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SCG 0018-4854:A YOUNG AND DYNAMIC

GROUP

1INAF-OABrera, Milano, I

2Università dell’Insubria, Como, I

3ESO-Chile

4Institute fur Astrophysik, Innsbruck, A

V. Presotto1,2, A. Iovino1 , E. Pompei 3, G. Temporin4

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OUTLINE

• What are compact groups and why they are important?

• SCG0018-4854

• Results

• Conclusions

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COMPACT GROUPS (CGs)

Selection criteria:• Richness: n≥4 with (m≤m1+3)• Isolation: RN≥3RG

• Compactness: G<26mag∙arcsec-2

SCGs sample:mmember<miso

=est-int>4

(Iovino 2002)

Properties:• Low dispersion: <>≈200km/s• High density: 300group108h2Mpc-2

• Lifetime ? cross≈0.016 1/H0

(Hickson 1982;1992)

Stephan’s quintet

Seyfert’s sextet

NEW

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INTERACTIONS IN CGs

• 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

Compact groups are perfect laboratories to test galaxies’ interactions

Aim: reveal evidence of interaction in SCG 0018-4854 to investigate its evolution history

SCG 0018-4854

1 This work2 Pompei et al. 20073 Danks & Alcaino 19814 Temporin et al. 2005

• 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 tailDouble 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 ---

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From the SCGs cat (Iovino 2002)

Data from FORS2 @ VLT/ESO

Multi-slit spectroscopy: M & m axis (except M axis NGC 88)Grism: 1400V with 0 5200Å 20.8Å/mm (0.49 Å/px)Texp: 4X2699s

Photometry: all galFilters: 1. R-band 6550Å (FWHM 1650Å) 2. H 6615Å (FWHM 61Å)Texp: 3X119s (R-band)

3X100s (H)

R-band

SCG 0018-4854

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NGC 92

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NGC 92

H 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

0.2Gyr<coll<0.7Gyr

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NGC 89

Fig D

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NGC 89

• Asymmetric stellar/gas radial velocity curve: AP=33-24% =>

recent interaction: 0.2Gyr<coll<0.7Gyr

• NLR: presence of gas multiple components (3/4)

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NGC 89

H

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

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NGC 88

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NGC 88

• Low surface brightness tidal tail≈14x10kpc SW direction

R-band

Gas => regular pattern of rotation

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NGC 87

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NGC 87 (major & minor axis)

• Face-on irregular• Star forming regions H• Velocity gradients along M&m axis + peculiar motions

H

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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<coll<0.7Gyr

• Spectroscopical confirmation of the galactic-scale outflow of NGC 89

Presotto et al. 2009 in preparation

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Thanks

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SCG 0018-4854 X-ray

KT ≈ 0.2 keV => coolest system detected so far

Trinchieri et al. 2008

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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

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SCG 0018-4854 gal properties

Galaxy V1

(km/s)

Class2 Activity2 Notes B mag1 M H(109 Mo)I

A (NGC 92)

3384 Saap SBG Tidal tailDouble 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