The galaxy growth may be characterized by interactions with other nearby galaxies that contribute to supermassive black holes (SMBH) that grow within their centers.
It is the conclusion of the meticulous examination through hundreds of galaxy images in the investigation of Rebecca Minsley, an undergraduate student at the Manoa Institute of Astronomy (ifA), University of Hawaii, who worked for 10 weeks with her mentor, the associate scientist for the Maunakea Andreea Petric spectroscopic explorer project. The work has been published in the Astrophysical Journal.
The gas and dust between the stars, called the interstellar medium (ISM), is the fuel for both growth SMBH as for the formation of new stars. But recent work shows that ISM may have different properties, especially being warmer, in galaxies that harbor a growing supermassive black hole in their nuclei, compared to galaxies that do not. Warmer gas is less likely to collapse into new stars, so this finding may suggest that a growing central SMBH decreases a galaxy's ability to form new stars.
What could be responsible for heating the ISM? Starlight, especially hot stars, can do this. But interactions between galaxies - when they collide or even pass close to each other - can produce large-scale shock waves that compress less dense gases, making them more likely to form stars. Minsley studied the shapes of 630 galaxies using images from the Pan-STARRS survey. She classified galaxies into mergers, early mergers, and non-mergers. And later compared the shapes to the light output of the same galaxies at longer mid-infrared wavelengths, where he could study the properties of the ISM.
"When galaxies get close enough, they go through a kind of galactic dance until they finally merge in a singular entity. These interactions have well-documented signatures that allowed me to classify our set of galaxies, "Minsley said." This project gave me a greater appreciation for the complexity and entanglement of all the processes that take place within galaxies and the ongoing research. Performing to deconstruct galactic systems is fascinating. "
Minsley and his collaborators discovered that inside galaxies with active black holes ISM is warmer, the proportions of hot molecular gas to other refrigerants are higher, and other characteristics of dust particles have a wider range of values than in galaxies where black holes are inactive.
"In the near universe we find that the warm ISM of the galaxies that harbor growing supermassive black holes in its centers it differs from those that do not, "explains Petric.
"We speculate that the same processes that channel fuel to SMBH also allow us to detect energy transfer back to the galaxy's ISM." Petric adds that more detailed future observations will allow researchers to confirm these energy transfer processes.