1. SCG 0018-4854: A YOUNG AND DYNAMIC GROUP
V. Presotto1,2, A. Iovino1 , E. Pompei 3, G. Temporin4
Goodmorning everybody, during these days we have travelled back to the origin of the universe, now I will bring you back to the local universe talking about SCG0018 a young and dynamic compact group.
1INAF-OABrera, Milano, I
2Università dell’Insubria, Como, I
3ESO-Chile
4Institute fur Astrophysik, Innsbruck, A
24-29 May 2009
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2. Lucchin School -Bertinoro-
OUTLINE
What are compact groups and why they are important?
SCG
Results
Conclusions
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3. Lucchin School -Bertinoro-
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≈ /H0
(Hickson 1982;1992)
Stephan’s quintet
SCGs sample:
Dmmember<Dmiso
Dm=mest-mint>4
(Iovino 2002)
Let me spend just few words to introduce you what are compact group. They are small, compact and isolated systems of few galaxies. Their most important characteristics are high density and low velocity dispersion. SCG0018 is part of the SCGs catalogue
Seyfert’s sextet
NEW
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4. 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 to investigate its evolution history
Compact groups are perfect laboratories to test galaxies interactions due to their typical density and dispersion. Infact tidal forces are really efficient in this environment. As a result, many galaxies in compact groups show morphological distortion, disturbed kinematic and intense activity. We then decide to reveal evidences of interaction in SCG0018 to investigate its evolutionary history.
24-29 May 2009
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5. Lucchin School -Bertinoro-
SCG
From the SCGs cat (Iovino 2002)
redshift: V≈3300 km/s (≈46Mpc)
richness: 4 gal in close proximity, R≈20 kpc
density2: 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
SCG0018 is a remarkably high density and low velocity dispersion group located at approximately 46 Mpc and it is composed by 4 gals. All four close members show disturbed morphology and late-type appearance. Note the extended tidal tail of gal A which was also supposed to have a double nucleus and gal B has a galactic-scale outflow well visible in Ha. Moreover all gals show intense activity.
1 This work
2 Pompei et al. 2007
3 Danks & Alcaino 1981
4 Temporin et al. 2005
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SCG
Data from 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)
R-band
The study is based on VLT observations, we obtained spectra along both axis of each gal and R-Ha imaging. Here I summarize the main results of the study.
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NGC 92
Let’s start with NGC 92 the dominant gal of the group
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8. NGC 92 Ha K
Asymmetric gas radial velocity curve: AP=23% => recent interaction:
presence of a 8-shape1 along minor axis => Nuclear bar misaligned with respect to PA major axis
Major axis kinematic reveal two main feature: gas rotates faster than stars and moreover it has an asymmetric rotation curve. We quantify this asymmetry with the AP. We obtain an high value which is a sign of recent interaction. Moreover we found double components in the emission line profile along the minor axis tracing an 8-shape. This is the sign of the presence of a nuclear bar. Therefore the bright knot thought to be a second nucleus is actually the elbow of the spiral arm pointing towards the observer as can be seen in the Ha and K-band image.
0.2Gyr<tcoll<0.7Gyr
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NGC 89
Let’s talk about NGC 89.
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10. NGC 89
Fig D
Asymmetric stellar/gas radial velocity curve: AP=33-24% => recent interaction: 0.2Gyr<tcoll<0.7Gyr
NLR: presence of gas multiple components (3/4)
Once again we find asymmetric and perturbed kinematic along major axis which are consistent with recent interaction at least within the last 0.7 Gyr. Moreover this is a Sy2 gal and in the inner regions the emission line profiles are quite complex. There’s the presence of multiple gas components, we fit it with at least ¾ .
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NGC 89 Ha
Temporin et al. 2005
Slit along minor axis intercepts the galactic-scale outflow. We obtain spectroscopical confirmation of this outflow and as we can see in the plot there’s not a clear correlation between outflow and surrounding gas. Green triangles are the outflow whereas blue circles is the gas.
SW direction: steep rise of gas velocity
Spectroscopical confirmation of the galactic-scale outflow
Not clear correlation between outflow & surrounding gas
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NGC 88
Just few words for the other two gals: NGC 88
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NGC 88
R-band
We found a low surface brightness tidal tail in the SW direction which is the opposite direction with respect to GC 92, the other gal with a tidal tail. Moreover there’s a sort o regular pattern of rotation of the gas along minor axis.
Low surface brightness tidal tail
≈14x10kpc SW direction
Gas => regular pattern of rotation
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14. Lucchin School -Bertinoro-
NGC 87
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15. NGC 87 (major & minor axis)Ha
Face-on irregular
Star forming regions Ha
Velocity gradients along M&m axis
+ peculiar motions
NGC 87 is a face-on irregular and we found velocity gradients along both axis.
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16. 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
In conclusion we found peculiar kinematics and morphological distortions probably due to interactions among galaxies
recent interaction: 0.2Gyr<tcoll<0.7Gyr
Spectroscopical confirmation of the galactic-scale outflow of NGC 89
Presotto et al in preparation
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Thanks
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18. SCG 0018-4854 X-ray KT ≈ 0.2 keV => coolest system detected so far
Coda mareale
Regioni isolate Ha
Emissione diffusa Ha
Asy level + immagine
Trinchieri et al. 2008
KT ≈ 0.2 keV => coolest system detected so far
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19. 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
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SCG gal properties
Galaxy V1
(km/s)
Class2
Activity2
Notes
B mag1
M H
(109 Mo)I
A (NGC 92)
3384
Saap
SBG
Tidal tail
Double nuclei 3
13.81
>3.29
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
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