A runaway black hole in cosmos: Gravitational wave or slingshot recoil?

F. Civano, M. Elvis, G. Lanzuisi, K. Jahnke, G. Zamorani, L. Blecha, A. Bongiorno, M. Brusa, A. Comastri, H. Hao, A. Leauthaud, A. Loeb, V. Mainieri, E. Piconcelli, M. Salvato, N. Scoville, J. Trump, C. Vignali, T. Aldcroft, M. BolzonellaE. Bressert, A. Finoguenov, A. Fruscione, A. M. Koekemoer, N. Cappelluti, F. Fiore, S. Giodini, R. Gilli, C. D. Impey, S. J. Lilly, E. Lusso, S. Puccetti, J. D. Silverman, H. Aussel, P. Capak, D. Frayer, E. Le Floch, H. J. McCracken, D. B. Sanders, D. Schiminovich, Y. Taniguchi

Research output: Contribution to journalArticlepeer-review

98 Scopus citations


We present a detailed study of a peculiar source detected in the COSMOS survey at z = 0.359. Source CXOC J100043.1+020637, also known as CID-42, has two compact optical sources embedded in the same galaxy. The distance between the two, measured in the HST/ACS image, is 0495 0005 that, at the redshift of the source, corresponds to a projected separation of 2.46 ± 0.02 kpc. A large (∼1200kms-1) velocity offset between the narrow and broad components of Hβ has been measured in three different optical spectra from the VLT/VIMOS and Magellan/IMACS instruments. CID-42 is also the only X-ray source in COSMOS, having in its X-ray spectra a strong redshifted broad absorption iron line and an iron emission line, drawing an inverted P-Cygni profile. The Chandra and XMM-Newton data show that the absorption line is variable in energy by ΔE = 500eV over four years and that the absorber has to be highly ionized in order not to leave a signature in the soft X-ray spectrum. That these features - the morphology, the velocity offset, and the inverted P-Cygni profile - occur in the same source is unlikely to be a coincidence. We envisage two possible explanations, both exceptional, for this system: (1) a gravitational wave (GW) recoiling black hole (BH), caught 1-10 Myr after merging; or (2) a Type 1/Type 2 system in the same galaxy where the Type 1 is recoiling due to the slingshot effect produced by a triple BH system. The first possibility gives us a candidate GW recoiling BH with both spectroscopic and imaging signatures. In the second case, the X-ray absorption line can be explained as a BAL-like outflow from the foreground nucleus (a Type 2 AGN) at the rearer one (a Type 1 AGN), which illuminates the otherwise undetectable wind, giving us the first opportunity to show that fast winds are present in obscured active galactic nuclei (AGNs), and possibly universal in AGNs.

Original languageEnglish (US)
Pages (from-to)209-222
Number of pages14
JournalAstrophysical Journal
Issue number1
StatePublished - 2010


  • Galaxies: active
  • Galaxies: formation
  • Galaxies: interactions
  • Galaxies: nuclei
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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