Discovering supernovae in the Virgo Cluster during the LSST era

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

Vera: We're looking at the paper: "Discovering supernovae in the Virgo Cluster during the LSST era".

Jocelyn: Here's the gist of the paper. This paper presents a statistical prediction of the number of very young supernovae that will be discovered during the 10-year LSST survey lifetime in the Virgo Cluster, focusing on Type Ia and Core Collapse SNe.

Vera: The Wide Fast Deep (WFD) program of LSST will announce approximately "∼ 1 million variable objects per night, including new explosive transients like novae, supernovae (SNe), tidal disruption events (TDEs), among others" While the survey depth offers an opportunity to discover new explosive transients in nearby galaxies within only a few hours after explosion, the "80 hour embargo and, especially, the 3 day cadence is a major limitation in this respect".

Jocelyn: To overcome these limitations, programs like DECam’s “Shadow” program are designed to re-observe LSST fields "1 and 2 days after the latest LSST exposure".

Vera: Shadow targets rich, nearby galaxy clusters including "Eridanus (around ∼ −21 deg Declination), Fornax (−35 deg), Dorado (−56 deg), Antlia (−35 deg), Hydra (−27 deg) and Virgo (+12 deg)".

Paper summary: Vera: So we've been looking at how these wide surveys, LSST and Shadow, can help us find new explosions in the Virgo Cluster over ten years.

Jocelyn: Yeah, this paper by Vinkó and Sárneczky is basically putting together a statistical prediction for those finds.

Subrahmanyan: It focuses on estimating the expected numbers of Type Ia and Core Collapse supernovae across different parts of Virgo during that LSST lifetime.

Vera: The title itself, "Discovering supernovae in the Virgo Cluster during the LSST era," tells you exactly what it's about—it’s a forecast for what we can expect to see.

Jocelyn: And they use this specific combination of LSST and Shadow observations to get those numbers.

Subrahmanyan: It suggests that Core Collapse supernovae might be more numerous than Type Ia SNe in this cluster environment, which is something I've been thinking about regarding star formation history.

Vera: Exactly, the rates they use show that High-SFR galaxies are much more likely to produce Core Collapse events compared to Quiescent ones for those specific explosion types.

Jocelyn: And the numbers they end up with suggest we could expect one to two Type Ia SNe and five to six Core Collapse SNe each year in Virgo, but only if we catch them within one or two days of explosion.

Subrahmanyan: That time window is crucial; it means these are very young events, which gives us a snapshot of the recent star formation activity in those galaxies.

Vera: It’s an important constraint for our observational strategy because it tells us exactly what we need to be looking for immediately after an LSST exposure.

Jocelyn: So if you're listening, think about that; over ten years, we're tracking a total of about seventy events in Virgo within that one or two-day window.

Subrahmanyan: This points toward the need for very fast follow-up capabilities to really nail down the nature of these transients in structure formation.

Vera: It’s clear that this work provides a concrete statistical expectation based on what the current survey limits allow us to observe.

Conclusion: Vera: So, we've just walked through how Vinkó and Sárneczky used the LSST and Shadow programs to predict how many new supernovae we might find in Virgo over ten years.

Jocelyn: Yeah, that study is titled "Discovering supernovae in the Virgo Cluster during the LSST era," and it’s really a statistical forecast based on what those specific survey capabilities can catch.

Subrahmanyan: It boils down to this: we're looking at nearby galaxy clusters, like Virgo, and using a lot of data from LSST plus follow-up programs to predict the total yield of new explosions over a decade.

Vera: The authors use the Wide Fast Deep program's detection power—that million variable objects per night—and then combine it with how likely those events are to happen based on what we already know about supernova rates in those specific galaxy types.

Jocelyn: It really shows that the way you design your follow-up, like using Shadow to look back just one or two days after the main LSST exposure, is actually what makes these predictions possible.

Subrahmanyan: And the authors find a pretty clear result: Core Collapse SNe end up dominating the expected discoveries in Virgo compared to Type Ia SNe over that ten-year period.

Vera: That’s because of how those galaxy types are distributed within the cluster—the way star formation rates change across those different sub-structures creates that difference in explosion rates.

Jocelyn: So, what this means for us is that if we want to really understand how massive structures like Virgo evolve, we need to be looking for these specific transients in those specific environments.

Subrahmanyan: It gives us a statistical map of where the most interesting events are likely to occur, telling us which parts of the cluster structure matter most for finding these young explosions.