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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 308818.0, MPI für Astronomie / Publikationen_mpia
Warm dust and spatially variable polycyclic aromatic hydrocarbon emission in thedwarf starburst galaxy NGC 1705
Authors:Cannon, J. M.; Smith, J.-D.; Walter, F.; Bendo, G. J.; Calzetti, D.; Dale, D. A.; Draine, B. T.; Engelbracht, C. W.; Gordon, K. D.; Helou, G.; Kennicutt, R. C.; Leitherer, C.; Armus, L.; Buckalew, B. A.; Hollenbach, D. J.; Jarrett, T. H.; Li, A.; Meyer, M. J.; Murphy, E. J.; Regan, M. W.; Rieke, G. H.; Rieke, M. J.; Roussel, H.; Sheth, K.; Thornley, M. D.
Date of Publication (YYYY-MM-DD):2006
Journal Abbrev.:The Astrophysical Journal
Start Page:293
End Page:302
Audience:Not Specified
Abstract / Description:We present Spitzer observations of the nearby dwarf starburst galaxy NGC 1705 obtained as part of the Spitzer Infrared Nearby Galaxies Survey. The galaxy morphology is very different shortward and longward of ~5 mum: optical and short-wavelength IRAC imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer wavelength IRAC and MIPS imaging reveals warm dust emission arising from two off-nuclear regions that are offset by ~250 pc from the SSC and that dominate the far-IR flux of the system. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2 × 105 Msolar, implying a global dust-to-gas mass ratio ~2-4 times lower than the Milky Way average, roughly consistent with the metallicity decrease). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed Halpha emission; these photons are unassociated with the SSC (although a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-strength PAH emission in the 11.3 mum band in the more luminous eastern peak; no PAH emission is detected in the SSC or the western dust emission complex. There is significant diffuse emission in the IRAC 8 mum band after starlight has been removed by scaling shorter wavelength data; the fact that IRS spectroscopy shows spatially variable PAH emission strengths compared to the local continuum within this diffuse gas suggests caution in the interpretation of IRAC diffuse 8 mum emission as arising from PAH carriers alone. The nebular metallicity of NGC 1705 falls at the transition level of ~0.35 Zsolar found by Engelbracht and collaborators, below which PAH emission is difficult to detect; the fact that a system at this metallicity shows spatially variable PAH emission demonstrates the complexity of interpreting diffuse 8 mum emission in galaxies. NGC 1705 deviates significantly from the canonical far-infrared versus radio correlation, having significant far-infrared emission but no detected radio continuum.
Free Keywords:Galaxies: Dwarf; Galaxies: Individual: NGC Number: NGC 1705; Galaxies: Irregular; Galaxies: ISM; Infrared: Galaxies
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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