Star Cluster Complexes and the Host Galaxy in Three HII Galaxies: Mrk 36, UM 408, and UM 461

TL;DR

This study analyzes star cluster formation in three low-luminosity HII galaxies, revealing a clumpy star formation mode with most recent bursts involving small, young clusters and a low overall star formation efficiency.

Contribution

It provides new insights into the ages, masses, and formation efficiency of star clusters in HII galaxies using high-resolution near-infrared imaging and evolutionary models.

Findings

Star formation efficiency is approximately 10%.

Star cluster complexes are formed by a few massive clusters (>10^4 M☉).

Recent star formation episodes are recent, simultaneous, and triggered internally.

Abstract

We present a stellar population study of three HII galaxies (Mrk 36, UM 408, and UM 461) based on the analysis of new ground-based high resolution near-infrared J, H and Kp broad-band and Br narrow-band images obtained with Gemini/NIRI. We identify and determine relative ages and masses of the elementary star clusters and/or star cluster complexes of the starburst regions in each of these galaxies by comparing the colors with evolutionary synthesis models that include the contribution of stellar continuum, nebular continuum and emission lines. We found that the current star cluster formation efficiency in our sample of low luminosity HII galaxies is ~10%. Therefore, most of the recent star formation is not in massive clusters. Our findings seem to indicate that the star formation mode in our sample of galaxies is clumpy, and that these complexes are formed by a few massive star clusters with masses > 10^4 Mo. The age distribution of these star cluster complexes shows that the current burst started recently and likely simultaneously over short time scales in their host galaxies, triggered by some internal mechanism. Finally, the fraction of the total cluster mass with respect to the low surface brightness (or host galaxy) mass, considering our complete range in ages, is less than 1%.