Murphy, E. J. and Helou, G. and Condon, J. J. and Schinnerer, E. and Turner, J. L. and Beck, R. and Mason, B. S. and Chary, R.-R. and Armus, L. (2010) The Detection of Anomalous Dust Emission in the Nearby Galaxy NGC 6946. Astrophysical Journal Letters, 709 (2). L108-L113. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20100303-095251524
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We report on the Ka-band (26-40 GHz) emission properties for 10 star-forming regions in the nearby galaxy NGC 6946. From a radio spectral decomposition, we find that the 33 GHz flux densities are typically dominated by thermal (free-free) radiation. However, we also detect excess Ka-band emission for an outer-disk star-forming region relative to what is expected given existing radio, submillimeter, and infrared data. Among the 10 targeted regions, measurable excess emission at 33 GHz is detected for half of them, but in only one region is the excess found to be statistically significant (≈7σ). We interpret this as the first likely detection of so-called "anomalous" dust emission outside of the Milky Way. We find that models explaining this feature as the result of dipole emission from rapidly rotating ultrasmall grains are able to reproduce the observations for reasonable interstellar medium conditions. While these results suggest that the use of Ka-band data as a measure of star formation activity in external galaxies may be complicated by the presence of anomalous dust, it is unclear how significant a factor this will be for globally integrated measurements as the excess emission accounts for ≲10% of the total Ka-band flux density from all 10 regions.
|Additional Information:||© 2010 American Astronomical Society. Print publication: Issue 2 (2010 February 1); received 2009 October 27; accepted for publication 2009 December 14; published 2010 January 11. We thank the anonymous referee for useful suggestions that helped to improve the content and presentation of this Letter. E.J.M. thanks William Reach and Roberta Paladini for stimulating discussions. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We are grateful to the SINGS team for producing high-quality data sets used in this study. Support for this work was provided by NASA through an award issued by JPL/Caltech.|
|Subject Keywords:||dust, extinction; galaxies: individual (NGC 6946); radiation mechanisms: thermal; radio continuum: general|
|Official Citation:||The Detection of Anomalous Dust Emission in the Nearby Galaxy NGC 6946 E. J. Murphy, G. Helou, J. J. Condon, E. Schinnerer, J. L. Turner, R. Beck, B. S. Mason, R.-R. Chary, and L. Armus 2010 ApJ 709 L108-L113 doi: 10.1088/2041-8205/709/2/L108|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||03 Mar 2010 23:46|
|Last Modified:||26 Dec 2012 11:48|
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