Day 1459

Friday.


1808.09974
Detecting the orbital motion of nearby supermassive black hole binaries with Gaia
D'Orazio, Loeb

Show that a 5yr Gaia mission could astrometrically detect the orbital motion of up to a hundred supermassive black hole binaries with sub-parsec separations in the hearts of nearby, bright active galactic nuclei (AGN).  The AGN lie out to a redshift of z=0.1 and in the V-band magnitude range 12<m_V<16.  The distribution of detectable binary masses peaks around 1e8 solar masses and is truncated above 1e9 Msun.


1808.10051
Improving Hickson-like compact group finders in redshift surveys: an implementation in the SDSS
Diaz-Gimenez et al

Present an algorithm to identify compact groups (CGs) that close follows Hickson's original aim and that improves the completeness of the samples of compact groups obtained from redshift surveys.  Instead of identifying CGs in projection first and then checking a velocity concordance criterion, identify them directly in redshift space using Hickson-like criteria.  The methodology was tested on a mock light cone of galaxies built from the outputs of a recent semi-analytic model of galaxy formation run on top of the Millennium Simulation I after scaling to represent the first-year Planck cosmology.  The new algorithm identifies nearly twice as meany CGs, no longer missing CGs that failed the isolation criterion because of velocity outliers lying in the isolation annulus.  The new CG sample picks up lower surface brightness groups, which are both looser and with fainter brightest galaxies, missed by the classic method.  A new catalogue of compact groups from SDSS is the natural corollary of this study.  The publicly available sample comprises 462 observational groups with four or more galaxy members, of which 406 clearly fulfill all the compact group requirements: compactness, isolation, and velocity concordance of all of their members.  The remaining 56 groups need further redshift information of potentially contaminating sources.  This constitutes the largest sample of groups that strictly satisfy all the Hickson's criteria in a survey with available spectroscopic information.


1808.10057
Forecasting gamma-ray bursts using gravitational waves
Akcay

Explore the intriguing possibility of employing future ground-based gravitational-wave interferometers to detect the inspired of binary neutron stars sufficiently early to alert EM observatories so that gamma-ray burst (GRB) can be observed in its entirety from its very beginning.  Quantify the ability to predict a GRB by computing the time a binary neutron star (BNS) system takes to inspire from its moment of detection to its final merger.  Define the moment of detection to be the instant at which the interferometer network accumulates a signal-to-noise ratio of 15.  For the computations, specifically consider BNS systems at luminosity distances of (i) D<=200 Mpc for the 3-interferometer advanced LIGO-Virgo network of 2020, and (ii) D<=1000 Mpc for Einstein Telescope's B and C configurations.  In the case of Advanced LIGO-Virgo, find that at best get a few minutes of warning time, thus expect no forecast of GRBs in the 2020s.  On the other hand, Einstein Telescope will provide us with advance warning times of more than 5 hrs for D<=100 Mpc.  Taking one hour as a benchmark advance warning time, obtain a corresponding range of roughly 600 Mpc for the Einstein Telescope C configurations.  Using current BNS merger event rates within this volume, show that Einstein C will forecast >~O(1e2) GRBs in the 2030s.  Reapply the warning-time computation to binary BH - NS inspires and find 1 to 3 tidal disruption events to be forecast by the same detector.  This is a pedagogical introduction to gravitational-wave astronomy written at a level accessible to PhD students, advanced under graduates, and colleagues in astronomy/astrophysics who wish to learn more about the underlying physics.  Though many of the results may be known to the experts, they might nonetheless find this article motivating and exciting.