The Absorption Signatures of Dwarf Galaxies: Thez = 1.04 Multicloud Weak MgiiAbsorber toward PG 1634+706

Abstract

We analyze high-resolution spectra of a multicloud weak [defined as W r Mg ð iiÞ < 0:3 8] absorbing system along the line of sight to PG 1634+706. This system gives rise to a partial Lyman limit break and absorption in Mg ii, Si ii, C ii, Si iii, Si iv, C iv, and O vi. The lower ionization transitions arise in two kinematic subsystems with a separation of '150 km s À1 . Each subsystem is resolved into several narrow components having Doppler widths of 3-10 km s À1 . For both subsystems, the O vi absorption arises in a separate, higher ionization phase, in regions dominated by bulk motions in the range of 30-40 km s À1 . The two O vi absorption profiles are kinematically offset by '50 km s À1 with respect to each of the two lower ionization subsystems. In the stronger subsystem, the Si iii absorption is strong, with a distinctive, smooth profile shape, and may partially arise in shock-heated gas. Moreover, the kinematic substructure of Si iv traces that of the lower ionization Mg ii, but may be offset by '3 km s À1 . On the basis of photoionization models constrained by the partial Lyman limit break, we infer a low metallicity of $0.03 solar for the low-ionization gas in both subsystems. The broader O vi phases have a somewhat higher metallicity, and they are consistent with photoionization; the profiles are not broad enough to imply production of O vi through collisional ionization. Various models, including outer disks, dwarf galaxies, and superwinds, are discussed to account for the phase structure, metallicity, and kinematics of this absorption system. We favor an interpretation in which the two subsystems are produced by condensed clouds far out in the opposite extremes of a multilayer dwarf galaxy superwind.

The UV spectrum of HS 1700+6416

“…However, the actual χ 2 -value is often spoiled by a few pixels that are contaminated by problems with the noise array or simply line blends (formerly noticed also by e.g. Charlton et al 2003;Ding et al 2003a,b;Zonak et al 2004). Even though we try to minimize the influence of bad pixel on the χ 2 by selecting the lines and intervals appropriate to be used for each system individually, a visual inspection is needed.…”

“…in Charlton et al 2003;Ding et al 2003aDing et al ,b, 2005Zonak et al 2004;Masiero et al 2005). Especially O vi is believed to arise in a spatially more extended, low density gas (e.g.…”

MgII absorption through intermediate redshift galaxies

“…However, it was not until the STIS spectrograph on HST provided high resolution UV spectra of absorption kinematics from a wide range of ionisation species, such as Siii, Siiv, Cii, Ciii, Civ, Nii, Nv, O vi, and neutral hydrogen, that multiphase photoionisation could be modelled in detail Ding et al 2003;Zonak et al 2004;Masiero et al 2005;.…”

“…Some weak absorbers have multiple "clouds" spread over 10-100 km s −1 , but most are single clouds. It has been suggested that these systems are associated with low surface brightness galaxies (Churchill & Le Brun 1997), intergalactic star forming "pockets" (Rigby et al 2002), or dwarf galaxies (Zonak et al 2004). …”

Gas Accretion via Lyman Limit Systems

“…At the time of the Ribaudo et al (2011b) study, there were only about 8 metallicity estimates in LLSs (see, e.g., Lehner et al 2009;Cooksey et al 2008;Zonak et al 2004;Tripp et al 2011) and about 50% of those had [X/H] −1.5. This is remarkable because as I will show below the sample of pLLSs and LLSs has increased by factors 3.5 and now 7 and yet the same fraction of very metal-poor gas has been found for the combined sample of pLLSs and LLSs.…”