Near-Infrared Low-Resolution Mapping of Early-Type Spirals

Details Near-Infrared Low-Resolution Mapping of Early-Type Spirals Near-Infrared Low-Resolution Mapping of Early-Type Spirals

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aj....111.1086g&link_type=abstract

Astronomical Journal v.111, p.1086

Astronomy and Astrophysics

Astronomy

16

Galaxies: Spiral, Galaxies: Stellar Content, Infrared: Galaxies

Scientific paper

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 ~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~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 τ_B_(0) ~ 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.

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