Steward Observatory/NSF’s NOIRLab Joint Colloquium Series: Meeting new challenges in low surface-brightness astronomy with the next generation of cosmological simulations

Abstract: A natural consequence of the hierarchical structure formation paradigm is that an overwhelming majority of galaxy mergers should be minor mergers (Msat/Mhost < 0.1). Minor mergers leave behind long-lived, but extremely faint and extended tidal features including tails, streams, loops and plumes which act as a fossil record for the host galaxy’s past interactions. In-depth studies of the size, shape and colour of these tidal features, therefore, allow us to infer the recent accretion history of the host galaxy. Past surveys, which have had to compromise between depth and area, have suffered from shallow imaging or small homogeneous samples – resulting in weak observational constraints on the role of galaxy mergers and interactions in galaxy evolution. Through a robust accounting of the large statistical and unbiased observations for of millions of objects undergoing tidal interactions which will be enabled by deep-wide imaging capabilities of new facilities like the Vera C. Rubin Observatory, Euclid and JWST, we will soon have the capability to obtain a vastly more detailed and holistic understanding of the formation and evolution of galaxies, perform novel tests of fundamental cosmological predictions and elucidate a number of key unresolved tensions which exist in the largely unexplored low-surface-brightness Universe.

Using realistic synthetic observations produced with state-of-the-art cosmological hydrodynamical simulations we have performed a comprehensive investigation of the expected nature, frequency and visibility of tidal features and debris expected in the prevailing ΛCDM paradigm across a range of environments and stellar masses as well as their reliability as an indicator of galaxy accretion histories. We explore how observational biases such as projection effects, the point-spread-function and survey depth may affect the proper characterisation and measurement of tidal features.

Rubin Observatory is expected to recover much of the flux found in the outskirts of L* galaxies even at intermediate redshifts (z < 0.4). In our simulated sample, tidal features are ubiquitous around L* galaxies but are also relatively common even at significantly lower masses (M*>10^10 Msun). The fraction of stellar mass found in tidal features increases towards higher masses, rising to 10% for the most massive objects in our sample (M* ~10^11.5 Msun). When observed at sufficient depth, such objects frequently exhibit multiple (and sometimes very many) distinct tidal features often with complex shapes. The interpretation and characterisation of such features can vary significantly with image depth as well as galaxy orientation. I will detail the steps we are taking to fully understand these biases and develop the tools necessary to exploit data from upcoming facilities.

*Graduate students will meet with Dr. Martin for lunch on Thursday at 12:00 PM (AZ) in room N305.