Alma-Imf

Abstract

Aims. The processes that determine the stellar initial mass function (IMF) and its origin are critical unsolved problems, with profound implications for many areas of astrophysics. The W43-MM2&MM3 mini-starburst ridge hosts a rich young protocluster, from which it is possible to test the current paradigm on the IMF origin. Methods. The ALMA-IMF Large Program observed the W43-MM2&MM3 ridge, whose 1.3 mm and 3 mm ALMA 12 m array continuum images reach a ~2500 au spatial resolution. We used both the best-sensitivity and the line-free ALMA-IMF images, reduced the noise with the multi-resolution segmentation technique MnGSeg, and derived the most complete and most robust core catalog possible. Using two different extraction software packages, getsf and GExt2D, we identified ~200 compact sources, whose ~100 common sources have, on average, fluxes consistent to within 30%. We filtered sources with non-negligible free-free contamination and corrected fluxes from line contamination, resulting in a W43-MM2&MM3 catalog of 205 getsf cores. With a median deconvolved FWHM size of 3400 au, core masses range from ~0.1 M⊙ to ~70 M⊙ and the getsf catalog is 90% complete down to 0.8 M⊙. Results. The high-mass end of the core mass function (CMF) of W43-MM2&MM3 is top-heavy compared to the canonical IMF. Fitting the cumulative CMF with a single power-law of the form N(> log M) ∝ Mα, we measured α = −0.95 ± 0.04, compared to the canonical α = −1.35 Salpeter IMF slope. The slope of the CMF is robust with respect to map processing, extraction software packages, and reasonable variations in the assumptions taken to estimate core masses. We explore several assumptions on how cores transfer their mass to stars (assuming a mass conversion efficiency) and subfragment (defining a core fragment mass function) to predict the IMF resulting from the W43-MM2&MM3 CMF. While core mass growth should flatten the high-mass end of the resulting IMF, core fragmentation could steepen it. Conclusions. In stark contrast to the commonly accepted paradigm, our result argues against the universality of the CMF shape. More robust functions of the star formation efficiency and core subfragmentation are required to better predict the resulting IMF, here suggested to remain top-heavy at the end of the star formation phase. If confirmed, the IMFs emerging from starburst events could inherit their top-heavy shape from their parental CMFs, challenging the IMF universality.

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IX. Physical Properties and Spatial Distribution of Cores in IRDCs

“…Column (3) in Table 4 shows the temperature used for each core in the mass estimation. We confirmed that the dust emission is optically thin by using Equation (B.2) from Pouteau et al (2022). We find that 99% of cores have an optical depth smaller than 0.04, and the maximum value is ∼0.1.…”

Alma-Imf

“…Moreover, we showed that using both the bsens and cleanest images (see definitions in Sect. 3.2), the number of robust core detections could further increase by a factor of up to ∼2 (companion paper: Paper III, Pouteau et al 2022). Extracting these additional sources requires careful treatment of the line contamination to exclude emission peaks associated with line rather than continuum emission.…”

“…( 3)). According to Motte et al (2018b) and the companion paper, Paper III (Pouteau et al 2022), we estimate that about 20 cores (i.e., the most massive 3% of the core sample) could be partially optically thick. Therefore, their masses would be underestimated by factors of 15-40% when using Eq.…”

Unveiling the Formation of the Massive DR21 Ridge

“…In the DR21 cloud, the formation of high-mass stars would be directly related to the lifetime of the massive ridge. This potentially shorter phase of high-mass star formation might fit with the observed shallow slope of the core mass function (CMF) in high-mass star-forming regions (Liu et al 2018;Motte et al 2018b;Pouteau et al 2022) compared to the power-law tail of the initial mass function (IMF), as well as the slightly shallower IMFs in young clusters (< 4 Myr) of Cygnus X (Maia et al 2016). However, further work with, e.g., the ALMA-IMF sample (Motte et al 2022) will be needed to better understand the evolution of these topheavy CMFs in high-mass star-forming regions and how it connects with the IMF of young stellar clusters, as well as the evolution of high-mass star-forming clouds and filaments (Pouteau et al 2022).…”