Tobias Buck

Astronomy graduate student

I am a PhD student in Astronomy at the Max-Planck-Institut für Astronomie (MPIA) in Heidelberg, Germany. I am working both in the Galaxy Formation Group led by Andrea V. Macciò (now at New York University Abu Dhabi and the Milky Way Group led by Hans-Walter Rix. I focus my research on the formation of Milky Way type galaxies in high-resolution cosmological hydrodynamical simulations. My main interest lies in the satellite galaxies of Milky Way type galaxies as cosmological probes of structure formation and the build-up of the stellar disc and its structure in a cosmological context.

I am a fellow of the "International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg" (IMPRS-HD).

Research Interest

I am interested in the process of galaxy formation. It is fascinating how the Universe was able to evolve from an almost homogenous state at the time when the CMB was released to a highly structured state with dark matter filaments and halos, galaxy clusters and galaxies. Thus, I study galaxy formation in a cosmological context using hydrodynamical simulations. Some cool Movies can be found here.

High resolution hydrodynamical simulation of Milky Way type galaxies

As part of my PhD I am running high-resolution hydrodynamical simulations of analogues of our own Milky Way. These simulations are state of the art in terms of resolution and modelling technique. The resulting galaxies show surprisingly thin discs of stars and spiral arms of young stars. The simulation volume is furthermore filled with a wealth of smaller satellite galaxies well in agreement with the Milky Way's companions. More information can soon be found in my recent paper.

NIHAO XV: The environmental impact of the host galaxy on galactic satellite and field dwarf galaxies

The two major galaxies in the Local Group, the Milky Way and its companion the Andromeda galaxy, both host a large number of small satellite galaxies. The properties of these small galaxies are significantly effected by the environment of Milky Way and Andromeda. In this recent work I studied the effect that the Milky Way has on the properties of its satellite galaxies and what the observational possibilities are in finding strongly effected galaxies. The Milky Way environment leads to a significant loss of mass, both dark matter mass as well as gas mass. Using the simulations we are able to establish a relation between the mass of a satellite before falling onto the Milky Way and its stellar mass today, thus, being able to account for the mass loss and give estimates of the mass prior to infall for observed Milky Way satellites. Furthermore, this study nicely shows that modern high-resolution simulations are finally able to predict the right number, stellar mass and structure of small dwarf galaxies. See this paper for more information.

Stars behind Bars I: The Milky Way's central stellar populations

The Milky Way is a barred spiral galaxy and thus its central region, the bulge, looks somewhat like a peanut. In a series of two recent papers I studied the properties and the formation of such a structure in a high-resolution cosmological hydrodynamical simulation of a Milky Way type galaxy. I find very good agreement between the properties of the simulated bulge and Milky Way's bulge. Especially the morphology and the kinematics of stars are in excellent agreement. I further test observational ways to distinguish between stars in the bar and the surrounding disc. See this paper for more information.

The edge of galaxy formation II: Milky Way satellite after accretion

The second part of my side project dealed with the evolution of Milky Way satellites after their accretion onto the Milky Way. Using idealised simulations of various different orbits for one satellite we find that all structural parameters are influenced by the accretion history and quantify the effect of the orbit. Satellites show severe dark matter mass loss after infall while the stellar mass stays nearly constant. Due to that the rotation curves and velocity dispersion profiles of the stars are altered significantly. See this paper for more information.

The edge of galaxy formation I: MW-satellites before accretion

In a side project I contributed to the exploration of the formation of the smallest galaxies we know of - the satellites of the Milky Way. In this paper we show that the global properties of Milky Way satellites such as total stellar mass are already in place before their accretion. Furthermore we find that galaxy formation on these mass scales is barely able to alter the host dark matter halo of the smallest galaxies. For more information see our paper.

Giant UV bright clumps at high redshift

Disc galaxies in the eraly universe are observed to have an irregular morphology opposed to the nice spiral structure we see in present day disc galaxies. These early galaxies show several giant kpc sized off-center clumps which mostly stick out in the UV images. Early simulation work suggested these are giant star cluster due to violent disc instabilities. In this paper, part of my first PhD project, I could show that these clumps are the result of a non-linear mapping of stellar mass into stellar light. Using the NIHAO simulations we find clumps in stellar light matching the observed features clumps but we do not see clumps in stellar mass. In NIHAO the clumps result from the strong contribution of young stars to the UV light. Since stars in the simulations form clustered also the light morphology is clumpy. See my paper, my poster or my talk slides if you are interested.

The stability of satellite planes

In a small project continuing the work of my master thesis I analysed the stability of planes of satellites. The observed seemingly alignment of satellites of our own Milky Way and of its companion Andromeda in a thin planar structure is sometimes interpreted as a challenge to the widely accepted cosmological concordance model of cold dark matter. In this work I used dark matter only simulations to study the stability of thin planar structures. Such thin planes are present in the concordance cosmology but not stable. More details can be found in this paper or on my Poster.

Thin Satellite planes from filamentary accretion

The satellite galaxies of the companion galaxy of our Milky Way - Andromeda (M31) - are observed to be aligned in a thin seemingly rotating planar structure. In my master thesis I ran dark matter only simulations of Milky Way mass dark matter haloes to search for such configurations. In this paper we find that filamentary accretion of satellites from coherent directions ca explain the planar alignment.

The formation of the Hyades

During bachelor studies I explored several formation scenarios of the Hyades open star cluster. In order to match the observed present day properties of the Hyades the model star cluster needed to be much more massive at formation time and loose a significant amount of stars to the galaxy. The observable feature of this model are pronounced tidal tails of stars leaving the star cluster via the lagrangian points. See my bachelor thesis for more details.

Publications

Link to ADS

Refereed Papers

  • NIHAO XV: The environmental impact of the host galaxy on galactic satellite and field dwarf galaxies (Buck et al. 2018, arXiv,): ADS, astro-ph
  • Stars behind bars I: The Milky Way's central stellar populations (Buck et al. 2017, arXiv,): ADS, astro-ph
  • Inspiraling Halo Accretion Mapped in Lyman-alpha Emission around a z~3 Quasar (Battaia et al. 2017, MNRAS,): ADS, astro-ph
  • The edge of galaxy formation II: evolution of Milky Way satellite analogues after infall (Frings et al. 2017, MNRAS,): ADS, astro-ph
  • The edge of galaxy formation I: formation and evolution of MW-satellites analogues before accretion (Macciò et al. 2017, MNRAS,): ADS, astro-ph
  • NIHAO XIII: Clumpy discs or clumpy light in high-redshift galaxies? (Buck et al. 2017, MNRAS, 468, 3628): ADS, astro-ph
  • NIHAO XII: galactic uniformity in a ΛCDM universe (Dutton et al. 2017, MNRAS, 467, 4937): ADS, astro-ph
  • NIHAO IX: the role of gas inflows and outflows in driving the contraction and expansion of cold dark matter haloes (Dutton et al. 2016, MNRAS, 461, 2658): ADS, astro-ph
  • Simulated ΛCDM analogues of the thin plane of satellites around the Andromeda galaxy are not kinematically coherent structures (Buck et al. 2016, MNRAS, 460, 4348): ADS, astro-ph
  • NIHAO - IV: core creation and destruction in dark matter density profiles across cosmic time (Tollet et al. 2016, MNRAS, 456, 3542): ADS, astro-ph
  • The response of dark matter haloes to elliptical galaxy formation: a new test for quenching scenarios (Dutton et al. 2015, MNRAS, 453, 2447): ADS, astro-ph
  • Evidence for Early Filamentary Accretion from the Andromeda Galaxy’s Thin Plane of Satellites (Buck et al. 2015, ApJ, 809, 49): ADS, astro-ph

Conferences and Workshops

Invited Talks

  • Königstuhl Colloquium (13.4.2018), MPIA, Heidelberg
  • MPA Colloquium (10.1.2018), MPA, Munich

Theses

Curriculum Vitae

Academic Education

2015 - present
Graduate student, Max-Planck-Institut für Astronomie, Heidelberg, Germany
06/2015
Master's Degree, University of Heidelberg, Germany, Advisor: Prof. Dr. Andrea Macciò, Thesis title: "The Emergence of spatially and kinematically coherent Planes of Satellite Galaxies in high-resolution Dark Matter only simulations
2013 - 2015
Master's Programme, University of Heidelberg, Germany
07/2013
Bachelors's Degree, University of Heidelberg, Germany, Advisor: Prof. Dr. Andreas Just, Thesis title: "Dynamical analysis of the Hyades star cluster using direct N-body simulations"
2010 - 2013
Bachelor's Programme, University of Heidelberg, Germany

Fellowships/Scholarships

2015 - present
Member of the "International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg" (IMPRS-HD)
2010 - 2015
Studienstiftung des deutschen Volkes e.V.

A more detailed pdf version of my CV can be found here

Coding

  • For my PhD project I intensively use the python package pynbody to which I also contribute own code.
  • During my bachelors and masters studies at the University Heidelberg I participated a lot in the robotics lab. My first project was a xylophon robot, the second was a self driving car and the third was a 3D display using the Persistence Of Vision technique. Most projects can also be found on my github.

Outside Astronomy

Outside astronomy I love to do music. I am heavily involved in the Spielmannszug TSV Malente as one of the conductors and where I am teaching kids on how to play instruments. I am further involved in the drum line of Spielmannszug TSV Malente "link".

Movies

I am interested in the process of galaxy formation. It is fascinating how the Universe was able to evolve from an almost homogenous state at the time when the CMB was released to a highly structured state with dark matter filaments and halos, galaxy clusters and galaxies. Thus, I study galaxy formation in a cosmological context using hydrodynamical simulations. Below you can find some cool movies.

Contact Me

  • (+49/0) 6221-528-286
  • buck 'at' mpia 'dot' de
  • Max-Planck-Insitut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
  • tobias-buck