arXiv subjects

P. Salucci

Publications and source records attributed to P. Salucci.

At least 37 records · Page 2Linked to original sources

arXiv2011

Probing dark matter haloes of spiral galaxies at poorly explored distances using satellite kinematics

We present the results of a pilot project designed to study the distribution of dark matter haloes out to very large radii in spiral galaxies. As dynamical probe we use their rotation curves and the motions population of satellite galaxies. In this pilot stage, we observed seven late-type spiral galaxies of about the same luminosity M_R ~ -22 (and approximately the same mass). We investigate the kinematics of these galaxies, and the radial and angular distribution of their satellites. Using VIMOS at the VLT, we carried out a spectroscopic survey in seven 14' x 14' fields each around a late-type isolated spiral galaxy. We obtained radial velocities and spatial distributions for 77 candidate satellites. After removing the interlopers, we are left with 61 true satellites. In combination with the rotation curves of the primary galaxies, satellites are used to probe the gravitational potential of the primaries and derive the dark matter halo properties by means of standard mass modeling techniques. We find (a) that the dark matter haloes of luminous spirals (M_R ~ -22) have virial radii of ~400 kpc and virial masses of 3.5 x 10^12 Msun; (b) that the radial velocity and angular distributions of the satellites around the primaries are isotropic; and (c) that the resulting mass distribution is in good agreement with that found in the optical regions of spirals and described by the universal rotation curve of spirals once extrapolated to large radii. The results obtained in this pilot phase of the project are already interesting and limited only by small number statistics. The full project involving an order of magnitude more targets, would very likely provide us with a definitive picture of the dark matter distribution around spirals out to their virial radii and beyond.

astro-ph.CO↗

arXiv2010

The inner structure of very massive elliptical galaxies: implications for the inside-out formation mechanism of z~2 galaxies

We analyze a sample of 23 supermassive elliptical galaxies (central velocity dispersion larger than 330 km s-1), drawn from the SDSS. For each object, we estimate the dynamical mass from the light profile and central velocity dispersion, and compare it with the stellar mass derived from stellar population models. We show that these galaxies are dominated by luminous matter within the radius for which the velocity dispersion is measured. We find that the sizes and stellar masses are tightly correlated, with Re ~ M*^{1.1}$, making the mean density within the de Vaucouleurs radius a steeply declining function of M*: rho_e ~ M*^{-2.2}. These scalings are easily derived from the virial theorem if one recalls that this sample has essentially fixed (but large) sigma_0. In contrast, the mean density within 1 kpc is almost independent of M*, at a value that is in good agreement with recent studies of z ~ 2 galaxies. The fact that the mass within 1 kpc has remained approximately unchanged suggests assembly histories that were dominated by minor mergers -- but we discuss why this is not the unique way to achieve this. Moreover, the total stellar mass of the objects in our sample is typically a factor of ~ 5 larger than that in the high redshift (z ~ 2) sample, an amount which seems difficult to achieve. If our galaxies are the evolved objects of the recent high redshift studies, then we suggest that major mergers were required at z > 1.5, and that minor mergers become the dominant growth mechanism for massive galaxies at z < 1.5.

astro-ph.CO↗

arXiv2010

The dark matter density at the Sun's location

We derive the value of the dark matter density at the Sun's location (rho_0) without globally mass-modeling the Galaxy. 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. The result can be obtained in analytic form. 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 rho_0 = 0.43(11)(10)GeV/cm3, 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. We obtain a reliable estimate of rho_0, that, in addition, is ready to take into account any future change/improvement in the measures of the observational quantities it depends on.

astro-ph.GA↗

arXiv2009

A constant dark matter halo surface density in galaxies

We confirm and extend the recent finding that the central surface density r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core radius and central density, is nearly constant and independent of galaxy luminosity. Based on the co-added rotation curves of about 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(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/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 rho_0*r_0 is in sharp contrast to the systematical variations, by several orders of magnitude, of galaxy properties, including rho_0 and central stellar surface density.

astro-ph.CO↗

arXiv2008

Dark Matter in Gas-Rich Dwarf Galaxies

We investigate the distribution of dark matter (DM) in gas-rich, low-mass galaxies, confronting them with numerical cosmological simulations with cold dark matter (LCDM). We show that the derived rotation curves comply best with cored DM density profiles, whereas the signatures of the central cusps invariably predicted by LCDM simulations are not seen.

astro-ph↗

arXiv2007

The Baryonic and Dark Matter Properties of High Redshift Gravitationally Lensed Disk Galaxies

We present a detailed study of the structural properties of four gravitationally lensed disk galaxies at z=1. Modelling the rotation curves on sub-kpc scales we derive the values for the disk mass, the reference dark matter density and core radius, and the angular momentum per unit mass. The derived models suggest that the rotation curve profile and amplitude are best fit with a dark matter component similar to those of local spiral galaxies. The stellar component also has a similar length scale, but with substantially smaller masses than similarly luminous disk galaxies in the local universe. Comparing the average dark matter density inside the optical radius we find that the disk galaxies at z=1 have larger densities (by up to a factor of 7) than similar disk galaxies in the local Universe. Furthermore, the angular momentum per unit mass versus reference velocity is well matched to the local relation, suggesting that the angular momentum of the disk remains constant between high redshifts and the present day. Though statistically limited, these observations point towards a spirals' formation scenario in which stellar disks are slowly grown by the accretion of angular momentum conserving material.

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arXiv2007

The Universal Rotation Curve of Spiral Galaxies. II The Dark Matter Distribution out to the Virial Radius

In the current LambdaCDM 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.

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arXiv2006

NGC 3741: dark halo profile from the most extended rotation curve

We present new HI observations of the nearby dwarf galaxy NGC 3741. This galaxy has an extremely extended HI disk, which allows us to trace the rotation curve out to unprecedented distances in terms of the optical disk: we reach 42 B-band exponential scale lengths or about 7 kpc. The HI disk is strongly warped, but the warp is very symmetric. The distribution and kinematics are accurately derived by building model data cubes, which closely reproduce the observations. In order to account for the observed features in the data cube, radial motions of the order of 5-13 km/s are needed. They are consistent with an inner bar of several hundreds of pc and accretion of material in the outer regions. The observed rotation curve was decomposed into its stellar, gaseous and dark components. The Burkert dark halo (with a central constant density core) provides very good fits. The dark halo density distribution predicted by the LambdaCDM theory fails to fit the data, unless NGC 3741 is a 2.5-sigma exception to the predicted relation between concentration parameter and virial mass and has at the same time a high value of the virial mass (though poorly constrained) of 10$^{11}$ solar masses. Noticeably, MOND seems to be consistent with the observed rotation curve. Scaling up the contribution of the gaseous disk also gives a good fit.

astro-ph↗

arXiv2006

The radial profiles of the different mass components in galaxy clusters

AIMS. To derive the mass profiles of the different luminous and dark components in clusters. METHODS. The cluster mass profile is determined by using the Jeans equation applied to the projected phase-space distribution of about 3000 galaxies members of 59 nearby clusters from the ESO Nearby Abell Cluster Survey. The baryonic and subhaloes mass components are determined from the galaxies' luminosity-density profiles through scaling relations between luminosities and baryonic and dark halo masses. The baryonic mass component associated to the intra-cluster gas is determined using X-ray data from ROSAT. RESULTS. The baryon-to-total mass fraction decreases from a value of 0.12 near the center, to 0.08 at the distance of 0.15 virial radii, then it increases again, to reach a value of 0.14 at the virial radius. Diffuse, cluster-scale, dark matter dominates at all radii, but its contribution to the total mass content decreases outwards to the virial radius, where the dark matter in subhaloes may contribute up to 23 %, and the baryons 14 %, of the total mass. The dark mass, and diffuse dark mass profiles are well fit by both cuspy and cored models. The subhaloes mass distribution is not fit by either model.

astro-ph↗

arXiv2006

A Physical Model for Co-evolution of QSOs and of their Spheroidal Hosts

At variance with most semi-analytic models, in the Anti-hierarchical Baryon Collapse scenario (Granato et al. 2001, 2004) the main driver of the galaxy formation and evolution is not the merging sequence but are baryon processes. This approach emphasizes, still in the framework of the hierarchical clustering paradigm for dark matter halos, feedback processes from supernova explosions and from active nuclei, that tie together star formation in spheroidal galaxies and the growth of black holes at their centers. We review some recent results showing the remarkably successful predictive power of this scenario, which allows us to account for the evolution with cosmic time of a broad variety of properties of galaxies and active nuclei, which proved to be very challenging for competing models.

astro-ph↗

arXiv2006

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

We present new relationships between halo masses M_h and several galaxy properties, including r*-band luminosities L_r, stellar (M_star) and baryonic masses, stellar velocity dispersions (sigma), and black hole masses (M_BH). Approximate analytic expressions are given. In the galaxy halo mass range 3*10^(10) M_sun <= M_h <= 3*10^(13) M_sun the M_h-L_r, M_star-M_h, and M_BH-M_h are well represented by a double power law, with a break at M_h_break~3*10^(11) M_sun, corresponding to a mass in stars M_star~ 1.2*10^(10) M_sun, to a r*-band luminosity L_r~ 5*10^9 L_sun, to a stellar velocity dispersion sigma ~ 88 km/s, and to a black hole mass M_BH~ 9*10^(6) M_sun. The sigma-M_h relation can be approximated by a single power law, though a double power law is a better representation. 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 which marks the transition between the dominance of the stellar and the AGN feedback.

astro-ph↗

arXiv2005

Comment on "Scalar-tensor gravity coupled to a global monopole and flat rotation curves" by Lee and Lee

The recent paper by Lee and Lee (2004) may strongly leave the impression that astronomers have established that the rotation curves of spiral galaxies are flat. We show that the old paradigm of Flat Rotation Curves lacks, today, any observational support and following it at face value leads to intrinsically flawed alternatives to the Standard Dark Matter Scenario. On the other side, we claim that the rich systematics of spiral galaxy rotation curves, that reveals, in the standard Newtonian Gravity framework, the phenomenon of dark matter, in alternative scenarios, works as a unique benchmark.

astro-ph↗

arXiv2005

The dwarf galaxy DDO 47: testing cusps hiding in triaxial halos

We present HI data of the dwarf galaxy DDO 47, aimed at testing the hypothesis that dark halo triaxiality might induce non-circular motions resulting in rotation curves best fitted by cored halos, even if the dark matter halo is intrinsically cuspy. We performed a harmonic decomposition of the velocity field in order to search for alleged non-circular motions needed to ``hide'' a cusp: in DDO 47 non-circular motions are globally at a level of 2-3 km s$^{-1}$, far from being sufficient to reconcile the observed rotation curve with the $Λ$CDM predictions. We conclude that the dark matter halo around DDO 47 is truly cored and that a cusp cannot be hidden by non-circular motions. More details are shown in Gentile et al. (2006, ApJL in press, astro-ph/0506538).

astro-ph↗

arXiv2005

The dwarf galaxy DDO 47 as a dark matter laboratory: testing cusps hiding in triaxial halos

We present an analysis of high resolution HI data of the dwarf galaxy DDO 47, aimed at testing the hypothesis that dark halo triaxiality might induce non-circular motions resulting in rotation curves best fitted by cored halos, even if the dark matter halo is intrinsically cuspy. This hypothesis could be invoked in order to reconcile the predictions of the standard LambdaCDM theory with the rotation curves of disk galaxies. DDO 47 is an ideal case to test this hypothesis because it has a very regular velocity field, its rotation curve is best fitted by a cored halo and a NFW halo is inconsistent with the data. We analysed the velocity field through the higher-order harmonic terms in order to search for kinematical signatures of alleged non-circular motions needed to "hide" a cusp: the result is that globally non-circular motions are at a level of 2-3 km/s, and they are more likely to be associated to the presence of some spiral structure than to a global elongated potential (e.g. a triaxial halo). These non-circular motions are far from being sufficient to account for the discrepancy with the LambdaCDM predictions. We therefore conclude that the dark matter halo around the dwarf galaxy DDO 47 is truly cored and that a cusp cannot be hidden by non-circular motions.

astro-ph↗

arXiv2005

Baryons in Dark Matter Halos

We present here the preface and the Table of Content of the Proceedings of the Conference "Baryons in Dark Matter Halos" held in Cittanova/Novigrad (HR) on 5-9 October, 2004 and published on-line by PoS (http://pos.sissa.it) which is a new versatile, online proceedings and lecture notes publication service launched by SISSA, Trieste.

astro-ph↗

arXiv2005

The baryon content of the Universe

The large discrepancy between the amount of baryons that were synthesized in Big-Bang and that we detect at $z=0$ locked in stars inside galaxies and in hot/cold gas in galaxies. goup and clusters, is a well known crucial issue for present day cosmology. It is also thought that this riddle is at the backbone of how the ordinary matter has formed, inside dark potential wells, the structures we see today. Then, it is useful to reprint, by means of this archive, the first (pre- astro-ph era) published work in which the amount of "luminous" baryons was actually and suitably computed and the disagreement with the BBN predictions strongly claimed. This because 12 years after the method and the results are still up-to-date, and above all, people are occasionally found to know only later works (appeared on astro-ph) that were meant to be just (ours or other's) follow ups of the present paper.

astro-ph↗

arXiv2004

From First Galaxies to QSOs: feeding the baby monsters

We present a physical model for the coevolution of massive spheroidal galaxies and active nuclei at their centers. Supernova heating is increasingly effective in slowing down the star formation and in driving gas outflows in smaller and smaller dark matter halos. Thus the more massive protogalaxies virializing at early times are the sites of faster star formation. The correspondingly higher radiation drag causes a faster angular momentum loss by the gas and induces a larger accretion rate onto the central black hole. In turn, the kinetic energy of the outflows powered by the active nuclei can unbind the residual gas in a time shorter for larger halos. The model accounts for a broad variety of dynamical, photometric and metallicity properties of early-type galaxies, for the M_BH -- σrelation and for the local supermassive black-hole mass function.

astro-ph↗

arXiv2004

Super-massive Black Hole Demography: the Match between the Local and Accreted Mass Functions

We have performed a detailed analysis of the local super-massive black-hole (SMBH) mass function based on both kinematic and photometric data and derived an accurate analytical fit in the range 10^6 <= (M_BH/M_sun) <= 5*10^9. We find a total SMBH mass density of (4.2+/-1.1)*10^5 M_sun/Mpc^3, about 25% of which is contributed by SMBHs residing in bulges of late type galaxies. Exploiting up-to-date luminosity functions of hard X-ray and optically selected AGNs, we have studied the accretion history of the SMBH population. If most of the accretion happens at constant \dot{M_BH}/M_BH the local SMBH mass function is fully accounted for by mass accreted by X-ray selected AGNs, with bolometric corrections indicated by current observations and a standard mass-to-light conversion efficiency ε~10%. The analysis of the accretion history highlights that the most massive BHs accreted their mass faster and at higher redshifts (z>1.5), while the lower mass BHs responsible for most of the hard X-ray background have mostly grown at z<1.5. The accreted mass function matches the local SMBH mass function if ε~0.09(+0.04,-0.03) and the Eddington ratio λ=L/L_Edd \~0.3(+0.3,-0.1) (68% confidence errors). The visibility time, during which AGNs are luminous enough to be detected by the currently available X-ray surveys, ranges from ~0.1 Gyr for present day BH masses M_BH(z=0) ~10^6 M_sun to ~0.3 Gyr for M_BH(z=0) >= 10^9 M_sun. The mass accreted during luminous phases is >= 25-30% even if we assume extreme values of ε(ε\~0.3-0.4). An unlikely fine tuning of the parameters would be required to account for the local SMBH mass function accomodating a dominant contribution from 'dark' BH growth (due, e.g., to BH coalescence).

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