Showing papers by "Marios Karouzos published in 2012"
TL;DR: In this paper, the Caltech-Jodrell Bank flat-spectrum (CJF) sample of radio-loud active galaxies was used to study the apparent linear and angular evolution of the CJF jet ridge lines, as well as their morphology.
Abstract: Context Recent VLBI studies of the morphology and kinematics of individual BL Lac objects (S5 1803+784, PKS 0735+178, etc) have revealed a new paradigm for the pc-scale jet kinematics of these sources Unlike the apparent superluminal outward motions usually observed in blazars, most, if not all, jet components in these sources appear to be stationary with respect to the core, while exhibiting strong changes in their position angles As a result, the jet ridge lines of these sources evolve substantially, at times forming a wide channel-flow Aims We investigate the Caltech-Jodrell Bank flat-spectrum (CJF) sample of radio-loud active galaxies to study this new kinematic scenario for flat-spectrum AGN Comparing BL Lac objects and quasars in the CJF, we look for differences in the kinematics and morphologies of their jet ridge lines The large number of sources in the CJF sample, together with the excellent kinematical data available, allow us to perform a robust statistical analysis in this context Methods We develop a number of tools to extract information about the apparent linear and angular evolution of the CJF jet ridge lines, as well as their morphology We study both the radial and non-radial apparent motions in the CJF jets A statistical analysis of the extracted information allows us to test this new kinematic scenario and assess the importances of the radial and non-radial motions in flat-spectrum AGN jets in general and especially in BL Lacs compared to quasars We also use these tools to check the kinematics for (multi-wavelength) variable AGN Results We find that approximately half of the sample display appreciable apparent jet widths (>10 degrees), with BL Lac jet ridge lines showing significantly larger apparent widths than those of both quasars and radio galaxies In addition, BL Lac jet ridge lines are found to change their apparent width more strongly Finally, BL Lac jet ridge lines show the least apparent linear evolution, which translates into the smallest apparent expansion speeds for their components We find compelling evidence supporting a substantially different kinematic scenario for flat-spectrum radio-AGN jets and in particular for BL Lac objects In addition, we find that variability is closely related to the properties of a source’s jet ridge line Variable quasars are found to have “BL Lac like” behavior, relative to their non-variable counterparts
12 citations
TL;DR: In this paper, a new paradigm for active galactic jet kinematics has emerged through detailed investigations of BL Lac objects using very long baseline radio interferometry in this new scheme, most, if not all, jet components appear to remain stationary with respect to the core but show significant nonradial motions.
Abstract: A new paradigm for active galactic jet kinematics has emerged through detailed investigations of BL Lac objects using very long baseline radio interferometry In this new scheme, most, if not all, jet components appear to remain stationary with respect to the core but show significant non-radial motions This paper presents results from our kinematic investigation of the jets of a statistically complete sample of radio-loud flat-spectrum active galaxies, focusing on the comparison between the jet kinematic properties of BL Lacs and flat-spectrum radio-quasars It is shown that there is a statistically significant difference between the kinematics of the two AGN classes, with BL Lacs showing more bent jets, that are wider and show slower movement along the jet axis, compared to flat-spectrum radio-quasars This is interpreted as evidence for helically structured jets (© 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)
5 citations
TL;DR: In this article, a comparison between the jet kinematic properties of radio-loud flat-spectrum active galaxies and radio-quasars is made, and it is shown that there is a statistically significant difference between the kinematics of the two AGN classes, with BL Lacs showing more bent jets, that are wider and show slower movement along the jet axis.
Abstract: A new paradigm for active galactic jet kinematics has emerged through detailed investigations of BL Lac objects using very long baseline radio interferometry. In this new scheme, most, if not all, jet components appear to remain stationary with respect to the core but show significant non-radial motions. This paper presents results from our kinematic investigation of the jets of a statistically complete sample of radio-loud flat-spectrum active galaxies, focusing on the comparison between the jet kinematic properties of BL Lacs and flat-spectrum radio-quasars. It is shown that there is a statistically significant difference between the kinematics of the two AGN classes, with BL Lacs showing more bent jets, that are wider and show slower movement along the jet axis, compared to flat-spectrum radio-quasars. This is interpreted as evidence for helically structured jets.
16 Sep 2012
TL;DR: In this article, an optical spectroscopic investigation of the AKARI NEP field was conducted to study both star-formation and nuclear activity components of radio-loud active galaxies.
Abstract: Radio-loud active galaxies have been found to exhibit a close connection to galactic mergers and host galaxy star-formation quenching. We present preliminary results of an optical spectroscopic investigation of the AKARI NEP field. We focus on the population of radio-loud AGN and use photometric and spectroscopic information to study both their star-formation and nuclear activity components. Preliminary results show that radio-AGN are associated with early type, massive galaxies with relatively old stellar populations.
01 Aug 2012
TL;DR: In this article, the host galaxy properties of radio sources in the AKARI-North Ecliptic Pole (NEP) field were studied using an ensemble of multi-wavelength datasets.
Abstract: We study the host galaxy properties of radio sources in the AKARI-North Ecliptic Pole (NEP) field, using an ensemble of multi-wavelength datasets. We identify both radio-loud and radio-quiet AGN and study their host galaxy properties by means of SED fitting. We investigate the relative importance of nuclear and star-formation activity in radio-AGN and assess the role of radio-AGN as efficient quenchers of star-formation in their host galaxies.