The VDDF: Properties And Promise

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Talk given at the AAS meeting in DC (#207, I think) about the Velocity Dispersion Distribution Function and its feasibilty to study the dynamical evolution of early-type galaxies in rich clusters.

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The VDDF: Properties And Promise

  1. 1. Properties and Promise Robert C. Berrington Michael J. Pierce Sehyun Hwang (University of Wyoming) The Velocity Dispersion Distribution Function (VDDF) of Elliptical Galaxies: (E-mail: rberring@uwyo.edu)
  2. 2. The VDDF <ul><li>Originates from Schechter Luminosity Function </li></ul><ul><li>Transformed into velocity dispersion space (  ) via Faber-Jackson relation: </li></ul><ul><li>Takes the form: </li></ul><ul><li>Under the assumption galaxy halos are isothermal, we can convert the circular velocity (v c ) of spirals to  , and compare to Ellipticals. </li></ul>
  3. 3. Data and Motivation <ul><li>Total of 33 Abell clusters with an average of ~50 velocity dispersions/cluster. </li></ul><ul><ul><li>Spectral resolution 0.9 Å (on WIYN/Hydra) </li></ul></ul><ul><ul><li>S/N ~30-100 </li></ul></ul><ul><ul><li>  distribution yields VDDF </li></ul></ul><ul><li>Tracer of galaxy gravitational potential </li></ul><ul><ul><li>Minimal dependence on luminosity evolution. </li></ul></ul><ul><ul><li>Directly comparable with N-body simulations. </li></ul></ul><ul><ul><li>Quantitative measure of hierarchical merging? </li></ul></ul>
  4. 4. Individual Clusters <ul><li>Abell 1656 (Coma) </li></ul><ul><ul><li>Left: VDDF with best fit (solid curve) </li></ul></ul><ul><ul><li>Right: Error ellipses for best fit </li></ul></ul><ul><li>Abell 548 </li></ul><ul><ul><li>Same as above </li></ul></ul>
  5. 5. Properties and Promise <ul><li>Steeper low-  -end power laws (  ) have larger  * . </li></ul><ul><ul><li>Quantitative measure of hierarchical merging? </li></ul></ul><ul><ul><li>Directly comparable with models </li></ul></ul><ul><li>Weak correlation between cluster velocity dispersion (  cl ) and  * . </li></ul>
  6. 6. Closing Statements <ul><li>Pros </li></ul><ul><ul><li>Minimal dependence on Luminosity evolution </li></ul></ul><ul><ul><li>Galaxy merging is continuous </li></ul></ul><ul><ul><ul><li>Should see evolution in the VDDF for clusters at z~0.5 (versus z~1.0 for Luminosity evolution) </li></ul></ul></ul><ul><li>Cons </li></ul><ul><ul><li>Cluster and galaxy evolution is stochastic </li></ul></ul><ul><ul><li>Requires multiple moderate resolution (R ~ 6000) spectra of galaxies—difficult at high z </li></ul></ul>

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