The applicability of the JAGB method for measuring the distance of galaxies subject to different metal-enrichment rates

¹ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00100 Roma, Italy
² INAF, Observatory of Rome, Via Frascati 33, 00077 Monte Porzio Catone (RM), Italy
³ Dipartimento di Fisica, Sapienza, Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
⁴ ASI-Space Science Data Center, Via del Politecnico, I-00133 Rome, Italy
⁵ Istituto Nazionale di Astrofisica– Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy

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

Received: 10 April 2026
Accepted: 9 May 2026

Abstract

Context. The JAGB method has been proposed over the last years as a possible distance indicator for galaxies in the Local Group and beyond. The nature of the stars populating the J region, as well as the conditions of the star formation history and the structural properties of the galaxies for the direct application of this method, still needs to be investigated.

Aims. We aim to assess the robustness of the JAGB method in measuring the distance of galaxies, presenting a detailed theoretical analysis of the stars populating the J region of the (J − K_S, J) diagram. The primary goal of the present analysis is to identify the properties of the corresponding J luminosity function (JLF) that are insensitive to the metal-enrichment history of the interstellar medium and may therefore provide robust distance indicators.

Methods. We used a population synthesis approach, based on extant stellar models of asymptotic giant branch evolution coupled self-consistently with the description of the dust formation process in the wind. This was done to build synthetic distributions of stars on the (J−K_S,J) diagram and to calculate the corresponding JLF of the stars in the J region. The simulations were repeated for different hypotheses regarding the time variation of the metallicity of the interstellar medium in order to study the sensitivity of the JLF to the timescale of the metal-enrichment process.

Results. The statistics of the J region is mostly determined by the stars formed between ∼6 Gyr and ∼1 Gyr ago, because stars formed outside this time interval barely enter the JAGB box. The shape of the JLF changes significantly with the metal-enrichment, in particular through variations in the peak J magnitude, which changes over a range exceeding 0.3 mag. Conversely, the mean J magnitude, M_J^av, proves much less dependent on the previous history of the galaxy and thus a much more robust distance indicator: we find M_J^av = −6.2 ± 0.05 mag for all the cases investigated. The uncertainties connected to the still largely unknown process of mass loss suffered by low-mass stars during the evolution along the red giant branch are also commented on.