arXiv subjects

Liam P. Grimmett

Publications and source records attributed to Liam P. Grimmett.

3 recordsLinked to original sources

arXiv2026

Comparing Infrared & X-ray-selected Active Galactic Nuclei host galaxy star formation rates to the galaxy main sequence

A key method of exploring the relationship between active galactic nuclei (AGN) and their host galaxies is to determine the astrophysical properties of galaxies that host AGN, and compare them to those that do not. Star formation rates are believed to be strongly related to nuclear activity, both indirectly via their common fuel supply, and directly via the energy injected by the AGN either suppressing or enhancing star formation. Strong observational evidence of a direct link between nuclear activity and in-situ star formation has proven elusive, likely in part due to the very different timescales of nuclear activity and episodes of star formation. To overcome these challenges, some studies have demonstrated that evidence of the aforementioned link may be found in the distributions of AGN power and star formation rates. While previous attempts to determine these distributions have largely focused on X-ray-selected samples of AGN, in this study we also attempt to determine the star formation rate distributions of infrared-selected AGN. The results vary between our samples, but at low redshift (0.8 < z < 1.2) we find that more powerful X-ray-selected AGN are more likely to occur in galaxies with higher specific star formation rates, consistent with previous studies. At higher redshifts (1.0 < z < 1.8), this trend is reversed with higher power AGN tending to occur in galaxies with lower specific star formation rates. By contrast, infrared-selected galaxies at 1.0 < z < 1.8 show no evidence of a changing star formation rate distribution with AGN power.

astro-ph.GA↗

arXiv2020

Exoplanet detection and its dependence on stochastic sampling of the stellar Initial Mass Function

Young Moving Groups (YMGs) are close (<100pc), coherent collections of young (<100Myr) stars that appear to have formed in the same star-forming molecular cloud. As such we would expect their individual initial mass functions (IMFs) to be similar to other star-forming regions, and by extension the Galactic field. Their close proximity to the Sun and their young ages means that YMGs are promising locations to search for young forming exoplanets. However, due to their low numbers of stars, stochastic sampling of the IMF means their stellar populations could vary significantly. We determine the range of planet-hosting stars (spectral types A, G and M) possible from sampling the IMF multiple times, and find that some YMGs appear deficient in M-dwarfs. We then use these data to show that the expected probability of detecting terrestrial magma ocean planets is highly dependent on the exact numbers of stars produced through stochastic sampling of the IMF.

astro-ph.EP↗

arXiv2019

Dynamical evolution of star-forming regions: III. Unbound stars and predictions for Gaia

We use $N$-body simulations to probe the early phases of the dynamical evolution of star-forming regions and focus on mass and velocity distributions of unbound stars. In this parameter space study, we vary the initial virial ratio and degree of spatial and kinematic substructure and analyse the fraction of stars that become unbound in two different mass classes (above and below 8 M$_{\odot}$). We find that the fraction of unbound stars differs depending on the initial conditions. After 10 Myr, in initially highly subvirial, substructured simulations, the high-mass and lower-mass unbound fractions are similar at $\sim$23 per cent. In initially virialised, substructured simulations, we find only $\sim$16 per cent of all high-mass stars are unbound, whereas $\sim$37 per cent of all lower-mass stars are. The velocity distributions of unbound stars only show differences for extremely different initial conditions. The distributions are dominated by large numbers of lower-mass stars becoming unbound just above the escape velocity of $\sim$3 km s$^{-1}$ with unbound high-mass stars moving faster on average than lower-mass unbound stars. We see no high-mass runaway stars (velocity > 30 km s$^{-1}$) from any of our initial conditions and only an occasional lower-mass runaway star from initially subvirial/substructured simulations. In our simulations, we find a small number of lower-mass walkaway stars (with velocity 5-30 km s$^{-1}$) from all of our initial conditions. These walkaway stars should be observable around many nearby star-forming regions with Gaia.

astro-ph.SR↗