Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
28,062
result(s) for
"Radio astronomy"
Sort by:
A Quick Look at the 3 GHz Radio Sky. II. Hunting for DRAGNs in the VLA Sky Survey
Active galactic nuclei (AGNs) can often be identified in radio images as two lobes, sometimes connected to a core by a radio jet. This multicomponent morphology unfortunately creates difficulties for source finders, leading to components that are (a) separate parts of a wider whole, and (b) offset from the multiwavelength cross identification of the host galaxy. In this work we define an algorithm, DRAGNhunter, for identifying double radio sources associated with AGNs (DRAGNs) from component catalog data in the first epoch Quick Look images of the high-resolution (≈3″ beam size) Very Large Array Sky Survey (VLASS). We use DRAGNhunter to construct a catalog of >17,000 DRAGNs in VLASS for which contamination from spurious sources is estimated at ≈11%. A “high-fidelity” sample consisting of 90% of our catalog is identified for which contamination is <3%. Host galaxies are found for ≈13,000 DRAGNs as well as for an additional 234,000 single-component radio sources. Using these data, we explore the properties of our DRAGNs, finding them to be typically consistent with Fanaroff–Riley class II sources and to allow us to report the discovery of 31 new giant radio galaxies identified using VLASS.
Journal Article
Identification of 4876 Bent-tail Radio Galaxies in the FIRST Survey Using Deep Learning Combined with Visual Inspection
Bent-tail radio galaxies (BTRGs) are characterized by bent radio lobes. This unique shape is mainly caused by the movement of the galaxy within a cluster, during which the radio jets are deflected by the intracluster medium. A combined method, which involves a deep learning-based radio source finder along with visual inspection, has been utilized to search for BTRGs from the Faint Images of the Radio Sky at Twenty cm survey images. Consequently, a catalog of 4876 BTRGs has been constructed, among which 3871 are newly discovered. Based on the classification scheme of the opening angle between the two jets of the galaxy, BTRGs are typically classified as either wide-angle-tail (WAT) sources or narrow-angle-tail (NAT) sources. Our catalog comprises 4424 WATs and 652 NATs. Among these, optical counterparts are identified for 4193 BTRGs. This catalog covers luminosities in the range of 1.91 × 1020 ≤ L1.4 GHz ≤ 1.45 × 1028 W Hz−1 and redshifts from z = 0.0023 to z = 3.43. Various physical properties of these BTRGs and their statistics are presented. Particularly, by the nearest neighbor method, we found that 1825 BTRGs in this catalog belong to galaxy clusters reported in literature.
Journal Article
VLASS-based Survey of Transition State Galaxies and Their Relationship to Compact Peaked-spectrum Radio Sources
We present multifrequency and high-resolution studies of a sample of 24 radio transient sources discovered by comparing the NRAO VLA Sky Survey and the Very Large Array Sky Survey. All of them are characterized by a significant increase in radio flux density over the past two decades. Their convex spectra, small sizes, and high brightness temperatures are typical for young GHz-peaked spectrum (GPS) radio sources and indicative of an active galactic nucleus (AGN) buried in the host galaxy. On the other hand, they are much weaker than the archetypal GPS objects, and their parsec-scale radio structures, although indicating the presence of young radio jets, are similar to radio-quiet AGNs like Seyfert and low-ionization nuclear emission-line region galaxies. Based on the distribution of these objects in power−size (P−D) and peak frequency−size (νp−D) diagrams, we suggest that, after stabilizing their radio activity, some of the GHz-peaked radio transients (galaxies and quasars) will develop into radio-intermediate and radio-quiet quasars and low-frequency peaked-spectrum objects. We discuss several possible origins for the transient radio emission in our sources and conclude that changes in the accretion rate combined with low-power radio ejecta are the most probable cause. This is the scenario we also propose for one of our sources, 101841−13, which was independently identified as a candidate tidal disruption event (TDE) based on its infrared variability. However, we cannot exclude that 101841–13 or other sources in our sample are TDEs.
Journal Article
An AGN with an Ionized Gas Outflow in a Massive Quiescent Galaxy in a Protocluster at z = 3.09
We report the detection of an ionized gas outflow from an X-ray active galactic nucleus hosted in a massive quiescent galaxy in a protocluster at z = 3.09 (J221737.29+001823.4). It is a type-2 QSO with broad (W 80 > 1000 km s−1) and strong ( log(L[OIII] /erg s−1) ≈ 43.4) [O iii]λ λ 4959,5007 emission lines detected by slit spectroscopy in three-position angles using Multi-Object Infra-Red Camera and Spectrograph (MOIRCS) on the Subaru telescope and the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) on the Keck-I telescope. In the all slit directions, [O iii] emission is extended to ∼15 physical kpc and indicates a powerful outflow spreading over the host galaxy. The inferred ionized gas mass outflow rate is 22 ± 3 M ⊙ yr−1. Although it is a radio source, according to the line diagnostics using Hβ, [O ii], and [O iii], photoionization by the central QSO is likely the dominant ionization mechanism rather than shocks caused by radio jets. On the other hand, the spectral energy distribution of the host galaxy is well characterized as a quiescent galaxy that has shut down star formation several hundred Myr ago. Our results suggest a scenario that QSOs are powered after the shutdown of the star formation and help complete the quenching of massive quiescent galaxies at high redshift.
Journal Article
Radio science techniques for deep space exploration
\"Radio signals are used to communicate information between robotic space missions throughout the solar system and stations on Earth. These signals are altered in their electromagnetic properties between transmission and reception due to propagation effects caused primarily by intervening media as well as forces acting on the spacecraft. When observed for their scientific potential, such alternations can provide very valuable information about the nature and environment of the planetary bodies or solar system targets under exploration. This also applies to signals transmitted from one spacecraft and received at another, in the case of multi-spacecraft missions. The media that the radio links propagate through include planetary atmospheres, ionospheres, rings, plasma tori, cometary material, or the solar corona. The Doppler shift to the frequency of the signals caused by the relative motion between the spacecraft and ground stations, or any transmitter-receiver combination, can contain scientific information about the gravitational forces acting on the spacecraft resulting from the bulk mass, density distribution, and global interior structure of the planets or moons, among other effects\"-- Provided by publisher.
BOOK
Precise radio astrometry and new developments for the next generation of instruments
We present a technique-led review of the progression of precise radio astrometry, from the first demonstrations, half a century ago, until to date and into the future. We cover the developments that have been fundamental to allow high accuracy and precision astrometry to be regularly achieved. We review the opportunities provided by the next generation of instruments coming online, which are primarily: SKA, ngVLA, and pathfinders, along with EHT and other (sub)mm-wavelength arrays, Space-VLBI, Geodetic arrays, and optical astrometry from GAIA. From the historical development, we predict the future potential astrometric performance, and, therefore, the instrumental requirements that must be provided to deliver these. The next generation of methods will allow ultra-precise astrometry to be performed at a much wider range of frequencies (hundreds of MHz to hundreds of GHz). One of the key potentials is that astrometry will become generally applicable, and, therefore, unbiased large surveys can be performed. The next-generation methods are fundamental in allowing this. We review the small but growing number of major astrometric surveys in the radio, to highlight the scientific impact that such projects can provide. Based on these perspectives, the future of radio astrometry is bright. We foresee a revolution coming from: ultra-high-precision radio astrometry, large surveys of many objects, improved sky coverage, and at new frequency bands other than those available today. These will enable the addressing of a host of innovative open scientific questions in astrophysics.
Journal Article