MUSEQuBES: The Column Density, Covering Fraction, and Mass of O <scp>vi</scp>-bearing Gas in and Around Low-redshift Galaxies

Abstract

Abstract We present a study of O vi -bearing gas around 247 low-mass (median <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> = 8.7) galaxies at low redshifts (0.1 &lt; z &lt; 0.7) using background quasars as part of the MUSE Quasar-fields Blind Emitters Survey (MUSEQuBES). We find that the average O vi column density, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mfenced close="〉" open="〈"> <mml:mrow> <mml:mi>N</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">VI</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>/</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mn>14.1</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.09</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , measured within the virial radius for our sample, is significantly lower than for L * galaxies. Combining 253 star-forming galaxies (mostly more massive) from the literature with 176 star-forming galaxies from MUSEQuBES, we find that both <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="〉" open="〈"> <mml:mrow> <mml:mi>N</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">VI</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:mfenced> </mml:math> and the average covering fraction peak at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> ≈ 9.5. The virial temperature corresponding to this stellar mass is ideal for O vi production via collisional ionization. However, we argue that photoionization and/or nonequilibrium processes are necessary to produce the O vi associated with low-mass, dwarf galaxies ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> &lt; 9). The average O vi mass within the virial radius of dwarf galaxies is measured to be <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>5</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:msup> </mml:math> M ⊙ . The characteristic normalized impact parameter ( D / R vir ) at which the O vi covering fraction drops to half of its peak value is largest (≈1.1) for galaxies with stellar mass <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> ≈ 9.5. We report the presence of a highly ionized metal floor with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow>

Topics & Concepts