Properties and short-time evolution of nearby galaxies

TL;DR

This study analyzes a decade of VLBA radio observations of nearby galaxies, reconstructing high-resolution maps of their active galactic nuclei to understand their structure and evolution.

Contribution

It introduces a detailed data processing pipeline for VLBA data, including calibration and spectral analysis, applied to nearby galaxies for the first time.

Findings

Reconstructed milliarcsecond maps of NGC315 and 3C274's cores.

Detected structural changes over ten years in AGN regions.

Estimated velocities and accelerations of nuclear components.

Abstract

We analyze the results of processing of data of observations which had been carried out with the VLBA during 10 last years. All the data have been retrieved from archive of the National Radio Astronomy Observatory (USA NRAO, Socorro, New Mexico). Particularly, we examine data of VLBA observational sessions titled BK068, BL111, BL137, BL149, and BD086. Objects of our interest are near galaxies with z < 0.02. The radio maps of compact structure around the active galactic nuclei (AGN) reconstructed for two such galaxies (NGC315 and 3C274) in U frequency band (15 GHz) are presented. Some parameters of these sources are shown in Table 1. We have to perform the careful amplitude and phase calibration for all the data. Particularly, a correction of the delay caused by the Earth atmosphere has been made because it is necessary in this frequency range. Bright quasars close to the target sources (for instance, J0136+4751 and 3C279 correspondingly) are used as atmosphere calibrators. Secondly, the Multi Frequency Synthesis (MFS) method is used for final maps reconstruction as well as for estimation of spectral index values of core and jet of AGN of both objects. As a result, we can make some conclusions about the milliarcsecond structure of central regions of sources thanks to the using of these two methods of the VLBA data processing. Moreover, we can reveal some changes of this structure in 1999 - 2009, and estimate roughly the velocities and acceleration/deceleration values for brightest components of the nuclei of NGC315 and 3C274. Any polarization phenomena are not taken into account. We present results of processing of data of LL polarization for all the observational sessions.