YOUNG STELLAR POPULATIONS AND STAR CLUSTERS IN NGC 1705
YOUNG STELLAR POPULATIONS AND STAR CLUSTERS IN NGC 1705
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NGC 1705 中的年轻恒星群和星团
DOI：
10.1088/0004-6256/138/1/169
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
L. Greggio
中科院分区：
文献类型：
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作者：
F. Annibali;M. Tosi;M. Monelli;M. Sirianni;P. Montegriffo;A. Aloisi;L. Greggio
本文介绍了哈勃太空望远镜（HST）对晚型矮星系NGC 1705的光度测量，用宽视场行星相机2 （WFPC2）在F380W和F439W波段观测，用高级巡天相机/高分辨率通道（HRC）在F330W、F555W和F814W波段滤光片观测。我们将这些数据与WFPC2在F555W和F814W波段上获得的数据交叉关联，并得出交叉识别的单个恒星和候选星团的多波段彩色星等图（CMDs）。对于星系中心区域，HST-NICMOS F110W和F160W光度测量也可用，我们给出了所有波段测量的256个物体的U， B， V， I， J， H的CMDs。虽然我们之前基于F555W、F814W、F110W和F160W数据的研究使我们能够将NGC 1705的恒星形成历史追溯到哈勃时间，但新数据提供了对其近期演变的更好了解。利用合成的CMDs方法，我们证实了两个强烈的恒星形成爆发（SF）的存在。这两个爆发中较老的一个（B1）发生在10至15亿年前，与中央超级星团（SSC）的年龄相当。较年轻的爆发（B2）开始于约3myr以前，它仍然活跃。B2所产生的恒星质量约为~ 106 M☉，而B1的质量则低了~ 3倍。发作间期的特征可能是SF水平低得多，而不是完全停止。这两次爆发的空间分布明显：B1集中在中心，B2更分散，并呈现环状和弧形结构，使人想起膨胀的壳。这表明了一种反馈机制，在ngc1705中观测到的膨胀的超级气泡，可能是由10-15 Myr的爆发产生的，引发了当前强烈的SF活动。HRC出色的空间分辨率使我们能够可靠地识别NGC 1705中心~ 26″× 29″区域的12个星团（加上SSC），其中10个星团在所有UBVIJH波段都有测光。星团光度测定与GALEV人口综合模型的比较提供了年龄从≈10 Myr到≈1 Gyr，质量在≈104和105 M☉之间。中心区域明显的星团人口，包括一个SSC星团、一个稠密星团和几个规则星团，证实了ngc1705强烈的恒星形成活动。
We present Hubble Space Telescope (HST) photometry of the late-type dwarf galaxy NGC 1705 observed with the Wide-Field Planetary Camera 2 (WFPC2) in the F380W and F439W bands and with the Advanced Camera for Surveys/High-Resolution Channel (HRC) in the F330W, F555W, and F814W broad-band filters. We cross-correlate these data with previous ones acquired with the WFPC2 in the F555W, F814W bands, and derive multiband color–magnitude diagrams (CMDs) of the cross-identified individual stars and candidate star clusters. For the central regions of the galaxy, where HST-NICMOS F110W and F160W photometry is also available, we present U, B, V, I, J, H CMDs of the 256 objects with magnitudes measured in all bands. While our previous study based on F555W, F814W, F110W, and F160W data allowed us to trace the star formation history of NGC 1705 back to a Hubble time, the new data provide a better insight on its recent evolution. With the method of the synthetic CMDs, we confirm the presence of two strong bursts of star formation (SF). The older of the two bursts (B1) occurred between ∼10 and 15 Myr ago, coeval to the age of the central super star cluster (SSC). The younger burst (B2) started ∼3 Myr ago, and it is still active. The stellar mass produced by B2 amounts to ∼106 M☉, and it is a factor of ∼3 lower for B1. The interburst phase was likely characterized by a much lower level of SF rather than by its complete cessation. The two bursts show distinct spatial distributions: while B1 is centrally concentrated, B2 is more diffused, and presents ring and arclike structures that remind of an expanding shell. This suggests a feedback mechanism, in which the expanding superbubble observed in NGC 1705, likely generated by the 10–15 Myr burst, triggered the current strong SF activity. The excellent spatial resolution of the HRC allowed us to reliably identify 12 star clusters (plus the SSC) in the central ∼26″ × 29″ region of NGC 1705, 10 of which have photometry in all the UBVIJH bands. The comparison of the cluster photometry with the GALEV populations synthesis models provides ages from ≈10 Myr to ≈1 Gyr, and masses between ≈104 and 105 M☉. The conspicuous cluster population in the central regions, with one SSC, one populous cluster, and several regular ones, confirm the strong star-forming activity of NGC 1705.