Observations of Cold Dust in Nearby Elliptical Galaxies

Spectral energy distribution (SED) analyses, that include new millimeter (mm) to far-infrared (FIR) observations, obtained with continuum instruments on the Nobeyama and James Clerk Maxwell Telescopes and Infrared Space Observatory (ISO), are presented for seven, nearby (< 45Mpc) FIR-bright elliptical galaxies. These are analyzed together with archival FIR and short-wave radio data obtained from the NASA/IPAC Extragalactic Database (NED). The radio to infrared SEDs are best fit by power-law plus greybody models of dust residing in the central galactic regions within 2.4 kpc diameter and with temperatures between ∼ 21 and 28K, emissivity index ≃ 2, and masses from ∼ 1.6 to 19×10M⊙. The emissivity index is consistent with dust constituting amorphous silicate and carbonaceous grains previously modeled for stellar-heated dust observed in the Galaxy and other nearby extragalactic sources. Using updated dust absorption coefficients for this type of dust, dust masses are estimated that are similar to those determined from earlier FIR data alone, even though the latter results implied hotter dust temperatures. Fluxes and masses that are consistent with the new FIR and submm data are estimated for dust cooler than 20K within the central galactic regions. Tighter physical constraints for such cold, diffuse dust (if it exists) with low surface brightness, will need sensitive FIR-submm observations with the Spitzer Space Telescope, SCUBA2, or ALMA. 1 Ritter Astrophysical Research Center, University of Toledo, Mail Stop 113, 2801West Bancroft Street, Toledo, OH 43624; [email protected]. 2 Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, United Kingdom; [email protected]. 3 Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, United Kingdom; [email protected]. 4 Astronomisches Institut, Ruhr-Universität Bochum, 44780 Bochum, Germany; [email protected]. 5 Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1305, Japan; [email protected].