Calibration and Imaging of nearby AGN using mm-VLBI

Master Colloquium
Lena Debrecht
SCHEDULED
MPIfR

Blazars are powerful active galactic nuclei (AGN), which exhibit energetic jets pointing at a small angle to the observer. Understanding the formation and motion of these jets requires high-resolution observations. In this study we analysed three epochs of the blazar NRAO 150 (redshift z=1.52) observed with the Global mm-VLBI Array at 86 GHz and one epoch observed with the EVN at 22 GHz and 43 GHz. The aim of this study is to probe the jet's morphology via total intensity imaging and to model its kinematic behaviour. As the source points at a small angle to our line of sight, geometric projection effects need to be taken into account, which can alter the appearance of emission features. Within this work we examined a new kinematic model for NRAO 150 and fitted a helical model to the jet feature's trajectory. We tracked two emission features through all three epochs and report the detection of a counter-clockwise jet rotation for NRAO 150. The computed projected angular velocities are (–41.93 ± 11.80) deg/yr and (20.45 ± 14.19) deg/yr, and the projected radial velocities of (0.01 ± 0.01) mas/yr and (0.01 ± 0.02) mas/yr. We examined possible kinematic scenarios taking into account projection effects and interpreted how they relate to the observed jet features.

VLBI Imaging methods

Master Colloquium
Vanessa Pinto
SCHEDULED
MPIfR

In Very Long Baseline Interferometry (VLBI), calibration and imaging are strongly associated with each other. The traditional CLEAN algorithm has served as the defacto tool for tasks such as imaging, self-calibration, and polarization calibration. However, CLEAN suffers from limitations such as restricted final image resolution, lack of uncertainty quantification, and difficulty incorporating prior knowledge. As a result, alternative approaches, such as the Bayesian inference software resolve, have emerged as a method that outperforms CLEAN. This project aims to utilize resolve to overcome the limitations of CLEAN and specifically, to demonstrate the process that combines self-calibration and imaging for multiple sources simultaneously. We employ survey data for 38 target sources at 15 GHz drawn from the MOJAVE catalog. This approach allows us to generate high-resolution reconstructed images for each target source as well as joint antenna gain plots. A comparative analysis of images produced by resolve and CLEAN will highlight the improvement in resolution achieved with resolve. Furthermore, this project emphasizes the efficiency achievable through resolve’s automated approach for combining self-calibration and imaging for multiple sources.

Insights into chlorine chemistry through observations of hydrogen chloride in star-forming regions

Master Colloquium
Lennart Böhm
SCHEDULED
MPIfR

With the origin of chlorine presumed to be in core-collapse supernovae, stellar models predict the ratio of its two stable isotopes 35Cl/37Cl, between 1 and 4, but observations of Cl-bearing molecules have been limited due to their high-lying transitions. I will present observations of the HCl (1–0) line at 625 GHz, carried out using the SEPIA660 receiver on the APEX telescope. We detected both isotopes of HCl toward 27 Galactic sources, spanning a range of galactocentric radii, doubling the number of sources toward which it has previously been detected. Toward 11 sources we see pure emission with hints of an outflow wing while the remaining sources display complex profiles with both emission and absorption. In addition, the HCl detected in absorption toward NGC 4945, the first detection of this species in a nearby galaxy. For the Galactic sources, we obtained an isotopic ratio between 2.0 and 2.6 with an average value of 2.2+/-0.2. Further, we performed a radiative transfer analysis using RADEX with recently computed collisional rate coefficients between HCl and H2, which constrained HCl-bearing gas to trace warm, dense gas in the core and hot, translucent gas in the outflow.