Trident: a universal tool for generating synthetic absorption spectra from astrophysical simulations

Hydrodynamical simulations are increasingly able to accurately model physical systems on stellar, galactic, and cosmological scales, however, the utility of these simulations is often limited by our ability to directly compare them with the datasets produced by observers: spectra, photometry, etc. To address this problem, we have created Trident}, a Python-based, open-source tool for post-processing hydrodynamical simulations to produce synthetic absorption spectra and related data. Trident} can (i) create absorption-line spectra for any trajectory through a simulated dataset mimicking both background quasar and down-the-barrel configurations, (ii) reproduce the spectral characteristics of common instruments like the Cosmic Origins Spectrograph, (iii) operate across the ultraviolet, optical and infrared using customizable absorption line lists, (iv) trace simulated physical structures directly to spectral features, (v) approximate the presence of ion species absent from the simulation outputs, (vi) generate column density maps for any ion, and (vii) provide support for all major astrophysical hydrodynamical codes. The focus of Trident's development is for using simulated datasets to better interpret observations of the circumgalactic medium (CGM) and intergalactic medium (IGM), but it remains a general tool applicable in other contexts.Comment: 16 pages, 13 figures, published in ApJ, Code available at http://trident-project.or

Selective advantage for multicellular replicative strategies: A two-cell example

This paper develops a quasispecies model where cells can adopt a two-cell survival strategy. Within this strategy, pairs of cells join together, at which point one of the cells sacrifices its own replicative ability for the sake of the other cell. We develop a simplified model for the evolutionary dynamics of this process, allowing us to solve for the steady-state using standard approaches from quasispecies theory. We find that our model exhibits two distinct regimes of behavior: At low concentrations of limiting resource, the two-cell strategy outcompetes the single-cell survival strategy, while at high concentrations of limiting resource, the single-cell survival strategy dominates. Associated with the two solution regimes of our model is a localization to delocalization transition over the portion of the genome coding for the multicell strategy, analogous to the error catastrophe in standard quasispecies models. The existence of such a transition indicates that multicellularity can emerge because natural selection does not act on specific cells, but rather on replicative strategies. Within this framework, individual cells become the means by which replicative strategies are propagated. Such a framework is therefore consistent with the concept that natural selection does not act on individuals, but rather on populations.Comment: 4 pages, 2 figures, to be submitted to Physical Review Letter

Protostellar Feedback Processes and the Mass of the First Stars

We review theoretical models of Population III.1 star formation, focusing on the protostellar feedback processes that are expected to terminate accretion and thus set the mass of these stars. We discuss how dark matter annihilation may modify this standard feedback scenario. Then, under the assumption that dark matter annihilation is unimportant, we predict the mass of stars forming in 12 cosmological minihalos produced in independent numerical simulations. This allows us to make a simple estimate of the Pop III.1 initial mass function and how it may evolve with redshift.Comment: 6 pages, Proceedings of 'The First Stars and Galaxies: Challenges for the Next Decade", Austin, TX, March 8-11, 201