Génova-Santos, R.; Rebolo, R.; Rubiño-Martín, J. A.; López-Caraballo, C. H.; Hildebrandt, S. R.
Referencia bibliográfica
The Astrophysical Journal, Volume 743, Issue 1, article id. 67 (2011).
Fecha de publicación:
12
2011
Revista
Número de citas
20
Número de citas referidas
18
Descripción
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.
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