Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas around the Andromeda Galaxy

Howk, J. C.; Wotta, Christopher B.; Berg, Michelle A.; Lehner, N.; Lockman, Felix J.; Hafen, Zachary; Pisano, D. J.; Faucher-Giguère, Claude André; Wakker, Bart P.; Prochaska, J. Xavier; Wolfe, Spencer A.; Ribaudo, Joseph; Barger, Kat; Corlies, Lauren; Guhathakurta, Puragra; Jenkins, Edward B.; Kalirai, Jason; O’Meara, John M.; Peeples, Molly S.; Stewart, Kyle R.; Strader, Jay

doi:10.3847/1538-4357/aa87b4

Cited by 26 publications

(26 citation statements)

References 105 publications

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“…At these HI column densities the gas clouds are mostly ionized [25], but they allow us to trace the morphology and kinematics of this reservoir. Furthermore, the CGM of M 31 itself is quite clumpy with HI covering fractions below 5% at N HI ∼4×10 17 cm −2 [26]. As seen in Figure 2, these results are consistent with simulations, but are significantly lower than what was found from COS-HALOS [27].…”

Section: Current Observations Of the Cgmsupporting

confidence: 86%

“…Note that the HI structures detected by [22] are revealed to be much smaller, higher-N HI features by [24], illustrating the critical importance of resolution and sensitivity. [26] GBT pointings relative to M31 and M33, where the axes are labeled with the impact parameter from the center of M31. Aside from two filled circles, representing detections of HI associated with the Magellanic Stream, all AMIGA observations yielded non-detections.…”

Section: The Role Of 21-cm Hi Observations In the Next Decadementioning

confidence: 99%

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Completing the Hydrogen Census in the Circumgalactic Medium at z~0

Pisano,

Fox,

French

et al. 2019

Preprint

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Over the past decade, Lyman-α and metal line absorption observations have established the ubiquity of a gas-rich circumgalactic medium (CGM) around star-forming galaxies at z∼0.2 potentially tracing half of the missing baryonic mass within galaxy halos. Unfortunately, these observations only provide a statistical measure of the gas in the CGM and do not constrain the spatial distribution and kinematics of the gas. Furthermore, we have limited sensitivity to Lyman-α at z∼0 with existing instruments. As such, we remain ignorant of how this gas may flow from the CGM onto the disks of galaxies where it can fuel ongoing star-formation in the present day. Fortunately, 21-cm HI observations with radio telescopes can map HI emission providing both spatial and kinematic information for the CGM in galaxies at z=0. Observations with phased array feeds, radio cameras, on single-dish telescopes yield unmatched surface brightness sensitivity and survey speed. These observations can complete the census of HI in the CGM below N HI 10 17 cm −2 and constrain how gas accretion is proceeding in the local universe, particularly when used in concert with UV absorption line data.

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Section: Current Observations Of the Cgmsupporting

confidence: 86%

Section: The Role Of 21-cm Hi Observations In the Next Decadementioning

confidence: 99%

Completing the Hydrogen Census in the Circumgalactic Medium at z~0

Pisano,

Fox,

French

et al. 2019

Preprint

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“…Observations of H I 21 cm emission toward the QSOs observed with COS in the MS survey (Fox et al 2014) and Project AMIGA (Howk et al 2017) show only H I detections within…”

Section: Msmentioning

confidence: 97%

Project AMIGA: The Circumgalactic Medium of Andromeda*

Lehner

Berek

Howk

et al. 2020

ApJ

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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 ∼10 4-10 5.5 K ionized CGM. The metal and baryon masses of the 10 4-10 5.5 K CGM gas within R vir are 10 8 and 4×10 10 (Z/0.3 Z e) −1 M e , 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 ∼10 4-10 5.5 K CGM as extended as for M31 and their CGM (especially the warm-hot gas probed by O VI) are overlapping.

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“…Our result is, however, in slight disagreement with the estimate of Lehner et al (2020), who have found a lower limit for the metallicity of the cool CGM of M31 of 0.2 𝑍 . We recall that this limit was obtained combining detected OI absorption with non-detections of HI in emission (see Howk et al 2017). As also explained by Lehner et al (2020), absorption and emission measurements are characterised by inherently different spatial resolutions and it is therefore possible that their estimated metallicity might be affected by the beam dilution effect.…”

Section: Origin Of the Cool Gasmentioning

confidence: 93%

Inflow of low-metallicity cool gas in the halo of the Andromeda galaxy

Afruni,

Pezzulli,

Fraternali

2021

Preprint

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As the closest 𝐿 * galaxy to our own Milky Way, the Andromeda galaxy (M31) is an ideal laboratory for studies of galaxy evolution. The AMIGA project has recently provided observations of the cool (𝑇 ∼ 10 4 K) phase of the circumgalactic medium (CGM) of M31, using HST/COS absorption spectra along ∼ 40 background QSO sightlines, located up to and beyond the galaxy virial radius. Based on these data, and by the means of semi-analytic models and Bayesian inference, we provide here a physical description of the origin and dynamics of the cool CGM of M31. We investigate two competing scenarios, in which (i) the cool gas is mostly produced by supernova(SN)-driven galactic outflows or (ii) it mostly originates from infall of gas from the intergalactic medium. In both cases, we take into account the effect of gravity and hydrodynamical interactions with a hot corona, which has a cosmologically motivated angular momentum. We compare the outputs of our models to the observed covering factor, silicon column density and velocity distribution of the AMIGA absorbers. We find that, to explain the observations, the outflow scenario requires an unphysically large (> 100%) efficiency for SN feedback. Our infall models, on the other hand, can consistently account for the AMIGA observations and the predicted accretion rate, angular momentum and metallicity are consistent with a cosmological infall from the intergalactic medium.

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Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas around the Andromeda Galaxy

Cited by 26 publications

References 105 publications

Completing the Hydrogen Census in the Circumgalactic Medium at z~0

Completing the Hydrogen Census in the Circumgalactic Medium at z~0

Project AMIGA: The Circumgalactic Medium of Andromeda*

Inflow of low-metallicity cool gas in the halo of the Andromeda galaxy

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