Total Flux Density Variations in Extragalactic Radio Sources. III. Doppler Boosting Factors, Lorentz Factors, and Viewing Angles for Active Galactic Nuclei

1999 ◽  
Vol 521 (2) ◽  
pp. 493-501 ◽  
Author(s):  
A. Lahteenmaki ◽  
E. Valtaoja
Keyword(s):  
Active Galactic Nuclei ◽  
Flux Density ◽  
Galactic Nuclei ◽  
Total Flux ◽  
Radio Sources ◽  
Extragalactic Radio Sources

scholarly journals The Distant DRAGNs Survey

1996 ◽  
Vol 175 ◽  
pp. 513-514
Author(s):  
J. D. B. Law-Green
Keyword(s):  
Flux Density ◽  
Ambient Medium ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Cosmological Evolution ◽  
Radio Sources ◽  
Number Density ◽  
Extragalactic Radio Sources ◽  
Matched Samples

DRAGNs (Double Radio sources Associated with Galactic Nuclei, Leahy 1991) are the class of powerful extragalactic radio sources thought to be produced by the interaction of a jet with the ambient medium. They exhibit strong cosmological evolution in comoving number density; at z ≃ 2 the “classical double” FR II DRAGNs were ≃ 1000 times as common as they are now (Dunlop & Peacock 1990).To understand this, systematic studies of complete DRAGN samples at low and high z and differing levels of flux density are required, in order to resolve the P – z ambiguity. The Distant DRAGNs Survey is a long-term project to image with the VLA and MERLIN, matched samples of DRAGNs at high redshift.

scholarly journals Expanding Quasars and the Expansion of the Universe

1988 ◽  
Vol 129 ◽  
pp. 23-24
Author(s):  
M. H. Cohen ◽  
P. D. Barthel ◽  
T. J. Pearson ◽  
J. A. Zensus
Keyword(s):  
Active Galactic Nuclei ◽  
Upper Bound ◽  
Proper Motion ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Expansion Of The Universe ◽  
The Universe

The μ–z diagram (Figure 1) plots the observed internal proper motion μ versus redshift z for 32 extragalactic radio sources associated with active galactic nuclei. The observed points fall below an upper bound which decreases with redshift; there is a statistically significant anticorrelation between redshift and internal proper motion.

scholarly journals Examples of Extreme Intraday Variability

2001 ◽  
Vol 182 ◽  
pp. 113-117
Author(s):  
Lucyna Kedziora-Chudczer ◽  
David L. Jauncey ◽  
Mark A. Wieringa ◽  
Anastasios K. Tzioumis ◽  
Hayley E. Bignall
Keyword(s):  
Flux Density ◽  
Density Fluctuations ◽  
Total Flux ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Brightness Temperatures ◽  
Relativistic Beaming ◽  
Intraday Variability

AbstractWe present results of the ATCA IDV Survey of southern extragalactic radio sources. We discuss briefly the properties of the 22 new intraday variable sources discovered in the Survey. The follow-up observations of a few extreme examples of strong intraday variability are presented. We find that the characteristics of the total flux density fluctuations at different wavelengths are consistent with intersteller scintillations (ISS) of the microarcsecondsize soorten components. However, the scintillating components of a few extreme IDVs are characterized by the brightness temperatures far exceeding the TB = 1012 K limit. The relativistic beaming invoked in such sources would require Doppler factors up to as high as δ ~ 103.

scholarly journals CHILES VERDES: Radio Variability at an Unprecedented Depth and Cadence in the COSMOS Field

2021 ◽  
Vol 923 (1) ◽  
pp. 31
Author(s):  
Sumit K. Sarbadhicary ◽  
Evangelia Tremou ◽  
Adam J. Stewart ◽  
Laura Chomiuk ◽  
Charee Peters ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Flux Density ◽  
Galactic Nuclei ◽  
Density Variation ◽  
Time Variable ◽  
Host Galaxy ◽  
Radio Sources ◽  
Star Forming ◽  
Lower Variability ◽  
Cross Matching

Abstract Although it is well established that some extragalactic radio sources are time-variable, the properties of this radio variability, and its connection with host galaxy properties, remain to be explored—particularly for faint sources. Here we present an analysis of radio variable sources from the CHILES Variable and Explosive Radio Dynamic Evolution Survey (CHILES VERDES)—a partner project of the 1.4 GHz COSMOS H i Large Extragalactic Survey. CHILES VERDES provides an unprecedented combination of survey depth, duration, and cadence, with 960 hr of 1–2 GHz continuum VLA data obtained over 209 epochs between 2013 and 2019 in a 0.44 deg2 section of the well-studied extragalactic deep field, COSMOS. We identified 18 moderate-variability sources (showing 10%–30% flux density variation) and 40 lower-variability sources (2%–10% flux density variation). They are mainly active galactic nuclei (AGNs) with radio luminosities in the range of 1022–1027 W Hz−1, based on cross-matching with COSMOS multiwavelength catalogs. The moderate-variability sources span redshifts z = 0.22–1.56, have mostly flat radio spectra (α > −0.5), and vary on timescales ranging from days to years. The lower-variability sources have similar properties, but generally have higher radio luminosities than the moderate-variability sources, extending to z = 2.8, and have steeper radio spectra (α < −0.5). No star-forming galaxy showed statistically significant variability in our analysis. The observed variability likely originates from scintillation on short (∼week) timescales, and Doppler-boosted intrinsic AGN variability on long (month–year) timescales.

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