DETECTION OF ANOMALOUS MICROWAVE EMISSION IN THE PLEIADES REFLECTION NEBULA WITHWILKINSON MICROWAVE ANISOTROPY PROBEAND THE COSMOSOMAS EXPERIMENT

Abstract

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.

Using cm observations to constrain the abundance of very small dust grains in Galactic cold cores

“…Spinning dust emission has been detected in a variety of Galactic environments such as molecular clouds (Casassus et al 2008;Planck Collaboration XX 2011;Tibbs et al 2010Tibbs et al , 2013Génova-Santos et al 2015), dark clouds (Casassus et al 2006;AMI Consortium et al 2009;Dickinson et al 2010), Hii regions (Dickinson et al 2007;Tibbs et al 2012;Battistelli et al 2015), and reflection nebulae (Castellanos et al 2011;Génova-Santos et al 2011), however, it has never been used to constrain the physical properties of interstellar dust grains. Complex spinning dust models now exist, incorporating a variety of excitation and damping mechanisms acting on the dust grains (e.g., Ali-Haïmoud et al 2009;Hoang et al 2010Hoang et al , 2011Silsbee et al 2011).…”

New Radio Observations of Anomalous Microwave Emission in the H Ii Region Rcw175

“…AME was first identified as diffuse emission in the 10-60 GHz range in excess of the expected level of microwave emission from free-free, synchrotron, and thermal dust emission by experiments such as the Cosmic Background Explorer-DMR (COBE-DMR; Kogut et al 1996), the Saskatoon experiment (de Oliveira-Costa et al 1997), Owens Valley Radio Observatory (OVRO; Leitch et al 1997) and the Tenerife experiment (de Oliveira-Costa et al 1999). Several authors have found further statistical evidence of AME (see e.g., Banday et al 2003;Lagache 2003;de Oliveira-Costa et al 2004;Finkbeiner et al 2004;Davies et al 2006;Hildebrandt et al 2007;Lu et al 2012;Miville-Deschênes et al 2008), while it has also been detected directly in individual regions in a limited number of cases (see e.g., Watson et al 2005;Scaife et al 2007;Casassus et al 2008;AMI Consortium 2009;Murphy et al 2010;Dickinson et al 2010;Genova-Santos et al 2011;Planck collaboration 2011aPlanck collaboration , 2014a. Recent models predict that the AME is dominated by electric dipole emission from the smallest grains, possibly polycyclic aromatic hydrocarbons (PAHs; Draine & Lazarian 1998;Ysard et al 2010;Hoang et al 2010).…”

Observations of the Polarisation of the Anomalous Microwave Emission: A Review

“…The anomalous microwave emission (hereafter AME) is an excess of dust-correlated microwave (10-60 GHz) emission [1,2] which cannot be explained in terms of the standard physical mechanisms of continuum emission in this frequency range: synchrotron, free-free, and/or thermal dust emission. This AME has been measured by multiple cosmic microwave background (CMB) experiments on both large scales (e.g., COBE [1]; OVRO [2]; Saskatoon [3]; 19 GHz [4]; Python V [5]; Tenerife [6,7]; GBT [8][9][10]; COSMOSOMAS [11]; WMAP [12][13][14][15][16][17]; Planck [18,19]) as well as in pointed observations of specific Galactic dust clouds (e.g., COSMOSOMAS [20,21]; CBI [22][23][24]; AMI [25][26][27]; VSA [28,29]; RATAN-600 [30]; 8 GHz [31, Conklin data]; Planck [18]). Moreover, recent studies also show evidence of AME in nearby galaxies [32,33].…”