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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. - PowerPoint PPT Presentation
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Stephan’s Quintet (SQ):A Multi-galaxy Collision
C. K. Xu
IPAC, Caltech
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“Birth Certificate”: M.E. Stephan, 1876, CR Acad. Sci. Paris vol. 84, p641.
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Why is SQ interesting?
(1) It looks fantastic in every waveband.(2) It reveals surprises every time being looked at by a new instrument.(3) 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!
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6563 km/s786 km/s
5765 6620 km/s
6550 km/s
6583 km/s (Sbc sy2)
(S0/a)
(E)
(Sbc) (E)
(Sd)
Gallagher et al. (2001, AJ 122,163)
SQ seen in deep R band:
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1.4 GHz (VLA B-Array)
Radio Continuum --- A gigantic shock front (~40 kpc) in the intragroup medium (IGM)
Allan & Hartsuiker 1972, Nat. 239
1.4 GHz Westerbork
Xu et al. 2003, ApJ 595, 665
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Trinchieri et al. (2003, A&A, 401, 173)
X-ray (0.5-3 keV) on H imageX-ray (Chandra) on B-band image
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[OI]
[OI][SII]
H/[NII]
H/[NII]
[SII]
Xu et al. 2003, ApJ 595, 665
Blue contours: H (5700 km/sec comp.)Red contours: H (6600 km/sec comp.)
Spectroscopic confirmation of shock excitation:
double spectrograph, Palomar 200”
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R-bandISOCAM 15m
A starburst in the IGM -- A product of high speed (900km/s) galaxy-IGM collision
(Xu et al. 1999, ApJ 512, 178)
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Blue contours: H (5700 km/sec comp., intruder)Red contours: H (6600 km/sec comp., IGM)
IGM starburst (“SQ-A”)
(Xu et al. 1999, ApJ 512, 178)
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[OI]
[OI][SII]
H/[NII]
H/[NII]
[SII]
H/[NII]
[SII]
Shock frontRegions:
SQ-A region(IGM starburst)
Blue contours: H (5700 km/sec comp.)Red contours: H (6600 km/sec comp.)
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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
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6600 km/s HI
6000 km/s HIH2
H2
Bang!!!
~107K
Jog & Solomon (1992, ApJ 387, 152) model:
IGM intruder
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SQ-A: CO velocity
Lisenfeld et al. (2002, A&A 394, 823) (IRAM 30m)
BIMA, Gao & Xu, 2000, ApJL, 542, L82.
Molecular gas (CO) in the IGM starburst region (SQ-A):
intruder IGM
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HI maps(VLA C/D)
6600 km/sec
6000 km/sec
5700 km/sec
Williams et al.(2002, AJ, 123)
total
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GALEX image (blue: FUV, yellow: NUV)
Xu et al. 2005, ApJL 619, L95
• star formation rate
• tidal features (tidal dwarf
candidates, or tidally induced star
formation regions).
• size of the 7318b UV disk: ~80 kpc
SQ-tip
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
FUV contours on R image
old tail
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IRAM interferometer CO (beam=4.3x3.5”)
Lisenfeld et al. (2002, A&A 394, 823)
IRAM 30m CO (red) on 15um contours
Molecular gas in tidal tail:
SQ-A
SQ-B(tidal dwarf)
Lisenfeld et al. (2004, A&A 426, 471)
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New scenario:(Xu et al. 2005ApJL 619, 95)7319/7318ainteraction ->
Old theory:(Arp & Kormendy1972, ApJL 178, 111; Moles et al 1997, ApJL 485, 69): two parallel passes of N7320c (the old intruder)
Interaction history(before the intruder):
young tail (1-2 108 yr)
old tail (5-9 108 yr)
N7319
N7318a
young tail
6620 km/s
6583 km/s6550 km/s
5900 km/s
105 kpc
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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
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X-ray (XMM) contours, r-band image
R-band contours, XMM image
Trinchieri et al. 2005, A&A, in press
Connection of N7317with the group:In a large R band and X-ray halo.
X-ray colors:R: 0.3-1.5 keVG: 1.5-2.5 keV B: 2.5-6.0 keV
N7317 (E)
terminal shock?
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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?