Most massive stars form in dense clusters where gravitational interactions with other stars may be common. The two nearest forming massive stars, the BN object and Source I, located behind the Orion ...Nebula, were ejected with velocities of ∼29 and ∼13 km s−1 about 500 years ago by such interactions. This event generated an explosion in the gas. New ALMA observations show in unprecedented detail, a roughly spherically symmetric distribution of over a hundred 12CO J = 2−1 streamers with velocities extending from VLSR = −150 to +145 km s−1. The streamer radial velocities increase (or decrease) linearly with projected distance from the explosion center, forming a "Hubble Flow" confined to within 50″ of the explosion center. They point toward the high proper-motion, shock-excited H2 and Fe ii "fingertips" and lower-velocity CO in the H2 wakes comprising Orion's "fingers." In some directions, the H2 "fingers" extend more than a factor of two farther from the ejection center than the CO streamers. Such deviations from spherical symmetry may be caused by ejecta running into dense gas or the dynamics of the N-body interaction that ejected the stars and produced the explosion. This ∼1048 erg event may have been powered by the release of gravitational potential energy associated with the formation of a compact binary or a protostellar merger. Orion may be the prototype for a new class of stellar explosiozn responsible for luminous infrared transients in nearby galaxies.
Aims. Adaptive optics (AO) images are used to test the hypothesis that the explosive BN/KL outflow from the Orion OMC1 cloud core was powered by the dynamical decay of a non-hierarchical system of ...massive stars. Methods. Narrow-band H2, Fe ii, and broad-band Ks obtained with the Gemini South multi-conjugate AO system GeMS and near-IR imager GSAOI are presented. The images reach resolutions of 0.08 to 0.10′′, close to the 0.07′′ diffraction limit of the 8-m telescope at 2.12 μm. Comparison with previous AO-assisted observations of sub-fields and other ground-based observations enable measurements of proper motions and the investigation of morphological changes in H2 and Fe ii features with unprecedented precision. The images are compared with numerical simulations of compact, high-density clumps moving ~103 times their own diameter through a lower density medium at Mach 103. Results. Several sub-arcsecond H2 features and many Fe ii “fingertips” on the projected outskirts of the flow show proper motions of ~300 km s-1. High-velocity, sub-arcsecond H2 knots (“bullets”) are seen as far as 140′′ from their suspected ejection site. If these knots propagated through the dense Orion A cloud, their survival sets a lower bound on their densities of order 107 cm-3, consistent with an origin within a few au of a massive star and accelerated by a final multi-body dynamic encounter that ejected the BN object and radio source I from OMC1 about 500 yr ago. Conclusions. Over 120 high-velocity bow-shocks propagating in nearly all directions from the OMC1 cloud core provide evidence for an explosive origin for the BN/KL outflow triggered by the dynamic decay of a non-hierarchical system of massive stars. Such events may be linked to the origin of runaway, massive stars.
The proper motions of the three stars ejected from Orion's OMC1 cloud core are combined with the requirement that their center of mass is gravitationally bound to OMC1 to show that radio source I ...(Src I) is likely to have a mass around 15 M consistent with recent measurements. Src I, the star with the smallest proper motion, is suspected to be either an astronomical-unit-scale binary or a protostellar merger remnant produced by a dynamic interaction ∼550 yr ago. Near-infrared 2.2 m images spanning ∼21 yr confirm the ∼55 km s−1 motion of "source x" (Src x) away from the site of stellar ejection and point of origin of the explosive OMC1 protostellar outflow. The radial velocities and masses of the Becklin-Neugebauer (BN) object and Src I constrain the radial velocity of Src x to be km s−1. Several high proper-motion radio sources near BN, including Zapata 11 (ZRK2004 11) and a diffuse source near IRc 23, may trace a slow bipolar outflow from BN. The massive disk around Src I is likely the surviving portion of a disk that existed prior to the stellar ejection. Though highly perturbed, shocked, and reoriented by the N-body interaction, enough time has elapsed to allow the disk to relax with its spin axis roughly orthogonal to the proper motion.
The nuclear starburst within the central ∼15″ (∼250 pc; 1″ 17 pc) of NGC 253 has been extensively studied as a prototype for the starburst phase in galactic evolution. Atacama Large ...Millimeter/submillimeter Array (ALMA) imaging within receiver Bands 6 and 7 has been used to investigate the dense gas structure, kinetic temperature, and heating processes that drive the NGC 253 starburst. A total of 29 transitions from 15 molecular species/isotopologues have been identified and imaged at 1 5-0 4 resolution, allowing for the identification of five of the previously studied giant molecular clouds within the central molecular zone (CMZ) of NGC 253. Ten transitions from the formaldehyde (H2CO) molecule have been used to derive the kinetic temperature within the ∼0 5-5″ dense gas structures imaged. On ∼5″ scales we measure TK 50 K, while on size scales 1″ we measure TK 300 K. These kinetic temperature measurements further delineate the association between potential sources of dense gas heating. We have investigated potential heating sources by comparing our measurements to models that predict the physical conditions associated with dense molecular clouds that possess a variety of heating mechanisms. This comparison has been supplemented with tracers of recently formed massive stars (Brγ) and shocks (Fe ii). Derived molecular column densities point to a radially decreasing abundance of molecules with sensitivity to cosmic-ray and mechanical heating within the NGC 253 CMZ. These measurements are consistent with radio spectral index calculations that suggest a higher concentration of cosmic-ray-producing supernova remnants within the central 10 pc of NGC 253.
NGC 253 hosts the nearest nuclear starburst. Previous observations show a region rich in molecular gas, with dense clouds associated with recent star formation. We used the Atacama Large ...Submillimeter/Millimeter Array (ALMA) to image the 350 GHz dust continuum and molecular line emission from this region at 2 pc resolution. Our observations reveal ∼14 bright, compact (∼2-3 pc FWHM) knots of dust emission. Most of these sources are likely to be forming super star clusters (SSCs) based on their inferred dynamical and gas masses, association with 36 GHz radio continuum emission, and coincidence with line emission tracing dense, excited gas. One source coincides with a known SSC, but the rest remain invisible in Hubble near-infrared (IR) imaging. Our observations imply that gas still constitutes a large fraction of the overall mass in these sources. Their high brightness temperature at 350 GHz also implies a large optical depth near the peak of the IR spectral energy distribution. As a result, these sources may have large IR photospheres, and the IR radiation force likely exceeds L/c. Still, their moderate observed velocity dispersions suggest that feedback from radiation, winds, and supernovae are not yet disrupting most sources. This mode of star formation appears to produce a large fraction of stars in the burst. We argue for a scenario in which this phase lasts ∼1 Myr, after which the clusters shed their natal cocoons but continue to produce ionizing photons. The strong feedback that drives the observed cold gas and X-ray outflows likely occurs after the clusters emerge from this early phase.
We present a detailed characterization of the population of compact radio-continuum sources in W51 A using subarcsecond Very Large Array and Atacama Large Millimeter/submillimeter Array observations. ...We analyze their 2 cm continuum, the recombination lines (RLs) H77 and H30 , and the lines of , , and . We derive diameters for 10/20 sources in the range D ∼ 10−3 to ∼10−2 pc, thus placing them in the regime of hypercompact H ii regions (HC H ii's). Their continuum-derived electron densities are in the range ne ∼ 104 -105 cm−3, lower than typically considered for HC H ii's. We combined the RL measurements and independently derived ne, finding the same range of values but significant offsets for individual measurements between the two methods. We find that most of the sources in our sample are ionized by early B-type stars, and a comparison of ne versus D shows that they follow the inverse relation previously derived for ultracompact (UC) and compact H ii's. When determined, the ionized-gas kinematics is always (7/7) indicative of outflow. Similarly, 5 and 3 out of the 8 HC H ii's still embedded in a compact core show evidence for expansion and infall motions in the molecular gas, respectively. We hypothesize that there could be two different types of hypercompact (D < 0.05 pc) H ii regions: those that essentially are smaller, expanding UC H ii's; and those that are also hyperdense (ne > 106 cm−3), probably associated with O-type stars in a specific stage of their formation or early life.
ABSTRACT We sort 4683 molecular clouds between 10° < < 65° from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 m sources, mid-IR ...color-selected YSOs, H2O and CH3OH masers, and UCH ii regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial ( ∼ 0.7) with >75% of clumps with known distance being gravitationally bound ( < 2). These samples show a statistically significant increase in the median clump mass of ΔM ∼ 170-370 M from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at M ˙ ∼ 200 - 440 M Myr−1 for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ∼M−0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase lifetime of massive (M > 103 M ) starless clumps to be 0.37 0.08 Myr (M/103 M )−1; the majority (M < 450 M ) have phase lifetimes longer than their average freefall time.
Orion SrcI's Disk Is Salty Ginsburg, Adam; McGuire, Brett; Plambeck, Richard ...
The Astrophysical journal,
02/2019, Letnik:
872, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report the detection of NaCl, KCl, and their 37Cl and 41K isotopologues toward the disk around Orion SrcI. About 60 transitions of these molecules were identified. This is the first detection of ...these molecules in the interstellar medium not associated with the ejecta of evolved stars. It is also the first ever detection of the vibrationally excited states of these lines in the ISM above v = 1, with firm detections up to v = 6. The salt emission traces the region just above the continuum disk, possibly forming the base of the outflow. The emission from the vibrationally excited transitions is inconsistent with a single temperature, implying the lines are not in LTE. We examine several possible explanations of the observed high excitation lines, concluding that the vibrational states are most likely to be radiatively excited via rovibrational transitions in the 25-35 (NaCl) and 35-45 (KCl) range. We suggest that the molecules are produced by destruction of dust particles. Because these molecules are so rare, they are potentially unique tools for identifying high-mass protostellar disks and measuring the radiation environment around accreting young stars.
The fraction of stars forming in compact, gravitationally bound clusters (the "cluster formation efficiency" (CFE)) is an important quantity for deriving the spatial clustering of stellar feedback ...and for tracing star formation using stellar clusters across the universe. Observations of clusters in nearby galaxies have revealed a strong dependence of the CFE on the local gas density, indicating that more stars form in star clusters when the star formation rate surface density is higher. Previously, it has not been possible to test this relation at very young ages and in clusters with individual stars resolved due to the universally low densities in the cluster-forming regions in the Local Group. This has even led to the suggestion that the CFE increases with distance from the Sun, which would suggest an observational bias. However, the Central Molecular Zone of the Milky Way hosts clouds with densities that are orders of magnitude higher than anywhere else in the Local Group. We report a measurement of the CFE in the highest-density region in the Galaxy, Sgr B2, based on Atacama Large Millimeter/submillimeter Array observations of high-mass young stellar objects. We find that over a third of the stars (37 7%) in Sgr B2 are forming in bound clusters. This value is consistent with the predictions of environmentally dependent models for the CFE and is inconsistent with a constant CFE in the Galaxy.
Abstract
pyspeckit
is a toolkit and library for spectroscopic analysis in Python. We describe the
pyspeckit
package and highlight some of its capabilities, such as interactively fitting a model to ...data, akin to the historically widely-used
splot
function in
IRAF
.
pyspeckit
employs the Levenberg–Marquardt optimization method via the
mpfit
and
lmfit
implementations, and important assumptions regarding error estimation are described here. Wrappers to use
pymc
and
emcee
as optimizers are provided. A parallelized wrapper to fit lines in spectral cubes is included. As part of the
astropy
affiliated package ecosystem,
pyspeckit
is open source and open development, and welcomes input and collaboration from the community.
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