18 research outputs found
Sub-parsec supermassive Binary Quasars: expectations at z<1
We investigate the theoretical expectations for detections of supermassive
binary black holes that can be identified as sub-parsec luminous quasars.
To-date, only two candidates have been selected in a sample comprising 17,500
sources selected from the Sloan Digital Sky Survey (SDSS) Quasar Catalog at
z<0.70 (Boroson & Lauer 2009) In this Letter, we use models of assembly and
growth of supermassive black holes (SMBHs) in hierarchical cosmologies to study
the statistics and observability of binary quasars at sub-parsec separations.
Our goal is twofold: (1) test if such a scarce number of binaries is consistent
with theoretical prediction of SMBH merger rates, and (2) provide additional
predictions at higher redshifts, and at lower flux levels. We determine the
cumulative number of expected binaries in a complete, volume limited sample.
Motivated by Boroson & Lauer (2009), we apply the SDSS Quasar luminosity cut
(M_i<-22) to our theoretical sample, deriving an upper limit to the observable
binary fraction. We find that sub-parsec quasar binaries are intrinsically
rare. Our best models predict ~0.01 deg^-2 sub-parsec binary quasars with
separations below ~10^4 Schwarzschild radii (v_orb>2000 km/s) at z<0.7, which
represent a fraction ~6x10^-4 of unabsorbed quasars in our theoretical sample.
In a complete sample of ~10,000 sources, we therefore predict an upper limit of
~10 sub-parsec binary quasars. The number of binaries increases rapidly with
increasing redshift. The decreasing lifetime with SMBH binary mass suggests
that lowering the luminosity threshold does not lead to a significant increase
in the number of detectable sub-parsec binary quasars.Comment: ApJ Letters, in pres
Supermassive Black Hole Binaries: The Search Continues
Gravitationally bound supermassive black hole binaries (SBHBs) are thought to
be a natural product of galactic mergers and growth of the large scale
structure in the universe. They however remain observationally elusive, thus
raising a question about characteristic observational signatures associated
with these systems. In this conference proceeding I discuss current theoretical
understanding and latest advances and prospects in observational searches for
SBHBs.Comment: 17 pages, 4 figures. To appear in the Proceedings of 2014 Sant Cugat
Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed.
C.Sopuerta (Berlin: Springer-Verlag
The Gravitational Universe
The last century has seen enormous progress in our understanding of the Universe. We know the life cycles of stars, the structure of galaxies, the remnants of the big bang, and have a general understanding of how the Universe evolved. We have come remarkably far using electromagnetic radiation as our tool for observing the Universe. However, gravity is the engine behind many of the processes in the Universe, and much of its action is dark. Opening a gravitational window on the Universe will let us go further than any alternative. Gravity has its own messenger: Gravitational waves, ripples in the fabric of spacetime. They travel essentially undisturbed and let us peer deep into the formation of the first seed black holes, exploring redshifts as large as z ~ 20, prior to the epoch of cosmic re-ionisation. Exquisite and unprecedented measurements of black hole masses and spins will make it possible to trace the history of black holes across all stages of galaxy evolution, and at the same time constrain any deviation from the Kerr metric of General Relativity. eLISA will be the first ever mission to study the entire Universe with gravitational waves. eLISA is an all-sky monitor and will offer a wide view of a dynamic cosmos using gravitational waves as new and unique messengers to unveil The Gravitational Universe. It provides the closest ever view of the early processes at TeV energies, has guaranteed sources in the form of verification binaries in the Milky Way, and can probe the entire Universe, from its smallest scales around singularities and black holes, all the way to cosmological dimensions
EMISSION SIGNATURES FROM SUB-PARSEC BINARY SUPERMASSIVE BLACK HOLES. I. DIAGNOSTIC POWER OF BROAD EMISSION LINES
The Gravitational Universe
20 pages; submitted to the European Space Agency on May 24th, 2013 for the L2/L3 selection of ESA's Cosmic Vision programThe last century has seen enormous progress in our understanding of the Universe. We know the life cycles of stars, the structure of galaxies, the remnants of the big bang, and have a general understanding of how the Universe evolved. We have come remarkably far using electromagnetic radiation as our tool for observing the Universe. However, gravity is the engine behind many of the processes in the Universe, and much of its action is dark. Opening a gravitational window on the Universe will let us go further than any alternative. Gravity has its own messenger: Gravitational waves, ripples in the fabric of spacetime. They travel essentially undisturbed and let us peer deep into the formation of the first seed black holes, exploring redshifts as large as z ~ 20, prior to the epoch of cosmic re-ionisation. Exquisite and unprecedented measurements of black hole masses and spins will make it possible to trace the history of black holes across all stages of galaxy evolution, and at the same time constrain any deviation from the Kerr metric of General Relativity. eLISA will be the first ever mission to study the entire Universe with gravitational waves. eLISA is an all-sky monitor and will offer a wide view of a dynamic cosmos using gravitational waves as new and unique messengers to unveil The Gravitational Universe. It provides the closest ever view of the early processes at TeV energies, has guaranteed sources in the form of verification binaries in the Milky Way, and can probe the entire Universe, from its smallest scales around singularities and black holes, all the way to cosmological dimensions