The universal rotation curve of dwarf disk galaxies (original) (raw)
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The universal rotation curve of dwarf disc galaxies
Monthly Notices of the Royal Astronomical Society, 2016
We use the concept of the spiral rotation curves universality to investigate the luminous and dark matter properties of the dwarf disc galaxies in the local volume (size ∼11 Mpc). Our sample includes 36 objects with rotation curves carefully selected from the literature. We find that, despite the large variations of our sample in luminosities (∼2 of dex), the rotation curves in specifically normalized units, look all alike and lead to the lower mass version of the universal rotation curve of spiral galaxies found in Persic et al. We mass model the double normalized universal rotation curve V(R/R opt)/V opt of dwarf disc galaxies: the results show that these systems are totally dominated by dark matter whose density shows a core size between 2 and 3 stellar disc scalelengths. Similar to galaxies of different Hubble types and luminosities, the core radius r 0 and the central density ρ 0 of the dark matter halo of these objects are related by ρ 0 r 0 ∼ 100 M pc −2. The structural properties of the dark and luminous matter emerge very well correlated. In addition, to describe these relations, we need to introduce a new parameter, measuring the compactness of light distribution of a (dwarf) disc galaxy. These structural properties also indicate that there is no evidence of abrupt decline at the faint end of the baryonic to halo mass relation. Finally, we find that the distributions of the stellar disc and its dark matter halo are closely related.
Monthly Notices of the Royal Astronomical Society
We investigate the properties of the baryonic and the dark matter components in low surface brightness (LSB) disc galaxies, with central surface brightness in the B band μ0 ≥ 23 mag arcsec−2. The sample is composed by 72 objects, whose rotation curves show an orderly trend reflecting the idea of a universal rotation curve (URC) similar to that found in the local high surface brightness (HSB) spirals in previous works. This curve relies on the mass modelling of the coadded rotation curves, involving the contribution from an exponential stellar disc and a Burkert cored dark matter halo. We find that the dark matter is dominant especially within the smallest and less luminous LSB galaxies. Dark matter halos have a central surface density Σ0 ∼ 100 M⊙pc−2, similar to galaxies of different Hubble types and luminosities. We find various scaling relations among the LSBs structural properties which turn out to be similar but not identical to what has been found in HSB spirals. In addition, t...
Monthly Notices of the Royal Astronomical Society, 2007
In the current ΛCDM cosmological scenario, N -body simulations provide us with a Universal mass profile, and consequently a Universal equilibrium circular velocity of the virialized objects, as galaxies. In this paper we obtain, by combining kinematical data of their inner regions with global observational properties, the Universal Rotation Curve (URC) of disk galaxies and the corresponding mass distribution out to their virial radius. This curve extends the results of Paper I, concerning the inner luminous regions of Sb-Im spirals, out to the edge of the galaxy halos.
The Rotation Curves of Dwarf Galaxies: A Problem for Cold Dark Matter
Astrophysical Journal, 2004
We address the issue of accuracy in recovering density profiles from observations of rotation curves of galaxies. We "observe" and analyze our models in much the same way as observers do the real galaxies. Our models include stellar disks, disks with bars, and small bulges. We find that the tilted ring model analysis produces an underestimate of the central rotational velocity. In some cases the galaxy halo density profile seems to have a flat core, while in reality it does not. We identify three effects, which explain the systematic biases: (1) inclination (2), small bulge, and (3) bar. Inclination effects are due to finite thickness of disk, bar, or bulge. Admixture of a non-rotating bulge component reduces the rotation velocity. A small (200-500 pc) bulge may be overlooked leading to systematic bias even on relatively large ∼ 1 kpc distances. In the case of a disk with a bar, the underestimate of the circular velocity is larger due to a combination of non-circular motions and random velocities. The effect of the bar depends on the angle that the bar makes with the line of sight. Signatures of bars can be difficult to detect in the surface brightness profiles of the model galaxies. The variation of inclination angle and isophote position angle with radius are more reliable indicators of bar presence than the surface brightness profiles. The systematic biases in the central ∼ 1kpc of galaxies are not large. Each effect separately gives typically a few km/serror, but the effects add up. In some cases the error in circular velocity was a factor of two, but typically we get about 20 percent effect. The result is the false inference that the density profile of the halo flattens in the central parts. Our observations of real galaxies show that for a large fraction of galaxies the velocity of gas rotation (as measured by emission lines) is very close to the rotation of stellar component (as measured by absorption lines). This implies that the systematic effects discussed in this paper are also applicable both for the stars and emission-line gas.
Disk galaxy rotation curves and dark matter distribution
Current Science 25 Apr 2008 vol.94 no.8 pp.960,986-95, 2008
After explaining the motivation for this article, I briefly recapitulate the methods used to determine,somewhat coarsely, the rotation curves of our Milky Way Galaxy and other spiral galaxies, especially in their outer parts, and the results of applying these methods. Recent observations and models of the very inner central parts of galaxian rotation curves are only briefly described. I then present the essential Newtonian theory of (disk) galaxy rotation curves. The next two sections present two numerical simulation schemes and brief results. Application of modified Newtonian dynamics to the outer parts of disk galaxies is then described. Finally, attempts to apply Einsteinian general relativity to the dynamics are summarized. The article ends with a summary and prospects for further work in this area.
Astronomy and Astrophysics, 2010
Context. The colour and metallicity gradients observed in spiral galaxies suggest that the mass-to-light ratio (M ⋆ /L) of the stellar disc is a function of radius. This is indeed predicted by chemo-photometric models of galactic discs. Aims. We investigate the distribution of luminous and dark matter in spiral galaxies, taking into account the radial dependence of the stellar M ⋆ /L, which is usually assumed to be constant in studies of the mass structure. Methods. From earlier chemo-photometric models and in agreement with the observed radial profiles of galaxy colours, we derive the typical average M ⋆ /L profile of the stellar discs of spiral galaxies. We computed the corresponding variable mass-to-light (VML) stellar surface density profile and then the VML disc contribution to the circular velocity. We used the latter, combined with a wellstudied dark matter velocity profile, to mass model co-added rotation curves. Results. By investigating rotation curves in the framework of VML stellar discs, we confirm the scenario obtained with the constant M ⋆ /L assumption: a dark matter halo with a shallow core, an inner baryon-dominated region, and a larger proportion of dark matter in smaller objects. However, the resulting size of the the dark halo core and of the inner baryon dominance region are somewhat smaller. The stronger role that VML discs have in the innermost regions is important for constraining the galaxy mass structure in both Λ cold dark matter and MOND scenarios.
Rotation curves of galaxies and the stellar mass-to-light ratio
Monthly Notices of the Royal Astronomical Society, 2018
Mass models of a sample of 171 low-and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c-M vir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 µm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration, and virial mass. Although accounting for a NFW dark halo profile can explain RC observations, the implied cM vir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L-colour correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L ratios of 51 galaxies (30 per cent of our sample) have unphysically negative values in the framework of the CDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of CDM cosmological structure formation, is not an appropriate profile for the dark haloes of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disc galaxies.
The Dark Matter Distribution in Disk Galaxies
Monthly Notices of The Royal Astronomical Society, 2001
We use high-quality optical rotation curves of 9 low-luminosity disk galaxies to obtain the velocity profiles of the surrounding dark matter halos. We find that they increase linearly with radius at least out to the edge of the stellar disk, implying that, over the entire stellar region, the density of the dark halo is about constant.
Dark Matter, Rotation Curves, and the Morphology of Galaxies
2021
In this thesis, we investigate some aspects of dark matter phenomenology and its predictive power in explaining the flattening of galaxy rotation curves at large distances. After outlining the Standard Model of particle physics, its symmetries and possible extensions in Chapter 2, we review key facts about dark matter and various types of dark matter models in Chapter 3. In Chapter 4 we discuss some alternatives to cold dark matter, which include modified Newtonian dynamics (MOND), superfluid dark matter and emergent gravity, and highlight the difficulties that are encountered in attempts to extend these frameworks to full-fledged relativistic settings. In Chapter 5 we turn to explore a completely different option, namely that flattened rotation curves reflect the presence of prolate dark-matter bulges or string-like objects around galaxies, without the need for any infrared modification of gravity. To test this model, we fit a number of galaxy rotation curves and find that the pres...