科研之友
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摘要
We present Herschel spectroscopy of atomic lines arising in photodissociation regions as well as ionization regions of nearby early-type galaxies (ETGs), focusing on the volume-limited Atlas3D sample. Our data include the [C II], [O I], and [N II] 122 and 205 mu m lines, along with ancillary data including CO and H I maps. We find that. ETGs have [C II]/FIR ratios slightly lower than spiral galaxies in the KINGFISH sample, and several ETGs have unusually large [N II] 122/[C II] ratios. The [N II] 122/[C II] ratio is correlated with UV colors and there is a strong anti-correlation of [C II]/FIR with NUV-K seen in both spirals and ETGs, likely due to a softer radiation field with fewer photons available to ionize carbon and heat the gas. The correlation thus makes a [C II] deficit in galaxies with redder stellar populations. The high [N II] 122/[C II] (and low [C II]/FIR) line ratios could also be affected by the removal of much of the diffuse, low-density gas, which is consistent with the low H I/H-2 ratios. [C II] is now being used as a star-formation indicator, and we find that it is just as good for ETGs as in spirals. The [C II]/CO ratios found are also similar to those found in spiral galaxies. Through the. use of the [N II] 205 mu m line, estimates of the percentage of [C II] emission arising from ionized gas indicate that. a significant portion could arise in ionized regions.
- 出版日期2017-5-1
