IV. Interacting Galaxies Examples of galaxies in interaction: Pairs of galaxies (NGC 4038/39) M 51 type (satellites) Arp 220 type Compact galaxy groups 2 1
B.A. Vorontsov-Velyaminov: Atlas and Catalog of Interacting Galaxies (1959) Search of Palomar Sky Survey for candidate interacting galaxies (limiting magnitude ca. 16 mag) Morphological classification of galaxy interactions and environment of galaxies 355 galaxies classified 3 Halton Arp: Atlas of Peculiar Galaxies (1966) Based upon Vorontssov-Velyaminov catalog 338 selected objects observed mit 5m Mt. Palomar Morphological classification focalized on spiral galaxies Hypothesis that magnetic fields are responsable for observed pecularities 4 2
Arp Atlas of Peculiar Galaxies 5 H. Arp & B.F. Madore: A Catalogue of Southen Peculiar Galaxies and Associations (1987) Based upon IIIa-J SRC southern sky survey 6445 peculiar galaxies selected out of a sample of 77838 objects Categories: - Galaxies with interacting companions - Interacting doubles, triples to quintets - Chains - Groups 6 3
7 1. Tidal Interactions Gravitional passages lead to tidal perturbations. Tadpole Galaxy 4
Perturbations passing a galaxy in retrograde direction are less perturbant (galaxy structure survives) than prograde encounters. 10 5
11 12 6
13 Tidal arms in M51 tidal arms: one only of HI, therefore not visible in the optical; one containing dust and visible as dust lane. 7
Schweizer, 1982, ApJ 252, 455 15 Gas Bridges M82 M81 Gas bridges within the M81 Group feed the high star formation in M82 by gas infall. NGC 3077 8
2. Merging Galaxies NGC 3314 9
Die Superantenne NGC 7252 video 10
3. Double Cores as Merger Relics e.g. NGC 4260 shows a double-core structure with extremely high star formation. X-ray observations even allow to discern 2 bright sources that can only be interpreted as BHs. 11
4. Ultra-luminous Infrared Galaxies ULIRGs are characterized by extraordinarily high infrared luminosities and hot dust. 12
All ULIRGs are merging galaxies without any exception. 13
5. The Antennae The Antennae is a ULIRG 14
In merging galaxies Super-Star Clusters are formed in the densest regions. 6. Star and Galaxy Formation in Tidal Arms Mirabel et al. (1992) 15
NGC 5291 Duc &Mirabel (1998) Arp 188, the Tadpole Galaxy: bright knots as DG precursors? bright star-formation knots are structured within the tail. 16
In numerical simulations mass is concentrating in the central regions but also clumping within the tidal arms. If the masses are large enough one can denote the clumps as Tidal Tail DGs. 7. Mergers in the deep Universe 17
9. Signatures of past interactions: Gas/dust and/or stellar disks/rings decoupled from the galaxy body Kinematically decoupled nuclei Photmetric signatures ( fine structure ): - Shells/ripples - filaments - Boxiness of the isophotes - X shape of isophotes 36 18
9.1. Harassment NGC 4438 as member of the Virgo Cluster reveals a slightly perturbed disk structure in the optical, but an irregular octopus-like structure in Hα. The disturbing process is called Harassment, an extremely rapid passage of a perturber. 9.2. Direct Collisions 19
Although the companions around the Cartwheel Galaxy seem to be disconnected, a fountain-like HI trail traces the link to the past intruder. 9.3. Ring Galaxies Some galaxies show bright rings partly with spokes, untypical structures for rotating disks. 20
Warps are (point-)symmetric distortions of the disk and probably the result of close passages such as of satellite galaxies. NGC 5719 9.4. Gas Accretion Shells and warped rings in E s are indicative for gas accretion. 21
9.5. Kinematicly decoupled components 43 5. Satellite Infall: Minor Mergers In NGC 1531 a satellite DG approaches the galaxy and exerts perturbations to the disk, leading to disk thickening and bending of 44 arms. 22
In NGC 6872 the approach of the satellite DG IC 4970 triggers bar formation. 45 The Magellanic Clouds 23
Tidal streams around NGC 5907 53 5.3. Minor-merger Models Observational facts: Sgr I : DG at d = 24 kpc, D GC = 16 kpc Tidal Streamers within the MWG and M31 Disk thickening in Galaxies with close Satellites but: thin Galactic Disks (the solar vicinity) (Edvardsson et al. 1993) Theoretical requirements: Hierarchical Merging but: total accreted mass of small companions from CDM scenario: m acc 6. 10 9 M (Tremaine 1980) Questions: Disk Heating Star-formation Trigger Bulge Formation Timescales and Structural Effects of Perturbations Simulations: Realistic Models and Initial Conditions? Adequate Numerical Treatment? 54 24
Model by Katheryn Johnston Computer model of a small satellite galaxy orbiting a larger (edge-on) disk galaxy. As the satellite orbits, stars are stripped from the satellite and orbit in the halo of the larger galaxy. (Kathryn Johnston, Wesleyan): see the bending and tumbling of the satellite s figure axis! 56 25
Initial Conditions M sat = 10 9 M D GC,sat = 18 kpc v = 200 km/s i = 20 Results: Disruption of satellite with mass loss 80%; Satellite sinks into equatorial plane within 1.5 Gyrs; Satellite moves radially inwards 57 Results: Satellite spirals towards the center leaving behind a spur of strippedoff stars: tidal streamers? 20% of the original mass forms a still bound unit in the center; the displacement with respect to the center (0,0) of the giant galaxy is indicative for an orbiting (double) 58 core. 26
Satellite trajectories shows a double core 59 750 Myrs 900 Myrs face-on perturbations disk heating 1.05 Gyrs 1.20 Grys 0.85 Gyrs 1.35 Gyrs 1.50 Grys 2.45 Gyrs 60 27
Close encounters of galaxies lead to energy transfer according to the Impuls Approximation measurable as disk thickening. 2 2 4G M2 M ΔE 4 2 3b v 61 1 r 2 h 28