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射电连续谱和蓝致密矮星系的HI研究

Radio Continuum and HI study of Blue Compact Dwarf Galaxies

S. Ramya, N. G. Kantharia, T. P. Prabhu

备注：
39 pages, 8 figures, 38 sub-figures. Accepted for publication in ApJ
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摘要：

本文介绍了用巨米波射电望远镜（GMRT）对Mrk 104、Mrk 108、Mrk 1039、Mrk 1069和IZw 97五个蓝致密矮（BCD）星系的多频射电连续谱和21 cm HI观测结果。在610 MHz和325 MHz的无线电连续辐射被检测到从所有观察到的星系，而只有少数被检测到在240 MHz。在我们的样本中，有三个星系是星系团的成员，两个星系（Mrk 1069和I Zw 97）是孤立星系。来自Mrk 104和Mrk 108的射电辐射被认为包含了整个光学星系，而来自Mrk 1039、Mrk 1069和I Zw 97的射电辐射则被限制在大质量的HII区域。我们认为，这表明后一组星系中的恒星形成最近被触发，星系演化的环境起着一定的作用。根据610 MHz辐射计算的恒星形成率（SFR）在0.01-0.1 M太阳/年的范围内，这与BCD中单个恒星形成区的SFR相似。综合无线电频谱的四个星系的频率范围内的数据是可用的。我们发现，其中两个星系Mrk 1069和Mrk 1039，在低频率，这是很好地拟合自由-自由吸收，而其他两个星系，Mrk 104和Mrk 108，在最低的GMRT频率，显示一个幂律的营业额。孤立星系中平坦的光谱、局部的恒星形成和射电连续谱支持了随机自传播恒星形成（SSPSF）。对四个星系Mrk 104、Mrk 108、Mrk 1039和Mrk 1069的HI观测显示，扩展的盘大到光学尺寸的1.1-6倍。所有观测到的BCD（除了Mrk 104）都显示出半功率宽度为~50-124 km/s的旋转盘。在我们的示例中，固体旋转是常见的。我们注意到，潮汐矮（TD）的起源是可能的两个BCD在我们的样本。

英文摘要：

The multifrequency radio continuum and 21cm HI observations of five blue compact dwarf (BCD) galaxies, Mrk 104, Mrk 108, Mrk 1039, Mrk 1069 and I Zw 97 using the Giant Meterwave Radio Telescope (GMRT) are presented here. Radio continuum emission at 610 MHz and 325 MHz is detected from all the observed galaxies whereas only a few are detected at 240 MHz. In our sample, three galaxies are members of groups and two galaxies (Mrk 1069 and I Zw 97) are isolated galaxies. The radio emission from Mrk 104 and Mrk 108 is seen to encompass the entire optical galaxy whereas the radio emission from Mrk 1039, Mrk 1069, I Zw 97 is confined to massive HII regions. This, we suggest, indicates that the star formation in the latter group of galaxies has recently been triggered and that the environment in which the galaxy is evolving plays a role. Star formation rates (SFR) calculated from 610 MHz emission is in the range 0.01-0.1 M_sun/yr; this is similar to the SFR obtained for individual star forming regions in BCDs. The integrated radio spectra of four galaxies are modelled over the frequency range where data is available. We find that two of the galaxies Mrk 1069 and Mrk 1039, show a turnover at low frequencies which is well fitted by free-free absorption whereas the other two galaxies, Mrk 104 and Mrk 108, show a power law at the lowest GMRT frequencies. The flatter spectrum, localized star formation and radio continuum in isolated galaxies lend support to stochastic self-propagating star formation (SSPSF). The HI observations of four galaxies Mrk 104, Mrk 108, Mrk 1039 and Mrk 1069 show extended disks as large as ~1.1-6 times the optical size. All the observed BCDs (except Mrk 104) show rotating disk with a half power width of ~50-124 km/s. Solid body rotation is common in our sample. We note that the tidal dwarf (TD) origin is possible for two of the BCDs in our sample.

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