ABSTRACT
The Andromeda galaxy (M 31) is our closest neighbouring spiral galaxy, making it an ideal target for studying the physics of the interstellar medium in a galaxy very similar to our own. ...Using new observations of M 31 at 4.76 GHz by the C-Band All-Sky Survey (C-BASS), and all available radio data at 1° resolution, we produce the integrated spectrum and put new constraints on the synchrotron spectral index and anomalous microwave emission (AME) from M 31. We use aperture photometry and spectral modelling to fit for the integrated spectrum of M 31, and subtract a comprehensive model of nearby background radio sources. The AME in M 31 is detected at 3σ significance with a peak near 30 GHz and flux density 0.27 ± 0.09 Jy. The synchrotron spectral index of M 31 is flatter than our own Galaxy at α =−0.66 ± 0.03 with no strong evidence of spectral curvature. The emissivity of AME averaged over the total emission from M 31 is lower than typical AME sources in our Galaxy, implying that AME is not uniformly distributed throughout M 31 and instead is likely confined to sub-regions – this will need to be confirmed using future higher resolution observations around 20–30 GHz.
Observational work on Galactic foregrounds with the C-Band All Sky Survey (C-BASS) at 4.76 GHz is presented in intensity and polarisation, with a focus on Anomalous Microwave Emission (AME). ...Observations with the QUIJOTE experiment, the 100 m Green Bank Telescope, and the CO Mapping Array Pathfinder are also used, together with multiwavelength data in the range 408 MHz – 0.7 µm. In addition, C-BASS data is analysed, quantifying the effectiveness of the removal of systematics through simulations and setting an optimal effective frequency.C-BASS provides the most sensitive map of polarised synchrotron emission at . 1 ◦ scales, uncovering many large-scale Galactic features for the first time. This map will be crucial in the search for cosmological B-modes. An absolute measurement of polarisation fractions is presented, which shows a maximum of 27±2% near the North Polar Spur, implying that the magnetic fields in the NPS are significantly tangled at sub-parsec scales. A method of quantifying the coherence of polarisation angles is presented, and the physical nature of new sources is discussed, finding that spurs extend much further than the NPS, favouring the possibility of multiple local supernovae shells imprinting these large-scale loops.Spectral variations of AME across a single region are detected for the first time, with a radial decrease in the peak frequency across the λ Orionis PDR from ≈ 35 GHz in the inner region to ≈ 21 GHz. This suggests that the local radiation field plays a key role in determining the peak frequency by changing the size distribution of spinning dust carriers. A strong spatial correlation of AME with thermal dust emission and PAHs is seen at 1◦ scales, supporting the spinning dust hypothesis. This study also confirms PDRs as favourable regions for strong AME. The need for multiple datasets in the range 1–20 GHz to improve the Commander component separation is highlighted, since the present-day reduction suffers from significant degeneracies between AME and free-free emission.A follow-up study of the region at arcminute scales with the GBT and COMAP reveals that AME does not originate from compact dust cores; being largely diffuse, while the free-free emission is well traced by Hα emission. This breakdown of the correlation between dust and AME at smaller scales suggests that the spinning dust grains can coagulate in dense molecular clouds, leading to a reduced emissivity: a mechanism that spinning dust models do not account for. A preliminary analysis of C-BASS data using Commander reveals that AME is ubiquitous in sky, uncovering a large filament of AME tracing a dust structure on the outside of the NPS; the largest AME source discovered to-date.
Abstract
We present early results from the CO Mapping Array Project (COMAP) Galactic Plane Survey conducted between 2019 June and 2021 April, spanning 20° <
ℓ
< 40° in Galactic longitude and ∣
b
∣ < ...1.°5 in Galactic latitude with an angular resolution of 4.′5. We present initial results from the first part of the survey, including the diffuse emission and spectral energy distributions of H
ii
regions and supernova remnants (SNRs). Using low- and high-frequency surveys to constrain free–free and thermal dust emission contributions, we find evidence of excess flux density at 30 GHz in six regions, which we interpret as anomalous microwave emission. Furthermore we model ultracompact H
ii
contributions using data from the 5 GHz CORNISH catalog and reject these as the cause of the 30 GHz excess. Six known SNRs are detected at 30 GHz, and we measure spectral indices consistent with the literature or show evidence of steepening. The flux density of the SNR W44 at 30 GHz is consistent with a power-law extrapolation from lower frequencies with no indication of spectral steepening in contrast with recent results from the Sardinia Radio Telescope. We also extract five hydrogen radio recombination lines (RRLs) to map the warm ionized gas, which can be used to estimate electron temperatures or to constrain continuum free–free emission. The full COMAP Galactic Plane Survey, to be released in 2023/2024, will span
ℓ
∼ 20°–220° and will be the first large-scale radio continuum and RRL survey at 30 GHz with 4.′5 resolution.
Anomalous Microwave Emission (AME) is a major component of Galactic emission in the frequency band 10 to 60 GHz and is commonly modelled as rapidly rotating spinning dust grains. The ...photodissociation region (PDR) at the boundary of the \(\lambda\)-Orionis Hii region has been identified by several recent analyses as one of the brightest spinning dust emitting sources in the sky. We investigate the Barnard 30 dark cloud, a dark cloud embedded within the \(\lambda\)-Orionis PDR. We use total-power observations of Barnard 30 from the CO Mapping Array Project (COMAP) pathfinder instrument at 26 to 34GHz with a resolution of 4.5 arcminutes alongside existing data from Planck, WISE, IRAS, ACT, and the 1.447GHz GALFACTS survey. We use aperture photometry and template fitting to measure the spectral energy distribution of Barnard 30. We find that the spinning dust is the dominant emission component in the 26 to 34GHz range at the \(7 \sigma\) level (\(S_{30GHz} = 2.85\pm0.43\)Jy). We find no evidence that polycyclic aromatic hydrocarbons are the preferred carrier for the spinning dust emission, suggesting that the spinning dust carriers are due to a mixed population of very small grains. Finally, we find evidence for variations in spinning dust emissivity and peak frequency within Barnard 30, and that these variations are possibly driven by changes in dust grain population and the total radiation field. Confirming the origin of the variations in the spinning dust spectrum will require both future COMAP observations at 15GHz combined with spectroscopic mid-infrared data of Barnard 30.
The Andromeda galaxy (M31) is our closest neighbouring spiral galaxy, making it an ideal target for studying the physics of the interstellar medium in a galaxy very similar to our own. Using new ...observations of M31 at 4.76GHz by the C-Band All-Sky Survey (C-BASS), and all available radio data at \(1^\circ\) resolution, we produce the integrated spectrum and put new constraints on the synchrotron spectral index and anomalous microwave emission (AME) from M31. We use aperture photometry and spectral modelling to fit for the integrated spectrum of M31, and subtract a comprehensive model of nearby background radio sources. The AME in M31 is detected at \(3\sigma\) significance with a peak near 30GHz and flux density \(0.27\pm0.09\)Jy. The synchrotron spectral index of M31 is flatter than our own Galaxy at \(\alpha = -0.66 \pm 0.03\) with no strong evidence of spectral curvature. The emissivity of AME, averaged over the total emission from M31 is lower than typical AME sources in our Galaxy, implying that AME is not uniformly distributed throughout M31 and instead is likely confined to sub-regions -- this will need to be confirmed using future higher resolution observations around 20--30GHz.
We present early results from the COMAP Galactic Plane Survey conducted between June 2019 and April 2021, spanning \(20^\circ<\ell<40^\circ\) in Galactic longitude and \(|b|<1.\!\!^{\circ}5\) in ...Galactic latitude with an angular resolution of \(4.5^{\prime}\). The full survey will span \(\ell \sim 20^{\circ}\)- \(220^{\circ}\) and will be the first large-scale radio continuum survey at \(30\) GHz with sub-degree resolution. We present initial results from the first part of the survey, including diffuse emission and spectral energy distributions (SEDs) of HII regions and supernova remnants. Using low and high frequency surveys to constrain free-free and thermal dust emission contributions, we find evidence of excess flux density at \(30\,\)GHz in six regions that we interpret as anomalous microwave emission. Furthermore we model UCHII contributions using data from the \(5\,\)GHz CORNISH catalogue and reject this as the cause of the \(30\,\)GHz excess. Six known supernova remnants (SNR) are detected at \(30\,\)GHz, and we measure spectral indices consistent with the literature or show evidence of steepening. The flux density of the SNR W44 at \(30\,\)GHz is consistent with a power-law extrapolation from lower frequencies with no indication of spectral steepening in contrast with recent results from the Sardinia Radio Telescope. We also extract five hydrogen radio recombination lines to map the warm ionized gas, which can be used to estimate electron temperatures or to constrain continuum free-free emission. The full COMAP Galactic plane survey, to be released in 2023/2024, will be an invaluable resource for Galactic astrophysics.
