Near-infrared adaptive optics imaging of infrared luminous galaxies: the brightest cluster magnitude - star formation rate relation

TL;DR

This study establishes a near-infrared relation between the brightest super star cluster magnitude and the host galaxy's star formation rate in luminous IR galaxies, revealing physical constraints beyond random sampling effects.

Contribution

First to demonstrate a near-infrared brightest cluster magnitude–SFR relation, expanding previous optical studies and analyzing physical constraints influencing the relation.

Findings

The relation is M_K ~ -2.6 log SFR, consistent with optical results.

Scatter is smaller than expected from random sampling, indicating physical constraints.

The relation is affected by extinction and age effects, not fully explained by simple color conversions.

Abstract

We have established a relation between the brightest super star cluster magnitude in a galaxy and the host star formation rate (SFR) for the first time in the near infrared (NIR). The data come from a statistical sample of ~ 40 luminous IR galaxies (LIRGs) and starbursts utilizing K-band adaptive optics imaging. While expanding the observed relation to longer wavelengths, less affected by extinction effects, it also pushes to higher SFRs. The relation we find, M_K ~ - 2.6 log SFR, is similar to that derived previously in the optical and at lower SFRs. It does not, however, fit the optical relation with a single optical to NIR color conversion, suggesting systematic extinction and/or age effects. While the relation is broadly consistent with a size-of-sample explanation, we argue physical reasons for the relation are likely as well. In particular, the scatter in the relation is smaller than expected from pure random sampling strongly suggesting physical constraints. We also derive a quantifiable relation tying together cluster-internal effects and host SFR properties to possibly explain the observed brightest SSC magnitude vs. SFR dependency.