arXiv subjects

Mika Juvela

Publications and source records attributed to Mika Juvela.

At least 91 records · Page 5Linked to original sources

arXiv2019

Multi-scale analysis of the Monoceros OB 1 star-forming region: I. The dense core population

Current theories and models attempt to explain star formation globally, from core scales to giant molecular cloud scales. A multi-scale observational characterisation of an entire molecular complex is necessary to constrain them. We investigate star formation in G202.3+2.5, a ~10x3 pc sub-region of the Monoceros OB1 cloud with a complex morphology harbouring interconnected filamentary structures. We aim to connect the evolution of cores and filaments in G202.3+2.5 with the global evolution of the cloud and to identify the engines of the cloud dynamics. In this first paper, the star formation activity is evaluated by surveying the distributions of dense cores and protostars, and their evolutionary state, as characterised using both infrared observations from the Herschel and WISE telescopes and molecular line observations with the IRAM 30-m telescope. We find ongoing star formation in the whole cloud, with a local peak in star formation activity around the centre of G202.3+2.5 where a chain of massive cores (10-50 Msun) forms a massive ridge (>150 Msun). All evolutionary stages from starless cores to Class II protostars are found in G202.3+2.5, including a possibly starless, large column density (8x10^{22} cm-2), and massive (52 Msun) core. All the core-scale observables examined in this paper point to an enhanced star formation activity centred on the junction between the three main branches of the ramified structure of G202.3+2.5. This suggests that the increased star-formation activity results from the convergence of these branches. To further investigate the origin of this enhancement, it is now necessary to extend the analysis to larger scales, in order to examine the relationship between cores, filaments and their environment. We address these points through the analysis of the dynamics of G202.3+2.5 in a joint paper.

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arXiv2019

Synthetic observations of dust emission and polarisation of Galactic cold clumps

The Planck Catalogue of Galactic Cold Clumps (PGCC) contains over 13000 sources detected based on their cold dust signature. They are believed to consist of a mixture of quiescent, pre-stellar, and already star-forming objects. We extracted PGCC-type objects from cloud simulations and examined their physical and polarisation properties. The comparison with the PGCC catalogue helps to characterise the PGCC sample and provides valuable tests for numerical simulations of interstellar medium. We used several MHD snapshots to define the density field of our models. Sub-millimetre images of the surface brightness and polarisation were obtained with radiative transfer calculations. We examined the statistics of synthetic cold clump catalogues and examined the variations of the clump polarisation fraction p. The clump sizes, aspect ratios, and temperatures in the synthetic catalogue are similar to the PGCC. The fluxes and column densities are smaller by a factor of a few. Rather than with an increased dust opacity, this could be explained by increasing the average column density of the models by a factor of two to three, close to N(H2)= 10^22 cm-2. When the line of sight is parallel to the mean magnetic field, the polarisation fraction tends to increase towards the clump centres, contrary to observations. When the field is perpendicular, the polarisation fraction tends to decrease towards the clumps, but the drop in $p$ is small (e.g. from p~8% to p~7%). Magnetic field geometry reduces the polarisation fraction in the simulated clumps by only Δp~1% on average. The larger drop seen towards the actual PGCC clumps suggests some loss of grain alignment in the dense medium, such as predicted by the radiative torque mechanism. The statistical study is not able to quantify dust opacity changes at the scale of the PGCC clumps.

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arXiv2019

Magnetic fields in the infrared dark cloud G34.43+0.24

We present the B-fields mapped in IRDC G34.43+0.24 using 850\,$μ$m polarized dust emission observed with the POL-2 instrument at JCMT. We examine the magnetic field geometries and strengths in the northern, central, and southern regions of the filament. The overall field geometry is ordered and aligned closely perpendicular to the filament's main axis, particularly in regions containing the central clumps MM1 and MM2, whereas MM3 in the north has field orientations aligned with its major axis. The overall field orientations are uniform at large (POL-2 at 14$\arcsec$ and SHARP at 10$\arcsec$) to small scales (TADPOL at 2.5$\arcsec$ and SMA at 1.5$\arcsec$) in the MM1 and MM2 regions. SHARP/CSO observations in MM3 at 350\,$μ$m from Tang et al. show a similar trend as seen in our POL-2 observations. TADPOL observations demonstrate a well-defined field geometry in MM1/MM2 consistent with MHD simulations of accreting filaments. We obtained a plane-of-sky magnetic field strength of 470$\pm$190\,$μ$G, 100$\pm$40\,$μ$G, and 60$\pm$34\,$μ$G in the central, northern and southern regions of G34, respectively, using the updated Davis-Chandrasekhar-Fermi relation. The estimated value of field strength, combined with column density and velocity dispersion values available in the literature, suggests G34 to be marginally critical with criticality parameter $\rm λ$ values 0.8$\pm$0.4, 1.1$\pm$0.8, and 0.9$\pm$0.5 in the central, northern, and southern regions, respectively. The turbulent motions in G34 are sub-Alfvénic with Alfvénic Mach numbers of 0.34$\pm$0.13, 0.53$\pm$0.30, and 0.49$\pm$0.26 in the three regions. The observed aligned B-fields in G34.43+0.24 are consistent with theoretical models suggesting that B-fields play an important role in guiding the contraction of the cloud driven by gravity.

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arXiv2019

First Sub-pc Sale Mapping of Magnetic Fields in the Vicinity of a Very Low Luminosity Object, L1521F-IRS

L1521F is found to be forming multiple cores and it is cited as an example of the densest core with an embedded VeLLO in a highly dynamical environment. We present the core-scale magnetic fields (B-fields) in the near vicinity of the VeLLO L1521F-IRS using submm polarization measurements at 850$~μ$m using JCMT POL-2. This is the first attempt to use high-sensitivity observations to map the sub-parsec scale B-fields in a core with a VeLLO. The B-fields are ordered and very well connected to the parsec-scale field geometry seen in our earlier optical polarization observations and the large-scale structure seen in Planck dust polarization. The core scale B-field strength estimated using Davis-Chandrasekhar-Fermi relation is $\rm 330\pm100~μ$G which is more than ten times of the value we obtained in the envelope (envelope in this paper is "core envelope"). This indicates that B-fields are getting stronger on smaller scales. The magnetic energies are found to be 1 to 2 orders of magnitude higher than non-thermal kinetic energies in the envelope and core. This suggests that magnetic fields are more important than turbulence in the energy budget of L1521F. The mass-to-flux ratio of 2.3$\pm$0.7 suggests that the core is magnetically-supercritical. The degree of polarization is steadily decreasing towards the denser part of the core with a power law slope of -0.86.

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arXiv2019

Galactic continuum surveys with the new 850 micron MKID camera at the EAO/JCMT 15-m telescope

This white paper gives a brief summary of Galactic continuum surveys with the next generation 850 micron camera at the James Clerk Maxwell Telescope (JCMT) in the next decade. This new camera will have mapping speeds at least 10-20 times faster than the present SCUBA-2 camera, and will enable deep (<10 mJy/beam) and extensive continuum surveys such as a wider (-5 deg.<l<240 deg., |b|<2-5 deg.) Galactic Plane survey, a larger Gould Belt survey, and a follow-up survey of all Planck compact objects visible from the northern hemisphere. These surveys will provide a complete census of molecular clouds, filaments, and dense cores across the Galaxy, vital for studying star formation in various environments.

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arXiv2019

Cloud G074.11+00.11: a stellar cluster in formation

We present molecular line and dust continuum observations of a Planck-detected cold cloud, G074.11+00.11. The cloud consists of a system of curved filaments and a central star-forming clump. The clump is associated with several infrared sources and H2O maser emission. We aim to determine the mass distribution and gas dynamics within the clump, to investigate if the filamentary structure seen around the clump repeats itself on a smaller scale, and to estimate the fractions of mass contained in dense cores and filaments. The velocity distribution of pristine dense gas can be used to investigate the global dynamical state of the clump, the role of filamentary inflows, filament fragmentation and core accretion. We use molecular line and continuum observations from single dish observatories and interferometric facilities to study the kinematics of the region. The molecular line observations show that the central clump may have formed as a result of a large-scale filament collision. The central clump contains three compact cores. Assuming a distance of 2.3 kpc, based on Gaia observations and a three-dimensional extinction method of background stars, the mass of the central clump exceeds 700 solar masses, which is roughly 25% of the total mass of the cloud. Our virial analysis suggests that the central clump and all identified substructures are collapsing. We find no evidence for small-scale filaments associated with the cores. Our observations indicate that the clump is fragmented into three cores with masses in the range [10,50] solar masses and that all three are collapsing. The presence of an H2O maser emission suggests active star formation. However, the CO lines show only weak signs of outflows. We suggest that the region is young and any processes leading to star formation have just recently begun.

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arXiv2019

Submillimeter continuum variability in Planck Galactic cold clumps

In the early stages of star formation, a protostar is deeply embedded in an optically thick envelope such that it is not directly observable. Variations in the protostellar accretion rate, however, will cause luminosity changes that are reprocessed by the surrounding envelope and are observable at submillimeter wavelengths. We searched for submillimeter flux variability toward 12 Planck Galactic Cold Clumps detected by the James Clerk Maxwell Telescope (JCMT)-SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE) survey. These observations were conducted at 850 um using the JCMT/SCUBA-2. Each field was observed three times over about 14 months between 2016 April and 2017 June. We applied a relative flux calibration and achieved a calibration uncertainty of ~ 3.6% on average. We identified 136 clumps across 12 fields and detected four sources with flux variations of ~ 30%. For three of these sources, the variations appear to be primarily due to large-scale contamination, leaving one plausible candidate. The flux change of the candidate may be associated with low- or intermediate-mass star formation assuming a distance of 1.5 kpc, although we cannot completely rule out the possibility that it is a random deviation. Further studies with dedicated monitoring would provide a better understanding of the detailed relationship between submillimeter flux and accretion rate variabilities while enhancing the search for variability in star-forming clumps farther away than the Gould Belt.

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arXiv2018

Compressed magnetic field in the magnetically-regulated global collapsing clump of G9.62+0.19

How stellar feedback from high-mass stars (e.g., H{\sc ii} regions) influences the surrounding interstellar medium and regulates new star formation is still unclear. To address this question, we observed the G9.62+0.19 complex in 850 $μ$m continuum with the JCMT/POL-2 polarimeter. An ordered magnetic field has been discovered in its youngest clump, the G9.62 clump. The magnetic field strength is determined to be $\sim$1 mG. Magnetic field plays a larger role than turbulence in supporting the clump. However, the G9.62 clump is still unstable against gravitational collapse even if thermal, turbulent, and magnetic field support are taken into account all together. The magnetic field segments in the outskirts of the G9.62 clump seem to point toward the clump center, resembling a dragged-in morphology, indicating that the clump is likely undergoing magnetically-regulated global collapse. However, The magnetic field in its central region is aligned with the shells of the photodissociation regions (PDRs) and is approximately parallel to the ionization (or shock) front, indicating that the magnetic field therein is likely compressed by the expanding H{\sc ii} regions that formed in the same complex.

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arXiv2018

Dust polarisation studies on MHD simulations of molecular clouds: methods comparison for the relative orientations analysis

Context. Polarized dust emission can be used as a probe for magnetic fields at different scales. In particular, the analysis of the relative orientation between the density structures and the magnetic field projected on the plane of the sky can provide information on the role of magnetic fields in shaping the structure of molecular clouds. Aims. The relative orientation has been investigated using different methods. Our goal is to explicitly compare two of them: the Rolling Hough Transform (RHT) and the gradient technique. Methods. We have applied the RHT method and the gradient technique to two regions, identified in surface brightness maps at 353 GHz generated via MHD simulations post-processed using radiative transfer modelling. For both methods we have derived the relative orientation between the magnetic field and the density structures, to which we have applied two different statistics, the histogram of relative orientation (HRO) statistic and the projected Rayleigh statistic (PRS). Results. The samples of pixels selected by each method are substantially different. When the methods are applied to the same pixel selection, the results in terms of relative orientation as a function of column density are consistent between each other. When each method is applied to its own pixel selection, the differences are apparent. In Region 1, the RHT method roughly reproduces the observed trend of the relative orientation becoming more perpendicular for increasing column density, while the gradient method, applied at the same resolution as RHT, gives the opposite trend, with the relative orientation moving towards a more parallel alignment. In Region 2, the situation is reversed. The inconsistent results, which are due to the different pixel selections operated by the methods and to the intrinsic differences between them, provide complementary valuable information. Abridged.

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arXiv2018

Dust spectrum and polarisation at 850 um in the massive IRDC G035.39-00.33

The dust sub-millimetre polarisation of star-forming clouds carries information on dust and the role of magnetic fields in cloud evolution. With observations of a dense filamentary cloud G035.39-00.33, we aim to characterise the dust emission properties and the variations of the polarisation fraction. JCMT SCUBA-2/POL-2 data at 850um are combined with Planck 850um (353GHz) data to map polarisation fractions. With previous SCUBA-2 observations (450um and 850um) and Herschel data, the column densities are determined via modified blackbody fits and via radiative transfer modelling. Models are constructed to examine how the polarisation angles and fractions depend on potential magnetic field geometries and grain alignment. POL-2 data show clear changes in the magnetic field orientation. The filament has a peak column density of N(H2)~7 10^22 cm-2, a minimum dust temperature of T~12 K, and a mass of some 4300Msun for the area N(H2)> 5 10^21 cm-2. The estimated average value of the dust opacity spectral index is beta ~ 1.9. The ratio of sub-millimetre and J band optical depths is tau(250 um)/tau(J) ~ 2.5 10^-3, more than four times the typical values for diffuse medium. The polarisation fraction decreases as a function of column density to p ~ 1% in the central filament. Because of noise, the observed decrease of p(N) is significant only at N(H2)>2 10^22 cm-2. The observations suggest that the grain alignment is not constant. Although the data can be explained with a complete loss of alignment at densities above ~ 10^4 cm-3 or using the predictions of radiative torques alignment, the uncertainty of the field geometry and the spatial filtering of the SCUBA-2 data prevent strong conclusions. G035.39-00.33 shows strong signs of dust evolution and the low polarisation fraction is suggestive of a loss of polarised emission from its densest parts.

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arXiv2018

A holistic perspective on the dynamics of G035.39-00.33: the interplay between gas and magnetic fields

Magnetic field is one of the key agents that play a crucial role in shaping molecular clouds and regulating star formation, yet the complete information on the magnetic field is not well constrained due to the limitations in observations. We study the magnetic field in the massive infrared dark cloud G035.39-00.33 from dust continuum polarization observations at 850 $\micron$ with SCUBA-2/POL-2 at JCMT. The magnetic field tends to be perpendicular to the densest part of the main filament (F$_{M}$), whereas it has a less defined relative orientation in the rest of the structure, where it tends to be parallel to some diffuse regions. A mean plane-of-the-sky magnetic field strength of $\sim$50 $μ$G for F$_{M}$ is obtained using Davis-Chandrasekhar-Fermi method. Based on $^{13}$CO (1-0) line observations, we suggest a formation scenario of F$_{M}$ due to large-scale ($\sim$10 pc) cloud-cloud collision. Using additional NH$_3$ line data, we estimate that F$_{M}$ will be gravitationally unstable if it is only supported by thermal pressure and turbulence. The northern part of F$_{M}$, however, can be stabilized by a modest additional support from the local magnetic field. The middle and southern parts of F$_{M}$ are likely unstable even if the magnetic field support is taken into account. We claim that the clumps in F$_{M}$ may be supported by turbulence and magnetic fields against gravitational collapse. Finally, we identified for the first time a massive ($\sim$200 M$_{\sun}$), collapsing starless clump candidate, "c8", in G035.39-00.33. The magnetic field surrounding "c8" is likely pinched, hinting at an accretion flow along the filament.

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arXiv2018

The supernova-regulated ISM. IV. A comparison of simulated polarization with Planck observations

The efforts for comparing dust polarization measurements with synthetic observations from MHD models have previously concentrated on the scale of molecular clouds. Here we extend the model comparisons to kiloparsec scales, taking into account hot shocked gas generated by supernovae, and a non-uniform dynamo-generated magnetic field at both large and small scales down to 4 pc spatial resolution. Radiative transfer calculations are used to model dust emission and polarization on the top of MHD simulations. We compute synthetic maps of column density $N_H$, polarization fraction $p$, and polarization angle dispersion $S$, and study their dependencies on the important properties of the MHD simulations. These include the large-scale magnetic field and its orientation, the small-scale magnetic field, and supernova-driven shocks. Similar filament-like structures of $S$ as seen in the Planck all-sky maps are visible in our synthetic results, although the smallest scale structures are absent from our maps. Supernova-driven shock fronts and $S$ do not show significant correlation. Instead, $S$ can clearly be attributed to the distribution of the small-scale magnetic field. We also find that the large-scale magnetic field influences the polarization properties, such that, for a given strength of magnetic fluctuation, a strong plane-of-the-sky mean field weakens the observed $S$, while strengthening $p$. The anticorrelation of $p$ and $S$, and decreasing $p$ as a function of $N_H$ are consistent across all synthetic observations. The magnetic fluctuations follow an exponential distribution, rather than Gaussian, characteristic of flows with intermittent repetitive shocks. The observed polarization properties and column densities are sensitive to the line of sight distance over which the emission is integrated.

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arXiv2018

Planck Cold Clumps in the $λ$ Orionis complex. II. Environmental effects on core formation

Based on the 850 $μ$m dust continuum data from SCUBA-2 at James Clerk Maxwell Telescope (JCMT), we compare overall properties of Planck Galactic Cold Clumps (PGCCs) in the $λ$ Orionis cloud to those of PGCCs in the Orion A and B clouds. The Orion A and B clouds are well known active star-forming regions, while the $λ$ Orionis cloud has a different environment as a consequence of the interaction with a prominent OB association and a giant Hii region. PGCCs in the $λ$ Orionis cloud have higher dust temperatures ($Td=16.13\pm0.15$ K) and lower values of dust emissivity spectral index ($ β=1.65\pm0.02$) than PGCCs in the Orion A (Td=13.79$\pm 0.21$K, $β=2.07\pm0.03$) and Orion B ($Td=13.82\pm0.19$K, $β=1.96\pm0.02$) clouds. We find 119 sub-structures within the 40 detected PGCCs and identify them as cores. Of total 119 cores, 15 cores are discovered in the $λ$ Orionis cloud, while 74 and 30 cores are found in the Orion A and B clouds, respectively. The cores in the $λ$ Orionis cloud show much lower mean values of size R=0.08 pc, column density N(H2)=$(9.5\pm1.2) \times 10^{22}$ cm$^{-2}$, number density n(H2)=$(2.9 \pm 0.4)\times10^{5}$ cm$^{-3}$, and mass $M_{core}$=$1.0\pm0.3$ M$_{\odot}$ compared to the cores in the Orion A (R=0.11pc, $N(H2)=(2.3\pm0.3) \times 10^{23}$ cm$^{-2}$, n(H2)=$(3.8\pm0.5) \times 10^{5}$cm$^{-3}$, and $M_{core}$=$2.4 \pm 0.3$ M$_{\odot}$) and Orion B (R=0.16pc, N(H2)=$(3.8 \pm 0.4) \times 10^{23}$cm$^{-2}$, n(H2)=$(15.6\pm1.8)\times10^{5}$ cm$^{-3}$, and $M_{core}$= $2.7\pm0.3$ M$_{\odot}$) clouds. These core properties in the $λ$ Orionis cloud can be attributed to the photodissociation and external heating by the nearby Hii region, which may prevent the PGCCs from forming gravitationally bound structures and eventually disperse them. These results support the idea of negative stellar feedback on core formation.

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arXiv2018

The TOP-SCOPE survey of PGCCs: PMO and SCUBA-2 observations of 64 PGCCs in the 2nd Galactic Quadrant

In order to understand the initial conditions and early evolution of star formation in a wide range of Galactic environments, we carried out an investigation of 64 \textit{Planck} Galactic Cold Clumps (PGCCs) in the second quadrant of the Milky Way. Using the $^{13}$CO and C$^{18}$O $J = 1 - 0$ lines, and 850\,$μ$m continuum observations, we investigated cloud fragmentation and evolution associated with star formation. We extracted 468 clumps and 117 cores from the $^{13}$CO line and 850\,$μ$m continuum maps, respectively. We make use of the Bayesian Distance Calculator and derived the distances of all 64 PGCCs. We found that in general, the mass-size plane follows a relation of $m\sim r^{1.67}$. At a given scale, the masses of our objects are around 1/10 of that of typical Galactic massive star-forming regions. Analysis of the clump and core masses, virial parameters, densities, and mass-size relation suggests that the PGCCs in our sample have a low core formation efficiency ($\sim$3.0\%), and most PGCCs are likely low-mass star-forming candidates. Statistical study indicates that the 850\,$μ$m cores are more turbulent, more optically thick, and denser than the $^{13}$CO clumps for star formation candidates, suggesting that the 850\,$μ$m cores are likely more appropriate future star-formation candidates than the $^{13}$CO clumps.

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arXiv2018

Near-infrared scattering as a dust diagnostic

We examine the possibility of using near-infrared scattering to constrain the local radiation field and the dust properties, for example, the size distribution of the grains, and maximum grain size. We use radiative transfer modelling to examine the constraints provided by J, H, and K bands in combination with mid-infrared surface brightness at 3.6 $μ$m. We use a spherical one-dimensional and elliptical three-dimensional cloud models to study the observable effects of different grain size distributions with varying absorption and scattering properties. As an example, we analyse observations of a molecular cloud in Taurus, TMC-1N. The observed surface brightness ratios between the bands change when the dust properties are changed. However, even a small change of 10% in the surface brightness of one channel changes the estimated powerlaw exponent of the size distribution $γ$ by up to ~30% and the estimated strength of the radiation field K_ISRF by up to ~60%. The maximum grain size A_max and $γ$ are always strongly anti-correlated. For example, overestimating the surface brightness by 10% changes the estimated radiation field strength by ~20% and the exponent of the size distribution by ~15%. The analysis of our synthetic observations indicates that the relative uncertainty of the parameter distributions are on average A_max, $γ$ ~25%, and the deviation between the estimated and correct values $Δ$ Q <15%. We show that scattered infrared light can be used to derive meaningful limits for the dust parameters. However, errors in the surface brightness data can result in considerable uncertainties in the derived parameters.

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arXiv2017

Herschel and SCUBA-2 observations of dust emission in a sample of Planck cold clumps

Analysis of all-sky Planck submillimetre observations and the IRAS 100um data has led to the detection of a population of Galactic cold clumps. The clumps can be used to study star formation and dust properties in a wide range of Galactic environments. Our aim is to measure dust spectral energy distribution (SED) variations as a function of the spatial scale and the wavelength. We examine the SEDs at large scales using IRAS, Planck, and Herschel data. At smaller scales, we compare with JCMT/SCUBA-2 850um maps with Herschel data that are filtered using the SCUBA-2 pipeline. Clumps are extracted using the Fellwalker method and their spectra are modelled as modified blackbody functions. According to IRAS and Planck data, most fields have dust colour temperatures T_C ~ 14-18K and opacity spectral index values of beta=1.5-1.9. The clumps/cores identified in SCUBA-2 maps have T~ 13K and similar beta values. There are some indications of the dust emission spectrum becoming flatter at wavelengths longer than 500um. In fits involving Planck data, the significance is limited by the uncertainty of the corrections for CO line contamination. The fits to the SPIRE data give a median beta value slightly above 1.8. In the joint SPIRE and SCUBA-2 850um fits the value decreases to beta ~1.6. Most of the observed T-beta anticorrelation can be explained by noise. The typical submillimetre opacity spectral index beta of cold clumps is found to be ~1.7. This is above the values of diffuse clouds but lower than in some previous studies of dense clumps. There is only tentative evidence of T-beta anticorrelation and beta decreasing at millimetre wavelengths.

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arXiv2017

The TOP-SCOPE survey of Planck Galactic Cold Clumps: Survey overview and results of an exemplar source, PGCC G26.53+0.17

The low dust temperatures (<14 K) of Planck Galactic Cold Clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. TOP-SCOPE is a joint survey program targeting ~2000 PGCCs in J=1-0 transitions of CO isotopologues and ~1000 PGCCs in 850 micron continuum emisison. The objective of the TOP-SCOPE survey and the joint surveys (SMT 10-m, KVN 21-m and NRO 45-m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, the length and the mean line-mass (M/L) of the G26 filament are ~6200 Msun, ~12 pc and ~500 Msun/pc, respectively. Ten massive clumps including eight starless ones are found along the filament. The most massive Clump as a whole may be still in global collapse while its denser part seems to be undergoing expansion due to outflow feedback. The fragmentation in G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, non-magnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index ($β$) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed due to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.

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arXiv2017

Detection of interstellar ortho-D2H+ with SOFIA

We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 micron) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) onboard the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T<18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of ~500 000 yr for the core, with an uncertainty of ~200 000 yr. The core material has probably been pre-processed for another 500 000 years in conditions corresponding to those in the ambient molecular cloud. The inferred time scale is more than ten times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+para) fractional abundances of ~$10^{-9}$ in the outer envelope. This confirms the central role of H3+ in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D3+ should be abundant in these conditions.

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