Friday, 19 June 2009

Velocity dispersion at z~2

from van Dokkum, Kriek, & Franx 2009,

This paper presents the first directly-measured velocity dispersion of a compact quiescent galaxy at z~2. A dispersion of 510 (+165, -95) km/s is measured by fitting galaxy templates to an ultra-deep near-IR (Gemini) spectrum; the dispersion uncertainty is calculated through Monte Carlo simulations.

Such a high dispersion is unparalleled in the local universe, as shown in the figure above. Candidate high-sigma objects were already known, but the dispersions in these cases were indirect (inferred from masses and radii) and so it was conceivable that systematic effects could have been at play. Reassuringly, the stellar masses inferred from SED fitting and the velocity dispersion are in decent agreement with each other, so the previous results apparently are not just due to severely overestimated masses.

No comments: