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This is the homepage of the of the weekly Astrophysics journal club at the Division of Particle physics and astrophysics at the University of Helsinki. The meetings are of an unofficial nature and the main driver is to get together and discuss recent interesting papers. This meeting differs from the Seminar series in that people are not expected to talk about their own research and in that no credits will be awarded to students. The meetings are open to everyone and the aim is to stimulate discussion about recent results and provide the possibility to
 learn about research that is not necessarily connected to one's own field of expertise.

All topics are welcome ranging from planetary science to larger scales involving stellar
 astrophysics, Milky Way studies, galaxies and cosmology.
The only requirement is that the
 presented papers should be interesting to a wider audience and that they should be presented 
in such a way that also a non-expert can follow the presentation. In the meetings we discuss one paper each week for about 45 minutes.
 All meetings are in English.

Location: Conference room C310 on the third floor.

Time: Thursdays at 10.15-11.00am during term time.

Speakers: Please contact Peter Johansson, Mikael Granvik or Clif Kirkpatrick if you want to present a paper.

Present Program: The next talk will be on the 12th of December

Presenter: Akke Viitanen:
Paper title: Constraining black hole-galaxy scaling relations from the large-scale clustering of Active Galactic Nuclei and implied mean radiative efficiency
Authors: Shankar, F., Allevato, V., Bernardi, M. et al.
Reference: 2019, Nature Astronomy in press, ArXiv: 1910.10175

Abstract: A supermassive black hole has been found at the centre of nearly every galaxy observed with sufficient sensitivity. The masses of these black holes are observed to increase with either the total mass or the mean (random) velocity of the stars in their host galaxies. The origin of these correlations remains elusive. Observational systematics and biases severely limit our knowledge of the local demography of supermassive black holes thus preventing accurate model comparisons and progress in this field. Here we show that the large-scale spatial distribution of local active galactic nuclei (AGN), believed to be accreting supermassive black holes, can constrain the shape and normalization of the black hole-stellar mass relation thus bypassing resolution-related observational biases. In turn, our results can set more stringent constraints on the so-called "radiative efficiency", a fundamental parameter describing the inner physics of supermassive black holes that is closely linked to their spin, geometry, and ability to release energy. The mean value of the radiative efficiency can be estimated by comparing the average total luminous output of AGN with the relic mass density locked up in quiescent supermassive black holes at galaxy centres today. For currently accepted values of the AGN obscured fractions and bolometric corrections, our newest estimates of the local supermassive black hole mass density favour mean radiative efficiencies of ~10-20\%, suggesting that the vast majority of supermassive black holes are spinning moderately to rapidly. With large-scale AGN surveys coming online, our novel methodology will enable even tighter constraints on the fundamental parameters that regulate the growth of supermassive black holes. 

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