Dissecting early-type dwarf galaxies into their multiple components. (5th March 2015)

• Record Type: Journal Article
• Authors: Janz, Joachim; Laurikainen, Eija; Lisker, Thorsten; Salo, Heikki
• Editors: Montmerle, Thierry
• Is Part Of: Proceedings of the International Astronomical Union. Volume 10:Number H16(2012)Highlights
• Page Start: 364
• Page End: 364
• Publication Date: 2015-03-05
• Subjects: galaxies: dwarf–galaxies: photometry–galaxies: structure–galaxies: clusters: individual: (Virgo Cluster); Astronomy -- Congresses; Astronomy -- Periodicals; 520
• DOI: 10.1017/S1743921314011363
• Languages: English
• ISSNs: 1743-9213

Abstract

Abstract: Early-type dwarf galaxies are often thought to be either more diffuse versions of giant ellipticals or to be low-mass disk galaxies that were quenched and heated by the environment. In both cases, the picture that most astronomers have in mind probably is that of a dynamically hot, regular shaped galaxy, in which any previous substructure has either been smeared out, or has never been there. However, the early-type dwarfs are not that simple. We analyzed ~100 such objects in the Virgo cluster using deep near-infrared images and found that the majority has a multi-component structure, sometimes even with bars or lenses. The study was done by applying GALFIT to images from the SMAKCED collaboration ( S tellar content, MA ss and K inematics of C luster E arly-type D warfs, http://www.smakced.net ). The sample comprises early-type galaxies in the Virgo cluster in a brightness range of −19 ≤ M r ≤ −16 mag, and the data is complete down to M r =−16.73 mag. The images typically reach a signal-to-noise ratio of 1 per pixel of ~0.25" at a surface brightness of ~22.5 mag/arcsec 2 in the H -band. The galaxies were fitted with two-dimensional models, either with a simple Sérsic model or inner and outer components, as well as bars and lenses. Only a fraction of 31% of the galaxies can be fitted with a single Sérsic function. This fraction of "simple" galaxies turns out to be a strong function of luminosity, with a smaller fraction for brighter objects. The bar fraction is 14% and also in 14% of the galaxies lenses were fitted. When comparing the flattening distribution, the early-type dwarfs are more similar to spiral galaxies than to elliptical or lenticular galaxies. It is disputable whether or not the dwarfs follow a common relation with the bright elliptical galaxies, e.g. in the brightness versus size diagram. At the same time, they appear as smooth continuation of bright late-type galaxies in this diagram. The inner and outer components, as well as the simple galaxies have similar flattening distributions. The inner components are mostly fitted with Sérsic- n values close to~1, i.e. with nearly exponential profiles. We argue that the inner components in the early-type dwarfs are not be bulges but may form parts of the disks, in which the matter was re-distributed during the transformation process from a late-type progenitor.