%0 Generic %1 lebouteiller2017neutral %A Lebouteiller, V. %A Pequignot, D. %A Cormier, D. %A Madden, S. %A Pakull, M. W. %A Kunth, D. %A Galliano, F. %A Chevance, M. %A Heap, S. R. %A Lee, M. Y. %A Polles, F. L. %D 2017 %K heating mechanism metal photoelectric poor x-ray %T Neutral gas heating by X-rays in primitive galaxies: Infrared observations of IZw18 with Herschel %U http://arxiv.org/abs/1702.07377 %X (abridged) The dominant thermal mechanisms in the neutral interstellar medium, which acts as a star-forming gas reservoir, are uncertain in extremely metal-poor galaxies. Our objective is to identify the heating mechanisms in one such galaxy, IZw18, and assess the diagnostic value of fine-structure cooling lines. We also seek to constrain the mass of H$_2$, which, despite being an important catalyst and tracer of star formation, remains elusive in this object. Building on a previous photoionization model within a multi-sector topology, we provide additional constraints from the CII and OI lines and the dust mass recently measured with Herschel. The heating of the HI region appears to be mainly due to photoionization by radiation from a bright X-ray binary source, while photoelectric effect (PE) is negligible. The CII and OI lines imply an average X-ray luminosity of $4\times10^40$ erg s$^-1$, while the NeV upper limits bring strong constraints to the soft X-ray flux arising from the binary. A negligible amount of H$_2$ is predicted, but $łesssim10^7$ M$_ødot$ of H$_2$ may be hidden in sufficiently dense clouds of order $łesssim10$ pc in size. Regardless of the presence of significant amounts of H$_2$, CII and OI do not trace the so-called CO-dark gas, but the almost purely atomic medium. Although the CII+OI/TIR ratio is close to values found in more metal-rich sources, it cannot be safely used as a PE heating efficiency proxy. This ratio seems to be kept stable due to a correlation between the X-ray luminosity and the star-formation rate. We propose that X-ray heating is an important process in extremely metal-poor sources. The weak PE heating due to the low dust-to-gas ratio could be compensated for by the larger occurrence and power of X-ray binaries in low-metallicity galaxies. We speculate that X-ray heating may quench star formation.

@misc{lebouteiller2017neutral, abstract = {(abridged) The dominant thermal mechanisms in the neutral interstellar medium, which acts as a star-forming gas reservoir, are uncertain in extremely metal-poor galaxies. Our objective is to identify the heating mechanisms in one such galaxy, IZw18, and assess the diagnostic value of fine-structure cooling lines. We also seek to constrain the mass of H$_2$, which, despite being an important catalyst and tracer of star formation, remains elusive in this object. Building on a previous photoionization model within a multi-sector topology, we provide additional constraints from the [CII] and [OI] lines and the dust mass recently measured with Herschel. The heating of the HI region appears to be mainly due to photoionization by radiation from a bright X-ray binary source, while photoelectric effect (PE) is negligible. The [CII] and [OI] lines imply an average X-ray luminosity of $4\times10^{40}$ erg s$^{-1}$, while the [NeV] upper limits bring strong constraints to the soft X-ray flux arising from the binary. A negligible amount of H$_2$ is predicted, but $\lesssim10^7$ M$_\odot$ of H$_2$ may be hidden in sufficiently dense clouds of order $\lesssim10$ pc in size. Regardless of the presence of significant amounts of H$_2$, [CII] and [OI] do not trace the so-called CO-dark gas, but the almost purely atomic medium. Although the [CII]+[OI]/TIR ratio is close to values found in more metal-rich sources, it cannot be safely used as a PE heating efficiency proxy. This ratio seems to be kept stable due to a correlation between the X-ray luminosity and the star-formation rate. We propose that X-ray heating is an important process in extremely metal-poor sources. The weak PE heating due to the low dust-to-gas ratio could be compensated for by the larger occurrence and power of X-ray binaries in low-metallicity galaxies. We speculate that X-ray heating may quench star formation.}, added-at = {2017-02-27T10:36:10.000+0100}, author = {Lebouteiller, V. and Pequignot, D. and Cormier, D. and Madden, S. and Pakull, M. W. and Kunth, D. and Galliano, F. and Chevance, M. and Heap, S. R. and Lee, M. Y. and Polles, F. L.}, biburl = {https://www.bibsonomy.org/bibtex/268e696ea94e234ccc10bd001db8de617/miki}, description = {[1702.07377] Neutral gas heating by X-rays in primitive galaxies: Infrared observations of IZw18 with Herschel}, interhash = {2274a554ac83fdaa87b5f1633bd313e4}, intrahash = {68e696ea94e234ccc10bd001db8de617}, keywords = {heating mechanism metal photoelectric poor x-ray}, note = {cite arxiv:1702.07377Comment: Accepted for publication in A&A}, timestamp = {2017-02-27T10:36:10.000+0100}, title = {Neutral gas heating by X-rays in primitive galaxies: Infrared observations of IZw18 with Herschel}, url = {http://arxiv.org/abs/1702.07377}, year = 2017 }