SCG 0018-4854:
A YOUNG AND DYNAMIC
GROUP
V. Presotto1,2, A. Iovino1 , E. Pompei 3, G. Temporin4
1INAF-OABrera,
2Università
Milano, I
dell’Insubria, Como, I
3ESO-Chile
4Institute
24-29 May 2009
Lucchin School -Bertinoro-
fur Astrophysik, Innsbruck, A
1
OUTLINE
• What are compact groups and why
they are important?
• SCG0018-4854
• Results
• Conclusions
24-29 May 2009
Lucchin School -Bertinoro-
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COMPACT GROUPS (CGs)
Selection criteria:
• Richness: n≥4 with (m≤m1+3)
• Isolation: RN≥3RG
• Compactness: mG<26mag∙arcsec-2
Properties:
• Low dispersion: <s>≈200km/s
• High density:
300<dgroup<108h2Mpc-2
• Lifetime ? tcross≈0.016 1/H0
Stephan’s quintet
SCGs sample:
Dmmember<Dmiso
Dm=mest-mint>4
(Hickson 1982;1992)
Seyfert’s sextet
24-29 May 2009
Lucchin School -Bertinoro-
(Iovino 2002)
3
INTERACTIONS IN CGs
Compact groups are perfect laboratories to test galaxies’ interactions
• Tidal forces => morphological distorsion
and disturbed kinematics
• Gas infall => triggering of strong burst of
star formation or feeding an AGN
• Galaxies merger => new galaxy + TDGs
Aim: reveal evidence of interaction
in SCG 0018-4854 to investigate
its evolution history
24-29 May 2009
Lucchin School -Bertinoro-
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SCG 0018-4854
From the SCGs cat (Iovino 2002)
• redshift: V≈3300 km/s (≈46Mpc)
• richness: 4 gal in close proximity,
R≈20 kpc
• density2: 104.88 gal/Mpc-3
• velocity dispersion2: ≈120 km/s
Galaxy
V1
(km/s)
Class2
Activity2
Notes
A (NGC 92)
3384
Saap
SBG
Tidal tail
Double nuclei 3
B (NGC 89)
3284
SB0/a pec
Sy2
Outflow 4
C (NGC 87)
3415
Irr
SFG
---
D (NGC 88)
3432
SBab pec
LINER
---
1
This work
Pompei et al. 2007
3 Danks & Alcaino 1981
4 Temporin et al. 2005
2
24-29 May 2009
Lucchin School -Bertinoro-
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SCG 0018-4854
R-band
Data from FORS2 @ VLT/ESO
Multi-slit spectroscopy: M & m
axis (except M axis NGC 88)
Grism: 1400V with l0 5200Å
20.8Å/mm (0.49 Å/px)
Texp: 4X2699s
Photometry: all gal
Filters: 1. R-band 6550Å
(FWHM 1650Å)
2. Ha 6615Å
(FWHM 61Å)
Texp: 3X119s (R-band)
3X100s (Ha)
24-29 May 2009
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NGC 92
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NGC 92
Ha
K
• Asymmetric gas radial velocity curve:
AP=23% => recent interaction:
0.2Gyr<
t
coll<0.7Gyr
• presence of a 8-shape1 along minor
axis => Nuclear bar misaligned with
respect to PA major axis
24-29 May 2009
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NGC 89
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NGC 89
Fig D
• Asymmetric stellar/gas radial velocity curve: AP=33-24% => recent
interaction: 0.2Gyr<
t
coll<0.7Gyr
• NLR: presence of gas multiple components (3/4)
24-29 May 2009
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NGC 89
Ha
Temporin et al. 2005
• SW direction: steep rise of gas velocity
• Spectroscopical confirmation of the galactic-scale outflow
• Not clear correlation between outflow & surrounding gas
24-29 May 2009
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NGC 88
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NGC 88
R-band
• Low surface brightness tidal tail
≈14x10kpc SW direction
Gas => regular pattern of rotation
24-29 May 2009
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NGC 87
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NGC 87
(major & minor axis)
Ha
• Face-on irregular
• Star forming regions Ha
• Velocity gradients along M&m axis
+ peculiar motions
24-29 May 2009
Lucchin School -Bertinoro-
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CONCLUSIONS
• We found peculiar kinematics and morphological
distortions probably due to interactions among
galaxies
• No double nucleus for NGC 92
• Recent interaction: 0.2Gyr<tcoll<0.7Gyr
• Spectroscopical confirmation of the galactic-scale
outflow of NGC 89
Presotto et al. 2009 in preparation
24-29 May 2009
Lucchin School -Bertinoro-
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Thanks
24-29 May 2009
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SCG 0018-4854 X-ray
Trinchieri et al. 2008
KT ≈ 0.2 keV => coolest system detected so far
24-29 May 2009
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SCG 0018-4854 X-ray
• Phase 3b
• Hi bridge between
NGC 92 and NGC 88
• NGC 89 completely
stripped of HI
Pompei et al.2007
24-29 May 2009
Lucchin School -Bertinoro-
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SCG 0018-4854 gal
properties
Galaxy
V1
(km/s)
Class2
Activity2
Notes
B mag1
MH
(109 Mo)I
A (NGC 92)
3384
Saap
SBG
Tidal tail
Double nuclei
13.81
>3.29
3
B (NGC 89)
3284
SB0/a pec
Sy2
Outflow 4
14.18
<0.02
C (NGC 87)
3415
Irr
SFG
---
14.67
0.81
D (NGC 88)
3432
SBab pec
LINER
---
14.98
2.52
24-29 May 2009
Lucchin School -Bertinoro-
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