The sigma - L correlation in Nearby Early-Type Galaxies

Abstract

Early-type galaxy velocity dispersions and luminosities are correlated. The correlation estimated in local samples (< 100 Mpc) differs from that measured more recently in the SDSS. This is true even when systematics in the SDSS photometric and spectroscopic parameters have been accounted-for. We show that this is also true for the ENEAR sample if galaxy luminosities are estimated using distances which have been corrected for peculiar motions. We then show that, because the estimate of the `true' distance is derived from a correlation with velocity dispersion, in this case the D_n-sigma relation, using it in the sigma-L relation leads to an artificially tight relation with a biased slope. Making no correction for peculiar velocities results in a sigma-L relation which is very similar to that of the SDSS, although with larger scatter. We also measure the sigma-L correlation in a mock ENEAR catalog, in which the underlying galaxy sample has the same sigma-L correlation as seen in the SDSS. The mock catalog produces the same D_n-sigma relation as the data, the same biased slope when D_n-sigma distances are used to estimate luminosities, and good agreement with the input sigma-L relation when redshift is used as the distance indicator. This provides further evidence that the true sigma-L relation of ENEAR galaxies is indeed very similar to that of SDSS early-types. Our results suggest that local sigma-L relations which are based on Fundamental Plane distances should also be re-evaluated. Our findings also have important implications for black hole demographics; the best direct estimates of the masses of supermassive black holes come from local galaxies, so estimates of the black hole mass function are more safely made by working with the Mbh-sigma correlation than with Mbh-L.

9 pages, 9 figures. Accepted by AJ. A new appendix describes systematics effects we found in the SDSS velocity dispersion measurements (sigmas < 150 km/s are biased towards larger values; this bias was not present in the Bernardi et al. 2003 sample) and luminosity measurements

Cited by in corpus (7)

• Curvature in the scaling relations of early-type galaxies
• Dissecting the Red Sequence--I. Star Formation Histories of Quiescent Galaxies: The Color-Magnitude vs. the Color-Sigma Relation
• The SDSS-UKIDSS Fundamental Plane of Early-type Galaxies
• A Search for the Most Massive Galaxies. II. Structure, Environment and Formation
• The Kormendy Relation for early-type galaxies. Dependence on the magnitude range
• The Fundamental Plane for early-type galaxies. Dependence on the magnitude range
• The effects of stellar populations on galaxy scaling relations in the 6dF Galaxy Survey