arXiv subjects

Jaime E. Pineda

Publications and source records attributed to Jaime E. Pineda.

At least 19 recordsLinked to original sources

arXiv2026

ACES VIII: A Survey of Compact, High-Velocity Features Observed in CS(2-1)

The extreme kinematics of the Milky Way's Central Molecular Zone (CMZ) are influenced by processes such as dynamical shearing, cloud collisions, and stellar feedback. These events are visible in molecular data as vertically spiked features in position-velocity (PV) diagrams referred to as high velocity dispersion compact clouds (HVCCs). Using ALMA CMZ Exploration Survey (ACES) CS (2-1) molecular data, we identify a total of 235 HVCC candidates, 163 of which are visually identified, and an additional 72 identified via automated dendrogram methods. For each HVCC we catalog and report the physical and kinematic properties, explore line ratios of the cold dense gas tracer \HNCO with C-shock tracers, classify the morphology of their PV diagrams, and view their position-position-velocity distribution. The sample includes structures which are compact (d<5 pc) and have large velocity extents (20 km/s $<Δ\mathrm{V} <$ 140 km/s), with most structures showing thin, `spiked' PV morphologies. We highlight areas of high ratios between HNCO and C-shock tracers along the edge of known orbital streams, implying a buildup of bar lane gas accreting onto the CMZ. We also find a collection of HVCCs overlapping with the 50 km/s cloud and known circumnuclear disk features. This catalog will be used for future investigation of nuclear inflow and determining dominant mechanisms disrupting average CMZ gas flows.

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arXiv2026

ACES VII. Compact Continuum Source Catalog of the Central Molecular Zone

The Central Molecular Zone (CMZ) resides in the inner few hundred parsecs of our Galaxy, and despite being the largest reservoir of dense molecular gas in the Milky Way, it has a relatively low present-day star formation rate (SFR) of $\sim0.08~M_{\odot}~\text{yr}^{-1}$. Continuum and spectral line observations from the Atacama Large Millimeter/submillimeter Array (ALMA) CMZ Exploration Survey (ACES) provide the first full-coverage, high-resolution map of the inner 200 parsecs of the CMZ at 3 mm. In this paper we present the ACES catalog of compact continuum sources, the most complete catalog of potential sites of star formation in the CMZ to date. Using an automated dendrogram-based source extraction procedure in combination with a by-eye morphological classification scheme, we produce a `full' catalog of 1735 detections in total. Additionally, we use spectral index measurements to generate a `filtered' catalog of 567 sources with minimal contamination from non-thermal filaments and extended free-free emission. We find that 359 ($\sim63\%$) of the filtered catalog sources are located at column densities $< 10^{23}$ cm$^{-2}$, outside of the densest molecular cloud regions, 195 of which have not been identified in previous surveys. After cross-referencing with various catalogs generated from data at different wavelengths, we consider it likely that many of these newly discovered detections are produced by pre/protostellar sources or compact HII regions.

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arXiv2026

MIAO-ALMA: Shocks and Protostellar Outflows in 70 $μ$m-dark clumps with $L/M$ $<$ 1 $L_{\odot}$/$M_{\odot}$

To investigate the initial conditions of high-mass star-forming regions, we use SiO (2-1) emission to trace early shock-related kinematics toward sixteen 70 $μ$m-dark and massive clumps with luminosity-to-mass ratios ($L/M$) $< 1\,L_{\odot}/M_{\odot}$, as part of the Multiwavelength Line-Imaging Survey of the 70 $μ$m-dark and bright clouds (MIAO) project. Using ALMA observations at a spatial resolution of $\sim$0.06 pc and a velocity resolution of 0.21 km s$^{-1}$, we identify a total of thirty-seven outflows with a variety of morphologies. Outflow parameters were derived by integrating the HCO$^+$ (1-0) line wings, excluding the quiescent dense core component traced by H$^{13}$CO$^+$ (1-0). We find that outflow masses and velocities show moderate positive correlations with the masses of their driving cores. Owing to the high sensitivity of our observations, which yield longer projected outflow lengths compared to previous studies, the derived outflow dynamical ages span $\sim10^{3}$-$10^{5}$ yr. We detect six narrow-linewidth (0.6-1.4 km s$^{-1}$) and three broad ($>$ 2 km s$^{-1}$) SiO (2-1) features not associated with outflows driven by clearly identified protostars. Lacking coincident 3 mm dust continuum cores, their origins may be young outflows from undetected low-mass protostars, dissipating shocks, cloud-cloud collisions, or projection effects when the outflows lie close to the plane of the sky. The detection of these shocks and outflows in such extremely young environments demonstrates that protostellar activity has already begun.

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arXiv2026

Electron temperature and emission measure of HII regions in the central molecular zone (CMZ) from H40 αrecombination line and continuum emissions by ALMA CMZ Exploration Survey - ACES -

Star formation activity in the Central Molecular Zone (CMZ) directly manifests itself as radio continuum free-free emission (Bremsstrahlung) and radio recombination line emission from HII regions surrounding newly formed massive stars. We derive the overall distribution of the HII regions and their fundamental properties: electron temperature ($\Te$) and emission measure ($EM$), and hence electron density in the form of two dimensional distribution maps over the CMZ by analyzing the ACES (ALMA CMZ Exploration Survey) \h40 (99.02 GHz) recombination line and 99.6 GHz continuum emission data with synthesized beam widths of $2''.45$ (0.097 pc at 8.2 kpc) and $2''.14$, respectively. We apply the 'TeEM' method ($\Te$--$EM$ mapping), which creates $\Te$ and $EM$ maps from input 2D maps of the continuum and integrated line intensity. The analysis covers the entire ACES field from $l\sim -0^\circ.6$ to $+0^\circ.8$ and from $b\sim -0^\circ.2$ to $+0^\circ.1$. The area analyzed is complete and includes previously known HII regions such as Sgr B2, Sgr B1, the Sickle, the Pistol, thermal filaments (Bridges), Sgr A HII regions, the Minispiral, and many other known HII regions. Sgr C is not included in the analysis due to the insufficient signal-to-noise ratio in the recombination line map. The mean electron temperature over the CMZ is determined to be $\Tcmz= 5872 \pm 78 ~{\rm (SE)} ~\pm 3682~{\rm (SD)}$ K (SE:standard error of the mean, SD: pixel-to-pixel standard deviation). Some HII regions, such as Sgr B2 Main and the Minispiral, exhibit large scatter and an internal $\Te$ gradient of several thousand K per parsec. The $EM$ distribution is more diverse, varying by orders of magnitude from $\sim 10^5$ to $\sim 3\times 10^8$ \emunit within the CMZ, as well as within individual HII regions.

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arXiv2026

SKAO-ALMA Synergies in Star Formation Science

We highlight the potential for synergies between the SKA telescopes and ALMA, which will begin to be significant already with SKA Early Science. Broadly within star formation science, we focus on 1) (simultaneous) time domain and variability studies (e.g., of (proto-)stars), which is systematically opening a new observing window that will enable us to better constrain the physics of extreme stellar flares and their interplay with mass accretion in young stars, 2) possibilities for complementary coverage of different transitions of molecules as tracers of the ISM (e.g., H2CO to trace density and temperature), and 3) radio recombination lines to trace ionised gas at different densities. Furthermore, we address synergies in terms of the spatial resolution of both observatories and new capabilities not only on the SKAO side but extending to the ALMA2030 wideband sensitivity upgrade.

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arXiv2026

Preferential alignment of Class 0, Class I protostellar disks in multiple systems across nine nearby molecular clouds

Protostellar disk orientations in multiple systems provide critical insights into the primary mechanisms that govern the formation of multiple-star systems, their subsequent dynamical evolution, and their impact on planet-forming disks. We present a disk alignment study of 512 Class 0, Class I, and flat-spectrum protostars across nine nearby molecular clouds within 500 pc, utilizing data from the CAMPOS and VANDAM surveys. Our sample includes 74 binaries and 31 high-order multiple systems. We find that multiple systems with projected pair separations up to 6000 au exhibit preferential disk alignment with respect to each other across all evolutionary classes, deviating significantly from the random distribution predicted by turbulent fragmentation models. This suggests that the formation of multiple systems cannot be explained by turbulent fragmentation alone. Disk alignment on scales of a few thousand au is also difficult to explain by disk fragmentation as the dominant origin. We further find that the degree of nearest-neighbor disk alignment in higher-order multiples is comparable to that in binaries. Finally, we identify a significant deficit of flat-spectrum protostellar disks in high-order multiple systems as compared to younger Class 0 and Class I phases. The decline is consistent with rapid dynamical evolution, in which most higher-order systems dissolve by the end of the Class I phase.

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arXiv2026

A JWST, ALMA and VLA survey of the Ophiuchus-A star-forming region: Unveiling hidden dust mass and connecting infrared outflows to their radio origins

We present an infrared, millimetre, and radio survey of 20 Class 0-III young stellar objects in the Ophiuchus A L1688 star-forming cluster, combining high-resolution (7-25 au) VLA and JWST observations with archival ALMA data. We implement physically motivated models to derive dust and ionised gas properties, spectral behaviour and their relative contributions through the millimetre-centimetre radio spectral energy distribution. Our models reveal circumstellar dust disks that are, on average, tens to hundreds of times more massive than millimetre-only estimates (subject to uncertainties arising from the choice of dust opacity) and contain millimetre-sized grains even at the Class 0 stage. Owing to the VLA's high resolution we are able to connect outflows to their origins, detecting protostellar jet emission on scales of 10s-1000s au. Our results represent a homogeneous characterisation of the dust and ionised gas properties in Ophiuchus and present a potential solution to the long-standing 'missing disk mass' problem. However, our understanding is still limited by resolution and sensitivity at frequencies <40 GHz. Future facilities like the SKA and ngVLA are needed to provide the necessary capabilities to fully spatially resolve this emission (<0.18") even in one of the closest star-forming regions.

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arXiv2026

Chemical Complexity in the Early Stages of Star Formation in the SKAO Era

About 350 molecules have been identified in the interstellar medium (ISM), including complex molecules relevant to prebiotic chemistry. A remarkable level of molecular diversity has been observed from the earliest stages of star formation, providing the initial chemical inventory inherited by planetary systems. Radio observations have played a pivotal role in these discoveries, starting with the identification of the first polyatomic molecule, $\text{NH}_3$ (Cheung et al. 1968). (Sub-)millimeter observations have revealed complex organic molecules of prebiotic relevance, including formamide ($\text{NH}_2\text{CHO}$), glycolaldehyde ($\text{CH}_2\text{OHCHO}$), and even urea ($(\text{NH}_2)_2\text{CO}$), and hydroxylamine ($\text{NH}_2\text{OH}$), which are possible precursors of RNA nucleotides (Ceccarelli et al. 2023; Jiménez-Serra et al. 2020). However, in dense protostellar regions, dust opacity hampers the detection of molecular emission. Additionally, large molecules and those containing heavy atoms, which have rotational transitions at lower frequencies, often remain inaccessible to current instruments. The Square Kilometre Array Observatory (SKAO) will provide an unprecedented combination of sensitivity and angular resolution at radio wavelengths. This will allow for the detection of prebiotic species and offer new insights into the chemical pathways that shape emerging planetary systems (Jiménez-Serra et al. 2022). This chapter details the scientific questions and advancements that the SKAO, and more specifically, SKA-Mid equipped with the Band 5 receivers, will pursue in the field of astrochemistry, focusing on the chemical complexity in both high-mass and solar-type star-forming regions.

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arXiv2026

Unveiling Complex Chemistry in Planet-forming Disks with the SKAO

The chemical composition of planets is inherited from that of the natal protoplanetary disk at the time of planet formation. In recent years, we have made huge progress in characterizing disk chemistry. (Sub-)millimeter interferometers, such as ALMA, allowed us to detect emission lines from simple to complex organic molecules and to probe their radial and vertical distribution in disks. On the other hand, JWST has started to unveil the composition of disk ices, and line emission from the innermost disk regions. The advent of SKA will open new domains in the field, by observing emission lines from heavier molecules including heavy carbon chains and rings, and prebiotic molecules with peak emission in the cm range. Moreover, SKA will probe molecular emission from regions which are obscured by dust opacity at mm wavelengths, hence from the disk midplane, and often from the inner 30 au region. These observations will constrain the initial conditions for disk evolution and planet formation, allowing us to predict the chemical composition of the forming planets and their atmospheres. Comparison with forthcoming results on exoplanet atmospheres and on the chemistry of pristine bodies in the Solar System will provide new hints on the origin and evolution of planetary systems including our own.

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arXiv2026

ALMA Central molecular zone Exploration Survey (ACES) VI: ALMA Large Program Reveals a Highly Filamentary Central Molecular Zone

The Central Molecular Zone (CMZ) of the Milky Way is the way station that primarily controls how much gas flows from the disk of the Galaxy towards the central nucleus. While this region is well documented to have extreme gas properties that clearly distinguish it from the rest of the Galaxy, the properties of the bulk molecular gas at high angular resolution are relatively unexplored. Band 3 data from the ALMA (Atacama Large Millimeter/Submillimeter Array) large program ACES (ALMA CMZ Exploration Survey) reveal the highly filamentary nature of CMZ molecular gas at high resolution (3" or 0.1pc) across the entire CMZ. Visual inspection of these data suggests that there are at least two general classes of elongated structures, which we identify as: i) large-scale (10 pc) filamentary structures (LFs) and ii) a ubiquitous population of small-scale (about 1 pc) filamentary structures (SFs). We present detailed morphological and kinematic properties towards three structures in each category, as well as their association with magnetic fields and the correlation of HNCO 4(0,4)-3(0,3) with other molecular species. Our investigation reveals that these structures are largely coherent in position-position-velocity space. The alignment with the magnetic field structure is mixed, with some parallel, some perpendicular, and some intermediate alignments. We find that LFs likely trace pieces of contiguous CMZ orbital structures and are a manifestation of global CMZ dynamics. The second class, SFs, are pervasive and may be the result of complicated turbulence and shearing dynamics in the CMZ gas flows, as seen in numerical simulations.

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arXiv2026

Magneto-Gravitational Regulated Streamer Accretion onto a Class 0 Protostellar System

How do magnetic fields shape the way young stars gather gas from their birth clouds? Using high-resolution Atacama Large Millimeter/submillimeter Array observations of a young triple protostellar system HOPS-182, we identify an elongated stream of gas, or accretion streamer, that extends over several thousand astronomical units (1 astronomical unit is the Earth-Sun distance) and carries a substantial flow of material toward the system. The gas speeds along this filament increase toward the star in a way consistent with gravitational free-fall, while the streamer's shape closely follows the magnetic field threading the region. By comparing the strengths of gravity and magnetic tension and measuring how the gas rotates compared with the local magnetic field, we show that the field is strong enough to help confine and guide the infalling gas and efficiently remove angular momentum. These results suggest that a substantial fraction of the material falling onto young protostellar systems can be funneled through elongated, magnetically structured accretion streamers.

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arXiv2026

PRODIGE -- envelope to disk with NOEMA VIII. Sulfur oxides trace a shock caused by a streamer in the inner envelope of a protostar

(Abridged) Recently, streamers have been observed causing shocks at the outer edge of protoplanetary disks. The study of sulfur-bearing species can help us to understand the physical and chemical changes caused by infalling streamers toward their landing positions. We study the physical properties traced by SO$_2$ and SO toward the Class I protostar Per-emb 50, which is possibly related to the streamer infalling toward its disk. We present new NOEMA A-array observations as part of the large program "Protostars and Disks: Global Evolution" (PRODIGE). We analyzed the morphology of SO$_2$ and SO, and complement our interpretations with additional H_$2$CO and CO data from the same program. We compared the SO$_2$ and SO morphology with an infalling-rotating model. We applied Bayesian model selection to the brightest SO$_2$ line to disentangle the different kinematic components traced by this molecule. We used Local Thermodynamic Equilibrium (LTE) and non-LTE analyses to determine the temperature and density of the SO$_2$ emission. There are two separate peaks of SO$_2$ emission offset toward the southwest of Per-emb 50, one brighter (peak 1) at about 180 au from the protostar, and a weaker one (peak 2) at about 400 au. Peak 2 is blueshifted with respect to an infalling-rotating envelope. We propose that this peak is caused by the shock between the inner envelope and the streamer. Peak 1 is consistent with the expected envelope motion, and could thus be caused by shocks at the disk-envelope interface, but potential streamer influence cannot be neglected. Both peaks show abundance ratios consistent with a low velocity shock ($\sim 3-4$ \kms) when compared with shock models. Streamers can affect the physical and chemical structure of both disks and envelopes, suggesting that streamers can play an important role in shaping both structures in the embedded stages of star formation.

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arXiv2026

ALMA Central molecular zone Exploration Survey (ACES) V: CS(2-1), SO(2_3-1_2), CH3CHO(5_1,4-4_1,3), HC3N(11-10), and H40a lines data

We present data from the ALMA Central Molecular Zone Exploration Survey (ACES) Large Program, which provides broad spectral-line and 3 mm continuum coverage of the Central Molecular Zone (CMZ) at a spatial resolution of 0.1 pc. The survey delivers homogeneous, wide-field mosaics that enable direct comparisons of the physical and chemical conditions across diverse environments in the Galactic center. In this data release paper, we present the CS(2-1), SO(2_3-1_2), CH3CHO(5_1,4-4_1,3), HC3N(11-10), and H40a lines observed simultaneously within two broad spectral windows. These lines reveal pronounced spatial and chemical variations across the CMZ, tracing distinct components of molecular gas, shock-affected regions, and ionized structures. The high angular resolution and multi-line capability of the ACES dataset make it a powerful resource for future studies of gas dynamics, star formation activity, and the physical connection between the CMZ and Sgr A*.

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arXiv2026

ALMA Central Molecular Zone Exploration Survey (ACES)-IV. Data of the two intermediate-width spectral windows

We release the intermediate-width spectral window data from the ALMA Central Molecular Zone Exploration Survey (ACES) Large Program, which covers SiO(2-1), SO(2_2-1_1), H13CO+(1-0), H13CN(1-0), HN13C(1-0), and HC15N (1-0), among other molecular line transitions, with an angular resolution of ~2 arcsec and a velocity resolution of 1.7 km s-1 . The full cubes of the two spectral windows as well as the key data products will be available to the community. We also present the integrated brightness, peak brightness, centroid velocity, and Galactic longitude-velocity maps of the six lines. We briefly discuss morphological correlations between the continuum and the molecular line emission, and brightness ratios between pairs of isotopologue or isotopomer lines. We highlight features and trends in the data that will be followed up in upcoming ACES science papers.

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arXiv2026

ALMA Central Molecular Zone Exploration Survey (ACES) II: 3mm continuum images

The ALMA Central Molecular Zone Exploration Survey, ACES, has mapped $\gtrsim1000$ square arcminutes at 3 mm toward the center of our Galaxy. ACES provides the first large-scale, high-resolution ($\sim2.5$") view of the central $\sim200$ parsecs of the Milky Way. In this work, we describe the continuum data processing and present the continuum data products. In the combined mosaic of 45 individual ALMA mosaics, the typical RMS noise achieved is $\sim0.1$ mJy per $\sim2.5$" beam, though there is a tail of substantially higher noise toward regions with bright continuum structure, especially around Sgr A* and Sgr B2. In-band spectral indices are measurable for a small fraction of the brightest and most compact sources, enabling distinction between dust-dominated and free-free- or synchrotron-dominated sources. To recover emission on large angular scales, we present the GBT MUSTANG-2 Three millimeter Extended Nucleus Survey (TENS), a new 10"resolution survey of the CMZ, which we combine with the ACES image by feathering. To demonstrate the quality and reliability of the ACES data, we compare to previously-published ALMA data obtained with higher resolution and sensitivity, finding overall good agreement with past results, but some disagreement toward the brightest sources.

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arXiv2026

ALMA Central molecular zone Exploration Survey (ACES) III: Molecular line data reduction and HNCO and HCO$^{+}$ data

The ALMA Central molecular zone Exploration Survey (ACES) large program has observed the inner ~ 200 pc of the Milky Way at 3 mm (Band 3) using ALMA's 12m, 7m, and Total Power arrays. With an angular resolution of ~ 2", ACES provides a contiguous, multi-scale view of the Central Molecular Zone (CMZ) via the dust continuum and a suite of molecular lines. We present an overview of the molecular line data processing for ACES and describe the first data release. We showcase the HNCO (4-3) and HCO$^{+}$ (1-0) data, which were targeted at high spectral resolution (0.2 km s$^{-1}$) to trace the kinematics of the molecular gas in the CMZ. The HNCO and HCO$^{+}$ maps are compared with previous single-dish CMZ surveys and discrete ALMA observations of CMZ clouds to demonstrate the quality of the data. We highlight the ubiquity of parsec-scale, linear absorption features traced by HCO$^{+}$. Their origin is unknown, and ACES provides the first opportunity to study these enigmatic features throughout the CMZ. We release the HNCO and HCO$^{+}$ cubes for all 45 ACES fields, along with the full cube mosaics which combine all fields into a contiguous mosaic of the CMZ. We additionally provide advanced products of these full mosaics, including integrated and peak intensity, noise, and position-velocity maps. These products provide substantial legacy value for the community, offering an unparalleled view of the physical and kinematic structure of the dense gas in the CMZ.

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arXiv2026

ALMA Central Molecular Zone Exploration Survey (ACES) I: Overview

The mass flows and energy cycles within the inner regions of galaxies exert a powerful influence on the evolution of the galaxy population. The centre of the Milky Way is the only galactic nucleus for which it is possible to resolve the physical mechanisms that drive these cycles, namely star formation and feedback, while also tracing global (>100 pc) processes which determine where and when star formation and feedback occur. We present an overview of ACES, the 'Atacama Large Millimeter/submillimeter Array (ALMA) CMZ Exploration Survey', a ~1.5" angular resolution, 0.2-3 km/s spectral resolution ALMA Band 3 (85-102 GHz), survey of the 'Central Molecular Zone' (CMZ) -- the inner-100 pc of the Galaxy (l = 359.4 deg to 0.8 deg). ACES spectral setup is tuned to observe optimal tracers of the physical, chemical, and kinematic conditions in over 70 spectral features (e.g. HCO+, HNCO, SiO, H40alpha, complex molecules) of the gas in the CMZ, to derive the properties of all potentially star-forming Galactic Centre gas, from global scales (100 pc) to dense ~0.05 pc structures that are expected to host individual star-forming cores, down to sub-sonic (<0.4 km/s) velocity resolution. In this overview paper, we provide the scientific justification for the ACES survey, explain the choice of observational setup, and describe the data legacy products. Finally, we show some of the initial ACES data which highlight the power of ACES' combination of high angular resolution, unprecedented spatial dynamic range, sensitivity, spectral resolution and spectral bandwidth as an illustration of how ACES aims to understand how global processes set the location, intensity, and timescales for star formation and feedback in the CMZ.

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arXiv2026

Deuterium fractionation and CO depletion in Barnard 5

Deuterium fractionation provides a key diagnostic of the physical and chemical evolution of prestellar and protostellar cores, where it is strongly linked to CO depletion in cold, dense gas. We present the first spatially resolved maps of deuterium fraction and CO depletion in the Barnard 5 (B5) region of the Perseus molecular cloud, covering both a starless core and the protostellar core hosting the Class 0/I source IRAS 03445+3242. Using IRAM 30~m observations of N$_2$H$^+$(1--0), N$_2$D$^+$(1--0), H$^{13}$CO$^+$(1--0), and DCO$^+$(2--1), complemented by C$^{18}$O(2--1) data, we derive column density, deuterium fraction, and CO depletion maps. We find that the deuterium fraction in both mentioned nitrogen- and carbon-bearing species increases from the protostellar to the starless core, reaching $R_D^{\rm N_2H^+}=0.43\pm0.10$ and $R_D^{\rm HCO^+}=0.09\pm0.02$ in the starless core, compared with $0.15\pm0.03$ and $0.05\pm0.01$, respectively, in the protostellar core. The CO depletion factor also rises from $4.1\pm0.1$ to $5.0\pm0.1$ across the same transition. While the embedded YSO reduces deuteration in the dense inner gas, the less dense envelope traced by HCO$^+$ is only slightly affected at our resolution. Our analysis confirms that CO freeze-out and the presence of a protostar jointly regulate deuterium chemistry in star-forming regions.

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