DESIVAST: A Catalog of Low-Redshift Voids using Data from the DESI DR1 Bright Galaxy Survey

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Next we'll be talking about the paper "DESIVAST: A Catalog of Low-Redshift Voids using Data from the DESI DR1 Bright Galaxy Survey".

Jocelyn: The paper was written by Hernan Rincon, Segev BenZvi, Kelly Douglass, Dahlia Veyrat, Jessica Nicole Aguilar et al. from Department of Physics & Astronomy, University of Rochester and Lawrence Berkeley National Laboratory and Department of Physics, Boston University and Dipartimento di Fisica Aldo Pontremoli, Università degli Studi di Milano and Department of Physics & Astronomy, University College London and Institute for Computational Cosmology, Department of Physics, Durham University and Instituto de Física, Universidad Nacional Autónoma de México and Institut de Física d’Altes Energías (IFAE), The Barcelona Institute of Science and Technology Campus UAB and Department of Physics, Universidad de los Andes and Observatorio Astronómico, Universidad de los Andes and Institut d’Estudis Espacials de Catalunya (IEEC) and Institute of Cosmology and Gravitation, University of Portsmouth and Institute of Space Sciences ICE-CSIC Campus UAB and Fermi National Accelerator Laboratory and Center for Cosmology and Astroparticle Physics, The Ohio State University and Department of Physics, The Ohio State University (15) and The Ohio State University (17) and School of Mathematics and Physics, University of Queensland and National Science Foundation NOIRLab and Department of Physics, Southern Methodist University and Institute for Astronomy, University of Edinburgh and Institute of Astronomy, University of Cambridge and Sorbonne Université CNRS/IN2P3 Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE) and Institución Catalana de Recerca i Estudis Avançats and Department of Physics and Astronomy, Siena College and Departamento de Física, Universidad de Guanajuato - DCI and Instituto Avanzado de Cosmología A. C. and Department of Physics and Astronomy, University of Waterloo and Perimeter Institute for Theoretical Physics and Waterloo Centre for Astrophysics, University of Waterloo and Instituto de Astrofísica de Andalucía (CSIC) and Department of Física EEBE, Universitat Politècnica de Catalunya and Department of Physics and Astronomy, Sejong University and CIEMAT.

Vera: Stay tuned as we take you through the paper and discuss its implications.

Jocelyn: We also have Subrahmanyan with us today — guest researcher.

Vera: Alright, let's get started.

Summary: Vera: Building on that initial scope and the data collection strategy, let’s look at the core findings presented in "DESIVAST: A Catalog of Low-Redshift Voids using Data from the DESI DR1 Bright Galaxy Survey," specifically regarding the different counts derived from their three distinct void-finding methods.

Jocelyn: The paper highlights a massive variation in results, showing that VoidFinder found one thousand four hundred eighty-four interior voids, while the V2REVOLVER method only found three hundred eighty-six. This is an enormous difference in raw numbers.

Subrahmanyan: That discrepancy isn't a mistake; it’s actually a demonstration of how the algorithms are fundamentally different ways of interpreting the same physical data. They are identifying distinct topological features that require different mathematical approaches to see them clearly at all.

Vera: It’s fascinating to see how VoidFinder defines these as discrete, self-contained regions, which is why it finds so many, whereas V2 seems more prone to merging adjacent voids into larger single structures.

Jocelyn: The mechanics of using sphere-growing versus applying Voronoi tessellation perfectly illustrate this difference in how we define boundaries. We aren're essentially comparing two different ways to draw a line around the emptiness.

Subrahmanyan: These differing counts are incredibly valuable because they show us exactly which types of underdensities we might miss if we only rely on one algorithm, providing a more complete and robust picture of cosmic structure.

Vera: So, while the numbers are different, it seems like these varied findings are critical to fully understanding the complexity of the environment within our local volume.

Jocelyn: That’s right; we need all three perspectives to paint a complete picture that can be used for reliable studies. This leads us into how they handled comparisons with existing catalogs, which is where the real rigor comes in.

Improvements: Vera: Moving toward the validation process, the authors dedicated significant effort to comparing their DESIVAST catalog against an overlapping SDSS void catalog, and that comparison is absolutely vital for establishing trust in this work.

Jocelyn: They found generally consistent physical properties between the two surveys, which is a huge relief for validation; however, they also noted that differences in volume overlap are significant because of varying galaxy selection criteria and survey masks.

Subrahmanyan: That difference highlights the inherent challenge when using magnitude-limited samples, showing how our initial observational choices dictate what kind of voids we can actually detect across different surveys. We're seeing the limits of our own instruments.

Vera: The paper suggests that focusing on a volume-limited sample, rather than weighting for tracer density, is a deliberate methodological improvement to avoid those artificially large voids that were seen in previous SDSS studies.

Jocelyn: Exactly; by restricting the sample to z less than or equal to zero point two four, we' are comparing apples-to-apples when creating our void catalogs in this low-redshift regime, maximizing accuracy for the specific environment we are studying.

Subrahmanyan: This careful focus allows us to better test modified gravity models against a set of data that is consistent and reliable across different cosmological theories than the traditional high redshift comparisons we've seen. It grounds the theoretical work in observable reality.

Vera: It’s interesting that they found that focusing on this local volume reduces some of the biases related to how distant galaxies appear, which makes sense for getting a reliable measure of current cosmic structure.

Jocelyn: We're now looking at how these results are presented and what it all means for the future, so let's wrap up our discussion with the final conclusions.

Improvements (Continued): Vera: So, in addition to the comparisons, we need to look at how they handled statistical uncertainties and cosmic variance when building this massive catalog of voids.

Jocelyn: They used simulated mock catalogs—specifically AMTL BGS mocks for DESI—to estimate the impact of statistical noise and cosmic variance on their void properties. This is a powerful technique for quantifying uncertainty.

Subrahmanyan: That process allows us to move beyond just a single measurement; we can now quantify the range of possible results based on the known fluctuations in matter distribution, which is crucial when trying to constrain cosmological parameters.

Vera: The use of mock catalogs ensures that we aren're not just getting one "perfect" result, but a statistical spread that reflects reality, which is a huge leap forward in our ability to interpret these void observations.

Jocelyn: It’s especially interesting how they are designing the final fiducial volume to reduce edge effects, removing regions near the boundaries because those edge voids behave so differently from the interior ones.

Subrahmanyan: By controlling for those boundary effects, we' are ensuring that our reported median effective radii are truly representative of the bulk cosmic structure, not just artifacts of where the survey ended and began.

Vera: It’s clear that "DESIVAST: A Catalog of Low-Redshift Voids using Data from the DESI DR1 Bright Galaxy Survey" has been designed with a high degree of technical rigor to ensure its results are trustworthy across different observational methods.

Jocelyn: We need to understand how these improvements allow us to see the real structure, and that leads perfectly into our final wrap-up before we transition to the next paper.

Conclusion: Vera: Wrapping up, what’s the big picture takeaway for all of us regarding this massive catalog of voids? It's a foundational piece of data.

Jocelyn: The core message is that while there are differences in the volume overlap between DESIVAST and SDSS—especially with V2VIDE—we have established a robust, publicly available tool for future studies using this data.

Subrahmanyan: And even though we saw discrepancies in the overlap, the agreement in median effective radii across the three different methods suggests a very high degree of confidence in the physical sizes of these underdensities. The measurements are consistent with each other.

Vera: It’s clear that "DESIVAST: A Catalog of Low-Redshift Voids using Data from the DESI DR1 Bright Galaxy Survey" provides a powerful new foundation for both astrophysics and cosmology, offering us a clearer view than ever before.

Jocelyn: We're really excited to see what happens when the full, complete DESI survey is released, extending this work even further into mapping these voids across the entire sky.

Subrahmanyan: I’m hopeful that this foundational data will lead to revolutionary discoveries in how the universe expands and evolves as we continue to map these structures.

Vera: We'll be excited to see those results in action when we return next time, so keep following our conversations on this topic.