We present Atacama Large Millimeter/submillimeter Array observations of the brightest cluster galaxy Hydra-A, a nearby (z = 0.054) giant elliptical galaxy with powerful and extended radio jets. The observations reveal CO(1-0), CO(2-1), 13CO(2-1), CN(2-1), SiO(5-4), HCO+(1-0), HCO+(2-1), HCN(1-0), HCN(2-1), HNC(1-0) and H2CO(3-2) absorption lines against the galaxy’s bright and compact active galactic nucleus. These absorption features are due to at least 12 individual molecular clouds which lie close to the centre of the galaxy and have velocities of approximately −50 to +10 km s−1 relative to its recession velocity, where positive values correspond to inward motion. The absorption profiles are evidence of a clumpy interstellar medium within brightest cluster galaxies composed of clouds with similar column densities, velocity dispersions and excitation temperatures to those found at radii of several kpc in the Milky Way. We also show potential variation in a ∼10 km s−1 wide section of the absorption profile over a two year timescale, most likely caused by relativistic motions in the hot spots of the continuum source which change the background illumination of the absorbing clouds.

中文翻译：

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Hydra-A AGN的分子吸收线调查

我们展示了阿塔卡马大毫米/亚毫米阵列对最亮星团 Hydra-A 的观测结果，Hydra-A 是附近 (z = 0.054) 巨大椭圆星系，具有强大且扩展的射电射流。观测结果显示 CO(1-0)、CO(2-1)、13CO(2-1)、CN(2-1)、SiO(5-4)、HCO+(1-0)、HCO+(2-1) )、HCN(1-0)、HCN(2-1)、HNC(1-0) 和 H2CO(3-2) 对星系明亮而致密的活动星系核的吸收线。这些吸收特征归因于至少 12 个独立的分子云，它们靠近星系中心，相对于其衰退速度具有大约 -50 到 +10 公里 s-1 的速度，其中正值对应于向内运动。吸收曲线证明在由具有相似柱密度的云组成的最亮星团星系中存在块状星际介质，速度色散和激发温度与在银河系中几个 kpc 半径处发现的那些。我们还显示了两年时间尺度内吸收剖面的 10 km s-1 宽部分的潜在变化，这很可能是由连续源热点中的相对论运动引起的，这些运动改变了吸收云的背景照明。