2008/02/29 by Ian D. McGreer, Greg L. Bryan · 3 citations
Physics and Astronomy · Social Sciences · #Accretion (finance) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Educational Leadership and Practices #Halo #Population #Protostar #Star formation #Stars #astro-ph
paper · pdf · doi:10.1086/590530
13 pages, 11 figures, with referee suggestions; ApJ accepted
arxiv created 2008/08/01 · openalex publication_date 2008/09/18 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We use numerical simulations to investigate the importance of HD formation and cooling on the first generation of metal-free stars in a ΛCDM cosmology. We have implemented and tested non-equilibrium HD chemistry in an adaptive mesh refinement simulation code and applied it to two situations. (1) It is first applied to the formation of 10 5 -10 6 M ☉ halos which form in the absence of any ionizing source ("unperturbed" halos). We show, in agreement with previous work, that HD cooling is of only marginal importance for most halos; however, we find that for the lowest mass halos, with masses a few times 10 5 M ☉ , HD cooling can equal or surpass the H 2 cooling rate. This leads to a population of stars formed in halos with effective HD cooling that are less massive by a factor of ~6 compared to halos dominated by H 2 cooling. (2) In the second part of the paper, we ionize the halos in order to explore the impact of HD cooling in the presence of an ample population of free electrons. This leads to cooler temperatures (due to the electron-catalyzed production of H 2 ), implying somewhat lower resulting protostellar mass. Adding HD chemistry changes this by lowering the temperature further, to the level of the CMB. We find that HD cooling dominates over H 2 cooling in the density range 10 2 -10 6 cm −3 , but above this density, the temperature rises and H 2 cooling dominates again. Because of this, the accretion rate on to the protostar is almost the same as in the H 2 case (at least for accreted masses below 50-100 M ☉ ); therefore we argue that HD cooling in ionized halos will probably not result in a population of significantly lower mass stars.