auto-multithresh: A General Purpose Automasking Algorithm Kepley, Amanda A.; Tsutsumi, Takahiro; Brogan, Crystal L. ...
Publications of the Astronomical Society of the Pacific,
02/2020, Letnik:
132, Številka:
1008
Journal Article
Recenzirano
Odprti dostop
Producing images from interferometer data requires accurate modeling of the sources in the field of view, which is typically done using the clean algorithm. Given the large number of degrees of ...freedom in interferometeric images, one constrains the possible model solutions for clean by masking regions that contain emission. Traditionally this process has largely been done by hand. This approach is not possible with today's large data volumes which require automated imaging pipelines. This paper describes an automated masking algorithm that operates within clean called auto-multithresh. This algorithm was developed and validated using a set of ∼1000 Atacama Large Millimeter/submillimeter Array (ALMA) images chosen to span a range of intrinsic morphology and data characteristics. It takes a top-down approach to producing masks: it uses the residual images to identify significant peaks and then expands the mask to include emission associated with these peaks down to lower signal-to-noise noise. The auto-multithresh algorithm has been implemented in CASA and has been used in production as part of the ALMA Imaging Pipeline starting with Cycle 5. It has been shown to be able to mask a wide range of emission ranging from simple point sources to complex extended emission with minimal tuning of the parameters based on the point-spread function of the data. Although the algorithm was developed for ALMA, it is general enough to have been used successfully with data from other interferometers with appropriate parameter tuning. Integrating the algorithm more deeply within the minor cycle could lead to future performance improvements.
We present EMPIRE, an IRAM 30 m large program that mapped λ = 3-4 mm dense gas tracers at ∼1-2 kpc resolution across the whole star-forming disk of nine nearby massive spiral galaxies. We describe ...the EMPIRE observing and reduction strategies and show new whole-galaxy maps of HCN(1−0), HCO+(1−0), HNC(1−0), and CO(1−0). We explore how the HCN-to-CO and IR-to-HCN ratios, observational proxies for the dense gas fraction and dense gas star formation efficiency, depend on host galaxy and local environment. We find that the fraction of dense gas correlates with stellar surface density, gas surface density, molecular-to-atomic gas ratio, and dynamical equilibrium pressure. In EMPIRE, the star formation rate per unit dense gas is anticorrelated with these same environmental parameters. Thus, although dense gas appears abundant in the central regions of many spiral galaxies, this gas appears relatively inefficient at forming stars. These results qualitatively agree with previous work on nearby galaxies and the Milky Way's Central Molecular Zone. To first order, EMPIRE demonstrates that the conditions in a galaxy disk set the gas density distribution and that the dense gas traced by HCN shows an environment-dependent relation to star formation. However, our results also show significant ( 0.2 dex) galaxy-to-galaxy variations. We suggest that gas structure below the scale of our observations and dynamical effects likely also play an important role.
We use new ALMA observations to investigate the connection between dense gas fraction, star formation rate (SFR), and local environment across the inner region of four local galaxies showing a wide ...range of molecular gas depletion times. We map HCN (1-0), HCO+ (1-0), CS (2-1), 13CO (1-0), and C18O (1-0) across the inner few kiloparsecs of each target. We combine these data with short-spacing information from the IRAM large program EMPIRE, archival CO maps, tracers of stellar structure and recent star formation, and recent HCN surveys by Bigiel et al. and Usero et al. We test the degree to which changes in the dense gas fraction drive changes in the SFR. (tracing the dense gas fraction) correlates strongly with ICO (tracing molecular gas surface density), stellar surface density, and dynamical equilibrium pressure, PDE. Therefore, becomes very low and HCN becomes very faint at large galactocentric radii, where ratios as low as become common. The apparent ability of dense gas to form stars, (where dense is traced by the HCN intensity and the star formation rate is traced by a combination of H and 24 m emission), also depends on environment. decreases in regions of high gas surface density, high stellar surface density, and high PDE. Statistically, these correlations between environment and both and are stronger than that between apparent dense gas fraction ( ) and the apparent molecular gas star formation efficiency . We show that these results are not specific to HCN.
Abstract We report observations of the ground state transitions of 12 CO, 13 CO, C 18 O, HCN, and HCO + at 88–115 GHz in the inner region of the nearby galaxy IC 342. These data were obtained with ...the 16 pixel spectroscopic focal plane array Argus on the 100 m Robert C. Byrd Green Bank Telescope (GBT) at 6″–9″ resolution. In the nuclear bar region, the intensity distributions of 12 CO(1–0) and 13 CO(1–0) emission trace moderate densities, and differ from the dense gas distributions sampled in C 18 O(1–0), HCN(1–0), and HCO + (1–0). We observe a constant HCN(1–0)-to-HCO + (1–0) ratio of 1.2 ± 0.1 across the whole ∼1 kpc bar. This indicates that the HCN(1–0) and HCO + (1–0) lines have intermediate optical depth, and that the corresponding n H 2 of the gas producing the emission is of order 10 4.5−6 cm −3 . We show that HCO + (1–0) is thermalized and HCN(1–0) is close to thermalization. The very tight correlation between the HCN(1–0) and HCO + (1–0) intensities across the 1 kpc bar suggests that this ratio is more sensitive to the relative abundance of the two species than to the gas density. We confirm an angular offset (∼10″) between the spatial distribution of molecular gas and the star formation sites. Finally, we find a breakdown of the L IR – L HCN correlation at high spatial resolution due to the effect of incomplete sampling of star-forming regions by HCN emission in IC 342. The scatter of the L IR – L HCN relation decreases as the spatial scale increases from 10″ to 30″ (170–510 pc), and is comparable to the scatter of the global relation at a scale of 340 pc.
ABSTRACT Using the Atacama Large Millimeter/submillimeter Array, we have made the first high spatial and spectral resolution observations of the molecular gas and dust in the prototypical blue ...compact dwarf galaxy II Zw 40. The and emission is clumpy and distributed throughout the central star-forming region. Only one of eight molecular clouds has associated star formation. The continuum spectral energy distribution is dominated by free-free and synchrotron; at 870 m, only 50% of the emission is from dust. We derive a CO-to-H2 conversion factor using several methods, including a new method that uses simple photodissocation models and resolved CO line intensity measurements to derive a relationship that uniquely predicts for a given metallicity. We find that the CO-to-H2 conversion factor is 4-35 times that of the Milky Way (18.1-150.5 ). The star formation efficiency of the molecular gas is at least 10 times higher than that found in normal spiral galaxies, which is likely due to the burst-dominated star formation history of II Zw 40 rather than an intrinsically higher efficiency. The molecular clouds within II Zw 40 resemble those in other strongly interacting systems like the Antennae: overall they have high size-linewidth coefficients and molecular gas surface densities. These properties appear to be due to the high molecular gas surface densities produced in this merging system rather than to increased external pressure. Overall, these results paint a picture of II Zw 40 as a complex, rapidly evolving system whose molecular gas properties are dominated by the large-scale gas shocks from its ongoing merger.
We use Atacama Large Millimeter/submillimeter Array and Institute for Radio Astronomy in the Millimeter 30 m telescope data to investigate the relationship between the spectroscopically traced dense ...gas fraction and the cloud-scale (120 pc) molecular gas surface density in five nearby, star-forming galaxies. We estimate the dense gas mass fraction at 650 and 2800 pc scales using the ratio of HCN (1−0) to CO (1−0) emission. We then use high-resolution (120 pc) CO (2−1) maps to calculate the mass-weighted average molecular gas surface density within 650 or 2770 pc beam where the dense gas fraction is estimated. On average, the dense gas fraction correlates with the mass-weighted average molecular gas surface density. Thus, parts of a galaxy with higher mean cloud-scale gas surface density also appear to have a larger fraction of dense gas. The normalization and slope of the correlation do vary from galaxy to galaxy and with the size of the regions studied. This correlation is consistent with a scenario where the large-scale environment sets the gas volume density distribution, and this distribution manifests in both the cloud-scale surface density and the dense gas mass fraction.
The ALMA Interferometric Pipeline Heuristics Hunter, Todd R.; Indebetouw, Remy; Brogan, Crystal L. ...
Publications of the Astronomical Society of the Pacific,
07/2023, Letnik:
135, Številka:
1049
Journal Article
Recenzirano
Odprti dostop
Abstract
We describe the calibration and imaging heuristics developed and deployed in the Atacama Large Millimeter/submillimeter Array (ALMA) interferometric data processing pipeline, as of ALMA ...Cycle 9 operations. The pipeline software framework is written in Python, with each data reduction stage layered on top of tasks and toolkit functions provided by the Common Astronomy Software Applications package. This framework supports a variety of tasks for observatory operations, including science data quality assurance, observing mode commissioning, and user reprocessing. It supports ALMA and Very Large Array interferometric data along with ALMA and NRO 45 m single dish data, via different stages and heuristics. In addition to producing calibration tables, calibrated measurement sets, and cleaned images, the pipeline creates a WebLog which serves as the primary interface for verifying the quality assurance of the data by the observatory and for examining the contents of the data by the user. Following the adoption of the pipeline by ALMA Operations in 2014, the heuristics have been refined through annual prioritized development cycles, culminating in a new pipeline release aligned with the start of each ALMA Cycle of observations. Initial development focused on basic calibration and flagging heuristics (Cycles 2–3), followed by imaging heuristics (Cycles 4–5). Further refinement of the flagging and imaging heuristics, including the introduction of parallel processing, proceeded for Cycles 6–7. In the 2020 release, the algorithm to identify channels to use for continuum subtraction and imaging was substantially improved by the addition of a moment difference analysis. A spectral renormalization stage was added for the 2021 release (Cycle 8) to correct high spectral resolution visibility data acquired on targets exhibiting strong celestial line emission in their autocorrelation spectra. The calibration heuristics used in the low signal-to-noise regime were improved for the 2022 release (Cycle 9). In the two most recent Cycles, 97% of ALMA data sets were calibrated and imaged with the pipeline, ensuring long-term automated reproducibility of results. We conclude with a brief description of plans for future additions, including a self-calibration stage, support for multi-configuration imaging, and complete calibration and imaging of full polarization data.
ABSTRACT We present the first results from the EMPIRE survey, an IRAM large program that is mapping tracers of high-density molecular gas across the disks of nine nearby star-forming galaxies. Here, ...we present new maps of the 3 mm transitions of HCN, HCO+, and HNC across the whole disk of our pilot target, M51. As expected, dense gas correlates with tracers of recent star formation, filling the "luminosity gap" between Galactic cores and whole galaxies. In detail, we show that both the fraction of gas that is dense, f dense traced by HCN/CO, and the rate at which dense gas forms stars, SFE dense traced by IR/HCN, depend on environment in the galaxy. The sense of the dependence is that high-surface-density, high molecular gas fraction regions of the galaxy show high dense gas fractions and low dense gas star formation efficiencies. This agrees with recent results for individual pointings by Usero et al. but using unbiased whole-galaxy maps. It also agrees qualitatively with the behavior observed contrasting our own Solar Neighborhood with the central regions of the Milky Way. The sense of the trends can be explained if the dense gas fraction tracks interstellar pressure but star formation occurs only in regions of high density contrast.
Summary
This is a cross-sectional study to assess differences in bone quality in young Asian and Caucasian (
n
= 30/group) men between 25 and 35 years. We found that Asians had smaller bones, ...thicker and denser cortices, and more plate-like trabeculae, but stiffness did not differ between groups.
Introduction
We conducted a cross-sectional study to assess differences in bone quality in young Asian and Caucasian (
n
= 30/group) men between 25 and 35 years.
Methods
We measured bone mineral density (BMD) at the spine, total hip (TH), femoral neck (FN), and forearm by dual energy X-ray absorptiometry (DXA), and bone geometry, density, microarchitecture, and mechanical competence at the radius and tibia by high-resolution peripheral quantitative computed tomography (HR-pQCT) with application of individual trabecula segmentation (ITS) and trabecular and whole bone finite element analysis (FEA). We measured load-to-strength ratio to account for differences in bone size and height, respectively. We used Wilcoxon rank sum and generalized linear models adjusted for height, weight, and their interaction for comparisons.
Results
Asians were 3.9 % shorter and weighed 6.5 % less than Caucasians. In adjusted models: by DXA, there were no significant race-based differences in areal BMD; by HR-pQCT, at the radius, Asians had smaller total and trabecular area (
p
= 0.003 for both), and denser (
p
= 0.01) and thicker (
p
= 0.04) cortices at the radius; by ITS, at the radius Asians, had more plate-like than rod-like trabeculae (PR ratio
p
= 0.01), greater plate trabecular surface (
p
= 0.009) and longer rod length (
p
= 0.002). There were no significant race-based differences in FEA or the load-to-strength ratio.
Conclusions
Asians had smaller bones, thicker and denser cortices, and more plate-like trabeculae, but biomechanical estimates of bone strength did not differ between groups. Studies are needed to determine whether these differences persist later in life.
We mapped 3 mm continuum and line emission from the starburst galaxy M82 using the Combined Array for Research in Millimeter-wave Astronomy. We targeted the HCN, HCO+, HNC, CS, and HC sub(3)N lines, ...but here we focus on the HCN and HCO+ emission. The map covers a field of 1'.2 with an asymptotically =5" resolution. The HCN and HCO+ observations are short spacings corrected. The molecular gas in M82 had been previously found to be distributed in a molecular disk, coincident with the central starburst, and a galactic scale outflow which originates in the central starburst. With the new short spacings-corrected maps we derive some of the properties of the dense molecular gas in the base of the outflow. From the HCN and HCO+ J = (1-0) line emission, and under the assumptions of the gas being optically thin and in local thermodynamic equilibrium, we place lower limits on the amount of dense molecular gas in the base of the outflow. The lower limits are 7 x 10 super(6) M sub(middot in circle) and 21 x 10 super(6) M sub(middot in circle), or > ~2% of the total molecular mass in the outflow. The kinematics and spatial distribution of the dense gas outside the central starburst suggests that it is being expelled through chimneys. Assuming a constant outflow velocity, the derived outflow rate of dense molecular gas is > or =, slanted0.3 M sub(middot in circle) yr super(-1), which would lower the starburst lifetime by > or =, slanted5%. The energy required to expel this mass of dense gas is (1-10) x 10 super(52) erg.
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