Chary, R. and Becklin, E. E. and Evans, A. S. and Neugebauer, G. and Scoville, N. Z. and Matthews, K. and Ressler, M. E. (2000) High-Resolution Infrared Imaging of the Compact Nuclear Source in NGC 4258. Astrophysical Journal, 531 (2). pp. 756-763. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20170228-075334335
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We present high-resolution imaging of the nucleus of NGC 4258 from 1 to 18 μm. Our observations reveal that the previously discovered compact source of emission is unresolved even at the near-infrared resolution of ~0.”2 FWHM, which corresponds to about 7 pc at the distance of the galaxy. This is consistent with the source of emission being the region in the neighborhood of the purported 3.5 × 10^7 M☉ black hole. After correcting for about 18 mag of visual extinction, the infrared data are consistent with an F_ν ∝ ν^(-1.4±0.1) spectrum from 1.1 to 18 μm, implying a nonthermal origin. Based on this spectrum, the total extinction-corrected infrared luminosity (1-20 μm) of the central source is 2 × 10^8 L☉. We argue that the infrared spectrum and luminosity of the central source obviates the need for a substantial contribution from a standard, thin accretion disk at these wavelengths and calculate the accretion rate through an advection-dominated accretion flow to be M ~ 10^(-3) M☉ yr^(-1). The agreement between these observations and the theoretical spectral energy distribution for advection-dominated flows provides evidence for the existence of an advection-dominated flow in this low-luminosity active galactic nucleus.
|Additional Information:||© 2000 American Astronomical Society. Received 1999 May 5; accepted 1999 October 26. This work is based on observations made at the W. M. Keck Observatory, the Palomar Observatory, and with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We wish to acknowledge the contributions made by members of the NICMOS Instrument Definition Team to this project. We are grateful to Steve Willner for his help with clarifying the discussion in the Appendix. We would also like to thank the staffs of the respective observatories for their assistance. The W. M. Keck Observatory is a scientific partnership between the University of California and the California Institute of Technology.|
|Subject Keywords:||accretion, accretion disks; galaxies: individual (NGC 4258) ; galaxies: nuclei; infrared: general; radiation mechanisms: non-thermal|
|Official Citation:||R. Chary et al 2000 ApJ 531 756|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||28 Feb 2017 16:02|
|Last Modified:||28 Feb 2017 16:02|
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