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Register a new userSMA Submillimeter Observations of HL Tau: Revealing a compact molecular outflow
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Authors
Alba M. Lumbreras
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We present archival high angular resolution ($sim$ 2$$) $^{12}$CO(3-2) line and continuum submillimeter observations of the young stellar object HL Tau made with the Submillimeter Array (SMA). The $^{12}$CO(3-2) line observations reveal the presence of a compact and wide opening angle bipolar outflow with a northeast and southwest orientation (P.A. = 50$^circ$), and that is associated with the optical and infrared jet emanating from HL Tau with a similar orientation. On the other hand, the 850 $mu$m continuum emission observations exhibit a strong and compact source in the position of HL Tau that has a spatial size of $sim$ 200 $times$ 70 AU with a P.A. $=$ 145$^circ$, and a dust mass of around 0.1 M$_odot$. These physical parameters are in agreement with values obtained recently from millimeter observations. This submillimeter source is therefore related with the disk surrounding HL Tau.
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We present Submillimeter Array (SMA) 1.35 mm subarcsecond angular resolution observations toward the LkH{alpha} 234 intermediate-mass star-forming region. The dust emission arises from a filamentary structure of $sim$5 arcsec ($sim$4500 au) enclosing VLA 1-3 and MM 1, perpendicular to the different outflows detected in the region. The most evolved objects are located at the southeastern edge of the dust filamentary structure and the youngest ones at the northeastern edge. The circumstellar structures around VLA 1, VLA 3, and MM 1 have radii between $sim$200 and $sim$375 au and masses in the $sim$0.08-0.3 M$_{odot}$ range. The 1.35 mm emission of VLA 2 arises from an unresolved (r$< 135$ au) circumstellar disk with a mass of $sim$0.02 M$_{odot}$. This source is powering a compact ($sim$4000 au), low radial velocity ($sim$7 km s$^{-1}$) SiO bipolar outflow, close to the plane of the sky. We conclude that this outflow is the large-scale counterpart of the short-lived, episodic, bipolar outflow observed through H$_2$O masers at much smaller scales ($sim $180 au), and that has been created by the accumulation of the ejection of several episodic collimated events of material. The circumstellar gas around VLA 2 and VLA 3 is hot ($sim$130 K) and exhibits velocity gradients that could trace rotation. There is a bridge of warm and dense molecular gas connecting VLA 2 and VLA 3. We discuss the possibility that this bridge could trace a stream of gas between VLA 3 and VLA 2, increasing the accretion rate onto VLA 2 to explain why this source has an important outflow activity.
Haro 2 , a nearby dwarf starburst dwarf galaxy with strong Ly alpha emission, hosts a starburst that has created outflows and filaments. The clear evidence for galactic outflow makes it an ideal candidate for studying the effects of feedback on molecular gas in a dwarf galaxy. We observed CO(2-1) in Haro 2 at the Submillimeter Array in the compact and extended configurations, and have mapped the molecular emission with velocity resolution 4.1 km/s and spatial resolution 2.0x1.6. With this significant increase of resolution over previous measurements we see that the molecular gas comprises two components: bright clumps associated with the embedded star clusters of the starburst, and fainter extended emission east of the starburst region. The extended emission coincides with an X-ray bubble and has the kinematic signatures of a shell or bubble expanding with velocity +-35 km/s. We suggest that the starburst winds that created the X-Ray bubble have entrained molecular gas, and that the apparent velocity gradient across the photometric axis is an artifact caused by the outflow. The molecular and X-ray activity is on the east of the galaxy and the ionized outflow and optical filaments are west; their relationship is not clear.
We present Submillimeter Array (SMA) observations toward the high-mass star-forming region IRAS 18566+0408. Observations at 1.3 mm continuum and in several molecular line transitions were performed in the compact (2.4 angular resolution) and very-extended (~0.4 angular resolution) configurations. The continuum emission from the compact configuration shows a dust core of 150 Msun, while the very-extended configuration reveals a dense (2.6 x 10^7 cm^-3) and compact (~4,000 AU) condensation of 8 Msun. We detect 31 molecular transitions from 14 species including CO isotopologues, SO, CH3OH, OCS, and CH3CN. Using the different k-ladders of the CH3CN line, we derive a rotational temperature at the location of the continuum peak of 240 K. The 12CO(2-1), 13CO(2-1), and SO(6_5-5_4) lines reveal a molecular outflow at PA ~135^o centered at the continuum peak. The extended 12CO(2-1) emission has been recovered with the IRAM 30 m telescope observations. Using the combined data set, we derive an outflow mass of 16.8 Msun. The chemically rich spectrum and the high rotational temperature confirm that IRAS 18566+0408 is harboring a hot molecular core. We find no clear velocity gradient that could suggest the presence of a rotational disk-like structure, even at the high resolution observations obtained with the very-extended configuration.
Outflowing motions, whether a wind launched from the disk, a jet launched from the protostar, or the entrained molecular outflow, appear to be an ubiquitous feature of star formation. These outwards motions have a number of root causes, and how they manifest is intricately linked to their environment as well as the process of star formation itself. Using the ALMA Science Verification data of HL Tau, we investigate the high velocity molecular gas being removed from the system as a result of the star formation process. We aim to place these motions in context with the optically detected jet, and the disk. With these high resolution ($sim 1$) ALMA observations of CO (J=1-0), we quantify the outwards motions of the molecular gas. We find evidence for a bipolar outwards flow, with an opening angle, as measured in the red-shifted lobe, starting off at 90$^circ$, and narrowing to 60$^circ$ further from the disk, likely because of magnetic collimation. Its outwards velocity, corrected for inclination angle is of order 2.4 km s$^{-1}$.
We use the Submillimeter Array to observe, at 1.4 mm, the blue-lobe of the L1157 outflow at high spatial resolution (~ 3). We detected SiO, H_2CO, and CH_3OH lines from several molecular clumps that constitute the outflow. All three molecules were detected along the wall of the inner cavity that is supposedly related with the later ejection event. On the other hand, no emission was detected towards positions related to an old ejection episode, likely due to space filtering from the interferometer. The H_2CO and CH_3OH emission is detected only at velocities close to the systemic velocity. The spatial distributions of the H_2CO and CH_3OH are similar. These emission lines trace the U-shaped structure seen in the mid-infrared image. In contrast, the SiO emission is detected in wider velocity range with a peak at ~14 km s/s blue-shifted from the systemic velocity. The SiO emission is brightest at the B1 position, which corresponds to the apex of the U-shaped structure. There are two compact SiO clumps along the faint arc-like feature to the east of the U-shaped structure. At the B1 position, there are two velocity components; one is a compact clump with a size of ~1500 AU seen in the high-velocity and the other is an extended component with lower velocities. The kinematic structure at the B1 position is different from that expected in a single bow shock. It is likely that the high-velocity SiO clump at the B1 position is kinetically independent from the low-velocity gas. The line ratio between SiO (5--4) and SiO (2--1) suggests that the high velocity SiO clumps consist of high density gas of n ~ 10^5 - 10^6 cm^-3, which is comparable to the density of the bullets in the extremely high velocity (EHV) jets. It is likely that the high-velocity SiO clumps in L1157 have the same origin as the EHV bullets.
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