Over the last few month, about a dozen new satellite galaxy candidates around the Milky Way have been discovered. Each new satellite acts as an important test of the Vast Polar Structure (VPOS), the plane of satellites rotating around our Galaxy. Today we put a preprint on the arXiv in which we show that the new objects align well with the VPOS, confirming my earlier work.

We also find that, even though the footprint of the Dark Energy Survey – the observational campaign which uncovered the majority of the new satellites – lies close to the VPOS, the alignment of the DES satellites with the VPOS is stronger than expected due to the footprint shape. We also predict the proper motions of the new satellites, assuming that they, like observed for the classical ones, preferentially orbit within the VPOS.

In addition we provide predictions for the velocity dispersions of the new objects under the assumption that they are either (1) dark-matter-free star clusters obeying Newtonian Dynamics, (2) dark-matter dominated dwarf galaxies following empirical scaling relations, or (3) that their dynamics follows MOND. These predictions are the main reason why we decided to publish the preprint before acceptance by a journal: we want to avoid that the measurements of the velocity dispersions become available before our predictions (which would make them look like post-dictions).

The current edition of our university magazine “think” features an article about my and Stacy McGaugh’s work on dwarf galaxies titled “Challenging Conventional Wisdom“. Click the link to read it online.

So, here is my paper number four of this year (it’s been a long, cold winter, what else than research was I supposed to do with my time?). In this one, I check whether a number of recently discovered objects in the halo of the Milky Way are aligned with the Vast Polar Structure (VPOS). This is interesting because those objects which move in a common sense in the VPOS probably share a common origin, so we might learn something from knowing which objects are well associated with the VPOS. I find that the most-distant known globular cluster of the Milky Way (which others say might also be a satellite galaxy) is aligned with the structure, just like the other ‘young’ globular clusters. In addition I find that one recently discovered stellar streams aligns very well with the VPOS. In fact, that stream appears to have the same orientation and distance as the well known Palomar 5 stream, and even the estimated metallicity appears to be consistent. Might it be directly connected to the Pal 5 stream? Maybe, but it will require numerical models to check if that stream could in principle be 140 degree long.
“The Vast Polar Structure of the Milky Way Attains New Members“, Marcel S. Pawlowski & Pavel Kroupa, 2014, ApJ, 790, 74 (or on the arXiv: 1407.2612)

And here comes another new paper already. This one was processed extremely quickly, even for a letter: I submitted it on the day before I left for my Europe trip, got the referee report less than two weeks later while at the MODEST14 conference, adjusted and re-submitted the paper two days later. It was accepted an hour after re-submission, I got the proofs while in Strasbourg, corrected them and a day after my visit to Vienna the Letter was already published, exactly 4 weeks after the initial submission. I didn’t even find the time to out it on the arXiv before that, so it went there this week.

So, what is the paper about? The presence of satellite galaxy planes around both the Milky Way and Andromeda makes one wonder whether the fact that these two are part of the Local Group increases the chances to find co-orbiting planes of satellite galaxies like the VPOS. This we tested using the cosmological ELVIS simulations, which contain both isolated hosts and hosts in Local-Group-like pairs. We find no significant difference in the occurrence of satellite planes around both types of hosts, in fact such planes are extremely unlikely for both if the simulated dark matter sub-halos are identified with satellite galaxies.

Co-orbiting Planes of Sub-halos are Similarly Unlikely around Paired and Isolated Hosts; Marcel S. Pawlowski & Stacy S. McGaugh; 2014, ApJL, 789, 24.

Our new paper “Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies” has been accepted a few weeks ago, and now we have finally made the preprint available here.

The reason for the delay was that we had to prepare and coordinate several press releases related to the paper. These appear today:

Case Western Reserve University (me): “Nearby satellite galaxies don’t fit standard model”

Rochester Institute of Technology (David Merritt): “Map of universe questioned; dwarf galaxies don’t fit standard model”

Swinburne University of Technology (Duncan Forbes): “Nearby satellite galaxies challenge standard model of galaxy formation”

Australian National University (Helmut Jerjen): “Milky Way debris came from galaxy collision”

University of Vienna (Gerhard Hensler): “Neues ‘Geburtsszenario’ für Satellitengalaxien” (in German)