The 2.3 GHz continuum survey of the GEM project

Abstract

Context. Determining the spectral and spatial characteristics of the radio continuum of our Galaxy is an experimentally challenging endeavour for improving our understanding of the astrophysics of the interstellar medium. This knowledge has also become of paramount significance for cosmology, since Galactic emission is the main source of astrophysical contamination in measurements of the cosmic microwave background (CMB) radiation on large angular scales. Aims. We present a partial-sky survey of the radio continuum at 2.3 GHz within the scope of the Galactic Emission Mapping (GEM) project, an observational program conceived and developed to reveal the large-scale properties of Galactic synchrotron radiation through a set of self-consistent surveys of the radio continuum between 408 MHz and 10 GHz. Methods. The GEM experiment uses a portable and double-shielded 5.5-m radiotelescope in altazimuthal configuration to map 60-degree-wide declination bands from different observational sites by circularly scanning the sky at zenithal angles of 30 • from a constantly rotating platform. The observations were accomplished with a total power receiver, whose front-end high electron mobility transistor (HEMT) amplifier was matched directly to a cylindrical horn at the prime focus of the parabolic reflector. The Moon was used to calibrate the antenna temperature scale and the preparation of the map required direct subtraction and destriping algorithms to remove ground contamination as the most significant source of systematic error. Results. We used 484 h of total intensity observations from two locations in Colombia and Brazil to yield 66% sky coverage from δ = −51.• 73 to δ = +34.• 78. The observations in Colombia were obtained with a horizontal HPBW of 2.• 30 ± 0.• 13 and a vertical HPBW of 1.• 92 ± 0.• 18. The pointing accuracy was 6. 84 and the RMS sensitivity was 11.42 mK. The observations in Brazil were obtained with a horizontal HPBW of 2.• 31 ± 0.• 03 and a vertical HPBW of 1.• 82 ± 0.• 12. The pointing accuracy was 5. 26 and the RMS sensitivity was 8.24 mK. The zero-level uncertainty of the combined survey is 103 mK with a temperature scale error of 5% after direct correlation with the Rhodes/HartRAO survey at 2326 MHz on a T -T plot. Conclusions. The sky brightness distribution into regions of low and high emission in the GEM survey is consistent with the appearance of a transition region as seen in the Haslam 408 MHz and WMAP K-band surveys. Preliminary results also show that the temperature spectral index between 408 MHz and the 2.3 GHz band of the GEM survey has a weak spatial correlation with these regions; but it steepens significantly from high to low emission regions with respect to the WMAP K-band survey.

An improved model of diffuse galactic radio emission from 10 MHz to 5 THz

“…There are two ways to further improve the GSM in the future: adding more data sets and improving the algorithm. On the data side, many high quality maps will become available in the near future, such as CBASS (King et al 2010;Irfan et al 2015), SPASS (Carretti et al 2009), GMIMS (Wolleben et al 2009), GEM (Tello et al 2013), and QUI-JOTE (Génova-Santos et al 2015). Some of these upcoming maps will fill in the gap between 2.3 GHz and 23 GHz.…”

An improved source-subtracted and destriped 408-MHz all-sky map

“…Remarkably, it is still widely used (Macellari et al 2011;Planck Collaboration et al 2011;Guzmán et al 2011;Ghosh et al 2012;Peel et al 2012;Lu et al 2012;Iacobelli et al 2013;Planck Collaboration et al 2013) over 30 years since the full-sky version was first released. Although total-power radio surveys have been made more recently at 1.4 GHz (Reich & Reich 1986;Reich et al 2001) and 2.3 GHz (Jonas et al 1998), and new data at higher frequencies are forthcoming (King et al 2014;Hoyland et al 2012;Tello et al 2013), the Haslam map is likely to remain a widely used template of synchrotron emission. However, the sky at frequencies of ∼ 100-1400 MHz is still poorly understood, and the fidelity of the synchrotron template is rather poor compared to modern CMB data.…”

Beam Calibration of Radio Telescopes with Drones

“…Traditionally, beam calibration has been done using bright astronomical sources such as the sun (e.g. Kraus 1966), the moon (Tello et al 2013), and known bright radio sources such as Cassiopeia A, Taurus A, Cygnus A, and Virgo A (Baars et al 1977). Having the source driftscan over the extent of the beam gives one a measure of the beam shape convolved with the source.…”