Abstract
Context. High-mass star formation typically takes place in a crowded environment, with a higher likelihood of young forming stars affecting and being affected by their surroundings and neighbours, as well as links between different physical scales affecting the outcome. However, observational studies are often focused on either clump or disc scales exclusively. Aims. We explore the physical and chemical links between clump and disc scales in the high-mass star formation region W3 IRS4, a region that contains a number of different evolutionary phases in the high-mass star formation process, as a case-study for what can be achieved as part of the IRAM NOrthern Extended Millimeter Array (NOEMA) large programme named CORE: “Fragmentation and disc formation in high-mass star formation”. Methods. We present 1.4 mm continuum and molecular line observations with the IRAM NOEMA interferometer and 30 m telescope, which together probe spatial scales from ~0.3−20′′ (600−40 000 AU or 0.003−0.2 pc at 2 kpc, the distance to W3). As part of our analysis, we used XCLASS to constrain the temperature, column density, velocity, and line-width of the molecular emission lines. Results. The W3 IRS4 region includes a cold filament and cold cores, a massive young stellar object (MYSO) embedded in a hot core, and a more evolved ultra-compact (UC)H II region, with some degree of interaction between all components of the region that affects their evolution. A large velocity gradient is seen in the filament, suggesting infall of material towards the hot core at a rate of 10−3−10−4 M⊙ yr−1, while the swept up gas ring in the photodissociation region around the UCH II region may be squeezing the hot core from the other side. There are no clear indications of a disc around the MYSO down to the resolution of the observations (600 AU). A total of 21 molecules are detected, with the abundances and abundance ratios indicating that many molecules were formed in the ice mantles of dust grains at cooler temperatures, below the freeze-out temperature of CO (≲35 K). This contrasts with the current bulk temperature of ~50 K, which was obtained from H2CO. Conclusions. CORE observations allow us to comprehensively link the different structures in the W3 IRS4 region for the first time. Our results argue that the dynamics and environment around the MYSO W3 IRS4 have a significant impact on its evolution. This context would be missing if only high resolution or continuum observations were available.
Highlights
Star formation is an inherently multi-scale phenomenon, with different processes having the potential to affect, guide, or govern its outcome from the scales of the entire Galaxy down to the scale of individual protostars, both for individual stars and for stellar populations in general
We explore the physical and chemical links between clump and disc scales in the high-mass star formation region W3 IRS4, a region that contains a number of different evolutionary phases in the high-mass star formation process, as a case-study for what can be achieved as part of the IRAM NOrthern Extended Millimeter Array (NOEMA) large programme named CORE: “Fragmentation and disc formation in high-mass star formation”
A large velocity gradient is seen in the filament, suggesting infall of material towards the hot core at a rate of 10−3−10−4 M yr−1, while the swept up gas ring in the photodissociation region around the UCH II region may be squeezing the hot core from the other side
Summary
Star formation is an inherently multi-scale phenomenon, with different processes having the potential to affect, guide, or govern its outcome from the scales of the entire Galaxy (for example Galactic gravitational potential, spiral arms, magnetic fields, metallicity) down to the scale of individual protostars (for example turbulence, magnetic fields, fragmentation, rotation, infall, outflow), both for individual stars and for stellar populations in general (for recent reviews see for example Zinnecker & Yorke 2007; Dobbs et al 2014; André et al 2014; Offner et al 2014; Padoan et al 2014; Li et al 2014a,b; Molinari et al 2014; Tan et al 2014; Krumholz et al 2014). One over-arching task within star formation research is to understand what processes dominate on which scales, and what minimum range of scales and set of processes must be included and understood in order to predict the outcome of star formation. Understanding the interplay between different scales and processes will give constraints to both global properties, such as the star formation timescale and efficiency, and will reveal what key factors determine the outcome of star formation. This is a challenging task given the range of temperatures, densities, scales, and processes that are relevant for star formation in general, and in the complex regions where high-mass stars ( 8 M ) are formed. The distances to high-mass star formation regions are typically 2 kpc, leading to trade-offs between resolution to capture small-scale processes and both field-of-view and sensitivity to the larger scale emission needed to link sites of star formation with their neighbours and environment
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