Detalles de publicación
PP 015010
New radio observations of anomalous microwave emission in the HII region RCW175
(1) Department of Physics, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
(2) CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
(3) Instituto de Astrofísica de Canarias, C/ Va Lactea, s/n, E38205 - La Laguna (Tenerife), Spain
(4) Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
(5) Infrared Processing Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
(6) Scientific Support Office, Directorate of Science and Robotic Exploration, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
(7) IAS, CNRS (UMR 8617), Universit ́e Paris-Sud 11, bˆatiment 121, 91400 Orsay, France
We have observed the HII region RCW175 with the 64-m Parkes telescope at 8.4 GHz and 13.5 GHz in total intensity, and at 21.5 GHz in both total intensity
and polarization. High angular resolution ranging from 1 arcmin to 2.4 arcmin, high sensitivity, and polarization capability enable us to perform a detailed study of the different constituents of the HII region. For the first time, we resolve three distinct regions at microwave frequencies, two of which are part of the same annular diffuse structure. Our observations enable us to confirm the presence of anomalous microwave emission from RCW175. Fitting the integrated flux density across the entire region with the currently available spinning dust models, using physically motivated assumptions, indicates the presence of at least two spinning dust components: a warm component (Tgas = 5800 K) with a relatively large hydrogen number density nH = 26.3/cm3 and a cold component (Tgas = 100 K) with a hydrogen number density of nH = 150/cm3. The present study is an example highlighting the potential of using high angular-resolution microwave data to break model parameter degeneracies. Thanks to the spectral coverage and angular resolution of the Parkes observations, we have been able to derive one of the first anomalous microwave emission/excess maps, at 13.5 GHz, showing clear evidence that the bulk of the anomalous emission arises in particular from one of the source components, with some additional contribution from the diffuse structure. A cross-correlation analysis with thermal dust emission has shown a high degree of correlation with one of the regions within RCW175. In the center of RCW175, we find an average polarized emission at 21.5 GHz of 2.2±0.2(rand.)±0.3(sys.)% of the total emission, where we have included both systematic and statistical uncertainties at 68% CL. This polarized emission could be due to sub-dominant synchrotron emission from the region and is thus consistent with very faint or non-polarized emission associated with anomalous microwave emission.
and polarization. High angular resolution ranging from 1 arcmin to 2.4 arcmin, high sensitivity, and polarization capability enable us to perform a detailed study of the different constituents of the HII region. For the first time, we resolve three distinct regions at microwave frequencies, two of which are part of the same annular diffuse structure. Our observations enable us to confirm the presence of anomalous microwave emission from RCW175. Fitting the integrated flux density across the entire region with the currently available spinning dust models, using physically motivated assumptions, indicates the presence of at least two spinning dust components: a warm component (Tgas = 5800 K) with a relatively large hydrogen number density nH = 26.3/cm3 and a cold component (Tgas = 100 K) with a hydrogen number density of nH = 150/cm3. The present study is an example highlighting the potential of using high angular-resolution microwave data to break model parameter degeneracies. Thanks to the spectral coverage and angular resolution of the Parkes observations, we have been able to derive one of the first anomalous microwave emission/excess maps, at 13.5 GHz, showing clear evidence that the bulk of the anomalous emission arises in particular from one of the source components, with some additional contribution from the diffuse structure. A cross-correlation analysis with thermal dust emission has shown a high degree of correlation with one of the regions within RCW175. In the center of RCW175, we find an average polarized emission at 21.5 GHz of 2.2±0.2(rand.)±0.3(sys.)% of the total emission, where we have included both systematic and statistical uncertainties at 68% CL. This polarized emission could be due to sub-dominant synchrotron emission from the region and is thus consistent with very faint or non-polarized emission associated with anomalous microwave emission.