Millimeter interferometry of W3 IRS5: a trapezium in the making

Abstract

Context. Although most young massive stars appear to be part of multiple systems, it is poorly understood how this multiplicity influences the formation of massive stars. The high-mass star-forming region W3 IRS5 is a prime example of a young massive cluster where the cluster center is resolved into multiple subsources at cm and infrared wavelengths, a potential proto-Trapezium system. Aims. We investigate the protostellar content in the 1.4 mm continuum down to subarcsecond scales and study the compact outflow components, also tracing the outflows back to their driving sources via the shocktracing SiO and SO 2 emission. Methods. The region W3 IRS5 was mapped with the PdBI at 1.4 mm and 3.4 mm in the AB configurations, tuning the receivers to observe the molecular transitions SO 2 (22 2,20 -22 1,21 ), SO 2 (8 3,5 -9 2,8 ), SiO (2-1), and SiO (5-4).Results. In the continuum we detect five sources, one of them for the first time, while counterparts were detected in the NIR, MIR or at radio wavelengths for the remaining four sources. Three of the detected sources are within the inner 2100 AU, where the protostellar number density exceeds 10 6 protostars pc −3 assuming spherical symmetry. Lower limits for the circumstellar masses of the detected sources were calculated, ranging from ∼0.3 to ∼40 M although they were strongly affected by the spatial filtering of the interferometer, losing up to ∼90% of the single-dish flux. However, the projected separations of the sources ranging between ∼750 and ∼4700 AU indicate a multiple, Trapezium-like system. We disentangled the compact outflow component of W3 IRS5, detecting five molecular outflows in SiO, two of them nearly in the line of sight direction, which allowed us to see the collapsing protostars in the NIR through the cavities carved by the outflows. The SO 2 velocity structure indicates a rotating, bound system, and we find tentative signatures of converging flows as predicted by the gravoturbulent star formation and converging flow theories. Conclusions. The obtained data strongly indicate that the clustered environment has a major influence on the formation of high-mass stars; however, our data do not clearly allow us to distinguish whether the ongoing star-forming process follows a monolithic collapse or a competitive accretion mechanism.

Hydrides in young stellar objects: Radiation tracers in a protostar-disk-outflow system

“…At least six radio sources are in the Herschel beam. They represent "hypercompact" H II regions produced by highmass YSOs, at least two of which are O stars (van der Tak et al 2005;Rodón et al 2008). In this paper, we report the observations of major hydrides towards W3 IRS5 apart from H 2 O, CH + , and OH, which are studied in other projects of WISH (Chavarría et al 2010;Wampfler et al, in prep.…”

Water in massive star-forming regions: HIFI observations of W3 IRS5

“…The absorption in the H 2 O lines is blue-shifted (P-Cygni profile), suggesting an expansion of the envelope, as also detected by Benz et al (2010) in the hydride lines of W3 IRS5. The expansion is probably powered by the multiple outflows known to exist in W3 IRS5 (Rodón et al 2008). The p-H 2 O 1 11 -0 00 and o-H 2 O 2 12 -1 01 lines have a double plateau in absorption at −38 and −42 km s −1 .…”

Complex molecule formation around massive young stellar objects

“…NGC7538 IRS9 and NGC7538 IRS1 are located in Perseus, and NGC7538 IRS1 is known to house a bright hot core 19 and is situated in the middle of a cluster of continuum peaks and molecular outflows. W3 IRS5 is associated with at least five young stellar objects, two of which are massive [20][21][22][23][24] , and is known to present strong S-bearing molecular lines 25 . In summary all three sources are known to have complicated structures with many different potential origins of complex molecular emission.…”