Hubble Space Telescope NICMOS Imaging of W3 IRS 5: A Trapezium in the Making?

We present Hubble Space Telescope NICMOS imaging of W3 IRS 5, a binary high-mass protostar. In addition to the two protostars, NICMOS images taken in the F222M and F160W filters show three new 2.22 micron sources with very red colors; these sources fall within a region 5600 AU in diameter, and are coincident with a 100 solar mass dense molecular clump. Two additional point sources are found within 0.4'' (800 AU) of one of the high-mass protostars; these may be stellar companions or unresolved emission knots from an outflow. We propose that these sources constitute a nascent Trapezium system in the center of the W3 IRS 5 cluster containing as many as five proto OB stars. This would be the first identification of a Trapezium still deeply embedded in its natal gas.Comment: accepted to ApJ letter

High-Resolution Continuum Imaging at 1.3 and 0.7 cm of the W3 IRS 5 Region

High-resolution images of the hypercompact HII regions (HCHII) in W3 IRS 5 taken with the Very Large Array (VLA) at 1.3 and 0.7 cm are presented. Four HCHII regions were detected with sufficient signal-to-noise ratios to allow the determination of relevant parameters such as source position, size and flux density. The sources are slightly extended in our ~0.2 arcsecond beams; the deconvolved radii are less than 240 AU. A comparison of our data with VLA images taken at epoch 1989.1 shows proper motions for sources IRS 5a and IRS 5f. Between 1989.1 and 2002.5, we find a proper motion of 210 mas at a position angle of 12 deg for IRS 5f and a proper motion of 190 mas at a position angle of 50 deg for IRS 5a. At the assumed distance to W3 IRS 5, 1.83 +/- 0.14 kpc, these offsets translate to proper motions of ~135 km/s and ~122 km/s$ respectively. These sources are either shock ionized gas in an outflow or ionized gas ejected from high mass stars. We find no change in the positions of IRS 5d1/d2 and IRS 5b; and we show through a comparison with archival NICMOS 2.2 micron images that these two radio sources coincide with the infrared double constituting W3 IRS 5. These sources contain B or perhaps O stars. The flux densities of the four sources have changed compared to the epoch 1989.1 results. In our epoch 2002.5 data, none of the spectral indicies obtained from flux densities at 1.3 and 0.7 cm are consistent with optically thin free-free emission; IRS 5d1/d2 shows the largest increase in flux density from 1.3 cm to 0.7 cm. This may be an indication of free-free optical depth within an ionized wind, a photoevaporating disk, or an accretion flow. It is less likely that this increase is caused by dust emission at 0.7 cm.Comment: 13 pages, 3 figures To be published in The Astrophysical Journa

The Diverse Stellar Populations of the W3 Star Forming Complex

An 800 sq-arcmin mosaic image of the W3 star forming complex obtained with the Chandra X-ray Observatory gives a valuable new view of the spatial structure of its young stellar populations. The Chandra image reveals about 1300 faint X-ray sources, most of which are PMS stars in the cloud. Some, but not all, of the high-mass stars producing hypercompact and ultracompact H II (UCHII) regions are also seen, as reported in a previous study. The Chandra images reveal three dramatically different embedded stellar populations. The W3 Main cluster extends over 7 pc with about 900 X-ray stars in a nearly-spherical distribution centered on the well-studied UCHII regions and high-mass protostars. The cluster surrounding the prototypical UCHII region W3(OH) shows a much smaller (<0.6 pc), asymmetrical, and clumpy distribution of about 50 PMS stars. The massive star ionizing the W3 North H II region is completely isolated without any accompanying PMS stars. In W3 Main, the inferred ages of the widely distributed PMS stars are significantly older than the inferred ages of the central OB stars illuminating the UCHIIs. We suggest that different formation mechanisms are necessary to explain the diversity of the W3 stellar populations: cluster-wide gravitational collapse with delayed OB star formation in W3 Main, collect-and-collapse triggering by shock fronts in W3(OH), and a runaway O star or isolated massive star formation in W3 North.Comment: To appear in the Astrophysical Journal. 21 pages, 5 figures. A version with high-quality figures is available at http://www.astro.psu.edu/users/edf/W3_Chandra.pd

Structure and Composition of Molecular Clouds with CN Zeeman Detections I: W3OH

We have carried out a multi-species study of a region which has had previous measurements of strong magnetic fields through the CN Zeeman effect in order to to explore the relationship between CN and N$_2$H$^+$, both of which have evidence that they remain in the gas phase at densities of 10$^5$ - 10$^6$ cm$^{-3}$. To achieve this we map the 1 arcmin$^2$ region around the UCHII region of W3(OH) using the Combined Array for Millimeter-wave Astronomy (CARMA). Approximately 105 hours of data were collected in multiple array configurations to produce maps with an effective resolution of $\sim$ 2.5\arcsec at high signal-to-noise in CN, C$^{18}$O, HCN, HCO$^+$, N$_2$H$^+$, and two continuum bands (91.2 GHz and 112 GHz). These data allow us to compare tracer molecules associated with both low and high density regions to infer gas properties. We determine that CARMA resolves out approximately 35% of the CN emission around W3(OH) when compared with spectra obtained from the IRAM-30 meter telescope. The presence of strong absorption lines towards the continuum source in three of the molecular transitions infers the presence of a cold, dark, optically thick region in front of the continuum source. In addition, the presence of high-velocity emission lines near the continuum source shows the presence of hot clumpy emission behind the continuum source. These data determine that future high-resolution interferometric CN Zeeman measurements which cannot currently be performed (due to technical limitations of current telescopes) are feasible. We confirm that CN is indeed a good tracer for high density regions; with certain objects such as W3(OH) it appears to be a more accurate tracer than N$_2$H$^+$.Comment: 33 pages, 16 figures. Accepted by Ap

Signatures of inflow motion in cores of massive star formation: Potential collapse candidates

Using the IRAM 30 m telescope, a mapping survey in optically thick and thin lines was performed towards 46 high mass star-forming regions. The sample includes UC H{\sc ii} precursors and UC H{\sc ii} regions. Seventeen sources are found to show "blue profiles", the expected signature of collapsing cores. The excess of sources with blue over red profiles ([$N_{\rm blue}$ -- $N_{\rm red}$]/$N_{\rm total}$) is 29% in the HCO$^+$ $J$=1--0 line, with a probability of 0.6% that this is caused by random fluctuations. UC H{\sc ii} regions show a higher excess (58%) than UC H{\sc ii} precursors (17%), indicating that material is still accreted after the onset of the UC H{\sc ii} phase. Similar differences in the excess of blue profiles as a function of evolutionary state are not observed in low mass star-forming regions. Thus, if confirmed for high mass star-forming sites, this would point at a fundamental difference between low- and high-mass star formation. Possible explanations are inadequate thermalization, stronger influence of outflows in massive early cores, larger gas reserves around massive stellar objects or different trigger mechanisms between low- and high- mass star formation

Dust and HCO+ Gas in the Star Forming Core W3-SE

We report new results from CARMA observations of both continuum and HCO+(1-0) emission at 3.4 mm from W3-SE, a molecular core of intermediate mass, together with the continuum observations at 1.1 and 0.85/0.45 mm with the SMA and JCMT. A continuum emission core elongated from SE to NW (~10"), has been observed at the and further resolved into a double source with the SMA at 1.1 mm, with a separation of ~4". Together with the measurements from the Spitzer and MSX at mid-IR, we determined the SED of W3-SE and fit it with a thermal dust emission model, suggesting the presence of two dust components with different temperatures. The emission at mm/submm wavelengths is dominated by a major cold (~41 K) with a mass of ~65 Msun. In addition, there is a weaker hot component (~400 K) which accounts for emission in the mid-IR, suggesting that a small fraction of dust has been heated by newly formed stars. We also imaged the molecular core in the HCO+(1-0) line using CARMA at an angular resolution ~6". With the CARMA observations, we have verified the presence of a blue-dominated double peak profile toward this core. The line profile cannot be explained by infall alone. The broad velocity wings of the line profile suggest that other kinematics such as outflows within the central 6" of the core likely dominate the resulting spectrum. The kinematics of the sub-structures of this core suggest that the molecular gas outside the main component appears to be dominated by the bipolar outflow originated from the dust core with a dynamical age of >30000 yr. Our analysis, based on the observations at wavelengths from mm/submm to mid-IR suggests that the molecular core W3-SE hosts a group of newly formed young stars and protostars.Comment: 14 pages, 8 figures; accepted by Ap

Different Evolutionary Stages in the Massive Star Forming Region W3 Main Complex

We observed three high-mass star-forming regions in the W3 high-mass star formation complex with the Submillimeter Array and IRAM 30 m telescope. These regions, i.e. W3 SMS1 (W3 IRS5), SMS2 (W3 IRS4) and SMS3, are in different evolutionary stages and are located within the same large-scale environment, which allows us to study rotation and outflows as well as chemical properties in an evolutionary sense. While we find multiple mm continuum sources toward all regions, these three sub-regions exhibit different dynamical and chemical properties, which indicates that they are in different evolutionary stages. Even within each subregion, massive cores of different ages are found, e.g. in SMS2, sub-sources from the most evolved UCHII region to potential starless cores exist within 30 000 AU of each other. Outflows and rotational structures are found in SMS1 and SMS2. Evidence for interactions between the molecular cloud and the HII regions is found in the 13CO channel maps, which may indicate triggered star formation.Comment: Accepted for publication in ApJ, 22 pages, 23 figure

Molecular Line Emission from Massive Protostellar Disks: Predictions for ALMA and the EVLA

We compute the molecular line emission of massive protostellar disks by solving the equation of radiative transfer through the cores and disks produced by the recent radiation-hydrodynamic simulations of Krumholz, Klein, & McKee. We find that in several representative lines the disks show brightness temperatures of hundreds of Kelvin over velocity channels ~10 km s^-1 wide, extending over regions hundreds of AU in size. We process the computed intensities to model the performance of next-generation radio and submillimeter telescopes. Our calculations show that observations using facilities such as the EVLA and ALMA should be able to detect massive protostellar disks and measure their rotation curves, at least in the nearest massive star-forming regions. They should also detect significant sub-structure and non-axisymmetry in the disks, and in some cases may be able to detect star-disk velocity offsets of a few km s^-1, both of which are the result of strong gravitational instability in massive disks. We use our simulations to explore the strengths and weaknesses of different observational techniques, and we also discuss how observations of massive protostellar disks may be used to distinguish between alternative models of massive star formation.Comment: 15 pages, 9 figures, emulateapj format, accepted for publication in ApJ. Resolution of figures severely degraded to fit within size limits. Download the full paper from http://www.astro.princeton.edu/~krumholz/recent.htm

Submillimeter Emission from Water in the W3 Region

We have mapped the submillimeter emission from the 1(10)-1(01) transition of ortho-water in the W3 star-forming region. A 5'x5' map of the W3 IRS4 and W3 IRS5 region reveals strong water lines at half the positions in the map. The relative strength of the Odin lines compared to previous observations by SWAS suggests that we are seeing water emission from an extended region. Across much of the map the lines are double-peaked, with an absorption feature at -39 km/s; however, some positions in the map show a single strong line at -43 km/s. We interpret the double-peaked lines as arising from optically thick, self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted lines originate in emission near W3 IRS4. In this model, the unusual appearance of the spectral lines across the map results from a coincidental agreement in velocity between the emission near W3 IRS4 and the blue peak of the more complex lines near W3 IRS5. The strength of the water lines near W3 IRS4 suggests we may be seeing water emission enhanced in a photon-dominated region.Comment: Accepted to A&A Letters as part of the special Odin issue; 4 page

The Detection of Outflows in the IR-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 Msol molecular core distinguished by its lack of HII regions and mid-IR emission. New observations were obtained of the SiO 2-1 and 5-4 lines with the SEST 15-m telescope and the H2 (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, and spatial maps of the line wing emission exhibit a bipolar morphology with the peaks of the red and blue wing separated by 30". 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 which 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 I(N) is a rare example of a molecular core in an early stage of cluster formation.Comment: 4 pages, LaTeX, 3 ps figures, accepted by ApJ