Dust emission in star-forming dwarf galaxies: General properties and the nature of the submm excess

Abstract

We studied the global characteristics of dust emission in a large sample of emission-line star-forming galaxies. The sample consists of two subsamples. One subsample (SDSS sample) includes ∼4000 compact star-forming galaxies from the Sloan Digital Sky Survey (SDSS), which were also detected in all four bands at 3.4 μm, 4.6 μm, 12 μm, and 22 μm of the WISE all-sky survey. The second subsample (Herschel sample) is a sample of 28 compact star-forming galaxies observed with Herschel in the FIR range. Data of the Herschel sample were supplemented by the photometric data from the Spitzer observations, GALaxy Evolution Explorer (GALEX) survey, SDSS, Wide-Field Infrared Survey Explorer (WISE), Two Micron All Sky Survey (2MASS), NRAO VLA Sky Survey (NVSS), and Faint Images of the Radio Sky at Twenty-cm (FIRST) survey, as well as optical and Spitzer spectra and data in submm and radio ranges. It is found that warm dust luminosities of galaxies from the SDSS sample and cold and warm dust luminosities of galaxies from the Herschel sample are strongly correlated with Hβ luminosities, which implies that one of the main sources of dust heating in star-forming galaxies is ionising UV radiation of young stars. Likely, a significant fraction of dust is located inside H ii and surrounding regions. We found tight correlations between masses of cold and warm dust, again implying the same source of dust heating. Using the relation between warm and cold dust masses for estimating the total dust mass in star-forming galaxies with an accuracy better than ∼0.5 dex is proposed. On the other hand, it is shown for both samples that dust temperatures do not depend on the metallicities. The dust-to-neutral gas mass ratio strongly declines with decreasing metallicity, similar to that found in other studies of local emission-line galaxies, high-redshift gamma-ray burst hosts, and damped Ly-α absorbers. On the other hand, the dust-to-ionised gas mass ratio is about one hundred times as high implying that most of dust is located in the neutral gas. It is found that thermal free-free emission of ionised gas in compact star-forming galaxies is important in the submm and mm ranges, and it might be responsible for the submm emission excess. This effect is stronger in galaxies with lower metallicities and is also positively affected by an increased star-formation rate.

Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies

“…That there is not much dust-obscured hidden star formation is also implied by the observed thermal freefree cm radio emission in dwarf galaxies with optical and infrared observations. Its flux density is consistent with the value derived from the flux density of the Hβ emission line (Izotov et al 2014b), indicating that there is not a considerable amount of additional star formation, not seen in the UV range, in our galaxies.…”

Mid-Infrared Colors of Dwarf Galaxies: Young Starbursts Mimicking Active Galactic Nuclei

“…Our results suggest that star formation, and not AGN activity, is responsible for the red WISE colors for the majority of the dwarf galaxy population (also see Izotov et al 2014). We propose a small sample of dwarf galaxy AGN candidates that require follow-up observations to confirm black hole activity.…”

“…Low-mass SMBHs that exist in dwarf galaxies power AGNs that have such low luminosities that star formation in their hosts becomes a significant source of contamination. In particular, it has been shown that lowmetallicity dwarf starburst galaxies are capable of heating dust to very high temperatures (Hirashita & Hunt 2004;Reines et al 2008;Griffith et al 2011;Izotov et al 2011Izotov et al , 2014Rémy-Ruyer et al 2015), producing red mid-IR colors. This was recently explored in O'Connor et al (2016), who found that galaxies with low stellar masses have predominantly red WISE colors, which the authors associate with higher specific star formation rates (sSFRs) in these galaxies.…”

Can Dust Injected by SNe Explain the NIR–MIR Excess in Young Massive Stellar Clusters?

“…In fact, Relaño et al (2016) and Reines et al (2008) required an additional ∼ 1000-K blackbody component of "uncertain origin" to fit their observed IR SEDs. Similar excesses, more prevalent in the MIR, have also been observed in a number of blue compact dwarf galaxies (e.g: I Zw 18, II Zw 40, Mrk 930 and Haro 11 (Rémy-Ruyer et al 2015;Vanzi et al 2000;Izotov et al 2014)). Therefore, these observations not only point to the existence of a very hot dust component (∼400-1000 K), but also give compelling evidence for the presence of a persistent (i.e.…”