Microwave emission from dust revisited

Monthly Notices of the Royal Astronomical Society

Casassus

Davies

et al. 2010

Lynds dark cloud LDN1622 represents one of the best examples of anomalous dust emission, possibly originating from small spinning dust grains. We present Cosmic Background Imager (CBI) 31-GHz data of LDN1621, a diffuse dark cloud to the north of LDN1622 in a region known as Orion East. A broken ring-like structure with diameter approximate to 20 arcmin of diffuse emission is detected at 31 GHz, at approximate to 20-30 mJy beam-1 with an angular resolution of approximate to 5 arcmin. The ring-like structure is highly correlated with far-infrared (FIR) emission at 12-100 mu m with correlation coefficients of r approximate to 0.7-0.8, significant at similar to 10 Sigma. The FIR-correlated emission at 31 GHz therefore appears to be mostly due to radiation associated with dust. Multifrequency data are used to place constraints on other components of emission that could be contributing to the 31-GHz flux. An analysis of the GB6 survey maps at 4.85 GHz yields a 3 Sigma upper limit on free-free emission of 7.2 mJy beam-1 (less than or similar to 30 per cent of the observed flux) at the CBI resolution. The bulk of the 31-GHz flux therefore appears to be mostly due to dust radiation. Aperture photometry, at an angular resolution of 13 arcmin and with an aperture of diameter 30 arcmin, allowed the use of IRAS maps and the Wilkinson Microwave Anisotropy Probe 5-yr W-band map at 93.5 GHz. A single modified blackbody model was fitted to the data to estimate the contribution from thermal dust, which amounts to similar to 10 per cent at 31 GHz. In this model, an excess of 1.52 +/- 0.66 Jy (2.3 Sigma) is seen at 31 GHz. Correlations with the IRAS 100 mu m gave a coupling coefficient of 18.1 +/- 4.4 mu K (MJy sr-1)-1, consistent with the values found for LDN1622

Section: Analysis and Discussionmentioning

confidence: 99%

Infrared-correlated 31-GHz radio emission from Orion East

Monthly Notices of the Royal Astronomical Society

Casassus

Davies

et al. 2010

“…The prevailing idea is that the majority of AME arises from electric dipole emission from rapidly rotating dust grains (Draine & Lazarian 1998a). This spinning dust hypothesis is increasingly favoured by observational results, although alternative mechanisms have been proposed (Draine & Lazarian 1999;Bennett et al 2003;Meny et al 2007;Jones 2009;Nashimoto et al 2019Nashimoto et al , 2020. For the purpose of this paper, it is assumed that the majority of AME originates from spinning dust grains.…”

Section: Anomalous Microwave Emissionmentioning

confidence: 98%

Detection of spectral variations of Anomalous Microwave Emission with QUIJOTE and C-BASS

Cepeda-Arroita

Harper

Monthly Notices of the Royal Astronomical Society

et al. 2021

Anomalous Microwave Emission (AME) is a significant component of Galactic diffuse emission in the frequency range 10-60 GHz and a new window into the properties of sub-nanometre-sized grains in the interstellar medium. We investigate the morphology of AME in the ≈10○ diameter λ Orionis ring by combining intensity data from the QUIJOTE experiment at 11, 13, 17 and 19 GHz, and the C-Band All Sky Survey (C-BASS) at 4.76 GHz, together with 19 ancillary datasets between 1.42 and 3000 GHz. Maps of physical parameters at 1○ resolution are produced through Markov Chain Monte Carlo (MCMC) fits of spectral energy distributions (SEDs), approximating the AME component with a log-normal distribution. AME is detected in excess of 20 σ at degree-scales around the entirety of the ring along photodissociation regions (PDRs), with three primary bright regions containing dark clouds. A radial decrease is observed in the AME peak frequency from ≈35 GHz, near the free-free region to ≈21 GHz, in the outer regions of the ring, which is the first detection of AME spectral variations across a single region. A strong correlation between AME peak frequency, emission measure and dust temperature is an indication for the dependence of the AME peak frequency on the local radiation field. The AME amplitude normalized by the optical depth is also strongly correlated with the radiation field, giving an overall picture consistent with spinning dust where the local radiation field plays a key role.

“…Upper limits on AME polarization are thus not supportive of large grains as the origin of AME. Jones (2009) pointed out an alternative possibility that resonant tunnelling may be associated with stochastically-heated very small grains, since they spend much of their time at low temperatures, where resonant tunnelling becomes important (Meny et al 2007). In this case a good correlation of AME with the mid-infrared excess emission (20-60 µm) is expected.…”

Section: Other Emission Mechanisms?mentioning

confidence: 99%

The State-of-Play of Anomalous Microwave Emission (AME) research

Ali-Haı̈moud

Barr

et al. 2018

New Astronomy Reviews

Anomalous Microwave Emission (AME) is a component of diffuse Galactic radiation observed at frequencies in the range ≈ 10-60 GHz. AME was first detected in 1996 and recognised as an additional component of emission in 1997. Since then, AME has been observed by a range of experiments and in a variety of environments. AME is spatially correlated with far-IR thermal dust emission but cannot be explained by synchrotron or free-free emission mechanisms, and is far in excess of the emission contributed by thermal dust emission with the power-law opacity consistent with the observed emission at sub-mm wavelengths. Polarization observations have shown that AME is very weakly polarized ( 1 %). The most natural explanation for AME is rotational emission from ultra-small dust grains ("spinning dust"), first postulated in 1957.