We present a Radio Recombination Line (RRL) survey of the Galactic plane from the H i Parkes All-sky Survey and associated Zone of Avoidance survey, which mapped the region l = 196°–0°–52° and ...|b| ≤ 5° at 1.4 GHz and 14.4 arcmin resolution. We combine three RRLs, H168α, H167α, and H166α to derive fully sampled maps of the diffuse ionized emission along the inner Galactic plane. The velocity information, at a resolution of 20 km s−1, allows us to study the spatial distribution of the ionized gas and compare it with that of the molecular gas, as traced by CO. The longitude–velocity diagram shows that the RRL emission is mostly associated with CO gas from the molecular ring and is concentrated within the inner 30° of longitude. A map of the free–free emission in this region of the Galaxy is derived from the line-integrated RRL emission, assuming an electron temperature gradient with Galactocentric radius of 496 ± 100 K kpc−1. Based on the thermal continuum map, we extracted a catalogue of 317 compact (≲15 arcmin) sources, with flux densities, sizes, and velocities. We report the first RRL observations of the southern ionized lobe in the Galactic Centre. The line profiles and velocities suggest that this degree-scale structure is in rotation. We also present new evidence of diffuse ionized gas in the 3-kpc arm. Helium and carbon RRLs are detected in this survey. The He line is mostly observed towards H ii regions, whereas the C line is also detected further away from the source of ionization. These data represent the first observations of diffuse C RRLs in the Galactic plane at a frequency of 1.4 GHz.
I give a summary of the observations of Anomalous Microwave Emission (AME) from HII regions. AME has been detected in, or in the vicinity of, HII regions. Given the difficulties in measuring accurate ...SEDs over a wide range of frequencies and in complex environments, many of these detections require more data to confirm them as emitting significant AME. The contribution from optically thick free-free emission from UCHII regions may be also be significant in some cases. The AME emissivity, defined as the ratio of the AME brightness to the 100 μm brightness, is comparable to the value observed in high-latitude diffuse cirrus in some regions, but is significantly lower in others. However, this value is dependent on the dust temperature. More data, both at high frequencies (>~5 GHz) and high resolution (~1′ or better) is required to disentangle the emission processes in such complex regions.
We present the derivation of the free-free emission on the Galactic plane between ℓ= 20° and 44° and |b|≤ 4°, using radio recombination line (RRL) data from the H i Parkes All Sky Survey (HIPASS). ...Following an upgrade of the RRL data reduction technique, which improves significantly the quality of the final RRL spectra, we have extended the analysis to three times the area covered in Alves et al. The final RRL map has an angular resolution of 14.8 arcmin and a velocity resolution of 20 km s−1.
The electron temperature (T
e) distribution of the ionized gas in the area under study at 1.4 GHz is derived using the line and continuum data from the present survey. The mean T
e on the Galactic plane is 6000 K. The first direct measure of the free-free emission is obtained based on the derived T
e distribution. Subtraction of this thermal component from the total continuum leads to the first direct measurement of the synchrotron emission at 1.4 GHz. A narrow component of width 2° is identified in the latitude distribution of the synchrotron emission. We present a list of H ii regions and supernova remnants (SNRs) extracted from the present free-free and synchrotron maps, where we confirm the synchrotron nature of the SNRs G42.0−0.1 and G41.5+0.4 proposed by Kaplan et al. and the SNR G35.6−0.4 recently re-identified by Green.
The latitude distribution for the RRL-derived free-free emission shows that the Wilkinson Microwave Anisotropy Probe (WMAP) maximum entropy method is too high by ∼50 per cent, in agreement with other recent results. The extension of this study to the inner Galaxy region ℓ=−50° to 50° will allow a better overall comparison of the RRL result with WMAP.
Wilkinson Microwave Anisotropy Probe (WMAP) data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these ...components. Here we examine the sky variation at intermediate and high latitudes using a cross-correlation technique. In particular, we compare the observed emission in several global partitions of the sky plus 33 selected sky regions to three 'standard' templates. The regions are selected using a criterion based on the morphology of these template maps.
The synchrotron emission shows evidence of steepening between GHz frequencies and the WMAP bands. There are indications of spectral index variations across the sky, but the current data are not precise enough to accurately quantify this from region to region.
The Hα template correlated emission derived from the global fits shows clear evidence of deviation from a free-free spectrum. If this spectrum is decomposed into a contribution from both free-free and spinning dust emission in the warm ionized medium of the Galaxy, the derived free-free emissivity corresponds to a mean electron temperature of ∼6000 K (a value critically dependent on the impact of dust absorption on the Hα intensity), and the spinning dust emission has a peak emission in intensity typically in the range 40-50 GHz. However, the analysis of the smaller regions is generally unrevealing and the analysis presented here does not unambiguously demonstrate the presence of spinning dust emission in the warm ionized medium, as advocated by Dobler & Finkbeiner.
The anomalous microwave emission associated with dust is detected at high significance in most of the 33 fields studied. The anomalous emission correlates well with the Finkbeiner et al. model 8 predictions (FDS8) at 94 GHz, and is well described globally by a power-law emission model with an effective spectral index between 20 and 60 GHz of β≈−2.7. It is clear that attempts to explain the emission by spinning dust models require multiple components, which presumably relates to a complex mix of emission regions along a given line of sight. An enhancement of the thermal dust contribution over the FDS8 predictions by a factor ∼1.2 is required with such models. Furthermore, the emissivity varies by a factor of ∼50 per cent from cloud to cloud relative to the mean.
The significance of these results for the correction of cosmic microwave background data for Galactic foreground emission is discussed.
The large-scale radio/microwave sky has been mapped over a range of frequencies from tens of MHz to tens of GHz, in intensity and polarization. The emission is primarily synchrotron radiation from ...cosmic ray electrons spiralling in the Galactic magnetic field, in addition to free–free radiation from warm ionized gas. Away from the Galactic plane, the radio sky is dominated by very large (tens of degrees) loops, arcs, spurs and filaments, including the well-known North Polar Spur (NPS), which forms part of Loop I with a diameter of ∼ 120 ∘ . In polarization data, such features are often more discernible due to their high polarization fractions suggesting ordered magnetic fields, while the polarization angles suggest fields that are parallel to the filament. The exact nature of these features are poorly understood. We give a brief review of these features, focussing on the NPS/Loop I, whose polarization directions can be explained using a simple expanding shell model, placing the centre of the shell at a distance of ∼100–200 pc. However, there is significant evidence for a larger distance in the range ∼500–1000 pc, while larger distances including the Galactic Centre are unlikely. We also briefly discuss other large-scale curiosities in the radio sky such as the microwave haze and anti-correlation of H α filaments and synchrotron polarized intensity.
A refined model for spinning dust radiation Ali-Haïmoud, Yacine; Hirata, Christopher M.; Dickinson, Clive
Monthly notices of the Royal Astronomical Society,
05/2009, Letnik:
395, Številka:
2
Journal Article
Many studies of anomalous microwave emission (AME) have computed an AME emissivity to compare the strength of the AME detected in different regions. Such a value is usually defined as the ratio ...between the intensity of the AME at 1 cm and the thermal dust emission at 100 μm. However, as studies of Galactic dust emission have shown, the intensity of the thermal dust emission at 100 μm is strongly dependent on the dust temperature, which has severe implications for the AME emissivity defined in this way. In this work, we illustrate and quantify this effect and find that the AME emissivity decreases by a factor of 11.1 between dust temperatures of 20 and 30 K. We, therefore, conclude that computing the AME emissivity relative to the 100 μm emission does not allow for accurate comparisons between the AME observed in different environments. With this in mind, we investigate the use of other tracers of the dust emission with which to compute the AME emissivity and we ultimately conclude that, despite the difficulty in deriving its value, the column density of the dust would be the most suitable quantity with which to compute the AME emissivity.
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