Discrete clouds of neutral gas between the galaxies M31 and M33

Wolfe, Spencer A.; Pisano, D. J.; Lockman, Felix J.; McGaugh, Stacy S.; Shaya, E.

doi:10.1038/nature12082

Cited by 70 publications

(95 citation statements)

References 25 publications

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“…They appear to emerge from M 31's HI disk. We also identified at these low radial velocities HI components positionally located close to the M 31/M 33 HI bridge at systemic velocities Wolfe et al 2013). Here, the confusion of M 31 HI gas with that of HVC complex H is most severe.…”

Section: Results and Comparison With Previous Studiesmentioning

confidence: 81%

“…To minimize systematic biases due to this Milky Way gas confusion, previous HI studies of M 31 and its environment either focused on structures at M 31's systemic velocities Wolfe et al 2013) around v LSR = −300 km s −1 or instead used upper radial velocity thresholds Westmeier et al 2005) ranging between −160 km s −1 ≤ v LSR ≤ −140 km s −1 . For the northern portion of the Leiden/Argentine/Bonn survey data (Kalberla et al 2005, LAB), the Leiden-Dwingeloo survey (Hartmann & Burton 1997, LDS), Blitz et al (1999) extended the analyzed radial velocity range up to v LSR ≤ −85 km s −1 and identified the "M 31 cloud" apparently connected in HI emission to M 31's disk.…”

Section: Introductionmentioning

confidence: 99%

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A survey of HI gas toward the Andromeda galaxy

Kerp

Kalberla

Bekhti

et al. 2016

A&A

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Context. The subsequent coalescence of low-mass halos over cosmic time is thought to be the major formation channel of massive spiral galaxies like the Milky Way and the Andromeda galaxy (M 31). The gaseous halo of a massive galaxy is considered to be the reservoir of baryonic matter persistently fueling the star formation in the disk. Because of its proximity, M 31 is the ideal object for studying the structure of the halo gas in great detail. Aims. Using the latest neutral atomic hydrogen (HI) data of the Effelsberg-Bonn HI Survey (EBHIS) allows comprising a comprehensive inventory of gas associated with M 31. The primary aim is to differentiate between physical structures belonging to the Milky Way Galaxy and M 31 and accordingly to test the presence of a M 31 neutral gaseous halo. Methods. Analyzing the spatially fully sampled EBHIS data makes it feasible to trace coherent HI structures in space and radial velocity. To disentangle Milky Way and M 31 HI emission we use a new approach, along with the traditional path of setting an upper radial velocity limit, by calculating a difference second moment map. Results. We argue that M 31's disk is physically connected to an asymmetric HI halo of tens of kpc size, the M 31 cloud. We confirm the presence of a coherent low-velocity HI filament located in between M 31 and M 33 aligned at the sky with the clouds at systemic velocity. The physical parameters of the HI filament are comparable to those of the HI clouds at systemic velocity. We also detected an irregularly shaped HI cloud that is is positionally located close to but offset from the stellar body of And XIX.

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Section: Results and Comparison With Previous Studiesmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

A survey of HI gas toward the Andromeda galaxy

Kerp

Kalberla

Bekhti

et al. 2016

A&A

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“…Subsequent observations with the GBT at higher angular resolution showed that most of the emission was concentrated into discrete clouds (Wolfe et al, 2013(Wolfe et al, , 2016. Assuming that these clouds are at a distance of 800 kpc, between M31 and M33, they have M HI = 0.4 − 3.3 × 10 5 M , sizes of a few kpc, and are not associated with any stars or stellar stream.…”

Section: M31-m33 Cloudsmentioning

confidence: 99%

Neutral Gas Accretion onto Nearby Galaxies

Lockman¹

2017

Gas Accretion Onto Galaxies

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While there is no lack of evidence for the accretion of stellar systems onto nearby galaxies, direct evidence for the accretion of gas without stars is scarce. Here we consider an inventory of starless gas "clouds" in and around galaxies of the Local Group to discern their general properties and see how they might appear in distant systems. The conclusion is that accreting gas without stars is detected almost entirely within the circumgalactic medium of large galaxies and is rare otherwise. If our Local Group is any example, the best place to detect starless gas clouds is relatively close to galaxies.

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“…gas in the outskirts of the disc (Koch et al 2015;Lehner et al 2015;Wolfe et al 2013;Lockman et al 2012) is ruled out. No high velocity clouds have been detected in CO (Combes & Charmandaris 2000;Miville-Deschênes et al 2005), while Galactic gas should be around 0 km s −1 .…”

Section: Different Velocity Componentsmentioning

confidence: 99%

Dense gas tracing the collisional past of Andromeda

Melchior

Combes

2015

A&A

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The central kiloparsec region of the Andromeda galaxy is relatively gas poor, while the interstellar medium appears to be concentrated in a ring-like structure at about 10 kpc radius. The central gas depletion has been attributed to a possible head-on collision 200 Myr ago, supported by the existence of an offset inner ring of warm dust. We present new IRAM 30 m radio telescope observations of the molecular gas in the central region, and the detection of CO and its isotopes 13 CO(2−1) and C 18 O(2−1), together with the dense gas tracers, HCN(1−0) and HCO+(1−0). A systematic study of the observed peak temperatures with non-local thermal equilibrium simulations shows that the detected lines trace dense regions with n H 2 in the range 2.5 × 10 4 −5.6 × 10 5 cm −3 , while the gas is very clumpy with a beam filling factor of 0.5−2 × 10 −2 . This is compatible with the dust mass derived from the far-infrared emission, assuming a dust-to-gas mass ratio of 0.01 with a typical clump size of 2 pc. We also show that the gas is optically thin in all lines except for 12 CO(1-0) and 12 CO(2-1), CO lines are close to their thermal equilibrium condition at 17-20 K, the molecular hydrogen density is larger than critical, and HCN and HCO+ lines have a subthermal excitation temperature of 9 K with a density smaller than critical. The average 12 CO/ 13 CO line ratio is high (∼21), and close to the 12 CO/C 18 O ratio (∼30) that was measured in the north-western region and estimated in the south-east stacking. The fact that the optically thin 13 CO and C 18 O lines have comparable intensities means that the secondary element 13 C is depleted with respect to the primary 12 C, as is expected just after a recent star formation. This suggests that there has been a recent starburst in the central region, supporting the head-on collision scenario.

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Discrete clouds of neutral gas between the galaxies M31 and M33

Cited by 70 publications

References 25 publications

A survey of HI gas toward the Andromeda galaxy

A survey of HI gas toward the Andromeda galaxy

Neutral Gas Accretion onto Nearby Galaxies

Dense gas tracing the collisional past of Andromeda

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