TheHerschelDwarf Galaxy Survey

Abstract

Context. The far-infrared (FIR) lines are important tracers of the cooling and physical conditions of the interstellar medium (ISM) and are rapidly becoming workhorse diagnostics for galaxies throughout the universe. There are clear indications of a different behavior of these lines at low metallicity that needs to be explored. Aims. Our goal is to explain the main differences and trends observed in the FIR line emission of dwarf galaxies compared to more metal-rich galaxies, and how this translates in ISM properties. ] 57 µm fine-structure cooling lines in a sample of 48 low-metallicity star-forming galaxies of the guaranteed time key program Dwarf Galaxy Survey. We correlate PACS line ratios and line-to-L TIR ratios with L TIR , L TIR /L B , metallicity, and FIR color, and interpret the observed trends in terms of ISM conditions and phase filling factors with Cloudy radiative transfer models. Results. We find that the FIR lines together account for up to 3 percent of L TIR and that star-forming regions dominate the overall emission in dwarf galaxies. Compared to metal-rich galaxies, the ratios of Harboring compact phases of a low filling factor and a large volume filling factor of diffuse gas, the ISM of low-metallicity dwarf galaxies has a more porous structure than that of metal-rich galaxies. Methods

A milestone toward understanding PDR properties in the extreme environment of LMC-30 Doradus

“…[O iii] is brighter than [C ii] by a factor of 2 to 60 throughout our 30Dor map. Figure 4 shows the ratio Cormier et al (2015) already noted the elevated [O iii] 88 µm/L TIR in dwarf galaxies compared to the normal galaxies of Brauher et al (2008). Given …”

“…E. Sturm). We also used two additional pointings east of R136, which were observed We refer to Cormier et al (2015) for the full description of the PACS observations and data reduction, and we summarize some of the main steps here. The data are reduced with the Herschel interactive processing environment (HIPE) v12.0.0 (Ott 2010) from Level 0 to Level 1.…”

“…intensity distribution). The red symbols are for the DGS galaxies (Cormier et al 2015). The colored diamonds correspond to the regions of 30Dor illustrated in Fig.…”

“…Large surveys probing the cooling of dwarf galaxies are possible for the first time with the Herschel Space Observatory (Pilbratt et al 2010; e.g., the Dwarf Galaxy Survey, DGS; Madden et al 2013). Recent studies taking advantage of the Herschel sensitivity, have modeled the dust and gas properties of a wide range of low metallicity galaxies on integrated galaxy scales (e.g., Rémy-Ruyer et al 2013Cormier et al 2012Cormier et al , 2015Cigan et al 2016) and find prominent differences between metal-rich and metal-poor galaxies. For example, from far-infrared (FIR) line ratios, Cormier et al (2015) determined that radiation fields over global galaxy scales are harder in starforming dwarf galaxies compared to more metal-rich galaxies.…”

Variable interstellar radiation fields in simulated dwarf galaxies: supernovae versus photoelectric heating

“…The total luminosity of the continuum infrared emission Lcont vs. the ratio of FIR lines to the continuum for all runs with PE heating, time-averaged over a time period from t=200 Myr to t=1000 Myr. The observed data from the Dwarf Galaxy Survey from Cormier et al (2015) are over-plotted as gray dots. The PE-only runs have their FIR-to-continuum ratios much lower than the observed dwarf galaxies, especially for the oxygen lines.…”