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Galaxy Formation

Galaxy Formation

Galaxy Formation

The Galaxy Formation group is funded by the SAW-2012-AIP-5 grant of the Leibniz Gemeinschaft entitled "The origin of the stellar components in galaxies".

Our group investigates the formation of galaxies in a cosmological context, focusing on the relation between the dynamical, chemical and structural evolution of galaxies and their formation, merger and accretion histories. We use hydrodynamical numerical simulations and develop our own routines to treat star formation, feedback processes, cooling and chemical enrichment. We also compare simulated galaxies with observations by calculating synthetic spectra from the simulated populations, and them mimicking the observational techniques so that the comparisons are reliable. We use these comparisons to better understand the limitations/successes of the models and to better interpret the biases present in observationally obtained galaxy properties.



Cecilia Scannapieco

Peter Creasey

Giovanni Guidi

Pierre-Antoine Poulhazan



Evolution of matter components in a constrained simulation of the Local Group



Simulations of the Milky Way and Local Group

The galaxies we understand best in the Universe are own Milky Way and those in the Local Group. By constructing ‘zoom’ simulations of our Local Group of galaxies we can understand the implications of our models of cosmology and the interactions between stellar populations and their host galaxies. These processes control the diversity of the galaxy population, determining whether a galaxy forms an elliptical or a spiral like the Milky way or Andromeda.


The gas distribution within and around the Milky Way and Andromeda galaxies

In Nuza et al. (2014) we study the distribution of gas within the LG using a constrained cosmological simulation with particular emphasis on the content and accretion/ejection of gas in our Milky Way and Andromeda candidates. For our study, we split the gaseous material in three different phases: cold, hot and HI. The first two phases are defined by imposing a temperature threshold of 105 K and are composed mainly of ionized gas, whereas the HI component comprises most of the neutral material in the galaxies.

In the plots below we show a view of the LG for the hot, cold and HI gas phases (from left to right). The virial radii of the Milky Way and Andromeda candidates are shown as dashed and solid lines respectively. In addition, we also show a Mollweide HI sky map from the simulated Local Standard of Rest position.

The figure below shows the hydrogen number density profile of the Milky Way averaged over a set of randomly selected sightlines (mean value: dashed line; standard deviation: shaded area). The thick solid line correspond to the direction towards the Andromeda candidate. For reference, estimates of the electron number density are also included (filled symbols).


Effects of environment of the formation of the Local Group galaxies

In this project, we investigate the relation between the environment of galaxies and properties such as morphologies, star formation rates and gas fractions (Creasey et al., 2015).

In the visualization (below) we perform a constrained simulation of the Local Group and mark 6 galaxies that are of similar stellar mass to our own Milky Way, along with the distribution of gas around them. The pair marked G1 and G2 are analogous to Andromeda and the Milky Way. Grey circles indicate the larger-scale environment (diameter 2.4 Mpc), and it is by analysing simulations such as these that we can see how environment affects galaxy properties.

Click here for animation

Image of zoom-simulation of the local volume in a radius of 10 Mpc about the the MW and M31 candidates (G1 and G2 respectively). In blue is the column density of gas and in orange-white is the star forming gas. Inset are magnifications of the 6 galaxies of similar mass to the MW.



The formation of the Milky Way and Andromeda in a constrained simulation of the Local Group

In this project, we investigate the formation of the Milky Way and Andromeda in a constrained simulation of the Local Group, and focus on the relation between their particular formation/merger histories and the evolution of their morphologies (Scannapieco et al., 2015). We use the code of Scannapieco et al. (2005, 2006, "CS model") which includes star formation, chemical enrichment, metal-dependent cooling and supernova feedback.

We also test the effects of including radiation pressure from stars using the model of Aumer et al. (2013, "MA model"). In this case, we find that the stellar components are younger, more disk-dominated and have smaller stellar masses.

The following figures show the distribution of stars at the present time, in face-on and edge-on views, for the Andromeda (G1) and Milky Way (G2) candidates and for our two simulations, and the evolution of the disk fraction and cosine of the angle between the angular momenta of the gas and the stars.


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