Letter to the Editor

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

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  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.