Massive Molecular Outflows Research Articles

SUBMILLIMETER ARRAY OBSERVATIONS OF THE MOLECULAR OUTFLOW IN HIGH-MASS STAR-FORMING REGION G240.31+0.07

We present Submillimeter Array observations toward the 10^{4.7} Lsun star-forming region G240.31+0.07, in the J=2-1 transition of 12CO and 13CO and at 1.3 mm continuum, as well as the 12CO and 13CO observations from the Caltech Submillimeter Observatory to recover the extended emission filtered out by the interferometer. Maps of the 12CO and 13CO emission show a bipolar, wide-angle, quasi-parabolic molecular outflow, roughly coincident with an IR nebula revealed by the Spitzer 3.6 and 4.5 micron emission. The outflow has ~98 Msun molecular gas, making it one of the most massive molecular outflows known, and resulting in a very high mass-loss rate of 4.1 by 10^{-3} Msun yr^{-1} over a dynamical timescale of 2.4 by 10^4 yr. The 1.3 mm continuum observations with a 4" by 3" beam reveal a flattened dusty envelope of ~150 Msun, which is further resolved with a 1.2" by 1" beam into three dense cores with a total mass of ~40 Msun. The central mm core, showing evidence of active star formation, approximately coincides with the geometric center of the bipolar outflow thus most likely harbors the powering source of the outflow. Overall our observations provide the best case to date of a well-defined wide-angle molecular outflow in a >10^4 Lsun star-forming region. The outflow is morphologically and kinematically similar to low-mass protostellar outflows but has two to three orders of magnitude greater mass, momentum, and energy, and is apparently driven by an underlying wide-angle wind, hence further supports that high-mass stars up to late-O types, even in a crowded clustering environment, can form as a scaled-up version of low-mass star formation.

Massive molecular outflows associated with UCHII/HII regions

Received date ; Accepted date Abstract. Aims: We searched for the molecular outflows from fifteen mole cular clouds associated with ultra-compact and compact HII (UCHII/HII) regions and discussed possible gas heating mechanism. Methods: Mapping observations of CO J = 3− 2 and J = 2− 1 lines were carried out with the KOSMA 3m-Telescope towards the 15 HII regions/molecular cloud complexes. Results: Ten molecular outflows were identified o ut of the fifteen HII region /molecular cloud complexes. The higher outflow detection rate (67%) suggested that such outflows are as common in high mass star forming regions as those in low mass star forming regions, which is consistent with the results o f other authors. The observations also showed that the outflo w might occur in the HII region. The integrated CO line intensity ratios (RICO(3−2)/ICO(2−1) ) were determined from the core component of the spectra as well as from both the blue and red wings. Maximum line intensity ratios from the wings and core components appeared to be related to the mid-infrared sources imaged by Midcourse Space Experiment (MSX). The relationship between the maximum line intensity ratios and MSX sources indicates that the molecular gas could be heated by the emission of dust associated with massive stars. Based on maser observations reported in the literature, we found that H 2O masers were only detected in seven regions. The H2O masers in these regions are located near the MSX sources and within the maximum line intensity ratio regions, suggesting that H 2O masers occur in relatively warm environments.

Discovery of an Extremely High Velocity, Massive, and Compact Molecular Outflow in Norma

G331.5–0.1 in the Norma spiral arm is one of the most luminous and extended cores of a giant molecular cloud (GMC), containing at least six massive and dense dust condensations. Here we report the discovery, from observations of several submillimeter molecular lines that were made using the Atacama Submillimeter Telescope (ASTE) and the Atacama Pathfinder Experiment Telescope (APEX), of an unresolved, extremely high velocity molecular outflow toward the brightest and most massive dust condensation. The outflow is massive and energetic (flow mass of ~55 M☉; momentum of ~2.4 × 103 M☉ km s−1; kinetic energy of ~1.4 × 1048 ergs). These values are characteristic of flows driven by young massive stellar objects with Lbol ~ 1 × 105 L☉. We also report the detection, using the Australia Telescope Compact Array (ATCA), of a compact radio continuum source that is located at the center of the outflow and therefore likely to be its driving energy source. It has an spectral index between 4.8 and 8.6 GHz of 1.1 ± 0.2, suggesting that it might correspond to a collimated jet.

Massive Molecular Outflows at High Spatial Resolution

We present high-spatial resolution Plateau de Bure Interferometer CO(2-1) and SiO(2-1) observations of one intermediate-mass and one high-mass star-forming region. The intermediate-mass region IRAS20293+3952 exhibits four molecular outflows, one being as collimated as the highly collimated jet-like outflows observed in low-mass star formation sources. Furthermore, comparing the data with additional infrared H2 and cm observations we see indications that the nearby ultracompact HII region triggers a shock wave interacting with the outflow. The high-mass region IRAS19217+1651 exhibits a bipolar outflow as well and the region is dominated by the central driving source. Adding two more sources from the literature, we compare position-velocity diagrams of the intermediate- to high-mass sources with previous studies in the low-mass regime. We find similar kinematic signatures, some sources can be explained by jet-driven outflows whereas other are better constrained by wind-driven models. The data also allow to estimate accretion rates varying from a few times 10^{-5}Msun/yr for the intermediate-mass sources to a few times 10^{-4}Msun/yr for the high-mass source, consistent with models explaining star formation of all masses via accretion processes.

(Sub-)mm Interferometry in Massive Star Forming Regions

(Sub-)mm interferometry is the most favorable technique to investigate the earliest stages of massive star formation. I will outline general applications in that field and discuss results of different sub-topics (hot core chemistry and massive molecular outflows). Furthermore, recent data obtained with the Submillimeter Array will be shown to present the unique capabilities of this new instrument. Finally, I will give a short outlook on the main physical topics of massive star formation to be tackled with (sub-)mm interferometry within the next decade.

A massive disk/envelope in shocked H2emission around an UCHII region

A multi-wavelength study of IRAS 07427-2400 in line and continuum emission was conducted to investigate the nature of a H2 v = 1-0 S(1) line emitting feature around this ultra-compact HII region. High resolution 3.6 cm continuum observations from the Very Large Array and 350 µm continuum observations from the Caltech Submillimeter Observatory, combined with archival far-infrared data of IRAS 07427-2400 show a flux density distribution indicating a luminous (L = 5.6 × 10 4 L� ) point source associated with an ultra-compact HII region. A Grey body model fit to the flux density distribution yields a dust emissivity index (β ∼ 0.66) indicative of a circumstellar disk/envelope. Our C 18 O map shows a dense core centered on the continuum source, with the major axis roughly aligned with the H2 feature. A position-velocity diagram of the C 18 Oc ore obtained along the major axis shows rotation with a velocity gradient of ∼0.1 km s −1 arcsec −1 .N ew COJ = 3-2 maps of the region are presented which reveal a massive molecular outflow from the IRAS source. We argue that the H2 feature arises in a disk/envelope around IRAS 07427-2400 and not in an outflow. We present a near-infrared HK band spectrum of the H2 features that shows several ro-vibrational emission lines of H2 and (FeII). Analysis of the line ratios indicates that the line emission is shock-excited and not due to fluorescence. We estimate an excitation temperature of ∼1600 K and an average extinction of Av ∼ 11 mag to the H2 feature. The line fluxes yield a mass accretion rate of u M ∼ 2.6 ± 0.9 × 10 −2 Myr −1 and a lifetime of ∼5360 ± 1200 yr resulting in a disk/envelope mass of 140 ± 50 M� . The resulting Jeans Mass of 2420 Mindicates that the disk/envelope will not undergo fragmentation. IRAS 07427-2400 represents one of the most massive YSOs known to date forming by means of accretion.

Massive molecular outflows

We present a mapping study of massive molecular outflows in 26 high-mass star-forming regions at 11'' spatial resolution. Bipolar morpholgy is found in 80% of the sources and the collimation is higher than previously thought. Additionally, we find that well known low-mass correlations continue up to the high-mass regime, and accretion rates are around 10^(-4) Msun/yr rising as high as 10^(-3) Msun/yr. A tight correlation between the outflow and the core mass is established, implying that the accretion rate is a rather linear function of the initial core mass. All the data suggest that massive outflows are qualitatively similar and just quantitatively enhanced compared to their low mass counterparts.

Warm Dust Emission Near W75 N IRS1: Evidence for Multiple Energetic Outflows

This paper presents 08 to 3'' resolution images of 1.3 and 3.3 mm continuum emission in the massive molecular outflow in W75 N. The mass of warm gas and dust near the center of the outflow is ~450 M☉ and represents approximately 45% of the core mass in the molecular cloud. Comparison of the distribution of warm dust emission with the locations of ultracompact H II regions indicates that the source VLA 3 probably contributes the most to the outflow dynamics. The location of VLA 2 near the 1 mm continuum peak and the presence of H2O masers suggests that this source may also contribute to the flow dynamics. The thermal jet source, VLA 1, has an estimated momentum rate that is 3 to 4 orders of magnitude less than that required to drive the large-scale CO outflow. If the ionized jet is the only outflow component, VLA 1 does not appear to be able to contribute significantly to the outflow energetics. Outflow parameter estimates that have been corrected for inclination and optical depth imply an outflow mass of more than a thousand solar masses and a mass outflow rate of ~0.2 M☉ yr-1. It is extremely unlikely that a single young stellar object can produce a flow of this magnitude; thus, several energetic outflows may be active.

Outflows and Luminous YSOs: A New Perspective on the G192.16 Massive Bipolar Outflow

We have obtained new observations of the massive molecular outflow in G192.16-3.82 in CO(J = 1-0) line and 3 mm continuum using the Owens Valley Radio Observatory millimeter-wave array. We have also imaged the outflow in the near-infrared J, H, and K bands and 2.12 μm H2 at Lowell Observatory and in the Ks band at the Apache Point Observatory. A large-field Palomar image shows that the outflow structure may extend more than 4 pc from the young stellar object (YSO), making it one of the largest known Galactic outflows. There is approximately 80 M☉ of molecular material in the high-velocity flow, and the mass flow rate is ~5 × 10-4 M☉ yr-1. The flow appears to be driven by an early-B star that is surrounded by approximately 17 M☉ of material. A biconical infrared reflection nebula is centered near the millimeter continuum peak, and shock-excited H2 emission is detected at the brightest peak in the K-band reflection nebula. H2 emission is also detected just beyond the highest velocity gas in the blueshifted CO outflow. The slope of the mass spectrum is approximately -2 at velocities below 15 km s-1 and decreases to as low as -8 at higher velocities. This is significantly steeper than in low-mass outflows, suggesting that the powering mechanism is less efficient at accelerating material in the flow. Alternatively, the outflow may have built up a substantial reservoir of low-velocity gas that steepens the mass spectrum. The observation of a wide outflow opening angle (~60°) and limb-brightened shell surrounding the high-velocity gas, together with shock-excited H2 emission and large bow shocks that extend up to 4 pc from the YSO, are consistent with the presence of both a poorly collimated disk-wind and a jet.

Interaction between a Massive Molecular Outflow and Dense Gas Associated with IRAS 22142+5206

We report results of 12CO, 13CO, and C18O (J = 1–0) observations made toward the luminous protostellar candidate IRAS 22142+5206 (~16,100 L⊙, at its kinematic distance of 4.5 kpc) using the 45 m telescope at Nobeyama Radio Observatory. We have discovered a massive CO outflow with a molecular mass of ~33 M⊙, which is among the more massive outflows reported to date. The outflow lobes extend to over ~2 pc from the IRAS source. Dense gas (~1140 M⊙) with an elliptical shape is also found around the source, with a velocity gradient of ~0.5 km s-1 pc-1 along its major axis. We find a cavity in the dense gas at positions where the CO outflow is prominent. We discuss the origin of the cavity, estimating the mechanical momentum and kinetic energy of the outflow, and conclude that the cavity was most likely created by the high-velocity jet of the outflow, which may have swept up part of the dense gas. We also carried out extensive 13CO observations toward the IRAS source using the Nagoya 4 m telescope in order to reveal the overall distribution of molecular gas around the source. The results of these observations indicate that the IRAS source is embedded in a molecular cloud with a mass of 7300 M⊙.

Water Ice in the Disk Around the Protostar AFGL 2136 IRS 1

The protostar AFGL 2136 IRS 1 illuminates the Juggler nebula and drives a massive molecular outflow. The line of sight toward AFGL 2136 also displays a rich spectrum of solid state absorption features. To investigate the distribution of ice-coated grains in the environment of IRS 1, we obtained narrowband images at six near-infrared wavelengths surrounding and including the 3.08 μm water ice feature. These images (specifically, a color map constructed from 2.14 and 3.60 μm images) provide vivid evidence for the presence of a disk around IRS 1 and appear to reveal, for the first time, the detailed distribution of water ice in the local environment of a protostar. Models of the 2-4 μm spectral energy distributions (SEDs) toward IRS 1 and the Juggler nebula suggest that the abundance of icy grains is larger along lines of sight through the disk than along lines of sight away from the equatorial plane of IRS 1. Thus, while we find evidence that icy grains exist throughout the cloud core containing AFGL 2136, it appears that the physical conditions in the circumstellar disk around IRS 1 are more conducive to ice mantle survival and/or growth than are physical conditions in its rarefied polar regions.

The Sagittarius B2 Star-forming Region. III. High-Resolution H52 alpha and H66 alpha Observations of Sagittarius B2 Main

view Abstract Citations (59) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Sagittarius B2 Star-forming Region. III. High-Resolution H52 alpha and H66 alpha Observations of Sagittarius B2 Main de Pree, C. G. ; Gaume, R. A. ; Goss, W. M. ; Claussen, M. J. Abstract The Galactic center star-forming region Sagittarius B2 Main [Sgr B2 (M)] has been observed with the Very Large Array in the continuum (7 mm and 1.3 cm) and in the radio recombination lines H52α, H66α, and He 66α. The H66α(∼0".25 resolution) and H52α(∼2".5 resolution) data provide high spatial resolution kinematics of the ionized gas associated with the massive stars. Both high spatial resolution and sensitivity to large-scale structures are essential to thoroughly sample the H II regions in Sgr B2 (M) where source sizes of the 36 H II regions range from unresolved (<0".3) to extended (∼10"). H66α recombination line emission has been detected toward 23 of the 36 continuum sources in Sgr B2 (M). The mean velocity of the detected sources is 62±2 km s-1. He 66α line emission is detected toward nine of the 36 continuum sources. The 1.3 cm helium and hydrogen data are used together as a high-resolution probe of Y+ values and variations within Sgr B2 (M). An average singly ionized helium abundance of <Y+> = 10.3%±1.2% is derived. Of the sources where a Y+ value is determined, only Sgr B2 F has an anomalously low value (Y+ ≤ 5%). The recombination line data are examined in detail toward several of the most unusual sources. A very broad radio recombination line (ΔVH66α ∼ 64 km s-1, ΔVH52α ∼ 59 km s-1) is measured, and high electron temperatures [Te(H66α)* = 26,400 K] are derived for Sgr B2 F. The broad lines and high temperatures may be due to a nonequilibrium environment at the edge of an expanding H II region. Assuming that the F and G H II regions have expanded in a dense molecular environment, they appear to be young, with an average age of <τ> = 0.7±0.3 x 104 yr. This lower limit on the age is consistent with the dynamical age of the nearby massive molecular outflow observed by Lis et al. A doubly peaked H66α line has been detected toward the ultracompact H II (UC HII) region Z10.24. This source may be either a very young (τ < 100 yr) shell source or the ionized base of a molecular outflow. The small number of morphological cometary H II regions in Sgr B2 (<5%) and the observed velocity gradients in those regions that do have a cometary morphology indicate that the moving star bow shock model cannot account for any of the H II regions in Sgr B2 (M). Publication: The Astrophysical Journal Pub Date: June 1996 DOI: 10.1086/177364 Bibcode: 1996ApJ...464..788D Keywords: ISM: KINEMATICS AND DYNAMICS; ISM: H II REGIONS; ISM: INDIVIDUAL NAME: SAGITTARIUS B2; GALAXY: CENTER; RADIO LINES: ISM full text sources ADS | data products SIMBAD (47) Related Materials (2) Part 1: 1995ApJ...449..663G Part 2: 1995ApJ...451..284D

The massive molecular outflow from CRL 2136 IRS 1

view Abstract Citations (32) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Massive Molecular Outflow from CRL 2136 IRS 1 Kastner, Joel H. ; Weintraub, David A. ; Snell, Ronald L. ; Sandell, G. ; Aspin, C. ; Hughes, D. H. ; Baas, F. Abstract Maps of rotational CO emission toward the star-formation region CRL 2136 reveal an arcminute-scale bipolar outflow that appears to be driven by the massive young stellar objects IRS 1. The projected outflow axis is roughly perpendicular to the disk plane previously inferred from near-infrared images and polarization maps. High-velocity wings are present in both (12)CO and (13)CO spectra, suggesting the (12)CO optical depths in the outflowing gas are large; we estimate the high-velocity gas contains approximately 50 solar mass, making this molecular outflow one of the more massive known. We find that the region within approximately 1 min of CRL 2136 constitutes a significant concentration of the molecular mass in the ambient cloud. Submillimeter photometry and mapping shows that CRL 2136 is a strong, extended source of continuum emission. The emission likely arises with grains heated to 40-60 K by IRS 1. Comparison of the estimated thermal dust mass (approximately 1 solar mass within approximately 8 sec of IRS 1), the mass in high-velocity gas, and the scattering dust mass we derived previously suggests that the gas-to-dust mass ratio in the outflow is between approximately 10 and approximately 100, where the value depends on what proportion of the submillimeter emission originates with dust in the ambient cloud and/or circumstellar disk. The apparent extreme youth of IRS 1 compared with the dynamical age of the outflow, and the tremendous mass of swept-up molecular material, suggests the outflow began early in the formation of the young stellar object and implies the outflow cannot be radiatively driven. We present evidence that infall toward IRS 1 is ongoing; transfer of angular momentum from this infalling material may drive the outflow. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/174015 Bibcode: 1994ApJ...425..695K Keywords: Interstellar Matter; Mass Distribution; Molecular Clouds; Radio Astronomy; Star Formation; Angular Momentum; Carbon Isotopes; Kinematics; Momentum Transfer; Near Infrared Radiation; Polarization (Waves); Radio Observation; Submillimeter Waves; Astrophysics; ISM: DUST; EXTINCTION; ISM: INDIVIDUAL ALPHANUMERIC: CRL 2136; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; STARS: FORMATION full text sources ADS | data products SIMBAD (8)

Star formation in the NGC 7538 molecular cloud - Near-infrared and radio spectroscopy

We present new CO millimeter-wave observations of the star-formation region NGC 7538 centered in the region around IRS 1--3, in which a large (rroughly-equal1.3 pc) and massive (75 M/sub sun/) high-velocity molecular outflow is identified. The correspondence of far-infrared emission with the extent of the molecular outflow leads to the proposal of an in situ mechanism for radiative acceleration of the gas, operable in cases where tau (dust) is insufficient to permit the ''snowplow'' outflow effect. We also synthesize new and previously published near infrared emission line observations of IRS 1--3, finding an apparent deficit in ionizing flux relative to the total far-infrared luminosity. We identify IRS 1 as the most luminous of the three sources, in which dust absorption within the ultracompact H II region has sharply reduced the ionizing flux. On this basis we argue that IRS 1 may also be the primary if not sole cuase of the molecular outflow.