AI 中文总结
该研究利用JWST/MIRI和NIRCam测量71个附近恒星形成星系漫射ISM的中红外颜色变化，发现其在极端环境中有明显差异，CMZs中PAH与连续谱颜色降低，恒星形成沙漠中7.7μm PAH发射低，所有环境构成相关连续趋势。
AI 中文摘要
我们展示了来自PHANGS-JWST调查的71个附近恒星形成星系的漫射星际介质（ISM）中，中红外（mid-IR）颜色变化的50-100 pc分辨率的JWST/MIRI和NIRCam测量结果。中红外发射追踪尘埃柱密度、星际辐射场的强度（U）和硬度，以及多环芳烃（PAHs）的物理状态（电荷、大小）和丰度。在恒星形成盘的漫射ISM中，追踪PAH带比的中红外颜色保持相当恒定。然而，它们在极端环境中表现出明显变化：高度恒星形成的中央分子区（CMZs）和恒星形成沙漠/宁静凸起。在CMZs中，PAH与连续谱（3.3/21、7.7/21和11.3/21μm）以及10/21μm连续谱颜色比正常盘低0.2-0.4 dex。我们将此归因于基于远红外尘埃颜色和高21μm/分子表面密度的更高U，我们认为这是恒星形成区域外U的良好追踪器。同时，恒星形成沙漠显示出低7.7μm PAH发射，导致低7.7/21μm和7.7/11.3μm，而所有其他中红外颜色保持典型。这表明在恒星形成沙漠中存在更多中性PAHs，其中低7.7μm可能反映了类似于早型和椭圆星系的ISM条件。所有环境都构成了7.7/11.3μm与特定恒星形成率的连续趋势的一部分。
英文摘要
We present $50{-}100\,$pc-resolution JWST/MIRI and NIRCam measurements of mid-infrared (mid-IR) color variations in the diffuse interstellar medium (ISM) of 71 nearby star-forming galaxies from the PHANGS-JWST survey. Mid-IR emission traces the dust column density, intensity ($U$) and hardness of the interstellar radiation field, and the physical state (charge, size) and abundance of polycyclic aromatic hydrocarbons (PAHs). Mid-IR colors that trace PAH band-ratios remain fairly constant in the diffuse ISM of star-forming disks. However, they show stark variations in extreme environments: highly star-forming central molecular zones (CMZs) and star-formation deserts/quiescent bulges. In CMZs, PAH-to-continuum ($3.3/21$, $7.7/21$, and $11.3/21\,μ$m) and the $10/21\,μ$m continuum colors are $0.2{-}0.4$ dex lower than in normal disks. We attribute this to higher $U$ based on the far-IR dust colors and the high $21\,μ{\rm m}/Σ_{\rm Mol}$, which we suggest to be a good tracer of $U$ outside star-forming regions. Meanwhile, star-formation deserts show low $7.7\,μ$m PAH emission, resulting in low $7.7/21\,μ$m and $7.7/11.3\,μ$m, while all other mid-IR colors remain typical. This suggests the presence of more neutral PAHs in star-formation deserts, where low $7.7\,μ$m likely reflects ISM conditions similar to early-type and elliptical galaxies. All environments form part of a continuous trend in $7.7/11.3\,μ$m vs.\ specific star-formation rate.
Commentsmain text 20 pages, 16 figures, 3 tables, published in ApJ
