The stellar initial mass function of nearby young moving groups

TL;DR

This work develops a Gaia DR3–based framework to derive IMFs for a large sample of NYMGs by detecting co-moving overdensities in a restricted 5D phase-space plus CMD, inferring individual masses with a Bayesian approach, and correcting for field contamination. The authors detect 33 NYMG candidates (44 literature groups) with 4166 member candidates, including 2545 new members, achieving a literature-recovery rate of $44\%-54\%$ and a contamination level of $16\%-24\%$. The mean IMF across NYMGs is consistent with the solar-neighborhood IMF, with parameters $m_c\approx0.25\,M_\odot$, $\sigma_c\approx0.45$, and $\alpha\approx-2.26$ for $m<1\,M_\odot$ and $m>1\,M_\odot$ following a power law, supporting the view that NYMGs are remnants of disrupted clusters. The methodology includes completeness corrections via GaiaUnlimited Selection Functions and contamination corrections via synthetic Besançon fields, providing a robust, bias-controlled view of NYMG IMFs and their implications for star-formation environments in the solar vicinity.

Abstract

The solar neighbourhood is populated by nearby, young moving groups (NYMGs) of stars that are candidates to be remnants of individual stellar clusters and associations, currently dispersing in the galactic disc. To derive the initial mass function (IMF) of a large sample of NYMGs, we developed and applied an algorithm that uses photometry and astrometry from Gaia DR3 to detect NYMGs in a kinematic space. We inferred individual masses from the photometry of both the detected and the previously known candidates. We estimated the IMFs for 33 groups, 30 of them for the first time, in an average mass range $0.1<m/M_\odot<5$ with some groups going as low as $0.02~M_{\odot}$ and as high as $10~M_{\odot}$. We parameterized these IMFs using a log-normal for $m<1~M_\odot$ and a power-law for $m>1~M_\odot$. We detected 4166 source candidate members of 44 known groups, including 2545 new candidates. We recovered 44-54\% of the literature candidates and estimated a contamination rate from old field stars of 16-24\%. The candidates of the detected groups distribute along young isochrones, which suggests that they are potential members of NYMGs. Parameterizations of both the average of the 33 IMFs based on our detections ($m_c=0.25\pm0.17~M_{\odot}$, $σ_c=0.45\pm0.17$, and $α=-2.26\pm0.09$) and the one based on the known candidates from the literature ($m_c=0.22\pm0.14~M_{\odot}$, $σ_c=0.45\pm0.17$, and $α=-2.45\pm0.06$) are in agreement with the IMF parameterization of the solar neighbourhood and young stellar associations. Our parameterization of the average IMF together with the distribution of the detected group members along young isochrones provide strong evidence suggesting that the NYMGs are remnants of individual stellar associations and clusters and that there are no systematic biases in our detection and in the literature in the range $0.1<m/M_{\odot}<10$.

Figures (15)

• Figure 1: Color-absolute magnitude diagram of the starting sample (grey points) and the $S_{\text{NYMG}}$ sample (coloured scale indicating the density of points). The solid lines indicate the limits of the MS and PMS locus, the black dashed curves show the isochrones from Phillips_2020, baraffe2015, and marigo2017 stellar evolutionary models for $10$ Myr, $30$ Myr, $100$ Myr, and $1$ Gyr, and the horizontal black dash-dotted lines indicate the $M_G$ values corresponding to the Turn-On (see Section \ref{['subsec:nymg_candidates']}) for the labelled masses. The red, orange, and blue dashed lines indicate the $0.1$, $0.2$, and $0.3~M_{\odot}$ evolutionary tracks respectively. The red arrow indicates two times the extinction vector for an M4 dwarf star with $A_V=0.22$ mag.
• Figure 2: Distribution of residuals between ten synthetic fields and $S_{\text{NYMG}}$ samples across the position space (top panel) and the LSR tangential velocity space (bottom panel). Dashed lines indicate the mean velocities of known open clusters according to the MOCA database.
• Figure 3: Resulting $K_{min,0.99}$ for all the hyper-parameter combinations as a function of the RPS density threshold $\rho_{\varepsilon_{r,v},N_{\text{min}}}$ corresponding to the hyper-parameter combination. The color-map for the top and bottom plots indicates the age $\mathcal{A}$ and the value of $N_{\text{min}}$ respectively.
• Figure 4: CMD distribution of all the 4166 candidate members detected in this work. The colour map shows the age of the identified groups according to MOCA. The black solid and dashed curve show the 1 Gyr and 100 Myr isochrones respectively. The rotated histogram shows the distribution of the detected NYMG ages according to MOCA. The age-axis of the histogram is the same as the colour bar axis.
• Figure 5: Recovery rates $f_r$ as a function of the mean distance of each detected group. The colour indicates the purity rate $f_p$. The dots correspond to all the recovered groups that are not part of the Sco-Cen complex while the crosses correspond to the ones that do belong. The blue dot indicates the mean recovery of the Sco-Cen complex groups.