Day 1575

Tuesday.

1905.10522
An extended catalog of galaxy-galaxy strong gravitational lenses discovered in DES using convolutional neural networks
Jacobs, et al

We search Dark Energy Survey (DES) Year 3 imaging for galaxy-galaxy strong gravitational lenses using convolutional neural networks, extending previous work with new training sets and covering a wider range of redshifts and colors. We train two neural networks using images of simulated lenses, then use them to score postage stamp images of 7.9 million sources from the Dark Energy Survey chosen to have plausible lens colors based on simulations. We examine 1175 of the highest-scored candidates and identify 152 probable or definite lenses. Examining an additional 20,000 images with lower scores, we identify a further 247 probable or definite candidates. After including 86 candidates discovered in earlier searches using neural networks and 26 candidates discovered through visual inspection of blue-near-red objects in the DES catalog, we present a catalog of 511 lens candidates.

1905.10739

Connecting galaxy structure and star formation: the role of environment in formation of S0 galaxies

Mishra, et al

In this work, we investigate the reason behind the increased occurrence of S0 galaxies in high density environments. Our sample comprises of $\sim$ 2500 spiral and $\sim$ 2000 S0 galaxies spanning a wide range of environments. Dividing the galaxies into categories of classical and pseudobulge hosting spiral and S0 galaxies, we have studied their properties as a function of the environment. We find that the fraction of pseudobulge hosting disc galaxies decreases with increase in density. The classical bulge hosting spirals and S0 galaxies follow a similar trend in less dense environments but towards higher densities, we observe an increase in the fraction of classical bulge host S0 galaxies at the expense of spirals. Comparing the structural and the star formation properties of galaxies on the size-mass and $NUV-r$ colour-mass planes respectively, we infer that classical bulge hosting spirals are likely to get transformed into S0 morphology. We notice a trend of galaxy structure with environment such that the fraction of classical bulge hosting spiral galaxies is found to increase with environment density. We also find that among classical bulge hosting spirals, the fraction of quenched galaxies increases in denser environments. We surmise that the existence of more classical bulge hosting spirals galaxies and more efficient quenching leads to the observed increased occurrence of S0 galaxies in high density environments. The relation between galaxy structure and environment also exists for the disc galaxies irrespective of their visual morphology, which is driven mainly by halo mass.

1905.10779

The star formation history n the solar neighborhood as told by massive white dwarfs

Isern

White dwarfs are the remnants of low and intermediate mass stars. Because of electron degeneracy, their evolution is just a simple gravothermal process of cooling. Recently, thanks to Gaia data, it has been possible to construct the luminosity function of massive (0.9 < M/Msun < 1.1) white dwarfs in the solar neighborhood (d < 100 pc). Since the lifetime of their progenitors is very short, the birth times of both, parents and daughters, are very close and allow to reconstruct the (effective) star formation rate. This rate started growing from zero during the early Galaxy and reached a maximum 6-7 Gyr ago. It declined and ~5 Gyr ago started to climb once more reaching a maximum 2 - 3 Gyr in the past and decreased since then. There are some traces of a recent star formation burst, but the method used here is not appropriate for recently born white dwarfs.