학술논문
Warm Dust and Spatially Variable PAH Emission in the Dwarf Starburst Galaxy NGC 1705
Document Type
Working Paper
Author
Cannon, John M.; Smith, John-David T.; Walter, Fabian; Bendo, George J.; Calzetti, Daniela; Dale, Daniel A.; Draine, Bruce T.; Engelbracht, Charles W.; Gordon, Karl D.; Helou, George; Kennicutt, Jr., Robert C.; Leitherer, Claus; Armus, Lee; Buckalew, Brent A.; Hollenbach, David J.; Jarrett, Thomas H.; Li, Aigen; Meyer, Martin J.; Murphy, Eric J.; Regan, Michael W.; Rieke, George H.; Rieke, Marcia J.; Roussel, Helene; Sheth, Kartik; Thornley, Michele D.
Source
Astrophys.J.647:293-302,2006
Subject
Language
Abstract
We present Spitzer observations of the dwarf starburst galaxy NGC 1705 obtained as part of SINGS. The galaxy morphology is very different shortward and longward of ~5 microns: short-wavelength imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer-wavelength data reveals warm dust emission arising from two off-nuclear regions offset by ~250 pc from the SSC. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2E5 solar masses, implying a global dust-to-gas mass ratio ~2--4 times lower than the Milky Way average). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed H Alpha emission; these photons are unassociated with the SSC (though a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-strength PAH emission in the 11.3 micron band in the eastern peak; no PAH emission is detected in the SSC or the western dust emission complex. There is significant diffuse 8 micron emission after scaling and subtracting shorter wavelength data; the spatially variable PAH emission strengths revealed by the IRS data suggest caution in the interpretation of diffuse 8 micron emission as arising from PAH carriers alone. The metallicity of NGC 1705 falls at the transition level of 35% solar found by Engelbracht and collaborators; the fact that a system at this metallicity shows spatially variable PAH emission demonstrates the complexity of interpreting diffuse 8 micron emission. A radio continuum non-detection, NGC 1705 deviates significantly from the canonical far-IR vs. radio correlation. (Abridged)
Comment: ApJ, in press; please retrieve full-resolution version from http://www.astro.wesleyan.edu/~cannon/pubs.html
Comment: ApJ, in press; please retrieve full-resolution version from http://www.astro.wesleyan.edu/~cannon/pubs.html