Chair: Matt Wiesner & Pat Burchat, on behalf of the Science Organizing Committee

The Rubin Community Workshop 2024 Science Organizing Committee has invited speakers doing meritorious, timely, Rubin-related research to speak on their work.

Speakers:

• Louise Edwards: "Exploring Galaxies and Large Structures in Rubin DP0.2: The BCG Merger Rate 1 Gyr ago"
• Jamie Robinson: "Solar System Alerts in Year 1 of LSST: The Effects of Template Generation"
• Ashley Villar: "Discovering Needles in the Vera C. Rubin Observatory Haystack"
• Nikki Arendse: "Detecting strongly lensed supernovae with LSST"

Abstracts:

Louise Edwards: "Exploring Galaxies and Large Structures in Rubin DP0.2: The BCG Merger Rate 1 Gyr ago"

DP0.2 truth and object catalogs are investigated in order to quantify the projection effects of close companions to Brightest Cluster Galaxies (BCGs). At z< 1, BCGs are believed to accumulate most of their mass from merging, though whether this is mostly from major or minor mergers is still debated. This potential merging activity can be studied by counting the number of companions close to BCGs and determining a merger rate. For galaxies with 4:1 flux ratios, (potential major mergers), we estimate a merger rate of 0.08 per Gyr at z~0.1. For 20:1 ratios (potential minor mergers), we calculate 0.26 per Gyr. Though the mass increase overall is small, the minor mergers could have a significant role to play.  DP0.2 is perfectly suited to help quantify the reliability of these measurements as simulated galaxies are available alongside access to the underlying cosmological simulations. With regards to BCG merger rates, combining object positions with redshifts from the truth catalog has cautioned that minor merging statistics may be upper limits, while major merging statistics are robust. Leading up to the first Rubin Data Releases, we can explore the transition of what flux ratio can reliably lead to real companions with only photometric data at hand. This is important as Rubin’s deep observations will detect many potential minor mergers with high S/N.

Jamie Robinson: "Solar System Alerts in Year 1 of LSST: The Effects of Template Generation"

The rapid delivery of alerts for astrophysical transients is an essential component of several Vera C. Rubin Observatory science goals to be accomplished by the Legacy Survey of Space and Time (LSST). Within 60 seconds of the shutter closing, the Rubin Observatory will issue world-wide public alerts for all transients observed in a given visit. Some transients may only be observable for short windows of time. Focusing on Solar System Objects (SSOs), the Near-Earth Objects allow us to investigate the smallest end of the SSO size distribution during their close approaches to Earth, and their discovery is essential for planetary defence. In addition, rare stochastic events such as the discovery of an interstellar object, like `Oumuamua in 2017, has great potential to compare the processes of formation and evolution in exoplanetary systems to that of our own Solar System. 

In order to generate alerts the Rubin Observatory Prompt Processing pipeline requires a template image of the static sky to perform difference imaging. This is a problem during the first year of LSST when visits will sample new areas of sky that do not yet have a suitable template image. It is expected that templates will be generated incrementally throughout year 1, however, this template generation strategy has not yet been finalised. To this end, we have simulated the effects of generating templates on timescales of days to weeks, requiring at least 4 previous images of sufficient quality for a given template to be generated. We analyse the results for the latest cadence simulation (baseline v3.4) and record the fractional area of each visit that had template coverage. Keeping only visits with ≥90% coverage we then assessed the discovery and characterisation of SSOs using the MAF.

We found that accounting for template generation introduces a time delay of ~50-70 days before SSO alerts start to flow. Due to the "loss" of these visits the year 1 SSO metrics for discovery and characterisation are significantly reduced compared to the baseline. This study highlights that special consideration of template generation in year 1 is required to allow early science discoveries from rapid follow up of alerts. It may be beneficial to consider adjustments to the baseline cadence during year 1 to prioritise template coverage, however, this will require new cadence simulations to assess the overall impact of such a strategy on the Rubin science goals.

Ashley Villar: "Discovering Needles in the Vera C. Rubin Observatory Haystack"

The eruptions, collisions and explosions of stars drive the universe’s chemical and dynamical evolution. The upcoming Vera C. Rubin Observatory will drastically increase the discovery rate of these transient phenomena, bringing time-domain astrophysics into the realm of “big data”. We will discover millions of stellar explosions annually! With this transition comes the important question: in this haystack of data, how do we identify the most interesting needles? How can we enable the discovery of new astrophysics? In this talk, I will describe ongoing efforts to rapidly identify and follow anomalous transients in the era of LSST.

Nikki Arendse: "Detecting strongly lensed supernovae with LSST"  

Strongly lensed supernovae are extremely rare and powerful probes that can give insights into high-redshift supernova physics, substructures in massive galaxies, and the expansion rate of the Universe. The lensed supernova field is at a turning point, as we will go from a handful of current discoveries to orders of magnitudes more with the advance of the Legacy Survey of Space and Time (LSST) at the Vera Rubin Observatory. In this talk, I will show results from a recent study that investigated the cosmological prospects of lensed type Ia supernovae in LSST. I will answer questions about the expected annual numbers, the impact of stellar microlensing, the feasibility of follow-up observations, and how to best separate lensed and unlensed type Ia supernovae. Finally, I will highlight some of the initiatives within the Dark Energy Science Collaboration (DESC) and the Strong Lensing Science Collaboration (SLSC) aimed at detecting lensed supernovae with LSST.