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Dust Abundance and Properties in the Nearby Dwarf Galaxies NGC 147 and NGC 185

Marleau, Francine R. and Noriega-Crespo, Alberto and Misselt, Karl A. (2010) Dust Abundance and Properties in the Nearby Dwarf Galaxies NGC 147 and NGC 185. Astrophysical Journal, 713 (2). pp. 992-1007. ISSN 0004-637X.

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We present new mid- to far-infrared images of the two dwarf compact elliptical galaxies that are satellites of M31, NGC 185, and NGC 147, obtained with the Spitzer Space Telescope. Spitzer's high sensitivity and spatial resolution enable us for the first time to look directly into the detailed spatial structure and properties of the dust in these systems. The images of NGC 185 at 8 and 24 μm display a mixed morphology characterized by a shell-like diffuse emission region surrounding a central concentration of more intense infrared emission. The lower resolution images at longer wavelengths show the same spatial distribution within the central 50" but beyond this radius, the 160 μm emission is more extended than that at 24 and 70 μm. On the other hand, the dwarf galaxy NGC 147, located only a small distance away from NGC 185, shows no significant infrared emission beyond 24 μm and therefore its diffuse infrared emission is mainly stellar in origin. For NGC 185, the derived dust mass based on the best fit to the spectral energy distribution is 1.9 × 10^3 M_⊙, implying a gas mass of 3.0 × 10^5 M_⊙. These values are in agreement with those previously estimated from infrared as well as CO and H I observations and are consistent with the predicted mass return from dying stars based on the last burst of star formation 1 × 10^9 yr ago. Based on the 70-160 μm flux density ratio, we estimate a temperature for the dust of ~17 K. For NGC 147, we obtain an upper limit for the dust mass of 4.5 × 10^2 M_⊙ at 160 μm (assuming a temperature of ~20 K), a value consistent with the previous upper limit derived using Infrared Space Observatory observations of this galaxy. In the case of NGC 185, we also present full 5-38 μm low-resolution (R ~ 100) spectra of the main emission regions. The Infrared Spectrograph spectra of NGC 185 show strong polycyclic aromatic hydrocarbons emission, deep silicate absorption features and H_2 pure rotational line ratios consistent with having the dust and molecular gas inside the dust cloud being impinged by the far-ultraviolet radiation field of a relatively young stellar population. Therefore, based on its infrared spectral properties, NGC 185 shows signatures of recent star formation (a few ×10^8 yr ago), although its current star formation rate is quite low.

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Noriega-Crespo, Alberto0000-0002-6296-8960
Additional Information:© 2010 The American Astronomical Society. Received 2009 July 8; accepted 2010 March 8; published 2010 March 29. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology, under NASA contract 1407. Support for this work was provided by NASA contract NAS7-03001. We thank the referee for her/ his careful reading of our manuscript; her/his comments have improved our presentation and discussion.
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Subject Keywords:dust, extinction; galaxies: dwarf; galaxies: individual (NGC 147, NGC 185); galaxies: ISM; infrared: galaxies; infrared: ISM; ISM: structure
Issue or Number:2
Classification Code:PACS: 98.56.Wm; 98.58.Ca; 98.58.Jg; 98.58.Bz; 98.62.Lv; 95.85.Gn.
Record Number:CaltechAUTHORS:20100607-082907978
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Official Citation:Francine R. Marleau et al 2010 ApJ 713 992 doi: 10.1088/0004-637X/713/2/992
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18575
Deposited By: Tony Diaz
Deposited On:27 Jun 2010 23:48
Last Modified:09 Mar 2020 13:19

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