Kinematic Analysis of an Ultrastrong Mg <scp>II</scp> Absorber at <i>z</i> ≈ 1.13 Linked to Circumgalactic Gas Structures

Abstract We present a spectroscopic and imaging analysis of the z gal ≈ 1.1334 ultrastrong Mg ii absorption system identified in the Very Large Telescope/UVES spectrum of a background quasar located at ρ ≈ 18 kpc from a star-forming galaxy. Low-ionization metal lines like Mg i , Fe ii , and Ca ii are also detected for this absorber. The H I lines are outside of the wavelength coverage. The Mg ii has a rest-frame equivalent width of W r (2796) = 3.185 ± 0.032 Å, with the absorption spread across Δ v ≈ 460 km s −1 in several components. A component-by-component ionization modeling shows several of these components having solar and higher metallicities. The models also predict a total h i column density of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mspace width="0.25em"/> <mml:mo stretchy="false">[</mml:mo> <mml:mi>N</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">I</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>/</mml:mo> <mml:msup> <mml:mrow> <mml:mspace width="0.1em"/> <mml:mtext>cm</mml:mtext> <mml:mspace width="0.1em"/> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">]</mml:mo> <mml:mo>≈</mml:mo> <mml:mn>22.5</mml:mn> </mml:math> , consistent with ultrastrong Mg ii absorbers being sub–damped Ly α and damped Ly α systems. The absorber is well within the virial radius of the nearest galaxy, which has a stellar mass M * = 4.7 × 10 10 M ⊙ , and a star formation rate of ≈8.3 M ⊙ yr −1 . The absorption is along the projected major axis of the galaxy with a velocity spread that is wider than the galaxy’s disk rotation. From the kinematic analysis of the absorber and the galaxy, the origin of the absorption can be attributed to a combination of circumgalactic gas structures, some corotating with the disk and the rest moving at line-of-sight velocities outside of the disk rotation.