The Multi-Phase Absorption Systems Toward PG 1206 + 459

Abstract

A high-resolution (R = 30, 000) ultraviolet spectrum is presented, which covers Lyα and many low-, intermediate-, and high-ionization transitions in the three Mg ii-selected absorption systems toward the quasar PG 1206 + 459. Three systems (A, B, and C), which are clustered within 1500 km s −1 at z ∼ 0.93, were originally identified in a spectrum obtained with the High Resolution Spectrograph (HIRES) on the Keck I telescope. A WIYN Gunn i-band image of the quasar field and spectroscopy of two galaxy candidates are presented. A multi-phase medium is seen in all three systems, consistent with smaller, denser clouds producing low-ionization transitions (Mg ii, Feii, and Si ii) and larger, diffuse, photoionized clouds giving rise to higher-ionization transitions (Civ, Nv, 1 Based in part on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.2 Based in part on observations obtained with the NASA/ESA Hubble Space Telescope, which is operated by the STScI for the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.3 Based in part on observations obtained with the WIYN 3.5-m telescope, a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories. (1) System A, a multi-cloud, weak Mg ii absorber at z = 0.9254, requires a super-solar metallicity in both low-and high-ionization phases, unless an α-group enhancement is included. The low-ionization absorption is produced in clouds with sizes of 10-70 pc, which are surrounded in velocity space by broader, high-ionization components. With the unusually complex velocity structure resolved in the Nv profiles, this system is unlikely to represent a traditional galaxy disk/corona. The most likely candidate host galaxy is a ∼ 2L * , apparently warped, spiral at an impact parameter of 43h −1 kpc. (2) System B, at z = 0.9276, has the strongest Mg ii absorption and has an approximately solar metallicity in the low-ionization phase. The smooth, broad high-ionization profiles may indicate a coronal structure similar to that of the Milky Way. The redshift of an L * galaxy (z = 0.9289), at an impact parameter of 38h −1 kpc is consistent with the redshift of this system. (3) System C, at z = 0.9342, has a single component in Mg ii, separated from the other two systems by ∼ +1000 km s −1 . The Lyα profile is not aligned with the Mg ii, requiring an additional velocity component offset by −40 km s −1 . System C lacks the small, low-ionization cloud characteristic of an isolated single-cloud, weak Mg ii absorber. Its absorption properties are similar to the "satellite clouds" of classic strong Mg ii absorbers, so this could be a high-velocity cloud in the galaxy group responsible for the systems, possibly related to a 0.2L * galaxy at an impact parameter of 43h −1 kpc.