Yu-Nung Su

Multiple jets from the high-mass (proto)stellar cluster AFGL 5142

We present studies of the massive protocluster AFGL 5142 in the J ¼ 2Y1 transition of the CO isotopologues, SO, CH3OH, and CH3CN lines, as well as in the continuum at 225 GHz and 8.4 GHz. The 225 GHz continuum emission reveals at least five dust continuum peaks. The strongest peaks, MM-1 and MM-2, are associated with hot cores with temperatures of 90 � 20 and 250 � 40 K, respectively. With similar core mass, the higher temperature and CH3CN abundance in the MM-2 core suggest that it might be at a more evolved stage than the MM-1 core. A total of 22 lines fromninemoleculesaredetected.Thelinestrengthvariesremarkablyintheregion.StrongSOemissionisfoundboth in molecular outflows and cloud cores. CH3OH emission, onthe contrary, is much weaker in molecular outflows, and isdetectedtowardhotcoresMM-1andMM-2,butisabsentinthelessmassiveandperhapslessevolvedcoresMM-3, MM-4, and MM-5. The CO and SO emission reveals at least three molecular outflows originating from the center of thedustcore.Theoutflowsarewellcollimated,withterminalvelocitiesupto50kms � 1 fromthecloudvelocity.Since jetlike outflows and disk-mediated accretion process are physically connected, the well-collimated outflows indicate that even in this cluster environment, accretion is responsible for the formation of individual stars in the cluster. Subject headingg s: H ii regions — ISM: clouds — ISM: individual (AFGL 5142) — ISM: kinematics and dynamics — masers — stars: formation

BIPOLAR MOLECULAR OUTFLOWS FROM HIGH-MASS PROTOSTARS

We report observations of the bipolar molecular outflows associated with the luminous (~2 × 104 L☉) far-IR sources IRAS 21519+5613 and IRAS 22506+5944, as well the dust and molecular gas condensations on which these outflows appear to be centered. The observations were made in 12CO, 13CO, C18O, and continuum at 3 mm with the BIMA array and in 12CO and 13CO with the NRAO 12 m telescope to recover extended emission filtered out by the interferometric array. We find that the outflow associated with each IRAS source shows a clear bipolar morphology in 12CO, with properties (i.e., total mass of order 10-100 M☉, mass-outflow rate 10-3 M☉, dynamical timescale 104-105 yr, and energetics) comparable with those of other massive outflows associated with luminous young stellar objects. Each outflow appears to be centered on a dust and gas condensation with a mass of 200-300 M☉, likely marking the location of the driving source. The outflow lobes of both sources are fully resolved along their major but not minor axes, and they have collimation factors that may be comparable with young low-mass stars. The mass-velocity diagrams of both outflows change in slope at a velocity of ~10 km s-1, suggesting that the high-velocity component (HVC) may drive the low-velocity component (LVC). Although the HVC of IRAS 21519+5613 shows evidence for deceleration, no such signature is seen in the HVC of IRAS 22506+5944. Neither HVC has a momentum supply rate sufficient to drive their corresponding LVCs, although it is possible that the HVC is more highly excited and hence its thrust underestimated. Like for other molecular outflows the primary driving agent cannot be ionized gas, leaving atomic gas as the other remaining candidate. Neither IRAS 21519+5613 nor IRAS 22506+5944 exhibits detectable free-free emission, which together with the observed properties of their molecular outflows and surrounding condensations make them credible candidates for high-mass protostars. The mass-accretion rate required to produce their observed IRAS luminosity is 10-4 M☉ yr-1, which is more than sufficient to quench the development of an UC-H II region. On the other hand, the individual IRAS sources may be associated with a group of stars whose dominant member is a main-sequence star that is responsible for the observed outflow. Such a star would be required to have a spectral type of ~B2 (luminosity of ~3000 L☉) or later to not excite a detectable UC-H II region; the time-averaged mass-accretion rate needed to produce this star is then 10-3 to 10-4 M☉ yr-1. Thus, regardless of the evolutionary stage of the outflow driving source, the inferred mass-accretion rate is much higher than that allowed by simple inside-out collapse models but can be accommodated by recently proposed variants.

MILKY WAY SUPERMASSIVE BLACK HOLE: DYNAMICAL FEEDING FROM THE CIRCUMNUCLEAR ENVIRONMENT

The supermassive black hole (SMBH), Sgr A*, at the Galactic center is surrounded by a molecular circumnuclear disk (CND) lying between 1.5 and 4 pc radii. The irregular and clumpy structures of the CND suggest dynamical evolution and episodic feeding of gas toward the central SMBH. New sensitive data from the Submillimeter Array and Green Bank Telescope reveal several >5-10 pc scale molecular arms, which either directly connect to the CND or may penetrate inside the CND. The CND appears to be the convergence of the innermost parts of large-scale gas streamers, which are responding to the central gravitational potential well. Rather than being a quasi-stationary structure, the CND may be dynamically evolving, incorporating inflow via streamers, and feeding gas toward the center.

Mapping the outflow from G5.89-0.39 in SiO J = 5 → 4

We have mapped the ultracompact H II region, G5.89-0.39, and its molecular surroundings with the Submillimeter Array at 28 × 18 angular resolution in 1.3 mm continuum, SiO J = 5 → 4, and eight other molecular lines. We have resolved for the first time the highly energetic molecular outflow in this region. At this resolution, the outflow is definitely bipolar and appears to originate in a 1.3 mm continuum source. The continuum source peaks in the center of the H II region. The axis of the outflow lines up with a recently discovered O5 V star.

Submillimeter Array Outflow/Disk Studies in the Massive Star-forming Region IRAS 18089–1732

Submillimeter Array observations of the massive star-forming region IRAS 18089-1732 in the 1 mm and 850 ?m band reveal outflow and disk signatures in different molecular lines. The SiO (5-4) data show a collimated outflow in the northern direction. In contrast, the HCOOCH3 (20-19) line, which traces high-density gas, is confined to the very center of the region and shows a velocity gradient across the core. The HCOOCH3 velocity gradient is not exactly perpendicular to the outflow axis but between an assumed disk plane and the outflow axis. We interpret these HCOOCH3 features as originating from a rotating disk that is influenced by the outflow and infall. On the basis of the (sub)millimeter continuum emission, the mass of the central core is estimated to be around 38 M?. The dynamical mass derived from the HCOOCH3 data is 22 M?, of about the same order as the core mass. Thus, the mass of the protostar/disk/envelope system is dominated by its disk and envelope. The two frequency continuum data of the core indicate a low dust opacity index ? ~ 1.2 in the outer part, decreasing to ? ~ 0.5 on shorter spatial scales.

Deuterium Fractionation as an Evolutionary Probe in Massive Protostellar/Cluster Cores

Clouds of high infrared extinction are promising sites of massive star/cluster formation. A large number of cloud cores discovered in recent years allow for the investigation of a possible evolutionary sequence among cores in early phases. We have conducted a survey of deuterium fractionation toward 15 dense cores in various evolutionary stages, from high-mass starless cores to ultracompact H II regions, in the massive star-forming clouds of high extinction, G34.43+0.24, IRAS 18151–1208, and IRAS 18223–1243, with the Submillimeter Telescope. Spectra of N2H+ (3-2), N2D+ (3-2), and C18O (2-1) were observed to derive the deuterium fractionation of N2H+, D frac ≡ N(N2D+)/N(N2H+), as well as the CO depletion factor for every selected core. Our results show a decreasing trend in D frac with both gas temperature and line width. Since colder and quiescent gas is likely to be associated with less evolved cores, larger D frac appears to correlate with early phases of core evolution. Such decreasing trend resembles the behavior of D frac in the low-mass protostellar cores and is consistent with several earlier studies in high-mass protostellar cores. We also find a moderate increasing trend of D frac with the CO depletion factor, suggesting that sublimation of ice mantles alters the competition in the chemical reactions and reduces D frac. Our findings suggest a general chemical behavior of deuterated species in both low- and high-mass protostellar candidates at early stages. In addition, upper limits to the ionization degree are estimated to be within 2 × 10–7 and 5 × 10–6. The four quiescent cores have marginal field-neutral coupling and perhaps favor turbulent cooling flows.

SPECTRAL LINE SURVEY TOWARD THE YOUNG MASSIVE PROTOSTAR NGC 2264 CMM3 IN THE 4 mm, 3 mm, AND 0.8 mm BANDS

Spectral line survey observations are conducted toward the high-mass protostar candidate NGC 2264 CMM3 in the 4 mm, 3 mm, and 0.8 mm bands with the Nobeyama 45 m telescope and the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope. In total, 265 emission lines are detected in the 4 mm and 3 mm bands, and 74 emission lines in the 0.8 mm band. As a result, 36 molecular species and 30 isotopologues are identified. In addition to the fundamental molecular species, many emission lines of carbon-chain molecules such as HC5N, C4H, CCS, and C3S are detected in the 4 mm and 3 mm bands. Deuterated molecular species are also detected with relatively strong intensities. On the other hand, emission lines of complex organic molecules such as HCOOCH3, and CH3OCH3 are found to be weak. For the molecules for which multiple transitions are detected, rotation temperatures are derived to be 7-33 K except for CH3OH. Emission lines with high upper-state energies (Eu > 150 K) are detected for CH3OH, indicating existence of a hot core. In comparison with the chemical composition of the Orion KL, carbon-chain molecules and deuterated molecules are found to be abundant in NGC 2264 CMM3, while sulfur-bearing species and complex organic molecules are deficient. These characteristics indicate chemical youth of NGC 2264 CMM3 in spite of its location at the center of the cluster forming core, NGC 2264 C.

INFALL AND OUTFLOW MOTIONS IN THE HIGH-MASS STAR-FORMING COMPLEX G9.62+0.19

We present the results of a high-resolution study with the Submillimeter Array toward the massive star-forming complex G9.62+0.19. Three submillimeter cores are detected in this region. The masses are 13, 30, and 165 M{sub sun} for the northern, middle, and southern dust cores, respectively. Infall motions are found with HCN (4-3) and CS (7-6) lines at the middle core (G9.62+0.19 E). The infall rate is 4.3 x 10{sup -3} M{sub sun} yr{sup -1}. In the southern core, a bipolar outflow with a total mass about 26 M{sub sun} and a mass-loss rate of 3.6 x 10{sup -5} M{sub sun} yr{sup -1} is revealed in SO (8{sub 7}-7{sub 7}) line wing emission. CS (7-6) and HCN (4-3) lines trace higher velocity gas than SO (8{sub 7}-7{sub 7}). G9.62+0.19 F is confirmed to be the driving source of the outflow. We also analyze the abundances of CS, SO, and HCN along the redshifted outflow lobes. The mass-velocity diagrams of the outflow lobes can be well fitted by a single power law. The evolutionary sequence of the centimeter/millimeter cores in this region is also analyzed. The results support that ultracompact H II regions have a higher blue excess than their precursors.

The disk-outflow system in the S255IR area of high-mass star formation

We report the results of our observations of the S255IR area with the Submillimeter Array (SMA) at 1.3 mm in the very extended configuration and at 0.8 mm in the compact configuration as well as with the IRAM 30 m at 0.8 mm. The best achieved angular resolution is about 0.4 arcsec. The dust continuum emission and several tens of molecular spectral lines are observed. The majority of the lines is detected only toward the S255IR-SMA1 clump, which represents a rotating structure (probably a disk) around the young massive star. The achieved angular resolution is still insufficient to make any conclusions about the Keplerian or non-Keplerian character of the rotation. The temperature of the molecular gas reaches 130-180 K. The size of the clump is about 500 AU. The clump is strongly fragmented as follows from the low beam-filling factor. The mass of the hot gas is significantly lower than the mass of the central star. A strong DCN emission near the center of the hot core most probably indicates a presence of a relatively cold (less than or similar to 80 K) and rather massive clump there. High-velocity emission is observed in the CO line as well as in lines of high-density tracers HCN, HCO+, CS and other molecules. The outflow morphology obtained from a combination of the SMA and IRAM 30 m data is significantly different from that derived from the SMA data alone. The CO emission detected with the SMA traces only one boundary of the outflow. The outflow is most probably driven by jet bow shocks created by episodic ejections from the center. We detected a dense high velocity clump associated apparently with one of the bow shocks. The outflow strongly affects the chemical composition of the surrounding medium.

SMA OBSERVATIONS OF THE HOT CORES OF DR21(OH)

Using the Submillimeter Array (SMA), we identified two bright hot subcores, MM1a and MM1b (size ~ 1” and mass ~ 0.5 M ⊙ ) separated by about 1.6”, in the 230 ㎓ continuum emission toward the massive star-forming region DR21(OH). Both display typical hot core characteristics but have slightly different chemical properties. For example, highly saturated species show stronger emission toward MM1a and seem to be evaporating directly from the grain mantles. In contrast, simple sulfur-bearing species have brighter emission at MM1b. These features indicate that MM1a is at an earlier stage than MM1b, and the small-scale chemical differences between these two cores may result from the age difference of the order of 10⁴ years.