We outline theoretical predictions for extended emission from Mg ii, tracing cool ∼104 K gas in the circumgalactic medium (CGM) of star-forming galaxies in the high-resolution TNG50 cosmological magnetohydrodynamical simulation. We synthesize surface brightness maps of this strong rest-frame ultraviolet metal emission doublet (λλ2796, 2803), adopting the assumption that the resonant scattering of Mg ii can be neglected and connecting to recent and upcoming observations with the Keck/KCWI, VLT/MUSE, and BlueMUSE optical integral field unit spectrographs. Studying galaxies with stellar masses 7.5 < log (M⋆/M⊙) < 11 at redshifts z = 0.3, 0.7, 1, and 2 we find that extended Mg ii haloes in emission, similar to their Ly α counterparts, are ubiquitous across the galaxy population. Median surface brightness profiles exceed 10−19 erg s−1 cm−2 arcsec−2 in the central $\sim \,$10 s of kpc, and total halo Mg ii luminosity increases with mass for star-forming galaxies, reaching 1040 erg s−1 for M⋆ ∼ 109.5 M⊙. Mg ii halo sizes increase from a few kpc to ≳ 20 kpc at the highest masses, and sizes are larger for haloes in denser environments. Mg ii haloes are highly structured, clumpy, and asymmetric, with isophotal axial ratio increasing with galaxy mass. Similarly, the amount and distribution of Mg ii emission depends on the star formation activity of the central galaxy. Kinematically, inflowing versus outflowing gas dominates the Mg ii luminosity at high and low galaxy masses, respectively, although the majority of Mg ii halo emission at z ∼ 0.7 traces near-equilibrium fountain flows and gas with non-negligible rotational support, rather than rapidly outflowing galactic winds.

中文翻译：

---

发射中的冷环星系介质：TNG50中的Mg ii晕

我们概述了 Mg ii 扩展发射的理论预测，在高分辨率 TNG50 宇宙磁流体动力学模拟中追踪了恒星形成星系的环银河介质 (CGM) 中的冷 ∼104 K 气体。我们合成了这种强静止框架紫外金属发射双峰 (λλ2796, 2803) 的表面亮度图，假设 Mg ii 的共振散射可以忽略不计，并与最近和即将使用 Keck/KCWI、VLT/MUSE 的观测结果相关联和 BlueMUSE 光学积分场单元光谱仪。研究恒星质量为 7.5 < 的星系 对数 (M⋆/M⊙) < 11 在红移 z = 0.3、0.7、1 和 2 时，我们发现发射中的扩展 Mg ii 晕，类似于它们的 Ly α 对应物，在整个星系群中无处不在。中心 $\sim \ 中表面亮度分布中值超过 10−19 erg s−1 cm−2 arcsec−2，kpc 为 10 s，对于恒星形成星系，总晕 Mg ii 光度随质量增加，达到 1040 erg s -1 表示 M⋆ ∼ 109.5 M⊙。最高质量时，Mg ii 晕的大小从几 kpc 增加到 ≳ 20 kpc，并且在更密集的环境中，晕的大小更大。Mg ii 晕是高度结构化的、块状的和不对称的，等轴轴比随着星系质量的增加而增加。同样，Mg ii 发射的数量和分布取决于中央星系的恒星形成活动。在运动学上，流入和流出的气体分别在高星系质量和低星系质量下主导 Mg ii 光度，尽管 z ∼ 0.7 处的大部分 Mg ii 晕发射跟踪近平衡喷泉流和具有不可忽略的旋转支持的气体，