Génova-Santos, R.; Rebolo, R.; Rubiño-Martín, J. A.; López-Caraballo, C. H.; Hildebrandt, S. R.
Bibliographical reference
The Astrophysical Journal, Volume 743, Issue 1, article id. 67 (2011).
Advertised on:
12
2011
Journal
Citations
20
Refereed citations
18
Description
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. = 56fdg24, decl. = 23fdg78
(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.
Related projects
Anisotropy of the Cosmic Microwave Background
The general goal of this project is to determine and characterize the spatial and spectral variations in the temperature and polarisation of the Cosmic Microwave Background in angular scales from several arcminutes to several degrees. The primordial matter density fluctuations which originated the structure in the matter distribution of the present
Rafael
Rebolo López