Sternberg Astronomical Institute Supernova Catalogue and Radial Distribution of Supernovae in the Host Galaxies O. S. Bartunov, D. Yu. Tsvetkov and N. N. Pavlyuk Sternberg Astronomical Institute, Moscow, Russia

Abstract. We present Supernova Catalogue and the results of investigation of Supernova radial distribution in the host galaxies based on the new data. We collected the available data on SNe and verified their coordinates, identifications of host galaxies and information about them, which was compiled from different sources and included in our catalogue. We corrected many errors in previous data, and found new data about galaxies. The catalogue is stored in RDBMS and was specially designed following the recommendations of Virtual Observatory. It is planned to make it available as a resource of Virtual Observatory. One of the primary goals is the scaling of our catalogue to include the large number of SNe expected to be discovered by forthcoming projects. We also raise several questions before SN community: the existing nomenclature scheme soon will become insufficient to handle large numbers of SNe; the current way of assigning SN identifications does not satisfy modern state of affairs: many SNe are discovered by closed projects and become available to the community after long time. We confirm the results of our previous study, which found significant differences in distribu- tions of types Ia, Ib/c and II SNe in the central parts of spiral galaxies: low rate of SNe Ia in the innermost parts and relatively high concentration of SNe Ib/c towards the centers of host galaxies. We discuss possibilities of future SNAP mission to provide data enabling to study evo- lution of SNe radial distributions with age and distance and possible improvement of estimates of cosmological parameters using more homogeneous samples of SNe Ia selected on the basis of their position in the host galaxies.

1. Introduction The collection and systematization of SN data and their presentation in a form con- venient for statistical and other studies are of particular interest at present time. The number of SN discoveries increased dramatically in recent years. SNe are widely used as ”standard candles” for constructing distance scales and for cosmological studies, some of them may be related to mysterious gamma-ray bursts. The first lists of SNe appeared in late 1950s and were repeatedly updated as the number of discoveries increased (Zwicky 1958, 1965; Kowal and Sargent 1971; Sargent et al. 1974). They presented also the basic data on the host galaxies, and catalogs by Karpowicz and Rudnicki (1968) and Flin et al. (1979) also contained a complete bibliography for each object. In the last twenty years, the Asiago Observatory Catalogue of SNe (Barbon et al. 1984, 1989, 1999) has received the greatest recognition. At present, continuously updated lists and catalogs of SNe can be found on the Internet. Among them we would like to mention the list of SNe maintained by the Central Bureau for Astronomical Telegrams (http://cfa-www.harvard.edu/cfa/ps/lists/Supernovae.html) and the online version of the Asiago Catalogue (http://web.pd.astro.it/supern). Studies of the SN distribution in galaxies are of great interest in elucidating the nature 1 of the stellar populations that provide SN explosions of a certain type. Although the presupernova stars have been detected for several type II SNe, the origin of precursors of other types is still an open question in many respects. Of particular interest is the possible difference between the populations of type-Ia presupernovae in galaxies of different types, ages and chemical compositions, which can affect the results of cosmological studies. Despite the rapid increase in the amount of data, the SN distributions in galaxies have been studied rarely in recent years. After the paper by Bartunov et al. (1992), which provides references to earlier works, we would like to note the papers by van den Bergh (1997), Wang et al. (1997), Howell et al. (2000), Tsvetkov et al. (2004). The latest studies have revealed some unexpected facts: deficiency of SNe Ia in the central parts of spiral galaxies and strong concentration of SNe Ib/c toward the centers, which deserve verification using larger amount of data and interpretation.

2. Supernova Catalogue The SAI Catalogue of SNe was originally intended for statistical studies, its compilation was started in 1986 on the basis of existing SNe lists and published data, it was described by Tsvetkov and Bartunov (1993) and Tsvetkov et al. (2004). Until recently Supernova Catalogue was stored as filebased system. The data on SNe were connected with the data on their host galaxies in the main file of the catalogue: each string presented data on SN and on its host galaxy. At the beginning of 2006 we started transformation of the catalogue to the database structure. We want to abandon traditional table, to follow relational approach and nor- malize data. The main reasons are: There are galaxies with multiple SNe outbursts. In the table the data on these host galaxies• is presented in several lines, corresponding to each SN. So when the information on one galaxy is updated, it is necessary to replace it in several lines. After the division of tasks of updating the data on SNe and on host galaxies this can• be done by different authors. It is possible to insert data on newly discovered SNe quickly and to update information on the galaxies more seldom, when new data become available. Only one author can make changes in the file at certain moment. But with growing num• ber of SN discoveries it is necessary to provide several authors with the possibility to edit the data simultaneously. This becomes possible with the new structure, the jobs of several authors can be duly distributed and coordinated. In the file the data is strictly formatted, and if the information for some SN does not• fit in the format, the structure of all file should be changed. In the database it is possible to foresee future changes, as the data of variable length are permissible. The task of adding new data to the catalogue can be further systematized and divided• into simple parts. Besides dividing all the data into two main tables with infor- mation on SNe: ”sn” and on the galaxies: ”galaxies”, the constant parts of inserted data are presented in separate tables - so called reference tables. While compiling the catalogue we payed special attention to the identification of the host galaxies, which is becoming increasingly difficult because of growing number of faint and distant SNe discovered in recent years. In addition, difficulties arise when a SN explodes in a multiple system or in a peculiar galaxy. Therefore we studied the sky field around each SN using various digital sky surveys. To find the most likely host galaxy, we use data on the radial velocity and brightness of the galaxies and SNe in addition to their sky position. If the host galaxy is multiple, it is specified in the description of the galaxy type, and SNe in such galaxies are excluded from sample for studying the radial distribution. The catalogue will be available for downloading as a text file (compatible with previous versions) and as dump database for installation on any user’s computer. In future we plan to make it a resource of Virtual Observatory.

3. Problem of SN designations Working on the catalogue, we have to deal with the currently accepted system of designations. Now it becomes clear that this system cannot meet growing demands. First of all, only 702 SNe per year can be designated, and very soon this number will be exceeded. The sequence of names in many cases does not reflect neither time order of discoveries nor order of outbursts. Besides, some recent projects do not report their discoveries to IAU Central Bureau for Astronomical Telegrams, and these SNe does not receive usual designations. So we suggest that this system should be modified to have enough capacity to designate thousands of SNe per year, it should be compatible with the present system and should provide possibility for closed projects to include their discoveries at any time without disordering the system. To increase the capacity without changing existing scheme we propose to prolong the designations, so after SN2008zz we should have SN2008aaa, SN2008aab, etc. The basic principle is that the year in the designation is the year when discovery image was obtained, not the year of actual discovery. For example, while investigating the SAI plate collection in 2005, Antipin (2005) discovered new SN on plate obtained in 1985. As now the last SN for this year is SN 1985U, this new object should be given name SN 1985V. It is clear, that the time order of discoveries cannot be reflected by the order of SNe names, so if some project makes the list of discovered SNe available after some period past actual observations were made, these SNe should be appended at the end of the list for the year of first SN observations. The SN names given by the project, such as SNLS-04D1ag for SN discovered by SNLS (http://www.cfht.hawaii.edu/SNLS), can be regarded as its proper name and also used for references; our catalogue already includes the table with unique identifications of SNe and their proper names. We also appeal to the teams carrying out specialized SN searches, aimed to investigate, for instance, only SNe Ia, to publish all their discoveries. This is vital for completeness of SN catalogues, for studies of radial distribution of SN and rates of their outbursts.

4. Radial distribution of SNe The method of analyzing the radial distribution is virtually identical to the method that we used previously (Bartunov et al. 1992). SN samples were selected from our catalogue. Only SNe with complete set of data on their host galaxies were included. For each SN we calculated the relative radial distance r = (∆α2 +∆δ2)0.5(a2 sin2 θ+b2 cos2 θ)0.5/ab where ∆α and ∆δ are the distances from the SN to the center of its host galaxy, a and b are the major and minor axes of the galaxy up to blue isophote 25m from square arcsecond, θ is the angle between the major axis and the radius-vector of SN. We also computed 1 1 absolute radial distance R = racz/H0, where z is the redshift, and H0 is 70 km s− Mpc− . Subsequently, we constructed the SN distribution histograms and corresponding plots of 2 2 SN surface density σ = Ni/π(ri ri 1), where Ni is the number of SNe in i-th radial bin, versus the radial distance r. − − The selection effects that affect the observed distributions were studied in detail by Tsvetkov et al. (2004). The main conclusion was that selection-free dependence of SN Figure 1. The distributions of SN surface density surface density on the relative radial distance can be obtained using SNe discovered by CCD and visual observations in the galaxies with redshift z < 0.017. About 7% of SNe is lost in the central regions of more distant galaxies, while photographic searches cannot discover about 20% of SNe in the centers of all galaxies. As at present time practically all discoveries are made using CCDs, the relative number of SNe discovered photographically is gradually decreasing. Besides, we are mostly interested not in the ”real” SN distribution, but in comparison of distributions for different SN types. So, in the present study we did not separate SNe discovered by different kinds of searches. The radial distributions of SNe are presented in Figs. 1-4. The distributions reveal significant difference between SNe of various types, especially in the central regions of galaxies. We should also note that the distributions for ”complete” and ”nearby” samples are practically identical, meaning that modern searches does not show such prominent selection effects that we observed in previous works. We confirm the decrease of SNe Ia density in the central parts of the spiral galaxies and high concentration of SNe Ib/c to the centers, first noted by van den Bergh (1997) and Wang et al (1997). At r > 0.5 the surface density of all types of SNe decreases with similar gradients. At r 1.5 the slope of decrease changes, and we observe the ”halo” of SNe. We note that the≈ distributions of SNe Ia and II in the outer parts of the galaxies is very similar. The cumulative radial distributions are less sensitive to the differences of SNe rates at Figure 2. The distributions of surface density for SNe from galaxies with z < 0.017. SN types colour coding is the same as on Fig.1 central parts of the galaxies, but clearly show the differences in their outer regions. The most prominent feature is almost identical behaviour for SNe Ia and II. SNe Ib/c are clearly more concentrated to the central parts, while the relative fraction of SNe Ia in the halo of E/S0 galaxies is much greater then for all other samples. The distributions of surface density versus radial distance in kpc show smaller differences between SN types, but still we see some depression for type Ia near centers of the galaxies and SNe Ib/c are clearly more concentrated towards central regions.

5. Future prospects As the number of SNe increases, especially at larger z, it would be possible to study evolution of radial distribution with age of the galaxies. Especially promising is the planned SNAP mission (http://snap.lbl.gov). The systematic search for SNe on 15 square degrees field with limiting magnitude about 30 and resolution 0.001 per pixel should provide as a by-product the data suitable for study of SNe radial distribution at z up to 1.7. At that distance a galaxy with diameter 20 kpc will be resolved and will allow to construct at least 3 bins for the histogram of SNe radial distribution. We should be able to study the evolution of radial distribution with z for various SNe types, and attempt to Figure 3. Cumulative radial distributions of SNe. improve the accuracy of estimations of cosmological parameters using more homogeneous samples of SNe Ia, for example, only SNe in the outer parts of the galaxies. Another important aspect is the study of SNe distribution relative to indicators of recent star formation, such as spiral arms, HII regions and OB-associations. Since our first work on this subject (Bartunov et al. 1994) the number of SNe available for the analysis increased nearly 10 times, and the quality of data (precise coordinates of SNe, availability and quality of images of galaxies and SNe) also improved greatly. Now we have started the work on association of SNe Ib/c with spiral arms, and we are planning to do it for other SN types also. This work will provide important data revealing the nature of SNe precursors.

6. Conclusions We should note that only the radial distribution of SNe Ia in ellipticals agrees well with the one expected from currently accepted suggestions about the nature of their precursors. This distribution is like that for the luminosity in elliptical galaxies. The distribution of type II SNe in spirals at central parts is similar to the ones for such indicators of recent star formation as HII regions and OB-associations, but in the Figure 4. The distributions of surface density versus radial distance in kpc. Four upper curves are for complete samples, lower curves are for SNe from galaxies with z < 0.017 outer parts of the galaxies SNe II belong to the same halo population as SNe Ia, which is quite unexpected. The strong difference between distributions of SNe II and SNe Ib/c in the centers of spiral galaxies is especially surprising, as the distributions of these objects relative to spiral arms and HII regions are similar (Bartunov et al. 1994; Van Dyk et al. 1996), indicating that masses and ages of their progenitors should be quite close. The difference between radial distributions of SNe Ib/c and SNe II might be a consequence of radial abundance gradients in spirals. The low rate of SNe Ia in the centers of spirals shows that they certainly do not belong to bulge population, so their progenitors in ellipticals and spirals should have different nature. Such distribution with a ”hole” at the center is observed for discs in some spiral galaxies. Type Ia SNe in spirals might belong to disc population of intermediate age. The rapid increase of the number of SN discoveries leads to new demands for the collection and systematization of data and their presentation. We have developed new structure for SN catalogue, compatible with the standards of Virtual Observatory, which allows storing of large amount of data and new approaches to their distribution and reduction. We propose a scheme for SNe designation and call for all groups discovering and studying SNe to cooperate with us in creation of SN database which should be able to meet growing demands of scientific community. This work was partly supported by the grants 05-02-17480 and 05-07-90225 of the Russian Foundation for Basic Research.

References Antipin, S.V. 2005, Variable Stars 25, No. 1 Barbon, R., Cappellaro, E., Ciatti, F., Turatto, M., & Kowal, C.T. 1984, A&A Suppl. Ser. 58, 735 Barbon, R., Cappellaro, E., & Turatto, M. 1989, A&A Suppl. Ser. 81, 421 Barbon, R., Buondi, V., Cappellaro, E., & Turatto, M. 1999, A&A Suppl. Ser. 139, 531 Bartunov, O.S., Makarova, I.N., & Tsvetkov, D.Yu. 1992, A&A 264, 428 Bartunov, O.S., Tsvetkov, D.Yu., & Filimonova, I.V. 1994, PASP 106, 1276 Flin, P., Karpowicz, M., Murawski, W., & Rudnicki, K. 1979, Catalogue of Supernovae, Warszawa: Panstwowe Wydawnictwo Naukowe Howell, D.A., Wang, L., & Wheeler, J.C. 2000, ApJ, 530, 1666 Karpowicz, M., & Rudnicki, K. 1968, Preliminary Catalogue of Supernovae, Warsaw: Warsaw University Press Kowal, C.T., & Sargent, W.L.W. 1971, AJ, 76, 756 Sargent, W.L.W., Searle, L., & Kowal, C.T. 1974, Supernovae and Supernova Remnants, Ed. C.B.Cosmovichi, Dordrecht: D.Reidel Publ., p.33. Tsvetkov, D.Yu., & Bartunov, O.S. 1993, Bull. Inform. CDS, 42, 17 Tsvetkov, D.Yu, Pavlyuk, N.N., & Bartunov, O.S. 2004, Astronomy Letters, 30, 729 Van Den Bergh, S. 1997, AJ 113, 197 Van Dyk, S.D., Hamuy, M., & Filippenko, A.V. 1996, AJ, 111, 2017 Wang, L., Hoflich, P., & Wheeler, J.C. 1997, ApJ, 483, L29 Zwicky, F. 1958, Handbuch der Physik, vol 51, Ed. S.Flugge, Berlin: Springer-Verlag, p.766. Zwicky, F. 1965, Stars and Stellar Systems, vol. VIII, Ed. L.H.Aller and M.C.McLaughlin, Chicago: Univ. of Chicago Press, p.367