The age sequence of young clusters in Perseus: Estimating ages from mass distributions

TL;DR

This work addresses the challenge of dating very young star clusters by exploiting the near-universal nature of the local IMF. The authors derive cluster mass distributions from Gaia DR3 memberships and 2MASS photometry, propagating uncertainties with Monte Carlo simulations, and then compare mass distributions across clusters with a KS-test framework over a grid of ages. They identify a consistent age sequence for the Perseus clusters, ranging from $1$ Myr (NGC 1333+Autochthe) to $5$–$8$ Myr (Alcaeus), with intermediate clusters occupying $2$–$4$ Myr, and validate the method using artificial clusters. The results agree with disc-fraction trends and with literature isochrone estimates, demonstrating that mass-distribution comparisons can serve as a useful complement to established age-dating techniques for young stellar populations.

Abstract

Establishing ages for young clusters is key for properly tracking the star formation history of a region. In this paper we investigate a new approach to estimating ages for young populations, based on the well-founded assumption that the initial mass function is the same throughout a star forming cloud. We trial this method for six young clusters in the Perseus star forming region. For all six clusters, we construct new member samples in a homogeneous way using Gaia DR3. We estimate masses by comparing 2MASS photometry to theoretical isochrones, including Monte Carlo simulations to propagate the errors. We compare the mass distributions of the clusters for a range of plausible ages, looking for a combination of ages that results in indistinguishable mass distributions across the region. We find the best fit for ages of 1 Myr for NGC1333+Autochthe, 2 Myr for IC348, 2-3 Myr for Heleus, 3-4 Myr for Mestor, 4-5 Myr for Electryon+Cynurus, and 5-8 Myr for Alcaeus. All other combinations of ages are ruled out by this criterion. The established age sequence is consistent with the relative ages inferred from disc fractions, and broadly aligns with the age sequence determined in previous studies using isochrone fitting. We suggest that this approach can be a useful complement and cross-check to established methods to estimate ages in young populations.

Figures (9)

• Figure 1: The final members of the clusters in spatial distribution (left) and in proper motion (right).
• Figure 2: CMDs from 2MASS photometry for all clusters. Isochrones shown (same in all panels) are from baraffe_2015 and are corrected for the distance to each cluster. The arrow depicts an extinction equivalent to 2.0 mags. For clarity the range in both axes is the same in all panels.
• Figure 3: Histogram of the J-magnitudes of the whole initial Perseus sample (7716 matches in 2MASS out of 8123). The cyan dashed line marks the completeness limit of the sample.
• Figure 4: The binned mean cumulative mass distributions of NGC 1333+Autochthe at 1 Myr and of Electryon+Cynurus at 4 Myr (top left) and at 8 Myr (bottom left). The top and bottom right panels show the histogram of the p-values from the KS-test. Note that the KS tests itself is conducted on unbinned mass distributions. The median p-value which we adopt per comparison is also given for each case in the right panel. The top panels correspond to a case where mass distributions are indistinguishable according to our test. The bottom panels correspond to a case of distinguishable mass distributions. The completeness limits in mass for these cases are $0.03\,M_{\odot}$ (NGC 1333+Autochthe at 1 Myr), $0.04\,M_{\odot}$ (Electryon+Cynurus at 4 Myr), and $0.08\,M_{\odot}$ (Electryon+Cynurus at 8 Myr).
• Figure 5: The median probabilities from our KS-tests that the clusters' mass distributions are drawn from the same parent distribution for all cluster and age combinations. The colour-scale also depicts the median probabilities.