An unknown structure in the galaxy revealed by high-contrast imaging

An unknown structure in the galaxy revealed by high-contrast imaging

Artist’s impression of a giant galaxy with a high-energy jet. Credit: ALMA (ESO/NAOJ/NRAO)

As a result of achieving high dynamic range imaging, a team of astronomers in Japan has detected for the first time a faint radio emission covering a giant galaxy with an active black hole at its center. The radio emission from gas is emitted directly from the central black hole. The team expects to understand how the black hole interacts with its host galaxy by applying the same technology to other quasars.

3C273, which is located at a distance of 2.4 billion light-years from Earth, is a quasar. A quasar is the nucleus of a galaxy believed to have a supermassive black hole at its center, which engulfs the material around it, emitting enormous radiation. Contrary to its lighter name, 3C273 is the first quasar ever discovered, the brightest and the best studied. It is one of the most frequently observed sources with telescopes because it can be used as a benchmark for location in the sky: in other words, 3C273 is a radio beacon.

When you see the headlight of a car, the dazzling brightness makes it difficult to see the darker surroundings. The same thing happens to telescopes when they observe bright objects. Dynamic range is the contrast between the brightest and darkest colors in an image. You need High Dynamic Range To detect the bright and dark parts of the telescope in a single shot. ALMA can regularly have dynamic imaging ranges of about 100, but commercially available digital cameras will usually have a dynamic range of several thousand. Radio telescopes are not very good at seeing things with great contrast.

3C273 has been known for decades as the most famous quasar, but knowledge has centered on its bright central core, where most radio waves come from. However, little is known about its host galaxy itself because the combination of a faint, diffuse galaxy with the nucleus 3C273 requires such high dynamic ranges to be detected. The research team used a technique called self-calibration to reduce radio wave leakage from 3C273 into the galaxy, which used 3C273 itself to correct the effects of Earth’s atmospheric fluctuations on the telescope system. They reached an imaging dynamic range of 85,000, which is the ALMA record for extragalactic objects.

An unknown structure in the galaxy revealed by high-contrast imaging

Quasar 3C273 observed by the Hubble Space Telescope (HST) (left). Excessive brightness results in radial light leakages caused by the light scattered by the telescope. At the bottom right is a high-energy jet of gas shooting around the central black hole. | 3C273 radio image observed by ALMA, showing faint and extended radio emission (in blue and white) around the core (right). The bright central source has been subtracted from the image. The same plane as the image on the left can be seen in orange. Image Credit: Komugi et al., NASA/ESA Hubble Space Telescope

The result of achieving high images Dynamic RangeDetect the dim team radio emission It spans tens of thousands of light-years above the host galaxy 3C273. Radio emissions around quasars usually suggest synchrotron emission, which comes from highly energetic events such as star-forming bursts or ultrafast jets emanating from the central core. A synchrotron jet is also present in 3C273, seen at the bottom right of the images. The primary characteristic of a synchrotron emission is its brightness changes with frequency, but the faint radio emission the team detected had a constant brightness regardless of radio frequency. After considering alternative mechanisms, the team found that this faint and extended radio transmission came from hydrogen gas In the galaxy it is directly activated by the 3C273 nucleus. This is the first time radio waves from such a mechanism have spanned tens of thousands of light years in the quasar host galaxy. Astronomers have ignored this phenomenon for decades at this famous cosmic lighthouse.

So why is this discovery so important? It has been a great mystery in galactic astronomy whether the energy from a quasar core could be strong enough to deny a galaxy the ability to form stars. A faint radio emission may help resolve it. Hydrogen gas is an essential component of star formation, but if light shines on it so intense that the gas has been broken apart (ionized), no stars can be born. Astronomers used to study whether this process occurs around quasars optical light Emitted by ionized gas. The problem with working with optical light is that cosmic dust absorbs light all the way into the telescope, so it’s hard to know how much light the gas emits.

Moreover, the mechanism responsible for giving off optical light is complex, forcing astronomers to make many assumptions. The radio waves detected in this study come from the same gas due to simple processes and are not absorbed by dust. Use radio waves It makes measuring the ionized gas produced by the 3C273 nucleus much easier. In this study, astronomers found that at least 7% of the light from 3C273 was absorbed by the gas at host galaxy, which produces ionized gas with a mass 10-100 billion times the mass of the Sun. However, 3C273 had a lot of gas just before star formation, so as a whole, star formation does not appear to have been strongly suppressed by the core.

says Shinya Komoji, assistant professor at Kogakuen University and lead author of the study published in Astrophysical Journal. “By applying the same technology to other quasars, we expect to understand how the galaxy evolves through its interaction with the central core.”

Astronomers discover a new radio source of unknown origin

more information:
Shinya Komugi et al, Detection of extended millimeter emission in the host galaxy 3C 273 and its reflections on QSO feedback via ALMA high dynamic range imaging, Astrophysical Journal (2022). DOI: 10.3847 / 1538-4357 / ac616e

Provided by ALMA Observatory

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