Multiwavelength study of the Carina–Sagittarius Arm

I. Astrometric and photometric search for new open clusters in the 320° ≤ l ≤ 325° region

¹ Facultad de Ciencias Astronómicas y Geofísicas, (UNLP), La Plata, Argentina
² Instituto de Astrofísica La Plata, (CONICET – UNLP), La Plata, Argentina
³ Facultad Regional Concepción del Uruguay, (UTN), Entre Ríos, Argentina

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 29 December 2025
Accepted: 9 June 2026

Abstract

Aims. Our main goal is to determine whether the lower stellar density observed in the Carina–Sagittarius Arm region (320° ≤ l ≤ 325°, |b| ≤ 1°) is an intrinsic structural feature of the spiral arm or a consequence of high interstellar reddening and extinction along the line of sight.

Methods. We performed a systematic search for new open clusters using the HDBSCAN algorithm on Gaia DR3 astrometric data. The physical reality of the candidates was validated through a multiwavelength analysis, integrating Gaia photometry with the near-IR photometry of the 2MASS catalog, the mid-IR photometric information of the WISE catalog to identify young stellar objects (YSOs), and the radio continuum emission at 843 MHz with the SUMSS survey to identify and associated interstellar material.

Results. We report the discovery of five new open clusters, the ESFERA sample. Our analysis reveals four young systems (10–50 Myr), with ESFERA 3 hosting YSOs, while ESFERA 5 is identified as a 2 Gyr old cluster. Although the region lacks massive star-forming complexes, these clusters trace active star formation within the region, although at a lower efficiency.

Conclusions. Our results suggest that this region represents an intrinsic star formation valley or low-density node (the string in a morphology of beads on a string) and is not an effect of extinction. The discovery of these clusters demonstrates that while the local surface density is below the critical threshold for massive complexes, star formation persists in isolated small-scale pockets throughout the arm.