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SURFACE BRIGHTNESS AND STELLAR POPULATIONS AT THE OUTER EDGE OF THE LARGE MAGELLANIC CLOUD: NO STELLAR HALO YET

机译:大麦哲伦云外缘的表面亮度和星空人口:还没有星光晕

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摘要

We present a high-quality color-magnitude diagram (CMD) for a 36′ x 36′ field located 8° ( approx= 7 kpc) from the Large Magellanic Cloud (LMC) center, as well as a precise determination of the LMC surface brightness derived from the resolved stellar population out to this large galactocentric radius. This deep CMD shows for the first time the detailed age distribution at this position, where the surface brightness is V approx= 26.5 mag arcsec~(-2). At a radius R approx= 474′ the main sequence is well populated from the oldest turnoff at I approx= 21.5 to the 2.5 Gyr turnoff at I approx= 19.5. Beyond this radius, a relatively strong gradient in the density of stars with ages in the approx= 2.5—4 Gyr range is apparent. There are some stars brighter and bluer than the main population, quite uniformly distributed over the whole area surveyed, which are well matched by a 1.5 Gyr isochrone and may be indicative of a relatively recent star formation, or merger, event. The surface brightness profile of the LMC remains exponential to this large galactocentric radius and shows no evidence of disk truncation. Combining the information on surface brightness and stellar population, we conclude that the LMC disk extends (and dominates over a possible stellar halo) out to a distance of at least 7 kpc. These results confirm that the absence of blue stars in the relatively shallow off-center CMDs of dwarf irregular galaxies is not necessarily evidence for an exclusively old stellar population resembling the halo of the Milky Way.
机译:我们为距麦哲伦星云(LMC)中心8°(约= 7 kpc)的36'x 36'场提供了高质量的色度图(CMD),以及LMC表面的精确确定亮度来自解决的恒星群体,直到这个大的半视心半径。该深CMD首次显示了该位置的详细年龄分布,其中表面亮度为V大约= 26.5 mag arcsec〜(-2)。在半径R大约= 474'处,主序列从I大约= 21.5的最旧关闭到I大约= 19.5的2.5 Gyr关闭填充得很好。在这个半径之外,年龄大约在2.5-4 Gyr范围内的恒星密度会出现一个相对较强的梯度。有一些恒星比主要种群更明亮和更蓝,在整个调查区域内分布均匀,与1.5 Gyr的等时线很好地匹配,可能表明是相对较新的恒星形成或合并事件。 LMC的表面亮度轮廓对于这个较大的半圆心半径保持指数级,并且没有显示出磁盘被截断的迹象。结合表面亮度和恒星总数的信息,我们得出结论,LMC盘向外延伸(并主导可能的恒星晕)至少7 kpc的距离。这些结果证实,矮不规则星系的相对较浅的偏心CMD中没有蓝星,并不一定表明类似银河系光晕的恒星恒星的存在。

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