Re-visiting the Canis Major star-forming region with Gaia data release 3 data

TL;DR

This study revisits the Canis Major star-forming region by leveraging Gaia DR3 astrometry and photometry to assemble a large, coherent membership census across a $16\, \mathrm{deg}^2$ field. By combining a Gaussian Mixture Model–based membership analysis with new FLAMES radial-velocity measurements, the authors identify 1,531 members (1,130 new candidates; 401 previously known) and uncover two main subgroups, Cluster A and Cluster B, at similar distances yet with distinct disc fractions. Distances and full 3D motions are inferred with Kalkayotl 2.0, revealing $d_A = 1{,}150^{+79}_{-88}$ pc and $d_B = 1{,}183^{+103}_{-108}$ pc and systemic $UVW$ distributions that overlap, indicating a broadly coeval population. Isochronal ages from BHAC15, PARSEC, and MIST place the mean age at $\sim$2–3 Myr for both clusters, while infrared-excess analysis suggests Cluster A may be somewhat younger due to a higher disc fraction. The work significantly expands the known CMa census, elucidates its kinematic structure, and sets the stage for future Gaia DR4 data and multi-wavelength spectroscopy to refine the region's star-formation history.

Abstract

Context: The Canis Major (CMa) star-forming region, a remote molecular cloud complex within the recently discovered Radcliffe Wave, remains under-explored in the literature. Aims: We revisit the stellar census in the CMa region, characterizing its stellar population, kinematics, and age using recent astrometric and photometric data from the third data release of the Gaia space mission (Gaia DR3). Methods: We conducted a membership analysis of Gaia DR3 sources across a 16 deg$^2$ field encompassing the youngest subgroups in CMa. This new stellar census, combined with spectroscopic observations, allowed us to investigate the structure, kinematics, and age of this region. Results: We identified 1531 objects as members of the CMa region, confirming 401 previously known members and introducing 1130 new candidate members. These objects have magnitudes ranging from 10 to 18 mag in the G band from Gaia DR3. We identified two subgroups of CMa stars in our sample labelled as Cluster A and Cluster B. They are located at roughly the same distance ($d_{A} = 1150^{+79}_{-88}$ pc and $d_{B} = 1183^{+103}_{-108}$ pc) and exhibit similar space motions that can be derived thanks to the precise radial velocities obtained in this study. The subgroups have a mean isochronal age of about 2-3 Myr. However, based on infrared photometry we show that Cluster A has a higher fraction of disc-bearing stars suggesting that it could be somewhat younger than Cluster B. Conclusions: Our analysis provides new insights into the stellar population of the Canis Major region, by identifying new members, characterizing their kinematics, and assessing their evolutionary stages. Future studies incorporating additional data from upcoming Gaia data releases, multi-wavelength and high-resolution spectroscopic observations will be essential to further advance our understanding of the history of star formation in this region.

Figures (10)

• Figure 1: Spatial distribution of 1 531 stars identified as members of CMa region, overlaid on Digitized Sky Survey 2 (DSS2) red-band image. The stars are colour-coded according to their subgroup membership: yellow symbols indicate stars belonging to Cluster A, while orange symbols represent stars assigned to Cluster B, as described in Section \ref{['subsec:subgroups']}.
• Figure 2: Parallaxes and proper motions of 1 531 stars identified in our membership analysis and colour-magnitude diagram of CMa sample found by our membership investigation. The empirical isochrone, derived in our analysis, is indicated by the solid black line. The individual membership probabilities of the stars are scaled from 0 to 1 and shown with different colours.
• Figure 3: Venn diagram comparing the number of stars in common between our analysis and the previous study by Santos2021.
• Figure 4: Left panel: Kernel density estimation of the radial velocity distribution for the sample of 90 members with available measurements. Right panel: Distribution of radial velocity uncertainties. The ticks in the horizontal axes mark the measurements for individual stars.
• Figure 5: Comparison of radial velocity data obtained from our observations and Gaia DR3 data. One source of our sample (namely Gaia DR3 3046207139539172864) is not shown to improve the visibility of the plot.