[astro-ph.GA] In the Central Molecular Zone (CMZ), shocks play a key role in triggering star formation and driving chemical enrichment. The Sgr B2 complex is a prime template, hosting massive protoclusters (N, M, S) and the northern G+0.693 cloud, which exhibits shock-induced prestellar signatures.
We report on G+0.633-0.0604, a newly identified shock-dominated and chemically rich cloud at the southern edge of Sgr B2, where the next star formation episodes are proposed. We characterise its physical properties and the shocks shaping it.
We present analyses on CH3CCH, CH3CN, HC3N, HNCO and several isotopologues of CO to infer the gas Tkin and density, using high-sensitivity spectral surveys from the Yebes 40m, IRAM 30m and APEX radio telescopes that covered ~100 GHz across the 31-275 GHz range. We also used 3 mm IRAM 30m mosaics (13’×13′) of Sgr B2 in HC3N, HNCO and C2H5OH to probe G+0.633 environment.
We identify three velocity components: a narrow main one (C1, vLSR~48.5 km/s; FWHM~10 km/s), and two broader, fainter components at higher velocities, C2 (~61 km/s; ~13 km/s) and C3 (~89 km/s; ~18 km/s), all showing similar properties (Tkin~55-90 K, NH2~(3-7)×1022 cm−2, nH2~(0.5-2.5)×104 cm−3) and extended distributions. C1 delineates G+0.633 physically and coincides with a peak in HNCO, supporting a shock-driven origin likely rooted in the cloud-cloud collision shaping Sgr B2 and also traced by C2, which extends north to G+0.693. C3 is kinematically unlinked and related to large-scale CMZ dynamics.
Of the three, C1 may represent a very early protocluster phase, yet to be confirmed. G+0.633 thus emerges as a new shock-dominated CMZ cloud resembling G+0.693, providing another unique laboratory to investigate how shocks drive molecular complexity and regulate the onset of cluster formation in the CMZ.
HC3N, HNCO and C2H5OH integrated intensity maps of the Sgr B2 region obtained with the IRAM 30m radio telescope for the three velocity components identified in G+0.633 (different columns). The integration was performed over their corresponding linewidths (43.5−53.5 km s−1 for C1 in red; 54.5−67.5 km s−1 for C2 in green, 80.0−98.0 km s−1 for C3 in cyan). Each map was normalised to its peak integrated intensity (indicated in the lower right corner), with the beam size shown in the lower left corner (∼25.9′′, 29.5′′and 30.4′′ for HC3N, HNCO and C2H5OH maps, respectively). Contours for HC3N and HNCO span 90 to 10% of the peak in steps of 10%, with the lowest level corresponding to ∼6−50σ (σ ≡ map rms) depending on the molecule and component. For C2H5OH, contours extend down to 20% of the peak (2.9σ for C1, 4.6σ for C2 and 2σ for C3). The 40−50 km s−1 “hole” feature observed in 13CO by Hasegawa et al. (1994) and Sato et al. (2000) is evident in the C1 maps and indicated by the white dashed circle, while the “clump” at ∼60−80 km s−1 is visible in C2. The green circle at G+0.633 position indicates the largest beam covered in the survey (∼56′′, Yebes 40m beam at ∼31 GHz). The coloured stars and the golden dashed square are the same as in Fig. 1. — [astro-ph.GA]
D. San Andrés (1 and 2), L. Colzi (1), V. M. Rivilla (1), M. Sanz-Novo (3), S. Martín (4 and 5), I. Jiménez-Serra (1), S. Zeng (6) ((1) Centro de Astrobiología (CAB), CSIC-INTA, Torrejón de Ardoz, Madrid, Spain, (2) Departamento de Física de la Tierra y Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, Madrid, Spain, (3) Center for Astrochemical Studies, Max-Planck-Institute für extraterrestrische Physik, Garching bei München, Germany, (4) European Southern Observatory, Vitacura, Santiago, Chile, (5) Joint ALMA Observatory, Vitacura, Santiago, Chile, (6) Star and Planet Formation Laboratory, Pioneering Research Institute (PRI), RIKEN, Hirosawa, Wako, Saitama, Japan)
Comments: 20 pages, 11 figures, 8 tables, 6 appendix – Accepted for publication in Astronomy & Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2607.01481 [astro-ph.GA] (or arXiv:2607.01481v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2607.01481
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From: David San Andrés
[v1] Wed, 1 Jul 2026 21:23:03 UTC (16,766 KB)
https://arxiv.org/abs/2607.01481
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