Hubble Space Telescope Observations of Tadpole Galaxies Kiso 3867, SBS0, SBS1, and UM461

TL;DR

This study uses Hubble Space Telescope imaging to analyze the star formation, cluster properties, and gas accretion effects in four nearby tadpole galaxies, revealing their stellar populations, cluster mass functions, and potential ionizing photon escape.

Contribution

First detailed multiband imaging analysis of four nearby tadpole galaxies focusing on their star complexes, clusters, and gas accretion effects, with new insights into their stellar populations and ionizing photon budgets.

Findings

Galaxies contain 3-10 young stellar complexes with masses 10^3-10^5 Msun.

Cluster mass function follows a power law with slope -1.12.

Theoretical Lyman continuum emission can explain observed Halpha emission, indicating possible photon escape.

Abstract

Tadpole galaxies are metal-poor dwarfs with typically one dominant star-forming region, giving them a head-tail structure when inclined. A metallicity drop in the head suggests that gas accretion with even lower metallicity stimulated the star formation. Here we present multiband HST WFC3 and ACS images of four nearby (<25 Mpc) tadpoles, SBS0, SBS1, Kiso 3867, and UM461, selected for their clear metallicity drops shown in previous spectroscopic studies. Properties of the star complexes and compact clusters are measured. Each galaxy contains from 3 to 10 young stellar complexes with 10^3-10^5 Msun of stars ~3-10 Myr old. Between the complexes, the disk has a typical age of ~3 Gyr. Numerous star clusters cover the galaxies, both inside and outside the complexes. The combined cluster mass function, made by normalizing the masses and counts before stacking, is a power law with a slope of -1.12+-0.14 on a log-log plot and the combined distribution function of cluster lifetime decays with age as t^{-0.65+-0.24}. A comparison between the summed theoretical Lyman continuum (LyC) emission from all the clusters, given their masses and ages, is comparable to or exceeds the LyC needed to excite the observed Halpha in some galaxies, suggesting LyC absorption by dust or undetected gas in the halo, or perhaps galaxy escape.