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arXiv 1007.0784astro-ph.CO
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晚型星系NGC 1311的年轻恒星星族

The Young Stellar Population of the Nearby Late-Type Galaxy NGC 1311

Paul B. Eskridge, Rogier A. Windhorst, Violet A. Mager, Rolf A. Jansen

备注：
AASTex, 34 pages, 13 postscript figures. Accepted for publication by The Astronomical Journal
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摘要：

利用哈勃空间望远镜获得的SBm星系NGC 1311的近紫外、光学和近红外图像，提取了PSF拟合的恒星光度学。紫外线和光学数据揭示了一群年龄在2-10百万年的热主序星。我们还发现了年龄在1000万年到4000万年之间的蓝超巨星和年龄在1000万年到10000万年之间的红超巨星。我们的近红外数据显示，恒星形成的证据可以追溯到~1 Gyr，与以前的工作一致。与等时线的拟合表明金属丰度为Z ~ 0.004。蓝超巨星与红超巨星的比例与这个金属丰度一致。这表明NGC 1311遵循晚型矮星系的光度-金属丰度关系。大约一半的热主序星和蓝超巨星位于NGC 1311内部的两个区域。这两个区域的跨度都在200个百分点左右，因此它们的交叉时间大致等于我们发现的占主导地位的年轻人口的1000万年年龄。超巨星的光度函数表明，从大约1亿年前到大约1500万年前，恒星形成率缓慢上升（每年0.001太阳质量），然后在大约1000万年前强烈增强（每年0.01太阳质量）。我们没有看到令人信服的证据表明NGC 1311在过去1亿年的恒星形成历史中存在空白，并且在最后一个Gyr中也没有。这反对爆发模式，而赞成最近恒星形成历史的喘息或呼吸模式。

英文摘要：

We have extracted PSF-fitted stellar photometry from near-ultraviolet, optical and near-infrared images, obtained with the Hubble Space Telescope, of the nearby (D ~ 5.5 Mpc) SBm galaxy NGC 1311. The ultraviolet and optical data reveal a population of hot main sequence stars with ages of 2-10 Myr. We also find populations of blue supergiants with ages between 10 and 40 Myr and red supergiants with ages between 10 and 100 Myr. Our near-infrared data shows evidence of star formation going back ~1 Gyr, in agreement with previous work. Fits to isochrones indicate a metallicity of Z ~ 0.004. The ratio of blue to red supergiants is consistent with this metallicity. This indicates that NGC 1311 follows the well-known luminosity-metallicity relation for late-type dwarf galaxies. About half of the hot main sequence stars and blue supergiants are found in two regions in the inner part of NGC 1311. These two regions are each about 200 pc across, and thus have crossing times roughly equal to the 10 Myr age we find for the dominant young population. The Luminosity Functions of the supergiants indicate a slowly rising star formation rate (of 0.001 Solar masses per year) from ~100 Myr ago until ~15 Myr ago, followed by a strong enhancement (to 0.01 Solar Masses per year) at ~10 Myr ago. We see no compelling evidence for gaps in the star-forming history of NGC 1311 over the last 100 Myr, and, with lower significance, none over the last Gyr. This argues against a bursting mode, and in favor of a gasping or breathing mode for the recent star-formation history.

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