Probing the Dust Properties of Galaxies up to Submillimetre Wavelengths I. The Spectral Energy Distribution of dwarf galaxies using LABOCA

TL;DR

This study investigates the dust properties of low-metallicity dwarf galaxies using submillimeter observations, revealing significant cold dust components and discrepancies in dust-to-gas ratios and star formation rates compared to expectations.

Contribution

It provides new insights into the dust mass and temperature distributions in dwarf galaxies by incorporating submillimeter data, highlighting the presence of cold dust and potential hidden gas reservoirs.

Findings

Detection of submillimeter excess in two galaxies.

At least 70% of dust mass resides in cold dust component.

Haro11 shows unusually high dust-to-gas ratio and deviates from the Schmidt law.

Abstract

We present 870 micron images of four low metallicity galaxies (NGC1705, Haro11, Mrk1089 and UM311) observed with the Large APEX BOlometer CAmera (LABOCA). We model their spectral energy distributions combining the submm observations of LABOCA, 2MASS, IRAS, Spitzer photometric data and the IRS data for Haro11. We find that a significant mass of dust is revealed when using submm constraints compared to that measured with only mid-IR to far-IR observations extending only to 160 microns. For NGC1705 and Haro11, an excess in submillimeter wavelengths is detected and we rerun our SED procedure adding a cold dust component (10K) to better describe the high 870 micron flux derived from LABOCA observations, which significantly improves the fit. We find that at least 70% of the dust mass of these two galaxies can reside in a cold dust component. We also show that the subsequent dust-to-gas mass ratios, considering HI and CO observations, can be strikingly high for Haro11 in comparison with what is usually expected for these low-metallicity environments. Furthermore, we derive the SFR of our galaxies and compare them to the Schmidt law. Haro11 falls anomalously far from the Schmidt relation. These results may suggest that a reservoir of hidden gas could be present in molecular form not traced by the current CO observations. We also derive the total IR luminosities derived from our models and compare them with relations that derive this luminosity from Spitzer bands. We find that the Draine & Li (2007) formula compares well to our direct IR determinations.