8 research outputs found
Negative Energy and Angular Momentum Modes of Thin Accretion Disks
This work derives the linearized equations of motion, the Lagrangian density,
the Hamiltonian density, and the canonical angular momentum density for general
perturbations [ with ] of a geometrically
thin self-gravitating, homentropic fluid disk including the pressure. The
theory is applied to ``eccentric,'' perturbations of a geometrically
thin Keplerian disk. We find modes at low frequencies relative to the
Keplerian frequency. Further, it shown that these modes can have negative
energy and negative angular momentum. The radial propagation of these low
frequency modes can transport angular momentum away from the inner region
of a disk and thus increase the rate of mass accretion. Depending on the radial
boundary conditions there can be discrete low-frequency, negative-energy,
modes.Comment: 24 pages, 8 figure
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 Arecibo Pisces-Perseus Supercluster Survey. I. Harvesting ALFALFA
We report a multi-objective campaign of targeted 21 cm H i line observations of sources selected from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey and galaxies identified by their morphological and photometric properties in the Sloan Digital Sky Survey. The aims of this program have been (1) to confirm the reality of some ALFALFA sources whose enigmatic nature suggest additional multiwavelength observations; (2) to probe the low signal-to-noise ratio (S/N) regime, below the ALFALFA reliability limit; and (3) to explore the feasibility of using optical morphology, color, and surface brightness to identify gas-rich objects in the region of the Pisces-Perseus Supercluster (PPS) whose H i fluxes are below the ALFALFA sensitivity limit at that distance. As expected, the reliability of ALFALFA detections depends strongly on the S/N of the H i line signal and its coincidence with a probable stellar counterpart identified by its optical properties, suggestive of ongoing star formation. The identification of low-mass, star-forming populations enables targeted H i line observations to detect galaxies with H i line fluxes below the ALFALFA sensitivity limits in fixed local volumes (D < 100 Mpc). The method explored here serves as the basis for extending the sample of gas-bearing objects as part of the ongoing Arecibo Pisces-Perseus Supercluster Survey (APPSS). © 2019. The American Astronomical Society. All rights reserved.This work has been supported by NSF grants AST-1211005, AST-1637339, and AST-1637271. R.G., M.P.H., L.L., and M.G.J. acknowledge support from NSF grants AST-1107390 and AST-1714828 and by grants from the Brinson Foundation. M.G.J. acknowledges support from the grant AYA2015-65973-C3-1-R (MINECO/FEDER, UE).Peer Reviewe