The Galactic Centre is surrounded by two giant plasma lobes known as the Fermi bubbles, extending ~10 kpc both above and below the Galactic plane. Spectroscopic observations of Fermi bubble directions at radio, ultraviolet and optical wavelengths have detected multi-phase gas clouds thought to be embedded within the bubbles, referred to as Fermi bubble high-velocity clouds (FB HVCs). Although these clouds have kinematics that can be modelled by a biconical nuclear wind launched from the Galactic Centre, their exact origin is unknown because there has so far been little information on their heavy metal abundances (metallicities). Here we show that FB HVCs have a wide range of metallicities from <20% of solar to ~320% of solar, based on a metallicity survey of twelve FB HVCs. These metallicities challenge the previously accepted tenet that all FB HVCs are launched from the Galactic Centre into the Fermi bubbles with solar or supersolar metallicities. Instead, we suggest that FB HVCs originate in both the Milky Way’s disk and halo. As such, some of these clouds may characterize the circumgalactic medium that the Fermi bubbles expand into, rather than material carried outwards by the nuclear wind, changing the canonical picture of FB HVCs. More broadly, these results reveal that nuclear outflows from spiral galaxies can operate by sweeping up gas in their haloes while simultaneously removing gas from their disks.

银河中心被称为费米气泡的两个巨大等离子叶包围，在银河平面上方和下方延伸约 10 kpc。在射电、紫外和光学波长对费米气泡方向的光谱观测已经检测到被认为嵌入气泡内的多相气体云，称为费米气泡高速云 (FB HVC)。虽然这些云的运动学可以通过从银河中心发射的双锥核风来模拟，但它们的确切来源尚不清楚，因为迄今为止关于它们的重金属丰度（金属度）的信息很少。在这里，我们根据对 12 个 FB HVC 的金属丰度调查显示，FB HVC 的金属丰度范围很广，从小于太阳能的 20% 到太阳能的 320% 不等。这些金属丰度挑战了之前公认的原则，即所有 FB HVC 都从银河中心发射到具有太阳或超太阳金属丰度的费米气泡中。相反，我们建议 FB HVCs 起源于银河系的圆盘和光晕。因此，这些云中的一些可能表征费米气泡膨胀进入的环银河介质，而不是由核风向外携带的物质，从​​而改变了 FB HVC 的典型图像。更广泛地说，这些结果表明，螺旋星系的核外流可以通过扫除其晕圈中的气体，同时从其盘中去除气体来进行。其中一些云可能表征费米气泡膨胀进入的环银河介质，而不是由核风向外携带的物质，从​​而改变了 FB HVC 的典型图像。更广泛地说，这些结果表明，螺旋星系的核外流可以通过扫除其晕圈中的气体，同时从其盘中去除气体来进行。其中一些云可能表征费米气泡膨胀进入的环银河介质，而不是由核风向外携带的物质，从​​而改变了 FB HVC 的典型图像。更广泛地说，这些结果表明，螺旋星系的核外流可以通过扫除其晕圈中的气体，同时从其盘中去除气体来进行。