Research
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Dwarf Galaxy Research Group

Thorsten Lisker   –   ZAH
People
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Populär/Schulen





Research

We seek to understand the environmentally influenced evolution of small, "dwarf" galaxies, which are so abundant in the present-day Universe. We investigate the structure and internal dynamics of dwarf galaxies through multiwavelength imaging and spectroscopic observing campaigns like SMAKCED (Stellar content, MAss and Kinematics of Cluster Early-type Dwarf galaxies) and FDS (Fornax Cluster Deep Survey), the influence of environment on dwarf galaxies and their progenitors through an analysis of galaxy clusters and groups with different characteristics, and the connection between the dark matter halo population and the visible dwarf galaxies, based on cosmological simulations and galaxy evolution models.

News

→ 14 PhD positions in EU network SUNDIAL, joins computer science and astronomy for galaxy evolution studies (23 Nov 2016)

→ Dwarf galaxy workshop focuses on combining knowledge, fostering exchange, and discussing future projects (04 Oct 2016)

→ Destroyed dwarf galaxies or massive star clusters? New insights into compact stellar systems (23 May 2016)

→ European Commission approves new Innovative Training Network SUNDIAL (02 May 2016)




14 PhD positions in EU network SUNDIAL, joins computer science and astronomy for galaxy evolution studies

23 Nov 2016

Our new EU Innovative Training Network "SUNDIAL" currently offers 14 PhD positions across Europe in astronomy and computer science. The application deadline is December 15, 2016:
SUNDIAL website
AAS Job Register entry
It covers topics such as detecting ultrafaint galaxy signals, developing automated models for galaxy recognition and classification, and developing new methods to compare observations and galaxy simulations as well as visualization.

Dwarf galaxy workshop focuses on combining knowledge, fostering exchange, and discussing future projects

04 Oct 2016

A discussion-intensive workshop on the present and future research on dwarf galaxies will be hosted at ESO headquarters (Garching, Germany) from October 10 to 13, 2016, organised by Drs. Eric Emsellem (ESO) and Thorsten Lisker (ZAH). The workshop format will be focusing on interaction and discussion within a small group of 35 invited, international participants, with the intention of promoting open exchange of ideas and defining new challenges for the future. In particular, the current and upcoming capabilities of simulations and instrumentation will be reviewed in the light of our advancing understanding of dwarf galaxy evolution. More information is provided at http://dwarfs2016.de/.

Destroyed dwarf galaxies or massive star clusters? New insights into compact stellar systems

23 May 2016

Globular clusters can not only be found around the Milky Way. Thousands of them form vast systems around the huge elliptical galaxies in the centers of galaxy clusters. There, astronomers discovered a new type of object in 1999: massive stellar systems that appear like oversized globular clusters. Are these already galaxies, rather than star clusters? At first, many scientists favoured a scenario in which these objects are remnants of disrupted dwarf galaxies – until a few years ago a plain statistical approach showed that the majority is consistent with simply being the largest members of the globular cluster population. However, we do know from observations and computer simulations that small galaxies occasionally get destroyed in the core regions of galaxy clusters. It thus remained open what fraction the surviving nuclei of such galaxies contribute to the compact stellar systems we observe.

In a recently published study, we analysed several hundred compact stellar systems in the Fornax galaxy cluster, 65 million lightyears from us. We used deep optical images that we acquired in Chile, at the 2.2m telescope of the Max Planck Society and the European Southern Observatory. About two dozen of the objects we observed exhibit an extended and partly distorted outer distribution of stars (Fig. 1), which is probably due to the tidal forces exerted by the galaxy cluster. Surprisingly, these peculiar objects are not located in the very central cluster area – where those forces would be strongest – but they seem to group around it (Fig. 2). Due to their location and motion, we believe that they do not belong to the population of central star clusters, but that they instead are part of the galaxy population. They were originally dwarf galaxies whose orbit carried them too close to the galaxy cluster center, eventually leading to their disruption. Only their stellar nuclei remained, as well as a little bit of material from the former galaxy body, which we are now observing as the faint outer extensions of these objects. To ultimately confirm this hypothesis, we are now hoping for high-quality spectroscopic measurements and high-resolution imaging data of the Hubble Space Telescope, in order to probe the compact stellar systems' age, metal content, and core structure.

 

Fig. 1: Selection of compact objects with extended and/or distorted structures. To the right of each object we show a reference image for how an unperturbed star cluster-like object would appear at the same location in our data.
 

Fig. 2: Spatial distribution of objects with extended structures (red), compared to dwarf galaxies (blue) and globular clusters (grey; larger symbols represent the most massive of them).
 

Original publication:
C. Wittmann, T. Lisker, A. Pasquali, M. Hilker & E.K. Grebel: Peculiar compact stellar systems in the Fornax cluster
2016, Monthly Notices of the Royal Astronomical Society, 459, 4450

European Commission approves new Innovative Training Network SUNDIAL

02 May 2016

Nine academic institutions and five partner organisations from nine European countries will form the new Innovative Training Network SUNDIAL, which the European Commission has now approved for implementation in 2017. SUNDIAL, the SUrvey Network for Deep Imaging Analysis & Learning, brings together a team of leading European astronomers and computational scientists who will embark on a broad and data science intensive research programme. As a multi-disciplinary collaboration, led by the University of Groningen, SUNDIAL will develop innovative computational methods and apply them to large astronomical datasets acquired in observational surveys, thereby training a new generation of computational/astronomy/data scientists. Our dwarf galaxy research group is leading Heidelberg University's involvement in the network, with a project on "Studying galaxy evolution in cluster environments through comparing observed and simulated galaxy and cluster properties."