59 research outputs found
Protoplanetary Disks in the Orion Nebula Cluster: Gas Disk Morphologies and Kinematics as seen with ALMA
We present Atacama Large Millimeter Array CO(32) and HCO(43)
observations covering the central region of
the Orion Nebula Cluster (ONC). The unprecedented level of sensitivity
(0.1 mJy beam) and angular resolution ( AU) of these line observations enable us to search for gas-disk
detections towards the known positions of submillimeter-detected dust disks in
this region. We detect 23 disks in gas: 17 in CO(32), 17 in HCO(43),
and 11 in both lines. Depending on where the sources are located in the ONC, we
see the line detections in emission, in absorption against the warm background,
or in both emission and absorption. We spectrally resolve the gas with km
s channels, and find that the kinematics of most sources are consistent
with Keplerian rotation. We measure the distribution of gas-disk sizes and find
typical radii of 50-200 AU. As such, gas disks in the ONC are compact in
comparison with the gas disks seen in low-density star-forming regions. Gas
sizes are universally larger than the dust sizes. However, the gas and dust
sizes are not strongly correlated. We find a positive correlation between gas
size and distance from the massive star Ori C, indicating that disks
in the ONC are influenced by photoionization. Finally, we use the observed
kinematics of the detected gas lines to model Keplerian rotation and infer the
masses of the central pre-main-sequence stars. Our dynamically-derived stellar
masses are not consistent with the spectroscopically-derived masses, and we
discuss possible reasons for this discrepancy.Comment: 42 pages, 31 figure
TurbuStat: Turbulence Statistics in Python
We present TurbuStat (v1.0): a Python package for computing turbulence
statistics in spectral-line data cubes. TurbuStat includes implementations of
fourteen methods for recovering turbulent properties from observational data.
Additional features of the software include: distance metrics for comparing two
data sets; a segmented linear model for fitting lines with a break-point; a
two-dimensional elliptical power-law model; multi-core fast-fourier-transform
support; a suite for producing simulated observations of fractional Brownian
Motion fields, including two-dimensional images and optically-thin HI data
cubes; and functions for creating realistic world coordinate system information
for synthetic observations. This paper summarizes the TurbuStat package and
provides representative examples using several different methods. TurbuStat is
an open-source package and we welcome community feedback and contributions.Comment: Accepted in AJ. 21 pages, 8 figure
Assessing the Impact of Astrochemistry on Molecular Cloud Turbulence Statistics
We analyze hydrodynamic simulations of turbulent, star-forming molecular
clouds that are post-processed with the photo-dissociation region
astrochemistry code 3D-PDR. We investigate the sensitivity of 15 commonly
applied turbulence statistics to post-processing assumptions, namely variations
in gas temperature, abundance and external radiation field. We produce
synthetic CO(1-0) and CI(P-P) observations and
examine how the variations influence the resulting emission distributions. To
characterize differences between the datasets, we perform statistical
measurements, identify diagnostics sensitive to our chemistry parameters, and
quantify the statistic responses by using a variety of distance metrics. We
find that multiple turbulent statistics are sensitive not only to the chemical
complexity but also to the strength of the background radiation field. The
statistics with meaningful responses include principal component analysis,
spatial power spectrum and bicoherence. A few of the statistics, such as the
velocity coordinate spectrum, are primarily sensitive to the type of tracer
being utilized, while others, like the delta-variance, strongly respond to the
background radiation field. Collectively, these findings indicate that more
realistic chemistry impacts the responses of turbulent statistics and is
necessary for accurate statistical comparisons between models and observed
molecular clouds.Comment: 27 pages, 21 figures, accepted to Ap
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 ( = 6.4--38 au), likely due to truncation by ongoing
photoevaporation. They have low spectral indices ()
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 = 0.6--18.4
10 yr. The photoevaporation timescales are
generally shorter than the 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.Comment: 17 pages, 12 figures, accepted for publication in Ap
Consensus guidelines for the use and interpretation of angiogenesis assays
The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference
Chemical Modeling of Orion Nebula Cluster Disks: Evidence for Massive, Compact Gas Disks with Interstellar Gas-to-dust Ratios
The stellar cluster environment is expected to play a central role in the evolution of circumstellar disks. We use thermochemical modeling to constrain the dust and gas masses, disk sizes, UV and X-ray radiation fields, viewing geometries, and central stellar masses of 20 class II disks in the Orion Nebula Cluster (ONC). We fit a large grid of disk models to 350 GHz continuum, CO J = 3 − 2, and HCO ^+ J = 4 − 3 Atacama Large Millimeter/submillimeter Array observations of each target, and we introduce a procedure for modeling interferometric observations of gas disks detected in absorption against a bright molecular cloud background. We find that the ONC disks are massive and compact, with typical radii <100 au, gas masses ≥10 ^−3 M _⊙ , and gas-to-dust ratios ≥100. The interstellar‐medium‐like gas-to-dust ratios derived from our modeling suggest that compact, externally irradiated disks in the ONC are less prone to gas-phase CO depletion than the massive and extended gas disks that are commonly found in nearby low-mass star-forming regions. The presence of massive gas disks indicates that external photoevaporation may have only recently begun operating in the ONC; though it remains unclear whether other cluster members are older and more evaporated than the ones in our sample. Finally, we compare our dynamically derived stellar masses with the stellar masses predicted from evolutionary models and find excellent agreement. Our study has significantly increased the number of dynamical mass measurements in the mass range ≤0.5 M _⊙ , demonstrating that the ONC is an ideal region for obtaining large samples of dynamical mass measurements toward low-mass M-dwarfs
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