Abstract
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 CII,
OI, and NII 122 and 205 micron lines, along with ancillary data including
CO and HI maps. We find ETGs have CII/FIR ratios slightly lower than spiral
galaxies in the KINGFISH sample, and several ETGs have unusually large NII
122/CII ratios. The NII 122/CII ratio is correlated with UV colors and
there is a strong anti-correlation of CII/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 CII deficit
in galaxies with redder stellar populations. The high NII 122/CII (and low
CII/FIR) line ratios could also be affected by the removal of much of the
diffuse, low density gas, which is consistent with the low HI/H2 ratios. CII
is now being used as a star formation indicator, and we find it is just as good
for ETGs as in spirals. The CII/CO ratios found are also similar to those
found in spiral galaxies. Through use of the NII 205 micron line, estimates
of the percentage of CII emission arising from ionized gas indicate a
significant portion could arise in ionized regions.
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