The nature of the interstellar medium of the starburst low-metallicity galaxy Haro11: a multi-phase model of the infrared emission
D. Cormier, V. Lebouteiller, S. C. Madden, N. Abel, S. Hony, F. Galliano, M. Baes, M. J. Barlow, A. Cooray, I. De Looze, M. Galametz, O. L. Karczewski, T. J. Parkin, A. Remy, M. Sauvage, L. Spinoglio, C. D. Wilson, R. Wu
(Submitted on 4 Sep 2012)
(abridged) Our goal is to describe the multi-phase ISM of the IR bright low-metallicity galaxy Haro 11, dissecting the photoionised and photodissociated gas components. We present observations of the mid- and far-IR 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. We find that the mid- and far-IR lines account for ~1% of the total IR luminosity L_TIR. Haro 11 is undergoing a phase of intense star formation, as traced by the brightest line [OIII] 88um, with L_[OIII]/L_TIR ~0.3%, and high ratios of [NeIII]/[NeII] and [SIV]/[SIII]. Due to their different origins, the observed lines require a multi-phase modeling comprising: a compact HII 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 HII region component, a diffuse low-ionisation gas is needed to explain the [NeII], [NII], and [CII] line intensities. The [OIII] 88um line intensity is not fully reproduced by our model, hinting towards the possible presence of yet another low-density high-ionisation medium. The [OI] emission is consistent with a dense PDR of low covering factor, and we find no evidence for an X-ray dominated component. The PDR component accounts for only 10% of the [CII] emission.
|Comments:||Accepted for publication in A&A, 23 pages, 13 figures|
|Subjects:||Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)|
|Cite as:||arXiv:1209.0804v1 [astro-ph.GA]|