A 33 GHz VSA survey of the Galactic plane from 27 to 46 degrees

TL;DR

This study used the VSA to survey the Galactic plane at 33 GHz, analyzing anomalous dust emission in HII regions and establishing its significance relative to other radio emissions.

Contribution

It provides the first detailed measurement of anomalous dust emission at 33 GHz in HII regions, combining VSA data with multi-frequency IR and radio observations.

Findings

Detected anomalous dust emission with high significance at 33 GHz.

Quantified the ratio of anomalous emission to FIR flux in HII regions.

Found anomalous emission constitutes about 41% of the total radio continuum at 33 GHz.

Abstract

The Very Small Array (VSA) has been used to survey the l = 27 to 46 deg, |b|<4 deg region of the Galactic plane at a resolution of 13 arcmin. The survey consists of 44 pointings of the VSA, each with a r.m.s. sensitivity of ~90 mJy/beam. These data are combined in a mosaic to produce a map of the area. The majority of the sources within the map are HII regions. We investigated anomalous radio emission from the warm dust in 9 HII regions of the survey by making spectra extending from GHz frequencies to the FIR IRAS frequencies. Acillary radio data at 1.4, 2.7, 4.85, 8.35, 10.55, 14.35 and 94 GHz in addition to the 100, 60, 25 and 12 micron IRAS bands were used to construct the spectra. From each spectrum the free-free, thermal dust and anomalous dust emission were determined for each HII region. The mean ratio of 33 GHz anomalous flux density to FIR 100 micron flux density for the 9 selected HII regions was 1.10 +/-0.21x10^(-4). When combined with 6 HII regions previously observed with the VSA and the CBI, the anomalous emission from warm dust in HII regions is detected with a 33 GHz emissivity of 4.65 +/- 0.4 micro K/ (MJy/sr) at 11.5{\sigma}. The anomalous radio emission in HII regions is on average 41+/-10 per cent of the radio continuum at 33 GHz.