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Fossil and Compact Groups C. Mendes de Oliveira, IAG/U.Sao Paulo, Brazil

Main collaborators: P. Amram, C. Balkowski, D. Bortoletto, E. Cypriano, H. Plana, L.Sodré,S.Temporim. Fossil and Compact Groups C. Mendes de Oliveira, IAG/U.Sao Paulo, Brazil. IAU S235 – Prague, Aug 2006 Galaxy Evolution across the Hubble time. Poor groups of galaxies

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Fossil and Compact Groups C. Mendes de Oliveira, IAG/U.Sao Paulo, Brazil

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  1. Main collaborators: P. Amram, C. Balkowski, D. Bortoletto, E. Cypriano, H. Plana, L.Sodré,S.Temporim Fossil and Compact Groups C. Mendes de Oliveira, IAG/U.Sao Paulo, Brazil IAU S235 – Prague, Aug 2006 Galaxy Evolution across the Hubble time

  2. Poor groups of galaxies • small systems (a few L* galaxies) • More than 50% of the nearby structure in the universe (Tully 1987) are in groups of 3-20 members • A small fraction of these live in compact groups (CGs are responsible for 1% of the luminosity density of the universe) • Compact Groups of galaxies (CGs) • 3-7 bright gal. with projected g/g separation ~ galaxy diameter • Low velocity dispersions (~200 km/s) • Fairly isolated (by selection) • CG  high fraction of interacting members • evolve through dynamical friction • merge to form one single galaxy ? • Fossil group (Vikhlinin et al. 1999; Jones et al. 2003)

  3. HI in Compact Groups different evolutionary stages Phase 3b: Gas in a cloud Phase 1: Low level ofinteraction Phase 2: Gas in tidal features Phase 3a. No HI in the galaxies Verdes Montenegro et al. 2001

  4. CGs are physical entities : • Diffuse intragroup matter is inferred in 75% of HCG => Physically bound (Hickson 1997, Mulchaey 2002,Ponman et al.) • The X-ray emitting CGs are the higher density groups and are dominated by a E. • CGs dominated by S do not show X-ray emission (Zabludoff & Mulchaey 1998) HCG 62 An X-ray Atlas of Groups of Galaxies Mulchaey, Davis, Mushotzky and Burstein (2003) http://www.ociw.edu/~mulchaey/Atlas/atlas.html

  5. Example of Compact Group: • INFALL • Stephan’s Quintet: • 5 members • 4 strongly interacting g. • 1 foreground g. • 3 g. with DV~0 • First intruder: possibly NGC 7320C • A new intruder with DV=1000 km/s Emitting shock region (radio continuum, X-ray, Ha,...) NGC 7331, 821 km/s, 30’ N7320C, 6000 km/s,3’ Stephan's Quintet Arp, 1973 N7319, 6650 km/s,Sb N7318B,5770 km/s, Sbpec N7318A,6620 km/s, E2 N7320,800 km/s, Sad N7317, 6563 km/s, E4 GEMINI/GMOS i-band

  6. Stephan's Quintet • Red contours HI (Williams et al 2002) • No HI in the galaxies ! • All the HI is in the tidal tails (1010 Mo) ! 12CO in the tidal tail (Lisenfeld et al. 2004) Star forming objects in the tail and in the intragroup medium

  7. HCG 31 • r-band • Gemini+GMOS • (Mendes de Oliveira 2006) • Red HI profiles • (VLA Verdes-Montenegro et al. 2005) • z = 0.013 • = 60 km/s • Gas-rich • Intense SFR

  8. CGs are bound structures showing numerous signs of interaction • Strong “velocity dispersion – morphology” correlation • Signs of interactions: • Interactions (which do not disrupt galaxy) are common (Mendes de Oliveira et al 1994, 1998; Amram et al 2003,etc). • Mergers exist but are rare (6% of galaxies are mergers, Zepf 1993). Most E galaxies in groups are old (Proctor et al. 2005, Mendes de Oliveira et al. 2005) • The CGs which show highest activity have low s. • Diffuse intergalactic light • Kinematics/dynamics • Disturbed velocity field (and rotation curves) • Double kinematic gas component • Kinematic warping • Gaseous versus stellar major-axis misalignment • HI deficiency in CGs (Verdes-Montenegro 2001) • Disruption of the galaxies: Central double nuclei

  9. R B May come from stripping of dwarf galaxies (bluer than the galaxies) dissolved into the group potential well (da Rocha & Mendes de Oliveira 2005) Diffuse light in HCG 79 (Seyfert’s sextet) ~ 46 ±11 % of the total light.

  10. CGs are bound structures showing numerous signs of interaction • Signs of interactions: • Interaction (who do not disrupt g.) are common (Mendes de Oliveira et al 1994, 1998; Amram et al 2003). • Mergers exist but are rare (6% of the galaxies, Zepf 1993) • The higher activity CGs have low s. • Diffuse intergalactic light • Kinematics/dynamics • Disturbed velocity field (and rotation curves) • Double kinematic gas component • Kinematic warping • Gaseous versus stellar major-axis misalignment • HI deficiency in CGs (Verdes-Montenegro 2001)

  11. HCG 16 c(Mendes de Oliveira et al 1998) Ha Stellar Axis Gas Axis R image of the central region (12’’) Interaction indicators

  12. z=0.60 z=0.45 z=0.30 z=0.15 z=0 z=0.60: DV/V=-[6,15]% z=0.45: DV/V=-[4,10]% z=0.30: DV/V=-[3,7]% z=0.15: DV/V=-[1,5]% z=0 : DV/V= 0% Beam smearing effects may bias the Tully-Fisher relation (shifted towards lower M/L) Mendes de Oliveira et al, 2003

  13. HCG 31 • Even @ low redshift • controversy exists on the nature and the history of the system ! • Pre-merging phase or chance alignment ? • How many galaxies ? • TDGs ? Color Ha velocity Field (Amram et al. 2004) White HI isovelocities (Verdes Montenegro et al 2005)

  14. GIRAFFE/VLT Seeing ~ 0.62” z=0.15 2.6 kpc/" z=0.30 4.4 kpc/ ’’ 150 km/s -150 km/s z=0.45 5.7 kpc/ ’’ z=0.60 6.7 kpc/ ’’

  15. low contrast r’-band low contrast Ha+[NII] net s~150 km/s CG infalling @ V~1700 km/s into the cluster Abell 1367 (Cortese et al 2006). Iglesias-Paramo et al.2002 Sakai et al. 2002 2 giant galaxies +10 dwarfs/ iHII highest density of star formation activity ever observed in the local clusters Shells high contrast r’-band high contrast Ha+[NII] net tidal forces + ram-pressure  the CG is fragmented and Ha blown out. Preprocessing galaxy evolution during the high redshift cluster assembly phase ?

  16. Do nearby CGs mimic the high redshift universe ? • Yes: high density + low s => high interaction rate • No: CGs are long-lived structures. Probably no isolated CGs in the • high z universe but CGs may fuel high z clusters? Produce fossil groups? CGs @ high z are difficult to detect (and are still to be discovered) 1 Mpc 18 galaxies within 2000 km/s • CG 6 @ z=0.22 • Lee et al. (2004) • = 700 km s Medium redshift example of CG? Core of a cluster ? Pompei et al. 2006 find no difference in properties of 11 compact groups with mean z=0.1

  17. 1 - Sistems dominated by a single giant elliptical galaxy (m12 ≥ 2 mag) 2 – Extended X-Ray emission: LX,bol ≥ 1042 h50-2 erg/s Fossil Groups: what are they ?

  18. Fossil groups: End products of merging of L* galaxies in low-density environments (Ponman et al. 94, Jones et al. 2003). Extreme case of dynamical friction • The most massive versions of today's CGs are the best candidate precursors of fossil groups: • CGs with • high s • neighborhoods • rich in low-luminosity • companions • E(s) Fossil group RXJ 0454.8-1806 @ z = 0.0314 (Mendes de Oliveira 2005). B image from Blanco+Mosaic (530 kpc) Red contours are ASCA (Yoshioka et al. 2004).

  19. Formation scenarios: • Massive end of • the elliptical galaxy distribution • (Yoshioka et al. 2004) • 2.Merging of bright galaxies in • groups (Jones et al. 2003) • If the merger interpretation is correct, fossil groups have seen little infall of luminous • galaxies since their collapse.

  20. What’s the origin of fossil groups? Merging of L* galaxies… • In the field.Andromeda and Milky Way when they merge - will they form a fossil group? Unlikely, the total mass will be 5x10^12 Msun and no X-ray gas • In Compact Groups. Multiple merger of L* (Ponman et al. 1994) D‘Onghia & Lake, 2004 ApJ,612,628

  21. All fossil groups known to date 15 Mendes de Oliveira, Cypriano & Sodré 2005, astro-ph/0509884

  22. Members Low S/N Non Members CMD – RXJ 1552.2+2013 sigma=795 km/s Gemini/GMOS data MdO, Cypriano and Sodré 2005

  23. Photometric lum. function Spectroscopic completeness function Spectroscopic lum. function Luminosity Function of RX J1552.2+2013 Mdo, Cypriano, Sodré Jr. 2005

  24. Dynamical friction does not deplete the faint-end for Given a mass function only the high mass end will be affected in fossil groups by dynamical friction and major merging. for Dynamical friction will not affect the mass function below

  25. In favour of merger hypothesis: • gap in luminosity function at L* • high L of central galaxy • strong correlation between LX of groups and Lopt of central galaxy Against the merger hypothesis: M/L ratios seem to be much higher in fossil groups than in clusters and groups (Yoshioka et al. 2004) • Khosroshahi et al. find no boxy galaxies in a sample of 7 first-ranked galaxies in fossil groups, indicating that these galaxies may have grown by accretion either than merger

  26. Summary/Conclusions. • Nearby CGs are very complex systems, tracing their history is a challenge (e.g. Stephan’s Quintet). Groups are in different evolutionary phases. • CGs are bound structures (X-rays) showing numerous signs of interaction. They are sites of formation of tidal dwarf galaxies, young clusters and intergalactic HII regions. • CGs infalling into clusters may provide a mechanism to form clusters @ high z • Do CGs mimic the high redshift universe ? Open question. • Yes: high density + low s => high interaction rate • No: CGs are long-lived structures. Probably no isolated CGs at high z • Interpretation of kinematics of distant galaxies (and TF relation) may need nearby sample of galaxies to disentangle beam-smearing from evolutionary effects. • There are less than two dozen fossil groups known. A fraction of them are fossil clusters. A search in the SDDS-DR4 yielded five candidate fossil clusters. • First ranked galaxies – mostly disky, favours accretion either than merging. A few are cD galaxies, most have ionized gas and half have very old ages. • The groups with determined luminosity functions have either flat or declining functions. • Groups like HCG 31, Stephan’s quintet could not have been the precursors of FGs • More high-redshift compact groups and fossil groups/clusters badly needed.

  27. Search for new fossil groups/clusters • Search for fossil groups in the SDSS-DR4 • Check profiles and colours to ensure that galaxy M1 (taken from LRG sample, Eisenstein 2001) is an early-type object. • A cone search is made within 1 Mpc to look for neighbours with M2 > M1+2 with accordant z-phot. • A cross-match with ROSAT all-sky Survey sources is made to choose only X-ray extended sources. dos Santos et al. 2006

  28. CGs are bound structures showing numerous signs of interaction • But: • Stellar populations of early-type g. in CGs are old (Proctor et al 1994, Mendes de Oliveira et al. 2005). • Crossing times are a fraction of the Hubble time. How can they survive so long? Mechanisms to explain the longevity of groups: continuous secondary infall, massive halos (Ramella 1994, Athanassoula et al. 1997,Flechoso & Dominguez-Tenreiro 2001,Zabludoff & Mulchaey ) • More satellite galaxies are predicted then seen in CGs ( Moore et al. 1999, Kyplin et al. 1999).

  29. Dwarf galaxies in HCG 68 Study of individual groups, taking into account detailed morphology give alpha = -1.2 (H68 and H44) Bomans et al. (2006) find very steep composite luminosity function of five groups using statistical background subtraction

  30. H42  =-1.7 photometric LF Photometric luminosity function alpha = -1.7 Spectroscopic luminosity function alpha= -1.2 Carrasco, Mendes de Oliveira and Infante 2006  =-1.2 spectroscopic LF

  31. Several groups detected in the background of HCG 42

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