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Superbubble Pairs Generated by Quasar-Driven Outflows Discovered

A research group headed by Professor Guilin Liu and Professor Zhicheng He from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) found superbubble pairs produced by quasar-driven outflows of three red quasars for the first time.

Superbubble Pairs Generated by Quasar-Driven Outflows Discovered

The surface brightness, line-of-sight velocity, and velocity dispersion maps of superbubble pairs. Image Credit: Image by SHEN Lu et al.

This study was reported in the journal Science Advances.

The observed number of huge galaxies is considerably lower compared to the forecast of the present galaxy evolution theory; thus, some mechanism is required to repress star formation and modulate the galaxy’s growth.

For the gap between theory and observation to be bridged, an outflow mechanism where a galaxy nucleus drives a huge amount of gas into intergalactic space at its rather active quasar stage was suggested to be a vital part of the galaxy evolution model. However, the outflow mechanism remained a theoretical assumption as a result of limitations in actual observations.

Earlier research by Professor Liu’s team found out direct proof of quasi-spherical outflows in highly luminous quasars at intermediate redshift. Red quasars are probably to push energetic outflows as the highly luminous quasars at each epoch.

The conventional quasar selection method tends to omit red quasars as a result of their faintness in optical bands. Provided this, the group utilized the Gemini-North Multi-Object Spectrographs to redress for the observations on red quasars and discovered that half of the sample galaxies feature considerable outflows.

Dissimilar to earlier found quasi-spherical outflows, such outflows displayed forms of spectacular superbubble pairs. The biggest pair prolonged over 60000 lightyears in diameter and went up to a maximum line-of-sight velocity of 1200 km s-1.

Such superbubble pairs, produced by quasar-driven outflows affecting the galactic gas, are at a short-lived “break-out” phase when they tend to escape from the dense surrounding of the galactic nucleus and pitch in the galactic halo.

Also, the research group executed numerical simulations and discovered that the energy of the outflow gas could have a considerable impact on the evolution of the galaxy.

The breakthrough of superbubble pairs is considered to be of great value to the research on the outflow mechanism. Initially, the presence of superbubble pairs is quite solid proof for outflow, whereas earlier observations depending solely on line-of-sight velocity field tended to confuse outflows with inflows, thereby making it hard to trustworthily determine outflows.

Furthermore, superbubble pairs offer a special chance to assess the outflow energy and evaluate the effect of outflows on the entire galaxy’s evolution.

Even though there have been few precedents for superbubble structures, this work is considered to be the first systematic breakthrough of superbubble structures present in a particular type of galaxy.

Also, the group has finished the first systematic survey of highly luminous quasars at intermediate redshift utilizing the integral field spectrograph, which is forecasted to affect the construction of the galaxy evolution paradigm profoundly.

Journal Reference

Shen, L., et al. (2023) Discovery of spectacular quasar-driven superbubbles in red quasars. Science Advances.

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