Analysis of spiral arms using anisotropic wavelets: gas, dust and magnetic fields in M51
Analysis of spiral arms using anisotropic wavelets: gas, dust and magnetic fields in M51
复制标题
使用各向异性小波分析旋臂：M51 中的气体、灰尘和磁场
DOI：
10.1051/0004-6361:20065225
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发表时间：
2006
影响因子：
6.5
通讯作者：
C. Horellou
中科院分区：
文献类型：
--
作者：
I. Patrikeev;A. Fletcher;A. Fletcher;R. Stepanov;R. Beck;E. M. Berkhuijsen;P. Frick;C. Horellou
上下文盘状星系中螺旋形磁场的起源是一个悬而未决的问题。目标。比较规则的磁场方向与气体螺旋臂的螺距角可以告诉我们螺旋冲击压缩是否是导致磁螺旋的原因。我们还希望看到ISM不同分量的脊是否显示出密度波理论所预期的大规模系统性变化。方法.我们已经开发出一种技术，隔离细长的结构在银河系的图像，如螺旋臂，使用各向异性小波和应用这一地图的CO，红外和无线电连续发射的大设计的螺旋星系M 51。结果确定了几千秒差距长的CO、红外线和无线电连续辐射脊之间的系统位移，以及沿沿着螺旋臂的俯仰角的几十度的大变化。我们发现两种类型的臂的极化无线电发射：一个有一个脊靠近脊的CO，具有类似的螺距角的CO和极化螺旋和规则的磁场;另一个并不总是与CO臂和其螺距角不同的方向，其规则的磁场。结论.规则磁场脊、致密气体和温暖尘埃之间的偏移与螺旋密度波触发的星星形成的预期序列是一致的，在气体进入激波和巨大分子云形成之间有数千万年的延迟，在云形成和年轻星星团出现之间也有类似的间隔。在CO臂的位置处，规则磁场的取向与螺旋臂的螺旋角相同，但是远离气体臂，规则磁场的取向显著变化。螺旋激波压缩可以解释一种强极化射电辐射臂的产生，但另一种不同的机制可能是造成第二种极化臂的原因。
Context. The origin of the spiral pattern of magnetic fields in disc galaxies is an open question. Aims. Comparison of the regular magnetic field orientation with the gaseous spiral arm pitch angles can tell us whether spiral shock compression is responsible for the magnetic spirals. We also wish to see whether the ridges of different components of the ISM show the large-scale, systematic shifts expected from density wave theory. Methods. We have developed a technique of isolating elongated structures in galactic images, such as spiral arms, using anisotropic wavelets and apply this to maps of the CO, infrared and radio continuum emission of the grand-design spiral galaxy M 51. Results. Systematic shifts between the ridges of CO, infrared and radio continuum emission that are several kpc long are identified, as well as large variations in pitch angle along spiral arms, of a few tens of degrees. We find two types of arms of polarized radio emission: one has a ridge close to the ridge of CO, with similar pitch angles for the CO and polarization spirals and the regular magnetic field; the other does not always coincide with the CO arm and its pitch angle differs from the orientation of its regular magnetic field. Conclusions. The offsets between ridges of regular magnetic field, dense gas and warm dust are compatible with the sequence expected from spiral density wave triggered star formation, with a delay of a few tens of millions of years between gas entering the shock and the formation of giant molecular clouds and a similar interval between the formation of the clouds and the emergence of young star clusters. At the position of the CO arms the orientation of the regular magnetic field is the same as the pitch angle of the spiral arm, but away from the gaseous arms the orientation of the regular field varies significantly. Spiral shock compression can explain the generation of one type of arm of strong polarized radio emission but a different mechanism is probably responsible for a second type of polarization arm.