Galaxy luminosity functions from far-UV to submillimetre at z=0 in the COLIBRE simulations

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

Vera: Today's paper: "Galaxy luminosity functions from far-UV to submillimetre at z=0 in the COLIBRE simulations".

Jocelyn: This research presents predictions from recent COLIBRE cosmological hydrodynamical simulations, post-processed with a calibration-free radiative transfer code called skirt,

Vera: First, who's behind it and why it matters.

Title and authors: Vera: So, we're talking about this paper titled "Galaxy luminosity functions from far-UV to submillimetre at z=zero in the COLIBRE simulations." It seems like they are looking at how galaxies look across a huge range of wavelengths, from the ultraviolet right down to the submillimetre.

Jocelyn: That title suggests a very broad view of galaxy populations, Vera; it's not just focusing on one specific light band but covering everything from young stars to warm dust emission. Who are the authors on this project? I want to know who is behind these cosmological simulations.

Subrahmanyan: The authors include folks like Shengdong Lu, Carlos S. Frenk, Cedric G. Lacey, Andrea Gebek, Joop Schaye, Shaun Cole, Sownak Bose, Nick Andreadis, Maarten Baes, Alejandro Ben´ıtez-Llambay4 and Evgenii Chaikin1 and Robert A. Crain5 among others. These are definitely heavy hitters in the simulation community.

Vera: Exactly; having names like Frenk and Schaye on the list tells us we’re dealing with a top-tier cosmological simulation effort, which is exciting because they're using COLIBRE simulations to generate these luminosity functions.

Jocelyn: And what does that mean for us observing the sky? It implies they are connecting the complex physics happening inside galaxies in those simulations directly to what we actually see across different telescopes.

Subrahmanyan: From a theoretical side, having such a large team suggests they have integrated multiple complex physical processes into their model, which is crucial when trying to understand how structure grows in the universe.

Vera: It really is; the implication here is that we're getting a way to test our models of galaxy formation using these simulated LFs as a benchmark for real observations.

Jocelyn: So, it sounds like this paper isn't just running simulations; they’re trying to create a direct link between the theoretical model and observable data across the spectrum.

The paper's summary: Vera: The core of this paper, "Galaxy luminosity functions from far-UV to submillimetre at z=zero in the COLIBRE simulations," boils down to them showing predictions for galaxy luminosity functions across a wide range of wavelengths at redshift zero.

Jocelyn: That's pretty impressive because those LFs cover everything from the far-ultraviolet all the way into the submillimetre, which is a massive spectral range to cover. What exactly are these LFs they’re calculating?

Subrahmanyan: They are using the output from their COLIBRE simulations, which they describe as state-of-the-art cosmological hydrodynamical simulations that explicitly model the multiphase interstellar medium and dust formation self-consistently.

Vera: That self-consistent modeling of dust is a big deal because it means they aren't just guessing how much light is absorbed or re-emitted; they are letting the simulation tell them about the dust distribution itself.

Jocelyn: And what's the main result they highlight? The summary mentions that this combined approach successfully predicts stellar population properties and the distribution of interstellar dust with "unprecedented agreement" across all wavelengths.

Subrahmanyan: That level of agreement suggests that their framework, which couples COLIBRE with a calibration-free radiative transfer code called skirt, is a very robust way to model galaxy formation in this cosmological context.

Vera: It’s the fact that they managed to get stellar population properties and dust distribution matching observations across such a wide spectral range that makes this study quite significant.

Jocelyn: So, in simpler terms, they've taken a complex simulation suite and paired it with a post-processing tool to predict how galaxies look light-wise from the ultraviolet to the submillimetre at today's cosmic epoch.

The paper's improvements: Vera: Now let’s talk about what the authors suggest as improvements for this research, because they aren't just presenting a final result; they are pointing out where things could get better.

Jocelyn: What kind of improvements are they suggesting? Are we talking about tweaking the input physics in COLIBRE, or is it more about refining how we process the data afterward?

Subrahmanyan: The paper points to several sources of uncertainty they systematically test, including the effect of different AGN feedback models, which showed little influence on LFs across all bands at redshift zero.

Vera: That’s interesting; so they found that changing how much feedback happens from active galactic nuclei didn't really shake the final luminosity function results across the spectrum.

Jocelyn: Then they also looked at star-forming region resampling, and that only affected the far-UV LF by up to zero point four dex, which is a pretty small adjustment compared to other uncertainties.

Subrahmanyan: They also tested how aperture size impacts the results, finding it primarily affects the bright end in the far-UV, r, and K bands. This suggests that how you define your measurement volume matters depending on what part of the spectrum you're looking at.

Vera: So, they’re showing us exactly where these modeling assumptions have their biggest impact—it’s not everywhere equally across all wavelengths or physical parameters.

Jocelyn: It sounds like the suggestion is really to focus on tuning those specific subgrid physics, like the dust grain size distribution or star formation efficiency, which are deeply tied into how the simulation runs.

Conclusion: Vera: So, to wrap things up on this paper, it seems they’ve established a very strong connection between their complex simulation setup and what we observe in terms of galaxy luminosity functions from far-UV to submillimetre at z=zero in the COLIBRE simulations.

Jocelyn: They’ve shown that when you combine COLIBRE with the skirt pipeline, you get predictions for LFs that match observations remarkably closely across the FUV to K band and even into those longer IR bands like seventy µm to eight hundred fifty µm.

Subrahmanyan: The implication is that this combination of simulation and radiative transfer modeling captures the bulk of the relevant physics governing stellar emission, dust attenuation, and dust re-emission in a broadly realistic manner for these galaxies.

Vera: They did find one specific limitation they wanted us to be aware of: a noteworthy result is that colibre-skirt predicts galaxies that are not bright enough at the bright end from eight to twenty-four µm, which leads to a truncated bright end relative to the observations.

Jocelyn: And they also mentioned that while the total infrared LF agrees well with observations at the faint end, it shows an underprediction of the bright end for those same IR bands.

Subrahmanyan: Overall, this paper on "Galaxy luminosity functions from far-UV to submillimetre at z=zero in the COLIBRE simulations" provides a very solid test for models of galaxy formation in a cosmological context by demonstrating how well their framework can reproduce observed properties.

Vera: It’s a really compelling piece of work that validates the use of this simulation pipeline for studying galaxy evolution across such a wide spectral range, and it makes us think about what's next on the horizon for these simulations.