The evolution of galaxies in groups

1. Claudia Mendes de Oliveira U. Sao Paulo The evolution of galaxies in groups Tonantzintla, Jul/2005

2. Plan of this class • General properties of loose, compact and fossil groups • Groups at intermediate redshifts • Evolution of the fraction of red galaxies in groups/clusters • Connection between clusters and groups • Transformation of galaxies – interactions and mergers • The formation of tidal dwarf galaxies and IHII • The Tully-Fisher relation for interacting galaxies • An evolutionary sequence for groups • Connection loose groups – compact groups • Connection compact groups – fossil groups

3. An Groups in the nearby universe • Loose groups – loose structures, they are the most common structures in the nearby universe – velocity dispersions of about 200 km/s and gal-gal separations of a few hundred kpc • Compact groups – compact structures, which are responsible for about only 1% of the luminosity density of the universe. However, their importance is in that they are good laboratories for the study of galaxy “transformation” – velocity dispersions of about 200 km/s and median separations of typically 60 kpc. • Fossil groups – groups formed by a single elliptical galaxy with a large X-ray halo surrounded by small companions. Could be the end products of compact groups.

4. Loose groups

5. Majewski et al. (2003) The Local Group

6. Members of the Local Group

8. Loose groupscatalogues

9. An De Vaucouleurs (1965) – 1st catalogue of groups • Groups were defined as overdensities in 2D, exhibiting similarities in redshift, morphology and apparent magnitude. Turner and Gott (1976) • Two-D computer algorith which looked for regions of the sky in which the number density of galaxies was enhanced by a given factor . Tully (1987), hierarquical method

10. An Cfa group catalogue - Huchra-Geller 1982, Huchra et al. 1983 • Friends-of-friends technique • Galaxies down to magnitude 14.5 ( magnitude limited) • Galaxies with velocities < 8000 km/s • A subsample named NB used only galaxies with v<4000 km/s.

12. An Groups from Garcia (1993) • Over 6000 galaxies from the Leda database • Galaxies down to magnitude B=14 • Galaxies with velocities < 5500 km/s

13. Other loose group samples • First large samples of groups contained about 1000 groups • They were constructed from different redshift surveys: Merchan, Maia e Lambas 2000, Giuricin et al. 2000, Tucker et al. 2000, Ramella et al. 2002 • More recently – 2dF galaxy redshift survey: 2200 groups (Merchan and Zandivarez Doos) and about 7000 groups (Eke et al. (2004) • SDSS+DR3 – over 10000 groups selected (Merchan and Zandivarez (2004)

14. Compact groupscatalogues

15. Compact groups – Hickson 1982 • Visual inspection of POSS - Groups with N>4 • Groups had to be fairly isolated (qN³ 3qG) • Surface brightness of the group < 26 mag/arcsec^2 • Magnitudes of the member galaxies had to be within 3 magnitudes of the brightest member An

16. Examples of compact groups of galaxies from Hickson's catalog. From Hunsberger et al. (1996) Exam

17. Hickson et al. (1992) • Radial Velocities • 92 groups with 3 galaxies • 69 groups com 4 galaxies • svel ~ 200 km/s • D ~ 39 h-1 kpc • rprojbetween 300 and 108h-1 Mpc-2 • High rproj and low svel = Interaction Laboratories

18. Dense, bound and isolated configurations (Sulentic, 1987; Hickson e Rood, 1988) • Chance alignments (Mamon, 1986, 1995; Walke e Mamon, 1989) • Edge-on filaments (Hernquist et al., 1995; Ostriker et al., 1996; Mulchaey et al., 1996) • Dense cores in loose groups(Diaferio et al., 1994, Governato et al., 1996) • Models

20. Ideal laboratory of interaction e.g. Verdes Montenegro et al. (2000) Coziol et al. Ponman et al.(96) Look at integrated properties of groups => compare with other environments IR,HI, CO, Warm gas, colours, X-rays What level of interaction? HCG 62 in X-rays This is the brightest Hickson group in X-rays

22. An Other compact-group samples • Older catalogues: Vorontsov-Velýaminov (1959, Atlas of Interacting Galaxies), Arp (1966, Atlas of Peculiar Galaxies), Shakhbazyan, Petrosyan, Baier, Tiersch (1973-1979, Compact Groups of Compact Galaxies”), Rose (1977, “a survey of compact groups of galaxies”). • Prandoni et al. 1994, Iovino 2002 (SCGs) • DPOSS compact groups, Iovino et al. 2003 • Compact groups from the Las Campanas Redshift Survey Allam and Tucker 2000 • CGs from the CFA2 Redshift survey , Barton et al. 96 • UZC-CGs, Focardi and Kelm 2002 • SDSS CGs - comissioning data – 153 deg2, 175 groups down to m=21. The majority does not have redshifts.

23. Fossil group

24. An Fossil groups • Groups with one large central elliptical galaxy and small companions (M2-M1 > 2.0) • They have an extended x-ray halo similar to rich groups and clusters • They may constitute a large fraction (about 20%) of the systems of similar mass. Samples of fossil groups: • Jones et al. (2003) – 5 groups • Vikhilinin et al. (1999) – 4 groups • Only 15 groups known to date

25. EXAMPLE OF FOSSIL GROUP Jones et al. 2003 About 15 known fossil groups to date (MdO 2005)

26. Observations of galaxies in groups – Galaxy populations • Loose groups contain preferentially late-type galaxies. • Compact groups have a fraction of 55% ellipticals (higher than loose groups but lower than clusters). • The few fossil groups which have been studied seem to have mostly early-type satellites, surrounding the large central elliptical galaxy

27. Morphology – density relation • Galaxy type correlates with density; It is also valid for groups (Postman and Geller 1984).

28. Fraction of emission-line galaxies vs. density in the SDSS Balogh et al.

29. Luminosity functions

30. Luminosity function of loose groups and the field • Stromlo-APM survey (Loveday et al. 1992) – 1769 galaxies down to bj=17.15. Found Mb=-19.5, α=-0.97 , φ*=1.4 x 10-2 • Las Campanas redshift survey (Lin et al. 1996) covered 18678 galaxies with <z>=0.1. Found M*=-20.29, α=-0.7 and φ *=1.9x 10 –2 • Cfa redshift survey (Marzke et al. 1994) covered 9063 galaxies with mz<15, for galaxies with vel>2500 km/s. The parameters were φ*=4.0 x 10 -2, M*=-18.8 and α=-1.0. If very nearby galaxies were included they found α=-1.87. • SDSS (Trentham et al. 2005) – find an α=-1.26 for Mr between –19 and –9. • Conclusion: faint-end of group LF is flat (α close to –1.0)!

31. In compact groups – dip around Mr=-18

32. Luminosity function of fossil groups

33. Survey of groups at medium redshifts Groups at z=0.4 • Main goal: compare star forming rates with those for nearby groups • Problem: background contamination

34. Groups at z=0.4 • Success rate in obtaining members with redshifts = 20% • 295 members in 26 groups • Typical group has 10 members

35. magnitude Wilman et al 2004 Groups at z~0.4 lowredshift F ração de galáxias passivas Evidence of evolution in groups of galaxies: Groups were more active environments in the past. Or better said: • The galaxies which formed the groups at intermediate redshifts were more active than the ones in the groups in the nearby universe. intermediate redshift

36. Red galaxy fraction High density All galaxies Low density MV < -20 Redshift (Bell et al 2004) Evolution of the fraction of passive galaxies Galaxies in the groups and in clusters had a larger fraction of blue galaxies at higher redshifts

37. 20 Star Formation Rate (OII eqiuv. Width) 15 10 5 Redshift 0 0.3 0.5 1.0 The star formation history of the universe Taxa de formação estelar total Grupos Aglomerados

38. Star formation vs. Morphology • The change in the star forming rate and the transformation of the morphology of a galaxy are distinct phenomena • Is their duration similar? • Are they caused by the same mechanism?

39. What is the connection between groups and clusters?

40. “clusters” “groups” Clusters accrete mass from the surrounding environment • History of cluster formation • Comparison of clusters today and in the past • How were the brightest galaxies formed? • Were clusters formed from the infall of groups? From z=0.1 to 0, a cluster accretes on average 10% of its mass mostly groups but also single galaxies

41. Nature ou Nurture? • Nature? Elliptical galaxies are formed in proto structures at high redshift and the rest of the populaton is formed by infall. • Or Nurture? The evolution of galaxies happen along a different route in dense environments.

42. Nurture -Transformation of galaxies • The transformation can be caused by internal or external processes • E.g. gas consuption, gas depletion, mergers • Mechanisms – what are viable mechanisms in groups? • Gravitational interactions • Mergers • Accretions

43. The Local Group

44. Compact groups of galaxies • They are a important tool - they are nearby analogs of the multiple interactions that happen often in the distant universe. • Sites for galaxy transformation • Groups that may fall into clusters • Perfect laboratories for studying processes that may be much more common in the distant universe

45. Environment where merging happens, at z=0 One can study local mergers to understand processes that happen at high z Interacting binaries and compact groups Local universe : few mergers High-z : enhanced merger frequency

46. Dynamical processes in dense groupsProcesses which may have been very important in the high-redshift universe, where interactions happened more often

47. Merging

50. HGC 31 Continuum beyond Ha Ha