10975(  1) - 04/03/06 11:18  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10975

Version: 1    Check-in Time: 03-Apr-2006 15:18:12

Title
Central mass concentrations of disk galaxies: the nuclear spiral connection
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Type             Cycle     Parallel Pointing Tolerance
AR               15        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Marc S. Seigar                University of California - Irvine
   CoI: Dr. Aaron J. Barth                University of California - Irvine             N
   CoI: Dr. Witold Maciejewski            University of Oxford                          N
   CoI: Dr. James S. Bullock              University of California - Irvine             N

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Abstract

The currently favored cosmological model, Lambda+ Cold Dark Matter (LCDM), is
remarkably successful at reproducing the large scale structure of the Universe.
However, small-scale observations have proven harder to explain. N-body simulations
of LCDM structure formation predict that the central density profiles of dark matter
halos should be very cuspy. Yet observations of rotation curves of late-type
galaxies are consistent with a constant density core. This could be due to a
fundamental problem with LCDM (which may be solved using warm dark matter), or late-
type galaxies may be biased due to their late epoch of formation, whereas more
typical galaxies will conform to the expectations of LCDM. Recent theoretical work
has shown that the structure of nuclear spirals is directly connected with galaxy
mass distributions on sub-kpc scales. Simulations by Maciejewski (2004a, b)
demonstrate that the pitch angle of nuclear spirals is determined by the central
mass concentration of a galaxy. Also, within ~100 pc the nature of the spiral
depends upon whether the density profile has a cusp or a constant density core.
These simulations open up the possibility that nuclear spiral structure can be used
as a novel and unique diagnotsic of the mass distributions and concentrations in the
inner regions of disk galaxies. The goal of this proposal is to quantify the
morphology of the nuclear spiral structure in a large sample of disk galaxies over a
wide range of Hubble types (from Sa to Sm), and to apply the models to derive the
very central mass concentrations and constrain the types of density profiles found
in disk galaxies.
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