Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-08-28
Astronomy and Astrophysics
Astrophysics
22 pages, including 10 figures; Accepted to the Astrophysical Journal
Scientific paper
10.1086/508913
Both gas accretion (infall) and winds (outflow) change a galaxy's metallicity and gas fraction, lowering the effective yield. Low effective yields in galaxies with rotation speeds < 120 km/s have been widely interpreted as the onset of SN-driven winds below a characteristic galaxy mass, but gas accretion is also a viable explanation. However, calculations presented here prove: (1) that metal-enriched outflows are the only mechanism that can significantly reduce the effective yield, but only for gas-rich systems; (2) that it is nearly impossible to reduce the effective yield of a gas-poor system, no matter how much gas is lost or accreted; and (3) that any subsequent star formation drives the effective yield back to the closed-box value. Thus, only gas-rich systems with low star formation rates (such as dwarf irregulars) can produce and maintain low effective yields, while massive gas-poor galaxies can never show low effective yields, even after experiencing substantial infall and/or outflow. The drop in effective yield seen in low mass galaxies is therefore less likely to be due to the onset of SN-driven winds than to the galaxies' surface densities falling entirely below the Kennicutt SF threshold. Additional calculations confirm that the fraction of baryonic mass lost through winds varies only weakly with galaxy mass, shows no sharp upturn at any mass scale, and does not require that >15% of baryons have been lost by galaxies of any mass. SN feedback is therefore unlikely to be effective for removing large amounts of gas from low mass disk galaxies. In addition, the dependence between metal-loss and galaxy mass is sufficiently weak that massive galaxies dominate metal enrichment of the IGM. The calculations in this paper provide limiting cases for any arbitrary chemical evolution history, as proven in an Appendix.
No associations
LandOfFree
The Metallicity of Galaxy Disks: Infall versus Outflow does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Metallicity of Galaxy Disks: Infall versus Outflow, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Metallicity of Galaxy Disks: Infall versus Outflow will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-106678