Abstract
The Hubble Space Telescope recently celebrated 25 years of operation. Some of the first images of extragalactic optical jets were taken by HST in the mid-1990s; with time baselines on the order of 20 years and state-of-the-art astrometry techniques, we are now able to reach accuracies in proper-motion measurements on the order of a tenth of a milliarcsecond per year. We present the results of a recent HST program to measure the kiloparsec-scale proper motions of eleven nearby optical jets with Hubble, the first sample of its kind. When paired with VLBI proper-motion measurements on the parsec scale, we are now able to map the full velocity profile of these jets from near the black hole to the final deceleration as they extend out into and beyond the host galaxy. We see convincing evidence that weak-flavor jets (i.e., FR Is) have a slowly increasing jet speed up to 100 pc from the core, where superluminal components are first seen.
Highlights
Many aspects of the physics of relativistic jets from super-massive black holes are not well understood, including the particle makeup of the jet, their lifetimes, and the speed profile of the plasma as it extends out of the host galaxy and into the intergalactic medium
We present some recent proper-motions results for three nearby optical jets obtained from archival and new Hubble Space Telescope (HST) data, enabled in major part by the long operating lifetime of HST and the resulting 20-year baselines from the original snapshot images of optical jets first taken in the 1990s
Typical numbers of globular clusters used to match the frames were ∼200–500 for Advanced Camera for Surveys Wide Field Camera (ACS/WFC), ∼15–30 for Wide Field Planetary Camera 2 (WFPC2) images, and ∼15–25 for ACS High Resolution Camera (ACS/HRC); corresponding systematic errors were ∼0.006, ∼0.03, and ∼0.05 pixels, or 0.003c, 0.015c, 0.025c over 13.25 years, respectively
Summary
Many aspects of the physics of relativistic jets from super-massive black holes are not well understood, including the particle makeup of the jet, their lifetimes, and the speed profile of the plasma as it extends out of the host galaxy and into the intergalactic medium. Hundreds of observations of jets with very long baseline interferometry (VLBI) in the radio have detected proper motions of jets on parsec and sub-parsec scales, relatively near to the black hole engine (e.g., [1,2,3,4,5]). Because these jets are highly relativistic, apparent superluminal motions can result from velocities near the speed of light coupled with relatively small viewing angles. We present some recent proper-motions results for three nearby optical jets obtained from archival and new HST data, enabled in major part by the long operating lifetime of HST and the resulting 20-year baselines from the original snapshot images of optical jets first taken in the 1990s
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