141 research outputs found
Radial Gas Flows in Colliding Galaxies: Connecting Simulations and Observations
(abridged) We investigate the detailed response of gas to the formation of
transient and long-lived dynamical structures induced in the early stages of a
disk-disk collision, and identify observational signatures of radial gas inflow
through a detailed examination of the collision simulation of an equal mass
bulge dominated galaxy. Stars respond to the tidal interaction by forming both
transient arms and long lived m=2 bars, but the gas response is more transient,
flowing directly toward the central regions within about 10^8 years after the
initial collision. The rate of inflow declines when more than half of the total
gas supply reaches the inner few kpc, where the gas forms a dense nuclear ring
inside the stellar bar. The average gas inflow rate to the central 1.8 kpc is
\~7 Msun/yr with a peak rate of 17 Msun/yr. The evolution of gas in a bulgeless
progenitor galaxy is also discussed, and a possible link to the ``chain
galaxy'' population observed at high redshifts is inferred. The evolution of
the structural parameters (the asymmetry and concentration) of both stars and
gas are studied in detail. Further, a new structural parameter (the compactness
parameter K) that traces the evolution of the size scale of the gas relative to
the stellar disk is introduced. Non-circular gas kinematics driven by the
perturbation of the non-axisymmetric structure can produce distinct emission
features in the "forbidden velocity quadrants'' of the position-velocity
diagram (PVD). The dynamical mass calculated using the rotation curve derived
from fitting the emission envelope of the PVD can determine the true mass to
within 20% to 40%. The evolution of the molecular fraction $M_H2/M_(H2 + HI)
and the compactness (K) are potential tracers to quantitatively assign the age
of the interaction.Comment: 52 pages, 20 figures (9 jpgs), accepted for publication in ApJ
Version with all figures at http://cfa-www.harvard.edu/~diono/ms.ps.g
Quantifying the Fragility of Galactic Disks in Minor Mergers
We perform fully self-consistent stellar dynamical simulations of the
accretion of a companion ("satellite") galaxy by a large disk galaxy to
investigate the interaction between the disk, halo, and satellite components of
the system during a merger. Our fiducial encounter begins with a satellite in a
prograde, circular orbit inclined thirty degrees with respect to the disk plane
at a galactocentric distance of six disk scalelengths. The satellite's mass is
10% of the disk's mass and its half-mass radius is about 1.3 kpc. The system is
modelled with 500 000 particles, sufficient to mitigate numerical relaxation
noise over the merging time. The satellite sinks in only ~1 Gyr and a core
containing ~45% of its initial mass reaches the centre of the disk. With so
much of the satellite's mass remaining intact, the disk sustains significant
damage as the satellite passes through. At the solar circle we find that the
disk thickens ~60%, the velocity dispersions increase by
\Delta\mbox{\boldmath\sigma} \simeq (10,8,8) km/s to km/s, and the asymmetric drift is
unchanged at ~18 km/s. Although the disk is not destroyed by these events
(hence "minor" mergers), its final state resembles a disk galaxy of earlier
Hubble type than its initial state, thicker and hotter, with the satellite's
core enhancing the bulge. Thus minor mergers continue to be a promising
mechanism for driving galaxy evolution.Comment: LaTeX with AASTeX macros; text only. For PostScript with figures
embedded, go to http://www.ucolick.org/~iwalker/ss
A Dynamical Model of the M101 / NGC 5474 Encounter
We present the first dynamical simulation that recreates the major properties
of the archetypal nearby spiral galaxy M101. Our model describes a grazing but
relatively close (14 kpc) passage of the companion galaxy NGC 5474 through
M101's outer disk approximately 200 Myr ago. The passage is retrograde for both
disks, which yields a relatively strong gravitational response while
suppressing the formation of long tidal tails. The simulation reproduces M101's
overall lopsidedness, as well as the extended NE Plume and sharp western edge
of the galaxy's disk. The post-starburst populations observed in M101's NE
Plume are likely a result of star formation triggered at the point of contact
where the galaxies collided. Over time, this material will mix azimuthally,
leaving behind diffuse, kinematically coherent stellar streams in M101's outer
disk. At late times after the encounter, the density profile of M101's disk
shows a broken "upbending" profile similar to those seen in spiral galaxies in
denser environments, further demonstrating the connection between interactions
and long-term structural changes in galaxy disks.Comment: 8 pages, 4 figures, accepted for publication in the Astrophysical
Journal (Letters). Updated to (mostly) match the published version.
Additional animations and simulation data are available at
http://astroweb.case.edu/hos/M101Sim
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