New star clusters discovered towards the Galactic anticentre direction using Gaia DR3 data

We report the discovery of 31 new open clusters (OCs) identified in \textit{Gaia}~DR3 data through a systematic search over 220 adjacent $1^\circ\times1^\circ$ fields towards the Galactic anticentre, in the direction of the Perseus arm gap. Eight of them display low-density structures, possibly indicating open cluster remnants properties. The objects were identified and characterized through a combined analysis of photometric, kinematic, and spatial distributions, a methodology successfully applied in our previous works. Their structural properties, mean proper motions, ages, distances and reddening were derived and their centres cross-matched with the available catalogues. The clusters are low-concentrated systems and are mostly located within $3<d<5$ kpc, exhibiting reddening up to $E(B-V)\approx1.5$, and ages from $\sim$20 Myr to 1 Gyr. The new OCs represent a significant increase in the anticentre cluster census: $31%$ for $3<d<4$ kpc and $12%$ for $d>4$ kpc. They do not belong to the Perseus arm, but may be associated with the Outer Norma arm. The Gulf of Camelopardalis region appears as an interruption in the Perseus arm, possibly reflecting low star-formation activity, dust obscuration, or that the Milky Way is a flocculent, rather than a grand-design spiral galaxy.

💡 Research Summary

This paper reports the discovery of 31 new open star clusters (OCs) in the direction of the Galactic anticentre, specifically targeting a region known as the “Gulf of Camelopardalis,” a perceived gap in the Perseus spiral arm. The discovery was made using high-precision astrometric and photometric data from the Gaia satellite’s third data release (DR3).

The research team conducted a systematic visual search over 220 adjacent 1-degree by 1-degree fields along the Galactic plane (138° ≤ l ≤ 160°, -5° ≤ b ≤ +5°). Their methodology involved dividing the stellar population in each field into “blue” and “red” subsamples based on the mean (G_BP - G_RP) colour index. They then visually inspected the vector point diagrams (proper motion space) and spatial distributions (sky charts) of these subsamples to identify clustered overdensities indicative of star clusters. This technique, refined in their previous works, is particularly effective at finding low-contrast, sparse clusters that might be missed by fully automated algorithms.

The 31 newly identified clusters are generally low-concentration systems. Their astrophysical parameters were derived, revealing distances mostly between 3 and 5 kiloparsecs from the Sun, reddening values E(B-V) up to approximately 1.5, and ages ranging from about 20 million years to 1 billion years. Notably, eight clusters exhibit very low-density structures, suggesting they could be open cluster remnants in advanced stages of dynamical dissolution.

A key finding is that these new clusters do not appear to be located on the Perseus arm itself. Instead, their distances place them closer to the Galactic centre than the expected location of the Perseus arm in this direction, hinting at a possible association with the Outer Norma arm. The discovery significantly enriches the cluster census in the anticentre region, increasing the number of known clusters by 31% in the 3-4 kpc distance range and by 12% beyond 4 kpc.

The study concludes that the apparent scarcity of young clusters and other tracers in the “Gulf of Camelopardalis” is unlikely to be solely due to observational detection limits. It may reflect genuinely low star formation activity in that segment, effects of dust obscuration, or it could be evidence supporting the view that the Milky Way is a flocculent spiral galaxy with patchy and discontinuous arms, rather than a grand-design spiral with two well-defined continuous arms. This work underscores the continued incompleteness of the Galactic cluster inventory and highlights the value of combined visual and astrometric techniques for discovering faint stellar systems.