Galaxy formation and evolution

Abstract:

We describe a correlation between the mass Mbh of a galaxy's central black hole and the luminosity-weighted line-of-sight velocity dispersion σe within the half-light radius. The result is based on a sample of 26 galaxies, including 13 galaxies with new determinations of black hole masses from Hubble Space Telescope measurements of stellar kinematics. The best-fit correlation is Mbh = 1.2(±0.2) × 108 M⊙(σe/200 km s-1)3.75 (±0.3)over almost 3 orders of magnitude in Mbh; the scatter in Mbh at fixed σe is only 0.30 dex, and most of this is due to observational errors. The Mbh-σe relation is of interest not only for its strong predictive power but also because it implies that central black hole mass is constrained by and closely related to properties of the host galaxy's bulge.

Abstract:

We report the serendipitous discovery of two objects close in projection with fairly strong emission lines at long wavelength (λ ∼ 9190 Å). One (A) seems not to be hosted by any galaxy brighter than V555 = 27.5, or I814 = 26.7 (Vega-based 3 σ limits in 1″.0 diameter apertures), while the other line is associated with a faint (I814 ≃ 24.4) red galaxy (B) offset by 2″.7 and 7 Å spectrally. Both lines are broad (FWHM ≈ 700 km s-1), are extended spatially, and have high equivalent widths [Wobsλ(A) > 1225 Å, 95% confidence limit; Wobsλ(B) ≈ 150 Å]. No secondary spectral features are detected for galaxy A. Blue continuum and the marginal detection of a second weak line in the spectrum of galaxy B is consistent with [O II] (the strong line) and Mg II (the weak line) at z = 1.466. By association, galaxy A is likely at z = 1.464, implying a rest-frame equivalent width of the [O II] emission line in excess of 600 Å and a projected separation of 30 h-150 kpc for the galaxy pair. Conventional wisdom states that isolated emission lines with rest-frame equivalent widths larger than ∼ 200 Å are almost exclusively Lyα. This moderate-redshift discovery therefore compromises recent claims of high-redshift Lyα emitters for which other criteria (i.e., line profile, associated continuum decrements) are not reported. We discuss observational tests to distinguish Lyα emitters at high redshift from foreground systems.