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Register a new userA Very Compact Extremely High Velocity Flow toward MMS 5 / OMC-3 Revealed with ALMA
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Both high- and low-velocity outflows are occasionally observed around a protostar by molecular line emission. The high-velocity component is called `Extremely High-Velocity (EHV) flow, while the low-velocity component is simply referred as `(molecular) outflow. This study reports a newly found EHV flow and outflow around MMS $5$ in the Orion Molecular Cloud 3 observed with ALMA. In the observation, CO $J$=2--1 emission traces both the EHV flow ($|v_{rm{LSR}} - v_{rm{sys}}|$ $simeq$ 50--100 $rm{km s^{-1}}$) and outflow ($|v_{rm{LSR}} - v_{rm{sys}}|$ $simeq$ 10--50 $rm{km s^{-1}}$). On the other hand, SiO $J$=5--4 emission only traces the EHV flow. The EHV flow is collimated and located at the root of the V-shaped outflow. The CO outflow extends up to $sim$ 14,000,AU with a position angle (P.A.) of $sim79^circ$ and the CO redshifted EHV flow extends to $sim$11,000 AU with P.A. $sim96^circ$. The EHV flow is smaller than the outflow, and the dynamical timescale of the EHV flow is shorter than that of the outflow by a factor of $sim 3$. The flow driving mechanism is discussed based on the size, time scale, axis difference between the EHV flow and outflow, and the periodicity of the knots. Our results are consistent with the nested wind scenario, although the jet entrainment scenario could not completely be ruled out.
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Using the Atacama Large Millimeter/submillimeter Array (ALMA), we investigated a peculiar millimeter source MMS 3 located in the Orion Molecular Cloud 3 (OMC-3) region in the 1.3 mm continuum, CO ($J$=2-1), SiO ($J$=5-4), C$^{18}$O ($J$=2-1), N$_2$D$^+$ ($J$=3-2), and DCN ($J$=3-2) emissions. With the ALMA high angular resolution ($sim$0.2), we detected a very compact and highly centrally condensed continuum emission with a size of 0.45 $times$ 0.32 (P.A.=0.22$^circ$). The peak position coincides with the locations of previously reported $Spitzer$/IRAC and X-ray sources within their positional uncertainties. We also detected an envelope with a diameter of $sim$6800 au (P.A.=75$^circ$) in the C$^{18}$O ($J$=2-1) emission. Moreover, a bipolar outflow was detected in the CO ($J$=2-1) emission for the first time. The outflow elongates roughly perpendicular to the long axis of the envelope detected in the C$^{18}$O ($J$=2-1) emission. Compact high-velocity CO gas in the (red-shifted) velocity range of 22-30 km s$^{-1}$, presumably tracing a jet, was detected near the 1.3 mm continuum peak. A compact and faint red-shifted SiO emission was marginally detected on the CO outflow lobe. The physical quantities of the outflow in MMS 3 are relatively smaller than those in other sources in the OMC-3 region. The centrally condensed object associated with the near-infrared and X-ray sources, the flattened envelope, and the faint outflow indicate that MMS 3 harbors a low mass protostar with an age of $sim$10$^3$ yr.
Using the $approx$15km ALMA long baselines, we imaged the Stokes $I$ emission and linearly polarized intensity ($PI$) in the 1.1-mm continuum band of a very young intermediate-mass protostellar source, MMS 6, in the Orion Molecular Cloud-3. The achieved angular resolution, $0.02{times}0.03$ ($approx$10 AU), shows for the first time a wealth of data on the dust emission polarization in the central 200 AU of a protostar. The $PI$ peak is offset to the south-west (SW) by $approx$20 AU with respect to the Stokes $I$ peak. Its polarization degree is 11 % with its $E$-vector orientation of P.A.${approx}135^{circ}$. A partial ring-like structure with a radius of $approx$80 AU is detected in $PI$ but not in the Stokes $I$. NW (north-west) and SE (south-east) parts of the ring are bright with a high polarization degree of $gtrsim$10 %, and their $E$-vector orientations are roughly orthogonal to those observed near the center. We also detected arm-like polarized structures, extending to 1000 AU scale to the north, with the $E$-vectors aligned along the minor axis of the structures. We explored possible origins of the polarized emission comparing with magnetohydrodynamical (MHD) simulations of the toroidal wrapping of the magnetic field. The simulations are consistent with the $PI$ emission in the ring-like and the extended arm-like structures observed with ALMA. However, the current simulations do not completely reproduce observed polarization characteristics in the central 50 AU. Although the self-scattering model can explain the polarization pattern and positional offset between the Stokes $I$ and $PI$, this model is not able to reproduce the observed high degree of polarization.
We present the first detection of the H40a, H34a and H31a radio recombination lines (RRLs) at millimeter wavelengths toward the high-velocity, ionized jet in the Cepheus A HW2 star forming region. From our single-dish and interferometric observations, we find that the measured RRLs show extremely broad asymmetric line profiles with zero-intensity linewidths of ~1100 kms-1. From the linewidths, we estimate a terminal velocity for the ionized gas in the jet of >500 kms-1, consistent with that obtained from the proper motions of the HW2 radio jet. The total integrated line-to-continuum flux ratios of the H40a, H34a and H31a lines are 43, 229 and 280 kms-1, clearly deviating from LTE predictions. These ratios are very similar to those observed for the RRL maser toward MWC349A, suggesting that the intensities of the RRLs toward HW2 are affected by maser emission. Our radiative transfer modeling of the RRLs shows that their asymmetric profiles could be explained by maser emission arising from a bi-conical radio jet with a semi-aperture angle of 18 deg, electron density distribution varying as r^(-2.11) and turbulent and expanding wind velocities of 60 and 500 kms-1.
We have carried out polarization calibration for archival JVLA ($sim$9 mm) full polarization observations towards the Class 0 young stellar object (YSO) OMC-3/MMS 6 (also known as HOPS-87), and then compared with the archival ALMA 1.2 mm observations. We found that the innermost $sim$100 au region of OMC-3/MMS 6 is likely very optically thick (e.g., $taugg$1) at $sim$1 mm wavelength such that the dominant polarization mechanism is dichroic extinction. It is marginally optically thin (e.g., $taulesssim$1) at $sim$9 mm wavelength such that the JVLA observations can directly probe the linearly polarized emission from non-spherical dust. Assuming that the projected long axis of dust grains is aligned perpendicular to magnetic field (B-field) lines, we propose that the overall B-field topology resembles an hourglass shape, while this hourglass appears $sim$40$^{circ}$ inclined with respect to the previously reported outflow axis. The geometry of this system is consistent with a magnetically regulated dense (pseudo-)disk. Based on the observed 29.45 GHz flux density and assuming a dust absorption opacity $kappa^{abs}_{29.45,GHz}=$0.0096 cm$^{2} $g$^{-1}$, the derived overall dust mass within a $sim$43 au radius is $sim$14000 $M_{oplus}$. From this case study, it appears to us that some previous 9 mm surveys towards Class 0/I YSOs might have systematically underestimated dust masses by one order of magnitude, owing to that they assumed the too high dust absorption opacity ($sim$0.1 cm$^{2}$ g$^{-1}$) for $sim$9 mm wavelengths but without self-consistently considering the dust scattering opacity.
We report the source size distribution, as measured by ALMA millimetric continuum imaging, of a sample of 13 AzTEC-selected submillimeter galaxies (SMGs) at z_photo ~ 3-6. Their infrared luminosities and star-formation rates (SFR) are L_IR ~ 2-6 x 10^12 L_sun and ~ 200-600 M_sun yr-1, respectively. The size of z ~ 3-6 SMGs ranges from 0.10 to 0.38 with a median of 0.20+0.03-0.05 (FWHM), corresponding to a median circularized effective radius (Rc,e) of 0.67+0.13-0.14 kpc, comparable to the typical size of the stellar component measured in compact quiescent galaxies at z ~ 2 (cQGs) --- R ~ 1 kpc. The median surface SFR density of our z ~ 3-6 SMGs is 100+42-26 M_sun yr-1 kpc-2, comparable to that seen in local merger-driven (U)LIRGsrather than in extended disk galaxies at low and high redshifts. The discovery of compact starbursts in z >~ 3 SMGs strongly supports a massive galaxy formation scenario wherein z ~ 3-6 SMGs evolve into the compact stellar components of z ~ 2 cQGs. These cQGs are then thought to evolve into the most massive ellipticals in the local Universe, mostly via dry mergers. Our results thus suggest that z >~ 3 SMGs are the likely progenitors of massive local ellipticals, via cQGs, meaning that we can now trace the evolutionary path of the most massive galaxies over a period encompassing ~ 90% of the age of the Universe.
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