High-Latitude Radio Emission in a Sample of Edge-on Spiral Galaxies
High-Latitude Radio Emission in a Sample of Edge-on Spiral Galaxies
复制标题
边缘螺旋星系样本中的高纬度射电发射
DOI：
10.1086/300827
复制
发表时间：
1998
期刊：
影响因子：
--
通讯作者：
B. Sorathia
中科院分区：
文献类型：
--
作者：
J. Irwin;J. English;B. Sorathia
为了寻找平面上下扩展的(≳1kpc)射电连续辐射，我们使用超大型阵列在其C构型中绘制了16个位于20厘米处的边缘星系图，并在D构型中绘制了这些星系中位于6和/或20厘米处的子集。对于五个星系，我们可以形成光谱指数、能量和磁场图(假设能量最小)。虽然这些星系部分是根据射电流量密度选择的，但它们的恒星形成率(SFR)各不相同，可能只有六个星系被认为是“星暴”星系。文中还给出了哈勃类型和隔离度的范围。星系在很大程度上落在FIR-射电连续谱关联上。它们还显示了红外表面亮度和温度之间的关系，将之前观察到的Lehnert&Heckman关系扩展到恒星形成率较低的星系。我们发现，除了一个星系外，所有星系都显示出非热高纬度射电连续发射的证据，这表明宇宙线(CR)晕在恒星形成星系中很常见。在这些星系中，有八个是新发现的。高纬度辐射可以在各种空间尺度上看到，并以离散和/或平滑的特征出现。在某些情况下，在大尺度上可以看到离散特征，这表明平滑的射电晕可能在一定程度上由离散特征和低空间分辨率组成。一般来说，离散的特征来自圆盘，但对CR扩散长度的估计表明，仅靠扩散不足以将粒子输送到所见的高纬度(一种情况下为15kpc)。因此，CRS可能通过低密度区域扩散和/或由其他机制(例如，风)辅助。我们搜索了高纬度射电辐射的流行与许多其他特性之间的关联，包括全球SFR、单位恒星形成面积的超新星输入率、A和环境，但没有发现与这些特性中的任何一个明显的关联。数据的一个子集充其量只允许与A的弱相关性。然而，我们的一个未检测到的(NGC 4517)发生在与Dahlem，Lisenfeld和Golla发现的阈值水平一致的阈值水平。与恒星形成指标缺乏良好相关性的原因可能是恒星形成过程的时间尺度与射电发射的持续时间不同。与环境等其他属性的相关性更难评估。然而，一些孤立的星系显示出强烈的射电晕，这表明相互作用不是产生面外发射所必需的。
We have mapped 16 edge-on galaxies at 20 cm using the Very Large Array in its C configuration, and a subset of these galaxies in the D configuration at 6 and/or 20 cm, in a search for extended (≳1 kpc) radio continuum emission above and below the plane. For five galaxies, we could form spectral index, energy, and magnetic field maps (assuming minimum energy). While the galaxies were partly chosen by radio flux density, they span a variety of star formation rates (SFRs), and only six might be considered "starburst" galaxies. A range of Hubble type and degree of isolation are also represented. The galaxies largely fall on the FIR–radio continuum correlation. They also display a correlation between IR surface brightness and warmth, extending the previously observed relation of Lehnert & Heckman to galaxies with lower star formation rates. We find that all but one galaxy show evidence for nonthermal high-latitude radio continuum emission, suggesting that cosmic-ray (CR) halos are common in star-forming galaxies. Of these, eight galaxies are new detections. The high-latitude emission is seen over a variety of spatial scales and in discrete and/or smooth features. In some cases, discrete features are seen on large scales, suggesting that smooth radio halos may consist, in part, of discrete features combined with low spatial resolution. In general, the discrete features emanate from the disk, but estimates of CR diffusion lengths suggest that diffusion alone is insufficient to transport the particles to the high latitudes seen (>15 kpc in one case). Thus CRs likely diffuse through low-density regions and/or are assisted by other mechanisms (e.g., winds). We searched for correlations between the prevalence of high-latitude radio emission and a number of other properties, including the global SFR, supernova input rate per unit star-forming area, A, and environment, and do not find clear correlations with any of these properties. A subset of the data allows, at best, for only a weak correlation with A. Our one nondetection (NGC 4517), however, occurs at a threshold level consistent with that found by Dahlem, Lisenfeld, & Golla. The lack of a good correlation with star formation indicators could be the result of the different timescales for star formation processes compared with the duration of the radio emission. Correlations with other properties, such as environment, are more difficult to assess. However, a few isolated galaxies display strong radio halos, indicating that an interaction is not necessary to produce the extraplanar emission.