Jianhang Chen

We present a spatially resolved study of cold molecular gas and dust in ten main-sequence galaxies at z = 1.1−1.6, using observations of CO(4−3), CO(3−2), [C I ](1−0), and dust continuum from the NOEMA ^3D survey. We find widespread spatially extended molecular gas and dust, with sizes comparable to those of the stellar disk, in contrast to those of centrally dominated starburst galaxies at similar redshifts. Among the targeted molecular gas tracers, the CO line ( J = 3 − 2 or J = 4 − 3) remains the most effective for mapping molecular gas distribution and kinematics. The spatially resolved correlations between different molecular gas tracers exhibit about twice the scatter as their galactic-integrated correlations, indicating that interstellar medium (ISM) conditions already deviate from global averages on scales of 3−6 kpc. This likely reflects the clumpy or inhomogeneous ISM in cosmic noon star-forming galaxies. Within our sample, both the molecular gas fraction and its depletion time are nearly constant across the galactic disks out to 2 × R _e , supporting a global linear Kennicutt-Schmidt law. These galaxies also have relatively small bulges, with bulge-to-total ratios between 6–24%, and are actively forming stars. These results provide a resolved view of how galaxies can remain on the star-forming main sequence during their secular evolution at late cosmic noon, an evolutionary stage supported by quasi-steady gas accretion and efficient gas transport via prominent spiral arms and/or bars.

Context . Spatially resolved galaxy kinematics have been most extensively studied at z ∼ 0 and z > 1. The emerging consensus is that disks are common out to z ∼ 3 − 6, albeit with larger disk velocity dispersions. In this picture, z ∼ 0.5 appears as a key transition in several fundamental aspects, such as the main driver of disk gas turbulence and baryonic-dark matter (DM) mass budget. While at z ∼ 0 multi-tracer spatially resolved characterisation is most readily accessible to study galaxy dynamics, studies with more than one tracer are still sparse for most galaxies outside the local Universe. Aims . We exploited a unique dataset covering spatially resolved cold molecular gas observations with ALMA and spatially resolved ionised gas line emission and stellar continuum with MUSE to study the resolved kinematics of six galaxies at 0.43 < z < 0.83. Obtained as part of the MUSE-ALMA Haloes program and selected by their association with neutral atomic hydrogen (H I ) absorption systems, the galaxies span stellar masses from log( M _⋆ /M _⊙ ) = 10.1 − 11.8. Methods . Using the new ALMA/CO observations and combining them with the existing MUSE ionised gas data and Hubble Space Telescope stellar morphologies, we determined the kinematic nature of the sources by applying morpho-kinematic criteria. For those identified as rotating disks, we employed the forward-modelling parametric kinematic fitting code D YSMAL P Y to jointly model the H β and CO(2-1) observations of the galaxies, and we compared the results to theoretical predictions for pressure support in galaxies. For the stellar kinematics, we used pPXF to fit rest-frame optical stellar absorption features. Results . We find that four of the six galaxies can be classified as disks, and two of these galaxies have previously identified galaxy group members. The four disk galaxies exhibit elevated gas velocity dispersions compared to z ∼ 0 disks, in agreement with the interpolation of observed trends between z ∼ 0 and z > 1. The results are consistent with marginally stable gaseous disks, where gravity-driving still plays a role in addition to stellar feedback, although we find tentative evidence of a differentiation between a dynamically hotter warm phase and the cold gas ( σ _0,Hβ ∼ 1.7× σ _0,CO ). We derived the average DM fraction ⟨ f _DM ⟩ = 0.42 ± 0.14, which is consistent with observations at comparable epochs and stellar masses and surface densities. This study highlights the use and completeness of analysing a sample of galaxies in a self-consistent manner and using multi-wavelength observations to explore the physics of disk settling in a relatively less explored redshift range.

We present NOEMA ^3D , a unique high-resolution study of purely molecular gas kinematics at z ~ 1.1 to 1.6, providing a dedicated view of cold gas dynamics at the late stages of the peak epoch of cosmic star formation. Using deep (≳20 h on source per target) IRAM–NOEMA CO observations of ten massive (10.45 ≤ log(M _⋆ /M _⊙ ) ≤ 11.43) main-sequence galaxies, complemented by high-resolution JWST imaging, we resolved the molecular gas kinematics and morphology on kiloparsec scales. We find that all galaxies exhibit ordered rotation with moderate intrinsic turbulence (median σ ₀ ~ 32 ± 10 km s ⁻¹ , median V _c / σ ₀ ~ 8.6 ± 2.9), consistent with dynamically turbulent disks at late cosmic noon. Modeling the axisymmetric rotation with the forward-modeling code DysmalPy , we find spatially coherent velocity residuals in all but one edge-on system. The inferred in-plane noncircular motions reach amplitudes of ~50–100 km s ⁻¹ , which are significantly larger than typically observed in local disk galaxies. Interpreting these noncircular motions as radial flows, we find that the velocity residuals spatially coincide with non-axisymmetric structures - spiral arms and bars – demonstrating a direct link between galaxy morphology and gas transport at z ~ 1–2. In spiral galaxies, the residual velocity patterns are typically dominated by inflows, while barred systems display an apparent inflow-outflow pattern, characteristic of in-plane bar-driven gas motions. We further find that the inferred molecular gas inflow rates are substantial, with a typical net inflow rate on the order of the star formation rate ( M ^˙¯ ~ −46M _⊙ /yr). This implies that spiral arms and bars at cosmic noon are highly efficient at funneling cold gas toward galaxy centers, perhaps driving the buildup of bulges and feeding central star forming regions and supermassive black holes.

Dense gas is the direct fuel for star formation, but measuring it has long been difficult at z ≥ 2, especially in unlensed star-forming main-sequence galaxies. In this work, we report the first detection of HNC (J = 5–4) and CN (N = 4–3) emission in a massive unlensed main-sequence galaxy, BX610, at z = 2.21. The velocity integrated emission of HNC(5–4)+CN(4–3) is concentrated in the galactic centre, coincident with the region of ongoing intense star formation. Based on line decomposition, we measure a line flux ratio HNC(5-4)∕CN(4-3) of 1.05 ± 0.23, similar to that of lensed starburst galaxies at comparable redshifts but lower than that of quasar host galaxies. The low HNC/CN ratio disfavours the presence of a strongly buried AGN in BX610, consistent with optical line diagnostics. The radiative transfer analysis favours the presence of dense gas with a density of (2-4) × 10 ⁶ cm ⁻³ and a kinetic temperature of 50–80 K. The derived abundance ratio between N (HNC) and N (CN) favours dense gas clouds near photodissociation regions, as commonly seen in typical starburst environments. The inferred dense-gas line luminosity closely follows the scaling relation between far-IR and dense-gas line luminosities established for local luminous infrared galaxies (LIRGs). Our observations support the view that star formation in cosmic noon galaxies is primarily controlled by the availability of dense gas, which could be enhanced in central galactic regions with efficient cold gas inflows as observed in BX610 along the inner spiral arms and a possible stellar bar.

We present gas-phase radial metallicity profiles for 20 main-sequence galaxies at 4 < z < 6 primarily based on JWST NIRSpec IFU observations obtained as part of the JWST-ALPINE-CRISTAL programme. Our study aims to connect the metallicity gradients of these galaxies with their kinematic properties from [C II ] 158 μm ALMA observations. We mapped the radial profiles of oxygen abundance using the strong-line method, leveraging the rich set of rest-frame optical emission lines. Linear fits to the annular-binned radial profiles show that, on average, the metallicity gradients are slightly positive with a median of +0.039 ± 0.010 dex kpc ⁻¹ . However, only three galaxies show a gradient > 0.05 dex kpc ⁻¹ at 1 σ , and none have a significant negative gradient. There are no substantial systematic offsets in gradients when using different line diagnostics. We investigated the correlation between the metallicity gradients and the intrinsic gas velocity dispersion σ ₀ as well as the V _rot / σ ₀ ratio of the disks. Combining our sample with mass-matched literature samples at 3 ≲ z ≲ 7, we found a negative shallow correlation between V _rot / σ ₀ and the metallicity gradients, but no strong relationships with σ ₀ . As V _rot / σ ₀ increases towards later cosmic times, the observed negative trend with V _rot / σ ₀ is consistent with the overall cosmic evolution of metallicity gradients from high to low redshifts. This suggests that disk maturity plays a crucial role in shaping the radial metallicity gradients. We do not find the metallicity gradients of disk galaxies to be significantly different from non-disk galaxies, which could be attributed to the frequent accretion events that took place in these gas-rich systems. Additionally, we find no strong dependence of metallicity gradients on stellar mass and only a marginal positive dependence on specific star-formation rate. Our study extends the efforts to connect the internal kinematics of galaxies with their gas-phase chemical enrichment at kiloparsec scales from cosmic noon to z > 4.

The interactions between gas and galaxies are of paramount importance to our understanding of structure formation. A fundamental element of such baryon cycle studies is a complete census of the condensed matter (stars and cold gas) in both galaxies and their immediate surroundings, the so-called circumgalactic medium. Of particular importance are the processes of converting molecular gas into stars and deciphering whether this < 100 K gas is tracing gas flows. The MUSE-ALMA Haloes survey assembled probes of the neutral atomic gas H I , ionised gas, and stellar component for a sample of 79 z ∼ 0.5 galaxies. This was achieved by combining absorption-line spectroscopy of background quasars with a projected impact parameter as low as 5 kpc and as high as 250 kpc to probe the low-density circumgalactic gas with emission-line tracers of both ionised gas and stars. This paper presents the Large Programme observational setup and releases the data characterising the molecular phase of some of the MUSE-ALMA Haloes targets so as to reach a complete census of their condensed baryons. ALMA’s unique millimetre coverage and high sensitivity are ideal for characterising the CO emission of these z ∼ 0.5 H I -selected galaxies. By measuring the molecular mass, kinematics, gas flows, and gas fractions, this project (i) quantifies the role of molecular gas in H I -rich galaxies, (ii) characterises the molecular phase of gas flows from morpho-kinematics analyses, and (iii) establishes a census of the condensed baryons in the interstellar and circumgalactic media. Ultimately, these results will provide unique insights into the baryon cycle – a crucial component of galaxy formation.

We present further results from the MUSE-ALMA Haloes survey, which includes 79 galaxies associated with strong H I absorption at z ∼ 0.5. As part of this effort, our ALMA Cycle 10 Large Program contributed new observations of 39 systems. This expands on the initial set of 21 systems in the MUSE-ALMA Haloes survey, bringing the total to 60 galaxies. Among the newly observed systems, we detect CO line emission in nine galaxies, corresponding to a 23% detection rate in a sample not selected by metallicity. When combined with prior MUSE-ALMA Haloes data, our total CO detection count rises to 12 out of 60 galaxies (20%), which effectively doubles the number of detected CO-emitting H I –selected galaxies at z ∼ 0.5 and probes a factor of ∼1.2 dex deeper in M H ₂ than earlier absorber studies. These sources, which were selected based on known circumgalactic H I gas, span a wide range of stellar masses and metallicities, providing a unique view of gas-rich environments. By comparing the molecular gas properties, traced through CO(2−1) and CO(3−2) transitions with existing information of their physical properties, such as star formation rates (SFRs) and gas-phase metallicities from VLT/MUSE and HST spectroscopy, we investigate how these systems relate to the population of normal star-forming galaxies at similar redshift. Our deep, unbiased CO observations of H I -selected galaxies reveal a dual behaviour in star formation efficiency. Low- M H ₂ systems form stars efficiently and follow the scaling relations of main-sequence galaxies, while high- M H ₂ systems exhibit suppressed star formation and lower-than-expected stellar masses, likely reflecting ongoing gas accretion or environmental regulation. This diversity indicates that H I absorbers trace both evolved, actively star-forming galaxies and younger or dynamically influenced systems that are still building their gas reservoirs. By reaching molecular gas masses more than 1 dex below previous studies, our survey provides a key step towards completing the baryon census at z ∼ 0.5 and characterising the molecular phase of the broader H I -selected population.

Rotation curves are a fundamental tool in the study of galaxies across cosmic time, and with the advent of large integral field unit (IFU) kinematic surveys there is an increasing need for efficient and flexible modelling tools. We present RotCurves, a parametric forward-modeling tool designed for rotation curve analysis at high-z, correcting for ``beam smearing" by projecting and convolving the beam PSF in the plane of the galaxy. We benchmark RotCurves against the established parametric code dysmalpy using synthetic observations. The typical runtime with RotCurves is a few ~10ms, a factor 250 faster than dysmalpy for a single realization. For well-resolved systems (PSF FWHM < Reff), the mock observed rotation and dispersion curves agree to within 5% up to 3Reff, where most of the discrepancies are in the inner disk. whereas in marginally resolved systems (PSF FWHM > 1.5 Reff) discrepancies increase to up to 15%. Using a built-in MCMC fitting procedure, RotCurves recovers well the intrinsic model parameters across a wide range of galaxy properties and accounting for realistic noise patterns. Systematic biases emerge for the effective radius and for low disk masses (Mdisk < 3x10^9 Msun). We show excellent parameter recovery at high signal-to-noise ratios (S/N > 25), with increasing deviations in parameter recovery at lower S/N. RotCurves is best suited for inclinations of 10 < i < 80. RotCurves is built as an exploratory tool for rapid testing of mass model assumptions, parameter studies and for efficiently processing large samples of observational data from large IFU surveys. The code is publicly available on github.