The impact of low Star-formation rates on the evolution of Dwarf Galaxies, LSBs, and extragalactic gas clouds
- Author(s)
- Gerhard Hensler, Patrick Steyleithner, Yannick Hein, Alessandro Boselli
- Abstract
Dwarf galaxies and low-surface brightness galaxies as well as extragalactic gas clouds, originating from ram-pressure stripping events and in tidal tails, are preferentially forming star clusters with low masses. This, however, questions whether the initial mass function (IMF) can be filled up to the most massive stars, because there exists a lower cluster mass limit to allow a full coverage of the stellar mass range with at least a single most massive star. The well-known universal IMFs (Salpeter, Kroupa, Chabrier) are usually applied to derive from observational indicators properties such as stellar masses, star-formation rates (SFRs), and the theoretically expected chemical enrichment of galaxies. The same assumption of a filled IMF is mostly applied to numerical models of galaxy evolution. While the long-living low-mass stars mostly contribute to the binding mass of clusters and the gravity of galaxies, massive stars act energetically on the interstellar medium (ISM), as e.g. regulating the star formation locally and energizing the ISM what can drive galactic outflows. Since low cluster masses do not allow complete stars to exist over the entire massive regime of the universal IMF, different recipes have been introduced how to assemble stellar masses. The one is assuming that stars in clusters form bottom up, filling the low-mass range at first according to the IMF, because the formation of massive stars would evaporate small gas clumps and quench further star formation. The second recipe is based on statistical reasons and assumes that any stellar mass can form at any times with the mass distribution which is prescribed by the probability distribution of the IMF. We have elaborated and compared (published by Steyrleithner & Hensler) the different effects of a filled but underpopulated IMF vs. a truncated IMF on the evolution of dwarf galaxies. There are two main issues; the one that a filled IMF regulates the star cluster formation more efficiently due to the mass dependence of Lyman continuum radiation and stellar winds, while as a second effect the cumulated supernovae typeII number and energies are smaller. Applying the stochastic sampling method to the cluster formation mostly forms more massive stars than a truncated IMF but with gaps in the whole high-mass range. However, playing dices sufficiently often approaches the truncated IMF effects. Both stellar mass recipes are then applied to observed gas clumps with low SFRs, as e.g. ram-pressure stripped clouds of a Virgo cluster galaxy. Halpha and UV brightnesses are then compared with the cluster ages derived from SEDs. Deviations from regular IMF populations of intermediate-mass vs. massive stars for incomplete IMFs should also have discernible consequences for the ratios of typical element yields from both mass regimes, as e.g. C/O, Fe/O, Ba/Mg.
- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- University of Vienna, Aix-Marseille Université
- Publication date
- 07-2024
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103003 Astronomy, 103004 Astrophysics
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/08d15146-74c4-466d-b58d-f90060b0d68a