National Radio Astronomy Observatory
  • Charlottesville, United States
Recent publications
We present a re-discovery of G278.94+1.35 a as possibly one of the largest known Galactic supernova remnants (SNRs) – that we name Diprotodon. While previously established as a Galactic SNR, Diprotodon is visible in our new Evolutionary Map of the Universe (EMU) and GaLactic and Extragalactic All-sky MWA (GLEAM) radio continuum images at an angular size of 3{{{{.\!^\circ}}}}33\times3{{{{.\!^\circ}}}}23 , much larger than previously measured. At the previously suggested distance of 2.7 kpc, this implies a diameter of 157 ×\times 152 pc. This size would qualify Diprotodon as the largest known SNR and pushes our estimates of SNR sizes to the upper limits. We investigate the environment in which the SNR is located and examine various scenarios that might explain such a large and relatively bright SNR appearance. We find that Diprotodon is most likely at a much closer distance of \sim 1 kpc, implying its diameter is 58 ×\times 56 pc and it is in the radiative evolutionary phase. We also present a new Fermi -LAT data analysis that confirms the angular extent of the SNR in gamma rays. The origin of the high-energy emission remains somewhat puzzling, and the scenarios we explore reveal new puzzles, given this unexpected and unique observation of a seemingly evolved SNR having a hard GeV spectrum with no breaks. We explore both leptonic and hadronic scenarios, as well as the possibility that the high-energy emission arises from the leftover particle population of a historic pulsar wind nebula.
The bright radio source, GLEAM J091734 - 001243 (hereafter GLEAM J0917 - 0012), was previously selected as a candidate ultra-high redshift ( z>5z \gt 5 ) radio galaxy due to its compact radio size and faint magnitude ( K(AB)=22.7K(\mathrm{AB})=22.7 ). Its redshift was not conclusively determined from follow-up millimetre and near-infrared spectroscopy. Here we present new HST WFC3 G141 grism observations which reveal several emission lines including [NeIII] λ\lambda 3867, [NeV] λ\lambda 3426 and an extended ( 4.8\approx 4.8\, kpc), [OII] λ\lambda 3727 line which confirm a redshift of 3.004±0.0013.004\pm0.001 . The extended component of the [OII] λ\lambda 3727 line is co-spatial with one of two components seen at 2.276 GHz in high resolution ( 60×2060\times 20\, mas) Long Baseline Array data, reminiscent of the alignments seen in local compact radio galaxies. The BEAGLE stellar mass ( 2×1011M\approx 2\times 10^{11}\,\textit{M}_\odot ) and radio luminosity ( L500MHz1028L_{\mathrm{500MHz}}\approx 10^{28}\, W Hz 1^{-1} ) put GLEAM J0917 - 0012 within the distribution of the brightest high-redshift radio galaxies at similar redshifts. However, it is more compact than all of them. Modelling of the radio jet demonstrates that this is a young, 50\approx 50\, kyr old, but powerful, 1039\approx 10^{39}\, W, compact steep spectrum radio source. The weak constraint on the active galactic nucleus bolometric luminosity from the [NeV] λ\lambda 3426 line combined with the modelled jet power tentatively implies a large black hole mass, 109M\ge 10^9\,\textit{M}_\odot , and a low, advection-dominated accretion rate, i.e. an Eddington ratio 0.03\le 0.03 . The [NeV] λ\lambda 3426/[NeIII] λ\lambda 3867 vs [OII] λ\lambda 3727/[NeIII] λ\lambda 3867 line ratios are most easily explained by radiative shock models with precursor photoionisation. Hence, we infer that the line emission is directly caused by the shocks from the jet and that this radio source is one of the youngest and most powerful known at cosmic noon. We speculate that the star-formation in GLEAM J0917 - 0012 could be on its way to becoming quenched by the jet.
Relativistic jets are thought to play a crucial role in the formation and evolution of massive galaxies and supermassive black holes. Blazars, which are quasars with jets aligned along our line of sight, provide insights into the jetted population and have been observed up to redshifts of z = 6.1. Here, we report the discovery and multi-wavelength characterization of the blazar VLASS J041009.05−013919.88 at z = 7 (age of the Universe ~750 Myr), which is powered by a ~7 × 10⁸ M⊙ black hole. The presence of this high-redshift blazar implies a large population of similar but unaligned jetted sources in the early Universe. Our findings suggest two possible scenarios. In one, the jet in J0410−0139 is intrinsically low power but appears highly luminous due to relativistic beaming, suggesting that most ultraviolet-bright quasars at this redshift host jets. Alternatively, if J0410−0139 represents an intrinsically powerful radio source, there should be hundreds to thousands of radio-quiet quasars at z ≈ 7 with properties like those of J0410−0139, a prediction in tension with observed quasar densities based on their ultraviolet luminosity function. These results support the hypothesis that the rapid growth of black holes in the early Universe may be driven by jet-enhanced or obscured super-Eddington accretion, potentially playing a key role in forming massive black holes during the epoch of reionization.
The Magellanic Stream (MS), a tail of diffuse gas formed from tidal and ram pressure interactions between the Small and Large Magellanic Clouds (SMC and LMC) and the Halo of the Milky Way, is primarily composed of neutral atomic hydrogen (HI). The deficiency of dust and the diffuse nature of the present gas make molecular formation rare and difficult, but if present, could lead to regions potentially suitable for star formation, thereby allowing us to probe conditions of star formation similar to those at high redshifts. We search for HCO+\text{HCO}^{+} , HCN, HNC, and C 2_2 H using the highest sensitivity observations of molecular absorption data from the Atacama Large Millimeter Array (ALMA) to trace these regions, comparing with HI archival data from the Galactic Arecibo L-Band Feed Array (GALFA) HI Survey and the Galactic All Sky Survey (GASS) to compare these environments in the MS to the HI column density threshold for molecular formation in the Milky Way. We also compare the line of sight locations with confirmed locations of stars, molecular hydrogen, and OI detections, though at higher sensitivities than the observations presented here. We find no detections to a 3 σ\sigma significance, despite four sightlines having column densities surpassing the threshold for molecular formation in the diffuse regions of the Milky Way. Here we present our calculations for the upper limits of the column densities of each of these molecular absorption lines, ranging from 3×10103 \times 10^{10} to 1×10131 \times 10^{13} cm 2^{-2} . The non-detection of HCO+\text{HCO}^{+} suggests that at least one of the following is true: (i) XHCO+,MSX_{\text{HCO}^{+}{}, \mathrm{MS}} is significantly lower than the Milky Way value; (ii) that the widespread diffuse molecular gas observed by Rybarczyk (2022b, ApJ, 928, 79) in the Milky Way’s diffuse interstellar medium (ISM) does not have a direct analogue in the MS; (iii) the HI-to- H2\text{H}_{2} transition occurs in the MS at a higher surface density in the MS than in the LMC or SMC; or (iv) molecular gas exists in the MS, but only in small, dense clumps.
The process of data collection is often demanding in terms of labor and resources. Thus, it is all more important to make the most use out of what has been gathered—not limited to the initial purpose it was collected for but extending to uses in different contexts. In this chapter, we discuss requirements for such a data reuse across projects. We will cover the aspects of Findability, Accessibility, Interoperability, and Reusability as stated in the FAIR principles. Following a brief introduction to the data life cycle and research data management, the focus shifts to the application of FAIR principles in radio astronomy. Finally, we will explore efforts in other domains, both within and beyond astronomy, and discuss what can be learned from their efforts.
The impending data avalanche poses a significant challenge for both data providers and scientists. Unlocking the full potential of this data for scientific communities relies on their accessibility, reusability, and processing in an open manner. Achieving this necessitates the establishment of common standards for data description, formats, and methods of delivery and utilisation by scientists. This chapter unfolds in a structured manner to address these challenges. The initial section introduces and describes the Virtual Observatory (VO) and the standards applicable to radio astronomy data. Following this, a detailed survey is conducted in the subsequent section, focusing on the institutes and centers that adhere to these VO standards in delivering radio astronomy data. Finally, the last section introduces the European initiative for Open Science in general, and the projects relevant to radio astronomy such as ESCAPE, that are foreseen to act as a platform for delivery of astronomy data and services, not only to the astronomy community but also to a broader audience.
This chapter presents the range of approaches, considerations, and issues involved in understanding the properties of sources in radio continuum datasets. It summarises traditional and more recent approaches for identifying and measuring sources, both blindly and in conjunction with complementary data, and explores the challenges arising from how to reliably handle complex, extended, and multicomponent objects. It distinguishes between the detection and the classification of sources, and discusses scenarios where these steps overlap. It then describes the construction of value-added catalogues or datasets linking the radio source properties with other photometric and spectroscopic measurements, and informing further classification of the radio sources. It concludes with an overview of approaches being actively used in major projects with current generation leading radio telescope facilities.
Fast radio bursts (FRBs) are millisecond-duration events detected from beyond the Milky Way. FRB emission characteristics favour highly magnetized neutron stars, or magnetars, as the sources¹, as evidenced by FRB-like bursts from a galactic magnetar2,3, and the star-forming nature of FRB host galaxies4,5. However, the processes that produce FRB sources remain unknown⁶. Although galactic magnetars are often linked to core-collapse supernovae (CCSNe)⁷, it is uncertain what determines which supernovae result in magnetars. The galactic environments of FRB sources can be used to investigate their progenitors. Here, we present the stellar population properties of 30 FRB host galaxies discovered by the Deep Synoptic Array (DSA-110). Our analysis shows a marked deficit of low-mass FRB hosts compared with the occurrence of star formation in the Universe, implying that FRBs are a biased tracer of star formation, preferentially selecting massive star-forming galaxies. This bias may be driven by galaxy metallicity, which is positively correlated with stellar mass⁸. Metal-rich environments may favour the formation of magnetar progenitors through stellar mergers9,10, as higher-metallicity stars are less compact and more likely to fill their Roche lobes, leading to unstable mass transfer. Although massive stars do not have convective interiors to generate strong magnetic fields by dynamo¹¹, merger remnants are thought to have the requisite internal magnetic-field strengths to result in magnetars11,12. The preferential occurrence of FRBs in massive star-forming galaxies suggests that a core-collapse supernova of merger remnants preferentially forms magnetars.
Polycyclic aromatic hydrocarbons (PAHs) are among the most widespread compounds in the universe, accounting for up to ~25% of all interstellar carbon. Since most unsubstituted PAHs do not possess permanent electric dipole moments, they are invisible to radio astronomy. Constraining their abundances relies on the detection of polar chemical proxies, such as aromatic nitriles. Here we report the detection of 2-cyanopyrene and 4-cyanopyrene, isomers of the recently detected 1-cyanopyrene. We find that these isomers are present in an abundance ratio of ~2:1:2, which mirrors the number of equivalent sites available for CN addition. We conclude that there is evidence that the cyanopyrene isomers formed by direct CN addition to pyrene under kinetic control in hydrogen-rich gas at 10 K and discuss constraints on the H/CN ratio for PAHs in the Taurus molecular cloud (TMC-1). Our detections of the cyanopyrene isomers suggest that small PAHs like pyrene must be either formed in or transported to the cold interstellar medium, challenging assumptions about the origin and fate of PAHs in space.
Compact obscured nuclei (CONs) are relatively common in the centers of local (U)LIRGs, yet their nature remains unknown. Both AGN activity and extreme nuclear starbursts have been suggested as plausible nuclear power sources. The prevalence of outflows in these systems suggest that CONs represent a key phase in the nuclear feedback cycle, in which material is ejected from the central regions of the galaxy. Here, we present results from MUSE for the confirmed local CON galaxy NGC4418. For the first time we spatially map the spectral features and kinematics of the galaxy in the optical, revealing several previously unknown structures. In particular, we discover a bilateral outflow along the minor axis, an outflowing bubble, several knot structures and a receding outflow partially obscured by the galactic disk. Based on the properties of these features, we conclude that the CON in NGC4418 is most likely powered by an AGN.
Polycyclic aromatic hydrocarbons (PAHs) are organic molecules containing adjacent aromatic rings. Infrared emission bands show that PAHs are abundant in space, but only a few specific PAHs have been detected in the interstellar medium. We detect 1-cyanopyrene, a cyano-substituted derivative of the related four-ring PAH pyrene, in radio observations of the dense cloud TMC-1 using the Green Bank Telescope. The measured column density of 1-cyanopyrene is ∼ 1 .52×10 12 cm − 2 , from which we estimate that pyrene contains up to 0.1% of the carbon in TMC-1. This abundance indicates that interstellar PAH chemistry favors the production of pyrene. We suggest that some of the carbon supplied to young planetary systems is carried by PAHs that originate in cold molecular clouds.
Two sensitivity analysis techniques are applied to rate coefficients in a kinetic model of a dark molecular cloud, revealing that aromatic species such as cyanonaphthalene are sensitive to early hydrocarbon growth and ring-formation mechanisms.
Fast radio bursts (FRBs) are millisecond-duration radio transients whose origins remain unknown. As the vast majority of bursts are one-off events, it is necessary to pinpoint FRBs precisely within their host galaxies at the time of detection. Here we use two purpose-built outrigger telescopes to localize FRB 20210603A at the time of its detection by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Our very-long-baseline interferometry stations localized the burst to a 0.2" × 2" final ellipse in the disk of its host galaxy SDSS J004105.82+211331.9. A spatially resolved spectroscopic follow-up revealed recent star formation (Hα emission) on kiloparsec scales near the burst position. The excess dispersion measure is consistent with expectations from the nearly edge-on disk of the host galaxy, demonstrating the utility of FRBs as probes of the interstellar medium in distant galaxies. The excess dispersion measure, rotation measure and scattering are consistent with expectations for a pulse travelling from deep within its host galactic plane, strengthening the link between the local environment of FRB 20210603A and the disk of its host galaxy. Finally, this technique demonstrates a way to overcome the trade-off between angular resolution and field of view in FRB instrumentation, paving the way towards plentiful and precise FRB localizations.
Achieving amplification with high gain and quantum-limited noise is a difficult problem to solve. Parametric amplification using a superconducting transmission line with high kinetic inductance is a promising technology not only to solve this problem but also adding several benefits. Compared to other technologies, they have the potential to improve power saturation, achieve larger fractional bandwidths, and operate at higher frequencies. In this type of amplifier, the selection of the proper transmission line is a key element in its design. Given current fabrication limitations, traditional lines such as coplanar waveguides (CPW), are not ideal for this purpose, since it is difficult to make them with the proper characteristic impedance for good matching and slow enough phase velocity for making them more compact. Capacitively loaded lines, also known as artificial lines, are a good solution to this problem. However, few design rules or models have been presented to guide their accurate design. This fact is even more crucial considering that they are usually fabricated in the form of Floquet lines that have to be designed carefully to suppress undesired harmonics appearing in the parametric process. In this article we present, first, a new modeling strategy, based on the use of electromagnetic-simulation software, and, second, a first-principles model that facilitate and speed the design of CPW artificial lines and of Floquet lines made out of them. Then, we present comparisons with experimental results that demonstrate their accuracy. Finally, the theoretical model allows one to predict the high-frequency behavior of the artificial lines, showing that they are good candidates for implementing parametric amplifiers above 100 GHz.
We present low-frequency (0.40 – 1.25 GHz) radio observations and modeling of a Fast Blue Optical Transient (FBOT), AT2018cow [Nayana & Chandra(2021)]. Our data are best modeled as an inhomogeneous synchrotron emitting region expanding into an ionized circumstellar medium. We estimate the mass-loss rate of the progenitor star and shock parameters at multiple epochs post-explosion and find that the progenitor has gone through an enhanced phase of mass-loss close to its end-of-life.
The surface plasmon polariton (SPP) is an electromagnetic wave mode that occurs at the interface of a metal and a dielectric material. It possesses unique properties such as enhancing the strength of the electromagnetic field at the metal surface, achieving sub-wavelength focusing of light waves, and exhibiting low loss. Due to these characteristics, SPP holds great promise in various applications including super-resolution imaging, terahertz technology, biosensing, and optical communication. This paper proposes two Spoof SPP-based tri-band bandpass filters that replace the conventional sawtooth cell structure with a miniaturized labyrinth resonator structure. Upon investigating the dispersion characteristics of the resonators, we found that both resonator unit 1 and resonator unit 2 exhibit three modes, resulting in three notch points for each filter. Unlike most SPP-based structures, our design features a compact structure fed by a co-planar waveguide (CPW) without an added ground at the bottom, thereby reducing losses and improving efficiency. To achieve a smoother transition from CPW to the transmission structure, we utilize a segment of microstrip line structure synthesized by a logarithmic function. Both filters are of the same size, with dimensions totaling 192 mm × 42 mm. Based on our study, we have designed two filters with multiple notch points and have obtained good agreement between the simulation results and the actual test results.
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114 members
Richard Bradley
  • NRAO Technology Center (NTC)
Todd Russell Hunter
  • Atacama Large Millimeter/submillimeter Array (ALMA)
Alwyn Wootten
  • Atacama Large Millimeter/submillimeter Array (ALMA)
Robert F. Minchin
  • Very Long Baseline Array (VLBA)
Jeff Mangum
  • Atacama Large Millimeter/submillimeter Array (ALMA)
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Charlottesville, United States