Génova-Santos, R. and Rebolo, R. and Rubiño-Martin, J. A. and López-Caraballo, C. H. and Hilderbrandt, S. R. (2011) Detection of Anomalous Microwave Emission in the Pleiades Reflection Nebula with Wilkinson Microwave Anisotropy Probe and the COSMOSOMAS Experiment. Astrophysical Journal, 743 (1). p. 67. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20120201-150236975
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We present evidence for anomalous microwave emission (AME) in the Pleiades reflection nebula, using data from the seven-year release of the Wilkinson Microwave Anisotropy Probe and from the COSMOSOMAS (Cosmological Structures on Medium Angular Scales) experiment. The flux integrated in a 1° radius around R.A. = 56°.24, decl. = 23°.78 (J2000) is 2.15 ± 0.12 Jy at 22.8 GHz, where AME is dominant. COSMOSOMAS data show no significant emission, but allow one to set upper limits of 0.94 and 1.58 Jy (99.7% confidence level), respectively, at 10.9 and 14.7 GHz, which are crucial to pin down the AME spectrum at these frequencies, and to discard any other emission mechanisms which could have an important contribution to the signal detected at 22.8 GHz. We estimate the expected level of free-free emission from an extinction-corrected Hα template, while the thermal dust emission is characterized from infrared DIRBE data and extrapolated to microwave frequencies. When we deduct the contribution from these two components at 22.8 GHz, the residual flux, associated with AME, is 2.12 ± 0.12 Jy (17.7σ). The spectral energy distribution from 10 to 60 GHz can be accurately fitted with a model of electric dipole emission from small spinning dust grains distributed in two separated phases of molecular and atomic gas, respectively. The dust emissivity, calculated by correlating the 22.8 GHz data with 100 μm data, is found to be 4.36 ± 0.17 μK (MJy sr^(–1))^(–1), a value considerably lower than in typical AME clouds, which present emissivities of ~20 μK (MJy sr^(–1))^(–1), although higher than the 0.2 μK (MJy sr^(–1))^(–1) of the translucent cloud LDN 1780, where AME has recently been claimed. The physical properties of the Pleiades nebula, in particular its low extinction A_V ~ 0.4, indicate that this is indeed a much less opaque object than those where AME has usually been studied. This fact, together with the broad knowledge of the stellar content of this region, provides an excellent testbed for AME characterization in physical conditions different from those generally explored up to now.
|Additional Information:||© 2011 American Astronomical Society. Received 2011 June 13; accepted 2011 September 12; published 2011 November 22. We thank the referee for useful comments, which helped to extend the discussion on some important aspects. The color-scale image of Figure 1 is based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain. The Palomar Observatory Sky Survey was funded by the National Geographic Society. The Oschin Schmidt Telescope is operated by the California Institute of Technology and Palomar Observatory. The plates were processed into the present compressed digital format with their permission. The Digitized Sky Survey was produced at the Space Telescope Science Institute (STScI) under U.S. Government grant NAG W-2166. We acknowledge the use of the MPIfR Survey Sampler Web site at http://www.mpifr-bonn.mpg.de/survey.html, from which we obtained the 0.820 GHz data. We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). Support for LAMBDA is provided by the NASA Office of Space Science. Some of the results in this paper have been obtained using the HEALPix (Górski et al. 2005) package. This work has been partially funded by project AYA2010-21766-C03-02 of the Spanish Ministry of Science and Innovation (MICINN). J.A.R.-M. is a Ramón y Cajal fellow of the MICINN.|
|Subject Keywords:||cosmic background radiation; diffuse radiation; ISM: individual objects (Pleiades); radiation mechanisms: general; radio continuum: ISM|
|Official Citation:||Detection of Anomalous Microwave Emission in the Pleiades Reflection Nebula with Wilkinson Microwave Anisotropy Probe and the COSMOSOMAS Experiment R. Génova-Santos et al. 2011 ApJ 743 67|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||02 Feb 2012 00:18|
|Last Modified:||26 Dec 2012 14:46|
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