arXiv subjects

Ann-Marsha Alexis

Publications and source records attributed to Ann-Marsha Alexis.

3 recordsLinked to original sources

arXiv2026

LISA's view of the Galactic Halo: forecasts for the Galactic double white dwarf population using Gaia data

The population of close double white dwarfs (DWDs) in the Milky Way will make up the largest population of sources resolved by LISA, with a subset of the population having three-dimensional position and chirp mass measurements obtained from LISA observations. Because white dwarfs are the bulk of the Milky Way's stellar remnant population, the positions and masses of close DWDs resolved by LISA are defined by the stellar population properties that host them. Recent Gaia data has unveiled a triaxial accreted component of the Galactic stellar halo: the Gaia-Sausage-Enceladus, which contains stars that are more metal-rich than the extremely metal-poor population of stars residing in the stellar halo beyond 30 kpc. In this work, we assess the size and characteristics of the population of close DWDs using an empirically motivated Galactic model which incorporates the GSE and compare to the classical Galactic model that contains only a single very metal-poor halo population. To do this, we simulate a realistic present-day Galactic DWD population and determine its gravitational wave signal in LISA using LEGWORK. We find that incorporating the metal-rich population from the GSE imprints significant differences in the chirp mass and distance distributions of resolved DWDs, but that the strength and height of the gravitational wave foreground remains unchanged.

astro-ph.SR↗

arXiv2025

Picture an Astronomer: Best Practices for Retaining Talent in Astrophysics

Women are consistently underrepresented in astrophysics yet are simultaneously subject to disproportionate attrition at every career stage. This disparity between demonstrated efficacy in job performance and ultimate career outcome was the primary motivation for the Picture an Astronomer series, which included both targeted public outreach to increase representation of women in astrophysics and high-level, solution-oriented discussions among professional astronomers. In March 2025, more than 200 astronomers came together in a hybrid-format symposium focused on the state of the field for female scientists, combining scientific exchange with discussions of policies and practices to strengthen retention of talent in the field. This white paper is the result of those discussions, offering a wide range of recommendations developed in the context of gendered attrition in astrophysics but which ultimately support a healthier climate for all scientists alike.

astro-ph.IM↗

arXiv2025

Large-scale surveys of the quasar proximity effect

The UV radiation from high redshift quasars causes a local deficit in the neutral hydrogen absorption (Lyman-alpha forest) in their spectra, known as the proximity effect. Measurements from small samples of tens to hundreds of quasars have been used to constrain the global intensity of the UV background radiation, but so far the power of large-scale surveys such as the Sloan Digital Sky Survey and the Dark Energy Spectroscopic Instrument (DESI) survey has not been used to investigate the UV background in more detail. We develop a CDM-based halo model of the quasar proximity effect, which accounts by construction for the fact that quasars reside in overdense regions. We test this model on quasar Lyman-alpha spectra from the ASTRID cosmological hydrodynamic simulation, which includes self-consistent formation of quasar black holes and the intergalactic medium surrounding them. Fitting the model to individual quasar spectra, we constrain two parameters, r_eq (the radius at which the local quasar radiation intensity equals the background), and the quasar bias b_q (related to host halo mass). We find that r_eq can be recovered in an unbiased fashion with a statistical uncertainty of 25-50% from a single quasar spectrum. Applying such fitting to samples of millions of spectra from e.g., DESI would allow measurement of the UVBG intensity and its evolution with redshift with high precision. We use another, larger-scale, lower resolution simulation (Uchuu) to test how such a large sample of proximity effect measurements could be used to probe the spatial fluctuations in the intergalactic radiation field. We find that the large-scale structure of the UV radiation intensity could be mapped and its power spectrum measured on 100-1000 Mpc/h scales. This could allow the large-scale radiation field to join the density field as a dataset for constraining cosmology and the sources of radiation.

astro-ph.CO↗