Marcel S. Pawlowski (Dipl. Phys.)

PhD Student at Prof. Pavel Kroupa's research group Astrophysics of Stellar Populations, Dynamics and Dark Matter.

I am working on the distribution and origin of the MW satellite galaxies and the formation of tidal dwarf galaxies in galaxy encounters.

Contact

mpawlow [AT] astro [dot] uni-bonn [dot] de
Phone: (+49) 0228 73 3649

Auf dem Hügel 71
53121 Bonn
Germany
Room 3.012

RAS press release

Material for the Royal Astronomical Society press release of April 25.

Publications

• The VPOS: a vast polar structure of satellite galaxies, globular clusters and streams around the Milky Way; M. S. Pawlowski, J. Pflamm-Altenburg, P. Kroupa; MNRAS (accepted); 2012. It has been known for a long time that the satellite galaxies of the Milky Way (MW) show a significant amount of phase-space correlation, they are distributed in a highly inclined Disc of Satellites (DoS). We have extended the previous studies on the DoS by analysing for the first time the orientations of streams of stars and gas, and the distributions of globular clusters within the halo of the MW. It is shown that the spatial distribution of MW globular clusters classified as young halo clusters (YH GC) is very similar to the DoS, while 7 of the 14 analysed streams align with the DoS. The probability to find the observed clustering of streams is only 0.3 per cent when assuming isotropy. The MW thus is surrounded by a vast polar structure (VPOS) of subsystems (satellite galaxies, globular clusters and streams), spreading from Galactocentric distances as small as 10 kpc out to 250 kpc. These findings demonstrate that a near-isotropic infall of cosmological sub-structure components onto the MW is essentially ruled out because a large number of infalling objects would have had to be highly correlated, to a degree not natural for dark matter sub-structures. The majority of satellites, streams and YH GCs had to be formed as a correlated population. This is possible in tidal tails consisting of material expelled from interacting galaxies. We discuss the tidal scenario for the formation of the VPOS, including successes and possible challenges. The potential consequences of the MW satellites being tidal dwarf galaxies are severe. If all the satellite galaxies and YH GCs have been formed in an encounter between the young MW and another gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model.
• Making Counter-Orbiting Tidal Debris: The Origin of the Milky Way Disc of Satellites; M. S. Pawlowski, P. Kroupa, K. S. de Boer; Astronomy and Astrophysics; 2011. Using stellar-dynamical calculations it is shown for the first time that counter-orbiting material emerges naturally in tidal interactions of disc galaxies. Model particles on both pro- and retrograde orbits can be formed as tidal debris in single encounters with disc galaxies of 1-to-1 and 4-to-1 mass ratios. A total of 74 model calculations are performed for a range of different initial parameters. Interactions include fly-by and merger cases. The fraction of counter-orbiting material produced varies over a wide range (from a few up to 50 percent). All fly-by models show a similar two-phase behaviour, with retrograde material forming first. Properties of the prograde and retrograde populations are extracted to make an observational discrimination possible. During such encounters the tidal debris occupies a certain region in phase space. In this material, tidal-dwarf galaxies may form. The modelling therefore can explain why galaxies may have dwarf galaxies orbiting counter to the bulk of their dwarf galaxies. An example is the Sculptor dwarf of the Milky Way, which orbits counter to the bulk of the disc of satellites. The modelling thus supports the scenario of the MW satellites being ancient tidal-dwarf galaxies formed from gaseous material stripped from another galaxy during an encounter with the young MW. A possible candidate for this galaxy is identified as the Magellanic Cloud progenitor galaxy. Its angular motion fits the angular motion of the MW disc of satellites objects. This scenario is in agreement with Lynden-Bell’s original suggestion for the origin of the dSph satellites and the near-unbound orbit of the LMC.
• “Local-Group tests of dark-matter Concordance Cosmology: Towards a new paradigm for structure formation”; Kroupa, P.; Famaey, B.; de Boer, K. S.; Dabringhausen, J.; Pawlowski, M. S.; Boily, C. M.; Jerjen, H.; Forbes, D.; Hensler, G.; Metz, M.; in Astronomy and Astrophysics; 2010. Predictions of the Concordance Cosmological Model (CCM) of the structures in the environment of large spiral galaxies are compared with observed properties of Local Group galaxies. Five new possibly irreconcilable problems are uncovered. However, the Local Group properties provide hints that may lead to a solution of the above problems The DoS and bulge–satellite correlation suggest that dissipational events forming bulges are related to the processes forming phase-space correlated satellite populations. Such events are well known to occur since in galaxy encounters energy and angular momentum are expelled in the form of tidal tails, which can fragment to form populations of tidal-dwarf galaxies (TDGs) and associated star clusters. If Local Group satellite galaxies are to be interpreted as TDGs then the sub-structure predictions of CCM are internally in conflict. All findings thus suggest that the CCM does not account for the Local Group observations and that therefore existing as well as new viable alternatives have to be further explored. These are discussed and natural solutions for the above problems emerge.
• More in preparation.

Photos

TDG Bonn 2009

Conference photo: conferencephoto.jpg (7.5 MB); conferencephotomedium.jpg (964 kB); conferencephotosmall.jpg (438 kB)
MOND community: big (6.8 MB); medium (1.5 MB);small (476 kB);

Links

My personal website: marcelpawlowski.com; My blog: 8minutesold.com; Twitter: @8minutesold ; My portfolios: Seen.by, 500px