Spitzer Space Telescope - Theoretical Research Proposal #40229


Evolution of Dust in Elliptical Galaxies

Principal Investigator: William Mathews
           Institution: University of California, Santa Cruz

     Technical Contact: William Mathews, University of California, Santa Cruz

Co-Investigators: 
Fabrizio Brighenti, University of Bologna                             
Pasquale Temi, Nasa Ames Research Center & SETI Institute             

Science Category: nearby galaxies (z<0.05, v_sys<15,000 km/s) 
Dollars Approved: 79447 

Abstract:
We request funding to develop a theoretical understanding of the complex and
fascinating life cycle of interstellar dust in elliptical galaxies. Our recent
Spitzer observations show that many otherwise normal elliptical galaxies have
unexpected extended regions of cold dust with masses exceeding that of dust
produced by a normally evolving local old stellar population. The dust lifetime
is only ten million years in the hot interstellar gas. In one galaxy excess dust
is observed in a highly asymmetric, plume-like extension out to five kiloparsecs
from the center and coincident with warm gas that emits optical line emission.
Since the excess dust is highly transient, it must be internally produced (not
by mergers) on a frequent duty cycle of about ten million years. Evidently, the
extended dust in these normal ellipticals originates in small dusty nuclear
disks a few hundred parsecs in size which are commonly observed and contain
enough dust to account for the extended dust we observe. We request funding to
study the kinematic and thermal evolution of dust lost by normally evolving
stars, and to demonstrate in detail how dust from stars in galactic cores
collects into small disks. With gasdynamical computations we will show how disks
form in rotating elliptical galaxies and investigate their properties. Then we
will disrupt the disks with intermittent energy associated with the active
galactic nucleus (central black hole) and compute how heated dusty gas is
transported out into the hot gas in buoyant plumes. Preliminary calculations
show that dust eventually cools the buoyant gas, explaining the presence of
extended plumes of warm gas that emits optical emission lines. The astronomical
implications of this unexpected excess dust we observed with Spitzer -- and now
wish to study in more detail -- are far-reaching and provide new information
about energetic processes in galactic cores.