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Both gas accretion (infall) and winds (outflow) change a galaxys 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.
The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7,138 HII regions
Observations of H$_{2}$CO lines and continuum at 1.3 mm towards Sgr B2(N) and Sgr B2(M) cores were carried out with the SMA. We imaged H$_{2}$CO line absorption against the continuum cores and the surrounding line emission clumps. The results show th
We present an investigation into the absorber in front of the z=2.63 radio galaxy MRC 2025-218, using integral field spectroscopy obtained at the Very Large Telescope, and long slit spectroscopy obtained at the Keck II telescope. The properties of MR
Observations of two H$_2$CO ($3_{03}-2_{02}$ and $3_{21}-2_{20}$) lines and continuum emission at 1.3 mm towards Sgr B2(N) and Sgr B2(M) have been carried out with the SMA. The mosaic maps of Sgr B2(N) and Sgr B2(M) in both continuum and lines show a
We aim to characterize the outflow properties of a sample of early Class 0 phase low-mass protostars in Orion first identified by the Herschel Space Observatory. We also look for signatures of infall in key molecular lines. CO $J$=3-2 and $J$=4-3 map