European astronomers recently conducted extensive Very Long Baseline Interferometric (VLBI) observations on the radio jet structure of PKS 2215+020, a powerful quasar. The acquired VLBI data yielded crucial insights into the characteristics of this jet, indicating that PKS 2215+020 exhibits traits typical of a blazar. These findings, unveiled on February 17 in the Universe journal, shed light on the nature of this distant and luminous astronomical phenomenon.
Quasars, also known as quasi-stellar objects (QSOs), represent active galactic nuclei (AGN) distinguished by their extraordinary luminosity across various electromagnetic wavelengths, including radio, infrared, visible, ultraviolet, and X-ray spectra. Positioned as some of the brightest and most remote entities in the observable universe, quasars serve as indispensable tools for diverse studies in astrophysics and cosmology. Their significance extends to investigations concerning the large-scale structure of the cosmos, the epoch of reionization, and insights into supermassive black hole dynamics alongside the intergalactic medium.
PKS 2215+020 emerges as a formidable flat-spectrum radio quasar boasting a redshift of 3.572. With a rest-frame monochromatic power at 5 GHz approximately amounting to 20 RW/Hz, its supermassive black hole dwarfs the sun by an estimated factor of four billion in terms of mass.
Prior examinations of PKS 2215+020 unveiled a morphology primarily characterized by a luminous compact core, extending into a sequence of faint jet components. Notably, the most extended jet component both terminates and intensifies the brightness. This remarkably extensive radio jet structure spans roughly 1,950 light years in linear size, as projected onto the plane of the sky.
Led by Sándor Frey of the Konkoly Observatory in Budapest, Hungary, a team of astronomers embarked on a comprehensive inquiry into the jet of PKS 2215+020, aiming to elucidate its physical and geometrical properties. Leveraging the capabilities of the Very Long Baseline Array (VLBA) under the U.S. National Radio Astronomy Observatory (NRAO), they undertook the examination.
The team meticulously gathered and analyzed archival multi-epoch VLBI imaging data across five distinct frequency bands (ranging from 1.7 to 15.4 GHz) spanning epochs between 1995 and 2020, with a predominant focus on post-2010 data. The resulting images, boasting angular resolutions within the ∼1–10 mas scale, delineate the bright compact core region into discernible emission components at higher frequencies, alongside an extended, steep-spectrum feature ∼ 56 mas from the core at lower frequencies.
Through VLBI imaging, the team successfully derived the apparent proper motions of jet components within PKS 2215+020, a groundbreaking achievement for the first time. Notably, the jet exhibited moderately superluminal motion, with an apparent speed attaining 2.1 times the speed of light, and an apparent proper motion approximately registering at 0.02 mas per year.
Drawing from these data, the Doppler boosting factor within the inner relativistic jet was computed to be 11.5. Moreover, the jet's inclination to the line of sight was discerned to be 1.8 degrees, while its bulk Lorentz factor attained a measurement of 6.0.
The researchers underscored that the compiled data strongly advocate for PKS 2215+020's classification as a blazar. Typically categorized within the broader assembly of active galaxies housing AGNs, blazars represent the most prevalent extragalactic gamma-ray sources, distinguished by their relativistic jets aligned nearly precisely towards Earth.
The paper's authors accentuated that the modest apparent proper motion value and jet parameters ascertained for PKS 2215+020 mirror those observed in other radio AGNs at elevated redshifts (exceeding 3.5). This concurrence further solidifies the understanding of PKS 2215+020's nature and positions it within the broader context of high-redshift astronomical phenomena.