A prevailing enigma in the realm of astrophysics is the discrepancy between the theoretical predictions of massive galaxy numbers and their actual observed count. There's a significant shortfall in the latter, hinting at a potential mechanism at play that curtails star genesis and governs the galaxy's growth. To reconcile this disparity, theorists have posited an outflow mechanism, suggesting that during an intensely active quasar phase, a galactic nucleus expels massive volumes of gas into intergalactic space. However, empirical evidence to substantiate this outflow mechanism was hitherto elusive.
A past endeavor by Prof. LIU's group offered the first glimmers of such evidence by identifying quasi-spherical outflows in exceptionally radiant quasars with intermediate redshifts. Notably, red quasars, by virtue of being the most radiant quasars across epochs, are inclined to propel energetic outflows. Conventional methods for quasar identification often overlook red quasars due to their diminished visibility in optical spectra. To circumvent this limitation, the USTC team employed the Gemini-North Multi-Object Spectrographs, revealing that a significant half of the sample galaxies manifested pronounced outflows.
Diverging from the previously detected quasi-spherical outflows, these new outflows presented as resplendent superbubble pairs. The largest of these pairs spanned an astonishing 60,000 light-years in diameter and attained a peak line-of-sight velocity of 1,200 km s^-1.
Originating from the powerful impact of quasar-driven outflows on galactic gas, these superbubbles are in their ephemeral "break-out" phase. During this phase, they break free from the dense confines of the galactic nucleus and immerse themselves into the galactic halo. Complementary numerical simulations conducted by the team accentuated that the kinetic energy of this outflowing gas could be a pivotal factor influencing the evolutionary trajectory of its parent galaxy.
From the perspective of understanding outflow mechanisms, the discovery of these superbubble pairs is invaluable. Their very existence offers compelling evidence supporting the outflow phenomenon. Prior observational attempts that depended only on the line-of-sight velocity field were muddled, often conflating outflows with inflows and thereby obfuscating genuine outflow detections. The revelation of superbubble pairs not only resolves this ambiguity but also avails a unique means to compute the outflow's energy and quantify its bearing on the galaxy's overarching evolution.
While there have been sporadic identifications of superbubble structures in the past, this study stands out as the inaugural comprehensive discovery of such structures in a distinct galaxy classification. With this investigation, the team has conducted the premier systematic appraisal of highly luminous quasars at intermediate redshift, leveraging the integral field spectrograph. Such findings stand to fundamentally reshape our comprehension of the galaxy evolution blueprint.
Research Report:Discovery of spectacular quasar-driven superbubbles in red quasars
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University of Science and Technology of China
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