The Cosmic Ultraviolet Baryon Survey (CUBS). VII. On the Warm-hot Circumgalactic Medium Probed by O vi and Ne viii at 0.4 ≲ z ≲ 0.7
Zhijie Qu, Hsiao‐Wen Chen, Sean D. Johnson, Gwen C. Rudie, Fakhri S. Zahedy, David DePalma, Joop Schaye, Erin Boettcher, Sebastiano Cantalupo, Mandy C. Chen, Claude‐André Faucher‐Giguère, Jennifer I-Hsiu Li, John S. Mulchaey, Patrick Petitjean, Marc Rafelski
Abstract
Abstract This paper presents a newly established sample of 103 unique galaxies or galaxy groups at 0.4 ≲ z ≲ 0.7 from the Cosmic Ultraviolet Baryon Survey (CUBS) for studying the warm-hot circumgalactic medium (CGM) probed by both O vi and Ne viii absorption. The galaxies and associated neighbors are identified at <1 physical Mpc from the sightlines toward 15 CUBS QSOs at z QSO ≳ 0.8. A total of 30 galaxies or galaxy groups exhibit associated O vi λ λ 1031, 1037 doublet absorption within a line-of-sight velocity interval of ±250 km s −1 , while the rest show no trace of O vi to a detection limit of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>OVI</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>≈</mml:mo> <mml:mn>13.7</mml:mn> </mml:math> . Meanwhile, only five galaxies or galaxy groups exhibit the Ne viii λ λ 770, 780 doublet absorption, down to a limiting column density of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>NeVIII</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>≈</mml:mo> <mml:mn>14.0</mml:mn> </mml:math> . These O vi - and Ne viii -bearing halos reside in different galaxy environments with stellar masses ranging from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>star</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>8</mml:mn> </mml:math> to ≈11.5. The warm-hot CGM around galaxies of different stellar masses and star formation rates exhibits different spatial profiles and kinematics. In particular, star-forming galaxies with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>star</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>9</mml:mn> <mml:mo>–</mml:mo> <mml:mn>11</mml:mn> </mml:math> show a significant concentration of metal-enriched warm-hot CGM within the virial radius, while massive quiescent galaxies exhibit flatter radial profiles of both column densities and covering fractions. In addition, the velocity dispersion of O vi absorption is broad with σ υ > 40 km s −1 for galaxies of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>star</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo>></mml:mo> <mml:mn>9</mml:mn> </mml:math> within the virial radius, suggesting a more dynamic warm-hot halo around these galaxies. Finally, the warm-hot CGM probed by O vi and Ne viii is suggested to be the dominant phase in sub- L * galaxies with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>star</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>9</mml:mn> <mml:mo>–</mml:mo> <mml:mn>10</mml:mn> </mml:math> based on their high ionization fractions in the CGM.