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Register a new userInterferometric mapping of magnetic fields: The ALMA view of the massive star forming clump W43-MM1
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Here we present the first results from ALMA observations of 1 mm polarized dust emission towards the W43-MM1 high mass star forming clump. We have detected a highly fragmented filament with source masses ranging from 14Msun to 312Msun, where the largest fragment, source A, is believed to be one of the most massive in our Galaxy. We found a smooth, ordered, and detailed polarization pattern throughout the filament which we used to derived magnetic field morphologies and strengths for 12 out of the 15 fragments detected ranging from 0.2 to 9 mG. The dynamical equilibrium of each fragment was evaluated finding that all the fragments are in a super-critical state which is consistent with previously detected infalling motions towards W43-MM1. Moreover, there are indications suggesting that the field is being dragged by gravity as the whole filament is collapsing.
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We report millimeter interferometric observations of polarized continuum and line emission from the massive star forming region G34.4. Polarized thermal dust emission at 3 mm wavelength and CO $J=1 to 0$ line emission were observed using the Berkeley-Illinois-Maryland Association (BIMA) array. Our results show a remarkably uniform polarization pattern in both dust and in CO J=$1 to 0$ emission. In addition, the line emission presents a consistent uniform polarization pattern over most of the velocity channel maps. These uniform polarization patterns are aligned with the north-south main axis of the filament between the main millimeter source (MM) and the ultra-compact H {scriptsize II} region, which are the central sources in G34.4, suggesting a magnetic field orthogonal to this axis. This morphology is consistent with a magnetically supported disk seen roughly edge-on.
Here we present new ALMA observations of polarized dust emission from six of the most massive clumps in W43-Main. The clumps MM2, MM3, MM4, MM6, MM7, and MM8, have been resolved into two populations of fragmented filaments. From these two populations we extracted 81 cores (96 with the MM1 cores) with masses between 0.9 Msun to 425 Msun and a mass sensitivity of 0.08 M$_{odot}$. The MM6, MM7, and MM8 clumps show significant fragmentation, but the polarized intensity appears to be sparse and compact. The MM2, MM3, and MM4 population shows less fragmentation, but with a single proto-stellar core dominating the emission at each clump. Also, the polarized intensity is more extended and significantly stronger in this population. From the polarized emission, we derived detailed magnetic field patterns throughout the filaments which we used to estimate field strengths for 4 out of the 6 clumps. The average field strengths estimations were found between 500 $mu$G to 1.8 mG. Additionally, we detected and modeled infalling motions towards MM2 and MM3 from single dish HCO$^{+}(J=4 rightarrow 3)$ and HCN$(J=4 rightarrow 3)$ data resulting in mass infall rates of $dot{mathrm{M}}_{mathrm{MM2}} = 1.2 times 10^{-2}$ Msun yr$^{-1}$ and $dot{mathrm{M}}_{mathrm{MM3}} = 6.3 times 10^{-3}$ Msun yr$^{-1}$. By using our estimations, we evaluated the dynamical equilibrium of our cores by computing the total virial parameter $alpha_{mathrm{total}}$. For the cores with reliable field estimations, we found that 71% of them appear to be gravitationally bound while the remaining 29% are not. We concluded that these unbound cores, also less massive, are still accreting and have not yet reached a critical mass. This also implies different evolutionary time-scales, which essentially suggests that star-formation in high mass filaments is not uniform.
We present 1.3 mm ALMA dust polarization observations at a resolution of $sim$0.02 pc of three massive molecular clumps, MM1, MM4, and MM9, in the infrared dark cloud G28.34+0.06. With the sensitive and high-resolution continuum data, MM1 is resolved into a cluster of condensations. The magnetic field structure in each clump is revealed by the polarized emission. We found a trend of decreasing polarized emission fraction with increasing Stokes $I$ intensities in MM1 and MM4. Using the angular dispersion function method (a modified Davis-Chandrasekhar-Fermi method), the plane-of-sky magnetic field strength in two massive dense cores, MM1-Core1 and MM4-Core4, are estimated to be $sim$1.6 mG and $sim$0.32 mG, respectively. textbf{The ordered magnetic energy is found to be smaller than the turbulent energy in the two cores, while the total magnetic energy is found to be comparable to the turbulent energy.} The total virial parameters in MM1-Core1 and MM4-Core4 are calculated to be $sim$0.76 and $sim$0.37, respectively, suggesting that massive star formation does not start in equilibrium. Using the polarization-intensity gradient-local gravity method, we found that the local gravity is closely aligned with intensity gradient in the three clumps, and the magnetic field tends to be aligned with the local gravity in MM1 and MM4 except for regions near the emission peak, which suggests that the gravity plays a dominant role in regulating the gas collapse. Half of the outflows in MM4 and MM9 are found to be aligned within 10$^{circ}$ of the condensation-scale ($<$0.05 pc) magnetic field, indicating that the magnetic field could play an important role from condensation to disk scale in the early stage of massive star formation. We also found that the fragmentation in MM1-Core1 cannot be solely explained by thermal Jeans fragmentation or turbulent Jeans fragmentation.
We mapped the kinetic temperature structure of two massive star-forming regions, N113 and N159W, in the Large Magellanic Cloud (LMC). We have used $sim$1hbox{$,.!!^{primeprime}$}6,($sim$0.4,pc) resolution measurements of the para-H$_2$CO,$J_{rm K_ aK_c}$,=,3$_{03}$--2$_{02}$, 3$_{22}$--2$_{21}$, and 3$_{21}$--2$_{20}$ transitions near 218.5,GHz to constrain RADEX non-LTE models of the physical conditions. The gas kinetic temperatures derived from the para-H$_2$CO line ratios 3$_{22}$--2$_{21}$/3$_{03}$--2$_{02}$ and 3$_{21}$--2$_{20}$/3$_{03}$--2$_{02}$ range from 28 to 105,K in N113 and 29 to 68,K in N159W. Distributions of the dense gas traced by para-H$_2$CO agree with those of the 1.3,mm dust and emph{Spitzer},8.0,$mu$m emission, but do not significantly correlate with the H$alpha$ emission. The high kinetic temperatures ($T_{rm kin}$,$gtrsim$,50,K) of the dense gas traced by para-H$_2$CO appear to be correlated with the embedded infrared sources inside the clouds and/or YSOs in the N113 and N159W regions. The lower temperatures ($T_{rm kin}$,$<$,50,K) are measured at the outskirts of the H$_2$CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H$_2$CO are weakly affected by the external sources of the H$alpha$ emission. The non-thermal velocity dispersions of para-H$_2$CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H$_2$CO is related to turbulence on a $sim$0.4,pc scale. The dense gas heating appears to be dominated by internal star formation activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regions in the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane.
It has been proposed that the magnetic field, pervasive in the ISM, plays an important role in the process of massive star formation. To better understand its impact at the pre and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. To this end, we used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of $sim$2700 au in the massive protocluster W43-MM1. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows determined from CO molecular line emission, and of the major axis of the dense cores determined from 2D Gaussian fit in the continuum emission. We found that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20-50$^deg$ with respect to the magnetic field. The outflows could be oriented 50-70$^deg$ with respect to the magnetic field, or randomly oriented with respect to the magnetic field, similar to current results in low-mass star-forming regions. In conclusion, the observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20-50$^deg$ preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.
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