We derive the low redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial Galaxy And Mass Assembly (GAMA) dataset covering 180 deg 2 . We construct the mass function using a density-corrected maximum volume method, using masses corrected for the impact of optically thick and thin dust. We explore the galactic bivariate brightness plane (M − µ), demonstrating that surface brightness effects do not systematically bias our mass function measurement above 10 7.5 M . The galaxy distribution in the M −µ-plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria. The GSMF is fit with a double Schechter function, with M = 10 10.78±0.01±0.20 M , φ 1 = (2.93 ± 0.40) × 10 −3 h 3 70 Mpc −3 , α 1 = −0.62 ± 0.03 ± 0.15, φ 2 = (0.63 ± 0.10) × 10 −3 h 3 70 Mpc −3 , and α 2 = −1.50±0.01±0.15. We find the equivalent faint end slope as previously estimated using the GAMA-I sample, although we find a higher value of M . Using the full GAMA-II sample, we are able to fit the mass function to masses as low as 10 7.5 M , and assess limits to 10 6.5 M . Combining GAMA-II with data from G10-COSMOS we are able to comment qualitatively on the shape of the GSMF down to masses as low as 10 6 M . Beyond the well known upturn seen in the GSMF at 10 9.5 the distribution appears to maintain a single power-law slope from 10 9 to 10 6.5 . We calculate the stellar mass density parameter given our best-estimate GSMF, finding Ω = 1.66 +0.24 −0.23 ± 0.97h −1 70 × 10 −3 , inclusive of random and systematic uncertainties.

Context. Galaxy mergers and interactions are an integral part of our basic understanding of how galaxies grow and evolve over time. However, the effect that galaxy mergers have on star formation rates (SFR) is contested, with observations of galaxy mergers showing reduced, enhanced and highly enhanced star formation. Aims. We aim to determine the effect of galaxy mergers on the SFR of galaxies using statistically large samples of galaxies, totalling over 200 000, over a large redshift range, 0.0 to 4.0. Methods. We train and use convolutional neural networks to create binary merger identifications (merger or non-merger) in the SDSS, KiDS and CANDELS imaging surveys. We then compare the galaxy main sequence subtracted SFR of the merging and non-merging galaxies to determine what effect, if any, a galaxy merger has on SFR.Results. We find that the SFR of merging galaxies are not significantly different from the SFR of non-merging systems. The changes in the average SFR seen in the star forming population when a galaxy is merging are small, of the order of a factor of 1.2. However, the higher the SFR above the galaxy main sequence, the higher the fraction of galaxy mergers. Conclusions. Galaxy mergers have little effect on the SFR of the majority of merging galaxies compared to the non-merging galaxies. The typical change in SFR is less than 0.1 dex in either direction. Larger changes in SFR can be seen but are less common. The increase in merger fraction as the distance above the galaxy main sequence increases demonstrates that galaxy mergers can induce starbursts.

We have developed a new prior-based source extraction tool, XID+, to carry out photometry in the Herschel SPIRE maps at the positions of known sources. XID+ is developed using a probabilistic Bayesian framework which provides a natural framework in which to include prior information, and uses the Bayesian inference tool Stan to obtain the full posterior probability distribution on flux estimates. In this paper, we discuss the details of XID+ and demonstrate the basic capabilities and performance by running it on simulated SPIRE maps resembling the COSMOS field, and comparing to the current prior-based source extraction tool DESPHOT. We show that not only does XID+ perform better on metrics such as flux accuracy and flux uncertainty accuracy, we illustrate how obtaining the posterior probability distribution can help overcome some of the issues inherent with maximum likelihood based source extraction routines. We run XID+ on the COSMOS SPIRE maps from Her-MES, using a 24 µm catalogue as a prior and show the marginalised SPIRE colourcolour plot and marginalised contribution to the cosmic infrared background at the SPIRE wavelengths. XID+ is a core tool arising from the Herschel Extragalactic Legacy Project (HELP) and we discuss how additional work within HELP providing prior information on fluxes can and will be utilised. The software is available at https://github.com/H-E-L-P/XID_plus. We also provide the data product for COSMOS. We believe this is the first time that the full posterior probability of galaxy photometry has been provided as a data product.