Galactic bulges from hubble space telescope NICMOS observations: Global scaling relations

We investigate bulge and disk scaling relations using a volume-corrected sample of early-to intermediate-type disk galaxies in which, importantly, the biasing 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 surface brightness profiles spanning similar to 10 pc to the outer disk. Bulge and disk parameters, and bulge-to-disk ratios, are analyzed as a function of bulge luminosity, disk luminosity, galaxy central velocity dispersion, and galaxy Hubble type. Mathematical expressions are given for the stronger relations, which can be used to test and constrain galaxy formation models. Photometric parameters of both bulges and disks are observed to correlate with bulge luminosity and with central velocity dispersion. In contrast, for the unbarred, early to intermediate types covered by the sample, Hubble type does not correlate with bulge and disk components, nor their various ratios. In this sense, the early-to-intermediate spiral Hubble sequence is scale free. However, galaxies themselves are not scale free, the critical scale being the luminosity of the bulge. Bulge luminosity is shown to affect the disk parameters, such that central surface brightness becomes fainter, and scale length bigger, with bulge luminosity. The lack of significant correlations between bulge parameters (size, luminosity, or density) on disk luminosity, remains a challenge for secular evolution models of bulge growth. The average near-infrared bulge-to-total flux ratio for our S0-S0a galaxies is 0.25 (+/- 0.09).