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

Abstract

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.

Polycyclic Aromatic Hydrocarbons, the Anomalous Microwave Emission, and Their Connection to the Cold Neutral Medium

“…The fidelity of our study is likely most limited by the reliability of the AME maps, which result from an extensive and challenging component separation analysis (Planck Collaboration X 2016). While additional multifrequency data have in general validated the Planck Collaboration X (2016) AME maps, systematic discrepancies have been noted at the ∼10-20% level (Dickinson et al 2019;Poidevin et al 2019;Cepeda-Arroita et al 2021). In particular, the AME is often underestimated and free-free emission overestimated.…”

“…On the other hand, a recent study of the ρ Oph molecular cloud on arcminute scales found that PAH emission is much better correlated with AME than is the FIR dust emission (Arce-Tord et al 2020). Degree scale studies of AME in λ Orionis have found comparable levels of correlation between AME and either FIR emission or PAH emission (Bell et al 2019;Cepeda-Arroita et al 2021). However, Bell et al (2019) found a significantly stronger correlation between PAH mass and AME than between total dust mass and AME in λ Orionis.…”

The C-Band All-Sky Survey (C-BASS): Template Fitting of Diffuse Galactic Microwave Emission in the Northern Sky

“…In this work we will use a preliminary version of the C-BASS data, similar to that used by Dickinson et al (2019) and Cepeda-Arroita et al (2021). In the following sections we give an overview of the C-BASS data reduction pipeline.…”

“…In previous C-BASS papers (Irfan et al 2015; 1 Defined in brightness temperature units as T b ∝ ν β . Dickinson et al 2019;Cepeda-Arroita et al 2021) this resulted in an effective calibration uncertainty due to the beam of approximately 5 per cent.…”

“…However, it was found that the COMMANDER analysis derived AME amplitude can differ by 30-50 % when compared to other analyses due to correlations with free-free and synchrotron emission components even in mid-to-high latitude (b > 10 • ) regions (Planck Collaboration XXV 2016). Similarly Cepeda-Arroita et al (2021) found significant differences in the fitted AME amplitude when using both the C-BASS and 408 MHz data to constrain low frequencies rather than just the 408 MHz data alone in the λ-Orionis region.…”