Mapping the Complete Velocity Field of Extragalactic Jets from sub-parsec to kiloparsec Scales

University Of Maryland Baltimore County, Baltimore MD

Investigators

Abstract

Part 1 We now know that essentially all massive galaxies have a super-massive black hole (a million to billion times more massive than the sun) at their centers. Actively growing black holes, also known as active galactic nuclei, are some of the greatest 'recyclers' of matter and energy in the Universe. These accreting black holes are on the scale of our solar system, but have been observed to drive outflows of hot (ionized) gas, known as jets, reaching distances of up to a few million light years (equivalent to typical galaxy separations). These jets have a major impact on both their host galaxies and the clusters of galaxies in which they reside. However, it is still unclear how much energy these jets carry, how they are physically launched from the black hole, and how particles comprising the gas are accelerated to very high energies very far from the black hole engine. The goal of this project is to utilize over 30 years of archival radio imaging with NSF facilities along with new observations, to make the first-ever large compilation of time-lapse observations of dozens of jets over a much larger range of scales than ever before: from very close to the black hole (a few light years) to thousands or millions of light years. Because these jets are moving at nearly the speed of light, we can observe the movement of the gas within the jet on several-year timescales - work that is possible for a large number of jets now that extensive radio archives cover several decades. Mapping the velocity structure of jets will allow us to finally investigate the nature of bright 'knots' in the jet flow, probing regimes of extreme particle acceleration, and to calculate the total energy carried by jets in to the galactic and extra-galactic environment. This is not only critical for understanding the jet phenomenon itself, but will also allow us to improve large-scale computer models of how to Universe was built up over time. Part 2 A major open question in Astronomy is the nature of the bipolar jets of relativistic, ionized plasma seen to emanate from a subset of super-massive black holes at the centers of galaxies. An important tool that has been developed over the last two decades is the use of proper motions (motions on the sky) to track the movement of plasma within these jets, both with Very Long Baseline Interferometry (VLBI) and more compact interferometers like the Very Large Array (VLA). Because the plasma in these jets is relativistic (moving very close to the speed of light) and moving with a small angle to our line-of-sight, the motion of features in the jet flow can appear super-luminal (faster than light). A map of the velocity 'field' of a jet, from parsec scales (close to the black hole) to hundreds or thousands of parsecs (outside the host galaxy) is a very important constraint on jet models, showing exactly how gas is accelerated and deposits energy into the environment. Further, measurements of superluminal speeds allow us to constrain intrinsic properties of jets that are very difficult to determine through any other means (including theoretical modeling, due to degeneracies). In this proposal, we aim to dramatically increase the number of extragalactic jets with measured proper motions on the kiloparsec scale, primarily through the use of the VLA archives. Along with complimentary work using the VLBA, the overall goal is to build the first catalog of jets with velocity fields mapped from the scale of the black hole environment to the final terminus of the jet as it impacts the intergalactic medium. These goals will be accomplished by using both standard interferometric imaging techniques and a recently developed wavelet decomposition code. The science questions addressed by this work include the physical nature of the bright 'knot' structures in the jets, the origin of the anomalously high X-ray fluxes from these knots, the connection between morphological type and jet energetics, and the impact of jets on their environment. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.