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The polarization properties of radio sources at very low frequencies (<200 MHz) have not been widely measured, but the new generation of low-frequency radio telescopes, including the Low Frequency Array (LOFAR: a Square Kilometre Array Low…

We present a large sample of 501 radio-selected BL Lac candidates from the combination of the Sloan Digital Sky Survey (SDSS) Data Release 5 optical spectroscopy and from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio…

This paper presents a study of the local radio source population, by cross-comparing the data from the first data release (DR1) of the LOFAR Two-Metre Sky Survey (LoTSS) with the Sloan Digital Sky Survey (SDSS) DR7 main galaxy spectroscopic…

(abridged) We present a comprehensive study of a sample of 23 genuine radio-loud NLS1 galaxies which have the radio-loudness parameters greater than 100. The radio sources of the sample are ubiquitously compact. A significant fraction of…

Results are presented of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank (RGB) catalog which have been spectroscopically observed in the Sloan digital sky survey (SDSS) DR5. For 72 sources, the…

Type II quasars are luminous AGNs whose central engines and broad-line regions are obscured by intervening material; such objects only recently have been discovered in appreciable numbers. We study the multiwavelength properties of 291 type…

Determining the star-forming properties of radio-quiet quasars is important for understanding the co-evolution of star formation and black hole accretion. Here, we present the detection of the gravitationally-lensed radio-quiet quasars SDSS…

Blazars are radio-loud Active Galactic Nuclei (AGN) whose jets have a very small angle to our line of sight. Observationally, the radio emission are mostly compact or a compact-core with a 1-sided jet. With 2.5$^{\prime\prime}$ resolution…

We present Very Large Array observations at 1.4 and 5 GHz of a sample of 16 quasi-stellar objects (QSOs) at z = 1.78 to 2.71. Half of the chosen quasars are bright at mm wavelengths (250 or 350 GHz) while the other half were not detected at…

We report on the optical spectroscopic analysis of a sample of 99 low-luminosity quasi-stellar objects (LLQSOs) at $z\leq 0.06$ base the Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility of studying the faint end…

We present deep radio images at 1.4 GHz of a large and complete sample of BL Lacertae objects (BL Lacs) selected from the Deep X-ray Radio Blazar Survey (DXRBS). We have observed 24 northern sources with the Very Large Array (VLA) in both…

The cross-correlation of the Sloan Digital Sky Survey Data Release 7 with the Faint Images of the Radio Sky at Twenty-Centimeters survey allows for a multiwavelength statistical study of radio-optical galaxy properties on a very large…

We present results from a combined radio polarization and emission line study of five type 2 quasars at $z<0.2$ with the Karl G. Jansky Very Large Array (VLA) B-array at 5 GHz and Hubble Space Telescope (HST) [O III] observations. These…

Building the radio sky template are crucial for detecting the 21 cm emission line signal from the Epoch of Reionization (EoR), as well as for other cosmological research endeavors. Utilizing data from the LOFAR Two-meter Sky Survey (LoTSS)…

Occupying the intermediate-mass regime of the accretion--jet parameter space, radio continuum emission from active galactic nuclei with black hole mass M_BH <~ 10^6 Msun (low-mass AGNs) is a valuable probe to the physics of relativistic…

Narrow-line Seyfert 1 (NLS1) galaxies are a type of active galactic nuclei (AGN) that were originally classified as sources with little to no radio emission. Although the class is rather unified from an optical perspective, their radio…

Various studies have laid claim to finding an alignment of the polarization vectors or radio jets of active galactic nuclei (AGN) over large distances, but these results have proven controversial and so far, there is no clear explanation…

This paper presents the first high-resolution and high-sensitivity study of the radio properties of optically selected type~2 quasars. We used the Very Large Array at 8.4 GHz to observe 59 sources drawn from the Sloan Digital Sky Survey…

The effects of feedback from high luminosity radio-loud AGN have been extensively discussed in the literature, but feedback from low-luminosity radio-loud AGN is less well understood. The advent of high sensitivity, high angular resolution,…

We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky LOFAR imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS…