Central structural parameters of early-type galaxies as viewed with NICMOS on the Hubble Space Telescope

We present surface photometry for the central regions of a sample of 33 early-type (E, S0, and S0/a) galaxies observed at 1.6 mum (H band) using the Hubble Space Telescope. Dust absorption has less of an impact on the galaxy morphologies in the near-infrared than found in previous work based on observations at optical wavelengths. When present, dust seems to be most commonly associated with optical line emission. We employ a new technique of two-dimensional fitting to extract quantitative parameters for the bulge light distribution and nuclear point sources, taking into consideration the effects of the point-spread function. By parameterizing the bulge profile with a Nuker law, we confirm that the central surface brightness distributions largely fall into two categories, each of which correlates with the global properties of the galaxies. "Core" galaxies tend to be luminous elliptical galaxies with boxy or pure elliptical isophotes, whereas "power-law" galaxies are preferentially lower luminosity systems with disky isophotes. The infrared surface brightness profiles are very similar to those in the optical, with notable exceptions being very dusty objects. Similar to the study of Faber et al., based on optical data, we find that galaxy cores obey a set of fundamental plane relations wherein more luminous galaxies with higher central stellar velocity dispersions generally possess larger cores with lower surface brightnesses. Unlike most previous studies, however, we do not find a clear gap in the distribution of inner cusp slopes; several objects have inner cusp slopes (0.3 <<gamma><0.5) that straddle the regimes conventionally defined for core and power-law galaxies. The nature of these intermediate objects is unclear. We draw attention to two objects in the sample that appear to be promising cases of galaxies with isothermal cores that are not the brightest members of a cluster. Unresolved nuclear point sources are found in <similar to>50% of the sample galaxies, roughly independent of profile type, with magnitudes in the range m(H)(nuc) = 12.8 to 17.4 mag, which corresponds to M-H(nuc) = -12.8 to -18.4 mag. Although the detection rate of compact nuclei seems favored toward galaxies spectroscopically classified as weak active galactic nuclei, we find no significant correlation between the near-infrared nuclear luminosities and either the optical emission-line luminosities or the inferred black hole masses.