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Understanding the spectral properties of sources is crucial for the characterization of the radio source population. In this work, we have extensively studied the ELAIS N1 field using various low-frequency radio observations. For the first time, we presented the 1250 MHz observations of the field using the upgraded Giant Meterwave Radio Telescope (uGMRT) that reach a central off-source RMS noise of ∼ 12 μ Jy beam - 1 . A source catalog of 1086 sources is compiled at 5 σ threshold (>60 μ Jy) to derive the normalized differential source counts at this frequency, which is consistent with existing observations and simulations. We presented the spectral indices derived in two ways: two-point spectral indices and by fitting a power-law. The latter yielded a median α = - 0.57 ± 0.14 , and we identified nine ultra-steep spectrum sources using these spectral indices. Further, using a radio color diagram, we identified the three mega-hertz peaked spectrum (MPS) sources, while three other MPS sources are identified from the visual inspection of the spectra, the properties of which are discussed. In our study of the classified sources in the ELAIS N1 field, we presented the relationship between α and z. We found no evidence of an inverse correlation between these two quantities and suggested that the nature of the radio spectrum remains independent of the large-scale properties of the galaxies that vary with redshifts. [ABSTRACT FROM AUTHOR]

Radio detection at high time-frequency resolutions is a powerful means of remotely studying electron acceleration processes. Radio bursts have characteristics (polarization, drift, periodicity) making them easier to detect than slowly variable emissions. They are not uncommon in solar system planetary magnetospheres, the powerful Jovian "short bursts (S-bursts)" induced by the Io-Jupiter interaction being especially well-documented. Here we present a detection method of drifting radio bursts in terabytes of high resolution time-frequency data, applied to one month of ground-based Jupiter observations. Beyond the expected Io-Jupiter S-bursts, we find decameter S-bursts related to the Ganymede-Jupiter interaction and the main Jovian aurora, revealing ubiquitous Alfvénic electron acceleration in Jupiter's high-latitude regions. Our observations show accelerated electron energies are distributed in two populations, kilo-electron-Volts and hundreds of electron-Volts. This detection technique may help characterizing inaccessible astrophysical sources such as exoplanets. Jovian short bursts (S-bursts) are induced by the Io-Jupiter interaction. Here, the authors show a drifting radio burst detection method and report S-bursts related to Ganymede-Jupiter interaction and to Jovian aurora. [ABSTRACT FROM AUTHOR]

Radio-loud compact radio sources (CRSs) are characterised by morphological compactness of the jet structure centred on the active nucleus of the galaxy. Most of the local elliptical galaxies are found to host a CRS with nuclear luminosities lower than those of typical quasars, ≲ 10 42 erg s - 1 . Recently, low-luminosity CRSs with a LINER-like optical spectrum have been named Fanaroff–Riley (FR) type 0 to highlight their lack of substantially extended radio emission at kpc scales, in contrast with the other Fanaroff–Riley classes, full-fledged FR Is and FR II radio galaxies. FR 0s are the most abundant class of radio galaxies in the local Universe, and characterised by a higher core dominance, poorer Mpc-scale environment and smaller (sub-kpc scale, if resolved) jets than FR Is. However, FR 0s share similar host and nuclear properties with FR Is. A different accretion–ejection paradigm from that in place in FR Is is invoked to account for the parsec-scale FR 0 jets. This review revises the state-of-the-art knowledge about FR 0s, their nature, and which open issues the next generation of radio telescopes can solve in this context. [ABSTRACT FROM AUTHOR]

Several long-period radio transients have recently been discovered, with strongly polarized coherent radio pulses appearing on timescales between tens to thousands of seconds1,2. In some cases, the radio pulses have been interpreted as coming from rotating neutron stars with extremely strong magnetic fields, known as magnetars; the origin of other, occasionally periodic and less-well-sampled radio transients is still debated3. Coherent periodic radio emission is usually explained by rotating dipolar magnetic fields and pair-production mechanisms, but such models do not easily predict radio emission from such slowly rotating neutron stars and maintain it for extended times. On the other hand, highly magnetic isolated white dwarfs would be expected to have long spin periodicities, but periodic coherent radio emission has not yet been directly detected from these sources. Here we report observations of a long-period (21 min) radio transient, which we have labelled GPM J1839–10. The pulses vary in brightness by two orders of magnitude, last between 30 and 300 s and have quasiperiodic substructure. The observations prompted a search of radio archives and we found that the source has been repeating since at least 1988. The archival data enabled constraint of the period derivative to <3.6 × 10−13 s s−1, which is at the very limit of any classical theoretical model that predicts dipolar radio emission from an isolated neutron star.The discovery of a long-period radio transient, GPM J1839–10, prompted a search of radio archives, thereby finding that this source has been repeating since at least 1988. [ABSTRACT FROM AUTHOR]

Detection of the redshifted 21-cm signal of neutral hydrogen from the cosmic dawn and the epoch of reionization (EoR) is one of the final frontiers of modern observational cosmology. The inherently faint signal makes it susceptible to contamination by several sources like astrophysical foregrounds and instrumental systematics. Nevertheless, developments achieved in the recent developments will combine to make signal detection possible with the upcoming Square Kilometer Array (SKA), both statistically and via tomography. This review describes an indigenously developed end-to-end pipeline that simulates sensitive interferometric observations. It mainly focuses on the requirements for Hi detection in interferometers. In its present form, it can mimic the effects of realistic point source foregrounds and systematics—calibration error and position error on 21-cm observations. The performance of the pipeline is demonstrated for test cases with 0.01% calibration error and position error. Its performance is consistent across telescope, foreground and signal models. The focus of the simulation pipeline during the initial stages was for EoR science. But since this is a general interferometric simulation pipeline, it will be helpful to the entire SKA user community, irrespective of the science goals. [ABSTRACT FROM AUTHOR]

The Square Kilometre Array Observatory (SKAO) is perhaps the most ambitious radio telescope envisaged yet. It will enable unprecedented studies of the Sun, corona and heliosphere and help to answer many of the outstanding questions in these areas. Its ability to make a vast previously unexplored phase space accessible, also promises a large discovery potential. The Indian solar and heliospheric physics community has been preparing for this science opportunity. A significant part of this effort has been towards playing a leading role in pursuing science with SKAO precursor instruments. This paper briefly summarises the current status of the various aspects of work done as a part of this enterprise and our future goals. [ABSTRACT FROM AUTHOR]

Here we examine how our knowledge of present day Venus can inform terrestrial exoplanetary science and how exoplanetary science can inform our study of Venus. In a superficial way the contrasts in knowledge appear stark. We have been looking at Venus for millennia and studying it via telescopic observations for centuries. Spacecraft observations began with Mariner 2 in 1962 when we confirmed that Venus was a hothouse planet, rather than the tropical paradise science fiction pictured. As long as our level of exploration and understanding of Venus remains far below that of Mars, major questions will endure. On the other hand, exoplanetary science has grown leaps and bounds since the discovery of Pegasus 51b in 1995, not too long after the golden years of Venus spacecraft missions came to an end with the Magellan Mission in 1994. Multi-million to billion dollar/euro exoplanet focused spacecraft missions such as JWST, and its successors will be flown in the coming decades. At the same time, excitement about Venus exploration is blooming again with a number of confirmed and proposed missions in the coming decades from India, Russia, Japan, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). Here we review what is known and what we may discover tomorrow in complementary studies of Venus and its exoplanetary cousins. [ABSTRACT FROM AUTHOR]

Galaxies living in rich environments are suffering different perturbations able to drastically affect their evolution. Among these, ram pressure stripping, i.e. the pressure exerted by the hot and dense intracluster medium (ICM) on galaxies moving at high velocity within the cluster gravitational potential well, is a key process able to remove their interstellar medium (ISM) and quench their activity of star formation. This review is aimed at describing this physical mechanism in different environments, from rich clusters of galaxies to loose and compact groups. We summarise the effects of this perturbing process on the baryonic components of galaxies, from the different gas phases (cold atomic and molecular, ionised, hot) to magnetic fields and cosmic rays, and describe their induced effects on the different stellar populations, with a particular attention to its role in the quenching episode generally observed in high-density environments. We also discuss on the possible fate of the stripped material once removed from the perturbed galaxies and mixed with the ICM, and we try to estimate its contribution to the pollution of the surrounding environment. Finally, combining the results of local and high-redshift observations with the prediction of tuned models and simulations, we try to quantify the importance of this process on the evolution of galaxies of different mass, from dwarfs to giants, in various environments and at different epochs. [ABSTRACT FROM AUTHOR]

Compact steep-spectrum (CSS) and peaked-spectrum (PS) radio sources are compact, powerful radio sources. The multi-frequency observational properties and current theories are reviewed with emphasis on developments since the earlier review of O'Dea (PASP 110:493–532, https://doi.org/10.1086/316162, 1998). There are three main hypotheses for the nature of PS and CSS sources. (1) The PS sources might be very young radio galaxies which will evolve into CSS sources on their way to becoming large radio galaxies. (2) The PS and CSS sources might be compact, because they are confined (and enhanced in radio power) by interaction with dense gas in their environments. (3) Alternately, the PS sources might be transient or intermittent sources. Each of these hypotheses may apply to individual objects. The relative number in each population will have significant implications for the radio galaxy paradigm. Proper motion studies over long time baselines have helped determine hotspot speeds for over three dozen sources and establish that these are young objects. Multi-frequency polarization observations have demonstrated that many CSS/PS sources are embedded in a dense interstellar medium and vigorously interacting with it. The detection of emission line gas aligned with the radio source, and blue-shifted Hi absorption, and [OIII] emission lines indicates that AGN feedback is present in these objects—possibly driven by the radio source. Also, CSS/PS sources with evidence of episodic AGN over a large range of time-scales have been discussed. The review closes with a discussion of open questions and prospects for the future. [ABSTRACT FROM AUTHOR]

Neutral-atomic and molecular outflows are a common occurrence in galaxies, near and far. They operate over the full extent of their galaxy hosts, from the innermost regions of galactic nuclei to the outermost reaches of galaxy halos. They carry a substantial amount of material that would otherwise have been used to form new stars. These cool outflows may have a profound impact on the evolution of their host galaxies and environments. This article provides an overview of the basic physics of cool outflows, a comprehensive assessment of the observational techniques and diagnostic tools used to characterize them, a detailed description of the best-studied cases, and a more general discussion of the statistical properties of these outflows in the local and distant universe. The remaining outstanding issues that have not yet been resolved are summarized at the end of the review to inspire new research directions. [ABSTRACT FROM AUTHOR]