Galaxy formation and evolution

Abstract:

Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 10(10) times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1-4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 10(10) times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy's low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

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.