arXiv subjects

Adam Ginsburg

Publications and source records attributed to Adam Ginsburg.

At least 73 records · Page 4Linked to original sources

arXiv2024

A broad linewidth, compact, millimeter-bright molecular emission line source near the Galactic Center

A compact source, G0.02467-0.0727, was detected in ALMA \threemm observations in continuum and very broad line emission. The continuum emission has a spectral index $α\approx3.3$, suggesting that the emission is from dust. The line emission is detected in several transitions of CS, SO, and SO$_2$ and exhibits a line width FWHM $\approx160$ \kms. The line profile appears Gaussian. The emission is weakly spatially resolved, coming from an area on the sky $\lesssim1"$ in diameter ($\lesssim10^4$ AU at the distance of the Galactic Center; GC). The centroid velocity is $v_{LSR}\approx40$-$50$ \kms, which is consistent with a location in the Galactic Center. With multiple SO lines detected, and assuming local thermodynamic equilibrium (LTE) conditions, $T_\mathrm{LTE} = 13$ K, which is colder than seen in typical GC clouds, though we cannot rule out low-density, subthermally excited, warmer gas. Despite the high velocity dispersion, no emission is observed from SiO, suggesting that there are no strong ($\gtrsim10~\mathrm{km~s}^{-1}$) shocks in the molecular gas. There are no detections at other wavelengths, including X-ray, infrared, and radio. We consider several explanations for the Millimeter Ultra-Broad Line Object (MUBLO), including protostellar outflow, explosive outflow, collapsing cloud, evolved star, stellar merger, high-velocity compact cloud, intermediate mass black hole, and background galaxy. Most of these conceptual models are either inconsistent with the data or do not fully explain it. The MUBLO is, at present, an observationally unique object.

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arXiv2024

Death of the Immortal Molecular Cloud: Resolution Dependence of the Gas-Star Formation Relation Rules out Decoupling by Stellar Drift

Recent observations have demonstrated that giant molecular clouds (GMCs) are short-lived entities, surviving for the order of a dynamical time before turning a few percent of their mass into stars and dispersing, leaving behind an isolated young stellar population. The key question has been whether this GMC dispersal actually marks a point of GMC destruction by stellar feedback from the new-born stars, or if GMCs might be `immortal' and only dynamically decouple from their nascent stars due to stellar drift. We address this question in six nearby galaxies, by quantifying how the gas-star formation relation depends on the spatial scale for scales between the GMC diameter and the GMC separation length, i.e. the scales where an excess of GMCs would be expected to be found in the stellar drift scenario. Our analysis reveals a consistent dearth of GMCs near young stellar populations regardless of the spatial scale, discounting the notion of `immortal' GMCs that decouple from their nascent stars through stellar drift. Instead, our findings demonstrate that stellar feedback destroys most GMCs at the end of their lifecycle. Employing a variety of statistical techniques to test both hypotheses, we find that the probability that stellar feedback concludes the GMC lifecycle is about 2,000 times higher than the probability that stellar drift separates GMCs and young stellar regions. This observation strengthens the emerging picture that galaxies consist of dynamic building blocks undergoing vigorous, feedback-driven lifecycles that collectively regulate star formation and drive the baryon cycle within galaxies.

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arXiv2024

Massive clumps in W43-main: Structure formation in an extensively shocked molecular cloud

W43-main is a massive molecular complex located at the interaction of the Scutum arm and the Galactic bar undergoing starburst activities. We aim to investigate the gas dynamics, in particular, the prevailing shock signatures from the cloud to clump scale and assess the impact of shocks on the formation of dense gas and early-stage cores. We have carried out NOEMA and IRAM-30m observations at 3 mm with an angular resolution of $\sim$0.1 pc towards five massive clumps in W43 main. We use CH$_{3}$CCH and H$_{2}$CS lines to trace the extended gas temperature and CH$_{3}$OH lines to probe the volume density of the dense gas ($\gtrsim$10$^{5}$ cm$^{-3}$). The emission of SiO (2-1) is extensive across the region ($\sim$4 pc) and is mostly contained within a low-velocity regime, hinting at a large-scale origin of the shocks. The position-velocity maps of multiple tracers show systematic spatio-kinematic offsets supporting the cloud-cloud collision/merging scenario. We identify an additional extended velocity component in CCH emission, which coincides with one of the velocity components of the larger scale $^{13}$CO (2-1) emission, likely representing an outer, less dense gas layer in the cloud merging process. We find that the V-shaped, asymmetric SiO wings are tightly correlated with localised gas density enhancements, which is direct evidence of dense gas formation and accumulation in shocks. We resolve two categories of NH$_{2}$D cores: ones exhibiting only subsonic to transonic velocity dispersion, and the others with an additional supersonic velocity dispersion. The centroid velocities of the latter cores are correlated with the shock front seen by SiO. The kinematics of the $\sim$0.1 pc NH$_{2}$D cores are heavily imprinted by shock activities, and may represent a population of early-stage cores forming around the shock interface.

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arXiv2024

An updated modular set of synthetic spectral energy distributions for young stellar objects

Measured properties of young stellar objects (YSOs) are key tools for research into pre-main-sequence stellar evolution. YSO properties are commonly measured by comparing observed radiation to existing grids of template YSO spectral energy distributions (SEDs) calculated by radiative transfer. These grids are often sampled and constructed using simple models of mass assembly/accretion over time. However, because we do not yet have a complete theory of star formation, the choice of model sets the tracked parameters and range of allowed values. By construction, then, the assumed model limits the measurements that can be made using the grid. Radiative transfer models not constrained by specific accretion histories would enable assessment of a wider range of theories. We present an updated version of the Robitaille (2017) set of YSO SEDs, a collection of models with no assumed evolutionary theory. We outline our newly calculated properties: envelope mass, weighted-average dust temperature, disk stability, and circumstellar $A_{\rm V}$. We also convolve the SEDs with new filters, including JWST, and provide users the ability to perform additional convolutions. We find a correlation between the average temperature and millimeter-wavelength brightness of optically thin dust in our models and discuss its ramifications for mass measurements of pre- and protostellar cores. We also compare the positions of YSOs of different observational classes and evolutionary stages in IR color space and use our models to quantify the extent to which class and stage may be confused due to observational effects. Our updated models are released to the public.

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arXiv2024

Thermal Properties of the Hot Core Population in Sagittarius B2 Deep South

We report the discovery of 9 new hot molecular cores in the Deep South (DS) region of Sagittarius B2 using Atacama Large Millimeter/submillimeter Array Band 6 observations. We measure the rotational temperature of CH$_3$OH and derive the physical conditions present within these cores and the hot core Sgr B2(S). The cores show heterogeneous temperature structure, with peak temperatures between 252 and 662 K. We find that the cores span a range of masses (203-4842 M$_\odot$) and radii (3587-9436 AU). CH$_3$OH abundances consistently increase with temperature across the sample. Our measurements show the DS hot cores are structurally similar to Galactic Disk hot cores, with radii and temperature gradients that are comparable to sources in the Disk. They also show shallower density gradients than Disk hot cores, which may arise from the Central Molecular Zone's higher density threshold for star formation. The hot cores have properties which are consistent with those of Sgr B2(N), with 3 associated with Class II CH$_3$OH masers and one associated with an UCHII region. Our sample nearly doubles the high-mass star forming gas mass near Sgr B2(S) and suggest the region may be a younger, comparably massive counterpart to Sgr B2(N) and (M). The relationship between peak CH$_3$OH abundance and rotational temperature traced by our sample and a selection of comparable hot cores is qualitatively consistent with predictions from chemical modeling. However, we observe constant peak abundances at higher temperatures ($T \gtrsim 250$ K), which may indicate mechanisms for methanol survival that are not yet accounted for in models.

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arXiv2023

Far-Infrared Luminosity Bursts Trace Mass Accretion onto Protostars

Evidence abounds that young stellar objects undergo luminous bursts of intense accretion that are short compared to the time it takes to form a star. It remains unclear how much these events contribute to the main-sequence masses of the stars. We demonstrate the power of time-series far-infrared (far-IR) photometry to answer this question compared to similar observations at shorter and longer wavelengths. We start with model spectral energy distributions that have been fit to 86 Class 0 protostars in the Orion molecular clouds. The protostars sample a broad range of envelope densities, cavity geometries, and viewing angles. We then increase the luminosity of each model by factors of 10, 50, and 100 and assess how these luminosity increases manifest in the form of flux increases over wavelength ranges of interest. We find that the fractional change in the far-IR luminosity during a burst more closely traces the change in the accretion rate than photometric diagnostics at mid-infrared and submillimeter wavelengths. We also show that observations at far-IR and longer wavelengths reliably track accretion changes without confusion from large, variable circumstellar and interstellar extinction that plague studies at shorter wavelengths. We close by discussing the ability of a proposed far-IR surveyor for the 2030s to enable improvements in our understanding of the role of accretion bursts in mass assembly.

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arXiv2023

JWST Reveals Star Formation Across a Spiral Arm in M33

Young stellar objects (YSOs) are the gold standard for tracing star formation in galaxies but have been unobservable beyond the Milky Way and Magellanic Clouds. But that all changed when the James Webb Space Telescope was launched, which we use to identify YSOs in the Local Group galaxy M33, marking the first time that individual YSOs have been identified at these large distances. We present MIRI imaging mosaics at 5.6 and 21 microns that cover a significant portion of one of M33's spiral arms that has existing panchromatic imaging from the Hubble Space Telescope and deep ALMA CO measurements. Using these MIRI and Hubble Space Telescope images, we identify point sources using the new DOLPHOT MIRI module. We identify 793 candidate YSOs from cuts based on colour, proximity to giant molecular clouds (GMCs), and visual inspection. Similar to Milky Way GMCs, we find that higher mass GMCs contain more YSOs and YSO emission, which further shows YSOs identify star formation better than most tracers that cannot capture this relationship at cloud scales. We find evidence of enhanced star formation efficiency in the southern spiral arm by comparing the YSOs to the molecular gas mass.

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arXiv2023

CMZoom IV. Incipient High-Mass Star Formation Throughout the Central Molecular Zone

In this work, we constrain the star-forming properties of all possible sites of incipient high-mass star formation in the Milky Way's Galactic Center. We identify dense structures using the CMZoom 1.3mm dust continuum catalog of objects with typical radii of $\sim$0.1pc, and measure their association with tracers of high-mass star formation. We incorporate compact emission at 8, 21, 24, 25, and 70um from MSX, Spitzer, Herschel, and SOFIA, catalogued young stellar objects, and water and methanol masers to characterize each source. We find an incipient star formation rate (SFR) for the CMZ of ~0.08 Msun yr^{-1} over the next few 10^5 yr. We calculate upper and lower limits on the CMZ's incipient SFR of ~0.45 Msun yr^{-1} and ~0.05 Msun yr^{-1} respectively, spanning between roughly equal to and several times greater than other estimates of CMZ's recent SFR. Despite substantial uncertainties, our results suggest the incipient SFR in the CMZ may be higher than previously estimated. We find that the prevalence of star formation tracers does not correlate with source volume density, but instead ~75% of high-mass star formation is found in regions above a column density ratio (N_{SMA}/N_{Herschel}) of ~1.5. Finally, we highlight the detection of ``atoll sources'', a reoccurring morphology of cold dust encircling evolved infrared sources, possibly representing HII regions in the process of destroying their envelopes.

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arXiv2023

JWST reveals widespread CO ice and gas absorption in the Galactic Center cloud G0.253+0.016

We report JWST NIRCam observations of G0.253+0.016, the molecular cloud in the Central Molecular Zone known as The Brick, with the F182M, F187N, F212N, F410M, F405N, and F466N filters. We catalog 56,146 stars detected in all 6 filters using the crowdsource package. Stars within and behind The Brick exhibit prodigious absorption in the F466N filter that is produced by a combination of CO ice and gas. In support of this conclusion, and as a general resource, we present models of CO gas and ice and CO$_2$ ice in the F466N, F470N, and F410M filters. Both CO gas and ice may contribute to the observed stellar colors. We show, however, that CO gas does not absorb the Pf$β$ and Hu$ε$ lines in F466N, but that these lines show excess absorption, indicating that CO ice is also present and contributes to observed F466N absorption. The most strongly absorbed stars in F466N are extincted by $\sim$ 2 magnitudes, corresponding to $>$ 80\% flux loss. This high observed absorption requires very high column densities of CO, requiring total CO column that is in tension with standard CO abundance and/or gas-to-dust ratios. There is therefore likely to be a greater CO/H$_2$ ratio (X$_{CO} > 10^{-4}$) and more dust per H$_2$ molecule ($>0.01$) in the Galactic Center than the Galactic disk. Ice and/or gas absorption is observed even in the cloud outskirts, implying that additional caution is needed when interpreting stellar photometry in filters that overlap with ice bands throughout our Galactic Center. The widespread CO absorption in our Galactic Center hints that significant ice absorption is likely present in other galactic centers.

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arXiv2023

Digging into the Interior of Hot Cores with ALMA: Spiral Accretion into the High-mass Protostellar Core G336.01-0.82

We observed the high-mass star-forming core G336.01-0.82 at 1.3 mm and 0.05'' (~150 au) angular resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the Digging into the Interior of Hot Cores with ALMA (DIHCA) survey. These high-resolution observations reveal two spiral streamers feeding a circumstellar disk at opposite sides in great detail. Molecular line emission from CH$_3$OH shows velocity gradients along the streamers consistent with infall. Similarly, a flattened envelope model with rotation and infall implies a mass larger than 10 M$_\odot$ for the central source and a centrifugal barrier of 300 au. The location of the centrifugal barrier is consistent with local peaks in the continuum emission. We argue that gas brought by the spiral streamers is accumulating at the centrifugal barrier, which can result in future accretion burst events. A total high infall rate of ~$4\times10^{-4}$ M$_\odot$ yr$^{-1}$ is derived by matching models to the observed velocity gradient along the streamers. Their contribution account for 20-50% the global infall rate of the core, indicating streamers play an important role in the formation of high-mass stars.

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arXiv2023

A probable Keplerian disk feeding an optically revealed massive young star

The canonical picture of star formation involves disk-mediated accretion, with Keplerian accretion disks and associated bipolar jets primarily observed in nearby, low-mass young stellar objects (YSOs). Recently, rotating gaseous structures and Keplerian disks have been detected around a number of massive (M > 8 solar masses) YSOs (MYSOs) including several disk-jet systems. All of the known MYSO systems are located in the Milky Way, and all are embedded in their natal material. Here we report the detection of a rotating gaseous structure around an extragalactic MYSO in the Large Magellanic Cloud. The gas motions show radial flow of material falling from larger scales onto a central disk-like structure, the latter exhibiting signs of Keplerian rotation, i.e., a rotating toroid feeding an accretion disk and thus the growth of the central star. The system is in almost all aspects comparable to Milky Way high-mass young stellar objects accreting gas via a Keplerian disk. The key difference between this source and its Galactic counterparts is that it is optically revealed, rather than being deeply embedded in its natal material as is expected of such a young massive star. We suggest that this is the consequence of the star having formed in a low-metallicity and low-dust content environment, thus providing important constraints for models of the formation and evolution of massive stars and their circumstellar disks.

astro-ph.SR↗

arXiv2023

ALMA-IMF VIII -- Combination of Interferometric Continuum Images with Single-Dish Surveys and Structural Analysis of Six Protoclusters

We present the combination of ALMA-IMF and single-dish continuum images from the Mustang-2 Galactic Plane Survey (MGPS90) at 3 millimeters and the Bolocam Galactic Plane Survey (BGPS) at 1 millimeter. Six and ten out of the fiffteen ALMA-IMF fields are combined with MGPS90 and BGPS, respectively. The combination is made via the feathering technique. We used the dendrogram algorithm throughout the combined images, and performed further analysis in the six fields with combination in both bands (G012.80, W43-MM1, W43-MM2, W43-MM3, W51-E, W51-IRS2). In these fields, we calculated spectral index maps and used them to separate regions dominated by dust or free-free emission, and then performed further structural analysis. We report the basic physical parameters of the dust-dominated (column densities, masses) and ionized (emission measures, hydrogen ionization photon rates) structures. We also searched for multi-scale relations in the dust-dominated structures across the analyzed fields, finding that the fraction of mass in dendrogram leaves (which we label as "Leaf Mass Eficiency", LME) as a function of molecular gas column density follows a similar trend: a rapid, exponential-like growth, with maximum values approaching 100% in most cases. The observed behaviour of the LME with gas column is tentatively interpreted as an indicator of large star formation activity within the ALMA-IMF protoclusters. W51-E and G012.80 stand out as cases with comparatively large and reduced potential for further star formation, respectively.

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arXiv2023

Protostellar cores in Sagittarius B2 N and M

We present 500 AU and 700 AU resolution 1 mm and 3 mm ALMA observations, respectively, of protostellar cores in protoclusters Sagittarius B2 (Sgr B2) North (N) and Main (M), parts of the most actively star-forming cloud in our Galaxy. Previous lower resolution (5000 AU) 3 mm observations of this region detected $\sim$150 sources inferred to be young stellar objects (YSOs) with $M>8\mathrm{\,M}_\odot$. With a tenfold increase in resolution, we detect 371 sources at 3 mm and 218 sources in the smaller field of view at 1 mm. The sources seen at low resolution are observed to fragment into an average of two objects. About a third of the observed sources fragment. Most of the sources we report are marginally resolved and are at least partially optically thick. We determine that the observed sources are most consistent with Stage 0/I YSOs, i.e., rotationally supported disks with an active protostar and an envelope, that are warmer than those observed in the solar neighborhood. We report source-counting-based inferred stellar mass and the star formation rate of the cloud: 2800$\mathrm{\,M}_\odot$, 0.0038$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 N and 6900$\mathrm{\,M}_\odot$, 0.0093$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 M respectively.

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arXiv2023

The 107 GHz methanol transition is a dasar in G0.253+0.016

We present observations of population anti-inversion in the $3_1 - 4_0\ A^+$ transition of CH$_3$OH (methanol) at 107.013831 GHz toward the Galactic Center cloud G0.253+0.016 ("The Brick"). Anti-inversion of molecular level populations can result in absorption lines against the cosmic microwave background (CMB) in a phenomenon known as a "dasar." We model the physical conditions under which the 107 GHz methanol transition dases and determine that dasing occurs at densities below $10^6$ cm$^{-3}$ and column densities between $10^{13}$ and $10^{16}$ cm$^{-2}$. We also find that for this transition, dasing does not strongly depend on the gas kinetic temperature. We evaluate the potential of this tool for future deep galaxy surveys. We note that other works have already reported absorption in this transition (e.g., in NGC 253), but we provide the first definitive evidence that it is absorption against the CMB rather than against undetected continuum sources.

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arXiv2023

Isolating Dust and Free-Free Emission in ONC Proplyds with ALMA Band 3 Observations

The Orion Nebula Cluster (ONC) hosts protoplanetary disks experiencing external photoevaporation by the cluster's intense UV field. These ``proplyds" are comprised of a disk surrounded by an ionization front. We present ALMA Band 3 (3.1 mm) continuum observations of 12 proplyds. Thermal emission from the dust disks and free-free emission from the ionization fronts are both detected, and the high-resolution (0.057") of the observations allows us to spatially isolate these two components. The morphology is unique compared to images at shorter (sub)millimeter wavelengths, which only detect the disks, and images at longer centimeter wavelengths, which only detect the ionization fronts. The disks are small ($r_d$ = 6.4--38 au), likely due to truncation by ongoing photoevaporation. They have low spectral indices ($α\lesssim 2.1$) measured between Bands 7 and 3, suggesting the dust emission is optically thick. They harbor tens of Earth masses of dust as computed from the millimeter flux using the standard method, although their true masses may be larger due to the high optical depth. We derive their photoevaporative mass-loss rates in two ways: first, by invoking ionization equilibrium, and second using the brightness of the free-free emission to compute the density of the outflow. We find decent agreement between these measurements and $\dot M$ = 0.6--18.4 $\times$ 10$^{-7}$ $M_\odot$ yr$^{-1}$. The photoevaporation timescales are generally shorter than the $\sim$1 Myr age of the ONC, underscoring the known ``proplyd lifetime problem." Disk masses that are underestimated due to being optically thick remains one explanation to ease this discrepancy.

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arXiv2023

Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence

The Central Molecular Zone (CMZ; the central ~ 500 pc of the Galaxy) is a kinematically unusual environment relative to the Galactic disc, with high velocity dispersions and a steep size-linewidth relation of the molecular clouds. In addition, the CMZ region has a significantly lower star formation rate (SFR) than expected by its large amount of dense gas. An important factor in explaining the low SFR is the turbulent state of the star-forming gas, which seems to be dominated by rotational modes. However, the turbulence driving mechanism remains unclear. In this work, we investigate how the Galactic gravitational potential affects the turbulence in CMZ clouds. We focus on the CMZ cloud G0.253+0.016 (`the Brick'), which is very quiescent and unlikely to be kinematically dominated by stellar feedback. We demonstrate that several kinematic properties of the Brick arise naturally in a cloud-scale hydrodynamics simulation that takes into account the Galactic gravitational potential. These properties include the line-of-sight velocity distribution, the steepened size-linewidth relation, and the predominantly solenoidal nature of the turbulence. Within the simulation, these properties result from the Galactic shear in combination with the cloud's gravitational collapse. This is a strong indication that the Galactic gravitational potential plays a crucial role in shaping the CMZ gas kinematics, and is a major contributor to suppressing the SFR by inducing predominantly solenoidal turbulent modes.

astro-ph.GA↗

arXiv2023

Velocity-Coherent Substructure in TMC-1: Inflow and Fragmentation

Filamentary structures have been found nearly ubiquitously in molecular clouds and yet their formation and evolution is still poorly understood. We examine a segment of Taurus Molecular Cloud 1 (TMC-1) that appears as a single, narrow filament in continuum emission from dust. We use the Regularized Optimization for Hyper-Spectral Analysis (ROHSA), a Gaussian decomposition algorithm which enforces spatial coherence when fitting multiple velocity components simultaneously over a data cube. We analyze HC$_5$N (9-8) line emission as part of the Green Bank Ammonia Survey (GAS) and identify three velocity-coherent components with ROHSA. The two brightest components extend the length of the filament, while the third component is fainter and clumpier. The brightest component has a prominent transverse velocity gradient of $2.7 \pm 0.1$ km s$^{-1}$ pc$^{-1}$ that we show to be indicative of gravitationally induced inflow. In the second component, we identify regularly spaced emission peaks along its length. We show that the local minima between pairs of adjacent HC$_5$N peaks line up closely with submillimetre continuum emission peaks, which we argue is evidence for fragmentation along the spine of TMC-1. While coherent velocity components have been described as separate physical structures in other star-forming filaments, we argue that the two bright components identified in HC$_5$N emission in TMC-1 are tracing two layers in one filament: a lower density outer layer whose material is flowing under gravity towards the higher density inner layer of the filament.

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arXiv2023

CMZoom III: Spectral Line Data Release

We present an overview and data release of the spectral line component of the SMA Large Program, \textit{CMZoom}. \textit{CMZoom} observed $^{12}$CO(2-1), $^{13}$CO(2-1) and C$^{18}$O(2-1), three transitions of H$_{2}$CO, several transitions of CH$_{3}$OH, two transitions of OCS and single transitions of SiO and SO, within gas above a column density of N(H$_2$)$\ge 10^{23}$\,cm$^{-2}$ in the Central Molecular Zone (CMZ; inner few hundred pc of the Galaxy). We extract spectra from all compact 1.3\,mm \emph{CMZoom} continuum sources and fit line profiles to the spectra. We use the fit results from the H$_{2}$CO 3(0,3)-2(0,2) transition to determine the source kinematic properties. We find $\sim 90$\% of the total mass of \emph{CMZoom} sources have reliable kinematics. Only four compact continuum sources are formally self-gravitating. The remainder are consistent with being in hydrostatic equilibrium assuming that they are confined by the high external pressure in the CMZ. Based on the mass and density of virially bound sources, and assuming star formation occurs within one free-fall time with a star formation efficiency of $10\% - 75\%$, we place a lower limit on the future embedded star-formation rate of $0.008 - 0.06$\,M$_{\odot}$\,yr$^{-1}$. We find only two convincing proto-stellar outflows, ruling out a previously undetected population of very massive, actively accreting YSOs with strong outflows. Finally, despite having sufficient sensitivity and resolution to detect high-velocity compact clouds (HVCCs), which have been claimed as evidence for intermediate mass black holes interacting with molecular gas clouds, we find no such objects across the large survey area.

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