xiii. interacting galaxies - univie.ac.at · ... atlas and catalog of interacting galaxies ... 355...
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IV. Interacting Galaxies
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Examples of galaxies in interaction:
Pairs of galaxies (NGC 4038/39)
M 51 – type (satellites)
Arp 220 – type
Compact galaxy groups
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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
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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
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Arp Atlas of Peculiar Galaxies
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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
H. Arp & B.F. Madore: A Catalogue of Southen
Peculiar Galaxies and Associations (1987)
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Gravitional passages lead to Tadpole Galaxy
tidal perturbations.
1. Tidal Interactions
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Perturbations passing a
galaxy in retrograde
direction are less perturbant
(galaxy structure survives)
than prograde encounters.
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tidal arms: one only of HI,
therefore not visible in the
optical; one containing dust
and visible as dust lane.
Tidal arms in M51
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15 Schweizer, 1982, ApJ 252, 455
M82
M81
NGC 3077
Gas bridges within the
M81 Group feed the high
star formation in M82 by
gas infall.
Gas Bridges
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NGC 3314
2. Merging Galaxies
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Die Superantenne NGC 7252
video
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e.g. NGC 4260 shows
a double-core structure
with extremely high star
formation.
3. Double Cores as Merger Relics
X-ray observations even allow to
discern 2 bright sources that can
only be interpreted as BHs.
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4. Ultra-luminous Infrared Galaxies
ULIRGs are characterized by
extraordinarily high infrared
luminosities and hot dust.
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All ULIRGs are
merging galaxies
without any
exception.
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5. The Antennae
The Antennae is a ULIRG
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In merging galaxies
Super-Star Clusters
are formed in the
densest regions.
6. Star and Galaxy Formation in Tidal Arms
Mirabel et al. (1992)
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NGC 5291
Duc &Mirabel (1998)
Arp 188, the Tadpole Galaxy:
bright knots as DG
precursors?
bright star-formation knots
are structured within the tail.
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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
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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
9. Signatures of past interactions:
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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
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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.
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Warps are (point-)symmetric distortions
of the disk and probably the result of
close passages such as of satellite
galaxies.
NGC 5719
Shells and warped rings in E‘s are
indicative for gas accretion.
9.4. Gas Accretion
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9.5. Kinematicly decoupled components
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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
arms.
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In NGC 6872 the
approach of the
satellite DG
IC 4970 triggers
bar formation.
The Magellanic Clouds
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Tidal streams around NGC 5907
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5.3. Minor-merger Models Observational facts:
Sgr I : DG at d = 24 kpc, DGC = 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: macc 6.109 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?
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Model by Katheryn Johnston
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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!
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Initial Conditions:
Msat = 109 M
DGC,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
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Results:
• Satellite spirals
towards the center
leaving behind a
spur of stripped-
off 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)
core.
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shows a double core
Satellite trajectories
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face-on perturbations
disk heating
0.85 Gyrs
2.45 Gyrs
750 Myrs 900 Myrs
1.05 Gyrs 1.20 Grys
1.35 Gyrs 1.50 Grys
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Close encounters of galaxies lead to
energy transfer according to the
Impuls Approximation
measurable as disk thickening.
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h24
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rvb3
MMG4ΔE