Paolo Salucci

The cored distribution of dark matter in spiral galaxies

We present the Hi data for 5 spiral galaxies that, along with their Hα rotation curves, are used to derive the distribution of dark matter within these objects. A new method for extracting rotation curves from Hi data cubes is presented; this takes into account the existence of a warp and minimises projection effects. The rotation curves obtained are tested by taking them as input to construct model data cubes that are compared to the observed ones: the agreement is excellent. On the contrary, the model data cubes built using rotation curves obtained with standard methods, such as the first-moment analysis, fail the test. The Hi rotation curves agree well with the Hα data, where they coexist. Moreover, the combined Hα + Hi rotation curves are smooth, symmetric and extended to large radii. The rotation curves are decomposed into stellar, gaseous and dark matter contributions and the inferred density distribution is compared to various mass distributions: dark haloes with a central density core, � Cold Dark Matter (�CDM) haloes (NFW, Moore profiles), Hi scaling and MOND. The observations point to haloes with con

New Relationships between Galaxy Properties and Host Halo Mass, and the Role of Feedbacks in Galaxy Formation

We present new relationships between halo masses (Mh) and several galaxy properties, including r*-band luminosities (Lr), stellar (Mstar) and baryonic masses, stellar velocity dispersions (?), and black hole masses (MBH). Approximate analytic expressions are given. In the galaxy halo mass range 3 ? 1010 M? ? Mh ? 3 ? 1013 M? the Mh-Lr, Mstar-Mh, and MBH-Mh relations are well represented by a double power law, with a break at Mh,break ? 3 ? 1011 M?, corresponding to a mass in stars Mstar ~ 1.2 ? 1010 M?, to an r*-band luminosity Lr ~ 5 ? 109 L?, to a stellar velocity dispersion ? 88 km s-1, and to a black hole mass MBH ~ 9 ? 106 M?. The ?-Mh relation can be approximated by a single power law, although a double power law is a better representation. Although there are significant systematic errors associated with our method, the derived relationships are in good agreement with the available observational data and have comparable uncertainties. We interpret these relations in terms of the effect of feedback from supernovae and from the active nucleus on the interstellar medium. We argue that the break of the power laws occurs at a mass that marks the transition between the dominance of the stellar and the AGN feedback.

Dark Matter Scaling Relations

We investigate the structure of dark matter halos by means of the kinematics of a very large sample of spiral galaxies of all luminosities. The observed rotation curves show a universal profile which is the sum of an exponential thin disk term and a spherical halo term with a flat density core. We find that the Burkert profile proposed to describe the dark matter halo density distribution of dwarf galaxies also provides an excellent mass model for the dark halos around disk systems up to 100 times more massive. Moreover, we find that spiral dark matter core densities ρ0 and core radii r0 lie in the same scaling relation ρ0 = 4.5 × 10-2(r0/kpc)-2/3 M☉ pc-3 of dwarf galaxies with core radii up to 10 times smaller. At the highest masses ρ0 decreases with r0 faster than the - power law, implying a lack of objects with disk masses greater than 1011 M☉ and central densities greater than 1.5 × 10-2(r0/kpc)-3 M☉ pc-3 that can be explained by the existence of a maximum mass of about 2 × 1012 M☉ for a halo hosting a spiral galaxy.

The dark matter density at the Sun’s location

Aims. We derive the value of the dark matter density at the Sun’s location ( ) without globally mass-modeling the Galaxy. Methods. The proposed method relies on the local equation of centrifugal equilibrium and is independent of i) the shape of the dark matter density profile, ii) knowledge of the rotation curve from the galaxy center out to the virial radius, and iii) the uncertainties and the non-uniqueness of the bulge/disk/dark halo mass decomposition. Results. The result can be obtained in analytic form and it explicitly includes the dependence on the relevant observational quantities and takes their uncertainties into account. By adopting the reference, state-of-the-art values for these, we find = 0:43(11)(10) GeV/cm 3 , where the quoted uncertainties are respectively due to the uncertainty in the slope of the circular-velocity at the Sun location and the ratio between this radius and the length scale of the stellar exponential thin disk. Conclusions. We obtained a reliable estimate of , that, in addition has the merit of being ready to take into account any future change/improvement in the measures of the observational quantities it depends on.

A constant dark matter halo surface density in galaxies

We confirm and extend the recent finding that the central surface density � 0Dr0ρ0 of galaxy dark matter halos, where r0 and ρ0 are the halo core radius and central density, is nearly constant and independent of galaxy luminosity. Based on the co- added rotation curves of � 1000 spiral galaxies, mass models of individual dwarf irregular and spiral galaxies of late and early types with high-quality rotation curves and, galaxy-galaxy weak lensing signals from a sample of spiral and elliptical galaxies, we find that log � 0D = 2.15 ± 0.2, in units of log(M⊙ pc −2 ). We also show that the observed kinematics of Local Group dwarf spheroidal galaxies, are consistent with this value. Our results are obtained for galactic systems spanning over 14 magnitudes, belonging to different Hubble Types, and whose mass profiles have been determined by several independent methods. In the same objects, the approximate constancy of � 0D is in sharp contrast to the systematical variations, by several orders of magnitude, of galaxy properties, including ρ0 and central stellar surface density.

The universal rotation curve of spiral galaxies - II. The dark matter distribution out to the virial radius

In the current ACDM 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 of disc 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 haloes.

Joint formation of QSOs and spheroids: QSOs as clocks of star formation in spheroids

Direct and indirect observational evidence leads to the conclusion that high-redshift QSOs did shine in the core of early-type protogalaxies during their main episode of star formation. Exploiting this fact, we derive the rate of formation of this kind of stellar system at high redshift by using the QSO luminosity function. The elemental proportions in elliptical galaxies, the descendants of the QSO hosts, suggest that the star formation was more rapid in more massive objects. We show that this is expected to occur in dark matter haloes, when the processes of cooling and heating are considered. This is also confirmed by comparing the observed submm counts with those derived by coupling the formation rate and the star formation rate of the spheroidal galaxies with a detailed model for their SED evolution. In this scenario SCUBA galaxies and Lyman-break galaxies are early-type protogalaxies forming the bulk of their stars before the onset of QSO activity.

Mass function of dormant black holes and the evolution of active galactic nuclei

Under the assumption that accretion onto massive black holes powers active galactic nuclei (AGN), the mass function (MF) of the BHs responsible for their past activity is estimated. For this, we take into account not only the activity related to the optically selected AGN, but also that required to produce the Hard X–Ray Background (HRXB). The MF of the Massive Dark Objects (MDOs) in nearby quiescent galaxies is computed by means of the most recent results on their demography. The two mass functions match well under the assumption that the activity is concentrated in a single significant burst with � = L/LEdd being a weakly increasing function of luminosity. This behaviour may be indicative of some level of recurrence and/or of accretion rates insufficient to maintain the Eddington rates in low luminosity/low redshift objects. Our results support the scenario in which the early phase of intense nuclear activity occurred mainly in early type galaxies (E/S0) during the relatively short period in which they had still an abundant interstellar medium. Only recently, with the decline of the QSO luminosities, did the activity in late type galaxies (Sa/Sab) become statistically significant.

The baryon content of the Universe

We estimate the baryon mass density of the Universe due to the stars in galaxies and the hot gas in clusters and groups of galaxies. The galaxy contribution is computed by using the Efstathiou, Ellis & Peterson luminosity function, together with van der Marel and Persic & Salucci’s mass-to-light versus luminosity relationships. We find stars ≃ 0.002. For clusters and groups we use the Edge et al. X -ray luminosity function, and Edge & Stewart and Kriss, Cioffi & Canizares’ (gas mass )-luminosity relations. We find gas ≃ 0.001. The total amount of visible baryons is then b ≃ 0.003, i.e. less than 10 per cent of the lower limit predicted by standard primordial nucleosynthesis, implying that the great majority of baryons in the Universe are unseen.

The Dark Matter halo of the Milky Way, AD 2013

We derive the mass model of the Milky Way (MW), crucial for Dark Matter (DM) direct and indirect detection, using recent data and a cored dark matter (DM) halo profile, which is favoured by studies of external galaxies. The method used consists in fitting a spherically symmetric model of the Galaxy with a Burkert DM halo profile to available data: MW terminal velocities in the region inside the solar circle, circular velocity as recently estimated from maser star forming regions at intermediate radii, and velocity dispersions of stellar halo tracers for the outermost Galactic region. The latter are reproduced by integrating the Jeans equation for every modeled mass distribution, and by allowing for different velocity anisotropies for different tracer populations. For comparison we also consider a Navarro-Frenk-White profile. We find that the cored profile is the preferred one, with a shallow central density of ρH ~ 4 × 107M☉/kpc3 and a large core radius RH ~ 10 kpc, as observed in external spirals and in agreement with the mass model underlying the Universal Rotation Curve of spirals. We describe also the derived model uncertainties, which are crucially driven by the poorly constrained velocity dispersion anisotropies of halo tracers. The emerging cored DM distribution has implications for the DM annihilation angular profile, which is much less boosted in the Galactic center direction with respect to the case of the standard ΛCDM, NFW profile. Using the derived uncertainties we discuss finally the limitations and prospects to discriminate between cored and cusped DM profile with a possible observed diffuse DM annihilation signal. The present mass model aims to characterize the present-day description of the distribution of matter in our Galaxy, which is needed to frame current crucial issues of Cosmology, Astrophysics and Elementary Particles.