paper

SDSS J0025-10 at z=0.30: a (U)LIRG to optical QSO transition candidate

arXiv:1304.0396 · doi:10.1093/mnras/stt538

Abstract

We have characterized the amount, spatial distribution and kinematics of the molecular gas in the merging, double nucleus type 2 quasar SDSS J0025-10 at z=0.30 using the CO(1-0) transition, based on data obtained with ATCA. This is one of the scarce examples of quasar host galaxies where the CO emission has been resolved spatially at any redshift. We infer a molecular gas mass M(H2) = (6 +/- 1) x 1e9 Msun, which is distributed in two main reservoirs separated by ~9 kpc. ~60% of the gas is in the central region, associated with the QSO nucleus and/or the intermediate region between the two nuclei. The other 40% is associated with the northern tidal tail and is therefore unsettled. With its high infrared luminosity L(IR) = (1.1 +/- 0.3) x 1e12 Lsun, SDSS J0025-10 is an analogue of local luminous LIRGs and ULIRGs. On the other hand, the clear evidence for an ongoing major merger of two gas rich progenitors, the high L(IR) dominated by a starburst, the massive reservoir of molecular gas with a large fraction still unsettled, and the quasar activity are all properties consistent with a transition phase in the (U)LIRG-optical QSO evolutionary scenario. We propose that we are observing the system during a particular transient phase, prior to more advanced mergers where the nuclei have already coalesced. We argue that a fraction of the molecular gas reservoir is associated with a tidal dwarf galaxy identified in the optical HST image at the tip of the northern tidal tail. The formation of such structures is predicted by simulations of colliding galaxies.

arXiv commentAccepted for publication in MNRAS. 9 pages, 4 figures

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