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Investigations of Radio Jets in M87, 3C273, and 3C345


Biretta, John Anthony (1986) Investigations of Radio Jets in M87, 3C273, and 3C345. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/dsst-qp22.


We present observational studies of extra-galactic radio jets in M87, 3C273, and 3C345.

Observations of the M87 jet were made at 15 GHz with 0.12" resolution. All of the knots are clearly resolved both along and across the jet. Most of the knots are found to be smooth in appearance with no evidence of shocklike discontinuities. The brightest knot and the innermost knot are exceptions to this. The brightest knot (knot A) seems consistent with a shock caused by unsteady flow in the jet. Models for this feature are discussed. Combining our data with X-ray data suggests that the jet is neither freely expanding, thermally confined, nor ram pressure confined. The jet may, however, be magnetically confined.

We present 10.7 GHz VLBI observations of 3C273 with high north-south resolution. A strong, non-monotonic curvature is found in the jet at projected radii ≤ 5 pc. It is unlikely that this curvature can be caused by precession. Measurements of the core size show that bulk relativistic motion in the core is not required for consistency with the observed x-ray flux.

For 3C345 we present a systematic analysis of VLBI observations at 2.3, 5.0, 10.7, 22.2, and 89 GHz. Epochs are from 1979.25 through 1984.11. A newly ejected superluminal component (C4) is observed to accelerate, change position angle, undergo a large flux outburst, and have a flat spectrum. Older components C2 and C3 have different speeds, different position angles, and show little or no acceleration. The spectrum of C3 steepens as its flux decays. There are spectral index gradients such that both C4 and C3 are farther from the "core" at higher frequencies. The moving components define an opening angle of ~27° and also show direct evidence for expansion. The counter-jet to jet flux ratio is extremely small, -0.007±0.007.

These data for 3C345 are interpreted in terms of simple models involving spherical components or shocks in a relativistic jet. All of the emission regions show evidence for bulk relativistic motion with δ > 3. The particle energies and pressures dominate those of the magnetic fields, unless δ ≥ 20. If the emission regions consist of an electron-proton plasma, then the density of thermal electrons is much less than the density of relativistic electrons. The fluxes decay with time much more rapidly than the synchrotron half-life, but much more slowly than predicted by adiabatic expansion. An attractive model for the observed kinematics identifies the emitting regions as shocks in an apparently broad and curved jet; a curvature of ≥ 3° and γ ≥ 10 is required.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Astronomy
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Cohen, Marshall H.
Group:Owens Valley Radio Observatory (OVRO), Astronomy Department
Thesis Committee:
  • Unknown, Unknown
Defense Date:6 June 1985
Record Number:CaltechETD:etd-09092008-084712
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter I. adapted for Chapter II. adapted for Chapter III. adapted for Chapter IV.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3406
Deposited By: Imported from ETD-db
Deposited On:17 Sep 2008
Last Modified:19 Apr 2021 22:28

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