The dark matter halo shape of edge-on disk galaxies

O’Brien, J. C.; Freeman, K. C.; Kruit, P.

doi:10.1051/0004-6361/200912567

Cited by 55 publications

(44 citation statements)

References 38 publications

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“…To do this, we re‐generated H i moment maps, but now restricting the gas included to only those particles with densities near the classical value of ∼0.1 cm −3 . As expected, this eliminated the unrealistically high neutral hydrogen column densities in the highest density regions, but at the expense of leading to vertical density profiles that bore little resemblance to the Gaussian profiles observed in nature (O’Brien et al 2010). Such an extreme ‘cut’ to the definition of neutral hydrogen also led to a radial profile that bore little resemblance to an exponential.…”

Section: Discussionmentioning

confidence: 63%

“…The cold gas properties of DG1, DG1LT and nDG1 are compared directly with those from comparable dwarfs in (Tamburro et al 2009), in addition to the samples of O’Brien et al (2010) and Stanimirovic et al (1999). The bulk properties of DG1 (e.g.…”

Section: Methodsmentioning

confidence: 99%

“…Studies such as the The H i Nearby Galaxy Survey (THINGS; Walter et al 2008) provide excellent high‐resolution (spectral and spatial) data against which to compare our simulations. The gas properties of the simulations are compared directly with several of the most recent relevant empirical data sets (Stanimirovic et al 1999; Tamburro et al 2009; O’Brien, Freeman & van der Kruit 2010), in order to assess both their strengths and weaknesses.…”

Section: Introductionmentioning

confidence: 99%

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The cold gas content of bulgeless dwarf galaxies

Pilkington¹,

Gibson

Calura³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present an analysis of the neutral hydrogen (H I) properties of a fully cosmological hydrodynamical dwarf galaxy, run with varying simulation parameters. As reported by Governato et al., the high-resolution, high star formation density threshold version of this galaxy is the first simulation to result in the successful reproduction of a (dwarf) spiral galaxy without any associated stellar bulge. We have set out to compare in detail the H I distribution and kinematics of this simulated bulgeless disc with what is observed in a sample of nearby dwarfs. To do so, we extracted the radial gas density profiles, velocity dispersion ( e.g. velocity ellipsoid and turbulence) and the power spectrum of structure within the cold interstellar medium (ISM) from the simulations. The highest resolution dwarf, when using a high-density star formation threshold comparable to densities of giant molecular clouds, possesses bulk characteristics consistent with those observed in nature, though the cold gas is not as radially extended as that observed in nearby dwarfs, resulting in somewhat excessive surface densities. The linesof-sight velocity dispersion radial profiles have values that are in good agreement with the observed dwarf galaxies, but due to the fact that only the streaming velocities of particles are tracked, a correction to include the thermal velocities can lead to profiles that are quite flat. The ISM power spectra of the simulations appear to possess more power on smaller spatial scales than that of the Small Magellanic Cloud. We conclude that unavoidable limitations remain due to the unresolved physics of star formation and feedback within parsec-scale molecular clouds.

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Section: Discussionmentioning

confidence: 63%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The cold gas content of bulgeless dwarf galaxies

Pilkington¹,

Gibson

Calura³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…In the sample of late-type, gas-rich dwarf edge-on galaxies studied by O'Brien, Freeman & van der Kruit (2010b), the mean HI velocity dispersion increases as a function of the maximum rotational velocity of the HI disk from about 5 to 8 km s −1 for rotation velocities of 70 to 120 km s −1 . The scaleheight h of a Gaussian dust layer is related to the ISM velocity dispersion σ by…”

Section: Dustlanes In Disksmentioning

confidence: 97%

Galaxy Disks

Kruit

Freeman

2011

Annu. Rev. Astron. Astrophys.

243

115

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The disks of disk galaxies contain a substantial fraction of their baryonic matter and angular momentum, and much of the evolutionary activity in these galaxies, such as the formation of stars, spiral arms, bars and rings and the various forms of secular evolution, takes place in their disks. The formation and evolution of galactic disks is therefore particularly important for understanding how galaxies form and evolve, and the cause of the variety in which they appear to us. Ongoing large surveys, made possible by new instrumentation at wavelengths from the ultraviolet (GALEX), via optical (HST and large groundbased telescopes) and infrared (Spitzer) to the radio are providing much new information about disk galaxies over a wide range of redshift. Although progress has been made, the dynamics and structure of stellar disks, including their truncations, are still not well understood. We do now have plausible estimates of disk mass-to-light ratios, and estimates of Toomre's Q parameter show that they are just locally stable. Disks are mostly very flat and sometimes very thin, and have a range in surface brightness from canonical disks with a central surface brightness of about 21.5 B-mag arcsec −2 down to very low surface brightnesses. It appears that galaxy disks are not maximal, except possibly in the largest systems. Their HI layers display warps whenever HI can be detected beyond the stellar disk, with low-level star formation going on out to large radii. Stellar disks display abundance gradients which flatten at larger radii and sometimes even reverse. The existence of a well-defined baryonic (stellar + HI) Tully-Fisher relation hints at an approximately uniform baryonic to dark matter ratio. Thick disks are common in disk galaxies and their existence appears unrelated to the presence of a bulge component; they are old, but their formation is not yet understood. Disk formation was already advanced at redshifts of ∼ 2, but at that epoch disks were not yet quiescent and in full rotational equilibrium. Downsizing (the gradual reduction with time in the mass of the most actively star-forming galaxies) is now well-established. The formation and history of star formation in S0s is still not fully understood.

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“…We applied this method to our sample of galaxies in the third paper in this series: O'Brien et al (2010c). In that paper we also developed a new method to derive the thickness of the HI layer, or "flaring profile", as a function of galactocentric radius, which we used to measure the HI flaring of each galaxy in our sample.…”

Section: Introductionmentioning

confidence: 99%

The dark matter halo shape of edge-on disk galaxies

O’Brien¹,

Freeman²,

Kruit³

2010

A&A

Self Cite

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This is the fourth paper in a series in which we attempt to put constraints on the flattening of dark halos in disk galaxies. We observed for this purpose the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. As reported in earlier papers in this series we have for this purpose analysed the HI channel maps to accurately measure all four functions that describe as a function of galactocentric radius the planar HI kinematics and 3D HI distribution of a galaxy: the radial HI surface density, the HI vertical thickness, the rotation curve and the HI velocity dispersion. In this paper we analyse these data for the edge-on galaxy UGC 7321. We measured the stellar mass distribution (M = 3 × 10 8 M with M/L R < ∼ 0.2), finding that the vertical force of the gas disk dominates the stellar disk at all radii. Measurements of both the rotation curve and the vertical force field showed that the vertical force puts a much stronger constraint on the stellar mass-to-light ratio than rotation curve decomposition. Fitting of the vertical force field derived from the flaring of the HI layer and HI velocity dispersion revealed that UGC 7321 has a spherical halo density distribution with a flattening of q = c/a = 1.0 ± 0.1. However, the shape of the vertical force field showed that a non-singular isothermal halo was required, assuming a vertically isothermal HI velocity dispersion. A pseudo-isothermal halo and a gaseous disk with a declining HI velocity dispersion at high latitudes may also fit the vertical force field of UGC 7321, but to date there is no observational evidence that the HI velocity dispersion declines away from the galactic plane. We compare the halo flattening of UGC 7321 with other studies in the literature and discuss its implications. Our result is consistent with new n-body simulations which show that inclusion of hydrodynamical modelling produces more spherical halos.

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The dark matter halo shape of edge-on disk galaxies

Cited by 55 publications

References 38 publications

The cold gas content of bulgeless dwarf galaxies

The cold gas content of bulgeless dwarf galaxies

Galaxy Disks

The dark matter halo shape of edge-on disk galaxies

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