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Register a new userA derivation of the free-free emission on the Galactic plane between l=20 and 44 degrees
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We present the derivation of the free-free emission on the Galactic plane between l=20 and 44 degrees and |b| < 4 degrees, using Radio Recombination Line (RRL) data from the HI Parkes All-Sky Survey (HIPASS). Following an upgrade on 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. (2010). The final RRL map has an angular resolution of 14.8 arcmin and a velocity resolution of 20 km/s. A map of the electron temperature (Te) of the ionised gas is derived for the area under study using the line and continuum data from the present survey. The mean Te on the Galactic plane is 6000 K. The first direct measure of the free-free emission is obtained based on the derived Te map. Subtraction of this thermal component from the total continuum leaves the first direct measure of the synchrotron emission at 1.4 GHz. A narrow component of width 2 degrees is identified in the latitude distribution of the synchrotron emission. We present a list of HII regions and SNRs extracted from the present free-free and synchrotron maps, where we confirm the synchrotron nature of three objects: G41.12-0.21, G41.15+0.39 and G35.59-0.44. We also identify a bright (42 Jy) new double radio galaxy, J1841-0152, previously unrecognised owing to the high optical extinction in the region. The latitude distribution for the RRL-derived free-free emission shows that the WMAP Maximum Entropy Method (MEM) 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 degrees will allow a better overall comparison of the RRL result with WMAP.
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Radio recombination lines (RRLs) can be used to determine the emission measure unambiguously along the Galactic plane. We use the deep (2100s per beam) HI Parkes Zone of Avoidance survey which includes 3 RRLs (H$166alpha$, H$167alpha$ and H$168alpha$) within its bandwidth. The region $ell = 36degr$ to $44degr$, $b = -4degr$ to $+4degr$ is chosen to include emission from the Local, Sagittarius and Scutum arms. An $8degr times 8degr$ data cube centred at $(ell, b) = (40degr, 0degr)$ is constructed of RRL spectra with velocity and spatial resolution of 27$kms$ and 15.5 arcmin, respectively. Well-known hii regions are identified as well as the diffuse RRL emission on the Galactic plane. A Galactic latitude section of the integrated RRL emission across the Galactic plane delineates the brightness temperature ($T_{b}$) distribution which has a half-power width in latitude of $simeq 1fdg5$. A value of the electron temperature $T_{e} simeq 8000$ K is derived from a comparison with the WMAP free-free MEM model. The $T_{b}$ distribution from the present RRL data is combined with the WMAP 5-yr data to derive the anomalous dust on the Galactic ridge. In this paper we demonstrate that diffuse ionized emission on the Galactic ridge can be recovered using RRLs from the ZOA survey. This method is therefore able to complement the ha data at low Galactic latitudes, to enable an all-sky free-free template to be derived.
The overwhelming foreground causes severe contamination on the detection of 21-cm signal during the Epoch of Reionization (EoR). Among various foreground components, the Galactic free-free emission is less studied, so that its impact on the EoR observation remains unclear. To better constrain this emission, we perform the Monte Carlo simulation of H$alpha$ emission, which comprises direct and scattered H$alpha$ radiation from HII regions and warm ionized medium (WIM). The positions and radii of HII regions are quoted from the WISE HII catalog, and the WIM is described by an axisymmetric model. The scattering is off dust and free electrons that are realized by applying an exponential fitting to the HI4PI HI map and an exponential disk model, respectively. The simulated H$alpha$ intensity, the Simfast21 software, and the latest SKA1-Low layout configuration are employed to simulate the SKA observed images of Galactic free-free emission and the EoR signal. By analyzing the one-dimensional power spectra, we find that the Galactic free-free emission can be about $10^{5.4}$-$10^{2.1}$, $10^{5.0}$-$10^{1.7}$, and $10^{4.3}$-$10^{1.1}$ times more luminous than the EoR signal on scales of $0.1~{rm Mpc^{-1}} < k < 2~{rm Mpc^{-1}}$ in the 116-124, 146-154, and 186-194 MHz frequency bands, respectively. We further calculate the two-dimensional power spectra inside the EoR window and show that the power leaked by Galactic free-free emission can still be significant, as the power ratios can reach about $110%$-$8000%$, $30%$-$2400%$, and $10%$-$250%$ on scales of $0.5~{rm Mpc^{-1}} lesssim k lesssim 1~{rm Mpc^{-1}}$ in three frequency bands. Therefore, we indicate that the Galactic free-free emission should be carefully treated in future EoR detections.
We present optical ($UBVI_C$) observations of a rich and complex field in the Galactic plane towards $l sim 305^{circ}$ and $b sim 0^{circ}$. Our analysis reveals a significantly high interstellar absorbtion ($A_V sim 10$) and an abnormal extinction law in this line of sight. Availing a considerable number of color combinations, the photometric diagrams allow us to derive new estimates of the fundamental parameters of the two open clusters Danks~1 and Danks~2. Due to the derived abnormal reddening law in this line of sight, both clusters appear much closer (to the Sun) than previously thought. % Additionally, we present the optical colors and magnitudes of the WR~48a star and its main parameters were estimated. The properties of the two embedded clusters DBS2003~130 and 131, are also addressed. We identify a number of Young Stellar Objects which are probable members of these clusters. This new material is then used to revisit the spiral structure in this sector of the Galaxy showing evidence of populations associated with the inner Galaxy Scutum-Crux arm.
We present observations performed with the Green Bank Telescope at 1.4 and 5 GHz of three strips coincident with the anomalous microwave emission features previously identified in the Perseus molecular cloud at 33 GHz with the Very Small Array. With these observations we determine the level of the low frequency (~1 - 5 GHz) emission. We do not detect any significant extended emission in these regions and we compute conservative 3sigma upper limits on the fraction of free-free emission at 33 GHz of 27%, 12%, and 18% for the three strips, indicating that the level of the emission at 1.4 and 5 GHz cannot account for the emission observed at 33 GHz. Additionally, we find that the low frequency emission is not spatially correlated with the emission observed at 33 GHz. These results indicate that the emission observed in the Perseus molecular cloud at 33 GHz, is indeed in excess over the low frequency emission, hence confirming its anomalous nature.
We present an estimate of the polarized spectral index between the Planck 30 and 44 GHz surveys in $3.7^circ$ pixels across the entire sky. We use an objective reference prior that maximises the impact of the data on the posterior and multiply this by a maximum entropy prior that includes information from observations in total intensity by assuming a polarization fraction. Our parametrization of the problem allows the reference prior to be easily determined and also provides a natural method of including prior information. The spectral index map is consistent with those found by others between surveys at similar frequencies. Across the entire sky we find an average temperature spectral index of $-2.99pm0.03(pm1.12)$ where the first error term is the statistical uncertainty on the mean and the second error term (in parentheses) is the extra intrinsic scatter in the data. We use a clustering algorithm to identify pixels with actual detections of the spectral index. The average spectral index in these pixels is $-3.12pm0.03(pm0.64)$ and then when also excluding pixels within $10^circ$ of the Galactic plane we find $-2.92(pm0.03)$. We find a statistically significant difference between the average spectral indices in the North and South Fermi bubbles. Only including pixels identified by the clustering algorithm, the average spectral index in the southern bubble is $-3.00pm0.05(pm0.35)$, which is similar to the average across the whole sky. In the northern bubble we find a much harder average spectral index of $-2.36pm0.09(pm0.63)$. Therefore, if the bubbles are features in microwave polarization they are not symmetric about the Galactic plane.
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