Studies have shown that black holes and host galaxies grow together, and the larger the galaxy, the larger the black hole!

[Mobile software: Bo Ke Yuan] Over the past two decades, astronomers have concluded that most galaxies have massive black holes at their centers, and that the masses of black holes and host galaxies are correlated. But how are the two linked? Now, scientists at the University of Hawaii at Mānoa Institute for Astronomy may have revealed part of the answer. By carefully sifting through hundreds of galaxy images, researchers are beginning to more clearly define the picture of galaxy evolution. The growth of galaxies may be formed by interactions with other galaxies, which contribute to the growth of supermassive black holes at the centers of galaxies.

The gas and dust between stars, called the interstellar medium (ISM), is the fuel for the growth of supermassive black holes (SMBHs) and the formation of new stars. But new research suggests that the ISM may have different properties in galaxies with growing supermassive black holes at their cores compared to those without supermassive black holes. The hotter gas is less likely to collapse into new stars, so this finding may indicate that a growing central supermassive black hole is weakening the galaxy's ability to produce new stars.

What could be the cause of the interstellar medium heating up? The answer is that light (in all wavelengths), especially starlight from hot stars, can do it. But interactions between galaxies (when they collide with each other or even just pass close) can create massive shock waves that compress less dense gas, making it more likely to form stars. Astronomers used images from the Pan-STARRS survey to study 630 galaxy shapes. The galaxies were classified as merging, early-merging, and non-merging. These shapes were then compared to the light output of the same galaxies at longer mid-infrared wavelengths, where the properties of the interstellar medium can be studied.

When galaxies get close enough, they go through a kind of galactic dance until they eventually combine into a single system. These interactions have well-documented signatures that allow astronomers to classify groups of galaxies. This research project gives us a greater understanding of the complexity and entanglement of all the processes that occur within galaxies, and the ongoing study of deconstructing galaxies is fascinating. The researchers found that in galaxies with active black holes, the interstellar medium is hotter, the ratio of hot molecular gas to other coolants is greater, and other characteristics of dust particles have a wider range of values ​​than in galaxies where the black holes are dormant.

In our own cosmic neighborhood, it was discovered that the hot interstellar medium of galaxies with growing supermassive black holes at their centers is different from that of those without them. The same processes that deliver fuel to the supermassive black holes also allow us to detect energy transfers back to the interstellar medium of the galaxies. Future more detailed observations will allow researchers to confirm these energy transfer processes. IFA has been part of the prestigious REU program for almost 20 years and has trained more than 130 students, some of whom are now leaders in different fields of astronomy.

Because of this unique opportunity to work at the University of Hawaii, with its world-class facilities and scientists, IFA receives more than 500 applications each semester. Nader Haghighiour, principal investigator of the IFA REU program, noted, "Our mentors are world leaders in their fields, and our REU students are engaged in cutting-edge research. Rebecca, the researcher on this paper, is a great example of this, and we are very proud of our REU students, as almost all of them continue their studies in graduate school, and many of them receive national recognition."

During the fall 2020 semester, PETRIC and UH MāNOA undergraduate Diana Castaneda will continue to use a spectrometer aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) aircraft to study the interstellar medium in galaxies that host some of the most luminous growing supermassive black holes in the nearby universe. SOFIA's observations will allow Castaneda and PETRIC to gain a deeper understanding of the processes by which energy is transferred between growing supermassive black holes and the interstellar medium, with their findings published in the Astrophysical Journal.

Bo Ke Yuan | Research/From: University of Hawaii at Manoa

The research was published in the journal Astrophysics

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