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The Merging Binary Quasars LBQS 0103-2753A & LBQS 0103-2753B

19/04/2012

Quasars (QSOs) represent the most enigmatic and energetic observational objects in the Universe, inhabiting the very centers of active young galaxies. Such objects can emit up to a thousand times the energy output of the Milky Way where this emission from the central core active nucleus (AGN) is considerably red-shifted, a consequence of the expansion of space-time. Such active nuclei usually inhabit there own region of space. However, there are a few that buck that trend: exiting as dual active galactic nuclei (dAGN), where such dual active galaxies are extremely likely to represent merging galaxies with both nuclei in an active state.

In the standard Λ-CDM (cold dark matter with universal expansion) cosmology (Komatsu et al. 2009; Jarosik et al. 2011) galaxies regularly interact and merge. Hierarchical galaxy evolution permits galaxies to undergo multiple mergers throughout their lifetimes (Blumenthal et al. 1984; Spergel et al. 2007). Most massive galaxies contain supermassive black holes (SMBHs) within the central region of its host galaxy (Antonucci 1993; Urry & Padovani 1995), where accretion of gas onto the SMBH is suspected to drive phenomena associated with active galaxies (e.g., Soria et al. 2006a, 2006b; Nayakshin & King 2007; Micic et al. 2007; Levine et al. 2010).

When galaxies merge gas is driven to the central nuclear regions and can accrete onto the central SMBH, as the collision torques the gas in the outer regions of the galaxies causing an inward flow to the SMBH (Kau mann & Hhnelt 2000; Garca-Burillo et al. 2006; Hopkins et al. 2008). The cause of quasar activity has now been found to require high-densities of relatively cold gas around the central SMBH, and as such, it is achieved through these large-scale gas flows triggered by galaxy mergers (Sijacki et al. 2007). Fast forward a relatively large amount of time, and dual active galactic nuclei (AGNs) are natural by-products of hierarchical mergers of AGN galaxies that were once themselves the product of colliding galaxies (Hopkins et al. 2005).

The binary nature of LBQS 0103-2753 was discovered by Junkkarinen et al. (2001) in the course of ultraviolet spectroscopic observations with STIS aimed at understanding the broad absorption lines. The acquisition image revealed two AGN separated by 0.3 arcsec with magnitude V = 18.2 and V = 19.4 for components LBQS 0103-2753A and LBQS 0103-2753B, respectively. Each individual component of the binary object found by Junkkarinen et al. (2001) exhibited strong evidence of quasar activity. Coupled with this, observational analysis of the light spectrum of the two components show they are very near to each other, both showing red-shifts of ~ z =0.8 [LBQS 0103-2753A z = 0.834; LBQS 0103-2753B z = 0.858 (Junkkarinen et al. 2001)]. The very different ultraviolet spectra of LBQS 0103−2753 A and B show that this is a true binary, not a gravitationally lensed quasar. As such, the chances of finding two unrelated quasars within such close separations at almost identical red-shifts are slim to none. Hence, the one possible conclusion is that LBQS 0103-2753 is, in fact, a binary quasar.

Coupled with the identification work by Junkkarinen et al. (2001) is the work presented by Shields et al. (2012) which concludes that LBQS 0103-2753 is a dual active galactic nuclei still within the throes of a major merger. Shields et al. (2012) conclude that their images, obtained using the Hubble Space Telescope, show two rather large QSO galaxies with commensurate black holes with tidal interactions at an advanced stage of their merger. The exceptional nature of the present system lies in the vigorous, simultaneous fueling of both black holes, and the lack of obscuration of either nucleus in the line of sight. The large tidal arc and the prominent star formation regions found by Shields et al. (2011) suggest a gas-rich merger, consistent with the vigorous fueling required for the two luminous QSOs as outlined in many hierarchical galaxy formation models (Soria et al. 2006a, 2006b; Nayakshin & King 2007; Sijacki et al. 2007; Micic et al. 2007; Levine et al. 2010).

Journal References:

  • Antonucci, R. (1993) Unified Models For Active Galactic Nuclei & Quasars. Annual Review of Astronomy & Astrophysics. 31, pp. 473-521.
  • Junkkarinen, V.T. et al. (2001) LBQS 0103-2753: A 0.3 Arcsec Binary Quasar. The Astrophysical Journal: Letters, 549: pp.L155-L159.
  • Hopkins, P.F. et al. (2005) Black Holes In Galaxy Mergers: Evolution Of Quasars. The Astrophysical Journal, 630(2), pp. 705-715.
  • McGurk, R. C.et al. (2011) Spatially Resolved Spectroscopy Of SDSS J0952+2552: A Confirmed Dual Active Galactic Nucleus. The Astrophysical Journal Letters, 738 (1), Article I.D. L2.
  • Shields, G.A. et al. (2012) LBQS 0103-2753: A Binary Quasar In A Major Merger. The Astrophysical Journal, 744 (2), Article I.D. 151.

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