Astronomers explore properties of quasar 1604+159

Chinese astronomers have conducted multi-frequency polarimetric observations of a quasar known as 1604+159. Results of the observation campaign, published on August 13 on the preprint server arXivwill shed more light on the properties of this quasar, in particular its morphology and its magnetic field.

Quasars, or quasi-stellar objects (QSOs), are very high-luminosity active galactic nuclei (AGNs), emitting electromagnetic radiation observable in radio, infrared, visible, ultraviolet and X-ray wavelengths.

They are among the brightest and most distant objects in the known universe and serve as fundamental tools for many studies in astrophysics and cosmology. For example, quasars have been used to study the large-scale structure of the universe and the era of reionization. They have also improved our understanding of the dynamics of supermassive black holes and the intergalactic medium.

With a redshift of about 0.5, 1604+159 is a low spectral peak (LSP) quasar with a linear scale of 19,750 light-years/arcsecond. Previous observations have shown that it has a flat radio spectrum and low radio variability.

In an effort to gain more information about the properties of 1604+159, a team of astronomers led by Xu-Zhi Hu of the Shanghai Astronomical Observatory in China observed the quasar with the American Very Long Baseline Array (VLBA) and the Very Large Array (VLA).

“This work contains one observation with the Very Long Baseline Array and three observations with the Very Large Array, all in dual-polarization mode,” the researchers explained.

Observations show that 1604+159 has several lobes and bulges that together form a cocoon shape. In addition, the images show several bulges surrounding the core, jets and hot spots towards the edges of the quasar. The largest structure detected is about 50 arcseconds in size.

According to the paper, the 1604+159 has a global helical magnetic field extending from the jet base to the outer region of the jet. The helical magnetic field has a large intrinsic tilt angle, about 80 degrees, in the jet’s rest frame.

The study detected a polarization in the core of 1604+159. This polarization appears to be normal to the edges of the structure. However, the fractional polarization was found to be relatively high, about 60%, or about 15% higher than that of the core.

Observations showed that the quasar jet generally propagates in a collimating structure with several slight bends. As it bends, the jet exhibits a strong polarized intensity and a high fractional polarization towards the curvature edge.

The authors of the study conclude that the results suggest that the cocoon may be expanding. As a result, shocks formed during expansion heat the interstellar medium, contributing to the jet-driven AGN feedback.

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