How Massive Star Clusters Form and Evolve: A Near-IR Survey of the W51 Complex

TL;DR

This study uses near-infrared observations to analyze the young stellar populations and mass distribution in the W51 complex, revealing thousands of sources, new H2 emission features, and IMFs consistent with the Salpeter slope.

Contribution

It provides the first detailed near-infrared characterization of W51's proto-clusters, including mass estimates and IMF measurements, enhancing understanding of massive star cluster formation.

Findings

Over 3000 new sources identified in W51 region.

Estimated cluster masses range from 500 to 4700 solar masses.

IMF slopes are consistent with the Salpeter IMF for masses ≥8 solar masses.

Abstract

We present near-infrared JHKs and narrow-band H2(1-0) photometric observations of the W51A region, obtained with GTC EMIR, aiming to characterize its young stellar population and provide mass estimates for individual cluster members and the proto-clusters. Our observations reveal over 3000 new sources, out of which 88 are located in the proto-clusters, W51 IRS2 and W51 Main. The average extinction (AV), measured from the J-H color, of sources is 19 AV in W51 IRS2 and 14 AV in W51 Main. We document 17 new instances of H2 emission in the region by utilizing observations from the H2(1-0) narrow-band filter. Despite limited completeness, we estimated masses for each cluster member and estimated the total cluster mass to be in the range of 900-4700 solar masses for W51 IRS2 and 500-2700 solar masses for W51 Main, using an assumed age range of 1-3 Myr. We measured the initial mass function (IMF) in the proto-clusters assuming a range of ages from 1-3 Myr and found that the IMF slopes for both proto-clusters are consistent with the Salpeter IMF in the mass range greater than or equal to 8 solar masses within 1 to 2 sigma.