Knots Of H2 Emission Research Articles

A multiwavelength study of the IRAS 23139+5939 (G111.256−0.770) star-forming site and its relation to Sh2-157

ABSTRACTThe far-infrared source IRAS 23139+5939 (G111.25−0.77) is a well-studied massive star-forming region at the centre of a dense molecular clump. It is associated with a low-luminosity and variable methanol maser, a number of water maser clusters, and several compact H ii regions. We present new sub-arcsec-resolution broad- and narrow-band near- and mid-infrared calibrated images. These were analysed together with Wide-field Infrared Survey Explorer images and longer wavelength published data. We establish that IRAS 23139+5939 is a multiple massive young stellar object (YSO) with a spectral energy distribution characteristic of a Class I object. Its deeply embedded (AV = 21) central YSOs have a total luminosity of 3 × 104 L⊙ and a mass of 16 M⊙. We find several small knots of H2 emission in its vicinity, bordering a large CO outflow driven by the protostar. Their distribution suggests the presence of several YSOs with jets. A young embedded stellar cluster of size ∼40 arcsec (0.65 pc) is found around the massive protostar, with evidence of protoplanetary discs in more than 50 per cent of the likely members. We also report a large arc of H2 emission surrounding a nearby H α-emission star displaying a large infrared excess, with a total luminosity of 1.5 × 103 L⊙. Gaia Data Release 3 and very long baseline interferometry parallaxes indicate a common distance of 3.34 kpc to these two YSOs, a distance similar to that to Sh2-157, a nearby massive star-forming region, which appears connected to IRAS 23139+5939 by a warm dust filament.

Collision of protostellar jets in the star-forming region IC 1396N

Context. The bright-rimmed cloud IC 1396N is believed to host one of the few known cases where two bipolar CO outflows driven by young stellar objects collide. The CO outflows are traced by chains of knots of H2 emission, with enhanced emission at the position of the possible collision. Aims. The aim of this work is to use the proper motions of the H2 knots to confirm the collision scenario. Methods. A second-epoch H2 image was obtained, and the proper motions of the knots were determined with a time baseline of ~11 yr. We also performed differential photometry on the images to check the flux variability of the knots. Results. For each outflow (N and S), we classified the knots as pre-collision or post-collision. The axes of the pre-collision knots, the position of the possible collision point, and the axes of the post-collision knots were estimated. The difference between the proper motion direction of the post-collision knots and the position angle from the collision point was also calculated. For some of the knots, we obtained the 3D velocity using the radial velocity derived from H2 spectra. Conclusions. The velocity pattern of the H2 knots in the area of interaction (post-collision knots) shows a deviation from that of the pre-collision knots, consistent with being a consequence of the interaction between the two outflows. This favours the interpretation of the IC 1396N outflows as a true collision between two protostellar jets instead of a projection effect.

An infrared study of the high-mass, multistage star-forming region IRAS 12272−6240

ABSTRACT IRAS 12272−6240 is a complex star-forming region with a compact massive dense clump (DC) and several associated masers, located at a well-determined distance of d = 9.3 kpc from the Sun. For this study, we obtained sub-arcsec broad- and narrow-band near-infrared (near-IR) imaging and low-resolution spectroscopy with the Baade/Magellan telescope and its camera PANIC. Mosaics of size 2 × 2 arcmin2 in the JHKs bands and with narrow-band filters centred in the 2.12 μm H2 and 2.17 μm Br γ lines were analysed in combination with Hi-GAL/Herschel and archive IRAC/Spitzer and WISE observations. We found that the compact DC houses two Class I young stellar objects (YSOs) that probably form a 21000 -au-wide binary system. Its combined 1–1200 μm spectral energy distribution is consistent with an O9V central star with a $10^{-2} \, \mathrm{M}_\odot$ disc and a $1.3 \times 10^4 \, \mathrm{M}_\odot$ dust envelope. Its total luminosity is $8.5 \times 10^4 \, \mathrm{L}_\odot$. A series of shocked H2 emission knots are found in its close vicinity, confirming the presence of outflows. IRAS 12272−6240 is at the centre of an embedded cluster with a mean age of 1 Myr and 2.6 pc in size that contains more than 150 stars. At its nucleus, we found a more compact and considerably younger subcluster containing the YSOs. We also identified and classified the O-type central stars of two dusty radio/IR H ii regions flanking the protostars. Our results confirm that these elements form a single giant young complex where massive star formation processes started some 1 Myr ago and are still active.

PAH and H2 emission in the Ring Nebula

This paper presents the Spitzer IRS (Infra Red Spectrograph) detection of mid-infrared polycyclic aromatic hydrocarbon (PAH) emission features and H2 associated with dense knots in the ring of the “oxygen-rich” (C/O∼⃒0.6-0.8) planetary nebula (PN) NGC6720 (Ring Nebula). We explored a further three oxygen-rich extended PNe with similar dataset available. These turned out to be non-detection of PAHs, although two of these do contain H2 emission knots. The presence of PAHs is discussed in the context of a bottom-up formation mechanism, in which first small hydrocarbons, and later PAHs, are formed in warm dense knots inside the ionised regions of PNe.

XMMOBSERVATIONS OF TWO QUADRUPOLAR OUTFLOWS

X-ray images of two small dark clouds, L1455 and L723, have been obtained with the EPIC cameras on board the XMM-Newton telescope. Both regions contain multiple independent but overlapping bipolar flows in high-velocity CO, a collection of Herbig-Haro objects, and a number of filaments and knots of H2 emission. The field of view in each cloud was centered on the confluence of the nearly orthogonal CO flows. More than three dozen compact X-ray sources were detected. However, the Class 0/I protostars thought to be the driving sources of the flows in both clouds were not detected. Strong emission was observed from RNO 15, an optically visible, nebulous T Tauri star in the dense core of L1455. A thermal plasma model for the X-ray spectrum of RNO 15 gave a luminosity of L X ~ 1031.2 erg s–1. The heavily reddened Class II star L1455 IRS 5 in the same region was detected as a weak X-ray source. No emission was detected from IRS 1 or IRS 4, which have been suggested as the launch sites for separate outflows in L1455. X-ray emission was observed from IRAS 19156+1906 in L723. The thermal radio source VLA 2, which is offset ~10'' east of the IRAS position and is considered the most likely energy source for the strong east-west flow in L723, was not detected. The source of the more narrowly collimated north-south flow in L723 is unknown but may be an embedded infrared object at the X-ray and IRAS position.

Imaging study of NGC 3372, the Carina nebula -- II. Evidence of activity in the complex Trumpler 14/Car I photodissociation region

We present the results of an imaging survey, from the optical to the mid-infrared, of the dark cloud associated with Car I, a dense cloud that is subject to an intense ultraviolet radiation field from the rich stellar cluster Trumpler 14. New ground-based broad- and narrowband near-infrared and narrow-band optical images are analysed in combination with archived Spitzer/InfraRed Array Camera (IRAC) images to study this photodissociation region (PDR) and the triggering of a new generation of stars within the cloud, particularly close to its edges. Evidence is given of a clumpy morphology of the dense cloud. The ionization/dissociation front is delineated at the edges of these clumps. The existence of a number of embedded lowto intermediate-mass pre-main-sequence objects is confirmed by their considerable infrared excesses arising from discs and/or detectable X-ray emission. Most of the young stellar objects (YSOs) are located on or just behind ionization fronts, though a few are also outside the cloud. The infrared properties of the YSOs are discussed. Two Class I objects stand out, one of them is an FU Orionis system candidate that had an outburst of more than 3 mag in K between 1993 and 2003, with further evidence that it occurred in the 2000‐02 period. Molecular hydrogen line filamentary emission behind the Balmer and Brackett lines along the ionization front is seen delineating the edges of the dense cloud. This emission is also seen in all IRAC images. The diffuse, filamentary emission is very similar in all four 3.6, 4.5, 5.8 and 8 μm bands, though there seem to be subtle differences. Across a bright section of the ionization/dissociation front, we found that, within the observational uncertainties, the maximum emission in all four IRAC channels coincides with that of H2 2.12 μm. The western, embedded, dissociation front close to the CO peak (Car I-W) is seen delineated by a bright, long bar of emission in the 3‐12 μm images, in the Midcourse Space Experiment bands A and C and also in radio continuum and hydrogen line emission. These occur in the vicinity of a region of previously reported strong [C I], [C II] and [O I] emission, tracers of PDRs. A few bright, compact knots of H2 emission, some possibly associated with [S II] emission, are found within the cloud. These may be shock-excited.

Near infrared observations of the star formation region GGD12-15

Near infrared imaging observations in JHK broad bands and HZ v=10 S(1) narrow band of the star formation region GGD12-15 are presented in this article. The images reveal young compact infrared clusters and infrared nebulae in association with infrared sources, as well as outflow activities characterized by H 2 emission knots. Most of the infrared point sources are invisible in the optical wave band. The JHK′ photometric results of 76 infrared point sources contain 32 with infrared excess, and 5 with the characteristics of protostars, indicating very active star formation activities in the molecular clouds. Massive stars (defined as those with spectral types earlier than B8) account for ∼ 10 – 26 per cent of all stars of the clusters. The K′ magnitude distribution of GGD12-15 peaks at 15.0 mag, and spreads broadly from 13.0 mag to 16.0 mag. The peak of the [H-K′l color distribution occurs at ∼0.7 mag, above which the redder components of the cluster make up 70 per cent of the total. The newly-discovered H2 emission knots are concentrated in the central area of the clusters, and the spatial distribution has obvious relation to violent star formation activities. Five of the emission knots are located in the central part of the molecular outflow, indicating that they may have been excited by the same source as the molecular outflow.

Near-IR 2D-spectroscopy of the 4''$\rm\times$ 4''region around the Active Galactic Nucleus of NGC 1068 with ISAAC/VLT

New near-IR long slit spectroscopic data obtained with ISAAC on VLT/ANTU (ESO/Paranal) complement and extend our previously published near-IR data (Alloin et al. 2001) to produce Br and H2 emission line maps and line profile grids of the central 4 00 4 00 region surrounding the central engine of NGC 1068. The seeing quality together with the use of an 0:3 00 wide slit and 0:3 00 slit position osets allow one to perform 2D-spectroscopy at a spatial resolution 0:5 00 . Slit orientations (PA= 102 and PA= 12) were chosen so as to match respectively the equatorial plane and the axis of the suspected molecular/dusty torus in NGC 1068. The selected wavelength range from 2.1 to 2.2m is suitable to detect and analyze the Br and H2 emission lines at a spectral resolution corresponding to 35 km s 1 . An asymmetric distribution of H2 emission around the continuum peak is observed. No H2 emission is detected at the location of the strong 2.2m continuum core (coincident within error-bars with the central engine location), while two conspicuous knots of H2 emission are detected at about 1 00 on each side of the central engine along PA= 90, with a projected velocity dierence of 140 km s 1 : this velocity jump has been interpreted in Alloin et al. (2001) as the signature of a rotating disk of molecular material. From this new data set, we find that only very low intensity Br emission is detected at the location of the two main knots of H2 emission. Another knot with both H2 and Br emission is detected to the North of the central engine, close to the radio source C where the small scale radio jet is redirected and close to the brightest (OIII) cloud NLR-B. It has a counterpart to the South, placed almost symmetrically with respect to the central engine, although mainly visible in the Br emission. The northern and southern knots appear to be related to the ionization cone. At the achieved spectral resolution, the H2 emission line profiles appear highly asymmetric with their low velocity wing being systematically more extended than their high velocity wing. A simple way to account for the changes of the H2 line profiles (peak-shift with respect to the systemic velocity, width, asymmetry) over the entire 4 00 4 00 region, is to consider that a radial outflow is superimposed over the emission of the rotating molecular disk. We present a model of such a kinematical configuration and compare our predicted H2 emission profiles to the observed ones. Excitation of the H2 line is briefly discussed: X-ray irradiation from the central engine is found to be the most likely source of excitation. Given the fact that the material obscuring our direct view toward the central engine is Compton thick (NH 10 24 cm 2 ), the observed location of the main H2 knots at a distance of 70 pc from the central engine suggests that the rotating molecular disk is warped.

The Detection of Outflows in the Infrared-quiet Molecular Core NGC 6334/I(North).

We find strong evidence for outflows originating in the dense molecular core NGC 6334/I(North): a 1000 M middle dot in circle molecular core distinguished by its lack of H ii regions and mid-IR emission. New observations were obtained of the SiO &parl0;2-->1&parr0; and &parl0;5-->4&parr0; lines with the SEST 15 m telescope and of the H2 (nu=1-->0) S(1) line with the ESO 2.2 m telescope. The line profiles of the SiO transitions show broad wings extending from -50 to 40 km s-1, and spatial maps of the line-wing emission exhibit a bipolar morphology with the peaks of the red and blue wing separated by 30&arcsec;. The estimated mass-loss rate of the outflow is comparable to those for young intermediate- to high-mass stars. The near-IR images show eight knots of H2 emission. Five of the knots form a linear chain that is displaced from the axis of the SiO outflow; these knots may trace shock-excited gas along the path of a second, highly collimated outflow. We propose that NGC 6334/I(North) is a rare example of a molecular core in an early stage of cluster formation.

Herbig-Haro Flows from the L1641-N Embedded Infrared Cluster

We have discovered a large number of Herbig-Haro (HH) flows associated with the embedded infrared cluster surrounding the IRAS source 05338-0624, the driving source of the L1641-N molecular outflow. The best collimated HH flow in the region, HH 303, stretches in two groups of knots along a well-defined axis from the VLA source that coincides with the IRAS source. This HH flow is coaxial with the blue northern lobe of the molecular flow. To the north-northwest of the cluster we find a long series of very large and finely shaped bow shocks, which stretch on a well-defined axis away from the cluster. The most distant HH object, HH 310, is 6.3 pc in projection from the center of the cluster, making it the largest HH lobe known from a low-mass star. We identify the counterlobe with an already known chain of infrared H2 emission knots. Additionally, we find two very large fragmented bow shocks, HH 403 and 404, to the northeast of and facing away from the cluster. They lie on an axis that passes through the cluster at projected distances of 4.2 and 5.4 pc. In the opposite direction, to the southwest we identify the previously known object HH 127 at a projected distance of 5.2 pc from the cluster and within an angle of 10° of the HH 403/404 axis. HH 127 consists of three faint knots also on a line through the cluster. Precisely south of the VLA source and on the axis of the HH 303 jet, we find a large bow shock, HH 61, which is 5.9 pc in projection from the cluster, and which we believe is part of the counterflow to the HH 303 jet. Our CCD images and 13CO maps clearly show that HH 61 and HH 127 are located just beyond the well-defined edge of the L1641 cloud, which explains why they are optically visible. Our extensive C18O map of the region shows that the cluster is associated with a prominent cloud core. Our 12CO map reveals, in addition to the known L1641-N outflow, a large pair of compact low-velocity outflow lobes, a southeastern blueshifted lobe, and a northwestern redshifted lobe, separated by 2.7 pc and centered on the infrared cluster. The numerous outflows in the region provide evidence that a large number of the young stars in the loose cluster are presently in active mass-losing phases. The L1641-N cluster is clearly the presently most active site of low-mass star formation in the L1641 molecular cloud.

A Deflected Molecular Jet in the Bipolar Outflow NGC 2264G

Recently published H2 emission data for the bipolar molecular outflow NGC 2264G are compared to recent CO (2 → 1) observations and existing VLA images. Virtually all of the H2 emission associated with this outflow is found either behind clumps of swept-up ambient material (i.e., closer to the central source of the outflow) or along the axis of the highest velocity CO emission. The highest velocity CO features appear to arise in jets that emerge from H2 emission knots and generally follow a pattern consistent with a deflection of a jet at these points. These deflections appear to result in part from a temporal change in the direction of the bipolar axis of the outflowing material ejected from the central source. We propose that effects such as these play a role in degrading the collimation of jet-driven outflow lobes.

The L1448 Molecular Jet

view Abstract Citations (66) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The L1448 Molecular Jet Bally, John ; Lada, Elizabeth A. ; Lane, Adair P. Abstract We have obtained near-infrared images of the L1448 molecular outflow in the J, H, and K bands and through a 1% passband filter centered on the 2.122 microns V = 1-0 S(1) line of molecular hydrogen. We report the discovery of a highly collimated, clumpy, and bipolar molecular hydrogen jet associated with the L1448 molecular outflow. We estimate that the total H2 luminosity of the L1448 outflow is about 0.2 Lsun. Most of the line emission in the northern outflow lobe arises from a narrow, curving filament consisting of a chain of knots. Some H2 knots and the bow-shaped emission regions protruding several arcseconds to the west of the filament may be shocks associated with CO- and SiO-emitting "bullets" seen in millimeter-wave observations. We interpret the H2 emission in the context of a jet-driven model for molecular outflows. Bright H2 emission near the molecular "bullets" may be produced by shocks propagating into the moving medium, while the extended and curving filament may be driven by expanding bow shocks in the wakes of the "bullets." A conical 2.2 microns continuum nebula extends from the driving source of the L1448 outflow toward the blueshifted outflow lobe. Several knots of H2 emission to the northeast of the main L1448 H2 filament may be associated with a separate outflow emerging from L1448 IRS 3, which we estimate has a total H2 luminosity of about 0.01 Lsun. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173393 Bibcode: 1993ApJ...418..322B Keywords: INFRARED: INTERSTELLAR: CONTINUUM; ISM: INDIVIDUAL ALPHANUMERIC: L1448; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; STARS: FORMATION full text sources ADS | data products SIMBAD (19)