Skip to main content

Black holes altering galaxy evolution: how to find them?

Final Report Summary - BHS SHAPING GALAXIES (Black holes altering galaxy evolution: how to find them?)

Black holes, through their radiation, accretion disk winds, and jets of accelerated electrons or protons, deposit energy into the interstellar gas and drive winds in galaxies. Our goal was to find the impact of such feedback mechanisms on the gas that is capable of gravitationally collapsing and forming new stars: the dense, molecular clouds. We designed experiments that unambiguously proved that one of the most powerful feedback mechanisms of black holes, jets, do drive winds along their propagation axes and heat the gas to temperatures that are prohibitive of star formation.

For the small-scale physics parts of our project, we studied the prototype galaxy IC5063. This is a nearby elliptical that has undergone a merger and that has a disk in its center. Outflowing gas had already been detected in this galaxy. Using ultra-deep near-infrared data of this galaxy taken from the Very Large Telescope, we unambiguously proved that the jet is responsible for atomic (H, Fe) and molecular (H2) gas acceleration. The winds start in four different regions along the jet trail, where the plasma collides with gas clouds (Dasyra et al. 2015). Near the wind starting points, the gas has a velocity excess of 600 km/s to 1200 km/s with respect to the stars. The overall area in which the winds spread is impressively high, ~1 kpc^2. High H2 (1-0) S(3)/S(1) flux ratios indicate non-thermal excitation for the warm (>1000K) molecular gas in the wind. Following these results, we were awarded time at the largest millimeter facility to date, the Atacama Large Millimeter Array (ALMA) to study the excitation of the cold molecular gas, which is responsible for star formation. We proved that the CO in the jet-driven winds is more highly excited than the rest of the CO in the disk (Dasyra et al. 2016): the average CO(4-3)/CO(2-1) flux ratio is 1 for the disk and 5 for the jet-driven winds. Excitation temperatures of 30-100 K are common in the wind, whereas excitation temperatures of 3-10K are typical of star-forming complexes. The mass of the gas in the wind is at least 2 million solar masses.

New molecular winds were then sought into large samples of active galactic nuclei and radio galaxies in Herschel Space Telescope data and Institut de Radioastronomy Millimetrique (IRAM) 30m telescope data. The (sub-)mm data of ~60 radio galaxies were reduced in search of molecular gas outflows in CO. No outflow was detected due to the low integration times (for CO in emission) and due to the low probability of clouds being in front of the radio core (for CO in absorption). Contrarily, the detection fraction was high for the ~90 active galactic nuclei (AGN) in the entire Herschel archive. Up to 50% of the sources that were examined in various OH lines showed outflow signatures (Dasyra et al. 2017; in prep.). The study of the volume density of winds and their impact on star formation on global scales, will nonetheless require the use of a flux-limited representative sample in the ALMA archive.