An HST Proper-Motion Study of the Large-Scale Jet of 3c273

Abstract

The radio galaxy 3C 273 hosts one of the nearest and best-studied powerful quasar jets. Having been imaged repeatedly by the Hubble Space Telescope (HST) over the past twenty years, it was chosen for an HST program to measure proper motions in the kiloparsec-scale resolved jets of nearby radio-loud active galaxies. The jet in 3C 273 is highly relativistic on sub-parsec scales, with apparent proper motions up to 15c observed by very long baseline interferometry. In contrast, we find that the kiloparsec-scale knots are compatible with being stationary, with a mean speed of −0.2±0.5c over the whole jet. Assuming the knots are packets of moving plasma, an upper limit of 1c implies a bulk Lorentz factor Γ < 2.9. This suggests that the jet has either decelerated significantly by the time it reaches the kiloparsec scale, or that the knots in the jet are standing shock features. The second scenario is incompatible with the inverse Compton off the Cosmic Microwave Background (IC/CMB) model for the X-ray emission of these knots, which requires the knots to be in motion, but IC/CMB is also disfavored in the first scenario due to energetic considerations, in agreement with the recent finding of Meyer & Georganopoulos which ruled out the IC/CMB model for the X-ray emission of 3C 273 via gamma-ray upper limits.

The Origin of the X-Ray Emission in Two Well-aligned Extragalactic Jets: The Case for IC/CMB

“…There is another factor which likely makes these jets outliers in addition to the orientation angle. As noted previously, population-based evidence as well as individual limits on δ from both proper motions (in 3C 273; Meyer et al 2016) and deep Fermi/LAT limits on the IC/CMB emission imply most large-scale jets are only mildly relativistic. Here we require high values of the Lorentz factor on extremely large scales -assuming the maximum angle, the jets in OJ 287 and PKS 1510−089 deproject to lengths of at least 600 and 800 kpc.…”

Spectroastrometry and Reverberation Mapping: the Mass and Geometric Distance of the Supermassive Black Hole in the Quasar 3C 273

“…A remarkable point is that the vertical distribution Dθ1 systematically yields a larger inclination angle of ∼ 30 • , whereas the distribution Dθ2 yields an inclination angle of ∼ 6 • . The latter value is consistent with the inclination 3.8 • -15 • of the jet in 3C 273 measured by radio observations (e.g., Lobanov & Zensus 2001;Savolainen et al 2006;Meyer et al 2016;Jorstad et al 2017). The main reason for such a dichotomy is as follows (see also discussions in Grier et al 2017 andLi et al 2018).…”

“…First, 3C 273 displays a prominent radio jet (e.g., Courvoisier 1998). The viewing inclination measured through superluminal motion ranges from 3.8 • to ∼15 • (Lobanov & Zensus 2001;Savolainen et al 2006;Meyer et al 2016;Jorstad et al 2017). This provides a useful constraint if assuming an alignment between the rotation axis of the BLR and the jet.…”

Unraveling the Physics of Quasar Jets: Optical Polarimetry and Implications for the X-ray Emission Process

“…That was seen to be inconsistent with the observed properties of that source. While some of these sources are known to be highly beamed on parsec scales-for example, 3C 273 has apparent superluminal speeds as high as 15c [39]-it has always been assumed that jets must decelerate on kpc scales (e.g., [42,47], and moreover, in the case of 3C 273, a study of proper motions on the kiloparsec scales found an upper limit of 2c [40], highly inconsistent with the requirement of the IC-CMB model [36,40]. Individually, in fact, those models show that these knots are inconsistent with IC-CMB emission by large factors-anywhere from 2σ for the faintest components to over 20 σ for the brightest components.…”

“…More recently, analysis of Fermi observations of multiple other quasars [35][36][37][38] including the jets of 3C 273 and PKS 0637-752, also proved to be inconsistent with the IC-CMB emission process being dominant in the X-rays, as the same electron population would inverse-Comptonize optical synchrotron photons into the GeV gamma-ray band, thus requiring a similarly high beaming factor that overpredicts the observed low-state emissions detected by Fermi by orders of magnitude. While 3C 273 has components with varying apparent speeds, as high as 15c (see, e.g., [39]), those components are on parsec scales, while the observed X-ray emission is on projected scales of tens of kiloparsecs, where HST observations have failed to find any evidence of superluminal motions [40]. A similar problem exists for PKS 0637-752, where VLBI observations [41] show similarly fast, superluminal components.…”