Download 20140319_J.Gan

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Astronomical spectroscopy wikipedia, lookup

Microplasma wikipedia, lookup

Cosmic distance ladder wikipedia, lookup

Accretion disk wikipedia, lookup

Gravitational lens wikipedia, lookup

Star formation wikipedia, lookup

High-velocity cloud wikipedia, lookup

H II region wikipedia, lookup

Weak gravitational lensing wikipedia, lookup

Transcript
Galaxy Formation and Evolution, Mo, van den Bosch &
White, 2010
Galactic Dynamics, Binney & Tremaine 2008
Introduction
• Galaxy interactions are frequent in the
hierarchical scenario of galaxy formation.
• They play important in the evolution of the star
formation and morphology of galaxies.
• How to investigate them?
Galaxy interactions
 High-speed encounters, tidal heating
 Tidal stripping
 Dynamical friction
 Galaxy merging
 Galaxies in clusters
• Harassment
• Cannibalism
• Ram-pressure stripping
• Strangulation
Energy change of a particle q:
Energy change of the system S:
This energy is transferred to potential energy, which
becomes less negative, implying that the system S is
tidally heated and expands.
 Tidal radius: The radius where the tidal forces
exceed the binding forces.
 For a sub system of mass m moving on an orbit r in
an extended host system of mass M:
(Gan et al. 2010)
 The unbound mass outside rt are stripped gradually.
Tidal stream and tail
 The stripped stars move on
roughly the same orbit as the
satellite galaxy, forming an either
trail or lead stream (minor
mergers).
 All stars along the stream have
similar orbital energy, it can be
used to constrain the
gravitational potential of their
host system (Milky Way).
 ‘tidal tail’ is usually refered to
the structures formed by tidally
stripped stars in major mergers.
Sagittarius stream
Tidal tail formed by NGC 4038
and NGC 4039
As an object M moves through a sea of particles, the particles
passing by are accelerated towards the object. As a result, the
particle number density behind the object is higher than that in
front of it, and the net effect is a drag force (dynamical friction)
on the object.
The satellite halos sink to the
host system center due to
dynamical friction within a
merging timescale (Colpi et
al., 1999; Boylan-Kolchin et
al., 2008; Jiang et al., 2008).
Mass loss due to tidal
stripping weaken the effect
of dynamical friction.
Evolution of the orbital angular
momentum of a satellite halo
(Gan et al. 2010). A: tidal
stripping efficiency
 The merging processes typically are treated with simulation.
 The violent relaxation plays an important role during the
relaxation of the merger remnant.
 The remnant typically has little resemblance to its
progenitors in major merger, while not in minor merger.
 Disks that accrete small satellites typically survive but can
undergo considerable thickening (disk heated).
 Major mergers that involve one or more disk galaxies tend to
create tidal tails.
 The gas-rich merger (wet merger), in general, triggers new
starburst and AGN activity.
 High density in mass
and number
 High speed
 Hot gas (ICM)
• Harassment
• Cannibalism
• Ram pressure stripping
• Strangulation
Phoenix clusters simulation
 The cluster galaxies have typically high velocity and suffer
frequent encounters.
 The cumulative effect of multiple high-speed impulsive
encounters is generally referred to as galaxy harassment.
 The fragile disks of late-type (Sc-Sd) spiral galaxies can be
almost entirely destroyed by harassment. The disks lose very
substantial amounts of mass.
 The bound stars are also heated, which transforms the disk
into spheroidal component. Dwarf ellipticals are ubiquitous
in clusters.
 For more compact early-type (Sa-Sb) disk galaxies, they can
be significantly heated and become more easily to be
stripped by tides or ram pressure.
 A galaxy will sink to the cluster center if the dynamical
friction time is sufficiently short.
 This galaxy merged with the central galaxy and this
process is called galactic cannibalism.
 Cannibalism causes a mass increase of the central galaxy,
and a depletion of massive satellite galaxies.
 Hence, it causes an increase of the magnitude difference
between the first and second brightest galaxies in cluster:
ΔM12
 The magnitude gap ΔM12 can be used as a measure for the
dynamical age of the cluster.
 The Tdf is determined by various factors.
 A ram pressure is just like one feels wind drag when cycling.
 Gas stripping occurs where the pressure exceeds the
binding force per unit area.
(Font et al. 2008)
 Ram-pressure stripping may be efficient and quench star
formation in satellite galaxy. But there are still debate.
 Only the gas at relatively large galactocentric radii is being
stripped.
 The remaining non-stripped gas may actually be compressed
by the ram pressure, giving rise to enhanced star formation.
 The stripped gas may remain bound to the galaxy, fall back
and induce a later starburst.
 The outer parts of a satellite’s gas are stripped. Star formation
may continue at inner parts but the gas consumption time scale
is short (1-5Gyr).
 A gas reservoir surround the satellite: hot gas just falling; gas
shocked to high temperature; reheated and expelled gas by
feedback.
 The gas reservoir is hot and loosely bound to the satellite, so it
is fairly easily stripped off, either by tides or by ram pressure.
 If a large fraction of gas is stripped off from a satellite after it
is accreted into the cluster, its star formation rate will decline
gradually and this is called strangulation.
 The strangulation is believed to be responsible for the
morphology-density relation.
 The motion of satellite after accretion is determined by various
factors.
The morphology–distance
relation in Abell cluster.
(Park & Hwang 2009)
C3: −20.5 > Mr > −22.5
C2: −19.0 > Mr > −20.5
C1: −17.0 > Mr > −19.0
 Galaxy interactions are of diversity and complicated,
especially in clusters.
 The relative effects of various interactions need to be
analyzed statistically based a large sample of evolving
galaxies.
 It may be a way out to examine the magnitude gap and
morphology-density relation, following the hierarchical
growth of cluster.