Near-infrared low-resolution mapping of early-type spirals

We present low-resolution near-infrared (NIR: J,H,K) radial brightness and color profiles of a sample of eight early-type spirals. The brightness distribution was sampled along the major axis by shifting a fixed 28 '' aperture in steps of 14 '' using a single-element InSb photometer. We first examine the J-H and H-K radial profiles: (i) there is no evidence for large-scale radial gradients in the NIR colors; (ii) the distribution of (central) colors is remarkably tight, with standard deviation of similar to 0.05 mag; (iii) NIR colors do not show any clear dependence on galaxy inclination; (iv) H-K colors are similar to those observed in late-type spirals, while J-H is significantly redder. Second, we fit a composite model of bulge+disk to the radial brightness profiles. In the cases where the decomposition is successful we find that: (i) bulge-to-disk ratios tend to be higher than at optical wavelengths; (ii) disk scale lengths are shorter than in the optical, as we previously observed in a sample of Sc spirals; (iii) early-type spiral disks tend to be brighter, in terms of central surface brightness, than those of later types; (iv) by comparing our NIR bulge effective brightness with the optical one, as measured by other authors, we derive quite red colors, r-J similar to 2. Third, we calculate NIR mass-to-light (M/L) ratios for the central regions. When compared with those for a sample of Sc's studied in a previous paper, Sa's tend to have smaller NIR M/L ratios than Sc's, at least in their central regions. We attribute these properties to the presence of a metal-rich bulge population combined with the effect of extinction for which we infer an average value tau(B)(0)similar to 3. Finally, we find significant correlations of J-K with both central and total mass content, confirming that metallicity is mainly governed by galaxy mass. (C) 1996 American Astronomical Society.