Day 1496

Monday.

1811.00022
Roll of the Dice: a stochastically sampled IMF alters the stellar content of simulated dwarf galaxies
Applebaum, et al

Cosmo sims are reaching the resolution necessary to study ultra-faint dwarf galaxies.  Observations indicate that in small populations, the stellar IMF is not fully populated; rather, stars are sampled in a way that can be approximated as coming from an underlying probability density function.  To ensure the accuracy of cosmo sims in the ultra-faint regime, present an improved treatment of the IMF.  For the first time, implement a self-consistent, stochastically populated IMF in cosmo hydro sims.  test the method using high-resolution simulations of a MW halo, run to z=6, yielding a sample of nearly 100 galaxies.  also use an isolated dwarf galaxy to investigate the resulting systematic differences in galaxy properties.  Find that a stochastic IMF in simulations makes feedback bustier, strengthening feedback, and queuing SF earlier in small dwarf galaxies.  For galaxies in haloes with mass <~1e8.5 Msun, a stochastic IMF typically leads to lower stellar mass compared to a continuous IMF, sometimes by more than an order of magnitude.  Show that existing methods of ensuring discrete supernovae incorrectly determine the mass of the star particle and its associated feedback.  This leads to overcooling of surrounding gas, with at least ~10% higher SF and ~30% higher cold gas content.  Going forward, to accurately model dwarf galaxies and compare to observations, it will be necessary to incorporate a stochastically populated IMF that samples the full spectrum of stellar masses.


1811.00195 (Nature)
A decade of fast radio bursts
Lorimer

Modern astrophysics is undergoing a revolution.  As detector technology has advanced, and astronomers have been able to study the sky with finer temporal detail, a rich diversity of sources which vary on timescales from years down to a few nanoseconds has been found.  Among these are Fast Radio Bursts, with pulses of millisecond duration and anomalously high dispersion compared to Galactic pulsars, first seen a decade ago.  Since then, a new research community is actively working on a variety of experiments and developing models to explain this new phenomenon, and devising ways to use them as astrophysical tools.  In this article, describe how astronomers have reached this point, review the highlights from the first decade of research in the field, give some current breaking news, and look ahead to what might be expected in the next few years.


1811.00674
Quasar correlation and Bell's inequality
Steinbring

Viewing two sources at sufficient distance and angular separation can assure, by light-travel-time arguments, the acausality of their emitted photons.  Using these photons to set different apparatus parameters in a laboratory-based quantum-mechanical experiment could ensure those settings are independent too, allowing a decisive, loophole-free test of Bell's inequality.  Quasars are a natural choice for such objects, as they are visible up to high z and point like.  Yet applying them at the ultimate limit of the technique involves flux measurements in opposite directions on the sky.  This presents a challenge to proving randomness against either noise or an underlying signal.  By means of a "virtual" experiment and simple S/N calculations, bias in ground-based optical photometry while performing an Earth-wide test is explored, imposed by fluctuating sky conditions and instrumental errors including photometric zero points.  Analysis for one useful dataset from the Gemini 8-meter telescopes is presented, using over 14 years of archival images obtained with their Multi-Object Spectrograph (GMOS) instrument pair, serendipitously sampling thousands of quasars up to 180 degrees apart.  These do show correlation: an average pairwise broadband optical flux difference intriguingly consistent with the form of Bell's inequality. That is interesting in itself, if not also a harm to experimental setting independence; some considerations for future observations are discussed.