SDSS-V LVM：Trifid星云物理条件的解析
SDSS-V LVM: Resolving Physical Conditions in the Trifid Nebula
AI总结：
SDSS-V LVM通过高分辨率测绘Trifid星云的物理条件，验证了电离前沿对电子密度的影响，发现其在观测尺度上相对均匀。
摘要：
星际介质的化学丰度决定了恒星形成的初始条件，并为化学星系演化模型提供探测。然而，未解析的电子温度不均匀性可能导致丰度的系统性低估。我们旨在直接检验这一影响。我们利用SDSS-V局部体积测绘器，以0.24 pc的分辨率对Trifid星云（M 20）的物理条件进行空间测绘，该星云是被单颗中型O星电离的银河H II区域。我们利用各种发射线（例如，氢跃迁线和碰撞激发线，包括也较弱的极光线）并计算了空间解析的[O II]和[S II]电子密度图；[N II]、[O II]、[S II]、[S III]电子温度图；以及氧离子丰度图。我们发现由于电离前沿导致的电子密度内部变化，以及负的径向梯度。然而，我们没有发现电子温度和总氧丰度的明显梯度或结构，这使得Trifid星云在观测空间尺度上相对均匀的H II区域。我们将这些空间解析的特性与Trifid星云的等效积分测量进行比较，发现积分与空间解析条件之间没有显著差异。这个被单颗O星电离的孤立H II区域代表了一个理想的Strömgren球体测试案例。Trifid星云的物理条件表现正常，积分与解析测量之间没有显著差异。
英文摘要：
The chemical abundance of the interstellar medium sets the initial conditions for star formation and provides a probe of chemical galaxy evolution models. However, unresolved inhomogeneities in the electron temperature can lead to a systematic underestimation of the abundances. We aim to directly test this effect. We use the SDSS-V Local Volume Mapper to spatially map the physical conditions of the Trifid Nebula (M 20), a Galactic H II region ionized by a single mid-type O star, at 0.24 pc resolution. We exploit various emission lines (e.g., Hydrogen recombination lines and collisionally excited lines, including also faint auroral lines) and compute spatially resolved maps of [O II] and [S II] electron densities; [N II], [O II], [S II], [S III] electron temperatures; and the ionic oxygen abundances. We find internal variations of electron density that result from the ionization front, along with a negative radial gradient. However, we do not find strong gradients or structures in the electron temperature and the total oxygen abundance, making the Trifid Nebula a relatively homogeneous H II region at the observed spatial scale. We compare these spatially resolved properties with equivalent integrated measurements of the Trifid Nebula and find no significant variations between integrated and spatially resolved conditions. This isolated H II region, ionized by a single O-star, represents a test case of an ideal Strömgren sphere. The physical conditions in the Trifid Nebula behave as expected, with no significant differences between integrated and resolved measurements.
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