Galaxy formation and evolution

Abstract:

We present basic properties of ∼3,300 emission line galaxies detected by the FastSound survey, which are mostly Hα emitters at z ∼ 1.2–1.5 in the total area of about 20 deg2 , with the Hα flux sensitivity limit of ∼ 1.6 × 10−16 erg cm−2 s −1 at 4.5 sigma. This paper presents the catalogs of the FastSound emission lines and galaxies, which is open to the public. We also present basic properties of typical FastSound Hα emitters, which have Hα luminosities of 1041.8–1043.3 erg/s, SFRs of 20–500 M⊙/yr, and stellar masses of 1010.0–1011.3 M⊙. The 3D distribution maps for the four fields of CFHTLS W1–4 are presented, clearly showing large scale clustering of galaxies at the scale of ∼ 100–600 comoving Mpc. Based on 1,105 galaxies with detections of multiple emission lines, we estimate that contamination of non-Hα lines is about 4% in the single-line emission galaxies, which are mostly [OIII]λ5007. This contamination fraction is also confirmed by the stacked spectrum of all the FastSound spectra, in which Hα, [NII]λλ6548,6583, [SII]λλ6717,6731, and [OI]λλ6300,6364 are seen.

Abstract:

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Most, if not all, stars in the field are born in binary configurations or higher multiplicity systems. In dense stellar environment such as the Galactic Center (GC), many stars are expected to be in binary configurations as well. These binaries form hierarchical triple-body systems, with the massive black hole (MBH) as the third, distant object. The stellar binaries are expected to undergo large-amplitude eccentricity and inclination oscillations via the so-called 'eccentric Kozai-Lidov' mechanism. These eccentricity excitations, combined with post-main-sequence stellar evolution, can drive the inner stellar binaries to merge. We study the mergers of stellar binaries in the inner 0.1 pc of the GC caused by gravitational perturbations due to the MBH. We run a large set of Monte Carlo simulations that include the secular evolution of the orbits, general relativistic precession, tides and post-main-sequence stellar evolution. We find that about 13 per cent of the initial binary population will have merged after a few Myr and about 29 per cent after a few Gyr. These expected merged systems represent a new class of objects at the GC, and we speculate that they are connected to G2-like objects and the young stellar population.