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Register a new userObserving the Time Evolution of the Multi-Component Nucleus of 3C,84
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The advent of global mm-band Very Long Baseline Interferometry (VLBI) in recent years has finally revealed the morphology of the base of the two most prominent nearby, bright, extragalactic radio jets in M,87 and 3C,84. The images are quite surprising considering the predictions of jet theory and current numerical modeling. The jet bases are extremely wide compared to expectations and the nucleus of 3C,84 is very complicated. It appears as a double in 86,GHz observations with 50,$mu$as resolution and a triple nucleus with 30,$mu$as resolution with space-based VLBI by RadioAstron at 22,GHz. What is even odder is that the double and triple are arranged along an east-west line that is approximately orthogonal to the north-south large scale jet on 150,$mu$as $-$ 4,mas scales. We explore the emergence of an (east-west) double nucleus in the lower resolution 43,GHz Very Long Baseline Array (VLBA) imaging from August 2018 to April 2020. The double is marginally resolved. We exploit the east-west resolution associated with the longest baselines, $sim 0.08$,mas, to track a predominantly east-west separation speed of $approx 0.086pm 0.008$,c. We estimate that the observed mildly relativistic speed persists over a de-projected distance of $sim 1900-9800$ times the central, supermassive black hole, gravitational radius ($sim 0.3-1.5$,lt-yrs) from the point of origin.
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Nearby radio galaxies that contain jets are extensively studied with VLBI, addressing jet launching and the physical mechanisms at play around massive black holes. 3C 84 is unique in this regard, because the combination of its proximity and large SMBH mass provides a high spatial resolution to resolve the complex structure at the jet base. For 3C 84 an angular scale of 50 ${mu}$as corresponds to 200 - 250 Schwarzschild radii ($R_s$). Recent RadioAstron VLBI imaging at 22 GHz revealed an east-west elongated feature at the northern end of the VLBI jet, which challenges interpretations. Here we propose instead that the jet apex is not located within the 22 GHz VLBI core region but more upstream of the jet. We base our arguments on a 2D cross-correlation analysis of quasi-simultaneously obtained VLBI images at 15, 43, and 86 GHz, which measures the opacity shift of the VLBI core in 3C 84. With the assumption of the power law index ($k_r$) of the core shift being set to 1, we find the jet apex to be located $83 pm 7$ ${mu}$as north (upstream) of the 86 GHz VLBI core. Depending on the assumptions for $k_r$ and the particle number density power law index n, we find a mixed toroidal/poloidal magnetic field configuration, consistent with a region which is offset from the central engine by about 400-1500 $R_s$. The measured core shift is then used to estimate the magnetic field strength, which amounts to B = 1.80 - 4.0 G near the 86 GHz VLBI core. We discuss some physical implications of these findings.
We report a search for linear polarization in the active galactic nucleus (AGN) 3C 84 (NGC 1275) at observed frequencies of 239 GHz and 348 GHz, corresponding to rest-frame frequencies of 243 GHz and 354 GHz. We collected polarization data with the IRAM Plateau de Bure Interferometer via Earth rotation polarimetry. We do not detect linear polarization. Our analysis finds 3-sigma upper limits on the degree of polarization of 0.5% and 1.9% at 239 GHz and 348 GHz, respectively. We regard the influence of Faraday conversion as marginal, leading to expected circular polarizations <0.3%. Assuming depolarization by a local Faraday screen, we constrain the rotation measure, as well as the fluctuations therein, to be 10^6 rad/m^2. From this we estimate line-of-sight magnetic field strengths of >100 microG. Given the physical dimensions of 3C 84 and its observed structure, the Faraday screen appears to show prominent small-scale structure, with DeltaRM > 10^6 rad/m^2 on projected spatial scales <1 pc.
We report results from a deep polarization imaging of the nearby radio galaxy 3C$,$84 (NGC$,$1275). The source was observed with the Global Millimeter VLBI Array (GMVA) at 86$,$GHz at an ultra-high angular resolution of $50mu$as (corresponding to 250$R_{s}$). We also add complementary multi-wavelength data from the Very Long Baseline Array (VLBA; 15 & 43$,$GHz) and from the Atacama Large Millimeter/submillimeter Array (ALMA; 97.5, 233.0, and 343.5$,$GHz). At 86$,$GHz, we measure a fractional linear polarization of $sim2$% in the VLBI core region. The polarization morphology suggests that the emission is associated with an underlying limb-brightened jet. The fractional linear polarization is lower at 43 and 15$,$GHz ($sim0.3-0.7$% and $<0.1$%, respectively). This suggests an increasing linear polarization degree towards shorter wavelengths on VLBI scales. We also obtain a large rotation measure (RM) of $sim10^{5-6}~{rm rad/m^{2}}$ in the core at $gtrsim$43$,$GHz. Moreover, the VLBA 43$,$GHz observations show a variable RM in the VLBI core region during a small flare in 2015. Faraday depolarization and Faraday conversion in an inhomogeneous and mildly relativistic plasma could explain the observed linear polarization characteristics and the previously measured frequency dependence of the circular polarization. Our Faraday depolarization modeling suggests that the RM most likely originates from an external screen with a highly uniform RM distribution. To explain the large RM value, the uniform RM distribution, and the RM variability, we suggest that the Faraday rotation is caused by a boundary layer in a transversely stratified jet. Based on the RM and the synchrotron spectrum of the core, we provide an estimate for the magnetic field strength and the electron density of the jet plasma.
We present a kinematic study of the subparsec-scale radio jet of the radio galaxy 3C 84/NGC 1275 with the VLBI Exploration of Radio Astrometry (VERA) array at 22 GHz for 80 epochs from 2007 October to 2013 December. The averaged radial velocity of the bright component C3 with reference to the radio core is found to be $0.27 pm 0.02c$ between 2007 October and 2013 December. This constant velocity of C3 is naturally explained by the advancing motion of the head of the mini-radio lobe. We also find a non-linear component in the motion of C3 with respect to the radio core. We briefly discuss possible origins of this non-linear motion.
How did the universe evolve? The fine angular scale (l>1000) temperature and polarization anisotropies in the CMB are a Rosetta stone for understanding the evolution of the universe. Through detailed measurements one may address everything from the physics of the birth of the universe to the history of star formation and the process by which galaxies formed. One may in addition track the evolution of the dark energy and discover the net neutrino mass. We are at the dawn of a new era in which hundreds of square degrees of sky can be mapped with arcminute resolution and sensitivities measured in microKelvin. Acquiring these data requires the use of special purpose telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and the South Pole Telescope (SPT). These new telescopes are outfitted with a new generation of custom mm-wave kilo-pixel arrays. Additional instruments are in the planning stages.
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