arXiv subjects

Claudio Gavetti

Publications and source records attributed to Claudio Gavetti.

4 recordsLinked to original sources

arXiv2026

The dwarf galaxy NGC 185: the flagship of Andromeda's dwarf galaxies for the study of evolved multiple stellar populations

Reaching galaxies at 10-15 Mpc with HST and JWST requires star formation history (SFH) diagnostics that do not rely on the faint main sequence turn-off. We investigate whether horizontal branch (HB), red clump (RC), and red and asymptotic giant branch (RGB, AGB) stars can fill this role for dwarf elliptical galaxies, using NGC 185 as a test case. We use stellar evolution models of low- and intermediate-mass stars as inputs to population synthesis simulations that reproduce the colour distribution and luminosity function of stars in the (mF606W-mF814W, mF814W) diagram. The study of the stars populating the HB is used to derive the distance modulus and reddening, the average mass loss suffered by the stars during the ascending on the RGB and the SFH occurred during the ancient epochs, before 7 Gyr ago. The luminosity function of the RC gives us constraints on the recent SFH (<8 Gyr). The distribution of HB stars yields a reddening E(B-V)=0.20 mag and a distance modulus DM=24.10 mag for NGC 185. The average mass lost by low-mass stars during the RGB phase is 0.22 +- 0.01 Msun. Star formation was concentrated at early epochs, with half of the stars formed more than 11 Gyr ago. The morphology of the HB indicates essentially no metallicity spread among stars older than 8 Gyr, whereas the slope of the RGB suggests that part of the stars younger than 5-6 Gyr are slightly enriched in metals. Once RGB mass loss is adequately constrained, evolved stars can provide a reliable SFH for dwarf elliptical galaxies well beyond the reach of MSTO-based methods. We discuss the implications for more distant systems and the remaining uncertainties in the underlying stellar models.

astro-ph.GA↗

arXiv2026

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

The JAGB method has been proposed in recent years as a possible distance indicator for galaxies in the Local Group and beyond. However, the nature of the stars populating the J region, and the conditions required for the direct application of this method, still need to be clarified. We investigate the robustness of the JAGB method through a detailed theoretical analysis of the stars populating the J region of the (J-Ks, J) diagram. The main goal is to identify the properties of the corresponding J luminosity function (JLF) that are minimally affected by the previous evolutionary history of the host galaxy, particularly its metal enrichment history. We use a population synthesis approach based on AGB stellar evolution models coupled consistently with dust formation in the stellar wind. Synthetic stellar distributions in the (J-Ks, J) diagram and the related JLFs are calculated for different assumptions on the metallicity evolution of the interstellar medium, in order to study how the JLF depends on the efficiency of metal enrichment. We find that the JAGB population is dominated by stars formed between about 1 and 6 Gyr ago, while stars formed outside this interval contribute only marginally to the JAGB region. The shape of the JLF strongly depends on the metal enrichment history, and the position of the J-band peak varies by more than 0.3 mag among the different cases explored. Conversely, the mean J-band magnitude, MavJ, is much less sensitive to the previous history of the galaxy and therefore represents a more reliable distance indicator. For all the cases investigated we find MavJ = -6.2 +/- 0.05 mag. We also discuss the uncertainties related to the still poorly constrained mass-loss process experienced by low-mass stars during the red giant branch phase.

astro-ph.GA↗

arXiv2026

The role of mass loss in constraining quenching time in dwarf galaxies from AGB and RGB star counts

The capability of reconstructing the past star formation history of dwarf elliptical galaxies out of the Local Volume relies on modelling bright stellar populations currently evolving through the red giant branch (RGB) and the asymptotic giant branch (AGB) phases. Recent studies proposed the use of the relative fractions of RGB and AGB stars populating specific boxes in the observational colour-magnitude plane to infer the epoch within which 90\% of the stellar population of the galaxy formed (T90). We aim at understanding the physical process of stellar evolution that are constrained by the relationship between the relative fraction of AGB and RGB stars of dwarf galaxies and the T90 epoch. We use updated stellar models that include the description of dust formation in the wind, to undertake a population synthesis approach, to allow monitoring the variation of the NAGB/NRGB ratio with time. The effects of some specific ingredients, such as the mass loss experienced by low-mass stars during the RGB phase, and the details of the time variation of the star formation rate, are extensively explored and tested against data. The mass lost by low-mass stars during the RGB evolution proves the most relevant ingredients affecting the time variation of NAGB/NRGB: at metallicities ~ 1/10 solar, a mass loss ~ 0.25Msun is required to reproduce the observations. This analysis allows to derive a relationship between NAGB/NRGB and T90, with a ~ 1 Gyr uncertainty on T90.

astro-ph.GA↗

arXiv2025

A study of Andromeda to improve our knowledge on the evolution and dust production by AGB stars

We study the AGB population of the galaxy M31, based on available HST and Spitzer data, to characterize the individual sources in terms of mass, metallicity and formation epoch of the progenitors. Particular attention is dedicated to the derivation of the dust production rate of the stars, in the attempt of determining the global current dust production rate of the galaxy, divided between the silicates and the carbonaceous dust contributions. We use results from stellar evolution modelling complemented by the description of the dust formation process in the wind, to be used in a population synthesis approach, based on the star formation history and age-metallicity relationship obtained in previous investigations. The comparison between the results from synthetic modelling and the data available are used for the characterization of AGB stars in M31. We find that the bulk of the AGB population of M31 is composed by low-mass stars of different metallicity formed between 6 Gyr and 14 Gyr ago, with an additional, significant contribution from the progeny of 1.7-2.5Msun stars formed during the secondary peak in the star formation, which occurred between 1 and 2 Gyr ago. The dust production rate of the galaxy is mostly provided by carbon stars, whose contribution is of the order of 4x10^{-4} Msun/yr, completed by silicates production from massive AGB stars, occurring at a rate of 6x10^{-5} Msun/yr. The implications of the present results on the reliability of AGB modelling are also commented.

astro-ph.GA↗