Freeke van de Voort



My research focuses on understanding galaxy formation and evolution. For this purpose, I primarily use cosmological, hydrodynamical simulations, such as those in the OWLS, FIRE, and EAGLE simulation suites. I study the interplay between gas accretion (smooth or through mergers) and feedback (from stars or black holes) or, more broadly, how galaxies grow and how they reduce their own growth. I also collaborate on observational and instrumental projects and have even been awarded ALMA time to study minor mergers and star formation in early-type galaxies.

Background

Small fluctuations in the early universe, detectable via the cosmic microwave background radiation, grow into sheets and filaments that make up the cosmic web. Galaxies form in the densest regions of this web. Through galactic winds, they have an enormous impact on the environment they live in.

My research

I will briefly describe my contribution to our understanding of the universe by summarizing the (first author) papers I have written in chronological order.

Gas accretion onto galaxies and haloes
Metal-line cooling and supernova and AGN feedback do not impact gas accretion onto haloes much, but change the gas accretion rates onto galaxies by up to an order of magnitude. The fraction of gas accreted in the cold-mode is not strongly dependent on feedback.

Global gas accretion and AGN feedback
Cold-mode accretion fuels most of the star formation in the universe and is therefore responsible for the shape of the global star formation rate density. AGN feedback is needed to reduce (mostly hot-mode) accretion in massive galaxies.

HI absorption (LLSs, DLAs)
Most of the high column density HI absorbers (Lyman-limit systems and damped Lyman-alpha systems) at z=3 are flowing into the nearest galaxy and become part of the star-forming interstellar medium by z=2.

Properties of gaseous haloes
Cold-mode gas is typically colder and denser, has a much lower metallicity and is much more likely to be infalling than hot-mode gas. The scatter in these properties, however, is large and the difference between hot- and cold-mode gas decreases towards the centre of their haloes.

UV and soft X-ray metal-line emission
Current and upcoming instruments will be able to directly image the circumgalactic medium through UV and soft X-ray metal-line emission. This emission is, however, strongly biased towards high density and high metallicity and towards the temperature at which the line's emissivity peaks.

r-process elements from neutron star mergers
Neutron star mergers may be the source of all rapid neutron capture elements in the universe. Neutron star mergers are rare, but dynamical processes (such as galactic winds and galaxy mergers) are able to mix the gas and enrich most of the interstellar medium.

Misaligned gas discs in early-type galaxies
After the creation of a gas disc with its angular momentum misaligned from the stars, which dominate the potential, continued gas accretion keeps the gas disc misaligned much longer than expected. This movie fully explains the results.

Galaxy growth at fixed number density
Progenitors, descendants, and galaxies selected at fixed number density have masses different up to a factor of 3 over a wide redshift range (z=5-0). There are three regimes for galaxy growth: first, the gas accretion rate dominates, after which the star formation rate dominates, and finally galaxies grow mostly through mergers.

Hot haloes in SZ and soft X-ray
Dwarf galaxies have a much smaller baryon fraction than massive galaxies and their Sunyaev-Zel'dovich effect is thus reduced compared to the self-similar expectation. Soft X-ray emission from hot haloes is powered by stellar feedback for star-forming galaxies and by an accretion shock at the virial radius for massive galaxies.

Environmental effect on gas accretion
Satellite galaxies have much suppressed gas accretion rates compared to central galaxies of the same mass. This suppression is higher in larger haloes or denser environments and at smaller halocentric radii.

Star formation efficiency of molecular gas
Minor mergers can regenerate star formation in quenched early-type galaxies by bringing in fresh gas. This gas, however, forms stars at low efficiency, because it takes time for the gas to settle into a relaxed disc and is, at least initially, dynamically stable against collapse.