While I really hate to disagree about anything with the astro-man of the Karoo (especially on stellar astronomy!) , I am going to do so now, as I am an absolute “fiend” when it comes to galaxy data.
I should point out that the apparent B-band (in popular language, “Blue”) magnitude of WLM is near to 11, not its visual magnitude. As this is a dwarf irregular (or, in my opinion, a very late type spiral somewhere between Hubble type Sdm and Sm), its visual magnitude will probably turn out to be about half a magnitude less than its Blue magnitude.
(( The typical B-V color of a non-starburst Dwarf Irregular Galaxy is a color index of around B-V = 0.4 to 0.5 (which is a blue optical color), though I do point out that there are plenty of very quiescent dwarf irregular galaxies that are significantly redder than this.
Liese van Zee calculated median broadband optical colors of B-V = 0.42 and
U-B = -0.22 for a sample of dwarf irregulars.
Ron Buta in 1995 found B-V of 0.4 to 0.5 for Hubble numerical stage 8 to 10 galaxies. ))
Unfortunately, galaxy catalog data about WLM is scarce, as the galaxies in the south equatorial zone of the sky are still little studied relative to their northern counterparts. Though H.G. Corwin, to his great credit, has attempted to address this data scarcity with a rather obscure Galaxy Catalog known as the South-Equatorial Galaxy Catalogue (the SEGC)(= “the galaxy catalog formerly known as the ESGC”)
( http://ned.ipac.caltech.edu/Library/...HGCorwin/segc/ )
Fortunately, this data scarcity will soon to be a thing of the past, because of the VISTA and SkyMapper southern sky surveys.
In the absence of CCD surface photometry for WLM, elementary measurements like total magnitudes & color indices & diameters could still be substantially in error.
The apparent magnitude of WLM in LEDA is B-band (“blue”) magnitude 11.04
The revised aperture photometry (on the RC3 system) which is found in the back pages of the HYPERLEDA online galaxy catalog, gives a total B (blue) magnitude of B = 10.87 for this galaxy (bright!!), while the RC3 catalog itself gives B = 11.03 on the same system.
This revised aperture photometry of galaxies (I believe) originates in a paper by Prugniel and Heraudeau (1998, A&AS,128, 299)
(see Table 4, at http://vizier.u-strasbg.fr/viz-bin/V...urce=VII%2F206) .
(I have found Prugniel & Hereaudeau to be a very plausible source of good apparent magnitudes for galaxies….this galaxy catalog often gets closer to the apparent magnitude that is measured using CCD surface photometry , which more accurately includes the light of the outermost regions of a galaxy, than the RC3 does.)
The Hyperleda database gives an integrated apparent B-V color of 0.44 for WLM galaxy, while the photometry of 1977, ApJS, 34, 245 (= Ables & Ables) gives a much redder B-V color index of 0.62, which is a big discrepancy. The RC3 also gives an apparent (total) colour of B-V = 0.44 for this galaxy.
So I really hope I can find some better data than this!!
The distance of this nice little "extragalactic critter" is very well constrained, and the NED database gives a mean distance modulus of 25.08 from many individual distance determinations, but this average distance is probably a little too high , because this average value includes some distance determinations which are of low accuracy (e.g. Tully-Fisher method, Brightest Stars method, etc.) : :
There is a recent Near-infrared Cepheid distance Determination (nearly extinction-free!) of m-M =24.92, which should definitely be given some weight, and the multiple Cepheid and TRGB distance determinations mainly come out within the distance range
m-M = 24.8 to 25 (in distance modulus).
So, in my opinion, within the errors, the distance (from the Sun) of the WLM galaxy is very likely to be somewhere between 0.9 and 1 Megaparsecs. Actually, this distance difference of only 326,000 light years between “high” and “low” distance estimates for a galaxy is better then we can usually manage for most other galaxies!
I think, from this distance work, that we can reliably calculate that the blue (B-band) absolute magnitude of WLM is likely to be in the range – 13.8 to –14.1 , though in the absence of accurate CCD surface photometry that includes (in a measurement of a galaxy’s apparent magnitude) the flux from the very-extended outermost regions of this galaxy , one would have to say that current estimates of the apparent magnitude andabsolute luminosity of this galaxy might be a little too faint.
((
WLM is a very extended galaxy, in angular terms, as one would expect for dwarf galaxies located in and near the Local Group of Galaxies.
For instance, the NED and SIMBAD databases give dimensions of 11.5 by 4.0 arcminutes for this galaxy, but these dimensions are the standard D25 diameter that is usually given in the galaxy catalogs, and this diameter is normally considerably smaller than the full diameter of a galaxy
In contrast, the UGCA catalog gives dimensions of 11.99 by 5.00 arcminutes for WLM, and the SEGC gives the remarkably large angular dimensions of 16.98 by 7.94 arcminutes (!!)( as measured from a Schmidt plate, out to fainter isophotes than D25)
))
[ These last two larger estimates for the diameter (major axis & minor axis) of this galaxy come from:
- the UGCA catalog (= UGC-A)(= Catalog of Selected non-UGC Galaxies, by Nilson)(= Uppsala General Catalog Appendix)
(to lose friends & influence fewer people, just refer to WLM as UGCA 444)
- The South-Equatorial Galaxy Catalog (SEGC) of H.G. Corwin
]
In his comprehensive recent (2012) discussion of all of the known Dwarf galaxies in and near the Local Group of Galaxies,
(https://www.astrosci.ca/users/alan/N...nachie2012.pdf), Alan McConnachie derives a V-band (“visual”) absolute magnitude of –14.2 for this galaxy, as compared to a V-band luminosity of -16.8 for the SMC and -18.1 for the LMC, and WLM is also significantly less luminous than the likes of M32 and NGC 205.
So this interesting little galaxy is definitely “one of heaven’s lesser lights”.
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