T his sample is dedicated to Ron Knight whose hard work, dedication, and love of astronomy has been an inspiration to others.

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A. Background Theory

B. The Knight Supernova Sample

C. Possible Uses for the Sample

D. Galaxies with High SNII Rates

E. Galaxies with Lower SNII Rates

A. Background Theory

     Barton et al. (2000) have studied a sample of 502 close galaxy pairs and N-tuples from the Cfa2 red shift survey that are in the early stages of a merger. All of their galaxy pairs are separated by < 0.055 h^-1 Mpc. Barton et al. (2000) found that the equivalent width of H-alpha [EQW(H-alpha)] and the strength of other emission lines strongly anti correlated with pair spatial separation and velocity separation. Their data supports a simple picture in which a close pass between two disk galaxies initiates a burst of star formation in the pair, dramatically increasing their EQW(H-alpha) emission. Subsequently, the EQW(H-alpha) emission decreases as the pair separation increases, accounting for the anti correlation which they observe. They also find that their data is compatible with star burst models and orbit models, so long as the star burst lasts longer than ~ 10⁸ years, and the delay between the close pass and the initiation of the star burst is less than a few times 10⁷ years.

     Subsequent work by Wilson (2001), has shown that there is a significant population Sbc-Sdm spiral galaxies that are experiencing short duration bursts in their star formation rates. These Burst Spirals pass through a distinct epoch in which they produce SN II at a much higher rate than they produce SN Ia. This epoch of enhanced SNII production last for 1.35 x 10⁸ years for burst lengths of 1.00 x 10⁸ years.

     Wilson (2001) found that the Bursts Spirals are preferentially found in interacting galaxies with projected separation
< 0.20 Mpc and (20-140 micron) infra-red luminosity (L_IR ) > 1.26 x 10¹⁰ L_O. This means that the sample of Burst Spirals
are by and large synonymous with the group of post interaction burst spirals identified by Barton et al. (2000).

     Hence, based on the findings of Wilson (2001) and Barton et al. (2000), we believe that the following chain of events
best describes what happens when a spiral galaxy tidally interacts with a companion galaxy:

1. There is close pass between two galaxies (< 0.25 Mpc). (Note: At 200 km/sec a galaxy will travel only ~ 0.02 Mpc in 10⁸ years and so the observed projected separation between a Burst Spiral and its companion is only slightly larger than the projected separation at closest approach.)
2. A burst of star formation is initiated in one or both of the galaxies at or near closest approach. There is a delay in the onset of the burst following closest approach of a few by 10⁷ years. A comparison between the data of Barton et al. (2000) and both the orbital and star formation models rules out delays that are longer than ~ 5 x 10 ⁷ years.
3. The burst produces a substantial increase in the galaxy’s H-alpha and infrared luminosity, and hence leads to an overall marked increase in the galaxy’s current to integrated star formation rate (as measure by either the EQW(H-alpha) or SB_IR of the burst galaxy).
4. The burst in star formation lasts for at least ~ 10 ⁸ years, and ages as the two galaxies move further apart (Barton et al. 2000).
5. Shortly after the onset of the burst (~ 3 million years), there is a significant increase in the SNII/Ib/Ic rate in the burst galaxy. There is no corresponding increase in the SNIa rate.
6. The SNII/Ib/Ic rates do not return to their pre burst levels until ~ 1.35 x 10⁸ years after the onset of the burst.
7. In contrast, the SNIa rate does not become enhanced until well after the end of the burst.
8. There is a clear and well defined sample of Burst Spirals (SB_IR > 3.0 x 10⁷ L_O Kpc^-2 ) which are preferentially producing SNII/Ib/Ic but not SNIa.
9. There is an upper limit in the current burst strength that is observed in these Burst Spirals i.e. Log(L_IR) > 10.6 (in units L_O for H_O = 75 km/sec/Mpc). Consequently, it is easier to see bursts in smaller galaxies (D₂₅ < 30 Kpc) simply because the burst stands out more against the lower underlying star formation rate.

      The Knight Supernova Sample makes use of the fact that there is a well defined population of Sbc-Sdm spirals
which are preferentially producing SNII, but not SNIa, to facilitate the search for type II SN in nearby galaxies.

1. Barton, E. J., Geller, M. J., and Kenyon, S. J., 2000, Ap. J., 530, 660.
2. http://members.ozemail.com.au/~irgeo/contents.html

B. The Knight Supernova Sample

Galaxies predicted to have Lower SN II Rates

These include:

1. Galaxies with companions that have projected separation > 0.40 Mpc.
2. Galaxies with L_IR  < 1.26 x 10 ¹⁰ L_O and companions with projected separation < 0.25 Mpc.
3. Galaxies with L_IR < 1.26 x 10 ¹⁰ L_O and companions with projected separation between 0.25 Mpc and 0.40 Mpc.
4. NGC 6951 which has L_IR < 1.26 x 10 ¹⁰ L_O but is too near to the Milky Way to search for companions.

     Figure 1 shows a plot of the [40-120 micron] infrared luminosity^* (L _IR) [in units of 10⁹ L_O] versus the projected separation to their nearest companions for the galaxies with high predicted SNII rates (diamonds plus the yellow and orange circles) and the galaxies with lower predicted SNII rates (blue circles). The diamond symbols in the lighter colours indicate those galaxies which have had multiple SN of type II, Ib, Ic and/or no type.

     Figure 2 shows a plot of the infrared surface brightness (SB(IR)) [in units of 10 ⁶ L_O Kpc^-2] versus the galaxy size
 [D₂₅ in the RC3 catalogue measured in Kpc.] for the galaxies with high predicted SNII rates (diamonds plus the yellow and orange circles) and the galaxies with lower predicted SNII rates (blue circles). Again, the lighter coloured diamond symbols represent the galaxies with multiple SN of type II, Ib, Ic, and/or no type. Note: the dark line in this figure connects point with Log(L_IR ) = 10.1 in units of L_O .

      Figure 3 shows a plot of the logarithm of the infra-red luminoisty as a ratio of the galaxy's dynamical mass i.e. Log(L_IR/M_dyn) versus the logarithm of the dynamical mass (M_dyn). The daynamical mass is calculated using the formula:            
M_dyn  =  1.159 x 10⁵  x  D ₂₅ x (W₂₀/sin(i))²

where D₂₅ is the galaxy's major isophotal diameter [in Kpc] measure at the blue surface brightness level of 25.0 magnitudes per square arcsecond (RC3 catalogue), W₂₀ is neutral hydrogen line full width (in km/sec) measured at the 20 % level of maximum line intensity ( RC3 catalogue), and i is the inclination of the galaxy. Galaxies with inclinations < 30 ^o are not included in this plot because of the large uncertainty in their dynamical masses. Two diagonal dashed lines are shown in this plot. The lower line joins points which have Log(L_IR) = 10.1 (in units of L_O), while the upper line joins points with Log(L_IR ) = 10.6. Figure 3 highlights the fact that, in general, the galaxies in the High SNII Rate sample have larger current to integrated star formation rates [as measured by theirLog(L_IR/M_dyn)] than galaxies in the Lower SNII Rate sample i.e. a galaxy in the High SNII Rate sample will have a higher L_IR than a galaxy with similar dynamical mass in the Lower SNII Rate sample .

        Figure 4 shows a plot of the difference in total asymptotic B-band apparent magnitude between the companion galaxy and sample galaxy [m(comp) - m(main)] versus the logarithm of the sample galaxy's infrared luminosity (Log(L_IR )). The data point symbols are the same as for figures 1 through 3. The difference in B magnitudes is in the sense that when the sample galaxy is brighter than its nearest companion m(comp) - m(main) is positive.

        The general trend in figure 4 is that the more luminous the sample galaxy is in the infrared, the more likely it is to be brighter than its nearest companion galaxy. The visible trend in this figure is just an artifact produced by the random spread in total blue magnitudes in the galaxies sampled, coupled with the pairing process. The best way to see this is by analogy. Image that you had a room full of people randomly distributed in height. If you selected an exceptionally tall person [equivalent to selecting a spiral that is very luminous in the infrared] then if much more likely that their nearest companion will be shorter than them.Similarly if you selected an exceptionally short person then it is much more likely that their nearest companion will be taller than them. Hence, the simple fact that the High SNII Rate sample galaxies are found in infra-red luminosity spirals means that it is more likley that a High SNII Rate sample galaxy will be brighter than its nearest companion galaxy. Indeed, this is exactly what we observe, with virtually all of the High SNII Rate sample galaxies being as bright or brighter than their companion galaxies.

     The reader is referred to the paper by Wilson (2001) for a full explanation as to the selection criterion used
to separate the galaxies into the two groups, however, a number of important notes need to made.

Notes  

1. Figures 1 and 2 include galaxies from both the northern and southern celestial sky.
   
2. The spirals with high IR luminosity i.e. L _IR > 1.26 x 10¹⁰ L _O and no apparent companion closer than 1.50 Mpc  (highlighted in figure 1 by the lighter coloured circle symbols) form an interesting group. Even though these galaxies are just as bright in the infrared as the interacting Burst Spirals, not one of these galaxies has had an historical supernova.   More infrared bright, isolated galaxies would have to be observed before any definitive statement could be made, however, it would appear that the mechanism which causes the enhanced infrared emission in these galaxies does not necessarily lead to enhanced SN II production.
3. 13 out of the 15 galaxies with multiple supernova (i.e. 87 %) have companion galaxies with projected separations less than 0.4 Mpc., strongly suggesting that interactions play a major role in this phenomenon.
4. There are two northern and six southern spirals that we claim are probably disturbed by interaction. These include:

          NORTHERN

• NGC 5962 - An Scd galaxy UGC 9925 is located at a projected distance of 0.08 Mpc. UGC 9925  is only 0.1 magnitudes below the blue apparent magnitude threshold limit [i.e. galaxies must have a blue apparent magnitude greater than 15.0 when placed at a distance corresponding to a recession velocity of 2500 km/sec.] We believe that NGC 5962 could be tidally interacting with UGC 9925.
• NGC 3079 - This almost edge-on spiral appears to be highly disturbed and asymmetric. We believe that it is tidally  winteractingith the nearby [projected distance 0.05 Mpc.] S0 galaxy NGC 3073, even though this galaxy is 0.37 magnitudes below the blue apparent magnitude threhold.

          SOUTHERN

• IC 2627 - This S-shaped face-on Sbc spiral galaxy has one arm significantly longer and brighter than the other. It is very likely that this galaxy is being tidally disturbed - possibly by a recent merger.
• NGC 4027 - This galaxy is clearly affected by the tidal interaction with the nearby NGC 4027A [separation 0.01 Mpc]. The interaction has produced a prominent tadpole like tail on one side of the galaxy.
• NGC 4304 - In high contrast images of this galaxy there is curved spur sticking out of one side of the galaxy, strongly suggesting that this galaxy is being tidally disturbed by a recent interaction.
• NGC 4835 - The Scd Galaxy NGC 4835A at a projected separation of only 0.11 Mpc but it has no published 3 K recession velocity in the RC3 catalogue. Tidal interaction with NGC 4835A may be responsible for the high infrared luminosity of  NGC 4835.
• NGC 5861 - This galaxy has very prominent and well defined spiral arms with a couple of arc like spurs projecting from one arm. It could be tidally interacting with the E6 elliptical galaxy NGC 5858 that has a projected separation of only 0.08 Mpc. Unfortunately, NGC 5858 has no recession velocity and magnitude information in the RC3 catalogue.
• NGC 6907 - This S-shaped face-on spiral galaxy has one arm significantly stronger than the other, giving the galaxy a very lopsided appearance. There is a bright knot in the enhanced spiral arm. It is very likely that this galaxy is being tidally disturbed - possibly by a recent merger.

ADDITIONAL NOTE : The [40 - 120 micron] infrared luminosties are not fully colour corrected. All raw [40 - 120 micron] infrared fluxes have been multiplied by a scale factor of 1.472. This scale factor is the mean difference between raw infrared fluxes and colour corrected infrared fluxes for galaxies in the sample of Young et al 1996. This approximation introduces an
error ~ 10-15 % into the final infrared luminsoities.

C. Possible Uses for the Sample

1. Back to the Future

     The work of  Wilson (2001) predicts that, as a sample, the Sbc-sdm galaxies in the High SNII Rate sample will produce Type II/Ib/Ic supernova at a significantly higher rate than the Sbc-Sdm galaxies in the Lower SNII Rate sample. This is because the galaxies in the High SNII Rate sample are probably post-interacation spirals that are undergoing a burst in their star formation rates lasting for ~ 10 ⁸ years.

      We can actually use the Knight Supernova Sample to estimate the level of enhancement in the SNII rate in the High compared to the Lower SNII Rate sample. Since 1885, there have been 53 SN of type II, Ib, Ic or no type in the 40 galaxies of the High SNII Rate sample. In addition, 27 galaxies out of 40 (68 %) in the High SNII Rate sample have had at least one supernova of type II, Ib, Ic or no type. This compares with 7 SN of type II, Ib, Ic or not type in the 43 galaxies of the Lower SNII Rate sample ( i.e. 16 %).

      The stark difference between these two samples remains even if we remove the galaxies that were included in the High SNII Rate Sample for the sole reason that they have had multiple supernova [i.e. they did not satisfy the other selection criterion]. Excluding these galaxies there are still 36 SN of type II, Ib, Ic, or no type in the remaining 33 galaxies of the High SNII Rate sample and 20 galaxies out of these 33 (61 %) galaxies have had at least one SN of type II, Ib, Ic or no type.

      Thus, crudely speaking, the galaxies in the High SNII Rate sample are producing SNII/Ib/Ic at ~ 7 times the rate
of the galaxies in the Lower SNII Rate sample [36 from 33 galaxies compared to 7 from 43 galaxies.].

     We predict that the difference in observed SNII rate will continue, and we would expect at least ~ 50 supernova
of type  II, Ib, Ic to occur in the High SNII  Rate sample over the next 100 years compared to only ~ 7 in the
Lower SNII Rate sample. Of course, these number could increase given the better scrutiny and equipment available
to amateur astronomers in the 21st century.

NOTE: These predictions apply to the type of SNII/Ib/Ic observed by past observers and so the numbers could be
            affected by the detection of  larger numbers of the intrinsically faint IIn supernova in nearby spirals.


2. Optical/CDD Supernova Searches

      Astronomers who use this list can either:

• Observe galaxies in the High SN II Rate sample only - if they just interested in improving their chances of discovering a type II SN - or

• Observe roughly equal numbers of galaxies in both the High and Lower SNII Rate samples  - if they are interested in confirming the scientific predictions of this web page and the work of Wilson (2001). 

     If an observing is conducting a visual search for SNII using this sample they need to know that the rule-of-thumb that
they can observe typical SNII in galaxies on these lists, if the recession velocity of the galaxy is less than the size of their
 telescopes aperture x 100. For example, if you you have a 10" telescope, you could discover SNII in galaxies
out to a recession velocity of  10" x 100 = 1000 km/sec.

     Of course, an astronomer with a 8" telescope (or larger) and a CCD detector could discover SNII in all of the galaxies
on this list.

3. Study How Galaxy/Galaxy Interactions Affect the ISM & Star Formation Properties of Spirals.

The author strongly recommends that the following observations be made of galaxies in Knight Supernova Sample and their companions:

• Integrated H-alpha fluxes - to investigate star formation properties.
• 40 - 120 micron infra-red fluxes - to compare with the H-alpha fluxes to see which is the best star formation indicator.
• CO observation to determine H₂ masses and to see the affects of star formation on the CO/H₂ conversion ratio.
• High resolution HI observation to search for any HI clouds that are lurking close to interacting galaxies.
  
• Near infra-red images of the galaxies to determine the true pitch angle of the spiral patterns.
• Radial velocity measurements of HI or H-alpha to determine the rotation curves of the sample galaxies.
  

4. Searching for Type II SN Beyond a Recession Velocity of 3,000 km/sec

If anyone want to use this work to search for SNII beyond a recession velocity of 3,000 km/sec, they are strongly advised to observe Sb-Sdm spirals that have high IR luminosity i.e. L _IR > 1.26 x 10¹⁰ L and a companion closer than 0.25 Mpc. The companion should have a blue apparent magnitude that exceeds 15.0, when placed at the distance corresponding to a
recession velocity of 2,500 km/sec (H_O = 75 km/sec/Mpc).