In this paper we report the first successful demonstration of angular super-resolution (SR) obtained with a single-aperture radio telescope observing in the microwave K-band. Despite the potential scientific applications, in the past few decades little efforts have been devoted to the development of SR imaging techniques for Astronomy, while most of the technological improvement has concentrated on focal plane instrumentation. In recent years, some complex and ambitious techniques have been proposed to achieve SR with astronomical telescopes, but none of these techniques has gone beyond the stage of basic principles or could be used as a real SR imaging method. Variable-transmittance pupils, and specifically Toraldo Pupils (TPs), represent one viable approach to achieving SR in radio astronomy. In this work we show that by exploiting the active surface of the Sardinia Radio Telescope (SRT) to emulate a TP at the entrance pupil of the telescope it is indeed possible to achieve a main beam narrower than that expected by diffraction. The reduction in the width of the main beam is achieved at the expense of a lower antenna efficiency and higher sidelobes. We have also used the resulting SR beam to map an astronomical source and we show that we are able to recover some of the compact structure not visible using the nominal diffraction-limited telescope beam. Once the method will be adequately tested and optimized, it will provide the telescope users with a new observing option, promising to expand the scientific capabilities of the SRT.

The design, fabrication, and performance of a millimeter-wave waveguide orthomode transducer (OMT) operating over an extended W-band frequency range 70–116 GHz is presented. The OMT has been designed for integration within a cryogenic radio astronomy focal plane array millimeter-wave receiver. In addition to delivering necessary millimeter-wave performance, a custom mechanical housing incorporating suitable waveguide interfaces is required. Within the OMT, a turnstile junction performs polarization separation of a signal entering a bespoke circular waveguide interface into two orthogonally polarized outputs via WR10 standard waveguide flanges. The device’s internal architecture was optimized using a combination of proprietary software and a commercially available 3-dimensional electromagnetic field analysis package. In order to demonstrate required performance, compactness and reliable production, two approaches were taken with respect to device mechanical fabrication: platelet and split block direct machining methods. Both structures were manufactured and tested at room temperature. Due to advantages in machining and assembly, the split block concept was selected for inclusion with the array receiver.

Our group at Arcetri is currently carrying out a project devoted to the implementation of super-resolution on single-dish radio telescopes, which should result in an angular resolution better than the classical diffraction limit. A feasible method to achieve this goal consists of using variable transmittance pupils. The simplest transmittance pupils are binary phase shift masks, also known as Toraldo pupils, consisting of finite-width concentric coronae which modify the phase of the incident wavefront. In this work I show, through EM numerical simulations, that super-resolution can indeed be achieved on a Cassegrain radio telescope. I also discuss the inadequacy of simple analytical models to predict the performance of Toraldo pupils when optically interfaced to a telescope.

This paper describes the design and performance of the single-pixel receiver elements in the Cryogenic Array Receiver for Users of the Sardinia Observatory (CARUSO). CARUSO contains an array of 4x4 extended-W-band pixels, covering astronomical source frequencies from 70 to 116 GHz. CARUSO has recently been installed at the Gregorian focus of the 64 m diameter Sardinia Radio Telescope. Each cryogenic receiver pixel comprises a smooth walled feedhorn and a waveguide orthomode transducer for polarization separation. Each polarization channel comprises two low-noise amplification modules with a waveguide isolator between them, and an image-rejecting sub-harmonic mixer delivering the upper and lower sidebands, with a frequency tripler providing the local oscillator signal. The low noise amplifiers are based on two-stage MMIC amplifiers, incorporating InP high electron mobility transistors.

Over the years, there has been much speculation to understand whether (and how) it was possible to go below the diffraction limit. An advance in knowledge was achieved with the development of microwave techniques. In fact, more than fifty years after the publication of Toraldo’s article dealing with this topic, some experimental measurements in the range of microwaves confirmed the validity of his model. Since some measurements were performed in the region of near field, while Toraldo’s model refers to the far field, the need for a theoretical analysis in the framework of the Fresnel optics arose. The main goal of the present paper is to describe the problem of propagation in the near field (Fresnel optics) by using the same theoretical model already proposed by Toraldo. In order to test the validity of this new approach, the theoretical model has been compared with the FEKO simulation. The comparison of the theoretical model with the FEKO simulation in the far field for an open pupil (an open circular aperture) shows perfect agreement, as expected. We will demonstrate that there is also good agreement in the near field, although it is limited to the region around the main lobe, which is usually the region of main physical interest. Moving away from the main lobe, namely away from the optical axis, the agreement becomes less significant.

ABSTRACT We report observations, performed with the Atacama Large Millimeter/submillimeter Array (ALMA), of 1 mm dust continuum emission and molecular line emission in 13CO(2–1) and C18O(2–1), towards a sample of starless and protostellar clumps selected from a region, towards the ℓ = 224° field, of the Herschel Infrared GALactic Plane Survey (Hi-GAL). Using the ALMA images and a source extraction algorithm we have analysed the small-scale (∼1000 AU) structure of the clumps and their population of cores (or fragments). We find in general multiple cores in each Hi-GAL clump, both in the continuum and spectral lines, but we do not find a dominant fragmentation mode and the morphologies are very different among the various sources. Our results suggest that during the transition phase from clump to core, those sources with a higher core formation efficiency are also associated with parent clumps that are more likely to convert a higher fraction of their initial mass into a single or a few cores. We were able to obtain a core mass function, or CoMF, covering masses in the range ∼2 × 10−3 to ∼1 M⊙ for the C18O cores, and ∼4 × 10−2 to ∼10 M⊙ for the continuum cores. We find that the CoMF in our sample is much shallower than the higher mass ($\gtrsim 1$ M⊙) IMF, thus indicating that while approaching the final phase of fragmentation the mass function does not resemble the IMF more closely.

We present a new derivation of the Milky Way’s current star formation rate (SFR) based on the data of the Herschel InfraRed Galactic Plane Survey (Hi-GAL). We estimate the distribution of the SFR across the Galactic plane from the star-forming clumps identified in the Hi-GAL survey and calculate the total SFR from the sum of their contributions. The estimate of the global SFR amounts to 2.0 ± 0.7 M ⊙ yr −1 , of which 1.7 ± 0.6 M ⊙ yr −1 coming from clumps with reliable heliocentric distance assignment. This value is in general agreement with estimates found in the literature of last decades. The profile of SFR density averaged in Galactocentric rings is found to be qualitatively similar to others previously computed, with a peak corresponding to the Central Molecular Zone and another one around Galactocentric radius R gal ∼ 5 kpc, followed by an exponential decrease as log ( Σ SFR / [ M ⊙ yr − 1 kpc − 2 ] ) = a R gal / [ kpc ] + b , with a = −0.28 ± 0.01. In this regard, the fraction of SFR produced within and outside the solar circle is 84% and 16%, respectively; the fraction corresponding to the far outer Galaxy ( R gal > 13.5 kpc) is only 1%. We also find that, for R gal > 3 kpc, our data follow a power law as a function of density, similarly to the Kennicutt–Schmidt relation. Finally, we compare the distribution of the SFR density across the face-on Galactic plane and those of median parameters, such as temperature, luminosity/mass ratio, and bolometric temperature, describing the evolutionary stage of Hi-GAL clumps. We found no clear correlation between the SFR and the clump evolutionary stage.

We are currently carrying out a project devoted to the implementation of super-resolution (SR) on single-dish radio telescopes, which should result in an angular resolution better than the classical diffraction limit. A feasible method to achieve this goal consists of using variable transmittance pupils. The simplest transmittance pupils are binary phase shift masks, also known as Toraldo Pupils, consisting of finite-width concentric coronae which modify the phase of the incident wavefront. In previous works we have suggested that the active primary surface of a telescope could be used to simulate a Toraldo Pupil placed at the entrance pupil. In this paper we present new electromagnetic simulations whose goal is to assess the feasibility of this method using the shaped active surface of the 64-m Sardinia Radio Telescope.

We report on the feasibility study of a W-band multibeam heterodyne receiver for the Sardinia Radio Telescope (SRT), a general purpose fully steerable 64-m diameter antenna located on the Sardinia island, Italy, managed by INAF (“Istituto Nazionale di Astrofisica,” Italy). The W-band front-end is designed for the telescope Gregorian focal plane and will detect both continuum and molecular spectral lines from astronomical sources and radio emission from the Sun in the 3 mm atmospheric window. The goal specification of the receiver is a $4\times 4$ focal plane array operating in dual-linear polarization with a front-end consisting of feed-horns placed in cascade with waveguide Orthomode Transducers (OMTs) and LNAs (Low Noise Amplifiers) cryogenically cooled at $\approx $ 20 K. The instantaneous FoV (Field of View) of the telescope is limited by the shaping of the 64-m primary and 7.9-m secondary mirrors. The cryogenic modules are designed to fit in the usable area of the focal plane and provide high-quality beam patterns with high antenna efficiency across the 70 – 116 GHz Radio Frequency (RF) band. The FoV covered by the $4\times 4$ array is $2.15\times 2.15$ arcmin 2 , unfilled, with separation between contiguous elements of 43 arcsec. Dual-sideband separation (2SB) down-conversion mixers are designed to be placed at the cryostat output and arranged in four four-pixel down-conversion modules with 4 – 12 GHz Intermediate Frequency (IF) bands (both Upper Side Band and Lower Side Band selectable for any pixel and polarization). The receiver utilizes a mechanical derotator to track the parallactic angle.

We present the status of the Sardinia Radio Telescope (SRT) and its forthcoming update planned in the next few years. The post-process scenario of the upgraded infrastructure will allow the national and international scientific community to use the SRT for the study of the Universe at high radio frequencies (up to 116 GHz), both in single dish and in interferometric mode. A telescope like SRT, operating at high frequencies, represents a unique resource for the scientific community. The telescope will be ideal for mapping quickly and with relatively high angular resolution extended radio emissions characterized by low surface brightness. It will also be essential for spectroscopic and polarimetric studies of both Galactic and extragalactic radio sources. With the use of the interferometric technique, SRT and the other Italian antennas (Medicina and Noto) will operate within the national and international radiotelescope network, allowing astronomers to obtain images of radio sources at very high angular resolution.

Context. New-generation spectroscopic surveys of the Milky Way plane have been revealing the structure of the interstellar medium, allowing the simultaneous study of dense structures from single star-forming objects or systems to entire spiral arms. Aims. The good sensitivity of the new surveys and the development of dedicated algorithms now enable building extensive catalogues of molecular clouds and deriving good estimates of their physical properties. This allows studying the behaviour of these properties across the Galaxy. Methods. We present the catalogue of molecular clouds extracted from the (CO)-C-13 (1-0) data cubes of the Forgotten Quadrant Survey, which mapped the Galactic plane in the range 220 degrees < l < 240 degrees and -2.5 < b < 0 degrees in (CO)-C-12 (1-0) and (CO)-C-13 (1-0). We compared the properties of the clouds of our catalogue with those of other catalogues. Results. The catalogue contains 87 molecular clouds for which the main physical parameters such as area, mass, distance, velocity dispersion, and virial parameter were derived. These structures are overall less extended and less massive than the molecular clouds identified in the (CO)-C-12 (1-0) data-set because they trace the brightest and densest part of the (CO)-C-12 (1-0) clouds. Conversely, the distribution of aspect ratio, equivalent spherical radius, velocity dispersion, and virial parameter in the two catalogues are similar. The mean value of the mass surface density of molecular clouds is 87 +/- 55 M-circle dot pc(-2) and is almost constant across the galactocentric radius, indicating that this parameter, which is a proxy of star formation, is mostly affected by local conditions. Conclusions. In data of the Forgotten Quadrant Survey, we find a good agreement between the total mass and velocity dispersion of the clouds derived from (CO)-C-12 (1-0) and (CO)-C-13 (1-0). This is likely because in the surveyed portion of the Galactic plane, the H-2 column density is not particularly high, leading to a CO emission with a not very high optical depth. This mitigates the effects of the different line opacities between the two tracers on the derived physical parameters. This is a common feature in the outer Galaxy, but our result cannot be readily generalised to the entire Milky Way because regions with higher particle density could show a different behaviour.

Authors: D. Anish Roshi1 , N. Aponte1, E. Araya2, H. Arce3, L. A. Baker7, W. Baan35, T. M. Becker4, J. K. Breakall34, R. G. Brown5, C. G. M. Brum1, M. Busch6, D. B. Campbell7, T. Cohen24, F. Cordova1, J. S. Deneva8, M. Devogèle1, T. Dolch30, F. O. Fernandez-Rodriguez1, T. Ghosh9, P. F. Goldsmith10, L.I. Gurvits14,27, M. Haynes7, C. Heiles11, J. W. T. Hessel 35, 38, D. Hickson1, B. Isham12, R. B. Kerr13, J. Kelly28, J. J. Kiriazes5, J. Lautenbach1, M. Lebron15, N. Lewandowska16, L. Magnani17, P. K. Manoharan1, J. L. Margot 37, S. E. Marshall1, A. K. McGilvray1, A. Mendez36, R. Minchin18, V. Negron1, M. C. Nolan19, L. Olmi26, F. Paganelli9, N. T. Palliyaguru20, C. A. Pantoja15, Z. Paragi27, S. C. Parshley7, J. E. G. Peek6,21, B. B. P. Perera1, P. Perillat1, N. Pinilla-Alonso22,1, L. Quintero1, H. Radovan25, S. Raizada1, T. Robishaw23, M. Route31, C. J. Salter9,1, A. Santoni1, P. Santos1, S. Sau1, D. Selvaraj1, A. J. Smith1, M. Sulzer1, S. Vaddi1, F. Vargas33, F. C. F. Venditti1, A. Venkataraman1, H. Verkouter27, A. K. Virkki1, A. Vishwas7, S. Weinreb32, D. Werthimer11, A. Wolszczan29 and L. F. Zambrano-Marin1.

The Arecibo Observatory (AO) is a multidisciplinary research and education facility that is recognized worldwide as a leading facility in astronomy, planetary, and atmospheric and space sciences. AO's cornerstone research instrument was the 305-m William E. Gordon telescope. On December 1, 2020, the 305-m telescope collapsed and was irreparably damaged. In the three weeks following the collapse, AO's scientific and engineering staff and the AO users community initiated extensive discussions on the future of the observatory. The community is in overwhelming agreement that there is a need to build an enhanced, next-generation radar-radio telescope at the AO site. From these discussions, we established the set of science requirements the new facility should enable. These requirements can be summarized briefly as: 5 MW of continuous wave transmitter power at 2 - 6 GHz, 10 MW of peak transmitter power at 430 MHz (also at 220MHz under consideration), zenith angle coverage 0 to 48 deg, frequency coverage 0.2 to 30 GHz and increased Field-of-View. These requirements determine the unique specifications of the proposed new instrument. The telescope design concept we suggest consists of a compact array of fixed dishes on a tiltable, plate-like structure with a collecting area equivalent to a 300m dish. This concept, referred to as the Next Generation Arecibo Telescope (NGAT), meets all of the desired specifications and provides significant new science capabilities to all three research groups at AO. This whitepaper presents a sample of the wide variety of the science that can be achieved with the NGAT, the details of the telescope design concept and the need for the new telescope to be located at the AO site. We also discuss other AO science activities that interlock with the NGAT in the white paper.

We present the 360° catalogue of physical properties of Hi-GAL compact sources, detected between 70 and 500 $\mu$m. This release not only completes the analogous catalogue previously produced by the Hi-GAL collaboration for −71° ≲ ℓ ≲ 67°, but also meaningfully improves it because of a new set of heliocentric distances, 120 808 in total. About a third of the 150 223 entries are located in the newly added portion of the Galactic plane. A first classification based on detection at 70 $\mu$m as a signature of ongoing star-forming activity distinguishes between protostellar sources (23 per cent of the total) and starless sources, with the latter further classified as gravitationally bound (pre-stellar) or unbound. The integral of the spectral energy distribution, including ancillary photometry from λ = 21 to 1100 $\mu$m, gives the source luminosity and other bolometric quantities, while a modified blackbody fitted to data for $\lambda \ge 160~\mu$m yields mass and temperature. All tabulated clump properties are then derived using photometry and heliocentric distance, where possible. Statistics of these quantities are discussed with respect to both source Galactic location and evolutionary stage. No strong differences in the distributions of evolutionary indicators are found between the inner and outer Galaxy. However, masses and densities in the inner Galaxy are on average significantly larger, resulting in a higher number of clumps that are candidates to host massive star formation. Median behaviour of distance-independent parameters tracing source evolutionary status is examined as a function of the Galactocentric radius, showing no clear evidence of correlation with spiral arm positions.

The Sardinia Radio Telescope is going through a major upgrade aimed at observing the universe at up to 116 GHz.A budget of 18.700.000E has been awarded to the Italian National Institute of Astrophysics to acquire new state-of-the-art receivers, back-end, and high-performance computing, to develop a sophisticated metrology system and to upgrade the infrastructure and laboratories.

A novel, to the best of our knowledge, beam-shaping reflective surface for high-resolution millimeter/submillimeter-wave astronomy instruments is presented. The reflector design is based on Toraldo's super-resolution principle and implemented with annulated binary-phase coronae structure inspired by the achromatic magnetic mirror approach. A thin, less than half a free-space wavelength, reflective Toraldo pupil device operated in the W-band has been fabricated using mesh-filter technology developed at Cardiff University. The device has been characterized on a quasi-optical test bench and demonstrated expected reduction of the beam width upon reflection at oblique incidence, while featuring a sidelobe level lower than -10dB. The proposed reflective Toraldo pupil structure can be easily scaled for upper millimeter and infrared frequency bands as well as designed to transform a Gaussian beam into a flat-top beam with extremely low sidelobe level.

Aims. We present the Forgotten Quadrant Survey (FQS), an ESO large project that used the 12 m antenna of the Arizona Radio Observatory to map the Galactic plane in the range 220°  CO (1–0) and 13 CO (1–0), at a spectral resolution of 0.65 km s−1 and 0.26 km s−1 .Methods. We used the (1–0) transition of carbon monoxide to trace the molecular component of the interstellar medium. Our data set allows us to easily identify how the molecular dense gas is organised at different spatial scales: from the giant clouds with their denser filamentary networks, down to the clumps and cores that host the new-born stars and to obtain reliable estimates of their key physical parameters such as size and mass.Results. We present the first release of the data of the FQS survey and discuss their quality. Spectra with 0.65 km s−1 velocity channels have noise ranging from 0.8 K to 1.3 K for 12 CO (1–0) and from 0.3 K to 0.6 K for 13 CO (1–0). In this first paper, we used the 12 CO (1–0) spectral cubes to produce a catalogue of 263 molecular clouds. The clouds are grouped in three main structures corresponding to the Local, Perseus, and Outer arms up to a distance of ∼8.6 kpc from the Sun. This is the first self-consistent statistical catalogue of molecular clouds of the outer Galaxy obtained with a subarcminute spatial resolution and therefore able to detect not only the classical giant molecular clouds, but also the small clouds and to resolve the cloud structure at the sub-parsec scale up to a distance of a few kiloparsec. We found two classes of objects: structures with sizes above a few parsecs that are typical molecular clouds and may be self-gravitating, and subparsec structures that cannot be in gravitational equilibrium and are likely transient or confined by external pressure. We used the ratio between the Herschel H2 column density and the integrated intensity of the CO lines to calculate the CO conversion factor and we found mean values of (3.3 ± 1.4) × 1020 cm−2 (K km s−1 )−1 and (1.2 ± 0.4) × 1021 cm−2 (K km s−1 )−1 , for 12 CO (1–0) and 13 CO (1–0), respectively.Conclusions. The FQS contributes to the general effort in producing a new generation of high-quality spectroscopic data for the Galactic plane in the less-studied third Galactic quadrant toward the outer Galaxy. The FQS has produced a data set of great legacy value, largely improving the data quality both in terms of sensitivity and spatial resolution over previous data sets.

The concept of super-resolution refers to various methods for improving the angular resolution of an optical imaging system beyond the classical diffraction limit. A feasible method to design antennas and telescopes with angular resolution better than the diffraction limit consists of using variable transmittance pupils. The simplest transmittance pupils are binary phase shifts masks, also known as Toraldo Pupils, consisting of finite-width concentric coronae which modify the phase of the incident wavefront. In this work we present a preliminary feasibility study to determine if and how the active surface of the 32m Noto radio telescope can be used to modify the wavefront in the same way a Toraldo Pupil would do. Our preliminary analysis suggests that an ideal reflector with fully independent active panels would be able to achieve the super-resolution effect, but the real Noto active surface, where each actuator is connected to four distinct panels, adversely affects the operation of the simulated Toraldo Pupil. We are planning to apply the same analysis to the shaped active surface of the Sardinia Radio Telescope.

ABSTRACT The recent data collected by Herschel have confirmed that interstellar structures with a filamentary shape are ubiquitously present in the Milky Way. Filaments are thought to be formed by several physical mechanisms acting from large Galactic scales down to subparsec fractions of molecular clouds, and they might represent a possible link between star formation and the large-scale structure of the Galaxy. In order to study this potential link, a statistically significant sample of filaments spread throughout the Galaxy is required. In this work, we present the first catalogue of 32 059 candidate filaments automatically identified in the Herschel Infrared Galactic plane Survey (Hi-GAL) of the entire Galactic plane. For these objects, we determined morphological (length la and geometrical shape) and physical (average column density $N_{\rm H_{2}}$ and average temperature T) properties. We identified filaments with a wide range of properties: 2 ≤ la ≤ 100 arcmin, $10^{20} \le N_{\rm H_{2}} \le 10^{23}$ cm−2 and 10 ≤ T ≤ 35 K. We discuss their association with the Hi-GAL compact sources, finding that the most tenuous (and stable) structures do not host any major condensation. We also assign a distance to ∼18 400 filaments, for which we determine mass, physical size, stability conditions and Galactic distribution. When compared with the spiral arms structure, we find no significant difference between the physical properties of on-arm and inter-arm filaments. We compare our sample with previous studies, finding that our Hi-GAL filament catalogue represents a significant extension in terms of Galactic coverage and sensitivity. This catalogue represents a unique and important tool for future studies devoted to understanding the filament life-cycle.