EVEN MORE FUN WITH GALAXY DATA !
Firstly, I must warn readers that my notes on various galaxies throughout this thread are still in a somewhat tentative and incomplete state, as I may not have used the best available data to draw my conclusions. It is time to hit the literature and improve on what I have written!
In the below New Query, I relaxed the luminosity criterion somewhat (lowered it by 0.2 magnitudes) and also I made the colour criterion considerably more stringent ;
only those galaxies with a
very strong Ultraviolet excess of U-B < -0.04 were isolated.
So here is my new SQL query of the Hyperleda catalog of galaxies:
select objname, de2000, mabs, bt, ubt, t, vlg where t>2.7 and vlg<1800 and mabs<-20.5 and mabs>-20.7 and ubt<-0.04
Here I am asking the galaxy database to print the following parameters:
Object name,
declination,
blue absolute magnitude,
blue apparent magnitude,
observed U-B colour,
Hubble type (expressed as a numerical stage),
recession velocity (in the Local Group reference frame)
for :
all t > 2.7 (Hubble type Sb and later) galaxies
with Recession Velocity less than 1800 km/s
and Between Blue absolute magnitude -20.5 and -20.7
and with a U-B colour index of less than -0.04 (very strong ultraviolet excess)
This query isolates the identities of some more galaxies, possibly of somewhat lower luminosity, but many of them with very very strong excesses of ultraviolet light, indicating the presence of extreme concentrations of O and B stars.
Notes on some of the candidates for "high supernova rate galaxies" in this new query:
NGC 3621
According to most of the standard catalog data, this strongly star-forming galaxy has a relatively modest Luminosity and Size compared to many of the other Very Big and Very Luminous spirals under consideration for "high success rate" visual supernova search. For instance R. Brent Tully in the Nearby Galaxies Catalog gives a rather modest Blue absolute magnitude of minus 19.87.
However, for NGC 3621, the photographic surface photometry in the ESOLV Catalog measures a
truly enormous Major Axis angular dimension (out to the faint 26th B magn. per sq. arcsec isophotal ellipse) of 22.2 arcminutes !!
This is a plausible diameter measurement, as it corresponds rather well to the extent of the region of strong star formation seen in the GALEX satellite's Ultraviolet view of this galaxy:
Adopting this value as a reasonable measure of the angular diameter of the stellar distribution of this galaxy, and a physical scale of 2 kiloparsecs per arcminute of angular measure, the true diameter of NGC 3621 is
at least 140,000 light years , thus contradicting the idea that this is not a really big spiral galaxy.
In the absence of CCD magnitude measurements that include all of the light of the vastly extended outer regions of NGC 3621, I would have to regard any conclusions as to the total magnitude and the total luminosity of this galaxy as being very tentative. For galaxies of such large angular size, it can happen that CCD photometry adds half a magnitude to a galaxy's brightness as quoted in the catalogs!
This galaxy has a very blue U-B colour of -0.08 according to Hyperleda, and its distance is well-constrained (using Cepheid observations) at near to 22 million light years. The B-V optical colour of 0.46, as measured in the Carnegie-Irvine Galaxy Survey, is also notably blue. The rather nearby distance of this galaxy implies that supernovae should be bright and
easily detectable.
Incidentally, the outer spiral arms of NGC 3621 are not in the same plane as the inner region of the galaxy, as they are warped or bent in some way, so I do not anticipate that extinction will be so high that supernovae will become too faint for easy detection.
In summary, the nearness of this galaxy makes it a good prospect for visual supernova search. But I will have to do some more work before I can say for sure how big its population of OB stars is and how high its supernova rate is.
NGC 3359
This galaxy is an
excellent candidate for having a high rate of supernovae. The optical colours given in Hyperleda are
very very blue ::
B-V = 0.46 and U-B = -0.20
If this data is good, these values indicate that there is a very large population of O and B stars on this galaxy. This galaxy is probably undergoing an intense burst of current star formation. I should check the Far-ultraviolet luminosity to confirm this conclusion!
"Just for fun and profit", here is the Far ultraviolet + Near Ultraviolet view of NGC 3359 from GALEX, showing the intense far ultraviolet emission from the massive and luminous stars of the spiral arms:
NGC 4654
This interesting Virgo Cluster spiral is strangely distorted in its outer regions, and the galaxy catalogs give very blue optical colours for it. The admittedly uncertain distance measurements in the catalogs indicate that this galaxy is at least absolute Blue magnitude -20 in luminosity. R. Brent Tully, based on his surprisingly good redshift distances in the Nearby Galaxies Catalog, gave -20.3 in that catalogue.