The nature of the interstellar medium of the starburst low-metallicity galaxy Haro 11: a multi-phase model of the infrared emission

Abstract

Context. The low-metallicity interstellar medium (ISM) is profoundly different from that of normal systems, being clumpy with low dust abundance and little CO-traced molecular gas. Yet many dwarf galaxies in the nearby universe are actively forming stars. As the complex ISM phases are spatially mixed with each other, detailed modeling is needed to understand the gas emission and subsequent composition and structure of the ISM. Aims. Our goal is to describe the multi-phase ISM of the infrared bright low-metallicity galaxy Haro 11, dissecting the photoionised and photodissociated gas components. Methods. We present observations of the mid-infrared and far-infrared fine-structure cooling lines obtained with the Spitzer/IRS and Herschel/PACS spectrometers. We use the spectral synthesis code Cloudy to methodically model the ionised and neutral gas from which these lines originate. Results. We find that the mid-and far-infrared lines account for ∼1% of the total infrared luminosity L TIR , acting as major coolants of . Due to their different origins, the observed lines require a multi-phase modeling comprising: a compact H ii region, dense fragmented photodissociation regions (PDRs), a diffuse extended low-ionisation/neutral gas which has a volume filling factor of at least 90%, and porous warm dust in proximity to the stellar source. For a more realistic picture of the ISM of Haro 11 we would need to model the clumpy source and gas structures. We combine these 4 model components to explain the emission of 17 spectral lines, investigate the global energy balance of the galaxy through its spectral energy distribution, and establish a phase mass inventory. While the ionic emission lines of Haro 11 essentially originate from the dense H ii region component, a diffuse low-ionisation gas is needed to explain the

Linking dust emission to fundamental properties in galaxies: the low-metallicity picture

“…Instead, we replace the stellar component by a black body and impose a temperature T ≥ 1000 K. We obtain a best-fit temperature T = 30 000 K, corresponding to a maximum of the black-body emission around 0.1 µm in the UV, a sign of a young stellar population. This is consistent with the results of Adamo et al (2010) who found a maximum in the cluster formation history ∼3.5 Myr ago, and with the UV part of the SED presented in Cormier et al (2012). -HS 0822+3542 -The observed PACS upper limits at 70 and 100 µm are not consistent with the rest of the MIR to FIR photometry (see Fig.…”

VLT/MUSE view of the highly ionized outflow cones in the nearby starburst ESO338-IG04

“…The gas becomes optically thick for LyC photons only in the western and eastern outer regions of the galaxy. This pattern mimics the behavior of a giant H ii region, as found for similar galaxies (Haro 11, Cormier et al 2012), and confirms the existence of an in-out ionizing front that modifies the interstellar medium (ISM) states of the galaxy. Several cones of highly ionized gas expanding all the way into the galaxy halo are visible.…”

SÍGAME Simulations of the , , and Line Emission from Star-forming Galaxies at

“…In our Milky Way, dense PDRs and CO-dark H 2 gas is responsible for about ∼ 55% of the total [C II] emission, while the diffuse ionized gas and diffuse neutral gas contribute ∼ 20% and 25%, respectively (Pineda et al 2014). Cormier et al (2012) used CLOUDY to model the ISM of the nearby (z ∼ 0.021) starburst galaxy Haro 11, which has a metallicity (∼ 0.3 Z ) and a SFR (∼ 22 M yr −1 ) matching that of our simulations, and found that 10 % of the [C II] luminosity comes from dense PDRs and about 50 % from the diffuse ionized medium.…”

“…Galaxy-scale simulations have been developed that attempt to account for the observations of the above finestructure lines, in particular, how their emissions are linked to the ISM phases and to global galaxy properties, such as metallicity, star formation efficiency, ionization parameter, dust mass fraction, compactness and phase filling factors (e.g., Cormier et al 2012;Vallini et al 2013;Olsen et al 2015;Accurso et al 2017;Katz et al 2017). By combining codes of stellar population synthesis, radiative transfer, photoionization, and astrochemistry into simulations of starburst regions, Accurso et al (2017) found that the increases in the specific star formation rate of a galaxy leads to a decrease in the fraction of the [C II] emission coming from the molecular gas phase, due to stronger UV radiation fields which will tend to shrink the molecular regions.…”

“…Applied to local normal galaxies, their code predicts that as much as 60 − 80% of the [C II] emission emerges from the molecular gas. Cormier et al (2012) utilized the photoionisation code CLOUDY (Ferland et al 2013) to model a number of FIR fine-structure line emissions (including [C II], [O I], and [O III]) from the multi-phased ISM in the starburst low-metallicity galaxy Haro 11. They found that PDRs account for only 10 % of the [C II] emission, with the remaining emission arrising in the diffuse ionized medium, but a larger PDR contribution when lowering the density or including magnetic fields.…”