X-rays across the galaxy population: tracing star formation and AGN activity

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• James Aird (Leicester)
• Wednesday 17 October 2018, 14:30-15:30
• Physics West 117.

If you have a question about this talk, please contact Sean McGee.

I will present new work from a series of papers that combines large samples of galaxies with deep Chandra X-ray data to measure the distribution of X-ray luminosities across the galaxy population, using a sophisticated Bayesian technique. Our measurements allow us to trace two origins of the X-ray emission: star formation and AGN activity.

At low luminosities, we identify narrow peaks that we associate with star formation processes (tracing the combined emission from X-ray binaries throughout the galaxy). By tracking the position of these peaks as a function of stellar mass and redshift we provide new, independent measurements of the galaxy “star-forming main sequence”, based on the X-ray emission.

We also identify a tail in our distributions to higher X-ray luminosities that allows us to trace the incidence of AGN . We use these data to measure the distribution of AGN accretion rates across the galaxy population, as a function of stellar mass, redshift and star formation rate. Our results reveal a broad distribution of accretion rates in all galaxy types, reflecting the flickering of AGN accretion on short timescales relative to the evolution of galaxy properties. In star-forming galaxies, we find a broad correlation between the star formation rate and the incidence of AGN (traced by the fraction of galaxies with AGN and the average specific accretion rates), indicating the key role of cold gas in AGN fuelling. We also measure the AGN incidence in galaxies with a wider range of star formation rates at a fixed stellar mass, spanning the star-forming main sequence and quiescent galaxy populations. These measurements show enhancements in the incidence of AGN and reveal the variety of mechanisms that drive black hole growth across the galaxy population.

Paper I: http://adsabs.harvard.edu/abs/2017MNRAS.465.3390A

Paper II: http://adsabs.harvard.edu/abs/2018MNRAS.474.1225A

Paper III : https://arxiv.org/abs/1810.04683

This talk is part of the Astrophysics Talks Series series.

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• Astrophysics Talks Series
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• Physics West 117
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