ALMA2040: Mapping the Spatially Resolved Dust and Star Formation Physics Driving High-z Galaxy Assembly

arXiv:2610.22228 · astro-ph.IM, astro-ph.GA · Submitted 2026-10-15 · Read on arXiv

Listen

Transcript

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

Vera: We're looking at the paper: "ALMA2040: Mapping the Spatially Resolved Dust and Star Formation Physics Driving High-z Galaxy Assembly".

Jocelyn: The gist: ALMA2040 will transform resolved dust thermometry into a systematic survey science by measuring radial temperature gradients with ∼0.5–4 K precision, delivering extinction-free,

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

Paper summary: Vera: We started by looking at the problem of how dust temperature is unconstrained on sub-galactic scales at high redshift, which is a big issue because we need that temperature to convert continuum flux into dust mass and star formation rates.

Jocelyn: The paper sets out to address this by proposing ALMA2040 as a tool that can move us past the limitations of single-frequency measurements on hundreds of galaxies at z greater than one <ref:2610.22228#pg1>.

Subrahmanyan: They are essentially arguing that the current assumption of isothermal dust temperatures, like the fiducial temperature range of T dust being around twenty-five to thirty-five Kelvin drawn from brighter samples, leads to serious errors <ref:2610.22228#pg2>.

Vera: Specifically, if you apply an isothermal assumption across a galaxy with a negative temperature gradient, like forty Kelvin in the nucleus falling down to twenty-five Kelvin in the outer disk, it overestimates the central dust column by about sixty percent and underestimates the outer disk by about thirty percent <ref:2610.22228#pg2,an isothermal assumption across a galaxy with a>.

Jocelyn: That means that assuming constant temperature artificially steepens the inferred radial gas profile by a factor of approximately two which directly biases the resolved Kennicutt-Schmidt relation and corrupts dynamical stability measurements <ref:2610.22228#pg1>.

Subrahmanyan: So, they are saying that resolved dust thermometry is critical because it provides independent constraints on physical conditions like metallicity and ionization, which line-based gas tracers like CII are sensitive to but are complicated by local conditions.

Vera: The paper says that ALMA2040 will deliver the first extinction-free, temperature-calibrated resolved star formation law at z greater than two providing both the obscured SFR surface density and the cross-calibrated gas surface density from a large sample of dust continuum thermometry <ref:2610.22228#pg1>.

Jocelyn: This is significant because it gives us a way to get both the obscured star formation rate and the gas surface density simultaneously calibrated by temperature.

Subrahmanyan: And they mention that this is irreplaceable for unveiling these properties for hundreds of star-forming galaxies at z greater than two which will have JWST spatially resolved strong line metallicity from intergalactic field unit IFU, grism reconstruction, and multi-shutter array slit stepping observations <ref:2610.22228#pg1>.

Vera: The core idea of this ALMA2040 work is to move away from those assumptions and get a true picture of the dust physics driving high-z galaxy assembly.

Conclusion: Jocelyn: So, looking at the whole paper "ALMA2040: Mapping the Spatially Resolved Dust and Star Formation Physics Driving High-z Galaxy Assembly", what this really means is that we're finally getting a way to map the physical structure of high-redshift galaxies with dust.

Vera: It moves us from just seeing continuum sizes to understanding the actual thermal structure and gradients within those galaxies, which tells us about how energy is distributed throughout the interstellar medium.

Subrahmanyan: The authors are showing that resolving these temperature gradients allows us to disentangle whether we are looking at smooth gradients or localized thermal spikes driven by nuclear heating across cosmic noon.

Jocelyn: And this has implications for cosmology because it constrains the relationship between gas and dust, which in turn affects our models of structure formation.

Vera: The paper’s title points directly to the fact that this is about mapping the spatially resolved dust and star formation physics driving high-z galaxy assembly.

Jocelyn: So, ALMA2040 is designed to be a systematic survey science by measuring radial temperature gradients with about zero point five to four Kelvin precision.

Subrahmanyan: The implication is that this will allow us to uniquely trace radiative feedback and disk maturation from cosmic noon all the way back to cosmic dawn.

Daizhong Liu, Gergo Popping, Pierre Cox, Andreas Faisst, Mamta Pandey-Pommier, Dieu Nguyen, Roman Fernandez Aranda , Elisabete da Cunha , Andrea Lapi , Tanio Díaz Santos8, 12, řota Ikeda13, żqueline Hodge13, řabella Lamperti14, Manuel Aravena, 16, Irene Shivaei, 14, Adarsh Kumar, 17, Roberto Decarli, 18, Mahmoud Hamed, 14, Umberto Maio20, Gareth Jones2122 , Jianhang Chen23, Sylvia Adscheid24 *

State Key Laboratory of Radio Astronomy and Technology at Purple Mountain Observatory Chinese Academy of Sciences · European Southern Observatory · Sorbonne Universite UPMC Paris 6 and CNRS Institut déAstrophysique de Paris · Caltech/IPAC · Pole Scientific University Catholic of Lyon University of Lyon Department of Astronomy University of Michigan International Centre for Radio Astronomy Research The University of Western Australia ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions

astro-ph.IM, astro-ph.GA

Submitted: 2026-10-15

Updated: 2026-10-15

Comments: Part of the ALMA2040 White Paper Series. 10 pages main text including references, 5 figures

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 92/100

The gist: The gist: ALMA2040 will transform resolved dust thermometry into a systematic survey science by measuring radial temperature gradients with ∼0.5–4 K precision, delivering extinction-free,

Key concepts

Dust Temperature: Dust temperature is crucial because it links observed starlight to physical properties like gas mass. Current single-band observations cannot separate the total dust mass from local heating effects, which makes understanding galaxy physics difficult without knowing the actual temperature.
Radial Temperature Gradients: These are the changes in dust temperature as you move from the center to the outer regions of a galaxy. Measuring these gradients helps distinguish between smooth disk structures and localized, intense heating sources like nuclear activity or starbursts.
Extinction-Free Star-Formation Law: This is a new way to measure how fast galaxies are forming stars without needing complex corrections for dust obscuration. By using resolved dust temperatures, researchers can calibrate the relationship between the amount of obscured star formation and the actual gas content in the galaxy.
ALMA2040 Capabilities: ALMA2040 is a proposed next-generation instrument designed with increased sensitivity and multi-band receivers. It is expected to measure these temperature gradients with high precision, enabling a systematic survey of over 100 main-sequence galaxies across cosmic time.

Summary

The gist: ALMA2040 will transform resolved dust thermometry into a systematic survey science by measuring radial temperature gradients with ∼0.5–4 K precision, delivering extinction-free, temperature-calibrated resolved star-formation relations and tracing radiative feedback from cosmic noon to cosmic dawn.

The problem addressed

Interstellar dust reprocesses approximately half of the starlight emitted across cosmic history, but dust temperature remains largely unconstrained on sub-galactic scales at high redshift. Single-band ALMA imaging cannot separate the dust mass column from the local dust heating. To date, spatially resolved (< ∼ 0.5′′) multi-band dust temperatures exist in the literature for only ≈ 10 extreme systems at z > 1 1 galaxies, single-frequency measurements cannot separate the dust mass column from the local dust heating>.

Key scientific goals

The paper frames the scientific motivation around five core science goals (SG1–SG5):

** SG1: Radial temperature profiles and disk equilibrium. What is the intrinsic radial dust-temperature profile of normal star-forming galaxies at cosmic noon? Local spirals like M31 exhibit mild negative gradients of ≈ 5–10 K from center to outskirts. In contrast, the few mapped z > 4 extreme systems, such as hyperluminous quasar hosts, display central-to-outer temperature contrasts of ≈ 20 K driven by nuclear heating 4 extreme systems, such as hyperluminous quasar hosts, display central-to-outer temperature contrasts of ≈ 20 K driven by nuclear heating?>. Measuring whether smooth gradients or localized thermal spikes are generic in normal galaxies is essential to understanding radiative transfer and ISM energy balance during the peak of cosmic galaxy assembly.**

** SG2: Disentangling morphological compactness from temperature gradients. A cornerstone discovery of ALMA is that dusty star formation at z ≈ 2 is concentrated within compact submm cores whose effective radii are a factor of ≈ 2 smaller than the optical and near-infrared stellar light. However, because continuum brightness is temperature-weighted, warmer dust in the galactic nucleus naturally produces an artificially compact apparent size at shorter wavelengths near the SED peak. Spatially resolved temperature maps are required to decouple temperature gradients from mass column profiles, determining the true physical mass-size relation of high-z dust disks.**

** SG3: The extinction-free, temperature-calibrated resolved star-formation law. ALMA2040 will deliver the first extinction-free, temperature-calibrated resolved star-formation law at z > 2 2>. This provides both the obscured SFR surface density (ΣSFR) and the cross-calibrated gas surface density (Σgas) from a large sample of dust continuum thermometry. ALMA2040 is irreplaceable for unveiling these properties for hundreds of star-forming galaxies at z > 2 which will have JWST spatially-resolved strong-line metallicity from intergral field unit (IFU), grism reconstruction, and multi-shutter array slit-stepping observations 2 which will have JWST spatially-resolved strong-line metallicity from intergral field unit (IFU), grism reconstruction, and multi-shutter array slit-stepping observations>. **

** SG4: Dust, gas, and stellar geometry. Resolving dust temperatures provides the missing thermal dimension necessary to place strong constraints on the dust-star geometries. **

** SG5: Radiative heating sources and feedback mechanisms. Spatially resolved temperature maps down to (sub-)kpc scales to resolve the nuclear region and galactic sub-structures would provide the breakthrough diagnostic, distinguishing compact nuclear hot spots powered by AGN accretion from widespread mechanical heating across tens of kpcs at ´ z > 2 2>.**

Technical requirements for ALMA2040

ALMA2040 is designed to overcome the bottleneck where recovering both the dust column density and the temperature field requires at least two wellseparated, high-signal-to-noise continuum maps on matched physical scales. The ALMA2040 design envisions an expanded collecting area (i.e., 200–300 antennas in extended configurations of ∼ 20 km baseline), much wider instantaneous bandwidth (e.g., 512 GHz; here we assume 5-band multiplex, each with 64 GHz IF bandwidth), and upgraded quantum-limited receiver technology. This delivers a factor of ∼ 13× gain in point-source continuum sensitivity per band, and an aggregate gain of ∼ 30× across the 5 bands, boosting survey speed by ∼ 900× to reach a given continuum depth.

Performance and precision

Realistic visibility simulations demonstrate that ALMA2040 measures radial temperature gradients with ∼0.5–4 K precision (LIR ≈ 1012 L⊙ in 2 h on-source at z ≈ 2). These measurements will break the degeneracy between intrinsic compactness and temperature gradients, deliver the first extinction-free, temperature-calibrated resolved star-formation relations, and uniquely trace radiative feedback and disk maturation from cosmic noon to cosmic dawn.

Transformational survey potential

A reference ALMA2040 survey of ≥ 100 representative main-sequence galaxies spanning cosmic dawn (z ≈ 4–6) to cosmic noon (z ≈ 1–2) is envisioned ∼ 1,000 h sequentially per target), making such a survey impossible within normal TAC allocations ∼ 1,000 h sequentially per target), making such a survey impossible within normal TAC allocations>. This survey directly achieves the goals of Sect.

Improvements for AI systems

Inference of Radial Temperature Profiles: The improved AI system can determine What is the intrinsic radial dust-temperature profile of normal star-forming galaxies at cosmic noon? by analyzing multi-band continuum data to resolve smooth gradients or localized thermal spikes.
Morphological Decoupling: The system can decouple temperature gradients from mass column profiles, determining the true physical mass-size relation of high-z dust disks by using spatially resolved temperature maps to address the degeneracy between intrinsic compactness and temperature gradients.
Star Formation Law Calibration: The AI can deliver "the first extinction-free, temperature-calibrated resolved star-formation law at z > 2, providing both the obscured SFR surface density (ΣSFR) and the cross-calibrated gas surface density (Σgas)" from a large sample of dust continuum thermometry.
Feedback Mechanism Diagnostics: The system can distinguish compact nuclear hot spots powered by AGN accretion from widespread mechanical heating across tens of kpcs by resolving dust temperatures down to (sub-)kpc scales to analyze the origin of high-redshift dust heating sources.
Systematic Survey Science: The AI can execute a reference ALMA2040 survey of ≥ 100 representative main-sequence galaxies spanning cosmic dawn (z ≈ 4–6) to cosmic noon (z ≈ 1–2) to map dust emission out to ∼ 1.5 r50 at 1–2 kpc with precision that currently makes such a survey impossible within normal TAC allocations.

Abstract

Interstellar dust reprocesses approximately half of the starlight emitted across cosmic history. However, dust temperature, which is essential to convert continuum flux into dust mass, molecular gas mass, and obscured star-formation rates, remains largely unconstrained on sub-galactic scales at high redshift. While single-band ALMA imaging has characterized continuum sizes for hundreds of z>1 galaxies, single-frequency measurements cannot separate the dust mass column from the local dust heating. To date, spatially resolved (<0.5-arcsec) multi-band dust temperatures exist in the literature for only 10 extreme systems (quasars, hyperluminous starbursts, or strongly lensed galaxies) at z>1, with ongoing programs within a few years adding at most a few dozen submillimeter or UV-bright galaxies. This still leaves typical main-sequence disks largely unexplored across cosmic history. With an anticipated 30 times improvement in continuum sensitivity (compared to the current ALMA), simultaneous multi-band receivers, and (sub-)kpc angular resolution, ALMA2040 will transform resolved dust thermometry into a systematic survey science. Here, we present the scientific rationale and technical requirements, highlighting a future statistically meaningful survey with > 100 representative main-sequence galaxies across cosmic epochs. Realistic visibility simulations demonstrate that ALMA2040 measures radial temperature gradients with 0.5-4 K precision (L IR 10 12 L sun in 2 h on-source at z 2). These measurements will break the degeneracy between intrinsic compactness and temperature gradients, deliver the first extinction-free, temperature-calibrated resolved star-formation relations, and uniquely trace radiative feedback and disk maturation from cosmic noon to cosmic dawn.