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arXiv astro-ph/0209067astro-ph
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星暴NGC3049中的大量恒星成分:热星模的检验

The Massive Stellar Content in the Starburst NGC3049: A Test for Hot-Star Mode

Rosa M. Gonzalez Delgado, Claus Leitherer, Grazyna Stasinka, Timothy Heckman

摘要:

我们已经获得了高空间分辨率的紫外和光学STIS光谱和成像的富金属核星暴在NGC 3049。恒星连续谱和紫外吸收线谱被用来约束大质量恒星星族。在紫外光谱中检测到的CIV和SiIV的强烈蓝移恒星线表明,一个富含金属的紧凑的大质量(1 E6 Msol)年龄为3- 400万年的星团发出紫外光学连续谱。我们发现了强有力的证据,反对这个富含金属的星团中大质量恒星的枯竭。导出的年龄和初始质量函数的质量上限截止值也与光学波长下Wolf-Rayet(WR)特征的检测一致。作为第二个独立的约束质量恒星的内容,星云的发射线光谱模拟与光电离代码使用恒星光谱的演化综合模型。然而,当使用未覆盖的WR和/或Kurucz恒星大气时,星云谱线被3- 400万年的瞬时爆发很难再现,这是紫外线光谱所要求的。与观察到的线比建议的值相比,合成模型中高于24和54 eV的相应光子数太高。由于在这一制度的电离光谱是由WR星的发射占主导地位,这种观测和模型之间的差异很可能是对WR星的错误假设的结果。因此,我们得出结论,星云光谱的高金属丰度的星爆是很难再现的模型WR为主的人口。然而,Smith等人(2002年)的新模型集,覆盖WR和O大气层,并调整WR温度,预测一个更软的远紫外辐射场,提供了更好的匹配数据。

英文摘要:

We have obtained high-spatial resolution ultraviolet and optical STIS spectroscopy and imaging of the metal-rich nuclear starburst in NGC3049. The stellar continuum and the absorption line spectrum in the ultraviolet are used to constrain the massive stellar population. The strong, blueshifted stellar lines of CIV and SiIV detected in the UV spectra indicate a metal-rich, compact, massive (1E6 Msol) cluster of age 3--4 Myr emitting the UV-optical continuum. We find strong evidence against a depletion of massive stars in this metal-rich cluster. The derived age and the upper mass-limit cut-off of the initial mass function are also consistent with the detection of Wolf-Rayet (WR) features at optical wavelengths. As a second independentconstraint on the massive stellar content, the nebular emission-line spectrum is modeled with photoionization codes using stellar spectra from evolutionary synthesis models. However, the nebular lines are badly reproduced by 3--4 Myr instantaneous bursts, as required by the UV line spectrum, when unblanketed WR and/or Kurucz stellar atmospheres are used. The corresponding number of photons above 24 and 54 eV in the synthetic models is too high in comparison with values suggested by the observed line ratios. Since the ionizing spectrum in this regime is dominated by emission from WR stars, this discrepancy between observations and models is most likely the result of incorrect assumptions about the WR stars. Thus we conclude that the nebular spectrum of high-metallicity starbursts is poorly reproduced by models for WR dominated populations. However, the new model set of Smith et al. (2002) with blanketed WR and O atmospheres and adjusted WR temperatures predicts a softer far-UV radiation field, providing a better match to the data.

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