Speaker
Description
The bright [CII] 158 micron line can emit up to 1% of a galaxy's far-IR luminosity and has been suggested as an efficient tracer of star-formation in high-redshift galaxies, where it is shifted in to ALMA bands 4–7. However, a deficit of [CII] relative to IR luminosity is observed in galaxies with L_IR>10^11 L_sun, and the origins of this deficit are not yet fully understood, limiting its reliability as a star-formation tracer. Furthermore, [CII] can be be emitted from regions dominated by both neutral and ionised hydrogen, which further complicates interpretation of [CII] emission. I will present the results of a ALMA survey of both [CII] and [NII] 205 micron in 12 ALESS and AS2UDS submillmeter-selected galaxies at z~4.5. [NII] has a higher ionisation energy but similar critical density to [CII], so it can only be emitted from ionised regions of the interstellar medium. The ratio of [CII] to [NII] in our sample shows that ~75–95% of the [CII] originates from photodissociation regions and that this fraction is correlated with the strength of the [CII] deficit in each galaxy. I will also show the results of a dynamical analysis of our data.
