Project duration: ~1 year rotation. Potential to grow into thesis project.
PI: Bethan James (bjames@stsci.edu, www.stsci.edu/~bjames)
The only supermassive black holes we know inhabit the centers of galaxies and the scaling relationships that they satisfy imply hand-in-hand growth of the galaxy and the black hole, suggesting feedback. We have undertaken the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7) project, in which we look for signatures of this in the nearby universe, keeping in mind that all accreting black holes appear to ionize their circumnuclear gas to greater or lesser extent, and also produce bipolar synchrotron jets. In most cases such jets are quenched at about 1~kpc and have radio emission that is not terribly brighter than that from star formation.
To explore the connections between the accretion and circumnuclear star formation, we confine ourselves to galaxies that give several spatial resolution elements across them at multiple frequencies, and access to the SII line in the optical. As such, all galaxies are nearby and lie within z<0.02.
In total, we have 130 galaxies we have WiFeS IFU (integral field unit) data from Siding Spring 2.3m telescope, and for a a subset with GMRT and also ATCA radio imaging. IFU data is very powerful in that it allows us to map spectral maps (via 3D data cubes in x, y, and wavelength). In Figure 1 and 2 below, we show typical IFU images from our WiFeS datasets where the Halpha, NII and OIII emission line maps have been channeled into the red green and blue false color channels. Already we see a trend for star formation often being seen in ring-like features interpreted as the inner Lindbald resonance, where the synchrotron jets are perpendicular to the plane of this ring. In each case, linking the morphology and orientation of the star-forming gas with the alignment of the radio emission strongly suggests secular evolution feeding accretion of the supermassive black hole. In the specific case of the Carafe galaxy (Figure 3), we find signatures of a wet merger (with a binary black hole precursor) and we detect both its accreting central black holes in the emission lines, in the radio with synchrotron-like spectra and with Chandra in X-rays.Throughout this project, these kinds of multi-wavelength data analysis will be used to understand the nature of the feedback occurring within SMBH systems.
The project will involve analyzing the optical IFU WiFeS data; mapping the strong optical emission lines to create emission line maps and diagnostic images to trace signatures of star-formation and ionization from AGN around the SMBH. In order to accurately trace and align the synchrotron emission from jets, as well as understanding this in the context of the host galaxy morphology, analysis of archival multi-wavelength data (e.g. VLA data and HST continuum imaging) will also be needed.
We expect the project to result in at least one publication, which is to be led by the student.
Figure 1: NGC613 - top-left shows WiFeS IFU emission line maps where Halpha, NII and OIII emission line maps have been channeled into the red green and blue false color channels. The orange ring around the center represents a ring of star-formation perpendicular to the synchrotron jet, which can be seen clearly in the bottom right VLA image, originating from the central black hole. The contours from the jet emission are overlaid on the IFU emission line maps in the bottom right panel.
Figure 2: NGC5728. Clockwise from top left: HST continuum image overlaid with radio emission contours (white); the WiFeS IFU emission line maps, where the strong line emission maps have been used to create a color composite image - again a ring of star-formation can be seen perpendicular from the main jet; emission line diagnostic diagram, where points above the black line signify gas ionized by an active galactic nuclei whereas below the line shows gas ionized via photoionized from stars - such diagrams are instrumental in mapping the star-forming gas; radio emission map ; radio emission contours overlaid on the IFU color composite showing the direction of the biconical outflow.
Figure 3: The Carafe Galaxy. Here the WiFeS IFU data showed two accreting black holes (labelled), which clearly aligned with X-ray emission from Chandra data (bottom left panel). This multi-wavelength analysis allowed us to distinguish this galaxy as being a wet merger, with a binary black hole precursor.
