Dust and molecular content of the lensed quasar, MG0751+2716, at z = 3.2
Abstract
Context: Gravitational lenses offer unique opportunities to explore the molecular content around active galactic nuclei at high redshift, through the magnification and gain in angular resolution.
Aims: We study here the molecular and dust content of the high redshift (z=3.2), gravitationally lensed quasar MG0751+2716.
Methods: We used the IRAM Plateau de Bure interferometer to measure the CO J=3-2, J=4-3 and J=8-7 rotation lines and continuum flux between 1.1 mm and 3 mm in MG0751+2716. We use HST data and constraints from the high resolution MERLIN map at 6.2 cm to build an improved model of the lens.
Results: The position agreement between the CO emission and the millimeter continuum suggests that dust and molecules are closely related. A 500 km s-1 velocity gradient is tentatively detected from the CO lines across the central 0.5''. The continuum SED in the range 0.45 mm-204 mm exhibits the signatures of two components: synchrotron emission from a core/jet system, and thermal emission related to warm dust. The CO line intensities are compatible with warm, dense molecular gas, suggesting a location in the close environment of the quasar. These observational constraints lead us to consider a source/quasar model made of a point-like core, a radio jet, and a molecular and dusty ring-like structure (~460 pc in radius) located in a plane perpendicular to the jet axis and seen almost edge-on. For this configuration, we derive a total magnification of 16 for the quasar radiation at rest frequency above 350 GHz and a magnification of 25 below 350 GHz. The dust mass (assuming a likely temperature T=50 K) is M_dust=1.7 × 108 M_⊙, the mass of molecular material is M(H_2) = 6 × 1010 M_⊙ and a lower limit to the dynamical mass is M_dyn = 1.5 × 1010 M_⊙. Such values are comparable to those found in the small sample of CO detected sources at high redshifts.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- July 2007
- DOI:
- 10.1051/0004-6361:20066444
- Bibcode:
- 2007A&A...470...53A
- Keywords:
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- gravitational lensing;
- quasars: individual: MG0751+2716;
- cosmology: observations;
- quasars: general;
- radio lines: galaxies