Resolving the Assembly of Disk Galaxies from the Epoch of Reionisation to Cosmic Noon

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

Vera: We're looking at the paper: "Resolving the Assembly of Disk Galaxies from the Epoch of Reionisation to Cosmic Noon".

Jocelyn: The gist: ALMA2040 will transform our understanding of how galaxy disks formed and evolved by providing resolved CO,

C I: , and

C II: observations across z = 1 − 6.

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

Title and authors: Vera: Now let's talk about what this paper is actually proposing, which is titled "Resolving the Assembly of Disk Galaxies from the Epoch of Reionisation to Cosmic Noon". The main idea here is using ALMA2040 to match up different phases of galaxy evolution.

Jocelyn: It’s not just looking at one snapshot; it’s trying to map out how disks evolve from when they first assemble at high redshift, say z equals six all the way through to the growth phase around cosmic noon, which is z equals one or three <ref:2610.21441#pg3>.

Subrahmanyan: That mapping is important because it allows us to see if our current simulations of structure formation and galaxy evolution actually match what we observe in terms of disk properties over that entire time span.

Vera: The paper emphasizes that understanding the interplay between the gas accretion, feedback, and radial transport processes is what governs how these galaxies evolve.

Jocelyn: They are focusing on resolving these dynamics—the turbulence and flows—within those disks using those specific cold gas tracers like CO and C II.

Subrahmanyan: What this means for structure formation is that we need to move beyond just seeing the final state of a galaxy and look at the continuous process of its assembly.

Vera: And they highlight that current observational progress at z equals one, while good, still leaves fundamental questions about how gas gets fed into those disks.

Jocelyn: So this work is pushing for observations that can resolve these dynamics across a much broader cosmic timeline than we currently have access to.

The paper's summary: Vera: So, the summary of this paper really boils down to using ALMA2040 to provide sub-kpc scale constraints on the cold gas kinematics and morphology for a much larger sample of galaxies than what we can currently get from resolved stellar studies.

Jocelyn: That’s right; they are comparing what we see now, like the massive, highly star-forming galaxies at z greater than three with what ALMA2040 can do to resolve those progenitors <ref:2610.21441#pg2>.

Subrahmanyan: The core finding is that this capability will enable statistical resolved studies that are representative of the entire star-forming galaxy population, which is something we really need for a complete picture.

Vera: They stress that mapping C I and C II becomes increasingly critical when we look at lower mass galaxies, because those are where these cold gas tracers are expected to remain dominant.

Jocelyn: So they’re essentially saying that the observations of these specific molecules give us a unique window into heavily obscured regions where other ionised-gas tracers might be too faint.

Subrahmanyan: This helps us disentangle the different physical processes happening in those galaxies, like distinguishing between turbulence driven by feedback versus gravitational instabilities.

Vera: It’s about getting better constraints on the density and profiles of dark matter halos during this crucial epoch of galaxy assembly at z equals one to three <ref:2610.21441#pg1>.

The paper's improvements: Jocelyn: The paper suggests a few ways to make this work even better, focusing on how we can improve the resolution and sensitivity needed for these science cases.

Vera: One big improvement they suggest is needing sufficient angular resolution to actually identify non-axisymmetric structures, like spiral arms or bars, which is really hard right now.

Subrahmanyan: That kind of detail is key because those structures are where we expect the most significant mass redistribution and angular momentum transport to happen within the disk.

Jocelyn: They also point out that they need sensitivity to robustly discern non-circular motions in the gas, which means pushing line sensitivity up by a factor of ten compared to ALMA’s current capabilities.

Vera: So it comes down to needing a next-generation sub-/millimetre interferometer with ten times the line sensitivity and instantaneous coverage across all receiver bands.

Subrahmanyan: That tenfold increase in sensitivity is what unlocks the ability to robustly measure the impact of non-axisymmetric structures on angular momentum transport, which is a direct test of how mass moves around in these galaxies.

Conclusion: Jocelyn: So to wrap up, this paper on "Resolving the Assembly of Disk Galaxies from the Epoch of Reionisation to Cosmic Noon" shows us that ALMA2040 can provide the necessary gas-phase counterpart to Galactic archaeology studies by recovering cold-gas kinematics to large radii.

Vera: By doing this, we get a new statistical view of how the progenitors of present-day spiral galaxies assembled across a wide range of masses and cosmic epochs.

Subrahmanyan: It’s also about probing the densities and profiles of dark matter halos during the peak epoch when galaxy assembly is happening, which provides a new test for dark matter models.

Jocelyn: Ultimately, resolving these gas flows, tidal structures, and interaction-driven perturbations lets us see exactly how mass and angular momentum are redistributed both within galaxies and between them.

Vera: It’s a big step toward statistically understanding the assembly of disk galaxies from z equals six down to cosmic noon <ref:2610.21441#pg3>.

Jocelyn: We'll keep an eye on how this data helps settle those questions about gas accretion versus feedback as we move forward.

Subrahmanyan: I think the ability to constrain the evolution of dynamical scaling relations and dark matter density profiles at z greater than one is a very important piece for testing alternative dark matter models <ref:2610.21441#pg1>.