Mergers and the Central Parameter Relationships
The Central Parameter Relationships
HST studies of the nuclei of elliptical galaxies have revealed
the existence of a "central parameter relationship" (eg
Lauer etal 1995,
Byun etal 1996;
Gebhardt 1996;
Faber etal 1997).
Ellipticals have a range of nuclear surface
brightness profiles, which can be characterized by the "Nuker law". Ellipticals generally fall along a sequence
from power law cusp galaxies to flat core galaxies.
Correlations exist between
- inner slope (gamma),
- break radius (rb), and
- total magnitude (MV)
|
|
These are known as the central
parameter relationships:
data from
Faber etal (1997)
Look at the discrepant points:
- NGC 4486B: companion
to M87, possible stripped object?
- Fornax A: lots of tidal debris, merger remnant?
Begs the question: Are mergers consistent with the
central parameter relationship for ellipticals?
NICMOS imaging of the nuclei of young merger remnants
Sample
| NGC 34 |
tidal tail; AGN? |
|
NGC 3921 |
merger remnant |
| NGC 455 |
loops & plumes |
|
NGC 7252 |
merger remnant |
| NGC 474 |
shells |
|
NGC 7585 |
shells |
| NGC 2418 |
plumes |
|
NGC 7727 |
tails |
| NGC 3656 |
disturbed isophotes |
|
UGC 5814 |
plume + dust |
| IC 51 |
shells |
|
UGC 9829 |
distorted |
Observations
- NIC1: F110W
- NIC2: F110W, F160W, F187W
Preliminary Results:
van der Marel, Mihos, Zurek, Hernquist, & Heckman,
in prep
Comments:
- Dust is still a problem (ie NGC 3656's artificially
large break radius).
- Most nuclei are consistent with normal ellipticals.
- Four interesting objects:
- The three most discrepant points all show long tidal
features, indicative of a major merger.
- But the other young merger, NGC 7727, sits on the
canonical central parameter relationship.
- Evolution could drive these objects back towards "normal"
ellipticals, but very strong evolution may be needed.
