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The Compact Nucleus of the Deep Silicate Absorption Galaxy NGC 4418

Evans, A. S. and Becklin, E. E. and Scoville, N. Z. and Neugebauer, G. and Soifer, B. T. and Matthews, K. and Ressler, M. and Werner, M. and Rieke, M. (2003) The Compact Nucleus of the Deep Silicate Absorption Galaxy NGC 4418. Astronomical Journal, 125 (5). pp. 2341-2347. ISSN 0004-6256. doi:10.1086/374234.

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High-resolution Hubble Space Telescope (HST) near-infrared and Keck mid-infrared images of the heavily extinguished infrared-luminous galaxy NGC 4418 are presented. These data make it possible to observe the imbedded near-infrared structure on scales of 10–20 pc and to constrain the size of the mid-infrared–emitting region. The 1.1–2.2 μm data of NGC 4418 show no clear evidence of nuclear star clusters or of a reddened active galactic nucleus. Instead, the nucleus of the galaxy consists of a ~100–200 pc linear structure with fainter structures extending radially outward. The near-infrared colors of the linear feature are consistent with a 10–300 Myr starburst suffering moderate levels (a few magnitudes) of visual extinction. At 7.9–24.5 μm NGC 4418 has estimated size upper limits in the range of 30–80 pc. These dimensions are consistent with the highest-resolution radio observations obtained to date of NGC 4418, as well as the size of 50–70 pc expected for a blackbody with a temperature derived from the 25, 60, and 100 μm flux densities of the galaxy. Further, a spectral energy distribution constructed from the multiwavelength mid-infrared observations shows the strong silicate absorption feature at 10 μm, consistent with previous mid-infrared observations of NGC 4418. An infrared surface brightness of ~2.1 × 10^(13) L_⊙ kpc^(-2) is derived for NGC 4418. Such a value, though consistent with the surface brightness of warm ultraluminous infrared galaxies [L_(IR)(8–1000 μm) ≥ 10^(12) L_⊙], such as IRAS 05189-2524 and IRAS 08572+3915, is not large enough to distinguish NGC 4418 as a galaxy powered by an active galactic nucleus, as opposed to a lower surface brightness starburst.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Evans, A. S.0000-0003-2638-1334
Scoville, N. Z.0000-0002-0438-3323
Rieke, M.0000-0002-7893-6170
Additional Information:© 2003 American Astronomical Society. Received 2002 October 30. Accepted 2003 January 28. We thank B. Stobie, J. Mazzarella, D. Dale, A. Sargent, and L. Armus for useful discussions and assistance, and the anonymous referee for a careful reading of the manuscript. A. S. E. also thanks H. Spoon for providing ISO-PHT-S data for inclusion in Figure 4. A. S. E. and N. Z. S. were supported by NASA grant NAG 5-3042. A. S. E. was also supported by NSF grant AST 02-06262. This research has made use of the NASA/IPAC Extragalactic Database, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASANAG 5-3042
NSFAST 02-06262
Subject Keywords:galaxies: active; galaxies: individual (NGC 4418)
Issue or Number:5
Record Number:CaltechAUTHORS:20170223-081326326
Persistent URL:
Official Citation:A. S. Evans et al 2003 AJ 125 2341
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74489
Deposited By: Ruth Sustaita
Deposited On:23 Feb 2017 16:58
Last Modified:11 Nov 2021 05:27

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