Abstract
Parsec-scale massive black hole binaries (MBHBs) are expected to form in
hierarchical models of structure formation. Even though different observational
strategies have been designed to detect these systems, a theoretical study is a
further guide for their search and identification. In this work, we investigate
the hosts properties and the electromagnetic signatures of massive black holes
gravitationally bound on parsec-scales with primary mass $\rm
>\,10^7\,M_ødot$. For that, we construct a full-sky lightcone by the use
of the semi-analytical model L-Galaxies in which physically motivated
prescriptions for the formation and evolution of MBHBs have been included. Our
predictions show that the large majority of the MBHBs are placed either in
spiral galaxies with a classical bulge structure or in elliptical galaxies.
Besides, the scaling relations followed by MBHBs are indistinguishable from the
ones of single massive black holes. We find that the occupation fraction of
parsec-scale MBHBs reaches up to $\sim\,50\%$ in galaxies with $\rm
M_stellar\,>\,10^11\, M_ødot$ and drops below 10\% for $\rm
M_stellar\,<\,10^11\, M_ødot$. Our model anticipates that the majority
of parsec-scale MBHBs are unequal mass systems and lie at $z\,\sim\,0.5$,
with $\sim\,20$ objects per $deg^2$ in the sky. However, most of these
systems are inactive, and only $1\,-\,0.1$ objects per $deg^2$ have an
electromagnetic counterpart with a bolometric luminosity in excess of $10^43$
erg/s. Very luminous phases of parsec-scale MBHBs are more common at
$z\,>\,1$ but the number of binaries per $deg^2$ is $łesssim\,0.01$ at
$L_bol\,>\,10^45 erg/s$.
Description
Unveiling the hosts of parsec-scale massive black hole binaries: morphology and electromagnetic signatures
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