Galaxies and Black Holes Grow Together
Institute for Astronomy | University of Hawaii | 2020 May 20
Over the past two decades, astronomers have concluded that most, if not all, galaxies host massive black holes at their centers - and the masses of a black hole and its host galaxy are correlated. But how are the two connected? Now, a University of Hawaiʻi at Mānoa Institute for Astronomy (IfA) student participating in the National Science Foundation's (NSF) Research Experiences for Undergraduates (REU) program, may have revealed part of the answer.
- Pan-STARRS images of NGC 4088, NGC 0520, NGC 5218, NGC 4922 NED02, illustrating the different features used to classify galaxy mergers, including galaxy asymmetry, tidal tails, galactic shells, multiple nuclei and early/possible mergers for galaxies of similar brightness within 50 kpc of each-other. Credit: A. Petric/B. Bays
Undergraduate Rebecca Minsley, participated in IfA's 2019 REU program, working for ten weeks with her mentor Maunakea Spectroscopic Explorer Deputy Project Scientist Andreea Petric. Sifting meticulously though hundreds of images of galaxies, Minsley began to define a clearer picture of galaxy evolution. "Galaxy growth may be shaped by interactions with other galaxies which contributes to supermassive black holes (SMBH) that grow within the galaxy's center," Minsley explained.
Gas and dust between stars, called the interstellar medium (ISM), is the fuel for both SMBH growth and the formation of new stars. But recent work shows that the ISM may have different properties - especially being warmer - in galaxies that host a growing supermassive black hole in their nuclei, compared to those galaxies that do not. Warmer gas is less likely to collapse into new stars, so this finding may suggest that a growing central SMBH diminishes a galaxy's ability to make new stars.
What might be responsible for heating the ISM? Starlight, especially from hot stars, can do this. But interactions between galaxies - when they collide or even just pass close to each other - can produce large-scale shock waves that compress less dense gas, making it more likely to form stars. Minsley studied the shapes of 630 galaxies using images from the Pan-STARRS survey. She classified the galaxies into mergers, early mergers, and non-mergers. And then compared the shapes to the light output of the same galaxies at longer mid-infrared wavelengths, where she could study the properties of the ISM. ...
Molecular Gas and Dust Heating in Active Galaxies:
Growing Black Holes or Tidal Shocks? ~ Rebecca Minsley et al