Solar twins in Gaia DR3 GSP-Spec II. Age distribution and its implications for the Sun's migration

Abstract

Solar twins are among the most powerful tracers of Galactic disk evolution owing to their unique property of sharing nearly solar metallicities ([Fe/H] ~ 0) while spanning a wide range of ages. To grasp solar twins as relics of Galaxy evolution, individual twins must be tagged with ages. A sufficiently large and well-characterized stellar sample then allows us to construct an age distribution that encodes the star formation history beyond our local region, modulated by the efficiency of radial migration of stars. Based on our catalog of 6,594 high-quality local (<~ 300 pc) solar twins from the Gaia Data Release 3 spectroscopic (GSP-Spec) catalog, we derived their age distribution after carefully deconvolving the selection function. We find two distinct features: a narrow peak around ~ 2 Gyr and a broad bump extending over ~ 4--6 Gyr. First, we argue that the former corresponds to a relatively recent burst of star formation that occurred in the disk, including at least a local region within a few kiloparsecs of the Sun, which is in good agreement with previous results deduced from independent works. On the other hand, the older bump, closely associated with the Sun's birth epoch, is intriguing since this finding challenges the predicted presence of a corotation barrier built by the Galactic bar, which is thought to prevent stars born inside R_GC ~ 6 kpc from reaching the solar neighborhood. We propose that the large number of local twins with ages between 4 and 6 Gyr provides compelling evidence that the Sun's long-distance (>= 3 kpc) migration is shared by many inner disk stars. This, in turn, suggests a possible link with the epoch of bar formation, which may have triggered enhanced star formation in the inner disk and induced efficient radial migration.

Figures (11)

• Figure 1: (Deconvolved) probability density function (PDF) of the ages of solar twins determined with $M_{K_{\mathrm{s}}}$. The dotted black line shows the normalized age histogram of our solar twin catalog (same as the blue histogram in Fig. \ref{['fig:AgeHist0_K0']}). The blue line shows the normalized ratio between the observed and mock age histograms, as a rough estimate of the intrinsic age distribution. Orange and green lines represent the deconvolved, intrinsic age distributions obtained using the two different (RLS and RL) methods. Shaded regions indicate the statistical uncertainty in the deconvolved PDFs, estimated from $10^{4}$ Monte Carlo realizations assuming Poisson statistics for the original age histogram (see Appendix \ref{['app:StatBias']} for a validation of this uncertainty estimate). The upper axis provides reference $R_{\mathrm{birth}}$ values, based on the $\text{[Fe/H]}=0\,\mathrm{dex}$ slice of the age--$R_{\mathrm{birth}}$--[Fe/H] relation in 2023MNRAS.525.2208R. See Fig. \ref{['fig:DeconvHist_logg_G0']} for results using $\log g$ and those using $M_{G}$.
• Figure 2: Normalized histograms of the guiding radii, $R_{\mathrm{g}}$, for solar twins, color-coded by their ages determined with $M_{K_{\mathrm{s}}}$. Histograms for other orbital parameters are shown in Fig. \ref{['fig:OrbitParams_K0_ecc_zmax']}.
• Figure 3: Observed histogram of solar twin ages. Histograms shows the ages of stars with the relative age error smaller than $50\%$, determined using $M_{K_{\mathrm{s}}}$ for the observed (blue) and mock (orange) samples. See Fig. \ref{['fig:AgeHist0_logg_G0']} for results using $\log g$ and those using $M_{G}$.
• Figure 4: Selection function for solar twin ages determined with $M_{K_{\mathrm{s}}}$. 2D histogram in the central panel shows the distribution of the input true and output estimated ages for the mock solar twins. Top and right panels show the normalized marginal histograms for the input and output ages, respectively. See Fig. \ref{['fig:SelecFunc_logg_G0']} for results using $\log g$ and those using $M_{G}$.
• Figure 5: Dependence of the deconvolved $M_{K_{\mathrm{s}}}$-based age PDF obtained with the RLS method on the hyperparameter $\lambda$.