STScI Preprint #1232
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by Association of Universities for Research in Astronomy, Inc. (AURA), under NASA contract NAS5-26555.
In this paper, the third of a series dedicated to the investigation of the nuclear properties of spiral galaxies, we have (i) modelled the WFPC2 F606W nuclear surface brightness profiles of 41 spiral galaxies presented in Carollo et al. 1997c, 1998 with the analytical law introduced by Lauer et al. 1995, and (ii) deprojected these surface brightness profiles and their analytical fits, so as to estimate the nuclear stellar densities of bulges of spiral galaxies. We find that the nuclear stellar cusps (quantified by the average logarithmic slope of the surface brightness profiles within 0.1"-0.5") are significantly different for R1/4-law and exponential bulges. The former have nuclear properties similar to those of early-type galaxies, i.e., similar values of nuclear cusps for comparable luminosities, and increasingly steeper stellar cusps with decreasing luminosity. By contrast, exponential bulges have (underlying the light contribution from photometrically distinct, central compact sources) comparative shallower stellar cusps, and likely lower nuclear densities, than R1/4-law bulges.
1)Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
2) Hubble Fellow.
3) On assignment from the Space Science Dept. of the
European Space Agency.
4) Johns Hopkins
University, 3701 San Martin Drive, Baltimore, MD 21218.
5) On leave from the Scuola Normale
Superiore, Piazza dei Cavalieri 7, I56126 Pisa, Italy.