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Dwarf lenticular galaxies: structure and evolutionary census

Dwarf lenticular galaxies: structure and evolutionary census. Sil’chenko Olga K. and Startseva Marina A. Sternberg Astronomical Institute, Moscow, Russia Moiseev Alexei V. Special Astrophysical Observatory, Nizhnij Arkhyz, Russia. Where have S0s come from?.

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Dwarf lenticular galaxies: structure and evolutionary census

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  1. Dwarf lenticular galaxies: structure and evolutionary census Sil’chenko Olga K. and Startseva Marina A. Sternberg Astronomical Institute, Moscow, Russia Moiseev Alexei V. Special Astrophysical Observatory, Nizhnij Arkhyz, Russia

  2. Where have S0s come from? Fasano et al. (2000): At z>0.5 the population of S0s in clusters (where they dominate presently) is negligible, so they have formed 3-4 Gyr ago `en mass’. Wilman et al. (2009): At z=0.4 many S0s form IN GROUPS, at their outskirts, so they form probably through gravitational interaction.

  3. The NGC 80 group as a probable situ of S0 formation • Massive (>1014 solar masses, Ramella et al. 2002) • Rich (45 bright members, Mahdavi and Geller 2004) • X-ray luminous (log LX = 42.56, Mahdavi et al. 2000) • BUT disk galaxies dominate (only 3 Es).

  4. The NGC 80 group as a probable situ of S0 formation X-ray image (ASCA) Optical image (DSS)

  5. Startseva, Silchenko & Moiseev (2009): Astronomy Reports, in press • Two-colour (BV) surface photometry of 13 disk galaxies with the SCORPIO of the 6m telescope; • 9 of them are classified by us as S0s

  6. Startseva, Silchenko & Moiseev (2009): Astronomy Reports, in press • We have used the software GIDRA (Moiseev et al. 2004) to decompose two-dimensional images into Sersic components iteratively, starting from the outermost parts. • All S0s but two have appeared to possess two-tiers (`antitruncated’) disks and exponential bulges (`pseudobulges’?); • The remaining two which are the smallest contain only one exponential component (a disk?)

  7. Types of disk surface-brightness profiles: Exponential Truncated Freeman’s type II Antitruncated Pohlen & Trujillo 2006

  8. Two dwarf S0s fainter than MB=-17.5, both are located close to giant galaxies A satellite of NGC 80 (central group galaxy) A satellite of NGC 86

  9. … and both have pure disk structure – no bulges

  10. From UCM0018+2216 there is a smooth transition to the second part of the topic • According to Gallego et al. (1996) and to the data in their survey of emission-line galaxies UCM, this galaxy demonstrates a moderate-strength star formation burst. • Many other (most?) dwarf lenticulars in groups reveal also signs of current/recent star formation.

  11. The sample of nearby S0s by Sil’chenko (2008): a subsample of faint group S0s • All are very young!

  12. Images(SDSS) NGC 3156 NGC 3418 NGC 5379 NGC 5574

  13. SDSS colour maps (g’-r’) NGC 3156 NGC 3418 NGC 5379 NGC 5574

  14. Our own colour mapping: NGC 509

  15. NGC 3156: a disk-dominated S0

  16. NGC 3156: young stars in the nucleus SAURON data, January 2002

  17. NGC 3156: gas over the disk SAURON data, January 2002 [OIII] l5007

  18. NGC 5379: a disk-dominated S0 • A ring of star formation? • Solid-body rotation?

  19. NGC 5379: star formation over the whole disk nucleus SCORPIO data, March 2008 20” off 10” off

  20. NGC 5379: radial gas motionsor inner polar disk? [OIII] l5007 SAURON data, April 2007

  21. NGC 5379: complex pattern of the stellar velocity dispersion The young (disk-like?) nucleus and a ring of young stars shrudded by the dust

  22. Conclusions • `Downsizing’ in groups: small S0s are forming just now while giant S0s have formed 3-4 Gyr ago. • Mechanisms of transformation may be various: minor merging with gas-rich dwarfs for `isolated’ group members, `harassment’ for satellites of giant galaxies. • Small S0s are almost bulgeless long in the course of shaping; so for giant well-shaped S0s we may suggest late growth of their large pseudobulges and/or original presence of large `classic’ bulges.

  23. Acknowledgements • This paper makes use of data obtained from the Isaac Newton Group Archive which is maintained as part of the CASU Astronomical Data Centre at the Institute of Astronomy, Cambridge. • We use also the photometric images of the galaxies obtained in the frame of the SDSS project. Funding for the Sloan Digital Sky Survey (SDSS) and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, and the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web site is http://www.sdss.org/. • The most of our data have been obtained at the 6m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences.

  24. Kormendy’s diagram

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