# Herschel Spectroscopy of Early Type Galaxies

## TL;DR

This study uses Herschel spectroscopy to analyze atomic lines in early-type galaxies, revealing their gas properties, star formation indicators, and ionization conditions, with results comparable to spiral galaxies.

## Contribution

First detailed Herschel spectroscopic analysis of atomic lines in early-type galaxies, linking gas properties to stellar populations and star formation indicators.

## Key findings

- ETGs have slightly lower [CII]/FIR ratios than spirals.
- High [NII] 122/[CII] ratios correlate with redder UV colors.
- [CII] is an effective star formation indicator in ETGs.

## 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.