Deep K-band surface brightness photometry of dE galaxies

Abstract

Context. Dwarf elliptical galaxies (dEs) are the most abundant in the Universe. Research into these objects in connection with late-type dwarf galaxies is important for evaluating theories of dwarf galaxy formation and evolution. Aims. Our past studies (2000-2010) suggested a possible evolutionary link between early- and late-type dwarf galaxies. These results are based on deep near-infrared (NIR) surface photometry data of dwarf irregulars (dIs), blue compact dwarfs (BCDs), and a small sample of Virgo dEs. As a continuation of those works, in 2017 we embarked on a study of dEs using the same surface photometry methods, with the aim being to compare early- and late-type dwarfs based on homogeneous datasets. Methods. We selected 74 dEs from two different environments for which we obtained deep images. Isophotal analysis was performed on the images to obtain surface brightness profiles. The two sampled environments were the Local Volume and Virgo cluster, which provide the possibility to compare isolated evolution against evolution in crowded environments. To compare dwarf datasets homogeneously, we used the NIR Ks band which is known to be a better gauge of galaxy mass, with reduced extinction compared to visible bands. Results. In this first paper, we derive apparent physical parameters for 72 dEs from deep NIR imaging and provide preliminary fitting results of their surface brightness profiles. Two targets were undetected in the Ks images, indicating possible misclassification. Physical parameters of 16 dEs are measured for the first time and the parameters of the remaining 56 dEs are compared with the literature. We obtain a mean difference between the measured physical parameters and the results from prior studies of about 0.2″ for the galaxy center coordinates, ≈20″ for the semi-major axis, ≈0.4 mag for the total apparent magnitude, ≈0.11 for the ellipticity, and ≈14° for the position angle. We find well-fitting surface brightness profiles for the dEs using the hyperbolic secant (sech) model combined with an exponential component. Alternatively, we find good agreement with observations for a sech plus a de Vaucouleurs law.