Giulia Savorgnan (Swinburne Uni)

Giulia Savorgnan Colloquium: Supermassive black holes at z=0

Marsfield

Abstract

Supermassive black holes in local galaxies obey a surprisingly large number of scaling laws that involve the black hole mass and various properties of the host spheroid or galaxy. These "black hole mass scaling relations" reveal a strong symbiosis between galaxies and black holes, define important constraints about their co-evolution through the cosmic time, and set the boundary conditions (at z = 0) for theoretical models and simulations of galaxy evolution. Using Spitzer observations at 3.6 um, which is the best available wavelength band to trace the stellar mass, we performed state-of-the-art structural decompositions for 66 galaxies with a direct measure of their black hole mass. Thanks to a meticulous inspection of each galaxy's substructure - by means of photometric and isophotal analysis, unsharp masking, auxiliary information extracted from the literature, and, for the first time, kinematic maps - we were able to identify a priori the physical galaxy components. In this contribution, I will present updates and modifications to several black hole mass scaling relations, and discuss important implications for galaxy evolution models. In addition, I will address the issue of "overmassive" black holes in the M-sigma and M-L diagrams. Black holes that appear to be overmassive compared to expectations from the stellar velocity dispersion have been theoretically explained with their host galaxies having experienced more dry mergers than any other galaxy. In spite of that, we present empirical evidence supporting a scenario where the host galaxies of such overmassive black holes have undergone the lowest degree of dry merging. Claims of four overmassive black holes in the M-L diagram will be debunked by demonstrating that the luminosity of their host spheroids had been considerably underestimated. These four spheroids are unevolved relics of z = 2 quiescent compact massive spheroids, and I will confer about the important consequences of this.