Embedded Clusters in Giant Extragalactic HII Regions III. Extinction and Star Formation
Embedded Clusters in Giant Extragalactic HII Regions III. Extinction and Star Formation
复制标题
巨大河外 HII 区域中的嵌入式星团 III。
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
T. Prabhu
中科院分区：
文献类型：
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作者：
Y. Mayya;T. Prabhu
利用 BVR 宽带和 H α 发射线的光学光度数据，对 7 个星系中的 35 个巨大河外 HII 区域 (GEHR) 进行了恒星形成研究。使用这些天体的光谱数据来估计星际消光、金属丰度和星云对宽带的贡献。涉及 B-V 和 V-R 颜色的无量纲图以及巴尔默线与 B 波段连续谱的通量比用于研究恒星形成。与从电离气体巴尔默线导出的值相比，星团颜色表明恒星连续体的消光减少。与伴随着前一次爆发（t ~ 10 Myr）中富含红超巨星的年轻区域相比，仅具有一次恒星形成爆发的经典年轻（t < 3 Myr）区域的检测频率较低。星团恒星消光的减少、电离光子的破坏以及较老群体的存在（通常在空间上无法从较年轻的群体中分辨）所有这些因素共同导致大多数 GEHR 中观测到的巴尔默线等效宽度较低。提出了一种恒星形成的场景，它解释了GEHR的许多观察到的特性，包括核心晕结构、与星云气体相比，恒星辐射的消光减少、未检测到年轻的单爆发区域以及两个不同年龄群体的共存。
A study of star formation is carried out on 35 giant extragalactic HII regions (GEHRs) in seven galaxies using optical photometric data in BVR broad bands and in the emission line of H alpha. Interstellar extinction, metallicity and nebular contributions to the broad bands are estimated using spectroscopic data on these objects. Dimensionless diagrams involving B-V and V-R colors and the flux ratio of Balmer line to B band continuum are used to study star formation. The cluster colors indicate reduced extinction towards stellar continuum compared to the values derived from Balmer lines for the ionized gas. The frequency of detection of classical young (t < 3 Myr) regions with only one burst of star formation is found to be low as compared to young regions with an accompanying population rich in red supergiants from a previous burst (t ~ 10 Myr). Reduced extinction towards cluster stars, destruction of ionizing photons and the existence of older population, often spatially unresolvable from the younger population, all conspire to make the observed Balmer line equivalent widths low in a majority of the GEHRs. A scenario of star formation is suggested which explains many of the observed properties of GEHRs, including the core-halo structure, reduced extinction for the radiation from stars as compared to that from the nebular gas, non-detection of young single burst regions and the co-existence of two populations of different ages.