1,721,207 research outputs found
Dark Matter Decay and the Spiral Galaxy NGC891
No full textWe study the implications for NGC 891 of the decaying Dark matter (DDM) hypothesis which states that dark matter decays into hydrogen-ionizing photons on a time-scale of 1023 s. We are able to derive many details of the observed Hα emission of this galaxy using only its rotation curve and properties of our own very similar Galaxy. We also use the hypothesis to determine the distance and the peculiar velocity of NGC 891 and obtain agreement with an independent estimate of those quantities. The detailed agreement of the consequences of the DDM hypothesis with observations of NGC 891 provides strong support for this hypothesis. (author
The distribution of dark matter in galaxies
No full textThe distribution of the non-luminous matter in galaxies of different luminosity and Hubble type is much more than a proof of the existence of dark particles governing the structures of the Universe. Here, we will review the complex but well-ordered scenario of the properties of the dark halos also in relation with those of the baryonic components they host. Moreover, we will present a number of tight and unexpected correlations between selected properties of the dark and the luminous matter. Such entanglement evolves across the varying properties of the luminous component and it seems to unequivocally lead to a dark particle able to interact with the Standard Model particles over cosmological times. This review will also focus on whether we need a paradigm shift, from pure collisionless dark particles emerging from “first principles”, to particles that we can discover only by looking to how they have designed the structure of the galaxies
Dark Matter in Galaxies: Evidences and Challenges
No full textThe evidence of the phenomenon for which, in galaxies, the gravitating mass is distributed differently than the luminous mass, increases as new data become available. Furthermore, this discrepancy is well structured and it depends on the magnitude and the compactness of the galaxy and on the radius, in units of its luminous size Ropt, where the measure is performed. For the disk systems with - 13 ≥ MI≥ - 24 all this leads to an amazing scenario, revealed by the investigation of individual and coadded rotation curves, according to which, the circular velocity follows, from their centers out to their virial radii, an universal profile VURC(r/ Ropt, MI) function only of the properties of the luminous mass component. Moreover, from the Universal Rotation Curve, so as from many individual high quality RCs, we discover that, in the innermost regions of galaxies, the DM halo density profiles are very shallow. Finally, the disk mass, the central halo density and its core radius, come out all related to each other and to two properties of the distribution of light in galaxies: the luminosity and the compactness. This phenomenology, being absent in the simplest ΛCDM Cosmology scenario, poses serious challenges to the latter or, alternatively, it requires a substantial and tuned involvement of baryons in the formation of the galactic halos. On the other side, the URC helps to explain the two-accelerations relationship found by McGaugh et al. (J Phys Rev Lett 117:201101, 2016), in terms of only well known astrophysical processes, acting in a standard DM halos + luminous disks scenario
THE DISK CONTRIBUTION TO ROTATION CURVES OF SPIRAL GALAXIES
No full textWe formulate analytically the maximum disc hypothesis (MDH) in the framework of a
disc/halo mass decomposition, and apply it to a sample of suitably selected optical
rotation curves. We find that the resulting disc-to-total mass ratios show a definite
trend of increasing dark-to-luminous mass ratio with decreasing luminosity, in very
good agreement with our previous results obtained by means of different decomposition
techniques (Persic & Salucci). The same trend is also clearly discernible when the
mass ratios (at the same radius in disc length-scale units) obtained from published
MDH models are correlated with luminosity. We discuss possible reasons why previous
studies which have assumed a similar framework have missed this fundamental
systematics of dark matter
DARK MATTER IN SPIRAL GALAXIES
No full textThe Tully-Fisher relation is used to probe dark matter (DM) in the optical regions of spiral galaxies. By establishing it at several different isophotal radii in an appropriate sample of 58 galaxies with good B-band photometry and rotation curves, we find that some of its attributes such as scatter, residuals, nonlinearity, and bias dramatically decrease moving from the disk edge inward. We show how this behavior challenges any mass model which assumes no DM or a luminosity-independent DM mass fraction interior to the optical radius of spiral galaxies
ROTATING-DISK GALAXIES - YET ANOTHER CASE FOR DARK MATTER
No full textWe devise a method to probe the systematic variations of the dark matter mass fraction (DM) in the optical region of disk galaxies, based on studying the correlation between galaxy luminosity and the normalized radius where the rotation frequency exceeds a given multiple of the rotation frequency as measured at the optical disk radius. The results we find strongly suggest the ubiquitous existence of DM throughout the luminosity sequence of galaxies, thereby challenging the possibility that luminous matter alone can be responsible for the observed disk dynamics. By modeling the distribution of dark matter by means of a pseudoisothermal halo, we show that the disk-to-halo mass ratio at the optical edge, Adisk/Mhalo, has not the same value in all galaxies, but actually varies with luminosity. Remarkably, galaxies at the knee of the luminosity function have Mdisk/Mhalo ∼ 1
THE UNIVERSAL GALAXY ROTATION CURVE
No full textAnalyzing an extended set of selected galaxy rotation curves (with - 17.5 greater-than-or-equal-to M(B) greater-than-or-equal-to - 23.2), we find that for a given luminosity the rotation curves of spiral galaxies within the optical radius are a universal function, V(R) congruent-to 200(L(B)/L(B*))1/4 {1 + [0.12 - 0.24 log (L(B)/L(B*))](R/R(max) - 1)} km s-1 (where L(B*) = 6 x 10(10)h50(-2)L(B). and R(max) = 2.2 disk length scales are two suitable parameterization constants). This result implies strong systematic variations of both the amplitude and the profile of the circular velocity with luminosity, faint (bright) galaxies having low (high) velocities and steep (shallow) velocity gradients. Because luminous disks are self-similar, the observed progression of the shape of rotation curves with luminosity suggests that the dark-to-visible interplay varies with luminosity
NONLINEARITY OF THE TULLY-FISHER RELATION
No full textA systematic variation of the dark matter abundance in spiral galaxies, previously reported (Persic & Salucci), accounts for the observed non-linearity of the Tully-Fisher relation. Increasing proportions of dark mass at low luminosities, as revealed by optical rotation curves, make faint galaxies shift to higher rotation velocities for a given luminosity, thus inducing a curvature in the velocity-luminosity correlation
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