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Compact Groups: kinematics and star formation

Claudia Mendes de Oliveira U. Sao Paulo, Brazil Collaborators: P. Amram, C. Balkowski, H. Plana, E. Cypriano, L. Sodré Jr. Compact Groups: kinematics and star formation. Chania, Aug 2004. Compact Groups of Galaxies. Ideal laboratory of interactions, weak and strong

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Compact Groups: kinematics and star formation

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  1. Claudia Mendes de Oliveira U. Sao Paulo, Brazil Collaborators: P. Amram, C. Balkowski, H. Plana, E. Cypriano, L. Sodré Jr. Compact Groups: kinematics and star formation Chania, Aug 2004

  2. Compact Groups of Galaxies • Ideal laboratory of interactions, weak and strong • Nearby counterparts of high-redshift multiplets

  3. H92 Intergalactic HII regions

  4. Natural place to look for new objects formed in galaxy collisions: compact groups high galaxy density; low velocity dispersion (e.g., Iglesias-Páramo & Vílchez 2001; Gallagher et al. 2001) • Here: discovery of IHII in Stephan’s Quintet

  5. HCG 92 - HI (VLA-Williams et al 1998, 1999) M(HI)=0.5 109 MO M(HI)=1.33 109 MO V=6000 km/s M(HI)=1.6 109 MO V=5700 km/s M(HI)=4.8 109 MO M(HI)=1.6 109 MO V=6600 km/s

  6. Observations • Gemini North • r’ and g’ GMOS imaging with seeing of ~0.75” • multislit spectroscopy: masks 1” + R400 grating -> 8A resolution, 4000-8000A coverage

  7. multislit spectroscopy: • Detection of 4 HII regions on the HI tail (Williams et al. 2002) • projected distance to the closest bright member galaxy: > 25kpc Intergalactic HII regions (IHII)

  8. IHII radial velocities are within ±20 km/s of the HI velocity: physical association of the knots with the cloud

  9. metallicities • N2 calibrator (Denicoló, Terlevich & Terlevich 2002) [NII]λ6584/Hα <12+log(O/H)>=8.6 (Sun: 8.8±0.1) • object c: 8.64 ±0.25 using [OIII]/Hβ (Edmunds & Pagel 1984): 8.4 ±0.2 →the IHII have been formed from pre-enriched material

  10. ages: • Starburst99 (Leitherer et al. 1999): solar metallicity, Salpeter IMF, instantaneous burst • ages from EW(Hα): 3.2 – 5.6 Myr mean: 4.6 Myr

  11. mass: • mass from the emission rate of ionizing fotons, Q(H0) , estimated from L(Hα): (2.9±1.4) x 104 Msun • expected number of O stars: ~20 to ~200 • mass from the luminosity of the stellar component R-band luminosities corrected for line-emission: (4.5±2.8) x 104 Msun • Lower limits because of internal extinction region c: (Hα/Hβ)=4.4 → AR ~ 1 mag masses might be at least twice these values

  12. other examples of similar phenomena • Gerhard et al. (2002): Virgo cluster M~103 Msun dproj~18 kpc to NGC4388 • Ryan-Weber et al. (2004) and Oosterloo et al. (2004) – 10 other examples

  13. Summary of the IHII characteristics: 1- compact (except for region b) but resolved 2- high metallicities (~60% solar) 3- masses of the order of 104 Msun 4- ages ranging from 3.2 to 5.6 Myr 5- located far from bright galaxies 6- coincide in location and velocity with the HI tail

  14. What is the origin of the IHII in Stephan’s Quintet? • were they removed from one of the galaxies? typical ejection velocities ~200-300 km/s Teject > 108 yr Ages: a few Myr • probably they were formed where they are observed

  15. origins… → tidal interactions? → interactions with a hot intergalactic medium? → …?

  16. A few questions… • role of the IHII in the pollution of the intergalactic medium? • how common the IHII are?

  17. Kinematics of member galaxies in compact groups

  18. Motivation for studying internal kinematics Compact groups = a mixed-bag Groups with different evolutionary stages, sizes, HI content, X-ray properties, … Seyfert's sextet Various environments sampled In an attempt to learn something about the nature and the physics of the compact groups it is important to classify them according to their evolutionary stages.

  19. Kinematics of Galaxies in Compact Groups. 31 groups (104 galaxies) observed at ESO or CFHT with a Fabry-Perot System Data used to study: • Merging groups • Strongly interacting • Weakly interacting • Non-Groups • Single Irregular Galaxies • Evolutionary stages of the groups HCG 31 • Searches for tidal dwarf galaxy candidates • Tully-Fisher relation for the group galaxies.

  20. Fabry-Perot Observations   Integral Field Spectroscopy: • Large FOV • Spatial sampling : 0.5’’ à 1’’ (higher than in HI) • Spectral sampling : ~ 10 km.s-1 (emission line = higher resolution than stellar absorption lines) 

  21. HCG 31 A merging group

  22. HGC 31 Johnson & Conti, 2000

  23. HGC 31 Continuum beyond Ha Ha

  24. R > 50 000 1 px = 0.405 arcsec FSR = 155 km/s =48 cx spectral sampling = 3.3 km/s

  25. Tully-Fisher relation for compact group galaxies.

  26. Two previous studies on the internal kinematics of compact group galaxies 1) Nishiura et al. (2000) studied 30 galaxies and found that most have peculiar rotation curves + dynamical properties of the galaxies do not correlate with any galaxy/group parameter. 2) Rubin et al. (1991) studied 32 galaxies – found that 2/3 have peculiar rotation curves. They found a large offset of the TF relation with respect to the field relation in the sense that galaxies in compact groups have “too low velocities for their luminosities or, luminosities which are overbright for their rotation velocities”. HCGs have low M/L compared to field by 30% - this could be explained if they have smaller dark halos than their field counterparts. WE REVISIT THIS PROBLEM – 25 galaxies (13 in common)

  27. Rotation curves obtained from 2d velocity fields. DATA: Velocity fields for 29 galaxies Four were too peculiar for TF We used Vmax instead of Vflat (to be able to use more gal.) Control samples: Courteau (1997) and Verheijen (2001) Comparisons with previous studies: The 2D velocity maps obtained with a Fabry-Perot instrument allowed us to mimic a slit through our data in order to recover the rotation curves obtained from long slit spectroscopy.

  28. Lesson: The velocity fields of compact group galaxies are, in several cases, significantly affected by noncircular motions, local asymmetries and misalignments between the kinematic and stellar axes. A fine tuning of map parameters (center, inclination and position angle of the velocity fields) and an average of the velocities over a large sector of the galaxy are needed to derive reliable rotation curves and representative values of Vmax.

  29. Common mass-to-size relations. But: parameters for the TF relation are mostly derived in the inner parts of the galaxy, the agreement does not tell us much about the DM (outer halo). Our observations show that the galaxy halos have not been significantly stripped inside R25. Nevertheless, mass models using a common halo for the groups added to the individual star distributions of each galaxy should be performed to test this scenario.

  30. Asymmetric rotation curves • H91a and H96a present strong asymmetries • These are brightest galaxies in M51 like systems

  31. Main Conclusions 1) H31 and H92 contain several IHII, probably formed in HI clouds that were ejected from the group members 2) The IHII have metallicities close to solar, ages of a few Myrs and masses of a few 104 solar masses 3) H31 has a merger in its center

  32. Main Conclusions 4)Compact group galaxies follow the TF Larger scatter 5) A fine tunning of the parameters and an average of the velocities over a large sector of the galaxies are necessary to obtain meaninful RC's. 6) Outliers are most probably overbright for their velocities (one has double kinematic component) 7) Care should be taken when obtaining rotation curves of galaxies in dense environments with long slit.

  33. EFHARISTO!

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