The relativistic Jet in M84

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The elliptical galaxy M84 (NGC 4374, UGC 07494) hosts an FR-I radio continuum source (Laing & Bridle 1987, MNRAS, 228, 557) and a dusty, warped optical emission line “disk” (Baum et al. 1988, ApJS, 68, 643; Goudfrooij et al. 1994, A&ApS, 105, 341). HST imaging shows that the inner dust distribution is not relaxed, but filamentary and complex (Jaffe et al. 1994, AJ, 108, 1567). M84 is a member of the Virgo Cluster, at which distance 1 arcsec = 73 pc independent of Hubble's constant (Jacoby et al. 1990, ApJ, 356, 332). Our VLA imaging, at 6 cm with a resolution of 500 mas (36 pc) FWHM, shows that the two large-scale jets in M84 are initially asymmetric: the ratio R_I of the intensity of the northern main jet to the southern counterjet exceeds unity. However, these jets symmetrize (R_I ≃ 1) by a projected nuclear offset r_p ≃ 13 arcsec (950 pc). Is this VLA symmetrization trend consistent with Doppler boosting in a decelerating, but initially relativistic, jet? To test this, we obtained preliminary VLBA images of M84 at 18 cm and 4 cm, with resolutions of 11 mas (0.80 pc) and 1.9 mas (0.14 pc), respectively, and used them to evaluate R_I on pc scales for comparison with R_I on 100-pc (VLA) scales.