Probing the ISM properties of first galaxies through [CII] and CO line emission
The advent of ALMA, soon to be complemented by JWST and E-ELT, has started to revolutionize the study of the ISM in the first galaxies and, in the last few years, ALMA has enabled the first handful of detections of e.g. the [CII] 158um line emission in normal (SFR < 100 Msun/yr) galaxies at z > 6. However, a clear picture of [CII] line as a tracer of the star formation at high-z is still not emerging, given that some searches have been successful, while many others resulted in non-detections.
In this talk I will present a theoretical model that allows us to link the [CII] and CO emission from early galaxies to the their SFR, to assess the role of stellar feedback and low-metallicity in modulating the line emission, and shed light on the relative abundances of different ISM gas phases (molecular, neutral, ionized).
To this aim, we coupled state-of-the-art, high-resolution (30 pc), cosmological simulation of a main sequence galaxy at z~6 with sub-grid models that simultaneously account for the radiative transfer, clumpy structure, and photoevaporation feedback in the neutral diffuse and molecular gas. This allows us to compute the luminosity of [CII] and CO rotational lines, and to obtain high-resolution emission maps of our simulated galaxy. I will focus also on the predicted shape of the CO Spectral Line Energy Distribution (CO SLED), and on the expected value of the CO-to-H2 in galaxies during the Epoch of Reionization.