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Published September 1, 2020 | Submitted + Published
Journal Article Open

Project AMIGA: The Circumgalactic Medium of Andromeda

Abstract

Project AMIGA (Absorption Maps In the Gas of Andromeda) is a survey of the circumgalactic medium (CGM) of Andromeda (M31, R_(vir) ≃ 300 kpc) along 43 QSO sightlines at impact parameters 25 ≤ R ≤ 569 kpc (25 at R ≾ R_(vir)). We use ultraviolet absorption measurements of Si II, Si III, Si IV, C II, and C IV from the Hubble Space Telescope/Cosmic Origins Spectrograph and O VI from the Far Ultraviolet Spectroscopic Explorer to provide an unparalleled look at how the physical conditions and metals are distributed in the CGM of M31. We find that Si III and O VI have a covering factor near unity for R ≾ 1.2 R_(vir) and ≾1.9 R_(vir), respectively, demonstrating that M31 has a very extended ~10⁴–10^(5.5) K ionized CGM. The metal and baryon masses of the 10⁴–10^(5.5) K CGM gas within R_(vir) are ≳ 10⁸ and ≳ 4 × 10¹⁰ (Z/0.3 Z⊙)⁻¹ M⊙, respectively. There is not much azimuthal variation in the column densities or kinematics, but there is with R. The CGM gas at R ≾ 0.5 R_(vir) is more dynamic and has more complicated, multiphase structures than at larger radii, perhaps a result of more direct impact of galactic feedback in the inner regions of the CGM. Several absorbers are projected spatially and kinematically close to M31 dwarf satellites, but we show that those are unlikely to give rise to the observed absorption. Cosmological zoom simulations of ~L* galaxies have O VI extending well beyond R_(vir) as observed for M31 but do not reproduce well the radial column density profiles of the lower ions. However, some similar trends are also observed, such as the lower ions showing a larger dispersion in column density and stronger dependence on R than higher ions. Based on our findings, it is likely that the Milky Way has a ~10⁴–10^(5.5) K CGM as extended as for M31 and their CGM (especially the warm–hot gas probed by O VI) are overlapping.

Additional Information

© 2020 The American Astronomical Society. Received 2020 February 17; revised 2020 June 26; accepted 2020 June 30; published 2020 August 27. We thank David Nidever for sharing his original fits of the MS H i emission and Ben Oppenheimer for sharing the EAGLE simulations shown in Figure 19. Support for this research was provided by NASA through grant HST-GO-14268 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. C.-A.F.-G. and Z.H. were also supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522; by NASA through grants NNX15AB22G and 17-ATP17-0067; by STScI through grants HST-GO-14681.011 and HST-AR-14293.001-A; and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which was operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985. Facilities: HST(COS); HST(STIS); FUSE. Software: Astropy (Astropy Collaboration et al. 2018), emcee (Foreman-Mackey et al. 2013), Matplotlib (Hunter 2007), PyIGM (Prochaska et al. 2017a), yt (Turk et al. 2011), Trident (Hummels et al. 2017).

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Published - Lehner_2020_ApJ_900_9.pdf

Submitted - 2002.07818.pdf

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August 22, 2023
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