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The Circumgalactic Medium in Massive Halos

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Gas Accretion onto Galaxies

Part of the book series: Astrophysics and Space Science Library ((ASSL,volume 430))

Abstract

This chapter presents a review of the current state of knowledge on the cool (T ∼ 104 K) halo gas content around massive galaxies at z ≈ 0. 2–2. Over the last decade, significant progress has been made in characterizing the cool circumgalactic gas in massive halos of M h  ≈ 1012–14 M at intermediate redshifts using absorption spectroscopy. Systematic studies of halo gas around massive galaxies beyond the nearby universe are made possible by large spectroscopic samples of galaxies and quasars in public archives. In addition to accurate and precise constraints for the incidence of cool gas in massive halos, detailed characterizations of gas kinematics and chemical compositions around massive quiescent galaxies at z ≈ 0. 5 have also been obtained. Combining all available measurements shows that infalling clouds from external sources are likely the primary source of cool gas detected at \(d\gtrsim 100\) kpc from massive quiescent galaxies. The origin of the gas closer in is currently less certain, but SNe Ia driven winds appear to contribute significantly to cool gas found at d < 100 kpc. In contrast, cool gas observed at \(d\lesssim 200\) kpc from luminous quasars appears to be intimately connected to quasar activities on parsec scales. The observed strong correlation between cool gas covering fraction in quasar host halos and quasar bolometric luminosity remains a puzzle. Combining absorption-line studies with spatially resolved emission measurements of both gas and galaxies is the necessary next step to address remaining questions.

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Notes

  1. 1.

    Using stacked QSO spectra at the rest frames of all LRGs, it has been shown that the mean absorption equivalent width 〈 W 0 〉 of Mg II gas declines steadily with increasing projected distance in LRG halos (Zhu et al. 2014). The steady decline of 〈 W 0 〉 does not necessarily contradict the relatively flat W r (2796) versus d distribution for individual Mg II absorbers in Fig. 3, because 〈 W 0 〉 represents a weighted average of absorber strength and gas covering fraction. A direct comparison between 〈 W 0 〉 and Fig. 3 requires knowledge of the frequency distribution function of Mg II absorbers in LRG halos, f(W r ), and the underlying number density ratio between absorbing and non-absorbing LRGs.

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Acknowledgements

The author wishes to thank Sean Johnson, Rebecca Pierce, Michael Rauch, and Fakhri Zahedy for providing helpful input and comments. In preparing this review, the author has made use of NASA’s Astrophysics Data System Bibliographic Services.

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Correspondence to Hsiao-Wen Chen .

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Chen, HW. (2017). The Circumgalactic Medium in Massive Halos. In: Fox, A., Davé, R. (eds) Gas Accretion onto Galaxies . Astrophysics and Space Science Library, vol 430. Springer, Cham. https://doi.org/10.1007/978-3-319-52512-9_8

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