Consequences of bursty star formation on galaxy observables at high redshifts

摘要

The star formation histories (SFHs) of dwarf galaxies are thought to be\emph{bursty}, with large -- order of magnitude -- changes in the starformation rate on timescales similar to O-star lifetimes. As a result, thestandard interpretations of many galaxy observables (which assume a slowlyvarying SFH) are often incorrect. Here, we use the SFHs from hydro-dynamicalsimulations to investigate the effects of bursty SFHs on sample selection andinterpretation of observables and make predictions to confirm such SFHs infuture surveys. First, because dwarf galaxies' star formation rates changerapidly, the mass-to-light ratio is also changing rapidly in both the ionizingcontinuum and, to a lesser extent, the non-ionizing UV continuum. Therefore,flux limited surveys are highly biased toward selecting galaxies in the\emph{burst} phase and very deep observations are required to detect all dwarfgalaxies at a given stellar mass. Second, we show that a $\log_{10}[\nuL_{\nu}(1500{\rm \AA})/L_{{\rm H}\alpha}]>2.5$ implies a very recent quenchingof star formation and can be used as evidence of stellar feedback regulatingstar formation. Third, we show that the ionizing continuum can be significantlyhigher than when assuming a constant SFH, which can affect the interpretationof nebular emission line equivalent widths and direct ionizing continuumdetections. Finally, we show that a star formation rate estimate based oncontinuum measurements only (and not on nebular tracers such as the hydrogenBalmer lines) will not trace the rapid changes in star formation and will givethe false impression of a star-forming main sequence with low dispersion.