[en] Recent measurements of the Zeeman effect in dark-cloud cores provide important tests for theories of cloud dynamics and prestellar core formation. In this Letter, we report results of simulated Zeeman measurements, based on radiative transfer calculations through a snapshot of a simulation of supersonic and super-Alfvenic turbulence. We have previously shown that the same simulation yields a relative mass-to-flux ratio (core versus envelope) in agreement with the observations (and in contradiction with the ambipolar-drift model of core formation). Here, we show that the mass-to-flux and turbulent-to-magnetic-energy ratios in the simulated cores agree with the observed values as well. The mean magnetic field strength in the simulation is very low, B-bar=0.34 μG, presumably lower than the mean field in molecular clouds. Nonetheless, high magnetic field values are found in dense cores, in agreement with the observations (the rms field, amplified by the turbulence, is B_rms = 3.05 μG). We conclude that a strong large-scale mean magnetic field is not required by Zeeman effect measurements to date, although it is not ruled out by this work.

[en] Is the turbulence in cluster-forming regions internally driven by stellar outflows or the consequence of a large-scale turbulent cascade? We address this question by studying the turbulent energy spectrum in NGC 1333. Using synthetic ¹³CO maps computed with a snapshot of a supersonic turbulence simulation, we show that the velocity coordinate spectrum method of Lazarian and Pogosyan provides an accurate estimate of the turbulent energy spectrum. We then apply this method to the ¹³CO map of NGC 1333 from the COMPLETE database. We find that the turbulent energy spectrum is a power law, E(k) ∝ k ^-β, in the range of scales 0.06 pc ≤l ≤ 1.5 pc, with slope β = 1.85 ± 0.04. The estimated energy injection scale of stellar outflows in NGC 1333 is l_inj ∼ 0.3 pc, well resolved by the observations. There is no evidence of the flattening of the energy spectrum above the scale l_inj predicted by outflow-driven simulations and analytical models. The power spectrum of integrated intensity is also a nearly perfect power law in the range of scales 0.16 pc < l< 7.9 pc, with no feature above l_inj. We conclude that the observed turbulence in NGC 1333 does not appear to be driven primarily by stellar outflows.

[en] We report on the detection of the ground-state rotational line of ortho-D₂H⁺ at 1.477 THz (203 μm) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) on board 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 ∼5 × 10⁵ yr for the core, with an uncertainty of ∼2 × 10⁵ yr. The core material has probably been pre-processed for another 5 × 10⁵ years in conditions corresponding to those in the ambient molecular cloud. The inferred timescale is more than 10 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 ${\mathrm{H}}_3^{+}$ in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also ${\mathrm{D}}_3^{+}$ should be abundant in these conditions.

[en] We present a comparison of molecular clouds (MCs) from a simulation of supernova (SN) driven interstellar medium (ISM) turbulence with real MCs from the Outer Galaxy Survey. The radiative transfer calculations to compute synthetic CO spectra are carried out assuming that the CO relative abundance depends only on gas density, according to four different models. Synthetic MCs are selected above a threshold brightness temperature value, T _B,min = 1.4 K, of the J = 1 − 0 ¹²CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousands MCs. The comparison with the observations focuses on the mass and size distributions and on the velocity–size and mass–size Larson relations. The mass and size distributions are found to be consistent with the observations, with no significant variations with spatial resolution or chemical model, except in the case of the unrealistic model with constant CO abundance. The velocity–size relation is slightly too steep for some of the models, while the mass–size relation is a bit too shallow for all models only at a spatial resolution dx ≈ 1 pc. The normalizations of the Larson relations show a clear dependence on spatial resolution, for both the synthetic and the real MCs. The comparison of the velocity–size normalization suggests that the SN rate in the Perseus arm is approximately 70% or less of the rate adopted in the simulation. Overall, the realistic properties of the synthetic clouds confirm that SN-driven turbulence can explain the origin and dynamics of MCs.

[en] We have used high-resolution (∼2.''3) observations of the local (D_L = 46 Mpc) luminous infrared galaxy Arp 299 to map out the physical properties of the molecular gas that provides the fuel for its extreme star formation activity. The ¹²CO J = 3-2, ¹²CO J = 2-1, and ¹³CO J = 2-1 lines were observed with the Submillimeter Array, and the short spacings of the ¹²CO J = 2-1 and J = 3-2 observations have been recovered using the James Clerk Maxwell Telescope single dish observations. We use the radiative transfer code RADEX to estimate the physical properties (density, column density, and temperature) of the different regions in this system. The RADEX solutions of the two galaxy nuclei, IC 694 and NGC 3690, are consistent with a wide range of gas components, from warm moderately dense gas with T_kin > 30 K and n(H₂) ∼ 0.3-3 × 10³ cm^–3 to cold dense gas with T_kin ∼ 10-30 K and n(H₂) > 3 × 10³ cm^–3. The overlap region is shown to have a better constrained solution with T_kin ∼ 10-50 K and n(H₂) ∼ 1-30 × 10³ cm^–3. We estimate the gas masses and star formation rates of each region in order to derive molecular gas depletion times. The depletion times of all regions (20-50 Myr) are found to be about two orders of magnitude lower than those of normal spiral galaxies. This rapid depletion time can probably be explained by a high fraction of dense gas on kiloparsec scales in Arp 299. We estimate the CO-to-H₂ factor, α_co to be 0.4 ± 0.3(3 × 10^–4/x_CO) M_☉ (K km s^–1 pc²)^–1 for the overlap region. This value agrees well with values determined previously for more advanced merger systems.

[en] We present Atacama Large Millimeter/submillimeter Array maps of the starless molecular cloud core Ophiuchus/H-MM1 in the lines of deuterated ammonia (ortho-${\mathrm{N}\mathrm{H}}_2\mathrm{D}$), methanol (${\mathrm{C}\mathrm{H}}_3\mathrm{O}\mathrm{H}$), and sulfur monoxide (SO). The dense core is seen in ${\mathrm{N}\mathrm{H}}_2\mathrm{D}$ emission, whereas the ${\mathrm{C}\mathrm{H}}_3\mathrm{O}\mathrm{H}$ and SO distributions form a halo surrounding the core. Because methanol is formed on grain surfaces, its emission highlights regions where desorption from grains is particularly efficient. Methanol and sulfur monoxide are most abundant in a narrow zone that follows the eastern side of the core. This side is sheltered from the stronger external radiation field coming from the west. We show that photodissociation on the illuminated side can give rise to an asymmetric methanol distribution but that the stark contrast observed in H-MM1 is hard to explain without assuming enhanced desorption on the shaded side. The region of the brightest emission has a wavy structure that rolls up at one end. This is the signature of Kelvin–Helmholtz instability occurring in sheared flows. We suggest that in this zone, methanol and sulfur are released as a result of grain–grain collisions induced by shear vorticity.

[en] We present high-resolution (∼2.''5) observations of ¹²CO J = 6-5 toward the luminous infrared galaxy VV 114 using the Submillimeter Array. We detect ¹²CO J = 6-5 emission from the eastern nucleus of VV 114 but do not detect the western nucleus or the central region. We combine the new ¹²CO J = 6-5 observations with previously published or archival low-J CO observations, which include ¹³CO J = 1-0 Atacama Large Millimeter/submillimeter Array cycle 0 observations, to analyze the beam-averaged physical conditions of the molecular gas in the eastern nucleus. We use the radiative transfer code RADEX and a Bayesian likelihood code to constrain the temperature (T_kin), density (n_H2), and column density (N_¹²CO) of the molecular gas. We find that the most probable scenario for the eastern nucleus is a cold (T_kin = 38 K), moderately dense (n_H2 = 10^2.89 cm^–3) molecular gas component. We find that the most probable ¹²CO to ¹³CO abundance ratio ([¹²CO]/[¹³CO]) is 229, which is roughly three times higher than the Milky Way value. This high abundance ratio may explain the observed high ¹²CO/ ¹³CO line ratio (>25). The unusual ¹³CO J = 2-1/J = 1-0 line ratio of 0.6 is produced by a combination of moderate ¹³CO optical depths (τ = 0.4-1.1) and extremely subthermal excitation temperatures. We measure the CO-to-H₂ conversion factor, α_CO, to be 0.5^+0.6_-0.3 M_☉ (K km s^–1 pc²)^–1, which agrees with the widely used factor for ultra luminous infrared galaxies of Downes and Solomon (α_CO = 0.8 M_☉ (K km s^–1 pc²)^–1)

[en] We present the results of on-the-fly mapping observations of 44 fields containing 107 SCUBA-2 cores in the emission lines of molecules N₂H⁺, HC₃N, and CCS at 82–94 GHz using the Nobeyama 45 m telescope. This study aimed at investigating the physical properties of cores that show high deuterium fractions and might be close to the onset of star formation. We found that the distributions of the N₂H⁺ and HC₃N line emissions are approximately similar to the distribution of the 850 μm dust continuum emission, whereas the CCS line emission is often undetected or is distributed in a clumpy structure surrounding the peak position of the 850 μm dust continuum emission. Occasionally (12%), we observe CCS emission, which is an early-type gas tracer toward the young stellar object, probably due to local high excitation. Evolution toward star formation does not immediately affect the nonthermal velocity dispersion.

[en] We observed 146 Galactic clumps in HCN (4-3) and CS (7-6) with the Atacama Submillimeter Telescope Experiment 10 m telescope. A tight linear relationship between star formation rate and gas mass traced by dust continuum emission was found for both Galactic clumps and the high redshift (z > 1) star forming galaxies (SFGs), indicating a constant gas depletion time of ∼100 Myr for molecular gas in both Galactic clumps and high z SFGs. However, low z galaxies do not follow this relation and seem to have a longer global gas depletion time. The correlations between total infrared luminosities (L _TIR) and molecular line luminosities $(L_{\mathrm{m}\mathrm{o}\mathrm{l}}^{\mathrm{\prime <!--\; ???\; -->}})$ of HCN (4-3) and CS (7-6) are tight and sublinear extending down to clumps with L _TIR ∼ 10³ L _☉. These correlations become linear when extended to external galaxies. A bimodal behavior in the L _TIR–$L_{\mathrm{m}\mathrm{o}\mathrm{l}}^{\mathrm{\prime <!--\; ???\; -->}}$ correlations was found for clumps with different dust temperature, luminosity-to-mass ratio, and σ _line/σ _vir. Such bimodal behavior may be due to evolutionary effects. The slopes of L _TIR–L′_mol correlations become more shallow as clumps evolve. We compared our results with lower J transition lines in Wu et al. (2010). The correlations between clump masses and line luminosities are close to linear for low effective excitation density tracers but become sublinear for high effective excitation density tracers for clumps with L _TIR larger than L _TIR ∼ 10^4.5 L _☉. High effective excitation density tracers cannot linearly trace the total clump masses, leading to a sublinear correlations for both M _clump–L′_mol and L _TIR–L′_mol relations.

[en] We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the λ Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32–11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound bright-rimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32–11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity (∼0.8 $L_{\odot <!--\; ???\; -->}$) and accretion rate (6.3 × 10⁻⁷ $M_{\odot <!--\; ???\; -->}$ yr⁻¹) when compared with other young Class 0 sources (e.g., PACS Bright Red Sources) in the Orion complex. It has slightly larger internal luminosity (0.21 ± 0.01 $L_{\odot <!--\; ???\; -->}$) and outflow velocity (∼14 km s⁻¹) than the predictions of first hydrostatic cores (FHSCs). G192N might be among the youngest Class 0 sources, which are slightly more evolved than an FHSC. Considering its low internal luminosity (0.08 ± 0.01 $L_{\odot <!--\; ???\; -->}$) and accretion rate (2.8 × 10⁻⁸ $M_{\odot <!--\; ???\; -->}$ yr⁻¹), G192S is an ideal proto-brown dwarf candidate. The star formation efficiency (∼0.3%–0.4%) and core formation efficiency (∼1%) in PGCC G192.32–11.88 are significantly smaller than in other giant molecular clouds or filaments, indicating that the star formation therein is greatly suppressed owing to stellar feedback.