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Oscar Agertz. Profile photo.

Oscar Agertz

Assistant Professor / Associate senior university lecturer / Wallenberg Academy Fellow

Oscar Agertz. Profile photo.

The nature of damped HI absorbers probed by cosmological simulations: satellite accretion and outflows


  • Nils Henrik Pehlivan Rhodin
  • Oscar Agertz
  • Lise Christensen
  • Florent Renaud
  • Johan Peter Uldall Fynbo

Summary, in English

We use cosmological hydrodynamic zoom simulations to study the neutral gas distributionin and around galaxies that gives rise to high column density HILyαabsorption (dampedLyαsystems (DLAs) and sub-DLAs) in background quasar spectra. Such simulations oftensacrifice numerical resolution for volume that affects the lower density galaxy halo gas,and simulations have difficulties reproducing the span of projected separations (b) betweenabsorbing clouds and their hosts. Our simulations produce (sub-)DLAs over the entire probedparameter space (b50 kpc and metallicity−4[M/H]0.5) at all redshifts (z∼0.4−3.0),enclosing spectroscopically confirmed absorber-galaxy pairs. Recovering (sub-)DLAs atb20−30 kpc from a massive host galaxy requires high numerical resolution and efficientfeedback, and we show that these lines-of-sight are associated with dwarf satellites in the mainhalo, stripped metal-rich gas, and outflows. HIdisc- and halo gas significantly contributesto (sub-)DLAs around galaxies. At large redshifts the halo plays an increasingly importantrole, while at 0.4<z<1 the disc and halo contribute with∼60(80) and∼40(20) per centto column densities above the sub-DLA(DLA) lower limits. The distribution ofbfor sub-DLAs and DLAs overlap atz∼2−3, but evolves so that sub-DLAs on average are locatedat twice largerbbyz∼0.5. A weak correlation suggests that sub-DLA covering fractionsincrease with stellar mass more rapidly than those of DLA. This can explain why sub-DLAsare preferentially selected in more massive galaxies in the low-zUniverse.


  • Lund Observatory
  • eSSENCE: The e-Science Collaboration

Publishing year







Monthly Notices of the Royal Astronomical Society

Document type

Journal article


Oxford University Press


  • Astronomy, Astrophysics and Cosmology


  • Astrophysics - Astrophysics of Galaxies




  • ISSN: 0035-8711