Dwarf lenticular galaxies: Dwarf lenticular galaxies: structure and evolutionary structure and evolutionary

censuscensusSil’chenko Olga K. and Startseva Marina A.Sil’chenko Olga K. and Startseva Marina A.Sternberg Astronomical Institute, Moscow, Sternberg Astronomical Institute, Moscow,

RussiaRussiaMoiseev Alexei V.Moiseev Alexei V.

Special Astrophysical Observatory, Nizhnij Special Astrophysical Observatory, Nizhnij Arkhyz, RussiaArkhyz, Russia

Where have S0s come Where have S0s come from?from?

Fasano et al. (2000): At z>0.5 the Fasano et al. (2000): At z>0.5 the population of S0s in clusters (where they population of S0s in clusters (where they dominate presently) is negligible,dominate presently) is negligible,

so they have formed 3-4 Gyr ago `en so they have formed 3-4 Gyr ago `en mass’.mass’.

Wilman et al. (2009): At z=0.4 many S0s Wilman et al. (2009): At z=0.4 many S0s form IN GROUPS, at their outskirts, so form IN GROUPS, at their outskirts, so they form probably through gravitational they form probably through gravitational interaction.interaction.

The NGC 80 group as a The NGC 80 group as a probable situ of S0 formationprobable situ of S0 formation

Massive (>10Massive (>1014 14 solar masses, Ramella solar masses, Ramella et al. 2002)et al. 2002)

Rich (45 bright members, Mahdavi and Rich (45 bright members, Mahdavi and Geller 2004)Geller 2004)

X-ray luminous (log LX-ray luminous (log LXX = 42.56, = 42.56, Mahdavi et al. 2000)Mahdavi et al. 2000)

BUT disk galaxies dominate (only 3 BUT disk galaxies dominate (only 3 Es).Es).

The NGC 80 group as a The NGC 80 group as a probable situ of S0 formationprobable situ of S0 formation

Optical image (DSS)X-ray image (ASCA)

Startseva, Silchenko & Moiseev Startseva, Silchenko & Moiseev (2009): Astronomy Reports, in (2009): Astronomy Reports, in

presspress Two-colour (BV) surface photometry of 13 Two-colour (BV) surface photometry of 13

disk galaxies with the SCORPIO of the 6m disk galaxies with the SCORPIO of the 6m telescope;telescope;

9 of them are classified by us as S0s9 of them are classified by us as S0s

Startseva, Silchenko & Moiseev Startseva, Silchenko & Moiseev (2009): Astronomy Reports, in (2009): Astronomy Reports, in

presspress We have used the software GIDRA (Moiseev We have used the software GIDRA (Moiseev

et al. 2004) to decompose two-dimensional et al. 2004) to decompose two-dimensional images into Sersic components iteratively, images into Sersic components iteratively, starting from the outermost parts.starting from the outermost parts.

All S0s but two have appeared to possess All S0s but two have appeared to possess two-tiers (`antitruncated’) disks and two-tiers (`antitruncated’) disks and exponential bulges (`pseudobulges’?);exponential bulges (`pseudobulges’?);

The remaining two which are the smallest The remaining two which are the smallest contain only one exponential component (a contain only one exponential component (a disk?)disk?)

Types of disk surface-brightness Types of disk surface-brightness profiles:profiles:

Exponential

Truncated

Freeman’s type II

Antitruncated

Pohlen & Trujillo 2006

Two dwarf S0s fainter than MTwo dwarf S0s fainter than MBB=-=-17.5, both are located close to 17.5, both are located close to

giant galaxiesgiant galaxies

A satellite of NGC 80 (central group galaxy)

A satellite of NGC 86

… … and both have pure disk and both have pure disk structure – no bulgesstructure – no bulges

From UCM0018+2216 there is a From UCM0018+2216 there is a smooth transition to the second smooth transition to the second

part of the topicpart of the topic

According to Gallego et al. (1996) According to Gallego et al. (1996) and to the data in their survey of and to the data in their survey of emission-line galaxies UCM, this emission-line galaxies UCM, this galaxy demonstrates a moderate-galaxy demonstrates a moderate-strength star formation burst.strength star formation burst.

Many other (most?) dwarf lenticulars Many other (most?) dwarf lenticulars in groups reveal also signs of in groups reveal also signs of current/recent star formation.current/recent star formation.

The sample of nearby S0s by The sample of nearby S0s by Sil’chenko (2008): a subsample Sil’chenko (2008): a subsample

of faint group S0sof faint group S0s

All are All are very very young!young!

ImagesImages (SDSS)(SDSS)

NGC 3156

NGC 5379

NGC 3418

NGC 5574

SDSS colour maps SDSS colour maps (g’-r’)(g’-r’)

NGC 3156

NGC 3418

NGC 5379 NGC 5574

Our own colour mapping: NGC Our own colour mapping: NGC 509509

NGC 3156: a disk-NGC 3156: a disk-dominated S0dominated S0

NGC 3156: young stars in the NGC 3156: young stars in the nucleusnucleus

SAURON data, January 2002

NGC 3156: gas over the diskNGC 3156: gas over the disk

SAURON data, January 2002 [OIII]5007

NGC 5379: a disk-NGC 5379: a disk-dominated S0dominated S0

A ring of A ring of star star formationformation??

Solid-body Solid-body rotation?rotation?

NGC 5379: star formation over NGC 5379: star formation over the whole diskthe whole disk

SCORPIO data, March 2008

nucleus

10” off20” off

NGC 5379: radial gas motionsNGC 5379: radial gas motionsor inner polar disk?or inner polar disk?

SAURON data, April 2007[OIII] 5007

NGC 5379: complex pattern of NGC 5379: complex pattern of the stellar velocity dispersionthe stellar velocity dispersion

The young (disk-like?) nucleus and a ring of young stars shrudded by the dust

ConclusionsConclusions `Downsizing’ in groups: small S0s are `Downsizing’ in groups: small S0s are

forming just now while giant S0s have forming just now while giant S0s have formed 3-4 Gyr ago.formed 3-4 Gyr ago.

Mechanisms of transformation may be Mechanisms of transformation may be various: minor merging with gas-rich dwarfs various: minor merging with gas-rich dwarfs for `isolated’ group members, for `isolated’ group members, `harassment’ for satellites of giant galaxies.`harassment’ for satellites of giant galaxies.

Small S0s are almost bulgeless long in the Small S0s are almost bulgeless long in the course of shaping; so for giant well-shaped course of shaping; so for giant well-shaped S0s we may suggest late growth of their S0s we may suggest late growth of their large pseudobulges and/or original large pseudobulges and/or original presence of large `classic’ bulges.presence of large `classic’ bulges.

AcknowledgementsAcknowledgements This paper makes use of data obtained from the Isaac Newton This paper makes use of data obtained from the Isaac Newton

Group Archive which is maintained as part of the CASU Group Archive which is maintained as part of the CASU Astronomical Data Centre at the Institute of Astronomy, Astronomical Data Centre at the Institute of Astronomy, Cambridge. Cambridge.

We use also the photometric images of the galaxies obtained We use also the photometric images of the galaxies obtained in the frame of the SDSS project. Funding for the Sloan Digital in the frame of the SDSS project. Funding for the Sloan Digital Sky Survey (SDSS) and SDSS-II has been provided by the Sky Survey (SDSS) and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the the National Aeronautics and Space Administration, the Japanese Monbukagakusho, and the Max Planck Society, and Japanese Monbukagakusho, and the Max Planck Society, and the Higher Education Funding Council for England. The SDSS the Higher Education Funding Council for England. The SDSS Web site is http://www.sdss.org/.Web site is http://www.sdss.org/.

The most of our data have been obtained at the 6m telescope The most of our data have been obtained at the 6m telescope of the Special Astrophysical Observatory of the Russian of the Special Astrophysical Observatory of the Russian Academy of Sciences.Academy of Sciences.

Kormendy’s diagramKormendy’s diagram