The nature of late-type spiral galaxies: structural parameters, optical and near-infrared colour profiles, and dust extinction

TL;DR

This study provides detailed optical and near-infrared photometric profiles, dust extinction maps, and structural parameters for a sample of late-type spiral galaxies, revealing their homogeneous colour profiles and small, diverse bulges.

Contribution

It is the first photometric analysis of late-type spirals with measured stellar kinematics, combining high-resolution HST data with ground-based observations to study their structure and dust properties.

Findings

Colours are homogeneous within galaxies but vary between galaxies.

Most galaxies have small bulges with low Sersic index, often below 2.

Central light excesses are common, likely indicating nuclear clusters.

Abstract

We analyse V and H-band surface photometry of a sample of 18 Sb-Sd galaxies. Combining high resolution HST images with ground-based NIR observations, we extract photometric profiles, which cover the whole disk and provide the highest possible resolution. This is the first photometric study of late-type spirals for which the stellar kinematics have been measured. For 10 out of the 18 galaxies, HST data in both F160W (H) and F606W (V) are available, and, for those, we present colour maps and radial colour profiles at the resolution of the Hubble Space Telescope. Colours vary significantly from galaxy to galaxy, but tend to be highly homogeneous within each galaxy, with smooth and flat colour profiles. Some of the colour maps show jumps in the inner regions, likely due to dust. We determine extinction-maps in an almost model-independent way using the V-H colour map and the SAURON Mg b absorption line map of Ganda et al. (2007). The maps show that A_V ranges from 0 to 2 mag, in the center from 0 to 1.5 mag, in agreement with the models of Tuffs et al. (2004). We describe the surface brightness profiles as the superposition of an exponential disk and a Sersic bulge. The bulges are small (0.1-2.5 kpc), and show a shape parameter n ranging from ~ 0.7 to 3, with a mean value smaller than two: well below the value for the 'classical' de Vaucouleurs bulges. Most galaxies (16 out of 18) show a central light excess above the Sersic fit to the bulge, which can be interpreted as a nuclear cluster, as shown by previous studies. We provide zero-order estimates for the magnitude of these components. We discuss the correlations among the structural galaxy parameters and with other relevant quantities (abridged).