2015/05/20 by Amy Kimball, Mark Lacy, Kimball, Amy E +4
Physics and Astronomy · Engineering · Decision Sciences · #Astrophysical Phenomena and Observations #Mechanics and Biomechanics Studies #Scientific Measurement and Uncertainty Evaluation
paper · pdf · doi:10.48550/arxiv.1505.05262
We present observations and analysis of an unusual [C II] emission line in\nthe very luminous QSO SDSS J155426.16+193703.0 at z~4.6. The line is extremely\nbroad (FWHM 735 km/s) and seems to have a flat-topped or double-peaked line\nprofile. A velocity map of the line shows a gradient across the source that\nindicates large-scale rotation of star-forming gas. Together, the velocity map\nand line profile suggest the presence of a massive rotating disc with a\ndynamical mass Mdyn > 5x1010 Msun. Using the assumption of a rotating disc\norigin, we employ an empirical relation between galaxy disc circular velocity\nand bulge velocity dispersion (sigma) to estimate that sigma > 310 km/s,\nsubject to a correction for the unknown disc inclination. This result implies\nthat this source is consistent with the local M--sigma relation, or offset at\nmost by an order of magnitude in black hole mass. In contrast, the assumption\nof a bulge origin for the [C II] emission line would lead to a conclusion that\nthe black hole is nearly two orders of magnitude more massive than predicted by\nthe M--sigma relation, similar to previous findings for other high-redshift\nQSOs. As disc rotation may be a common origin for [C II] emission at high\nredshifts, these results stress that careful consideration of dynamical origins\nis required when using observations of this line to derive properties of\nhigh-redshift galaxies.\n