[madbadgalaxyman (Robert)]

Hello there, Supernova searchers,

In order to create a more reliable list of nearby high-supernova-rate Spiral Galaxies that are suitable for visual Supernova search, it will be necessary for me to remove a few galaxies from the above list, for reasons such as ::
- unfavourable galaxy orientation
- Observed strong excess of UV light coming mainly from an Active Galactic Nucleus rather than from OB stars
- Bad Data leading to erroneous conclusions regarding the luminosity and/or colour of a galaxy

In other words, I need to check the accuracy of the catalog data on the "High Supernova Rate" galaxies in the above Draft List, and I also need to assess the truth or otherwise of the tentative conclusions that I have drawn from this data.

Sadly, it remains very difficult to come to robust conclusions as to the values of even the most important physical parameters of many prominent southern galaxies, as data is too often scarce and of poor quality. Hopefully the SkyMapper and VISTA southern sky surveys will soon remedy this shocking situation!!
In order to refine my conclusions, I need to thoroughly check the literature, in case there are more accurate magnitudes and distances and luminosities available for these galaxies.

Also, there are several more good candidates for nearby and very luminous and High Supernova Rate Galaxies, which did not make it into the draft list of "High Supernova Rate" galaxies.......


Some more Nearby Spiral Galaxies which are "possibles or probables" for having a high rate of "easily detectable" core-collapse supernovae ::

(1) NGC 2997
Last time I considered the properties of NGC 2997, I concluded that this galaxy is arguably very comparable to other big Strongly Star-forming spiral galaxies like M100 and M61 and M83, but oddly, NGC2997 seems to have had relatively few reported supernovae. Perhaps this is due only to the fact that people were not looking...... at the time that the supernovae occurred in this galaxy.
If the reddening-corrected U-B and B-V colours of NGC 2997 are comparable to that of the other big "highly star forming" spirals on the list, the size of the O & B star population of this galaxy could be similar to that found in the other vigorously star-forming massive spirals. This galaxy is certainly very large in angular size and physical size;
for instance, the ESOLV photographic surface photometry measures a major axis diameter of 9.9 arcminutes to the standard D25 isophote, which corresponds to 110,000 Light Years across if the (very uncertain) distance of this galaxy is Distance Modulus 30.4
On the other hand, Hyperleda gives some Rather Red effective U-B and B-V colours for the inner parts of this galaxy, but these reddish optical colours might merely be the effect of reddening from the foreground dust screen of our Milky Way Galaxy.
I will have another look at the physical properties of NGC2997, to see if its properties are in accord with my initial impression. There are significant uncertainties as to its distance and luminosity, and as to how much its true optical colours are reddened by foreground dust from our own Galaxy.

(2) NGC 1097
NGC 1097 has a high blue luminosity, and it also has a High total infrared luminosity (5 x 10E10 solar luminosities) as given in the IRAS Revised Bright Galaxy sample, indicating that its total star forming rate is somewhat higher than that of a typical first-ranked Type Sbc or Sc spiral galaxy. A good fraction of the star formation in NGC 1097 could be in the tight ring of star-forming regions that exists near to its centre; so it is worth keeping in mind that occurring SNe could be in the crowded and high-surface-brightness central part of this galaxy. In the case of N1097, the star forming ring is only modestly obscured by dust, which is usually very heavy at the centre of a non-dwarf spiral galaxy.
This galaxy is selected as a very good prospect for having a high Star Formation Rate and a high Supernova Rate, on the grounds of its high infrared luminosity and its high total luminosity. ( I may find other good prospects in the aforementioned IRAS catalog, which gives the total infrared luminosity of many galaxies.).

(3) Messier 101
M101 is very luminous , and nearby, and very blue. Therefore, Supernovae should be frequent and bright.
This is a very blue (observed B-V = 0.45) spiral galaxy of similarly high luminosity to many other galaxies in the table. (it did not make it into the table because there was no total U-B value for it in Hyperleda)
Therefore M101 will have a high rate of occurring and observed core-collapse supernovae.

(4) NGC 1365
NGC 1365 did not make it into table because its colours are apparently a little too red , but it is a Very Luminous spiral galaxy which is large and massive. Its distance estimate is well constrained, and, from the recent published literature distance estimates, one can derive with high confidence the fact that NGC 1365 is undeniably one of the most luminous spiral galaxies found within a recession velocity of 2000 km/s.
(the luminosity of NGC 1365 is usually numerically expressed as Blue Absolute Magnitude of minus 21.0 or brighter. It could even be -21.5 . The catalog luminosity of NGC 1365 has to be regarded as a lower limit, in the absence of CCD surface photometry that includes its very extended outer regions )
Furthermore, the total infrared luminosity of this galaxy is much higher than that of one of the most luminous Virgo Cluster spirals like M61 and M100; this strongly suggests that this galaxy has a much higher star formation rate than "normal" high-luminosity spiral galaxies.
A high supernova rate is therefore very likely in NGC 1365; but it is conceivable that a large fraction of the OB stars and supernovae could be located in the highly-obscured central 'starburst' region.

(5) NGC 1084
Hyperleda gives a blue absolute magnitude of -20.69 for NGC 1084, which is similar to the luminosity of some of the less luminous galaxies in the table. The U-B colour index, as given in Hyperleda, is a very blue -0.09 . This very blue U-B colour would be an indicator that this galaxy has a very prominent population of O and B stars; I hope that this U-B value is correct, as good numbers of catalog U-B values have a very low accuracy. The IRAS Revised Bright Galaxy Catalog gives a Large total infrared luminosity of 3.5x10E10 solar luminosities for this galaxy. The general properties of N1084 are probably comparable to those of the other very luminous and strongly-star-forming spiral galaxies in the table, and the infrared luminosity indicates that there is particularly strong ongoing Star Formation. However, a very large distance uncertainty for this galaxy casts significant doubt on many of the conclusions in this paragraph.

(6) NGC 1087
The very blue optical colours given in the galaxy catalogs are very plausible, but there is still a high degree of uncertainty attaching to the luminosity and distance of this galaxy.