Euclid: Early Release Observations -- A glance at free-floating new-born planets in the sigma Orionis cluster

Abstract: We provide an early assessment of the imaging capabilities of the Euclid space mission to probe deeply into nearby star-forming regions and associated very young open clusters, and in particular to check to what extent it can shed light on the new-born free-floating planet population. This paper focuses on a low-reddening region observed in just one Euclid pointing where the dust and gas has been cleared out by the hot sigma Orionis star. One late-M and six known spectroscopically confirmed L-type substellar members in the sigma Orionis cluster are used as benchmarks to provide a high-purity procedure to select new candidate members with Euclid. The exquisite angular resolution and depth delivered by the Euclid instruments allow us to focus on bona-fide point sources. A cleaned sample of sigma Orionis cluster substellar members has been produced and the initial mass function (IMF) has been estimated by combining Euclid and Gaia data. Our sigma Orionis substellar IMF is consistent with a power-law distribution with no significant steepening at the planetary-mass end. No evidence of a low-mass cutoff is found down to about 4 Jupiter masses at the young age (3 Myr) of the sigma Orionis open cluster.

• The paper presents early Euclid observations that extend the σ Orionis cluster sequence by identifying candidate free-floating new-born planets.
• It employs high-resolution imaging over 0.58 square degrees and a refined photometric selection process anchored by seven spectroscopically confirmed substellar members.
• The findings reveal a continuous initial mass function down to ~4 Jupiter masses and hint at substellar binary systems, challenging traditional star formation models.

Euclid: Early Release Observations of Free-Floating New-Born Planets in the σ Orionis Cluster

The research paper discusses the early findings from the Euclid space mission, focusing on its imaging capabilities for exploring nearby star-forming regions and identifying new-born free-floating planets (FFPs) in the σ Orionis cluster. The Euclid mission, renowned for its high resolution and depth, aims to provide insights into stellar formation processes, particularly addressing the existence and potential discovery of low-mass, free-floating planetary bodies within stellar cradles.

Key Observations and Methodology

The study utilizes observations from the Euclid mission over a field within the Barnard 33 (Horsehead Nebula) region, part of the Orion B Giant Molecular Cloud complex. The focal area, identified as the ERO-SOri field, spans 0.58 square degrees, chosen specifically for its cleared low-reddening region affected by the intense radiation from the σ Orionis star. This area provides an optimal ground for analyzing planetary mass candidates down to a few times the mass of Jupiter.

A high-fidelity selection process is applied to distinguish bona-fide substellar members among the wide field of extragalactic and foreground stars. Seven confirmed σ Orionis substellar members, spectroscopically verified, serve as benchmarks for this method. These benchmarks help refine the search criteria, anchoring the identification of new candidates based on their measured photometric properties across Euclid's broad wavelength coverage.

Findings and Results

The study reveals several new candidate FFPs in close alignment with the σ Orionis cluster sequence. These candidates extend the cluster's sequence to fainter magnitudes, potentially representing some of the lowest mass objects within the cluster. The initial mass function (IMF) in this region, extended by combining Euclid and Gaia data, suggests a power-law distribution without a discernible low-mass cutoff down to about 4 Jupiter masses. These findings indicate that the IMF in very low-mass regimes remains consistent, challenging previous models predicting steepening at lower masses.

Additionally, the discovery within the σ Orionis cluster of potential substellar binary systems, close to Euclid's resolution limits, presents opportunities for further exploration of star formation dynamics in young stellar environments.

Implications and Future Work

The implications of these observations are significant. They not only contribute to a clearer picture of substellar populations and formation mechanisms but also bring into focus the broader question of how planetary and stellar formation processes differ across various environments. The potential ubiquity of free-floating planets challenges conventional star formation models, which typically do not account for the prevalence of planetary-mass objects unbound to a host star.

Future developments will necessitate utilizing Euclid's spectroscopic data to bolster the photometric findings and confirm the planetary nature of new candidates through characteristic spectral signatures. Moreover, expanding this study to other regions observed by Euclid will enable comparative analysis across different stellar nurseries, thereby refining our understanding of star formation under diverse conditions.

In conclusion, the observations and methodologies presented in this paper highlight the Euclid mission's capacity to advance our understanding of substellar object formation and distribution, paving the way for future research to unravel the complexities of the initial mass function at the scale of planetary masses.