We observed the [C II] line in 15 lensed galaxies at redshifts 1 < z <. 3 using HIFI on the Herschel Space Observatory and detected 14/15 galaxies at 3 sigma or better. High magnifications enable even modestly luminous galaxies to be detected in [C II] with Herschel. The [C II] luminosity in this sample ranges from 8x10(7) L-circle dot to 3.7x10(9) L-circle dot (after correcting for magnification), confirming that [C II] is a strong tracer of the ISM at high redshifts. The ratio of the [C II] line to the total far-infrared (FIR) luminosity serves as a measure of the ratio of gas to dust cooling and thus the efficiency of the grain photoelectric heating process. It varies between 3.3% and 0.09%. We compare the [C II]/FIR ratio to that of galaxies at z = 0 and at high redshifts and find that they follow similar trends. The [C II]/FIR ratio is lower for galaxies with higher dust temperatures. This is best explained if increased UV intensity leads to higher FIR luminosity and dust temperatures, but gas heating does not rise due to lower photoelectric heating efficiency. The [C II]/FIR ratio shows weaker correlation with FIR luminosity. At low redshifts highly luminous galaxies tend to have warm dust, so the effects of dust temperature and luminosity are degenerate. Luminous galaxies at high redshifts show a range of dust temperatures, showing that [C II]/FIR correlates most strongly with dust temperature. The [C II] to mid-IR ratio for the HELLO sample is similar to the values seen for low-redshift galaxies, indicating that small grains and PAHs dominate the heating in the neutral ISM, although some of the high [CII]/FIR ratios may be due to turbulent heating.

Gamma-ray bursts (GRBs) are the most luminous phenomena in the Universe, explosions whoseenergy is generated by supernovae or mergers of dense objects such as neutron stars. The GRBemission is divided into the prompt emission phase characterized by γ-ray radiation and the afterglowof lower energy radiation. The prompt emission phase is still not understood; as of now, there aretwo leading descriptions: the photospheric- and the synchrotron models. The synchrotron model hashad great success in describing GRB spectra, and specifically some of the brightest ones, although notwithout issues such as some observations being at odds with theory. On the other hand, photosphericmodels have had problems too of how to broaden the spectrum in order to explain the observeddata. One explanation for this broadening is that Radiation Mediated Shocks (RMSs) dissipate energybelow the photosphere. In this report, a time resolved spectral analysis of the prompt emission of GRB160625B – a very bright GRB known to produce synchrotron-like emission – is done. Komrad is animplementation of the Kompaneets RMS Approximation (KRA), which is a dissipative photosphericmodel. Komrad is then used to fit a photospheric model to the prompt emission of GRB 160625Bin order to explore whether photospheric models can account for synchrotron-like emission spectra.Great statistical support is found for the photospheric model in comparison to standard GRB fittingfunctions as well as a synchrotron function which is indicative of the photospheric model being able toexplain a synchrotron-like spectra.