1,107 research outputs found
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
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
THE DARK MATTER CONTENT OF SPIRAL GALAXIES
No full textWe present a new technique for calculating the fraction of dark material within the optical radius of spiral galaxies. The method employs the well-established observational result that spiral galaxies have similar central surface brightnesses, as well as published stellar synthesis evolutionary models, color-magnitude relations and optical rotation curves. No assumptions about the dark matter distribution are necessary. We find that the ratio of disk-to-dynamical mass within the optical radius increases roughly as L(B)0.4. This is in good agreement with the results of Persic and Salucci which are derived from independent considerations
DARK-MATTER IN SPIRAL GALAXIES AND THE ARIMOTO-JABLONKA PHOTOMETRIC MODEL
No full textWe use the recent stellar population synthesis models by Arimoto and Jablonka (1991), which by introducing the bulge into the calculation of galaxy masses mark a significant improvement over previous one-component models, to show that low-luminosity spiral galaxies have a higher dark matter fraction within the optical radius than high-luminosity spirals. In fact, the derived dark-to-visible mass ratio increases with decreasing luminosity, approximately as L(B)(-1/2). This conclusion agrees with previous results based on dynamical disc/halo decompositions of galaxy rotation curves (e.g. Persic and Salucci 1988). On the other hand, we do not find any strong trend between dark matter content and galaxy B-V colours, although we cannot exclude a weak one. Our results agree with Jablonka and Arimoto's (1992) conclusion that colours are not a primary indicator of the dark matter content of spiral galaxies. Instead, we confirm that the luminosity is a fundamental indicator of the dark mass fraction of spiral galaxies
A physical distance indicator for spiral galaxies
No full textIn this paper we derive a Tully Fisher relation from measured I band photometry and H alpha rotation curves of a large survey of southern sky spiral galaxies, obtained in Persic & Salucci (1995) by deprojecting and folding the raw H alpha data of Mathewson, Ford & Buchhorn (1992). We calibrate the relation by combining several of the largest clusters in the survey, using an iterative maximum likelihood procedure to account for observational selection effects and Malmquist bias. We also incorporate a simple model for the line of sight depth of each cluster. Our results indicate a Tully Fisher relation of intrinsic dispersion similar to 0.3 mag, corresponding to a distance error dispersion of 13%. Application of this relation to mapping the large scale velocity field is underway
Correlation functions of matter from galaxy rotation curves
No full textBased on the disk-halo decomposition method introduced by Persic & Salucci, we use 58 spiral rotation curves to measure the galaxy-background correlation function in the range 3-350 kpc (for H0 = 50 km s-1 Mpc-1). We find that (1) the two-point function is zeta(r) congruent-to (r0/r)1.76, with r0 congruent-to 7 Mpc (for OMEGA-0 = 1), and (2) higher order correlation functions are detected up to the sixth order and are found to fit the hierarchical expression
Dark matter halos around galaxies
No full textWe present evidence that all galaxies, of any Hubble type and luminosity, bear the kinematical signature of a mass component distributed differently from the luminous matter. We review and/or derive the DM halo properties of galaxies of different morphologies: spirals, LSBs, ellipticals, dwarf irregulars and dwarf spheroidals.
We show that the halo density profile M-h(x) = M-h(1)(1+a(2))x(3)/x(2)+a(2) (with x = R/R-opt), across both the Hubble and luminosity sequences: matches all the available data that include, for ellipticals: properties of the X-ray emitting gas and the kinematics of planetary nebulae, stars: and HI disks: for spirals, LSBs and dIrr's: stellar and HI rotation curves: and, finally. for dSph's the motions of individual stars.
The dark + luminous mass structure is obtained: (a) in spirals, LSBs. and dLrr's by modelling the extraordinary properties of the Universal Rotation Curve (URC), to which all these types conform (i.e. the URC luminosity dependence and the smallness of its rms scatter and cosmic variance); (b) in ellipticals and dSph's, by modelling the coadded mass profiles (or the M/L ratios) in terms of a luminous spheroid and the above-specified dark halo.
A main feature of galactic structure is that the dark and visible matter are well mixed already in the luminous region. The transition between the inner, star-dominated regions and the outer, halo-dominated region, moves progressively inwards with decreasing luminosity, to the extent that very-low-L stellar systems (disks or spheroids) are not self-gravitating, while in high-L systems the dark matter becomes a main mass component only beyond the optical edge. A halo core radius, comparable to the optical radius, is detected at all luminosities and for all morphologies. The luminous mass fraction varies with luminosity in a fashion common to all galaxy types: it is comparable with the cosmological baryon fraction at L > L, but it decreases by more than a factor 10(2) at L << L.
For each Hubble type, the central halo density increases with decreasing luminosity: sequences of denser stellar systems (dwarfs, ellipticals, HSBs. LSBs in decreasing order) correspond in turn to sequences of denser halos.
Then, the dark halo structure of galaxies fits into a well ordered pattern underlying a unified picture for the mass distribution of galaxies across the Hubble sequence
Statistics of matter distribution from halo dynamics
No full textThe galaxy-background correlation function at short distances is explored by means of the observed disk dynamics of spiral galaxies. Using both the sample of galaxies and the analytical method for dark-to-luminous mass decomposition from optical rotation curves presented by Persic and Salucci, individual sizes and mean densities are worked out for 42 extended halos (taken to be η = 10 times as massive as their respective disks) as functions of both the intensity and the gradient of the central velocity field. The statistics for the expected density enhancements within given distances from galactic centers shows simple properties which strongly tie galaxy-background and galaxy-galaxy correlation functions. In particular, we find that: (a) the two-point galaxy-background correlation function is in agreement with its galaxy-galaxy counterpart (slope γ = 1.76 +/- 0.03; clustering length r_0_ = (7.1 +/- 0.7)[η/10)gamma-2^(1/{OMEGA}_0_)]^1/γ^ h^-1^_50_ Mpc); (b) the three-point and four-point correlation functions fit the so-called hierarchical clustering expression; (c) the constants Q (for the three-point function) and R-a_ and R_b_ (for the four-point function) are found to be Q = 0.46 +/- 0.04 and R_a_ + 0.35 R_b_ = 0.19 +/- 0.05, in agreement with BBGKY hierarchy predictions. The main consideration which naturally follows is that on the scale of galaxies the statistics of matter seems to be highlighted with equal effectiveness by both the luminous point-object distribution and the dark- matter properties underlying the halo-influenced disk dynamics
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
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