As part of our large project to characterize the physical and chemical properties of the most massive star-forming molecular cloud in the Galaxy (Sagittarius B2, also known as SgrB2), we have conducted sensitive, high-resolution ALMA observations of the two main regions of the cloud: SgrB2(N) and SgrB2(M). We have discovered more than 40 dense cores in both regions, revealing the presence of two rich proto-clusters. These dense cores constitute the sites where new stars are forming. Moreover, most of these objects reveal a complex and rich chemistry, observable thanks to the detection of thousands of spectral lines associated with very different molecules - some of them related with sugars and with the first building blocks of life.

We use state-of-the-art telescopes like ALMA to study regions within our Galaxy where (high-mass) stars are forming. The complexity of the datasets requires the use of advanced softwares that allow the analysis and characterization of the physical and chemical properties of the first stages in the formation of stars.

This project is led by Álvaro Sánchez-Monge.

The above described molecular cloud complex SgrB2 harbors two main sites of active high-mass star formation, one of them is SgrB2(N). Our recent ALMA observations revealed a filamentary network within this region. The spatial structure, together with the presence of the massive central region, suggest that these filaments may be associated with accretion processes, transporting material from the outer regions to the central dense hub. The derived velocity gradients along the filaments are 10–100 times larger than those typically found on larger scales (∼1 pc) in other star-forming regions, resulting in mass accretion rates of about ~0.16 M$_\odot$ per year. Some filaments harbor dense cores that are likely forming stars and stellar clusters. The stellar content of these dense cores is in the order of 50% of the total mass. The timescales required for the dense cores to collapse and form stars, exhausting their gas content, are compared with the time scale of their accretion process onto the central hub. Therefore the cores may merge in the center when already forming stellar clusters but still containing a significant amount of gas, resulting in a ‘damp’ merger. The high density and mass of the central region, combined with the presence of converging filaments with high mass, high accretion rates and embedded dense cores already forming stars, suggest that Sgr B2(N) may have the potential to evolve into a super stellar cluster.

This research is part of Andreas Schwörer's PhD.
 

The giant molecular cloud Sagittarius B2 (SgrB2) is the most massive (∼ 10⁷ M_o) region with ongoing high-mass star formation in the Galaxy. SgrB2 has a higher density (> 10⁵ cm⁻³) and dust temperature (∼ 50 − 70 K) compared to other star forming regions in the Galactic plane. An envelope, surrounding the two hot cores, extends over 20 pc. The envelope contains more than 99% of the total mass of Sgr B2. This project focuses on the ionized content in the envelope. Using VLA, we observed the centimeter continuum emission in the envelope and dicovered that the envelope is filled with ionized gas. The ionized gas is found to be spatially correlated with the high-mass protostellar cores identified in the ALMA mm continuum map.  Also, non-thermal (synchrotron) emission is revealed from the spectral index of the continuum emission, which may be caused by the feedback processes of star-formation in the envelope of SgrB2.

This work is part of the PhD thesis of Fanyi Meng.