Isothermal Bondi accretion in Jaffe and Hernquist galaxies with a central black hole: fully analytical solutions

One of the most active fields of research of modern-day astrophysics is that of massive black hole formation and co-evolution with the host galaxy. In these investigations, ranging from cosmological simulations, to semi-analytical modeling, to observational studies, the Bondi solution for accretion on a central point mass is widely adopted. In this work we generalize the classical Bondi accretion theory to take into account the effects of the gravitational potential of the host galaxy, and of radiation pressure in the optically thin limit. Then, we present the fully analytical solution, in terms of the Lambert-Euler $W$-function, for isothermal accretion in Jaffe and Hernquist galaxies with a central black hole. The flow structure is found to be sensitive to the shape of the mass profile of the host galaxy. These results and the formulae that are provided, mostly important the one for the critical accretion parameter, allow for a direct evaluation of all flow properties, and are then useful for the above mentioned studies. As an application, we examine the departure from the true mass accretion rate of estimates obtained using the gas properties at various distances from the black hole, under the hypothesis of classical Bondi accretion. An overestimate is obtained from regions close to the black hole, and an underestimate outside a few Bondi radii; the exact position of the transition between the two kinds of departure depends on the galaxy model.Comment: 18 pages, 6 figures, submitted to ApJ, comments welcom

Systemic risk determinants in the European banking industry during financial crises, 2006-2012

The recent financial turmoil has stimulated a rich debate in banking and financial literature on the identification of systemic risk determinants and devices to forecast and prevent crises. This paper explores the contribution of corporate variables to systemic risk using the CoVaR approach (Adrian and Brunnermeier, 2016). Using balanced panel data on 141 European banks from 24 countries, which were listed from 2006Q1 to 2012Q4, we investigated the impact of corporate variables during the three regimes that characterised the European banking sector-the subprime crisis (2007Q3-2008Q3), the European Great Financial Depression (2008Q4-2010Q2), and the sovereign debt crisis (2010Q3-2012Q4). Our results show that size did not play a significant role in spreading systemic risk, while maturity mismatch did. However, the nature and intensity of these two determinants varied across the three regimes

Star formation in early-type galaxies: the role of stellar winds and kinematics

Early-type galaxies (ETGs) host a hot ISM produced mainly by stellar winds, and heated by Type Ia supernovae and the thermalization of stellar motions. High resolution 2D hydrodynamical simulations showed that ordered rotation in the stellar component results in the formation of a centrifugally supported cold equatorial disc. In a recent numerical investigation we found that subsequent generations of stars are formed in this cold disc; this process consumes most of the cold gas, leaving at the present epoch cold masses comparable to those observed. Most of the new stellar mass formed a few Gyrs ago, and resides in a disc.Comment: 2 pages, 1 figure, to appear in proceedings of IAU Symposium 315, "From Interstellar Clouds to Star-Forming Galaxies: Universal Processes?", P. Jablonka, F. Van der Tak & P. Andre', ed