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arXiv 0706.3174astro-ph
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NGC4438及其在无线电波段的环境

NGC4438 and its environment at radio wavelengths

Ananda Hota, D. J. Saikia, Judith A. Irwin

摘要:

利用VLA和GMRT对室女星系团中的活动星系NGC 4438进行了多频、射电连续谱和HI观测。VLA在4860和8460 MHz的高分辨率观测表明,在高度不对称的射电辐射波瓣之间存在着一个频谱倒置的射电核。这表明,这些叶的出现是由于活动星系核,而不是一个紧凑的核星暴。用GMRT进行的低频无线电连续观测探测到星系西侧的扩展发射,其光谱指数在较高频率下较平坦,并表明它是热发射和非热发射的混合物。HI观测显示,在NGC 4438的西侧有一个细长的结构,其位移约为4.1 kpc,大小约为9.8 kpc,质量为1.8*10^8太阳质量。速度场表明有系统的旋转。我们还探测到质量为1.2*10^8 M_sun的星系盘的HI辐射。我们检测到一个微弱的HI尾巴向北的NGC 4438接近恒星的尾巴在深光学观测。如果它位于NGC 4438的距离上,这个HI尾的总长度约为50 kpc,质量为1.4*10^8太阳质量。HI尾的速度约为-10 km/s,与IC 3355的HI发射速度相似,但不能排除该尾可能是前景银河系发射的可能性。我们根据不同的模型讨论了不同的结构。

英文摘要:

We present multi-frequency, radio-continuum and HI observations of NGC4438, the highly-disturbed, active galaxy in the Virgo cluster, with the VLA and the GMRT. High-resolution observations with the VLA at 4860 and 8460 MHz show the presence of an inverted-spectrum radio nucleus located between the highly asymmetric lobes of radio emission. This demonstrates that these lobes arise due to an AGN rather than a compact nuclear starburst. The low-frequency radio continuum observations made with the GMRT detect the extended emission on the western side of the galaxy whose spectral index is flatter at higher frequencies and suggests that it is a mixture of thermal and non-thermal emission. The HI observations show an elongated structure which is displaced by ~4.1 kpc on the western side of NGC4438 and has a size of ~9.8 kpc and a mass of 1.8*10^8 M_sun. The velocity field suggests systematic rotation. We also detect HI emission from the disk of the galaxy with a mass of 1.2*10^8 M_sun. We detect a faint HI tail towards the north of NGC4438 close to a stellar tail seen in deep optical observations. This HI tail has a total extent of ~50 kpc and a mass of 1.4*10^8 M_sun if it is at the distance of NGC4438. The velocity of the HI tail is ~-10 km/s similar to that of HI emission from IC 3355, but the possibility that the tail could be foreground Galactic emission cannot be ruled out. We discuss the different structures in the light of different models.

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