Benjamin L’Huillier


Cosmologist and Astrophysicist, Research Fellow at KASI, Daejeon, South Korea

Galaxy mass assembly

B. L'Huillier, F. Combes & B. Semelin 2012, A&A, 544, 68.

With Francoise Combes and Benoit Semelin, we have used multi-zoom simulations to investigate the way galaxies assemble their baryonic mass. We ran a series of N-body only and N=body + hydrodynamics simulations, zooming on a dense region (15 times the mean density of the Universe at z=0.46). I studied the mass assembly of galaxies, namely, how they assemble their baryonic mass, discriminating between the mass asseembled by mergers and by smooth accretion. To do this, I detected the dark matter and baryonic structures using a modified version of AdaptaHOP (Aubert et al 2004, Tweed et al. 2009), and buit merger trees. I found a mean accretion fraction of 77%, with low mass galaxies assembling their mass mostly from accretion. I also found some evidence for downsizing in these simulations: massive galaxies have have an old stellar populations, whereas low-mass galaxies form stars at every epoch.

I am currently comparing the statistical (mass function) and internal (concentration, spin) properties of haloes between the DM only and the hydrodynamic simulations, to understand how the baryonic physics shapes the haloes.

Some pictures and plots

Merger  tree of  a galaxy (Baryons). Snapshot
Left: Baryonic merger tree of a galaxy. Dark blue circles represent galaxies, and bright blue squares satellites. Right: Snapshot of a multi-zoom simulation at t = 9.1 Gyr. Upper left: gas and star. Upper right: dark matter. Bottom left: baryonic structures found with AdaptaHOP. Upper right: DM Haloes and subhaloes found by AdaptaHOP.