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Stephan’s Quintet (SQ): A Multi-galaxy Collision

Stephan’s Quintet (SQ): A Multi-galaxy Collision. C. K. Xu IPAC, Caltech. “Birth Certificate”: M.E. Stephan, 1876, CR Acad. Sci. Paris vol. 84, p641. Why is SQ interesting? It looks fantastic in every waveband. It reveals surprises every time being looked at by a new instrument.

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Stephan’s Quintet (SQ): A Multi-galaxy Collision

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  1. Stephan’s Quintet (SQ): A Multi-galaxy Collision C. K. Xu IPAC, Caltech

  2. “Birth Certificate”: M.E. Stephan, 1876, CR Acad. Sci. Paris vol. 84, p641.

  3. Why is SQ interesting? It looks fantastic in every waveband. It reveals surprises every time being looked at by a new instrument. Behind all the spectacular images and strange spectrographs, lies a very complex web of galaxy-galaxy and galaxy-IGM interactions. (4) It shows all kinds of interaction induced phenomena, including a large scale shock (~40 kpc), an IGM starburst, long tidal tails with tidal dwarf candidates, and a type II AGN. (5) How useful is the knowledge gained in studying this local (94 Mpc) system to our understanding of those multi-galaxy systems afar, such as multi-nuclei ULIRGs and multi-mergers in deep surveys? Who cares!

  4. SQ seen in deep R band: (S0/a) (Sbc sy2) 6583 km/s 6550 km/s (Sbc) (E) 5765 6620 km/s (Sd) (E) 786 km/s 6563 km/s Gallagher et al. (2001, AJ 122,163)

  5. Radio Continuum --- A gigantic shock front (~40 kpc) in the intragroup medium (IGM) 1.4 GHz (VLA B-Array) 1.4 GHz Westerbork Allan & Hartsuiker 1972, Nat. 239 Xu et al. 2003, ApJ 595, 665

  6. X-ray (Chandra) on B-band image X-ray (0.5-3 keV) on H image Trinchieri et al. (2003, A&A, 401, 173)

  7. Spectroscopic confirmation of shock excitation: Red contours: H (6600 km/sec comp.) Blue contours: H (5700 km/sec comp.) double spectrograph, Palomar 200” H/[NII] [SII] [OI] H/[NII] [SII] [OI] Xu et al. 2003, ApJ 595, 665

  8. A starburst in the IGM -- A product of high speed (900km/s) galaxy-IGM collision ISOCAM 15m R-band (Xu et al. 1999, ApJ 512, 178)

  9. Red contours: H (6600 km/sec comp., IGM) Blue contours: H (5700 km/sec comp., intruder) IGM starburst (“SQ-A”) (Xu et al. 1999, ApJ 512, 178)

  10. H/[NII] Red contours: H (6600 km/sec comp.) Blue contours: H (5700 km/sec comp.) Shock front Regions: [SII] H/[NII] [SII] [OI] H/[NII] SQ-A region (IGM starburst) [SII] [OI]

  11. SQ-A: A collision triggered starburst (Xu et al. 1999; 2003), • or a tidal dwarf (Plana et al. 1999, ApJL 516, L69) ? • Comparison: • Obs. facts collision tidal dwarf • 2 velocity (6600/6000 km/s) yes no • (IGM/intruder) • time scale OK (107 yr) too long (108 yr) • age of the starburst: 107 yr OK no • spatial link to the shock yes no

  12. Jog & Solomon (1992, ApJ 387, 152) model: IGM intruder H2 6600 km/s HI 6000 km/s HI H2 Bang!!! ~107K

  13. Molecular gas (CO) in the IGM starburst region (SQ-A): SQ-A: CO velocity BIMA, Gao & Xu, 2000, ApJL, 542, L82. intruder IGM Lisenfeld et al. (2002, A&A 394, 823) (IRAM 30m)

  14. 6600 km/sec total 6000 km/sec HI maps (VLA C/D) Williams et al. (2002, AJ, 123) 5700 km/sec

  15. LFUV (total)= 3.5 1010 L (ext. corr.) SFR (total)=6.7 M/yr SFR(SQ-A)=1.3 M/yr(20% of tot) SFR(N7319)=2.0 M/yr (tail: ~15%)SFR(N7318b)=3.4 M/yr GALEX image (blue: FUV, yellow: NUV) SQ-tip old tail FUV contours on R image • star formation rate • tidal features (tidal dwarf • candidates, or tidally induced star • formation regions). • size of the 7318b UV disk: ~80 kpc Xu et al. 2005, ApJL 619, L95

  16. Molecular gas in tidal tail: IRAM 30m CO (red) on 15um contours IRAM interferometer CO (beam=4.3x3.5”) SQ-A SQ-B (tidal dwarf) Lisenfeld et al. (2004, A&A 426, 471) Lisenfeld et al. (2002, A&A 394, 823)

  17. Interaction history (before the intruder): N7319 New scenario: (Xu et al. 2005 ApJL 619, 95) 7319/7318a interaction -> young tail N7318a Old theory: (Arp & Kormendy 1972, ApJL 178, 111; Moles et al 1997, ApJL 485, 69): two parallel passes of N7320c (the old intruder) 5900 km/s 6583 km/s 6550 km/s 6620 km/s young tail (1-2 108 yr) old tail (5-9 108 yr) 105 kpc

  18. Toomre & Toomre (1972) equal mass encounter, t = 200 Myr Indeed NGC7319 and 7318b have nearly equal mass: NGC7319: K=10.0 mag NGC7318a: K=10.3 mag FUV contours on a R-band image

  19. X-ray (XMM) contours, r-band image Connection of N7317 with the group: In a large R band and X-ray halo. terminal shock? N7317 (E) R-band contours, XMM image X-ray colors: R: 0.3-1.5 keV G: 1.5-2.5 keV B: 2.5-6.0 keV Trinchieri et al. 2005, A&A, in press

  20. One word summary: • we are just at the beginning of understanding SQ! • Remaining Questions: • Fate of the IGM gas (~1010 M): falling back to parent galaxies • (ULIRG-to-be?), or form new baby galaxies (tidal dwarfs)? • reason for the huge (80kpc) UV/HI disk of the intruder: a head-on • collision with 7318a (E) ~108 yrs ago (‘ring galaxy’ scenario)? • will the ‘intruder’ N7318b be eventually captured by the group? • secular evolution of galaxies in SQ: were 7318a (E) and 7320c (S0) • late type galaxies ~ 1 Gyrs ago? Will N7319 (Sbc) evolve into a • early type soon (it has no HI gas in the disk)? • How is the type II AGN triggered? • Is there any circum-nuclear starburst associated with the type II • AGN? Need high resolution (sub-arcsec) IR observations because • of the very high extinction (AV~5). • A challenge to simulators: Can this extremely complex system • be eventually simulated?

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