Day 1694

Monday.

2004.11397
Impacts of dust grains accelerated by supernovae on the Moon
Siraj, Loeb

There is evidence that ejecta from nearby supernovae have rained down on Earth in the past. Supernovae can accelerate pre-existing dust grains in the interstellar medium to speeds of $\sim 0.01 \mathrm{\;c}$. We investigate the survival and impact of dust grains from supernovae on the moon, finding that supernova dust grains can form detectable tracks with widths of $\sim 0.01 - 0.07 \mathrm{\; \mu m}$ and depths of $\sim 0.1 - 0.7 \mathrm{\; mm}$ in lunar rocks. These tracks could potentially shed light on the timings, luminosities, and directions of nearby supernovae.

2004.11387

Optimal void finders in weak lensing maps

Davies, et al

Cosmic voids are a key component of the large-scale structure that contain a plethora of cosmological information. Typically, voids are identified from the underlying galaxy distribution, which is a biased tracer of the total matter field. Previous works have shown that 2D voids identified in weak lensing maps -- weak lensing voids -- correspond better to true underdense regions along the line of sight. In this work, we study how the properties of weak lensing voids depend on the choice of void finder, by adapting several popular void finders. We present and discuss the differences between identifying voids directly in the convergence maps, and in the distribution of weak lensing peaks. Particular effort has been made to test how these results are affected by galaxy shape noise, which is a dominant source of noise in weak lensing observations. By studying the signal-to-noise ratios (SNR) for the tangential shear profile of each void finder, we find that voids identified directly in the convergence maps have the highest SNR but are also the ones most affected by galaxy shape noise. Troughs are least affected by noise, but also have the lowest SNR. The tunnel algorithm, which identifies voids in the distribution of weak lensing peaks, represents a good compromise between finding a large tangential shear SNR and mitigating the effect of galaxy shape noise.

2004.11388

Ultra-diffuse galaxies in the Coma cluster: probing their origin and AGN occupation fraction

Kovacs, et al

Ultra-diffuse galaxies (UDGs) exhibit low surface brightness, but their optical extent is comparable to Milky Way-type galaxies. Due to their peculiar properties, it remains ambiguous whether UDGs are the descendants of massive galaxies or they are puffed-up dwarf galaxies. In this work, we explore a population of 404 UDGs in the Coma cluster to study their origin and AGN occupation fraction. To constrain the formation scenario of UDGs, we probe the X-ray emission originating from diffuse gas and from the population of unresolved low-mass X-ray binaries (LMXBs) residing in globular clusters (GCs). It is expected that both the luminosity of the hot gas and the number of globular clusters and hence the luminosity from GC-LMXBs are proportional to the total dark matter halo mass. We do not detect statistically significant emission from the hot gas or from GC-LMXBs. The upper limits on the X-ray luminosities suggest that the bulk of the UDGs reside in low-mass dark matter halos, implying that they are genuine dwarf galaxies. This conclusion agrees with our previous results obtained for isolated UDGs, arguing that UDGs are a homogenous population of galaxies. To probe the AGN occupation fraction of UDGs, we cross-correlate the position of detected X-ray sources in the Coma cluster with the position of UDGs. We identify two UDGs that have a luminous X-ray source at 3.0" and 3.2" from the center of the galaxies, which could be off-center AGN. However, Monte Carlo simulations suggest that one of these sources could be the result of spatial coincidence with a background AGN. Therefore, we place an upper limit of $\lesssim0.5\%$ on the AGN occupation fraction of UDGs.

2004.11402

A missing outskirts problem?  Comparisons between stellar haloes in the Dragonfly Nearby Galaxies Survey and the TNG100 simulation

Merritt, et al

Low surface brightness galactic stellar halos provide a challenging but promising path towards unraveling the past assembly histories of individual galaxies. Here, we present detailed comparisons between the stellar halos of Milky Way-mass disk galaxies observed as part of the Dragonfly Nearby Galaxies Survey (DNGS) and stellar mass-matched galaxies in the TNG100 run of the IllustrisTNG project. We produce stellar mass maps as well as mock $g$ and $r$-band images for randomly oriented simulated galaxies, convolving the latter with the Dragonfly PSF and taking care to match the background noise, surface brightness limits and spatial resolution of DNGS. We measure azimuthally averaged stellar mass density and surface brightness profiles, and find that the DNGS galaxies generally have less stellar mass (or light) at large radii (>20 kpc) compared to their mass-matched TNG100 counterparts, and that simulated galaxies with similar surface density profiles tend to have low accreted mass fractions for their stellar mass. We explore potential solutions to this apparent "missing outskirts problem" by implementing several ad-hoc adjustments within TNG100 at the stellar particle level. Although we are unable to identify any single adjustment that fully reconciles the differences between the observed and simulated galaxy outskirts, we find that artificially delaying the disruption of satellite galaxies and reducing the spatial extent of in-situ stellar populations result in improved matches between the outer profile shapes and stellar halo masses, respectively. Further insight can be achieved with higher resolution simulations that are able to better resolve satellite accretion, and with larger samples of observed galaxies.