Great news from the Hubble Space Telescope: Our observing proposal “Andromeda and the Seven Dwarfs: M31 Mass, Satellite Orbits, and the Nature of the Satellite Plane”, was awarded observing time. The proposal is lead by Tony Sohn and is part of the HSTPROMO collaboration. For a whopping 48 orbits, the Space Telescope will observe our targets (green stars in my figure on the right). These measurements will reveal the proper motions (i.e. motions on the sky) of seven M31 satellite galaxies. This will be the first time that we will be able to study the full 3D motions (and thus 6D phase-space coordinates) of a sample of satellite galaxies outside of our Milky Way. And it will be a first step in determining how dynamically stable (or rotationally supported) the plane of satellite galaxies around Andromeda is.

Some great news today: I am happy to announce that I have been selected as one of the 11 fellows of the Klaus Tschira Boost Fund 2020. It is an honor to be included in such a group of amazing scientists (read about the other new fellows here), and I am grateful to be given this opportunity by German Scholars Organization and of course the Klaus Tschira Stiftung (check out their press release, German only).

The funding will support my research into phase-space correlations of satellite galaxies and the nature of Dark Matter. Among other things, I am especially excited that it will also allow me to organize a small, interdisciplinary hackathon-style workshop in late 2021 or early 2022. Stay tuned for further details.

Update: The AIP has also issued a press release about this, in German and English.

I’ll be giving a public talk in Potsdam this Thursday about my field of research, titled “Dark Matter and the Dance of Dwarf Galaxies”. It is part of our institute’s public outreach series Babelsberger Sternennächte (Babelsberg Starry Nights).

When: Thursday, January 16, 2020. At 7:15 pm.

Where: Leibniz-Institut für Astrophysik, An der Sternwarte 16, 14482 Potsdam

The talk is free, but it will be in German.

For more details follow this link.

Today my newest first-author paper appeared on the arXiv. It was recently accepted for publication in MNRAS. In it, I revisit the orbital alignment of the 11 classical satellite galaxies with their spatial distribution, the disk (or plane) of satellite galaxies. Gaia DR2 provided us with an entirely independent data set to compare with previous proper motion measurements that were based on ground-based observations or Hubble Space Telescope data. It turns out that the new Gaia data strikingly confirms our previous findings: the majority of the 11 classical (i.e. brightest) Milky Way satellite galaxies co-orbits within the plane defined by their positions. Combining the best-available proper motions from the different sources for each of the satellites even reveals a tighter clustering of their orbital poles (= directions of angular momentum around the Milky Way) than ever seen before. This is in line with a strong underlying correlation that becomes more and more apparent as measurement uncertainties are reduced.

We also compare the observed correlation with the state-of-the-art cosmological simulation IllustrisTNG, and find that similarly correlated satellite systems are exceedingly rare in this ΛCDM universe. The Planes of Satellite Galaxies Problem thus becomes even more severe with the addition of this new data.

If you don’t want to read the full 20-page paper, you can find a summary of our main findings in my corresponding Twitter thread.

Together with a fellow alumna of the German Scholar Association Leadership Academy, I am organizing a workshop on mental health and time management, lead by two coaches who are experts on these topics. The one-day workshop is primarily aimed at junior researchers in Berlin and Brandenburg (PhD students, postdocs, junior group leaders). We successfully obtained full funding, so we can offer the workshop air no cost to the participants (and it includes coffee, snacks, and a lunch).

Time: Saturday, October 26, 9:00 – 17:00

Place: BlauArt Tagungshaus, Potsdam

Cost: free!

See the flyer for more information, and sign up by contacting me or via our signup form.

My newest paper, recently accepted for publication in ApJ, is now available as a preprint on the arXiv: Do halos that form early, have high concentration, are part of a pair, or contain a central galaxy potential host more pronounced planes of satellite galaxies?

Planes of satellite galaxies are a problem for the standard model of cosmology, because structures as extreme as those observed around the Milky Way, the Andromeda galaxy, and Centaurus A are very rare in cosmological simulations. A possible solution is that some host halos with special properties or unique environments are more likely to host such extreme structures, an idea wich would then even allow us to learn about the host dark matter halos and their history from the fact that they are surrounded by a satellite plane. Buck et al. (2015) had proposed that there is such a correlation between satellite planes and the concentration parameter of the host dark matter halo (as a proxy of its formation time).

In my new paper, we have tested this claim with a larger set of simulated hosts, a more careful satellite selection, and using different methods to look for a correlation. No such correlation with halo concentration or formation time is present, nor do any of the simulated systems reproduce the observed narrow planes and their kinematic correlation (see plot, black symbol gives the observed value). The only correlations found have to do with the radial extent of the satellite system, a well known effect that was not sufficiently considered in the earlier study. We have also tested for environmental effects, and find that being situated in a paired configuration (like the Milky Way and Andromeda) does not help solve the satellite plane issue. Finally, we also looked at the dominant effect baryonic physics has on the distribution of satellite galaxies in a halo: the influence of having a central disk galaxy potential that results in additional tidal disruption compared to a pure dark-matter-only simulation. It turns out that this makes the issue worse, because the planes found in the presence of a central potential are on average wider than in equivalent simulations without such a potential. This indicates that, in contrast to many other small-scale issues of LCDM, the Planes of Satellite Galaxies problem is made worse when including baryonic effects.

For more explanations, read the paper of have a look at my corresponding Twitter thread.