Constraints on a Local Group X‐Ray Halo

Rasmussen, Jesper; Pedersen, K.

doi:10.1086/322380

Cited by 22 publications

(20 citation statements)

References 61 publications

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“…We estimate that if the background halo gas densities are in excess of 10 −4 cm −3 , the gas distribution of the simulated Magellanic System will be irreconcilable with observations. This estimate is in accord with observational upper limits (Rasmussen & Pedersen 2001).…”

Section: A P P E N D I X a : T H E Ro L E O F R A M P R E S S U R E Ssupporting

confidence: 91%

The role of dwarf galaxy interactions in shaping the Magellanic System and implications for Magellanic Irregulars

Besla

Kallivayalil

Hernquist

et al. 2012

Monthly Notices of the Royal Astronomical Society

351

506

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We present a novel pair of numerical models of the interaction history between the Large and Small Magellanic Clouds (LMC and SMC, respectively) and our Milky Way (MW) in light of recent high‐precision proper motions from the Hubble Space Telescope. Given the updated velocities, cosmological simulations of hierarchical structure formation favour a scenario where the Magellanic Clouds (MCs) are currently on their first infall towards our Galaxy. We illustrate here that the observed irregular morphology and internal kinematics of the Magellanic System (in gas and stars) are naturally explained by interactions between the LMC and SMC, rather than gravitational interactions with the MW. These conclusions provide further support that the MCs are completing their first infall to our system. In particular, we demonstrate that the Magellanic Stream, a band of H i gas trailing behind the Clouds 150° across the sky, can be accounted for by the action of LMC tides on the SMC before the system was accreted by the MW. We further demonstrate that the off‐centre, warped stellar bar of the LMC, and its one‐armed spiral can be naturally explained by a recent direct collision with its lower mass companion, the SMC. Such structures are key morphological characteristics of a class of galaxies referred to as Magellanic Irregulars, the majority of which are not associated with massive spiral galaxies. We infer that dwarf–dwarf galaxy interactions are important drivers for the morphological evolution of Magellanic Irregulars and can dramatically affect the efficiency of baryon removal from dwarf galaxies via the formation of extended tidal bridges and tails. Such interactions are not only important for the evolution of dwarf galaxies but also have direct consequences for the build‐up of baryons in our own MW, as LMC‐mass systems are believed to be the dominant building blocks of MW‐type haloes.

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Section: A P P E N D I X a : T H E Ro L E O F R A M P R E S S U R E Ssupporting

confidence: 91%

The role of dwarf galaxy interactions in shaping the Magellanic System and implications for Magellanic Irregulars

Besla

Kallivayalil

Hernquist

et al. 2012

Monthly Notices of the Royal Astronomical Society

351

506

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“…The density values assumed here are consistent with constraints on the density of the Local Group medium by various studies (e.g. Rasmussen & Pedersen 2001;Sembach et al 2003;Williams et al 2005).…”

Section: Ram-pressure Interactionsupporting

confidence: 90%

Gas and dark matter in the Sculptor group: NGC 300

Westmeier¹,

Braun²,

Koribalski³

2010

Monthly Notices of the Royal Astronomical Society

124

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We used the Australia Telescope Compact Array to map a large field of approximately $2^{\circ} \times 2^{\circ}$ around the Sculptor group galaxy NGC~300 in the 21-cm line emission of neutral hydrogen. We achieved a $5 \sigma$ \ion{H}{i} column density sensitivity of $10^{19}~\mathrm{cm}^{-2}$ over a spectral channel width of $8~\mathrm{km \, s}^{-1}$ for emission filling the $180'' \times 88''$ synthesised beam. The corresponding \ion{H}{i} mass sensitivity is $1.2 \times 10^{5}~\mathrm{M}_{\odot}$, assuming a distance of $1.9~\mathrm{Mpc}$. For the first time, the vast \ion{H}{i} disc of NGC~300 has been mapped over its entire extent at a moderately high spatial resolution of about $1~\mathrm{kpc}$. NGC~300 is characterised by a dense inner \ion{H}{i} disc, well aligned with the optical disc of $290^{\circ}$ orientation angle, and an extended outer \ion{H}{i} disc with a major axis of more than $1^{\circ}$ on the sky (equivalent to a diameter of about $35~\mathrm{kpc}$) and a different orientation angle of $332^{\circ}$. A significant fraction (about 43~per cent) of the total detected \ion{H}{i} mass of $1.5 \times 10^{9}~\mathrm{M}_{\odot}$ resides within the extended outer disc. We fitted a tilted ring model to the velocity field of NGC~300 to derive the rotation curve out to a radius of $18.4~\mathrm{kpc}$, almost twice the range of previous rotation curve studies. The rotation curve rises to a maximum velocity of almost $100~\mathrm{km \, s}^{-1}$ and then gently decreases again in the outer disc beyond a radius of about $10~\mathrm{kpc}$. Mass models fitted to the derived rotation curve yield good fits for Burkert and NFW dark matter halo models, whereas pseudo-isothermal halo models and MOND-based models both struggle to cope with the declining rotation curve. We also observe significant asymmetries in the outer \ion{H}{i} disc of NGC~300, in particular near the edge of the disc, which are possibly due to ram pressure stripping of gas by the intergalactic medium (IGM) of the Sculptor group. Our estimates show that ram pressure stripping can occur under reasonable assumptions on the density of the IGM and the relative velocity of NGC~300. The asymmetries in the gas disc suggest a proper motion of NGC~300 toward the south-east. At the same time, our data exclude IGM densities of significantly higher than $10^{-5}~\mathrm{cm}^{-3}$ in the vicinity of NGC~300, as otherwise the outer gas disc would have been stripped.Comment: 22 pages, 15 figures, accepted for publication in MNRA

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“…Constraints on the density of the Galactic corona from considerations of the survivability of the Magellanic Stream range from nd10 À4 cm À3 based on dynamical arguments [e.g., drag (Moore & Davis 1994)] to nd10 À5 cm À3 based on thermal considerations [e.g., heating and evaporation (Murali 2001)]. In either case, there would be little X-ray emission from the extended corona or Local Group medium at these densities, and no observational constraints on the extragalactic X-ray background observed by ROSAT are violated by the presence of such a medium (see Rasmussen & Pedersen 2001). …”

Section: Discussionmentioning

confidence: 99%

Highly Ionized High‐Velocity Gas in the Vicinity of the Galaxy

Sembach

Wakker²,

Savage³

et al. 2003

ASTROPHYS J SUPPL S

457

587

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We report the results of a FUSE study of high-velocity O vi absorption along complete sight lines through the Galactic halo in directions toward 100 extragalactic objects and two halo stars. The high-velocity O vi traces a variety of phenomena, including tidal interactions with the Magellanic Clouds, accretion of gas, outflowing material from the Galactic disk, warm/hot gas interactions in a highly extended Galactic corona, and intergalactic gas in the Local Group. We identify 84 high-velocity O vi features at !3 confidence at velocities of À500 < v LSR < þ500 km s À1 . The 84 O vi features have velocity centroids ranging from À372d" v v LSR d À 90 km s À1 to þ93d" v v LSR d þ 385 km s À1 , line widths b $ 16 72 km s À1 with an average of hbi ¼ 40 AE 13 km s À1 , and an average O vi column density hlog Ni ¼ 13:95 AE 0:34 with a median value of 13.97. Values of b greater than the 17.6 km s À1 thermal width expected for O vi at T $ 3 Â 10 5 K indicate that additional nonthermal broadening mechanisms are common. The O vi 1031.926 absorption is detected at !3 confidence along 59 of the 102 sight lines surveyed. The high-velocity O vi detections indicate that $60% of the sky (and perhaps as much as $85%, depending on data quality considerations) is covered by high-velocity H + associated with the O vi. We find that NðH þ Þe10 18 cm À2 if the high-velocity hot gas has a metallicity similar to that of the Magellanic Stream; this detection rate is considerably higher than that of high-velocity warm H i traced through its 21 cm emission at a comparable column density level. Some of the high-velocity O vi is associated with known H i structures (the Magellanic Stream, Complex A, Complex C, the Outer Spiral Arm, and several discrete H i HVCs). Some of the high-velocity O vi features have no counterpart in H i 21 cm emission, including discrete absorption features and positive velocity absorption wings extending from $100 to $300 km s À1 that blend with lower velocity absorption produced by the Galactic thick disk/halo. The discrete features may typify clouds located in the Local Group, while the O vi absorption wings may be tidal debris or material expelled from the Galactic disk. Most of the O vi features have velocities incompatible with those of the Galactic halo, even if the halo has decoupled from the underlying Galactic disk. The reduction in the dispersion about the mean of the high-velocity O vi centroids when the velocities are converted from the LSR to the GSR and LGSR reference frames is necessary (but not conclusive) evidence that some of the clouds are located outside the Galaxy. Most of the O vi cannot be produced by photoionization, even if the gas is irradiated by extragalactic ultraviolet background radiation. Several observational quantities indicate that collisions in hot gas are the primary ionization mechanism responsible for the production of the O vi. These include the ratios of O vi column densities to those of other highly ionized species (C iv, N v) and the strong correlation between N(O vi) and O ...

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Constraints on a Local Group X‐Ray Halo

Cited by 22 publications

References 61 publications

The role of dwarf galaxy interactions in shaping the Magellanic System and implications for Magellanic Irregulars

The role of dwarf galaxy interactions in shaping the Magellanic System and implications for Magellanic Irregulars

Gas and dark matter in the Sculptor group: NGC 300

Highly Ionized High‐Velocity Gas in the Vicinity of the Galaxy

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