3C120

1. 3C120 R. Craig Walker National Radio Astronomy Observatory Socorro, NM Collaborators: J.M. Benson, S.C. Unwin, M.B. Lystrup, T.R.Hunter, G. Pilbratt, P.E. Hardee, D. Harris VLBA 10th Anniversary June 9, 2003

2. Why 3C120? • Quasar-like properties but “nearby” • z=0.033 D~125 Mpc Scale: 0.6 pc/mas • One of closest superluminals • High angular rates (2.5 mas/yr) • Prime monitoring candidate • Large (~1') optical galaxy with emission lines • Underlying structure unclear – “train wreck” • Jet detected in optical and x-ray • Long history of observations HST images obtained from archive by D. Harris and T. Cheung

3. 3C120 VLBA 1.7 GHz Monitoring Project Observations so far: 1994.44, 1997.70, 2000.68, 2002.76 Also earlier MarkII observations at 1982.77, 1984.26, and 1989.85 50 pc (80 mas) Superluminal and slow moving components Possible helical pattern at 50 pc (80 mas)

4. Helical Pattern • Pattern near 50 pc (80 mas) looks like helix in projection and is moving slowly • Superluminal features move through it • Simple “beads on a string” model requires extremely small angle to line-of-sight • Reasonable geometry if high pressure (high brightness) region is toward outside of jet • Pattern follows wider opening angle helix than individual particles • Expected from instability theory

5. Preliminary Polarization Image Note 90° rotation

6. HELICAL INSTABILITIES • Work by Phil Hardee (See poster 17) • The VLBI data constrains: • Component speeds • Pattern speeds • Brightness distribution • Model with helical instabilities. Try to determine: • Viewing angle and flow speed • Internal and external sound speeds • Perturbation frequencies • Goal to learn about jet content and physics. Psuedo-synchrotron images for low, medium, and high frequency models for hot and warm jets. Multiple perturbation frequency models from side and from near 14° viewing angle

7. Note Gómez talk this meeting 3C120 VLBA High Resolution • Observations by Gómez, Marscher, Agudo, Alberdi and others • Monthly observations at 22 and 43 GHz with full polarization • Have shown evidence for: • Flashing components: External interactions (Gómez et al., Science 289, 2317) • Trailing components: Shock physics (Gómez et al., Ap. J. 561, L161, Agudo et al., Ap. J. 549, L183 • Xray correlation: X-ray dip at component ejection (Marscher et al Nature 417, 625) • Also monitored at 15 GHz by Homan, et al. (Ap. J. 549, 840) 22 GHz

8. 3C120 from 1" to 30" (VLA 5GHz) Walker Ap. J. 488, 675 Jet very one-sided 25 knot 4 knot is subluminal Note possible helical pattern Core Dynamic range (peak/rms) ~250,000

9. HST –VLBI/MERLIN – VLA Overlay • Radio knot at 4 has optical (and x-ray) counterparts on what looks like a spiral arm. • Superluminal motion in inner radio jet implies that the jet is close to the line-of-sight. • Is the “spiral arm” along the line-of-sight? The rest of the galaxy looks face on. Is it a tidal tail? • Low spatial resolution optical spectra are double peaked near the knot – and on the opposite side (Axon et al., Nature, 341, 631) 400 V • Hjorth et al see optical jet beyond 4 knot(ApJ 452, L17) 0 20 -400

10. Chandra X-ray Detections • X-rays seen at core, 4 and 25 knots, jet near 8 • Diffuse x-rays and weak radio near 25 knot (right) Probably synchrotron emission at 4 knot Emission mechanism at 25 knot is a puzzle, especially in the diffuse region to northeast Chandra data is a zero order grating image from Tahir Yaqoob

11. SUMMARY • 3C120 is a rich source of data on the jet phenomenon • VLBA monitoring provides dynamics for comparison with theory • High frequency observations of inner few pc • 1.7 GHz observations of helical pattern at 50 pc • Optical: possible interaction with spiral arm or tidal tail at 4" knot • X-ray: emission mechanism puzzle at 25" knot