, even though in terms of apparent brightness it is 0.50 mag. brighter. The main limitations of this dataset are: (1) it is restricted to elliptical and lenticular types at the bright end, (2) its coverage of 14th mag. objects is relatively thin (only 8 objects in total), and (3) large extrapolations7 were necessary for some objects. As far as the extrapolations are concerned though, we have good reason to believe from Young et al. (1998) that for most bright early-type and fainter galaxies of all types t-system total magnitudes are relatively insensitive to the exact surface brightness of the limiting isophote. At this stage, it is also worth mentioning that it will become evident from future papers in this series why most other sources were not included in our dataset. We have therefore chosen only to discuss the positive attributes of the selected sources here rather than the limitations of the others. As will be demonstrated, any minor error in the present dataset pales into virtual insignificance when most other sources of magnitudes for Virgo galaxies are investigated.Next Section: Acknowledgements
Title/Abstract Page: Total Magnitudes of Virgo
Previous Section: Bright-end consistency checks
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