Context. Extragalactic radio sources have been classified into two classes, Fanaroff-Riley I and II, which differ in morphology and radio power. Strongly emitting sources belong to the ...edge-brightened FR II class, and weakly emitting sources to the edge-darkened FR I class. The origin of this dichotomy is not yet fully understood. Numerical simulations are successful in generating FR II morphologies, but they fail to reproduce the diffuse structure of FR Is. Aims. By means of hydro-dynamical 3D simulations of supersonic jets, we investigate how the displayed morphologies depend on the jet parameters. Bow shocks and Mach disks at the jet head, which are probably responsible for the hot spots in the FR II sources, disappear for a jet kinetic power L sub(kin)< or = 10 super(43) ergs super(-1). This threshold compares favorably with the luminosity at which the FR I/FR II transition is observed. Methods. The problem is addressed by numerical means carrying out 3D HD simulations of supersonic jets that propagate in a non-homogeneous medium with the ambient temperature that increases with distance from the jet origin, which maintains constant pressure. Results. The jet energy in the lower power sources, instead of being deposited at the terminal shock, is gradually dissipated by the turbulence. The jets spread out while propagating, and they smoothly decelerate while mixing with the ambient medium and produce the plumes characteristic of FR I objects. Conclusions. Three-dimensionality is an essential ingredient to explore the FR I evolution becausethe properties of turbulence in two and three dimensions are very different, since there is no energy cascade to small scales in two dimensions, and two-dimensional simulations with the same parameters lead to FRII-like behavior.
Making Faranoff-Riley I radio sources Massaglia, S.; Bodo, G.; Rossi, P. ...
Astronomy and astrophysics (Berlin),
2019, 20190101, Letnik:
621
Journal Article
Recenzirano
Odprti dostop
Radio sources of low power are the most common in the universe. Their jets typically move at nonrelativistic velocity and show plume-like morphologies that in many instances appear distorted and ...bent. We investigate the role of magnetic field on the propagation and evolution of low-power jets and the connection between the field intensity and the resulting morphology. The problem is addressed by means of three-dimensional magnetohydrodynamic (MHD) simulations. We consider supersonic jets that propagate in a stratified medium. The ambient temperature increases with distance from the jet origin maintaining constant pressure. Jets with low magnetization show an enhanced collimation at small distances with respect to hydrodynamic (HD) cases studied in a previous paper. These jets eventually evolve in a way similar to the HD cases. Jets with higher magnetization are affected by strong nonaxisymmetric modes that lead to the sudden jet energy release. From there on, distorted plumes of jet material move at subsonic velocities. This transition is associated with the formation of structures reminiscent of the “warm spots” observed in wide-angle-tail (WAT) sources.
Making Faranoff-Riley I radio sources Massaglia, S.; Bodo, G.; Rossi, P. ...
Astronomy and astrophysics (Berlin),
01/2019, Letnik:
621
Journal Article
Recenzirano
Radio sources of low power are the most common in the universe. Their jets typically move at nonrelativistic velocity and show plume-like morphologies that in many instances appear distorted and ...bent. We investigate the role of magnetic field on the propagation and evolution of low-power jets and the connection between the field intensity and the resulting morphology. The problem is addressed by means of three-dimensional magnetohydrodynamic (MHD) simulations. We consider supersonic jets that propagate in a stratified medium. The ambient temperature increases with distance from the jet origin maintaining constant pressure. Jets with low magnetization show an enhanced collimation at small distances with respect to hydrodynamic (HD) cases studied in a previous paper. These jets eventually evolve in a way similar to the HD cases. Jets with higher magnetization are affected by strong nonaxisymmetric modes that lead to the sudden jet energy release. From there on, distorted plumes of jet material move at subsonic velocities. This transition is associated with the formation of structures reminiscent of the “warm spots” observed in wide-angle-tail (WAT) sources.
Context. Extragalactic radio sources have been classified into two classes, Fanaroff-Riley I and II, which differ in morphology and radio power. Strongly emitting sources belong to the ...edge-brightened FR II class, and weakly emitting sources to the edge-darkened FR I class. The origin of this dichotomy is not yet fully understood. Numerical simulations are successful in generating FR II morphologies, but they fail to reproduce the diffuse structure of FR Is. Aims. By means of hydro-dynamical 3D simulations of supersonic jets, we investigate how the displayed morphologies depend on the jet parameters. Bow shocks and Mach disks at the jet head, which are probably responsible for the hot spots in the FR II sources, disappear for a jet kinetic power ℒkin ≲ 1043 erg s-1. This threshold compares favorably with the luminosity at which the FR I/FR II transition is observed. Methods. The problem is addressed by numerical means carrying out 3D HD simulations of supersonic jets that propagate in a non-homogeneous medium with the ambient temperature that increases with distance from the jet origin, which maintains constant pressure. Results. The jet energy in the lower power sources, instead of being deposited at the terminal shock, is gradually dissipated by the turbulence. The jets spread out while propagating, and they smoothly decelerate while mixing with the ambient medium and produce the plumes characteristic of FR I objects. Conclusions. Three-dimensionality is an essential ingredient to explore the FR I evolution becausethe properties of turbulence in two and three dimensions are very different, since there is no energy cascade to small scales in two dimensions, and two-dimensional simulations with the same parameters lead to FRII-like behavior.
Radio sources of low power are the most common in the universe. Their jets typically move at nonrelativistic velocity and show plume-like morphologies that in many instances appear distorted and ...bent. We investigate the role of magnetic field on the propagation and evolution of low-power jets and the connection between the field intensity and the resulting morphology. The problem is addressed by means of three-dimensional magnetohydrodynamic (MHD) simulations. We consider supersonic jets that propagate in a stratified medium. The ambient temperature increases with distance from the jet origin maintaining constant pressure. Jets with low magnetization show an enhanced collimation at small distances with respect to hydrodynamic (HD) cases studied in a previous paper. These jets eventually evolve in a way similar to the HD cases. Jets with higher magnetization are affected by strong nonaxisymmetric modes that lead to the sudden jet energy release. From there on, distorted plumes of jet material move at subsonic velocities. This transition is associated with the formation of structures reminiscent of the `warm spots' observed in wide-angle-tail (WAT) sources.
Extragalactic radio sources have been classified into two classes, Fanaroff-Riley I and II, which differ in morphology and radio power. Strongly emitting sources belong to the edge-brightened FR II ...class, and weakly emitting sources to the edge-darkened FR I class. The origin of this dichotomy is not yet fully understood. Numerical simulations are successful in generating FR II morphologies, but they fail to reproduce the diffuse structure of FR Is. By means of hydro-dynamical 3D simulations of supersonic jets, we investigate how the displayed morphologies depend on the jet parameters. Bow shocks and Mach disks at the jet head, which are probably responsible for the hot spots in the FR II sources, disappear for a jet kinetic power L_kin < 10^43 erg/s. This threshold compares favorably with the luminosity at which the FR I/FR II transition is observed. The problem is addressed by numerical means carrying out 3D HD simulations of supersonic jets that propagate in a non-homogeneous medium with the ambient temperature that increases with distance from the jet origin, which maintains constant pressure. The jet energy in the lower power sources, instead of being deposited at the terminal shock, is gradually dissipated by the turbulence. The jets spread out while propagating, and they smoothly decelerate while mixing with the ambient medium and produce the plumes characteristic of FR I objects. Three-dimensionality is an essential ingredient to explore the FR I evolution because the properties of turbulence in two and three dimensions are very different, since there is no energy cascade to small scales in two dimensions, and two-dimensional simulations with the same parameters lead to FRII-like behavior.
Among radio galaxies, compact sources are a class of objects not yet well understood, and most of them cannot be included in classical populations of compact radio sources (flat spectrum AGN or ...compact steep spectrum sources). Our main goal is to analyze the radio and optical properties of a sample of compact sources and compare them with FRI/FRII extended radio galaxies. We selected in the Bologna Complete Sample a sub sample of Compact sources, naming it the C BCS sample. We collected new and literature sub-arcsecond resolution multi-frequency VLA images and optical data. We compared total and nuclear radio power with optical emission line measurements. The OIII luminosity - 408 MHz total power relation found in High and Low excitation galaxies, as well as in young (CSS) sources, holds also for the C BCSs. However, C BCSs present higher OIII luminosity than expected at a given total radio power, and they show the same correlation of Core Radio Galaxies, but with a higher radio power. C BCSs appear to be the high power tail of Core Radio Galaxies. For most of the C BCSs, the morphology seems to be strongly dependent to the presence of dense environments (e.g. cluster or HI-rich galaxies) and to a low age or restarted radio activity.
With the aim of exploring the properties of the class of FR 0 radio galaxies, we selected a sample of 108 compact radio sources, called FR0CAT, by combining observations from the NVSS, FIRST, and ...SDSS surveys. We included in the catalog sources with redshift ≤0.05, with a radio size ≲5 kpc, and with an optical spectrum characteristic of low-excitation galaxies. Their radio luminosities at 1.4 GHz are in the range 1038 ≲ νL1.4 ≲ 1040 erg s-1. The FR0CAT hosts are mostly (86%) luminous (−21 ≳ Mr ≳ −23) red early-type galaxies with black hole masses 108 ≲ MBH ≲ 109M⊙. These properties are similar to those seen for the hosts of FR I radio galaxies, but they are on average a factor ~1.6 less massive. The number density of FR0CAT sources is ~5 times higher than that of FR Is, and thus they represent the dominant population of radio sources in the local Universe. Different scenarios are considered to account for the smaller sizes and larger abundance of FR 0s with respect to FR Is. An age-size scenario that considers FR 0s as young radio galaxies that will all eventually evolve into extended radio sources cannot be reconciled with the large space density of FR 0s. However, the radio activity recurrence, with the duration of the active phase covering a wide range of values and with short active periods strongly favored with respect to longer ones, might account for their large density number. Alternatively, the jet properties of FR 0s might be intrinsically different from those of the FR Is, the former class having lower bulk Lorentz factors, possibly due to lower black hole spins. Our study indicates that FR 0s and FR I/IIs can be interpreted as two extremes of a continuous population of radio sources that is characterized by a broad distribution of sizes and luminosities of their extended radio emission, but shares a single class of host galaxies.
We extend the study of the radio emission in early-type galaxies (ETGs) in the nearby Universe (recession velocity < 7500 km s
−1
) as seen by the 150 MHz Low-Frequency ARray (LOFAR) observations and ...extend the sample from giant ETGs to massive (∼6 × 10
10
− 3 × 10
11
M
⊙
) ETGs (mETGS) with −25 <
M
K
< −23.5. Images from the second data release of the LOFAR Two-metre Sky Survey were available for 432 mETGs, 48% of which are detected above a typical luminosity of ∼3 × 10
20
W Hz
−1
. Most (85%) of the detected sources are compact, with sizes ≲4 kpc. The radio emission of 31 mETGs is extended on scales ranging from 2 to 180 kpc (median 12 kpc). In several cases, it is aligned with the host galaxy. We set a limit of ≲1% to the fraction of remnant or restarted objects, which is ≲16% of the extended sources. We found that the properties of the radio sources are connected with the stellar mass of the ETGs (the median radio power, the fraction of extended radio sources, and the link with the large-scale environment). However, these results only describe statistical trends because the radio properties of sources of similar stellar mass and environment show a large spread of radio properties. These trends break at the lowest host luminosities (
M
K
> −24.5). This effect is strengthened by the analysis of even less massive ETGs, with −23.5 <
M
K
< −21.5. This suggests that at a mass of ∼2 × 10
11
M
⊙
, a general transition occurs from radio emission produced from radio-loud active galactic nuclei (AGN) to processes related to the host galaxy and (or) radio quiet AGN. At this luminosity, a transition in the stellar surface brightness profile also occurs from Sérsic galaxies to those with a depleted stellar core, the so-called core galaxies. This finding is in line with previous results that indicated that only core galaxies host radio-loud AGN.
We explore the radio properties of powerful (rest-frame luminosity $ at 500 MHz) high-redshift ($z 3.5$) quasars. The aim of this study is to gain a better understanding of radio-loud sources at the ...epoch when they reach the highest space density. We selected 29 radio-loud quasars at low radio frequencies (76 MHz). Their radio spectra, covering the range from 76 MHz to 5 GHz, are generally well reproduced by a single power law. We created samples that were matched in radio luminosity at lower redshift (from $z to $z to investigate any spectral evolution. We find that the fraction of flat-spectrum radio quasars (FSRQs) strongly increases with redshift (from $ 8<!PCT!>$ at z=1.2 to $ 45<!PCT!>$ at z$>$3.5). This effect is also observed in quasars with lower luminosities (down to $ The increase in the fraction of FSRQs with redshift corresponds to a decrease in the steep- spectrum radio quasars. This result can be explained when we assume that the beaming factor and the slope of the luminosity function do not change with redshift and if high-redshift radio-loud sources can be recognized as quasars only when they are seen at a small viewing angle ($ but most of them, about 90<!PCT!> are obscured in the UV and optical bands. We also found a trend for the size of radio sources to decrease with increasing redshift. Because projection effects are insufficient to cause this trend, we suggest that the large amount of gas causing the nuclear obscuration also hampers the growth of the more distant sources.
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