Quasar 3C 298: a test-case for meteoritic nanodiamond 3.5 emission

Free access article

Issue		A&A Volume 467, Number 1, May III 2007


Page(s)		L7 - L10
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20077081

A&A 467, L7-L10 (2007)
DOI: 10.1051/0004-6361:20077081

Letter

Quasar 3C 298: a test-case for meteoritic nanodiamond 3.5 $\mu{\rm m}$ emission

J. A. de Diego¹, L. Binette¹, P. Ogle², A. C. Andersen³, S. Haro-Corzo¹, and M. Wold⁴

¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 70-264, 04510 México D.F., Mexico
e-mail: jdo@astroscu.unam.mx
² Spitzer Science Center, MS 220-6, California Institute of Technology, Pasadena, CA 91125, USA
³ Dark Cosmology Centre, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁴ European Southern Observatory, Karl-Schwarzschild str. 2, 85748 Garching bei München, Germany

(Received 11 January 2007 / Accepted 1 March 2007 )

Abstract
Aims.We calculate the dust emission expected at 3.43 and 3.53 $\mu{\rm m}$ if meteoritic (i.e. hydrogenated) nanodiamonds are responsible for most of the far-UV break observed in quasars.
Methods.We integrate the UV flux that hydrogenated nanodiamonds must absorb to reproduce the far-UV break. Based on laboratory spectra of H-terminated diamond surfaces, we analyse the radiative energy budget and derive theoretically the IR emission profiles expected for possible C-H surface stretch modes of the diamonds.
Results.Using as test case a spectrum of 3C 298 provided by the Spitzer Observatory, we do not find evidence of these emission bands.
Conclusions.While diamonds without surface adsorbates remain a viable candidate for explaining the far-UV break observed in quasars, hydrogenated nanodiamonds appear to be ruled out, as they would give rise to IR emission bands, which have not been observed so far.

Key words: galaxies: active -- ISM: dust, extinction -- infrared: galaxies -- ultraviolet: galaxies -- quasars: individual: 3C 298

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