The K-band luminosity functions of super star clusters in luminous infrared galaxies, their slopes, and the effects of blending

TL;DR

This study investigates the luminosity functions of super star clusters in luminous infrared galaxies using adaptive optics, revealing a shallower slope than in normal galaxies and assessing blending effects on observations.

Contribution

It introduces a K-band analysis of SSCs in high-SFR galaxies and quantifies blending effects, providing new insights into cluster luminosity functions in obscured, distant environments.

Findings

Luminosity functions are well-fit by a power-law with an average slope of ~1.9.

Blending effects slightly flatten the luminosity function slope by less than 0.1.

In the studied luminosity range, SSC luminosities are dominated by single clusters rather than multiple sources.

Abstract

Super star clusters (SSCs) are typically found in interacting galaxies and trace an extreme form of star-formation. We present a K-band study of SSC candidates in a sample of local luminous infrared galaxies (LIRGs) using two adaptive optics instruments (VLT/NACO and Gemini/ALTAIR/NIRI). In addition to facilitating SSC detections in obscured environments, this work introduces SSC studies in hosts with higher star-formation rates (SFRs) than most previous studies. We find that the luminosity functions (LFs) of the clusters are reasonably well-fitted by a single power-law with the values of the index \alpha ranging between 1.5 to 2.4 with an average value of \alpha ~ 1.9. This value appears to be less steep than the average \alpha ~ 2.2 in normal spiral galaxies. Due to the host galaxy distances involved (median $D_L$ ~ 70 Mpc) blending effects have to be taken into account, and are investigated using Monte Carlo simulations of blending effects for LFs and a photometric SSC analysis of the well-studied Antennae system which is artificially redshifted to distances of our sample. While blending tends to flatten LFs our analyses show that \Delta \alpha is less than ~ 0.1 in our sample. The simulations also show that in the luminosity range, $M_K < -13$, considered in this work the extracted SSC luminosities are generally dominated by a single dominant star cluster rather than several knots of SF. We present resolution- and distance-dependent SSC surface density confusion limits and show how blending rates and aperture sizes affect the LFs. The smallest possible apertures should be used in crowded regions.