arXiv subjects

Boris S. Kalita

Publications and source records attributed to Boris S. Kalita.

At least 19 recordsLinked to original sources

arXiv2026

SCALES. I. Bridging Lensed Clump - Giant Clump Scales in Lensed Galaxies at $z=1-4$

Dense star-forming regions in $z>1$ galaxies, often termed 'clumps', have been studied across two distinct regimes of telescope resolution, each motivating interpretations in tension with the other. In the SCALES series (Star-Forming Clumps As Layered Emergent Structures), we aim to connect star-forming structures across scales, from the $\sim100\,\mathrm{pc}$ clumps in lensed studies to the $\sim\mathrm{kpc}$-scale ''giant'' clumps in unlensed surveys. In this first paper, we present a difference-of-Gaussian (DoG) decomposition that simultaneously models $\sim100-300\,\mathrm{pc}$ (lensed) clumps and $\sim\mathrm{kpc}$-scale component (the extended component, or EC), which would together constitute the giant clumps seen at lower resolution. Here the EC is treated as a scale-separated local background rather than a physical object, absorbing all light that is not a compact clump. Applying this to 23 moderately lensed ($μ\approx 2-9$) galaxies at $z_{spec} = 1-4$ to evaluate clump properties (deferring ECs and giant clumps to the next work), we find their stellar mass to be capped at $\sim 10^{8.5}\,M_{\odot}$. We measure clump stellar mass function slope of $2.19 \pm 0.06$, which is higher than typical, and may reflect a physical truncation at the massive end. We also show that empirical correlations of clump surface densities and clump-to-host mass ratio with redshift are exaggerated by redshift-dependent detection bias, so $\sim100-300\,\mathrm{pc}$ clumps are largely co-similar across our range ($z = 1-4$). Finally, combining clump mass, size and age estimates with literature gas-dispersion measurements at similar scales, we argue that $\sim100\,\mathrm{pc}$ clumps are themselves composed of star-cluster-like sub-components at much smaller scales.

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arXiv2026

SCALES. II. The Internal Composition of Giant Star-Forming Clumps at $z = 1 - 4$

Star-forming structures of scale $\sim0.5-1\,\mathrm{kpc}$, dubbed 'giant' star-forming clumps, are routinely detected in unlensed surveys of $z > 1$ galaxies. Two scenarios are usually invoked to explain their existence -- genuine physical structures or resolution-driven artifacts -- yet distinguishing between them requires characterizing their internal structure. In this work, part of the Star-Forming Clumps As Layered Emergent Structures (SCALES) series, we hence ask: What is inside a giant clump? We analyze 23 lensed galaxies at $z=1-4$ with JWST/NIRCam using difference-of-Gaussian decomposition to model (lensed) clumps at $\sim 100-300\,\mathrm{pc}$ scales, and the surrounding extended component (EC) at giant clump scales. Associating clumps to ECs, we effectively identify 44 giant clumps. Characterizing giant clump stellar mass composition using the most massive member clump and the remaining constituent clumps, we find it consistent with random sampling of the host galaxy's clump population, and hence the clump stellar mass function. This conclusion agrees qualitatively with both prevailing scenarios -- (I) dominant long-lived giant clumps, although requiring constant renewal of their constituents, and (II) giant clumps as mere blended clump associations. However, most models make no strong claims about their internal mass distribution beyond order-of-magnitude statements, and our observations thus provide an empirical constraint against which such models can be re-evaluated. Finally, using the total mass budget of clumps and ECs, we find that the clump stellar mass function cannot be described by a single power law of slope $\approx 2$, but requires a break to a shallower slope at $\sim 10^{7.4}\,\mathrm{M_{\odot}}$.

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arXiv2026

CHAMPS: The COSMOS High-Redshift ALMA-MIRI Population Survey - A New Census of the Dusty Early Universe

Understanding how dust forms and evolves over cosmic time is a key open problem in extragalactic astrophysics. Galaxies in the early Universe were once thought to be mostly dust-poor, but recent discoveries of heavily dust-obscured galaxies near the Epoch of Reionization challenge models of early dust production and raise new questions about the true cosmic star formation rate density. In this paper, we present the COSMOS High-Redshift ALMA-MIRI Population Survey (CHAMPS), which sheds light on the dusty early universe at z>4. CHAMPS is a new 144h ALMA 1.2mm (band 6) large program mapping the combined JWST/NIRCam+MIRI footprint in the COSMOS field. It covers 0.2deg2 with a synthesized beam size of 1.1" and a sensitivity of 0.14mJy/beam. It is complemented, alongside JWST, by ancillary X-ray, UV, optical, sub-mm, and radio data. CHAMPS, optimized as a blind survey, detects above 5$σ$ approximately 385 individual dusty high-redshift sub-mm sources, 68 dusty AGN, and a dozen dusty galaxies at z>6. The galaxies are largely not detected in JWST/F150W, making them prototypical near-IR dark galaxies. We showcase three of the highest-redshift most dusty and massive candidate galaxies detected in CHAMPS with redshifts up to z=7.5. CHAMPS also enables stacks of thousands of galaxies grouped in bins of various physical parameters. Its sub-mm coverage of dust-attenuated JWST-identified galaxies provides robust constraints on dust masses and obscured star formation rates to study early dust formation and evolution. In addition, CHAMPS enables a blind search for luminous CO line emitters at z=0.4-2.7 and [CII]158$μ$m emitters at z=6.7.

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arXiv2026

Ubiquitous nuclear disks and bars embedded in massive galaxies in the cosmic morning

The morphology of the central regions of high-redshift galaxies remains relatively unexplored, while recent case studies suggest that giant disks can emerge without first developing a prominent central spheroid. Here, we investigate the inner structures of a mass-complete sample of 45 massive galaxies at $z=3$ in the TNG50 simulation. Through double-Sérsic profile decomposition, isodensity ellipse fitting, intrinsic three-dimensional shape measurements, and stellar kinematics, we find that these central structures are ubiquitously flattened and rotation-supported with low Sérsic indices ($n \lesssim 1$). This indicates that the central regions are predominantly nuclear disks and bars rather than bulges. Tracking their evolution, we show that these nuclear disks and bars emerge during gas-rich compaction and do not transform into spheroidal and dispersion-dominated systems until $z \lesssim 1$, before which extended stellar disks have already developed. Our results suggest that massive disks can assemble around rotation-supported centers and bulge-deficient massive galaxies may be a common outcome of galaxy evolution.

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arXiv2026

Gas Fraction and Depletion Time Drive the Main-Sequence Scatter in Massive Galaxies at $z\sim1.5$

We present ALMA Band 7 dust continuum observations of 57 massive ($M_\ast \gtrsim 10^{10.8}~M_\odot$) star-forming galaxies at $1.45 3σ$ detections for 55 galaxies. Combining the ALMA data with multiwavelength photometry, we reliably derive dust masses and infer molecular gas masses using metallicity-dependent gas-to-dust ratios estimated from individual metallicity measurements. The derived molecular gas mass ratio spans $μ_\mathrm{gas} = M_\mathrm{gas}/M_\ast=0.11\text{--}2.8$, with a median value of 0.65, corresponding to gas reservoirs more than an order of magnitude larger than in local galaxies at fixed stellar mass. The integrated Schmidt--Kennicutt relation is consistent with previous measurements over $z=0\text{--}2$. Across the MS, both molecular gas mass ratio and star formation efficiency scale approximately as $(\mathrm{sSFR}/\mathrm{sSFR}_\mathrm{MS})^{0.5}$, indicating that the MS scatter is driven nearly equally by variations in gas content and depletion time. The intrinsic scatter of $0.19$~dex suggests additional galaxy-to-galaxy diversity in star formation efficiency. Our results provide a controlled test of the unified gas scaling framework in the massive regime at $z\sim1.5$, demonstrating that the fundamental regulation of star formation through coupled modulation of gas supply and efficiency is already in place at cosmic noon.

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arXiv2026

Galactic bars are already mature at Cosmic Noon: bar strength and flatness at z ~ 1.5

In this work, we explore the nature of $z>1$ galactic bars. Once thought to be highly transient, our results demonstrate otherwise. Our sample consists of nine massive ($>10^{10.5}\,\rm M_{\odot}$) star-forming barred-spiral galaxies at $z_{\rm spec} \sim 1.5$. Using rest-frame near-IR (F444W) JWST/NIRCam imaging, we apply ellipse fitting along with 1D and 2D morphological modeling to directly measure bar properties. We find that five galaxies host flat surface brightness profiles (bar Sérsic index $<0.4$), indicative of highly evolved, "mature" bars. By contrast, only two galaxies show exponential profiles, characteristic of young bars, and these are also shorter in absolute length than the flat bars. We therefore conclude that a large fraction of bars at this epoch have already matured, thereby indicating the presence of well-settled disks required to facilitate bar formation and sustained evolution well before $z\sim1.5$. To assess the gravitational impact of the bars, we calculate the maximum transverse-to-radial force ratio ($Q_{b}$). We find that $Q_{b}$ values are comparable to, or weaker than, those of bars in the local Universe, Seven of the nine bars show only a marginal increase in strength with maturity (from exponential to flat bars). Contrarily however, the remaining two bars are flat, but have the lowest $Q_{b}$ values in our sample. We hence propose that the mature bars at $z\sim 1.5$ may experience phases of weakening due to rapid gas inflows and/or minor mergers. In conclusion, our work sheds light on the rapidly evolving nature of high-z bars and paves the way for larger statistical studies.

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arXiv2025

Ly-alpha emission reveals two satellite halos around massive groups at z ~ 3: the puzzling case of a quiescent central galaxy

We present the discovery and characterisation of two Ly$α$ nebulae (LANs), RO-1001-Sat and RO-0959-Sat, as satellite structures of two giant LANs at $z=2.920$ and 3.092. They are found neighbouring two out of four known giant LANs at $z\sim3$ in our MUSE follow-up observations, reinforcing the idea that Ly$α$ emission can be used to trace massive dark matter halos at high-$z$. This high occurrence of massive satellite halos agrees with simulations. With sizes of $\simeq80\times160$ and $80\times100~\mathrm{pkpc}^2$, the two nebulae are both $\sim$300pkpc from the main LANs. The Ly$α$ emission is only shifted by $\simeq100-300$ km s$^{-1}$ between each of the two pairs, suggesting connections via large-scale structure. RO-1001-Sat and RO-0959-Sat are estimated to have log$(M_\mathrm{h}/M_\odot)\simeq13.2\pm0.3$ and $12.8\pm0.3$, putting them potentially close to the regime of cold-mode accretion. The central brightest galaxies in the two halos are morphologically distinct despite having similar stellar mass $\sim10^{11}M_\odot$, one being an elliptical quiescent galaxy in RO-1001-Sat and the other being a dusty star-forming spiral in RO-0959-Sat. Intriguingly, the quiescent galaxy aligns well with the peak of the LAN as well as the potential well of the host halo, making it the first clear-cut case where the cold gas ought to be accreting onto the galaxy but with no observable star formation, either due to morphological quenching or, more likely, radio-mode feedback from an active galactic nucleus. Finally, we show a tentative detection of a Ly$α$ filament connecting RO-1001 and RO-1001-Sat. This work shows how panoramic MUSE (and in the future, BlueMUSE) observations of massive halo seeds can be used to efficiently search for additional halos, unveiling their large-scale structure and enabling the study of Ly$α$-selected galaxy groups.

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arXiv2025

A PAH deficit in the starburst core of a distant spiral galaxy

We present high-resolution and spatially-matched observations with JWST and ALMA of a starburst galaxy (PACS-830) at $z=1.46$. The NIRCam observations mainly trace the stellar light while the CO ($J$=5--4) observations map the dense molecular gas at kpc scales. Both datasets reveal the morphology to be that of a gas/dust rich bulge with two extending arms, together resembling a grand-design spiral galaxy. The more pronounced arm contributes 21 $\pm$ 6\% of the total CO emission. These results demonstrate that starburst activity at high redshift can be triggered, without undergoing a highly disruptive major merger. We assess the strength and distribution of star formation using two tracers: (1) Polycyclic Aromatic Hydrocarbons (PAHs) emission detected at $8~μ$m ($L_8$) with a MIRI/F1800W image, and (2) $L_\mathrm{IR}$, inferred from the CO ($J$=5--4) map. The spatial profiles of the $L_\mathrm{IR}$ and $L_8$ are dissimilar, thus leading to a significant deficit of mid-IR ($L_8$) emission in the nucleus. We hypothesize that this is due to the destruction of PAH molecules by the intense ionizing radiation field or decreased emission in the photodissociation region, as seen in nearby star-forming regions and consistent with the galaxy-wide properties of distant starbursts. This study reveals spatial variations in the $L_8$ to $L_\mathrm{IR}$ ratio for the first time at $z>1$, in agreement with expectations from theory. Our analysis underscores the pivotal role of joint high-resolution observations with JWST and ALMA in discerning the different phases of the interstellar medium (ISM) and revealing internal physics in galaxy substructures.

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arXiv2025

Unveiling Galaxy Structures: Systematic Analysis of Bulge+Disk Decomposition Using Simulated JWST/NIRCam Observations

Characterizing and accurately decomposing galaxies into structural components, such as bulges and disks, is essential for understanding galaxy formation and evolution, particularly at high redshift, where galaxies are compact and faint. Leveraging the unparalleled resolution and sensitivity of JWST and imaging data from CEERs program, we simulate galaxies with bulge+disk components and assess the effectiveness of single and double Sérsic model fittings, respectively. We first evaluate the performance of single Sérsic fits, and find it can recover total magnitudes (i.e., within 0.5 mag), and size (i.e., within 0.2 dex), down to 27 mag. The features that emerged in the residual map can properly reflect the underlying two-component structures. We also show that Sérsic indices can serve as proxies for the bulge-to-total flux ratio (B/T). For double Sérsic models, we find comparable accuracy in recovering bulge and disk magnitudes (i.e., within 0.5 mag), and effective radius (i.e., within 0.2 dex), down to 26 mag. To quantitatively determine whether a double Sérsic model better describes our two-component systems compared to a single Sérsic profile, we evaluate the Bayesian Information Criterion for both model configurations. To extend the applicability of our results to other NIRCam programs, we evaluate the signal-to-noise ratio (SNR) of the simulated galaxies and find that model parameters are reliably reproduced when the SNR exceeds 10. Our work demonstrates the detailed morphological measurement uncertainties using single and double Sérsic models, which provides an essential reference for future JWST/NIRCam-based morphological studies, especially for high-redshift galaxies.

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arXiv2025

Near-IR clumps and their properties in high-z galaxies with JWST/NIRCam

Resolved stellar morphology of $z>1$ galaxies was inaccessible before JWST. This limitation, due to the impact of dust on rest-frame UV light, had withheld major observational conclusions required to understand the importance of clumps in galaxy evolution. Essentially independent of this issue, we use the rest-frame near-IR for a stellar-mass dependent clump detection method and determine reliable estimations of selection effects. We exploit publicly available JWST/NIRCam and HST/ACS imaging data from CEERS, to create a stellar-mass based picture of clumps in a mass-complete sample of 418 galaxies within a wide wavelength coverage of $0.5-4.6\,μ$m and a redshift window of $1 < z < 2$. We find that a near-IR detection gives access to a larger, and possibly different, set of clumps within galaxies, with those also detected in UV making up only $28\%$. Whereas, $85\%$ of the UV clumps are found to have a near-IR counterpart. These near-IR clumps closely follow the UVJ classification of their respective host galaxies, with these hosts mainly populating the star-forming regime besides a fraction of them ($16\%$) that can be considered quiescent. The mass of the detected clumps are found to be within the range of $10^{7.5-9.5}\,\rm M_{\odot}$, therefore expected to drive gas into galaxy cores through tidal torques. The clump stellar mass function is found to have a slope of $-1.50 \pm 0.14$, indicating a hierarchical nature similar to that of star-forming regions in the local Universe. Finally, we observe a radial gradient of increasing clump mass towards the centre of galaxies.

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arXiv2025

A multi-wavelength investigation of spiral structures in $z > 1$ galaxies with JWST

Recent JWST observations have revealed the prevalence of spiral structures at $z > 1$. Unlike in the local Universe, the origin and the consequence of spirals at this epoch remain unexplored. We use public JWST/NIRCam data from the COSMOS-Web survey to map spiral structures in eight massive ($> 10^{10.5}\,\rm M_{\odot}$) star-forming galaxies at $z_{\rm spec} \sim 1.5$. We present a method for systematically quantifying spiral arms at $z>1$, enabling direct measurements of flux distributions. Using rest-frame near-IR images, we construct morphological models accurately tracing spiral arms. We detect offsets ($\sim 0.2 - 0.8\,\rm kpc$) between the rest-frame optical and near-IR flux distributions across most arms. Drawing parallels to the local Universe, we conclude that these offsets reflect the presence of density waves. For nine out of eighteen arms, the offsets indicate spiral shocks triggered by density waves. Five arms have offsets in the opposite direction and are likely associated with tidal interactions. For the remaining cases with no detected offsets, we suggest that stochastic 'clumpy' star formation is the primary driver of their formation. In conclusion, we find a multi-faceted nature of spiral arms at $z > 1$, similar to that in the local Universe.

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arXiv2024

Color profiles of disk galaxies at $z=1$-$3$ observed with JWST: Implications for outer-disk formation histories

We investigate the deconvolved color profiles of 223 disk galaxies at redshifts of $z=1$-3 observed by the James Webb Space Telescope (JWST) as part of the Cosmic Evolution Early Release Science survey (CEERS). The filters were selected to approximate the rest-frame $B-Y$ color, which is used to identify U-shaped color profiles -- those becoming progressively bluer with increasing radius, then turning redder beyond a specific point. We find that 36% of Type II (down-bending) disks exhibit U-shaped color profiles with a minimum at or near the disk break. In contrast, no Type I (single-exponential) disks and only 9% of Type III (up-bending) disks show such a profile. The presence of U-shaped color profiles in Type II disks likely arises from the interplay between a star-formation threshold and spiral- or bar-driven secular radial migration of older stars outward. The fraction of Type II disks exhibiting a U-shaped color profile remains almost consistent across two redshift bins, $z=1$-$2$ and $z=2$-$3$, but is significantly lower than that observed in the local Universe, likely because the secular process of radial migration at high redshift may not have had sufficient time to significantly influence the disk structure. The absence of U-shaped color profiles in Type II disks could point to rapid rather than secular radial star migration potentially caused by violent clump instabilities, transporting both younger and older stars to the outer disk. Our results provide useful constraints on the formation and evolution models of disk galaxies in the early Universe.

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arXiv2024

In-Situ Spheroid Formation in Distant Submillimeter-Bright Galaxies

The majority of stars in today's Universe reside within spheroids, which are bulges of spiral galaxies and elliptical galaxies. Their formation is still an unsolved problem. Infrared/submm-bright galaxies at high redshifts have long been suspected to be related to spheroids formation. Proving this connection has been hampered so far by heavy dust obscuration when focusing on their stellar emission or by methodologies and limited signal-to-noise ratios when looking at submm wavelengths. Here we show that spheroids are directly generated by star formation within the cores of highly luminous starburst galaxies in the distant Universe. This follows from the ALMA submillimeter surface brightness profiles which deviate significantly from those of exponential disks, and from the skewed-high axis-ratio distribution. The majority of these galaxies are fully triaxial rather than flat disks: the ratio of the shortest to the longest of their three axes is half, on average, and increases with spatial compactness. These observations, supported by simulations, reveal a cosmologically relevant pathway for in-situ spheroid formation through starbursts likely preferentially triggered by interactions (and mergers) acting on galaxies fed by non-co-planar gas accretion streams.

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arXiv2024

Crimson Behemoth: a Massive Clumpy Structure Hosting a Dusty AGN at $z=4.91$

The current paradigm for the co-evolution of galaxies and their supermassive black holes postulates that dust-obscured active galactic nuclei (AGNs) represent a transitional phase towards a more luminous and unobscured state. However, our understanding of dusty AGNs and their host galaxies at early cosmic times is inadequate due to observational limitations. Here, we present JWST observations of CID-931, an X-ray-detected AGN at a spectroscopic redshift of $z_{\rm spec}=4.91$. Multiband NIRCam imaging from the COSMOS-Web program reveals an unresolved red core, similar to JWST-discovered dusty AGNs. Strikingly, the red core is surrounded by at least eight massive star-forming clumps spread over $1.\!\!^{\prime\prime}6 \approx 10~{\rm kpc}$, each of which has a stellar mass of $10^9-10^{10}M_\odot$ and $\sim0.1-1~{\rm kpc}$ in radius. The whole system amounts to $10^{11}M_\odot$ in stellar mass, higher than typical star-forming galaxies at the same epoch. In this system, gas inflows and/or complex merger events may trigger clump formation and AGN activity thus leading to the rapid formation of a massive galaxy hosting a supermassive black hole. Future follow-up observations will provide new insights into the evolution of the galaxy-black hole relationship during such transitional phases in the early universe.

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arXiv2024

SCUBADive I: JWST+ALMA Analysis of 289 sub-millimeter galaxies in COSMOS-Web

JWST has enabled detecting and spatially resolving the heavily dust-attenuated stellar populations of sub-millimeter galaxies, revealing detail that was previously inaccessible. In this work we construct a sample of 289 sub-millimeter galaxies with detailed joint ALMA and JWST constraints in the COSMOS field. Sources are originally selected using the SCUBA-2 instrument and have archival ALMA observations from various programs. Their JWST NIRCam imaging is from COSMOS-Web and PRIMER. We extract multi-wavelength photometry in a manner that leverages the unprecedented near-infrared spatial resolution of JWST, and fit the data with spectral energy distribution models to derive photometric redshifts, stellar masses, star-formation rates and optical attenuation. The sample has an average z=2.6, A_V=2.5, SFR=270 and log(M*)=11.1. There are 81 (30%) galaxies that have no previous optical/near-infrared detections, including 75% of the z>4 sub-sample (n=28). The faintest observed near-infrared sources have the highest redshifts and largest A_V=4. In a preliminary morphology analysis we find that ~10% of our sample exhibit spiral arms and 5% host stellar bars, with one candidate bar found at z>3. Finally, we find that the clustering of JWST galaxies within 10 arcseconds of a sub-mm galaxy is a factor of 2 greater than what is expected based on either random clustering or the distribution of sources around any red galaxy irrespective of a sub-mm detection.

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arXiv2024

JWST/CEERS sheds light on dusty star-forming galaxies: forming bulges, lopsidedness and outside-in quenching at cosmic noon

We investigate the morphology and resolved physical properties of a sample of 22 IR-selected DSFG at cosmic noon using the JWST/NIRCam images obtained in the EGS field for the CEERS survey. The resolution of the NIRCam images allowed to spatially resolve these galaxies up to 4.4um and identify their bulge even when extinguished by dust. The goal of this study is to obtain a better understanding of the formation and evolution of FIR-bright galaxies by spatially resolving their properties using JWST in order to look through the dust and bridge the gap between the compact FIR sources and the larger optical SFG. Based on RGB images from the NIRCam filters, we divided each galaxy into several uniformly colored regions, fitted their respective SEDs, and measured physical properties. After classifying each region as SF or quiescent, we assigned galaxies to three classes, depending on whether active SF is located in the core, in the disk or in both. We find (i) that galaxies at a higher z tend to have a fragmented disk with a low core mass fraction. They are at an early stage of bulge formation. When moving toward a lower z, the core mass fraction increases, and the bulge growth is associated with a stabilization of the disk: the NIRCam data clearly point toward bulge formation in preexisting disks. (ii) Lopsidedness is a common feature of DSFGs. It could have a major impact on their evolution; (iii) 23% of galaxies have a SF core embedded in a quiescent disk. They seem to be undergoing outside-in quenching, often facilitated by their strong lopsidedness inducing instabilities. (iv) We show that half of our galaxies with SF concentrated in their core are good SMG counterpart candidates, demonstrating that compact SMGs are usually surrounded by a larger, less obscured disk. (v) Finally, we found surprising evidence for clump-like substructures being quiescent or residing in quiescent regions.

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arXiv2024

JWST and ALMA discern the assembly of structural and obscured components in a high-redshift starburst galaxy

We present observations and analysis of the starburst, PACS-819, at z=1.45 ($M_*=10^{10.7}$ M$_{ \odot}$), using high-resolution ($0^{\prime \prime}.1$; 0.8 kpc) ALMA and multi-wavelength JWST images from the COSMOS-Web program. Dissimilar to HST/ACS images in the rest-frame UV, the redder NIRCam and MIRI images reveal a smooth central mass concentration and spiral-like features, atypical for such an intense starburst. Through dynamical modeling of the CO J=5--4 emission with ALMA, PACS-819 is rotation-dominated thus has a disk-like nature. However, kinematic anomalies in CO and asymmetric features in the bluer JWST bands (e.g., F150W) support a more disturbed nature likely due to interactions. The JWST imaging further enables us to map the distribution of stellar mass and dust attenuation, thus clarifying the relationships between different structural components, not discernable in the previous HST images. The CO J = 5 -- 4 and FIR dust continuum emission are co-spatial with a heavily-obscured starbursting core (<1 kpc) which is partially surrounded by much less obscured star-forming structures including a prominent arc, possibly a tidally-distorted dwarf galaxy, and a clump, either a sign of an ongoing violent disk instability or a recently accreted low-mass satellite. With spatially-resolved maps, we find a high molecular gas fraction in the central area reaching $\sim3$ ($M_{\text{gas}}$/$M_*$) and short depletion times ($M_{\text{gas}}/SFR\sim$ 120 Myrs) across the entire system. These observations provide insights into the complex nature of starbursts in the distant universe and underscore the wealth of complementary information from high-resolution observations with both ALMA and JWST.

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arXiv2023

Fitting pseudo-S${\rm \acute{e}}$rsic(Spergel) light profiles to galaxies in interferometric data: the excellence of the $uv$-plane

Modern (sub)millimeter interferometers, such as ALMA and NOEMA, offer high angular resolution and unprecedented sensitivity. This provides the possibility to characterize the morphology of the gas and dust in distant galaxies. To assess the capabilities of current softwares in recovering morphologies and surface brightness profiles in interferometric observations, we test the performance of the Spergel model for fitting in the $uv$-plane, which has been recently implemented in the IRAM software GILDAS (uv$\_$fit). Spergel profiles provide an alternative to the Sersic profile, with the advantage of having an analytical Fourier transform, making them ideal to model visibilities in the $uv$-plane. We provide an approximate conversion between Spergel index and Sersic index, which depends on the ratio of the galaxy size to the angular resolution of the data. We show through extensive simulations that Spergel modeling in the $uv$-plane is a more reliable method for parameter estimation than modeling in the image-plane, as it returns parameters that are less affected by systematic biases and results in a higher effective signal-to-noise ratio (S/N). The better performance in the $uv$-plane is likely driven by the difficulty of accounting for correlated signal in interferometric images. Even in the $uv$-plane, the integrated source flux needs to be at least 50 times larger than the noise per beam to enable a reasonably good measurement of a Spergel index. We characterise the performance of Spergel model fitting in detail by showing that parameters biases are generally low (< 10%) and that uncertainties returned by uv$\_$fit are reliable within a factor of two. Finally, we showcase the power of Spergel fitting by re-examining two claims of extended halos around galaxies from the literature, showing that galaxies and halos can be successfully fitted simultaneously with a single Spergel model.

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