Monday 10/29/12

Title: The dust SED of dwarf galaxies I. The case of NGC 4214
Authors: Hermelo, Israel; Lisenfeld, Ute; Relaño, Monica; Tuffs, Richard J.; Popescu, Cristina C.; Groves, Brent
Publication: eprint arXiv:1210.7067
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Cosmology and Extragalactic Astrophysics, Astrophysics – Galaxy Astrophysics
Comment: 19 pages, 7 figures, accepted by A&A
Bibliographic Code: 2012arXiv1210.7067H

Abstract

The goal of the present study is to establish the physical origin of dust heating and emission based on radiation transfer models, which self-consistently connect the emission components from diffuse dust and the dust in massive star forming regions. NGC 4214 is a nearby dwarf galaxy with a large set of ancillary data, ranging from the ultraviolet (UV) to radio, including maps from SPITZER, HERSCHEL and detections from PLANCK. We mapped this galaxy with MAMBO at 1.2 mm at the IRAM 30 m telescope. We extract separate dust emission components for the HII regions (plus their associated PDRs on pc scales) and for the diffuse dust (on kpc scales). We analyse the full UV to FIR/submm SED of the galaxy using a radiation transfer model which self-consistently treats the dust emission from diffuse and SF complexes components, considering the illumination of diffuse dust both by the distributed stellar populations, and by escaping light from the HII regions. While maintaining consistency with the framework of this model we additionally use a model that provides a detailed description of the dust emission from the HII regions and their surrounding PDRs on pc scales. Due to the large amount of available data and previous studies for NGC 4214 very few free parameters remained in the model fitting process. We achieve a satisfactory fit for the emission from HII+PDR regions on pc scales, with the exception of the emission at 8\mi, which is underpredicted by the model. For the diffuse emission we achieve a good fit if we assume that about 30-70% of the emission escaping the HII+PDR regions is able to leave the galaxy without passing through a diffuse ISM, which is not an unlikely scenario for a dwarf galaxy which has recently undergone a nuclear starburst. We determine a dust-to-gas mass ratio of 350-390 which is close to the expected value based on the metallicity.

Title: Dwarf Galaxies with Ionizing Radiation Feedback. II: Spatially-resolved Star Formation Relation
Authors: Kim, Ji-hoon; Krumholz, Mark R.; Wise, John H.; Turk, Matthew J.; Goldbaum, Nathan J.; Abel, Tom
Publication: eprint arXiv:1210.6988
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics, Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 13 pages, 12 figures, submitted for publication in the Astrophysical Journal, Image resolution greatly reduced, High-resolution version of this article is available at http://www.jihoonkim.org/
Bibliographic Code: 2012arXiv1210.6988K

Abstract

We investigate the spatially-resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate. Because we have self-consistently calculated the location of ionized gas, we for the first time are able to make spatially-resolved mock observations of star formation tracers, such as H-alpha emission. We can also observe how stellar feedback manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3e11 Msun, we find that the correlation between star formation rate density (estimated from mock H-alpha emission) and molecular hydrogen density shows large scatter, especially at high resolutions of <~ 75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution. By examining the evolving environment around star clusters, we demonstrate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales results from a combination of stars drifting from their birthplaces, and molecular clouds being dispersed via ionizing radiation and supernova feedback.

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