Large Single-dish Telescopes Research Articles

A pilot study of Galactic radio recombination lines using FAST: Identification of diffuse ionized gas clumps and off-arm star-forming regions

Observing low-frequency decimeter hydrogen radio recombination lines (RRLs) with large single-dish telescopes, such as the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the L band, is a unique method for probing massive star formation on scales of hundreds of parsecs. This approach is particularly effective for detecting relatively weak and extended emissions from low-density gas ionized by massive stars. Deep, unbiased decimeter or centimeter RRL surveys with large single-dish telescopes can significantly enhance our understanding of the diffuse ionized gas along the Galactic plane. This, in turn, will improve our knowledge of the life cycle of matter in the interstellar medium and the dynamics of the Galaxy. In this context, we present a pilot project for such a blind L-band RRL survey targeting the Galactic plane and conducted using FAST. The results include the detection of RRL clumps and the identification of an off-arm active massive star-forming region near the Sagittarius-Carina arm. The ongoing and upcoming massive star formation in this region may be associated with the kink in the Sagittarius-Carina arm near 23$^ circ $ azimuth.

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Surveying the distant Universe.

During the most active period of star formation in galaxies, which occurs in the redshift range 1 < z < 3, strong bursts of star formation result in significant quantities of dust, which obscures new stars being formed as their UV/optical light is absorbed and then re-emitted in the infrared, which redshifts into the mm/sub-mm bands for these early times. To get a complete picture of the high- z galaxy population, we need to survey a large patch of the sky in the sub-mm with sufficient angular resolution to resolve all galaxies, but we also need the depth to fully sample their cosmic evolution, and therefore obtain their redshifts using direct mm spectroscopy with a very wide frequency coverage. This requires a large single-dish sub-mm telescope with fast mapping speeds at high sensitivity and angular resolution, a large bandwidth with good spectral resolution and multiplex spectroscopic capabilities. The proposed 50-m Atacama Large Aperture Submillimeter Telescope (AtLAST) will deliver these specifications. We discuss how AtLAST allows us to study the whole population of high-z galaxies, including the dusty star-forming ones which can only be detected and studied in the sub-mm, and obtain a wealth of information for each of these up to z ∼ 7: gas content, cooling budget, star formation rate, dust mass, and dust temperature. We present worked examples of surveys that AtLAST can perform, both deep and wide, and also focused on galaxies in proto-clusters. In addition we show how such surveys with AtLAST can measure the growth rate f σ 8 and the Hubble constant with high accuracy, and demonstrate the power of the line-intensity mapping method in the mm/sub-mm wavebands to constrain the cosmic expansion history at high redshifts, as good examples of what can uniquely be done by AtLAST in this research field.

Modeling and Analysis of the Active Surface System for the Large Single-Dish Sub-mm Telescope

Enlarging antenna diameter while maintaining an accurate reflective surface is important in the development of next-generation single-dish sub-mm telescopes. In this article, we propose an emulation and optimization method of the active surface system (EOMASS) for large single-dish sub-mm telescopes. The proposed method involves three main steps: 1) building an active surface system model (ASSM) based on the whole finite element model (FEM) of the large single-dish sub-mm telescope, which includes the main reflector, realistic adjustment models of actuators, backup structure and so on; 2) emulating the reflective surface deformation compensation under gravity based on the initial distribution of the actuators with the ASSM, in consideration of the manufacturing error of panels; and 3) further optimizing the number and distribution of actuators based on the illumination function, and predicting the performance of the sub-mm antenna due to the limited number of faulty actuators. As an application example, a 60 m single-dish sub-mm telescope is analyzed under gravity with the proposed EOMASS. The results demonstrate that the proposed EOMASS is an effective and advanced method, providing a feasible precision design of the active surface system for a large single-dish sub-mm telescope.

HEGrid: A high efficient multi-channel radio astronomical data gridding framework in heterogeneous computing environments

The challenge to fully exploit the potential of existing and upcoming scientific instruments like large single-dish radio telescopes is to process the collected massive data effectively and efficiently. As a ”quasi 2D stencil computation” with the ”Moore neighborhood pattern”, gridding is the most computationally intensive step in data reduction pipeline for radio astronomy studies, enabling astronomers to create correct sky images for further analysis. However, the existing gridding frameworks can either only run on multi-core CPU architecture or do not support high-concurrency, multi-channel data gridding. Their performance is then limited, and there are emerging needs for innovative gridding frameworks to process data from large single-dish radio telescopes like the Five-hundred-meter Aperture Spherical Telescope (FAST). To address those challenges, we developed a High Efficient Gridding framework, HEGrid, by overcoming the above limitations. HEGrid is the first effort to solve the gridding of multi-channel data from the large single-dish radio telescope by multi-pipeline concurrency in the CPU–GPU heterogeneous environment. Specifically, we propose and construct the gridding pipeline in heterogeneous computing environments and achieve multi-pipeline concurrency for high performance multi-channel processing. Furthermore, we propose pipeline-based co-optimization to alleviate the potential negative performance impact of possible intra- and inter-pipeline low computation and I/O utilization, including component share-based redundancy elimination, thread-level data reuse and overlapping I/O and computation. Our experiments are based on both simulated datasets and actual FAST observational datasets. The results show that HEGrid outperforms other state-of-the-art gridding frameworks by up to 5.5x and has robust hardware portability, including AMD Radeon Instinct GPU and NVIDIA GPU.

Solar Observations with Single-Dish INAF Radio Telescopes: Continuum Imaging in the 18 – 26 GHz Range

We present a new solar radio imaging system implemented through the upgrade of the large single-dish telescopes of the Italian National Institute for Astrophysics (INAF), not originally conceived for solar observations.During the development and early science phase of the project (2018 – 2020), we obtained about 170 maps of the entire solar disk in the 18 – 26 GHz band, filling the observational gap in the field of solar imaging at these frequencies. These solar images have typical resolutions in the 0.7 – 2 arcmin range and a brightness temperature sensitivity <10 K. Accurate calibration adopting the Supernova Remnant Cas A as a flux reference provided typical errors <3% for the estimation of the quiet-Sun level components and active regions flux measurements.As the first early scientific result of the project, we present a catalog of radio continuum solar imaging observations with Medicina 32-m and SRT 64-m radio telescopes, including the multi-wavelength identification of active regions, their brightness and spectral characterization. The interpretation of the observed emission as thermal bremsstrahlung components combined with gyro-magnetic variable emission paves the way for the use of our system for long-term monitoring of the Sun. We also discuss useful outcomes both for solar physics (e.g., study of the chromospheric network dynamics) and space weather applications (e.g., flare precursors studies).

A pilot study of interplanetary scintillation with FAST

ABSTRACT Observations of interplanetary scintillation (IPS) are an efficient remote-sensing method to study the solar wind and inner heliosphere. From 2016 to 2018, some distinctive observations of IPS sources like 3C 286 and 3C 279 were accomplished with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single-dish telescope in the world. Due to the 270–1620 MHz wide frequency coverage of the ultra-wideband (UWB) receiver, one can use both single-frequency and dual-frequency analyses to determine the projected velocity of the solar wind. Moreover, based on the extraordinary sensitivity owing to the large collecting surface area of FAST, we can observe weak IPS signals. With the advantages of both the wider frequency coverage and high sensitivity, and also with our radio frequency interference (RFI) mitigation strategy and an optimized model-fitting method, in this paper we analyse the fitting confidence intervals of the solar wind velocity and present some preliminary results achieved using FAST, which point to the current FAST system being highly capable of carrying out observations of IPS.

The atomic gas of star-forming galaxies atz∼ 0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope

Context.We report new H Iobservations of fourz ∼ 0.05 VALES galaxies undertaken during the commissioning phase of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST).Aims.FAST is the largest single-dish telescope in the world, with a 500 m aperture and a 19-Beam receiver. Exploiting the unprecedented sensitivity provided by FAST, we aim to study the atomic gas content, via the H I21 cm emission line, in low-zstar formation galaxies taken from the Valparaíso ALMA/APEX Line Emission Survey (VALES). Together with previous Atacama Large Millimeter/submillimeter Array (ALMA) CO(J = 1−0) observations, the H Idata provides crucial information to measure the gas mass and dynamics.Methods.As a pilot H Igalaxy survey, we targeted four local star-forming galaxies atz ∼ 0.05. In particular, one of them has already been detected in H Iby the Arecibo Legacy Fast ALFA survey (ALFALFA), allowing a careful comparison. We use an ON-OFF observing approach that allowed us to reach an rms of 0.7 mJy beam−1at a 1.7 km s−1velocity resolution within only 20 min ON-target integration time.Results.In this Letter, we demonstrate the extraordinary capability of the FAST 19-beam receiver to push the detectability of the H Iemission line of extra-galactic sources. The H Iemission line detected by FAST shows good consistency with the previous Arecibo telescope ALFALFA results. Our observations are put into context with previous multi-wavelength data to reveal the physical properties of these low-zgalaxies. We find that the CO(J = 1−0) and H Iemission line profiles are similar. The dynamical mass estimated from the H Idata is an order of magnitude higher than the baryon mass and the dynamical mass derived from the CO observations, implying that the mass probed by dynamics of H Iis dominated by the dark matter halo. In one case, a target shows an excess of CO(J = 1−0) in the line centre, which can be explained by an enhanced CO(J = 1−0) emission induced by a nuclear starburst showing high-velocity dispersion.

A direct localization of a fast radio burst and its host.

Fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. These attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. Here we report the subarcsecond localization of the fast radio burst FRB 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts and tidal disruption events. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.

The sensitivity of past and near-future lunar radio experiments to ultra-high-energy cosmic rays and neutrinos

Various experiments have been conducted to search for the radio emission from ultra-high-energy (UHE) particles interacting in the lunar regolith. Although they have not yielded any detections, they have been successful in establishing upper limits on the flux of these particles. I present a review of these experiments in which I re-evaluate their sensitivity to radio pulses, accounting for effects which were neglected in the original reports, and compare them with prospective near-future experiments. In several cases, I find that past experiments were substantially less sensitive than previously believed. I apply existing analytic models to determine the resulting limits on the fluxes of UHE neutrinos and cosmic rays (CRs). In the latter case, I amend the model to accurately reflect the fraction of the primary particle energy which manifests in the resulting particle cascade, resulting in a substantial improvement in the estimated sensitivity to CRs. Although these models are in need of further refinement, in particular to incorporate the effects of small-scale lunar surface roughness, their application here indicates that a proposed experiment with the LOFAR telescope would test predictions of the neutrino flux from exotic-physics models, and an experiment with a phased-array feed on a large single-dish telescope such as the Parkes radio telescope would allow the first detection of CRs with this technique, with an expected rate of one detection per 140 h.

A SiO 2-1 SURVEY TOWARD GAS-RICH ACTIVE GALAXIES

In order to study the feedback from active galactic nuclei (AGNs), we performed a survey of SiO J = 2-1 (v = 0) transition toward ten gas-rich active galaxies with the IRAM 30 m telescope. As the first survey of SiO in such galaxies, we detected SiO J = 2-1 (v = 0) emission in six galaxies above the 3 sigma level and one galaxy (NGC 3690) at the 2.7 sigma level. The detection rate is not related to the AGN type or to star formation activity. In comparison with M82, which is a pure star-forming galaxy without nuclear activity, our SiO detections could not be completely ascribed to being due to star formation activity. This suggests that the AGN feedback may be efficient in producing SiO molecules in such galaxies. Further surveys with large single-dish millimeter telescopes and interferometers are necessary for understanding the origin of SiO in galaxies with nuclear activity.

The Arecibo Observatory: Fifty astronomical years

Among its many accomplishments, the world’s largest single-dish telescope has detailed properties of the ionosphere, spotted the first planets discovered outside our solar system, and helped confirm the general theory of relativity.

THz Observations of the Cool Neutral Medium

AbstractThe astrophysical drivers for far-infrared spectroscopy of the Galactic interstellar medium using a 15m class telescope on Dome A are compelling. For the diffuse, atomic phase, the most important lines in the far-IR spectrum are OIat 63μm and CIIat 158μm. These are the dominant cooling lines of the cool, neutral medium, and they show rich spectral structure in Herschel observations at low latitudes. But theory predicts that they should both be highly sub-thermal in excitation, so that the level populations are not in equilibrium with the kinetic temperature of the gas. A large single dish telescope or an interferometer may be able to study the absorption and emission to determine the optical depth and column density of atoms and the physical conditions in the emission regions. Comparison of Herschel CIIspectra with 21-cm absorption spectra indicates that a significant fraction of the 158μm flux may be coming from the atomic rather than the molecular phase.

Measuring and calibrating galactic synchrotron emission

AbstractOur position inside the Galaxy requires all-sky surveys to reveal its large-scale properties. The zero-level calibration of all-sky surveys differs from standard ‘relative’ measurements, where a source is measured in respect to its surroundings. All-sky surveys aim to include emission structures of all angular scales exceeding their angular resolution including isotropic emission components. Synchrotron radiation is the dominating emission process in the Galaxy up to frequencies of a few GHz, where numerous ground based surveys of the total intensity up to 1.4 GHz exist. Its polarization properties were just recently mapped for the entire sky at 1.4 GHz. All-sky total intensity and linear polarization maps from WMAP for frequencies of 23 GHz and higher became available and complement existing sky maps. Galactic plane surveys have higher angular resolution using large single-dish or synthesis telescopes. Polarized diffuse emission shows structures with no relation to total intensity emission resulting from Faraday rotation effects in the interstellar medium. The interpretation of these polarization structures critically depends on a correct setting of the absolute zero-level in Stokes U and Q.

Unveiling the chemistry of hot protostellar cores with ALMA

High angular resolution mm-wave observations of the Orion-KL region, made with the IRAM Plateau de Bure interferometer (PdBI), reveal the presence of several cores of size 103 AU, which have distinct spectral signatures. Complex molecules such as ethanol, vinyl cyanide and dimethyl ether show different distributions and their relative abundance varies from core to core by orders of magnitude. The molecular column densities derived in the cores also differ widely from the beam-averaged column densities observed with large single-dish telescopes. Obviously, the predictions of hot core chemistry models must be checked against high resolution observations. ALMA, which allies sensitivity and high angular resolution, will be a key instrument for this type of studies.

The Case for a 30m Diameter Submillimeter Telescope on the Antarctic Plateau

AbstractA large single-dish submillimeter-wave telescope equipped with a focal plane array containing ~ 104 bolometers and costing about $120M could locate most protogalaxies in the southern sky within a year of operation.

Submillimeter Studies of Prestellar Cores and Protostars: Probing the Initial Conditions for Protostellar Collapse

Improving our understanding of the earliest stages of star formation is crucial to gain insight into the origin of stellar masses, multiple systems, and protoplanetary disks. We discuss recent advances made in this area, thanks to submillimeter mapping observations with large single-dish telescopes and interferometers. Although ambipolar diffusion appears to be too slow cores, there is nevertheless good evidence that the gravitational collapse of isolated protostellar cores is strongly magnetically controlled. We also argue that the beginning of protostellar collapse is much more violent in cluster-forming clouds than in regions of distributed star formation.

Radio Continuum Surveys of the Galaxy and Galaxies

Radio sky surveys give us basic information about the origin of the radio emission from the Galaxy. By mapping the sky at several radio frequencies a separation of the thermal and non-thermal emission components is possible. The major part of the low-frequency radio emission comes from the synchrotron process, the braking of relativistic electrons in magnetic fields. By mapping the linear polarization at several frequencies (required for the correction of the Faraday rotation) the orientation of the magnetic fields in the emitting regions can be deduced. Older all-sky surveys at 30, 150 and 408 MHz have now been supplemented by new observations of the Galaxy at 45 and 1420 MHz. These surveys, in addition to being important as tracers of the morphology of the magnetic fields in the Galaxy, are also required to correct for the ‘foreground’ features in cosmological studies of the COBE data and the PLANCK surveys in the future. Studies of the Galaxy in polarization have been made some years ago indicating high percentage of linear polarization in various directions. More recent work with good angular resolution has shown spectacular polarized intensity structures in selected regions. Low-frequency data with good angular resolution are urgently required for the interpretation of these features.Observations of nearby galaxies in radio continuum (both total power and polarized intensity) have given us the possibility to study magnetic fields in objects at known distances. Polarization observations of nearby galaxies have confirmed the existence of regular magnetic fields in practically every object so far studied. Originally data were obtained from large single-dish telescopes, notably from Effelsberg and Parkes. These data were greatly enhanced by the addition of higher resolution components from the VLA and ATCA respectively. These results indicate surprisingly homogeneous magnetic fields in most galaxies. High angular resolution observations with the GMRT at lower radio frequencies will add a new dimension to the data on galaxies.

Infrared and sub-millimeter searches for extra-solar planetary systems from Antarctica

Large single-dish telescopes and long baseline interferometers operating at mid-infrared to sub-millimeter wavelengths may provide the best opportunity to search for planets and protoplanets during the next several decades. The interior of Antarctica may be the best place to deploy such instrumentation, providing a viable compromise between the costs associated with space-based deployment and site quality.

The contribution of disks and envelopes to the millimeter continuum emission from very young low-mass stars

We investigate the question of disk formation during the protostar phase. We model the dust continuum emission from the dense cloud core using the cloud-collapse models of Terebey et al. (1984) and show that dust emission from the dense core is important when measured with large single-dish telescopes at 1.3 mm, but nearly negligible with interferometers at 2.7 mm. From published and new data, we conclude that massive disks are also seen toward a number of other sources including L1448 IRS 3, whose disk mass is estimated to be 0.5 solar mass. However, 1.3 mm data show that massive disks are relatively rare, occurring around perhaps 5 percent of young embedded stars. This implies that either massive disks occur briefly during the embedded phase or that relatively few young stars form massive disks. The median 1.3 mm flux density of IRAS-Dense cores in our sample is nearly the same as T Tauri stars in the sample of Beckwith et al. (1990). We conclude that the typical disk mass is not significantly higher during the embedded phase than during the later T Tauri phase.

Radio and Millimetre Observations of Less Complex Molecules

Progress in laboratory and astronomical instrumentation has renewed the already large interest for simple astrophysical molecules. On the laboratory side, one of the most notable advances has been the spectroscopic observation of an increasing number of small reactive molecular species. On the astronomical side, the access to submillimetre wavelengths and the completion of millimetric interferometers and large single-dish telescopes, have allowed the detection of many new molecular species and open the way for detailed studies of the distribution of molecules in interstellar and circumstellar clouds.