星系与质量集合（GAMA）：恒星形成历史与恒星质量增长的联系
Galaxy And Mass Assembly (GAMA): Linking Star Formation Histories and Stellar Mass Growth
摘要：
我们从星系和质量集合体（GAMA）巡天的观测中，给出了低质量（M* < 10^10 Msun）星系中随机恒星形成历史的证据。对于0.05<z<0.32之间的约73，000个星系，我们根据光谱Halpha测量计算了恒星形成率（SFR）和比恒星形成率（SSFR = SFR/M*），并应用来自Balmer递减的尘埃校正。我们发现SSFR对恒星质量的依赖性，使得SSFR随着恒星质量的增加而降低，对于完整的样本，SSFR随着恒星质量的增加而降低。我们使用简单的参数化指数下降的恒星形成的历史，研究恒星形成的时间尺度和形成红移的恒星质量的依赖。我们发现，以前拟合z~1星系样本的参数化方法不能恢复在0.05<z<0.32的GAMA样本中观测到的SSFR和恒星质量的分布。特别是，大量的低质量（M* < 10^10 Msun）星系被观测到具有比这些简单模型在0.05<z<0.32的红移范围内所能解释的更高的SSFR，即使在调用质量依赖的阶段演化时也是如此。对于这样一个大量的星系，以保持低恒星质量，但港口这样高的SSFR，需要一个弱的基本指数下降SFH叠加随机爆发的恒星形成晚发病。
英文摘要：
We present evidence for stochastic star formation histories in low-mass (M* < 10^10 Msun) galaxies from observations within the Galaxy And Mass Assembly (GAMA) survey. For ~73,000 galaxies between 0.05<z<0.32, we calculate star formation rates (SFR) and specific star formation rates (SSFR = SFR/M*) from spectroscopic Halpha measurements and apply dust corrections derived from Balmer decrements. We find a dependence of SSFR on stellar mass, such that SSFRs decrease with increasing stellar mass for star-forming galaxies, and for the full sample, SSFRs decrease as a stronger function of stellar mass. We use simple parametrizations of exponentially declining star formation histories to investigate the dependence on stellar mass of the star formation timescale and the formation redshift. We find that parametrizations previously fit to samples of z~1 galaxies cannot recover the distributions of SSFRs and stellar masses observed in the GAMA sample between 0.05<z<0.32. In particular, a large number of low-mass (M* < 10^10 Msun) galaxies are observed to have much higher SSFRs than can be explained by these simple models over the redshift range of 0.05<z<0.32, even when invoking mass-dependent staged evolution. For such a large number of galaxies to maintain low stellar masses, yet harbour such high SSFRs, requires the late onset of a weak underlying exponentially declining SFH with stochastic bursts of star formation superimposed.
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