We present new Atacama Large Millimeter/submillimeter Array (ALMA) continuum and NH2D, N2D+, and H2D+line emission at matched, ∼100 au resolution toward the dense star-forming cores SM1N and N6 within the Ophiuchus molecular cloud. We determine the density and temperature structure of SM1N based on radiative transfer modeling and simulated observations of the multiwavelength continuum emission at 0.8, 2, and 3 mm. We show that SM1N is best fit by either a broken power-law or Plummer-like density profile with high central densities (
- Award ID(s):
- 1910106
- PAR ID:
- 10333015
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 929
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 13
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract n ∼ 108cm−3), and an inner transition radius of only ∼80–300 au. The free-fall time of the inner region is only a few ×103yr. The continuum modeling rules out the presence of an embedded first hydrostatic core (FHSC) or protostar. SM1N is therefore a dynamically unstable but still starless core. We find that NH2D is likely depleted at high densities within SM1N. The nonthermal velocity dispersions increase from NH2D to N2H+and H2D+, possibly tracing increasing (but still subsonic) infall speeds at higher densities as predicted by some models of starless core contraction. Toward N6, we confirm the previous ALMA detection of a faint, embedded point source (N6-mm) in 0.8 mm continuum emission. NH2D and N2D+avoid N6-mm within ∼100 au, while H2D+is not strongly detected toward N6. The distribution of these tracers is consistent with heating by a young, warm object. N6-mm thus remains one of the best candidate FHSCs detected so far, although its observed (sub)millimeter luminosity remains below predictions for FHSCs. -
more » « less
ABSTRACT Molecular deuteration is a powerful diagnostic tool for probing the physical conditions and chemical processes in astrophysical environments. In this work, we focus on formaldehyde deuteration in the protobinary system NGC 1333 IRAS 4A, located in the Perseus molecular cloud. Using high-resolution ($\sim$100 au) ALMA (The Atacama Large Millimeter/submillimeter Array) observations, we investigate the [D$_2$CO]/[HDCO] ratio along the cavity walls of the outflows emanating from IRAS 4A1. Our analysis reveals a consistent decrease in the deuteration ratio (from $\sim$60-20 per cent to $\sim$10 per cent) with increasing distance from the protostar (from $\sim$2000 to $\sim$4000 au). Given the large measured [D$_2$CO]/[HDCO], both HDCO and D$_2$CO are likely injected by the shocks along the cavity walls into the gas-phase from the dust mantles, formed in the previous prestellar phase. We propose that the observed [D$_2$CO]/[HDCO] decrease is due to the density profile of the prestellar core from which NGC 1333 IRAS 4A was born. When considering the chemical processes at the base of formaldehyde deuteration, the IRAS 4A’s prestellar precursor had a predominantly flat density profile within 3000 au and a decrease of density beyond this radius.
-
Abstract G10.21-0.31 is a 70 μ m dark high-mass starless core ( M > 300 M ⊙ within r < 0.15 pc) identified in the Spitzer, Herschel, and APEX continuum surveys, and is believed to harbor the initial stages of high-mass star formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) and Submillimeter Array observations to resolve the internal structure of this promising high-mass starless core. Sensitive high-resolution ALMA 1.3 mm dust continuum emission reveals three cores of mass ranging within 11–18 M ⊙ , characterized by a turbulent fragmentation. Cores 1, 2, and 3 represent a coherent evolution of three different stages, characterized by outflows (CO and SiO), gas temperature (H 2 CO), and deuteration (N 2 D + /N 2 H + ). We confirm the potential for formation of high-mass stars in G10.21 and explore the evolution path of high-mass star formation. Yet, no high-mass prestellar core is present in G10.21. This suggests a dynamical star formation where cores grow in mass over time.more » « less
-
more » « less
Context. Hot cores are signposts of the protostellar activity of dense cores in star-forming regions. W43-MM1 is a young region that is very rich in terms of high-mass star formation, which is highlighted by the presence of large numbers of high-mass cores and outflows.Aims. We aim to systematically identify the massive cores in W43-MM1 that contain a hot core and compare their molecular composition.Methods. We used Atacama Large Millimeter/sub-millimeter Array (ALMA) high-spatial resolution (~2500 au) data to identify line-rich protostellar cores and carried out a comparative study of their temperature and molecular composition. Here, the identification of hot cores is based on both the spatial distribution of the complex organic molecules and the contribution of molecular lines relative to the continuum intensity. We rely on the analysis of CH3CN and CH3CCH to estimate the temperatures of the selected cores. Finally, we rescale the spectra of the different hot cores based on their CH3OCHO line intensities to directly compare the detections and line intensities of the other species.Results. W43-MM1 turns out to be a region that is rich in massive hot cores. It contains at least one less massive (core #11, 2M ⊙) and seven massive (16−100M ⊙) hot cores. The excitation temperature of CH3CN, whose emission is centred on the cores, is of the same order for all of them (120–160 K). There is a factor of up to 30 difference in the intensity of the lines of complex organic molecules (COMs). However the molecular emission of the hot cores appears to be the same or within a factor of 2–3. This suggests that these massive cores, which span about an order of magnitude in core mass, have a similar chemical composition and show similar excitation of most of the COMs. In contrast, CH3CCH emission is found to preferentially trace the envelope, with a temperature ranging from 50 K to 90 K. Lines in core #11 are less optically thick, which makes them proportionally more intense compared to the continuum than lines observed in the more massive hot cores. Core #1, the most massive hot core of W43-MM1, shows a richer line spectrum than the other cores in our sample, in particular in N-bearing molecules and ethylene glycol lines. In core #2, the emission of O-bearing molecules, such as OCS, CH3OCHO, and CH3OH, does not peak at the dust continuum core centre; the blueshifted and redshifted emission corresponds to the outflow lobes, suggesting formation via sublimation of the ice mantles through shocks or UV irradiation on the walls of the cavity. These data establish a benchmark for the study of other massive star-formation regions and hot cores. -
more » « less
ABSTRACT Low-mass stars like our Sun begin their evolution within cold (10 K) and dense (∼105 cm−3) cores of gas and dust. The physical structure of starless cores is best probed by thermal emission of dust grains. We present a high-resolution dust continuum study of the starless cores in the B10 region of the Taurus Molecular Cloud. New observations at 1.2 and 2.0 mm (12 and 18 arcsec resolution) with the NIKA2 instrument on the IRAM 30m have probed the inner regions of 14 low-mass starless cores. We perform sophisticated 3D radiative transfer modelling for each of these cores through the radiative transfer framework pandora, which utilizes RADMC-3D. Model best-fits constrain each cores’ central density, density slope, aspect ratio, opacity, and interstellar radiation field strength. These ‘typical’ cores in B10 span central densities from 5 × 104 to 1 × 106 cm−3, with a mean value of 2.6 × 105 cm−3. We find the dust opacity laws assumed in the 3D modelling, as well as the estimates from Herschel, have dust emissivity indices, β’s, on the lower end of the distribution constrained directly from the NIKA2 maps, which averages to β = 2.01 ± 0.48. From our 3D density structures and archival NH3 data, we perform a self-consistent virial analysis to assess each core’s stability. Ignoring magnetic field contributions, we find nine out of the 14 cores (64 per cent) are either in virial equilibrium or are bound by gravity and external pressure. To push the bounded cores back to equilibrium, an effective magnetic field difference of only ∼15 $\mu$G is needed.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ac5913
