M33盘的恒星考古学：最近的恒星形成历史和对与M31相互作用时间的限制
The Stellar Archeology of the M33 Disk: Recent Star-Forming History and Constraints on the Timing of an Interaction with M31
摘要：
利用MegaCam记录的图像研究了本星系群Sc星系M33的近期恒星形成历史。恒星盘的性质在R = 8 kpc附近发生变化。在这个半径范围内，恒星形成率（SFR）至少在过去的2.5亿年里一直保持不变，而在更大的半径范围内，SFR在同一时期内有所下降。内盘最近的SFR一直是恒定的，这表明M33至少在过去的0.5 Gyr内是孤立演化的，从而限制了最近与M31相互作用的时间。年轻恒星对恒星盘总质量的贡献随半径的变化而变化，峰值接近8 kpc。证据还提出，在过去的1亿年的SFR在银河系的南半部分已~ 0.4德克斯比北半部分高。最后，大小跨越许多kpc的结构，包含蓝色物体-可能是在中间时期形成的主序星-在磁盘边界附近被确定。有人认为，这些潮汐特征是从M33的主体中提取出来的，在某些情况下，是恒星形成的化石遗迹，发生在中间时期的扩展盘中。
英文摘要：
Images recorded with MegaCam are used to investigate the recent star-forming history (SFH) of the Local Group Sc galaxy M33. The properties of the stellar disk change near R = 8 kpc. Within this radius the star formation rate (SFR) has been constant with time during at least the past 250 Myr, while at larger radii the SFR has declined during this same time period. That the recent SFR in the inner disk has been constant suggests that M33 has evolved in isolation for at least the past ~ 0.5 Gyr, thereby providing a constraint on the timing of any recent interaction with M31. The fractional contribution that young stars make to the total mass of the stellar disk changes with radius, peaking near 8 kpc. Evidence is also presented that the SFR during the past 100 Myr in the southern half of the galaxy has been ~ 0.4 dex higher than in the northern half. Finally, structures with sizes spanning many kpc that contain blue objects - presumably main sequence stars that formed during intermediate epochs - are identified near the disk boundary. It is argued that these are tidal features that were pulled from the main body of M33 and - in some cases - are the fossil remnants of star formation that occured in an extended disk during intermediate epochs.
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