A homogeneous three-dimensional view of molecular cloud kinematics out to 2.5 kpc

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Abstract
Context. Understanding the large-scale dynamics of molecular clouds (MCs) is crucial to constraining the processes that govern star formation and the structure and evolution of the Galaxy. While gas tracers have traditionally been used to map MC kinematics, stellar tracers such as young stellar objects (YSOs) and open clusters (OCs) provide a complementary approach that enables direct comparisons between the stellar and gaseous components. Aims. We aim to compare the kinematics of young (≤30 Myr) OCs with YSOs in the same star-forming region, the latter being assumed to trace the motions of the parent cloud gas. Subsequently, we intend to reconstruct the three-dimensional (3D) motions of the main MC complexes within 2.5 kpc of the Sun using both YSOs and young OCs as tracers. Methods. Using Gaia Data Release 3 (DR3) astrometry and complementary spectroscopic surveys providing radial velocities (RVs), we compiled a unified sample of24 146 young stars, comprising YSOs and OC members. We applied robust clustering in proper-motion space to identify co-moving YSOs and derived cloud-averaged motions via Monte Carlo sampling. These motions were compared with the kinematics inferred from OCs younger than 30 Myr. Finally, we performed orbital integrations in a realistic Galactic potential to trace the past evolution of the clouds and to quantify their expansion and rotation. Results. We derive homogeneous 3D kinematics for 15 star-forming regions within 2.5 kpc. YSOs and OCs exhibit strongly consistent kinematics within each cloud, with a median spatial velocity offset of ≲2 km s −1 , allowing us to combine them into a unified tracer sample. The resulting bulk cloud motions show a median peculiar velocity of ≃9 km s −1 with respect to the Galactic rotation. We used our catalogue to trace back the Solar System’s voyage through the Orion cloud and the common origin of Lupus, Ophiuchus, and Corona Australis in the Sco-Cen region. Internally, we detected significant expansion in Orion and Ophiuchus (at a 5 σ level) and coherent rotation in at least six complexes, likely reflecting local processes such as stellar feedback and angular-momentum redistribution. Conclusions. Young OCs and YSOs exhibit broadly consistent kinematics, and therefore OCs can also be used to trace the bulk motion of the star-forming regions.
Funding Information
  • Xunta de Galicia (ED431B 2024/21)
  • Xunta de Galicia (ED431B 2024/02)
  • Xunta de Galicia (CITIC ED431G 2023/01)
  • Ministerio de Ciencia, Innovación y Universidades (PRE2022-104959)
  • Ministerio de Ciencia, Innovación y Universidades (PID2021122842OB-C22)
  • Ministerio de Ciencia, Innovación y Universidades (PID2021-127289NB-I00)
  • Ministerio de Ciencia, Innovación y Universidades (PID2024157964OB-C22)
  • Ministerio de Ciencia, Innovación y Universidades (MICIN/AEI/10.13039/501100011033)
  • Ministerio de Ciencia, Innovación y Universidades (PID2021-122842OB-C21)
  • Ministerio de Ciencia, Innovación y Universidades (PID2024-157964OB-C21)
  • Instituto de Ciencias del Cosmos, Universitat de Barcelona (CEX2024-001451-M)
  • Generalitat de Catalunya (2021-SGR-00679 GRC)
  • Ministerio de Ciencia, Innovación y Universidades (RYC2021-031683-I)
  • Swedish National Space Agency (2023-00146)
  • Horizon 2020 Framework Programme (101034413)
  • HORIZON EUROPE European Research Council (10113520)

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