Metal ions in circumgalactic medium
Abstract
Recent observations show high column densities of metal ions in extended halos of galaxies in the redshift range z∼ 0-3. Interpretation of these observations is critically sensitive to a model of ionization state of the circumgalactic gas. In order to explain observed OVI column densities models with thermal ionization equilibrium require metallicity of the halo gas to be as high as the solar one. As a consequence such extended halos would become the main reservouir of metals and missing. On the other hand, when a time-dependent radiation field of a nearby starburst galaxy is assumed to be the main ionization source observational OVI absorption data can be explained if the circumgaactic halos contain an order of magnitude lower amount of metals. Such a difference is due to a much lower fraction of OVI ions (f(OVI)∼ 0.1) under the thermal collisional ionization equilibrium than reached (typically f(OVI)≃ 0.4-0.6) in a time-dependent radiation field from the underlying star-forming galaxy superimposed on to the extragalactic background. Therefore we argue that high column densities of OVI recently observed in the halos of staforming galaxies even for low (∼ 0.1 Z_⊙) metallicities. As a result, the requirements to the sources of oxygen in such extended halos relax to a reasonably conservative level. We discuss a possibility of more advanced study of metal ions in extended galactic haloes using the WSO/Spectrum-UV facility.
- Publication:
-
40th COSPAR Scientific Assembly
- Pub Date:
- 2014
- Bibcode:
- 2014cosp...40E3476V