A direct measurement of the high-mass end of the velocity dispersion function at z ∼ 0.55 from SDSS-III/BOSS

• Published in: Monthly notices of the Royal Astronomical Society Vol. 468; no. 1; pp. 47 - 58
• Main Authors: Montero-Dorta, Antonio D., Bolton, Adam S., Shu, Yiping
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 11.06.2017; Royal Astronomical Society
• Subjects: ASTRONOMY AND ASTROPHYSICS; galaxies: evolution; galaxies: statistics; methods: analytical; methods: statistical; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; surveys; methods: analytical; surveys; gala-xies: statistics; methods: statistical; galaxies: evolution
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx321

Abstract We report the first direct spectroscopic measurement of the velocity dispersion function (VDF) for the high-mass red sequence (RS) galaxy population at redshift z ∼ 0.55. We achieve high precision by using a sample of 600 000 massive galaxies with spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third Sloan Digital Sky Survey (SDSS-III), covering stellar masses M * ≳ 1011 M⊙. We determine the VDF by projecting the joint probability density function (PDF) of luminosity L and velocity dispersion σ, i.e. p(L, σ), defined by our previous measurements of the RS luminosity function and L–σ relation for this sample. These measurements were corrected from red–blue galaxy population confusion, photometric blurring, incompleteness and selection effects within a forward-modelling framework that furthermore correctly accommodates the low spectroscopic signal-to-noise ratio of individual BOSS spectra. Our z ∼ 0.55 RS VDF is in overall agreement with the z ∼ 0 early-type galaxy (ETG) VDF at log10 σ ≳ 2.47; however, the number density of z = 0.55 RS galaxies that we report is larger than that of z = 0 ETG galaxies at 2.35 ≳ log10 σ ≳ 2.47. The extrapolation of an intermediate-mass L–σ relation towards the high-mass end in previous low-z works may be responsible for this disagreement. Evolutionary interpretation of this comparison is also subject to differences in the way the respective samples are selected; these differences can be mitigated in future work by analysing z = 0 SDSS data using the same framework presented in this paper. We also provide the sample PDF for the RS population (i.e. uncorrected for incompleteness), which is a key ingredient for gravitational lensing analyses using BOSS.