星系中的常见发射线

参见SFR

电离势

• H0 13.6
• He0 24.6
• S++ 34.8, O+ 35.1
• He+ 54.4, O++ 54.9
• O0可以电离到3种不同的O+状态（4S,2D,2P）,从O0（3P）到O+的电离势为13.62

光学波段

• [OII] doublet (3737A)
• [OIII] (4959A and 5007A)
• Balmer series (6563A, 4861A, 4340A, 4103A, ...).
• [NII]6583A
• 发射线的线比可以区分不同的电离机制，金属丰度 BPT diagram,详细的工作可参见[1]
• [NII]/[OII]: . intermediate mass stars are the main source of nitrogen en- richment in massive galaxies (Moll´a et al. 2015), the gas from their stellar winds should be, on average, extremely nitrogen- rich.
• SII：电离势 10.4ev

红外谱线

• 精细结构线 [2]

• 最强的线 [CII]158mu [OIII]88mu [OI]64mu，[OIII]来自HII区
• The new [OIV]25.9μm/[OIII]88μm vs [NeIII]15.6μm/[NeII]12.8μm diagram is proposed as the best diagnostic to separate: i) AGN activity from any kind of star formation; and ii) low-metallicity dwarf galaxies from starburst galaxies.
• the ([NeIII]15.6μm + [NeII]12.8μm)/([SIV]10.5μm + [SIII]18.7μm) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity.
• [CII] 158$\mu$m fine-structure line，trace regions of active star formation and is the main coolant of the cold, neutral atomic medium.[3]
• C原子的电离势11.2eV，因此C+在中性和电离去都存在，因此[CII]158mu能不能做SFR的指针有争议 (arXiv1910.0541),[CII]是PDR区域最有效的冷却线
• [NII]205mu, N原子的电离势是14.5ev，比H要高，因此[NII]线是在HII区才有

• both [CI] and CO emission trace gas that is predominantly molecular, with a density n ~ 500-1000 cm−3, [CII] traces lower density material (n ~ 100 cm−3) [4]

• weak [NII] 205 um: 恒星形成 [5]

coronal lines

• Higher-ionization, collisionally excited optical forbid�den lines, known as optical “coronal lines” (CLs; first discovered in the solar corona)

为什么在AGN中很弱?因为尘埃的沉降效应使得它们很弱[6]