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The Sightline towards the Quasar PG1543+489 : Evidence for Cool Halo Gas at z=0.1

Brenda L Frye (University of Arizona)

Évènements associés

  • The Sightline towards the Quasar PG1543+489 : Evidence for Cool Halo Gas at (...) : Le vendredi 13 juin 2014 de 15:00 à 16:00 - lieu : Salle 108, Bâtiment des Communs - Meudon

We examine the line of sight to the quasar PG1543+489 at z=0.401. The absorption line system at z=0.0749, ALS-1543, probes the outer halo of a disk galaxy `G1’ at a distance of 45h^-1kpc. By fitting profiles to the HI damping wings and to the NI lines in our HST/STIS spectroscopy, we measure a gas-phase abundance of 12+log(N/H)=8.6 +/- 0.2, one-tenth that of the star forming disk of G1. This low metallicity makes this ALS unlikely to be a part of a recent gas outflow event, especially given the nearly anti-polar alignment with respect to the disk of G1. From a joint analysis of the N I and Si II absorption lines we compute a kinetic gas temperature of 3.7 x 10^4 K, lower than expected for halo gas. To test the infall hypothesis, we construct a rotation curve for this edge-on galaxy. The UV metal lines are all systematically offset from the systemic redshift of G1 in the direction of rotation, and by an amount larger than the rotational velocity of the disk (by 70 km/s) from which we infer ALS-1543 to be orbiting and co-rotating with G1. If this is cool halo gas in the local universe then it appears to have escaped shock heating to the virial temperature, possibly owing to a low total mass (<10^12 solar masses). We report the discovery of the QSO host galaxy seen as a multi-line emission source at an angular separation of 7.33 arcsec, equating to 40 (physical) kpc, and discuss the implications of this extended emission line source for fueling its central supermassive black hole.