4. Basic statistics

In Fig. 1 the productivity of world wide supernova searches through the years is shown. The enormous improvement of the last few years stands out clearly. The dashed area refers to SNe brighter than 14 mag. It must be noted that, despite the renewed effort in SN search, the rate of discovery of bright SNe is not increasing.

In Fig. 2 we plot the distribution of redshifts and highlight (shaded area) the SNe discovered in the last 6 years. It appears that almost all SNe at redshift z>0.1 have been discovered recently and that the recent high-z surveys favour discoveries in the range 0.3 < z < 0.8.

In Fig. 3 the sky distribution of the 1447 supernovae both in equatorial (top panel) and galactic (bottom panel) coordinates is shown. Neglecting the avoidance zone defined by the galactic plane, the outcome of the SN searches of the last years makes the SN sky distributions more homogeneous compared with the same plot reported in ASC89. Overposed to the clustered pattern of the distribution of nearby parent galaxies is evident a smooth background component due to the high-z SNe.

Figure 4 shows the distribution of the difference between the SN and parent galaxy magnitude. The peak of the distribution is at $(m_{{\rm SN}}-m_{{\rm Gal}})=2.4$ with $\sigma=1.8$ which fairly compares with the same result found by Barbon (1968). These numbers may be useful to prepare the strategy of a SN search in given galaxy samples.

Table 5 shows the distribution of supernovae of different types according to the morphological type of their parent galaxies. With respect to Table 3 of ASC89, new SN types are now listed but the overall distribution remains unchanged. Note that the percentage of classified SNe has increased from 40% to almost 60% of total discoveries.

Concerning the distribution among different SN types (Fig. 5 top), it turns out that type Ia alone make 50% of all classified SNe, whereas Ib/c are only 7%. The same data of ASC89 give 22% and 6%. Actually, in ASC89 a major fraction of type I (54%) were missing a detailed subtype classification whereas in the present version this is only 14%. On the other hand, the percentage of type II SNe (34%) remains constant. These numbers show that, since the last decade, the chase for the SNIa is well under way.

The distribution of the parent galaxy morphological types is also shown in Fig. 5 (bottom). It stands out clearly that most SNe are found in spiral galaxies.

Finally, in Fig. 6 we plot the positions of all SNe with redshift in the Hubble diagram. The line is the expected location for "standard'' SNIa having $M({\rm max})=-19.50$, H₀=65 km s^-1 Mpc, q₀=0. We remark that some SNe, not of type Ia, laying above this line have poor photometry.

Acknowledgements

We are indebted to David Branch for having provided a number of corrections to a previous release of the Catalogue.