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射电星系B2 0838+ 32 A群大气中的激波加热

Shock heating in the group atmosphere of the radio galaxy B2 0838+32A

Nazirah N. Jetha, Martin J. Hardcastle, Trevor J. Ponman, Irini Sakelliou

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11 pages, 7 figures, Figure 3 in colour. Accepted, MNRAS
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摘要：

我们提出钱德拉和无线电观测，并分析斯隆数字巡天数据，射电星系B2 0838+32A（4C 32.26）和它的环境。这个射电星系位于附近一个星系团的中心，这个星系团通常被认为是阿贝尔695星系团，但我们认为，原来的阿贝尔星系团很可能是一个不相关的、远得多的系统。无线电源是一个重新启动的无线电星系，并使用我们的钱德拉数据，我们认为，目前活跃的叶超声波膨胀，驱动的冲击马赫数$2.4^{+1.0}_{-0.5}$到星际介质。这将是继半人马座A和NGC 3801之后，第三次发现围绕年轻射电源的强烈冲击。然而，与这两个系统相反，B2 0838+ 32 A的宿主星系没有显示最近合并的证据，而AGN光谱没有显示尘埃环面的证据，这意味着靠近中央黑洞的大量冷气体。相反，活动星系核的光谱是一种与存在辐射效率低的吸积流有关的类型，这种吸积流可以通过活动星系核加热和随后冷却热的X射线发射气体来控制。如果是正确的，这意味着B2 0838+ 32 A是我们可以直接看到由星际介质的热相吸积驱动的熵增加过程（冲击）的第一个来源。

英文摘要：

We present Chandra and radio observations, and analysis of Sloan Digital Sky Survey data, of the radio galaxy B2 0838+32A (4C 32.26) and its environment. The radio galaxy is at the centre of a nearby group that has often been identified with the cluster Abell 695, but we argue that the original Abell cluster is likely to be an unrelated and considerably more distant system. The radio source is a restarting radio galaxy and, using our Chandra data, we argue that the currently active lobes are expanding supersonically, driving a shock with Mach number $2.4^{+1.0}_{-0.5}$ into the inter-stellar medium. This would be only the third strong shock round a young radio source to be discovered, after Centaurus A and NGC 3801. However, in contrast to both these systems, the host galaxy of B2 0838+32A shows no evidence for a recent merger, while the AGN spectrum shows no evidence for the dusty torus that would imply a large reservoir of cold gas close to the central black hole. On the contrary, the AGN spectrum is of a type that has been associated with the presence of a radiativelyinefficient accretion flow that could be controlled by AGN heating and subsequent cooling of the hot, X-ray emitting gas. If correct, this means that B2 0838+32A is the first source in which we can directly see entropy-increasing processes (shocks) driven by accretion from the hot phase of the interstellar medium.

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