Galactic Bulges fromHubble Space TelescopeNICMOS Observations: Global Scaling Relations

We investigate bulge and disk scaling relations using a volume-correctedsample of early- to intermediate-type disk galaxies in which, importantly, thebiasing flux from additional nuclear components has been modeled and removed.Structural parameters are obtained from a seeing-convolved,bulge+disk+nuclear-component decomposition applied to near-infrared surfacebrightness profiles spanning ~10 pc to the outer disk. Bulge and diskparameters, and bulge-to-disk ratios, are analyzed as a function of bulgeluminosity, disk luminosity, galaxy central velocity dispersion, and galaxyHubble type. Mathematical expressions are given for the stronger relations,which can be used to test and constrain galaxy formation models. Photometricparameters of both bulges and disks are observed to correlate with bulgeluminosity and with central velocity dispersion. In contrast, for the unbarred,early to intermediate types covered by the sample, Hubble type does notcorrelate with bulge and disk components, nor their various ratios. In thissense, the early-to-intermediate spiral Hubble sequence is scale-free. However,galaxies themselves are not scale-free, the critical scale being the luminosityof the bulge. Bulge luminosity is shown to affect the disk parameters, suchthat central surface brightness becomes fainter, and scale-length bigger, withbulge luminosity. The lack of significant correlations between bulgepararmeters (size, luminosity or density) on disk luminosity, remains achallenge for secular evolution models of bulge growth.Comment: Accepted by Ap