We compare multi-epoch sub-arcsecond Very Large Array imaging of the 22 GHz water masers toward the massive protocluster NGC 6334I observed before and after the recent outburst of MM1B in ...(sub)millimeter continuum. Since the outburst, the water maser emission toward MM1 has substantially weakened. Simultaneously, the strong water masers associated with the synchrotron continuum point source CM2 have flared by a mean factor of 6.5 (to 4.2 kJy) with highly blueshifted features (up to 70 km s−1 from the LSR) becoming more prominent. The strongest flaring water masers reside 3000 au north of MM1B and form a remarkable bow shock pattern whose vertex coincides with CM2 and tail points back to MM1B. Excited OH masers trace a secondary bow shock located ∼120 au downstream. Atacama Large Millimeter Array images of CS (6-5) reveal a highly collimated north-south structure encompassing the flaring masers to the north and the nonflaring masers to the south seen in projection toward the MM3-UCHII region. Proper motions of the southern water masers over 5.3 years indicate a bulk projected motion of 117 km s−1 southward from MM1B with a dynamical time of 170 years. We conclude that CM2, the water masers, and many of the excited OH masers trace the interaction of the high-velocity bipolar outflow from MM1B with ambient molecular gas. The previously excavated outflow cavity has apparently allowed the radiative energy of the current outburst to propagate freely until terminating at the northern bow shock where it strengthened the masers. Additionally, water masers have been detected toward MM7 for the first time, and a highly collimated CS (6-5) outflow has been detected toward MM4.
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.1 mm dust continuum and CO 2-1 emission toward six dense cores within the Ophiuchus molecular cloud. We detect ...compact, subarcsecond continuum structures toward three targets, two of which (Oph A N6 and SM1) are located in the Ophiuchus A ridge. Two targets, SM1 and GSS 30, contain two compact sources within the ALMA primary beam. We argue that several of the compact structures are small (R 80 au) accretion disks around young protostars, based on their resolved, elongated structures, coincident radio and X-ray detections, or bipolar outflow detections. While CO line wings extend to 10-20 km s−1 for the more evolved sources GSS 30 IRS3 and IRS1, CO emission toward other sources, where detected, only extends a few km s−1 from the cloud vLSR. The dust spectral index toward the compact objects suggests either that the disks are optically thick at 1.1 mm or that significant grain growth has already occurred. We identify, for the first time, a single compact continuum source (R ∼ 100 au) toward N6 embedded within a larger continuum structure. SM1N is extended in the continuum but is highly centrally concentrated, with a density profile that follows a r−1.3 power law within 200 au and additional structure suggested by the uv-data. Both N6 and SM1N show no clear bipolar outflows with velocities greater than a few km s−1 from the cloud velocity. These sources are candidates to be the youngest protostars or first hydrostatic cores in the Ophiuchus molecular cloud.
ABSTRACT Filamentary structures are ubiquitous in molecular clouds, and have been recently argued to play an important role in regulating the size and mass of embedded clumps through fragmentation ...and mass accretion. Here, we reveal the dynamical state and fragmentation of filamentary molecular gas associated with the Serpens South protocluster through analysis of wide ( ) observations of NH3 (1, 1) and (2, 2) inversion transitions with the Green Bank Telescope. Detailed modeling of the NH3 lines reveals that the kinematics of the cluster and surrounding filaments are complex. We identify hierarchical structure using a dendrogram analysis of the NH3 emission. The distance between neighbor structures that are embedded within the same parent structure is generally greater than expected from a spherical Jeans analysis, and is in better agreement with cylindrical fragmentation models. The NH3 line width-size relation is flat, and average gas motions are sub- or trans-sonic over all physical scales observed. Subsonic regions extend far beyond the typical 0.1 pc scale previously identified in star-forming cores. As a result, we find a strong trend of decreasing virial parameter with increasing structure mass in Serpens South. Extremely low virial parameters on the largest scales probed by our data suggest that the previously observed, ordered magnetic field is insufficient to support the region against collapse, in agreement with large radial infall motions previously measured toward some of the filaments. A more complex magnetic field configuration in the dense gas, however, may be able to support the filaments.
Context. Ammonia and its deuterated isotopologues probe physical conditions in dense molecular cloud cores. The time-dependence of deuterium fractionation and the relative abundances of different ...nuclear spin modifications are supposed to provide a means of determining the evolutionary stages of these objects. Aims. We aim to test the current understanding of spin-state chemistry of deuterated species by determining the abundances and spin ratios of NH2D, NHD2 and ND3 in a quiescent, dense cloud. Methods. Spectral lines of NH3, NH2D, NHD2, ND3 and N2D+ were observed towards a dense, starless core in Ophiuchus with the APEX, GBT and IRAM 30-m telescopes. The observations were interpreted using a gas-grain chemistry model combined with radiative transfer calculations. The chemistry model distinguishes between the different nuclear spin states of light hydrogen molecules, ammonia and their deuterated forms. Different desorption schemes can be considered. Results. High deuterium fractionation ratios with NH2D/NH3 ~ 0.4, NHD2/ NH2D ~ 0.2 and ND3/ NHD2 ~ 0.06 are found in the core. The observed ortho/para ratios of NH2D and NHD2 are close to the corresponding nuclear spin statistical weights. The chemistry model can approximately reproduce the observed abundances, but consistently predicts too low ortho/para-NH2D, and too large ortho/para-NHD2 ratios. The longevity of N2H+ and NH3 in dense gas, which is prerequisite to their strong deuteration, can be attributed to the chemical inertia of N2 on grain surfaces. Conclusions. The discrepancies between the chemistry model and the observations are likely to be caused by the fact that the model assumes complete scrambling in principal gas-phase deuteration reactions of ammonia, which means that all the nuclei are mixed in reactive collisions. If, instead, these reactions occur through proton hop/hydrogen abstraction processes, statistical spin ratios are to be expected. The present results suggest that while the deuteration of ammonia changes with physical conditions and time, the nuclear spin ratios of ammonia isotopologues do not probe the evolutionary stage of a cloud.
We have detected bright HC7N J = 21 − 20 emission towards multiple locations in the Serpens South cluster-forming region using the K-Band Focal Plane Array at the Robert C. Byrd Green Bank Telescope. ...HC7N is seen primarily towards cold filamentary structures that have yet to form stars, largely avoiding the dense gas associated with small protostellar groups and the main central cluster of Serpens South. Where detected, the HC7N abundances are similar to those found in other nearby star-forming regions. Towards some HC7N 'clumps', we find consistent variations in the line centroids relative to NH3 (1,1) emission, as well as systematic increases in the HC7N non-thermal line widths, which we argue reveal infall motions on to dense filaments within Serpens South with minimum mass accretion rates of M ∼ 2-5 M Myr−1. The relative abundance of NH3 to HC7N suggests that the HC7N is tracing gas that has been at densities n ∼ 104 cm−3 for time-scales t 1-2 × 105 yr. Since HC7N emission peaks are rarely co-located with those of either NH3 or continuum, it is likely that Serpens South is not particularly remarkable in its abundance of HC7N, but instead the serendipitous mapping of HC7N simultaneously with NH3 has allowed us to detect HC7N at low abundances in regions where it otherwise may not have been looked for. This result extends the known star-forming regions containing significant HC7N emission from typically quiescent regions, like the Taurus molecular cloud, to more complex, active environments.
Massive young stellar objects (MYSOs) are known to undergo an evolutionary phase in which high mass accretion rates drive strong outflows. A class of objects believed to trace this phase accurately ...is the Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) Extended Green Object (EGO) sample, so named for the presence of extended 4.5 m emission on size scales of ∼0.1 pc in Spitzer images. We have been conducting a multiwavelength examination of a sample of 12 EGOs with distances of 1-5 kpc. In this paper, we present mid-infrared images and photometry of these EGOs obtained with the Stratospheric Observatory for Infrared Astronomy and subsequently construct spectral energy distributions (SEDs) for these sources from the near-infrared to submillimeter regimes using additional archival data. We compare the results from graybody models and several publicly available software packages that produce model SEDs in the context of a single massive protostar. The models yield typical R ∼ 10 R , T ∼ 103-104 K, and L ∼ 1-40 × 103 L ; the median L/M for our sample is 24.7 L /M . Model results rarely converge for R and T , but they do for L , which we take to be an indication of the multiplicity and inherently clustered nature of these sources even though, typically, only a single source dominates in the mid-infrared. The median L/M value for the sample suggests that these objects may be in a transitional stage between the commonly described "IR-quiet" and "IR-bright" stages of MYSO evolution. The median Tdust for the sample is less conclusive but suggests that these objects are either in this transitional stage or occupy the cooler (and presumably younger) part of the IR-bright stage.
We present combined interferometer and single dish telescope data of NH3 (J, K) = (1,1) and (2,2) emission toward the clustered star forming Ophiuchus B, C, and F Cores at high spatial resolution ...(~1200 AU) using the Australia Telescope Compact Array, the Very Large Array, and the Green Bank Telescope. While the large-scale features of the NH3 (1,1) integrated intensity appear similar to 850 is a subset of m continuum emission maps of the Cores, on 15'' (1800 AU) scales we find significant discrepancies between the dense gas tracers in Oph B, but good correspondence in Oph C and F. Using the CLUMPFIND structure identifying algorithm, we identify 15 NH3 clumps in Oph B, and three each in Oph C and F. Only five of the Oph B NH3 clumps are coincident within 30'' (3600 AU) of a submillimeter clump. We find v LSR varies little across any of the cores, and additionally varies by only ~1.5 km s-1 between them. The observed NH3 line widths within the Oph B and F Cores are generally large and often mildly supersonic, while Oph C is characterized by narrow line widths which decrease to nearly thermal values. We find several regions of localized narrow line emission ( Delta v 0.4 km s-1), some of which are associated with NH3 clumps. We derive the kinetic temperatures of the gas, and find they are remarkably constant across Oph B and F, with a warmer mean value (TK = 15 K) than typically found in isolated regions and consistent with previous results in clustered regions. Oph C, however, has a mean TK = 12 K, decreasing to a minimum TK = 9.4 K toward the submillimeter continuum peak, similar to previous studies of isolated starless clumps. There is no significant difference in temperature toward protostars embedded in the Cores. NH3 column densities, N(NH3), and abundances, X(NH3), are similar to previous work in other nearby molecular clouds. We find evidence for a decrease in X(NH3) with increasing N(H2) in Oph B2 and C, suggesting the NH3 emission may not be tracing well the densest core gas.
We present new measurements of the dust emissivity index, β, for the high-mass, star-forming OMC 2/3 filament. We combined 160−500 μm data from Herschel with long-wavelength observations at 2 mm and ...fit the spectral energy distributions across a ≃2 pc long, continuous section of OMC 2/3 at 15 000 AU (0.08 pc) resolution. With these data, we measured β and reconstructed simultaneously the filtered-out large-scale emission at 2 mm. We implemented both variable and fixed values of β, finding that β = 1.7−1.8 provides the best fit across most of OMC 2/3. These β values are consistent with a similar analysis carried out with filtered Herschel data. Thus, we show that β values derived from spatial filtered emission maps agree well with those values from unfiltered data at the same resolution. Our results contradict the very low β values (~0.9) previously measured in OMC 2/3 between 1.2 mm and 3.3 mm data, which we attribute to elevated fluxes in the 3.3 mm observations. Therefore, we find no evidence of rapid, extensive dust grain growth in OMC 2/3. Future studies with Herschel data and complementary ground-based long-wavelength data can apply our technique to obtain reliable determinations of β in nearby cold molecular clouds.
We present a Nobeyama 45 m Radio Telescope map and Australia Telescope Compact Array pointed observations of N2H+ 1-0 emission toward the clustered, low-mass star-forming Oph B Core within the ...Ophiuchus molecular cloud. We compare these data with previously published results of high-resolution NH3 (1,1) and (2,2) observations in Oph B. We use 3D CLUMPFIND to identify emission features in the single-dish N2H+ map, and find that the N2H+ 'clumps' match well similar features previously identified in NH3 (1,1) emission, but are frequently offset to clumps identified at similar resolution in 850 Delta *mm continuum emission. Wide line widths in the Oph B2 sub-Core indicate that non-thermal motions dominate the Core kinematics, and remain transonic at densities n ~ 3 X 105 cm-3 with large scatter and no trend with N(H2). In contrast, non-thermal motions in Oph B1 and B3 are subsonic with little variation, but also show no trend with H2 column density. Over all of Oph B, non-thermal N2H+ line widths are substantially narrower than those traced by NH3, making it unlikely NH3 and N2H+ trace the same material, but the v LSR of both species agree well. We find evidence for accretion in Oph B1 from the surrounding ambient gas. The NH3/N2H+ abundance ratio is larger toward starless Oph B1 than toward protostellar Oph B2, similar to recent observational results in other star-forming regions. The interferometer observations reveal small-scale structure in N2H+ 1-0 emission, which are again offset from continuum emission. No interferometric N2H+ emission peaks were found to be coincident with continuum clumps. In particular, the ~1 M B2-MM8 clump is associated with an N2H+ emission minimum and surrounded by a broken ring-like N2H+ emission structure, suggestive of N2H+ depletion. We find a strong general trend of decreasing N2H+ abundance with increasing N(H2) in Oph B which matches that found for NH3.
Understanding the early stages of star formation is a research field of ongoing development, both theoretically and observationally. In this context, molecular data have been continuously providing ...observational constraints on the gas dynamics at different excitation conditions and depths in the sources. We have investigated the Barnard 59 core, the only active site of star formation in the Pipe Nebula, to achieve a comprehensive view of the kinematic properties of the source. This information was derived by simultaneously fitting ammonia inversion transition lines (1, 1) and (2, 2). Our analysis unveils the imprint of protostellar feedback, such as increasing line widths, temperature, and turbulent motions in our molecular data. Combined with complementary observations of dust thermal emission, we estimate that the core is gravitationally bound following a virial analysis. If the core is not contracting, another source of internal pressure, most likely the magnetic field, is supporting it against gravitational collapse and limits its star formation efficiency.
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