TP-AGB和RHeB星对局域星系近红外光度的贡献：对高红移星系质量测量的启示
The Contribution of TP-AGB and RHeB Stars to the Near-IR Luminosity of Local Galaxies: Implications for Stellar Mass Measurements of High Redshift Galaxies
摘要：
利用高空间分辨率的HST WFC 3和ACS对分辨的恒星星族的成像，我们限制了热脉冲渐近巨星分支（TP-AGB）星和红氦燃烧（RHeB）星对23个邻近星系1.6 μ m近红外（NIR）光度的贡献。TP-AGB相的贡献高达17%的综合F160 W流量，即使红巨星分支人口众多。RHeB粒子数贡献可以匹配甚至超过TP-AGB贡献，提供高达21%的集成F160 W光。因此，由于恒星形成率在2500万年到几个Gyr的时间尺度上的波动，近红外质量与光（M/L）的比值应该会有很大的变化。我们比较我们的观测结果预测的基础上光学推导的恒星形成的历史和恒星星族合成（SPS）模型，包括模型的基础上帕多瓦等时线（用于流行的SPS计划）。SPS模型通常再现了样本中TP-AGB恒星的预期数量。然而，相同的SPS模型在TP-AGB恒星的F160 W通量贡献上给出了更大的差异，以2.3 +/-0.8的加权平均因子过度预测了通量。这个较大的偏移量是由预测的适度数量的年轻（<3亿年）的高光度TP-AGB恒星驱动的。最适合的SPS模型同时倾向于低估RHeB序列上的恒星数量和通量，对于具有大量RHeB的星系，通常是2.0+/-0.6倍。巧合的是，TP-AGB的过度预测和RHeBs的预测不足导致近红外M/L比率在快速恒星形成速率下基本不变。然而，星系的近红外光通量比可能比富AGB模型预测的要小得多，这一结果已经在一些中等红移的星暴后星系中观察到。（节录）
英文摘要：
Using high spatial resolution HST WFC3 and ACS imaging of resolved stellar populations, we constrain the contribution of thermally-pulsing asymptotic giant branch (TP-AGB) stars and red helium burning (RHeB) stars to the 1.6 um near-infrared (NIR) luminosities of 23 nearby galaxies. The TP-AGB phase contributes as much as 17% of the integrated F160W flux, even when the red giant branch is well populated. The RHeB population contribution can match or even exceed the TP-AGB contribution, providing as much as 21% of the integrated F160W light. The NIR mass-to-light (M/L) ratio should therefore be expected to vary significantly due to fluctuations in the star formation rate over timescales from 25 Myr to several Gyr. We compare our observational results to predictions based on optically derived star formation histories and stellar population synthesis (SPS) models, including models based on the Padova isochrones (used in popular SPS programs). The SPS models generally reproduce the expected numbers of TP-AGB stars in the sample. The same SPS models, however, give a larger discrepancy in the F160W flux contribution from the TP-AGB stars, over-predicting the flux by a weighted mean factor of 2.3 +/-0.8. This larger offset is driven by the prediction of modest numbers of high luminosity TP-AGB stars at young (<300 Myrs) ages. The best-fit SPS models simultaneously tend to under-predict the numbers and fluxes of stars on the RHeB sequence, typically by a factor of 2.0+/-0.6 for galaxies with significant numbers of RHeBs. Coincidentally, over-prediction of the TP-AGB and under-prediction of the RHeBs result in a NIR M/L ratio largely unchanged for a rapid star formation rate. However, the NIR-to-optical flux ratio of galaxies could be significantly smaller than AGB-rich models would predict, an outcome that has been observed in some intermediate redshift post-starburst galaxies. (Abridged)
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