arXiv subjects

Paolo Salucci

Publications and source records attributed to Paolo Salucci.

At least 37 records · Page 2Linked to original sources

arXiv2020

Paradigms and Scenarios for the Dark Matter Phenomenon

Well known scaling laws among the structural properties of the dark and the luminous matter in disc systems are too complex to be arisen by two inert components that just share the same gravitational field. This brings us to critically focus on the 30 year old paradigm, that, resting on a priori knowledge of the nature of dark matter (DM), has led us to a restricted number of scenarios, especially favouring the collisionless $Λ$Cold Dark Matter one. Motivated by such observational evidence, we propose to resolve the dark matter mystery by following a new paradigm: the nature of DM must be guessed/derived by deeply analyzing the properties of the dark and luminous mass distribution at galactic scales. The immediate application of this paradigm leads us to the existence of a direct interaction between dark and Standard Model particles which has finely shaped the inner regions of galaxies.

astro-ph.GA↗

arXiv2019

Galaxy sizes and the galaxy-halo connection -- I: the remarkable tightness of the size distributions

The mass and structural assembly of galaxies is a matter of intense debate. Current theoretical models predict the existence of a linear relationship between galaxy size ($R_e$) and the host dark matter halo virial radius ($R_h$).\\ By making use of semi-empirical models compared to the size distributions of central galaxies from the Sloan Digital Sky Survey, we provide robust constraints on the normalization and scatter of the $R_e-R_h$ relation. We explore the parameter space of models in which the $R_e-R_h$ relation is mediated by either the spin parameter or the concentration of the host halo, or a simple constant the nature of which is in principle unknown. We find that the data require extremely tight relations for both early-type and late-type galaxies (ETGs,LTGs), especially for more massive galaxies. These constraints challenge models based solely on angular momentum conservation, which predict significantly wider distributions of galaxy sizes and no trend with stellar mass, if taken at face value. We discuss physically-motivated alterations to the original models that bring the predictions into better agreement with the data. We argue that the measured tight size distributions of SDSS disk galaxies can be reproduced by semi-empirical models in which the $R_e-R_h$ connection is mediated by the \emph{stellar} specific angular momenta $j_{star}.$ We find that current cosmological models of galaxy formation broadly agree with our constraints for LTGs, and justify the strong link between $R_e$ and $j_{star}$ that we propose, however the tightness of the $R_e-R_h$ relation found in such ab-initio theoretical models for ETGs is in tension with our semi-empirical findings.

astro-ph.GA↗

arXiv2019

The universal rotation curve of low surface brightness galaxies IV: the interrelation between dark and luminous matter

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 $μ_0 \geq 23 \, mag \, arcsec^{-2}$. 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 $Σ_0 \sim 100 \, M_{\odot} pc^{-2}$, 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, the investigation of these objects calls for the introduction of a new luminous parameter, the stellar compactness $C_*$ (analogously to a recent work by Karukes \& Salucci), alongside with the optical radius and the optical velocity in order to reproduce the URC. Furthermore, a mysterious entanglement between the properties of the luminous and the dark matter emerges.

astro-ph.GA↗

arXiv2019

Black Hole Surrounded by a Dark Matter Halo in the M87 Galactic Center and its Identification with Shadow Images

In this paper we present a new black hole solution surrounded by dark matter halo in the galactic center using the mass model of M87 and that coming from the Universal Rotation Curve (URC) dark matter profile representing family of spiral galaxies. In both cases the DM halo density is cored with a size $r_0$ and a central density $ρ_0$: $ρ(r)= ρ_0/(1+r/r_0)(1+(r/r_0)^2)$. Since $r_0ρ_0=120 M_{\odot}$/pc$^2$ [Donato et al., MNRAS, 397, 1169, 2009], then by varying the central density one can reproduce the DM profile in any spiral. Using the Newman-Jains method we extend our solution to obtain a rotating black hole surrounded by dark matter halo. We find that, the apparent shape of the shadow beside the black hole spin $a$, it also depends on the central density of the surrounded dark matter $ρ_0$. As a specific example we consider the galaxy M87, with a central density $ρ_0=6.9\,\times 10^{6} M_{\odot}$/kpc$^3$ and a core radius $r_0=91.2$ kpc. In the case of M87, our analyses show that the effect of dark matter on the size of the black hole shadow is almost negligible compared to the shadow size of the Kerr vacuum solution hence the angular diameter $ 42$ $μ$as remains almost unaltered when the dark matter is considered. For a small totally dark matter dominated spiral such as UGC 7232, we find similar effect of dark matter on the shadow images compared to the M87. However, in specific conditions having a core radius comparable to the black hole mass and dark matter with very high density, we show that the shadow images decreases compared to the Kerr vacuum black hole. The effect of dark matter on the apparent shadow shape can shed some light in future observations as an indirect way to detect dark matter using the shadow images.

physics.gen-ph↗

arXiv2019

Constraints on cross-section and lifetime of dark matter with HAWC Observations of dwarf Irregular galaxies

It has been shown that the dynamics of dwarf Irregular (dIrr) galaxies are dominated by dark matter. It is also observed that these galaxies have low star formation rates and metallicities, and no gamma-ray emission at ultra very high energies is expected. Because of their distance, dark matter content and vast number, dIrr galaxies are good targets to perform indirect dark matter searches by ground-based and wide field of view gamma-ray experiments, like HAWC. We analyzed data at the position of 31 dIrr galaxies within the HAWC field-of-view and no significant excess was found. Here, we present the individual and combined limits on the annihilation cross-section and decay lifetime of weakly interacting massive particles with a mass between 1 and 100 TeV.

astro-ph.HE↗

arXiv2019

The distribution of dark matter in galaxies

The 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. \keywords{Dark matter \and Galaxies \and Cosmology \and Elementary particles}

astro-ph.GA↗

arXiv2019

The Radial Acceleration Relation (RAR): the crucial cases of Dwarf Discs and of Low Surface Brightness galaxies

McGaugh et al. (2016) have found, in a large sample of disc systems, a tight nonlinear relationship between the total radial accelerations $g$ and their components $g_b$ arisen from the distribution of the baryonic matter [McGaugh_2016]. Here, we investigate the existence of such relation in Dwarf Disc Spirals and Low Surface Brightness galaxies on the basis of [Karukes_2017] and [DiPaolo_2018]. We have accurate mass profiles for 36 Dwarf Disc Spirals and 72 LSB galaxies. These galaxies have accelerations that cover the McGaugh range but also reach out to one order of magnitude below the smallest accelerations present in McGaugh et al. (2016) and span different Hubble Types. We found, in our samples, that the $g$ vs $g_b$ relation has a very different profile and also other intrinsic novel properties, among those, the dependence on a second variable: the galactic radius, normalised to the optical radius $R_{opt}$, at which the two accelerations are measured. We show that the new far than trivial $g$ vs $(g_b, r/R_{opt})$ relationship is nothing else than a direct consequence of the complex, but coordinated mass distributions of the baryons and the dark matter (DM) in disc systems. Our analysis shows that the McGaugh et al. (2016) relation is a limiting case of a new universal relation that can be very well framed in the standard "DM halo in the Newtonian Gravity" paradigm.

astro-ph.GA↗

arXiv2018

The Dark Side Properties of Galaxies Requires (viable) Modifications to the Verlinde's Emergent Gravity Theory

Dark Matter is an unknown entity in the Universe. Although several fields of astrophysics \& cosmology are trying to endorse this elusive matter, however, its nature remains an open question. Recently, Verlinde\cite{verlinde2017emergent} has proposed the Emergent Gravity theory (EGT), which is creating severe issues for DM identity. In this work, we have examined the EGT in the light of the kinematics of the spiral and elliptical galaxies. Results show that the EGT predictions are in good agreement with latter, though some discrepancy appears in the former. This current work calls for refinement in EGT.

astro-ph.GA↗

arXiv2018

Kinematics of Spiral galaxies as a Portal to the Nature of Dark Matter

The gravitational field of Spiral galaxies is well traced by their rotation curves. Only recently it has become of extreme interest that the latter form a family ruled by two parameters of the {\it luminous} component: the disk length-scale $R_D$ and the magnitude $M_I$. This evidence is so strong and consequential that it must be taken as the starting point for the investigation on the issue of the dark matter in galaxies. The emerging fact is that structural quantities deeply rooted in the luminous components, like the disk length scales are found to tightly correlate with structural quantities deeply rooted in the dark component, like the DM halo core radii. This unexpected evidence may strongly call for a shift of paradigm with respect to the current Cold collisionless Dark Matter one.

astro-ph.GA↗

arXiv2018

Dark Matter in Galaxies: evidences and challenges

The 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 $R_{opt}$, where the measurement is performed. For the disk systems with $-13\geq M_I\geq -24$ 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 $V_{URC} (r/R_{opt}, M_I)$ 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 2016, in terms of only well known astrophysical processes, acting in a standard DM halos + luminous disks scenario

astro-ph.GA↗

arXiv2017

Searching for TeV DM evidence from Dwarf Irregular Galaxies with the HAWC Observatory

The dynamics of dwarf irregular (dIrr) galaxies are observed to be dominated by dark matter (DM). Recently, the DM density distribution has been studied for 31 dIrrs. Their extended DM halo (Burket type profile) makes these objects good candidates for DM searches. Located in Puebla (Mexico), the High Altitude Water Cherenkov (HAWC) Observatory is an optimal in- strument to perform such DM searches, because of its large sky coverage (8.4 sr per day). We analyzed a set of two years of HAWC data and we found no significant DM signal from dIrr galaxies. We present the upper limits for DM annihilation cross-section with dIrr galaxies.

astro-ph.HE↗

arXiv2017

Evidences for Collisional Dark Matter In Galaxies?

The more we go deep into the knowledge of the dark component which embeds the stellar component of galaxies, the more we realize the profound interconnection between them. We show that the scaling laws among the structural properties of the dark and luminous matter in galaxies are too complex to derive from two inert components that just share the same gravitational field. In this paper we review the 30 years old paradigm of collisionless dark matter in galaxies. We found that their dynamical properties show strong indications that the dark and luminous components have interacted in a more direct way over a Hubble Time. The proofs for this are the presence of central cored regions with constant DM density in which their size is related with the disk lenghtscales. Moreover we find that the quantity $ρ_{DM}(r,L,R_D) ρ_\star (r,L,R_D)$ shows, in all objects, peculiarities very hardly explained in a collisionless DM scenario.

astro-ph.CO↗

arXiv2017

The radial dependence of dark matter distribution in M33

The stellar and gaseous mass distributions, as well as the extended rotation curve in the nearby galaxy M33 are used to derive the radial distribution of dark matter density in the halo and to test cosmological models of galaxy formation and evolution. Two methods are examined to constrain dark mass density profiles. The first method deals directly with fitting the rotation curve data in the range of galactocentric distances $0.24\,\text{kpc}\leq r\leq22.72\,\text{kpc}.$ As found in a previous paper by \citet{Corbelli:2014lga}, and using the results of collisionless $Λ-$Cold Dark Matter numerical simulations, we confirm that the Navarro-Frenkel-White (hereafter NFW) dark matter profile provides a better fit to the rotation curve data than the cored Burkert profile (hereafter BRK) profile. The second method relies on the local equation of centrifugal equilibrium and on the rotation curve slope. In the aforementioned range of distances we fit the observed velocity profile, using a function which has a rational dependence on the radius, and derive the slope of the rotation curve. Following \citet{Salucci:2010qr} we then infer the effective matter densities. In the radial range $9.53\,\text{kpc}\leq r\leq22.72\,\text{kpc}$ the uncertainties induced by the luminous matter (stars and gas) becomes negligible, because the dark matter density dominates, and we can determine locally the radial distribution of dark matter. With this second method we tested the NFW and the BRK dark matter profiles and confirm that both profiles are compatible with the data even though in this case the cored BRK density profile provides a more reasonable value for the baryonic-to-dark matter ratio.

astro-ph.GA↗

arXiv2017

Dark Matter Strikes Back

Mc Gaugh et al. (2016) have found, by investigating a large sample of Spirals, a tight non linear relationship between the total radial acceleration, connected with the Dark Matter phenomenon, and its component which comes from the distribution of baryonic matter, as the stellar and HI disks. The strong link between these two quantities is considered by them and by other researchers, as challenging the scenario featuring the presence of DM halos in galaxies. Or, at least, to indicate the peculiar nature of the underlying dark matter particles. We have explored this issue by investigating a larger number of galaxies by means of several techniques of analysis. Our results support and even increase, both qualitatively and quantitatively, the validity of McGaugh et al. (2016) 's relationship. However, we prove that such relationship exists also in the scenario featuring dark matter halos + ordinary baryonic matter and that it arises by the fact the DM is less concentrated than the luminous matter and it is progressively more abundant in lower luminosity objects. These properties are due to well known astrophysical effects: the implications of this relationship for the properties of dark matter halos are nothing of new or of unexpected. The relationship, definitively, is not a portal to go beyond the standard picture of $Λ$CDM galaxy formation.

astro-ph.GA↗

arXiv2017

The universal rotation curve of dwarf disk galaxies

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 $\sim11$ 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 ($\sim$ 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 scale lengths. 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 \sim 100\hspace{0.1cm} \mathrm{M_\odot 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.

astro-ph.GA↗

arXiv2014

Dynamical signatures of a LCDM-halo and the distribution of the baryons in M33

We map the neutral atomic gas content of M33 using high resolution VLA and GBT observations and fit a tilted ring model to determine the orientation of the extended gaseous disk and its rotation curve. The disk of M33 warps from 8 kpc outwards without substantial change of its inclination with respect to the line of sight. Rotational velocities rise steeply with radius in the inner disk, reaching 100 km/s in 4 kpc, then the rotation curve becomes more perturbed and flatter with velocities as high as 120-130 km/s out to 23 kpc. We derive the stellar mass surface density map of M33's optical disk, via pixel -SED fitting methods based on population synthesis models, which highlights variations in the mass-to-light ratio. The stellar mass surface further out is estimated from deep images of outer disk fields. Stellar and gas maps are then used in the dynamical analysis of the rotation curve to constrain the dark matter distribution which is relevant at all radii. A dark matter halo with a Navarro-Frenk-White density profile in a LCDM cosmology, provides the best fit to the rotation curve for a dark halo concentration C=10 and a total halo mass of 4.3 10^{11}Msun. This imples a baryonic fraction of order 0.02 and the evolutionary history of this galaxy should account for loss of a large fraction of its original baryonic content.

astro-ph.GA↗

arXiv2014

Rotation Curve with MOND and Dark Matter Halo profile for ESO138-G014

This paper is devoted to solve the galactic rotation problem for ESO138-G014 galaxy based on two theories: dark matter and Modified Newtonian Dynamics. Here we did the rotation curve analysis with two possible choices for the dark matter density profile, namely Burkert and Navarro, Frenk and White profiles. The analysis shows the dark matter distribution favored to Burkert profile (cored dark matter). The standard hypothesis for most spiral galaxies are known to be embedded in dark matter haloes has now been overshadowed by Modified Newtonian Dynamics, known as MOND, the leading alternative of dark matter. MOND addresses the problem of a new fundamental constant $a_0$, called the acceleration constant, at which acceleration scale of Newton second law fails to hold. In this respect, we investigate this issue by testing the rotation curve within the MOND framework with the observations to obtain the reliable disk mass, $M_D$. We investigate whether ESO138-G014 is compatible with MOND or dark matter is still favorable for the galactic rotation problem.

astro-ph.GA↗

arXiv2014

$R^n$ gravity is kicking and alive: the cases of Orion and NGC 3198

We analyzed the Rotation Curves of two crucial objects, the Dwarf galaxy Orion and the low luminosity Spiral NGC 3198, in the framework of $R^n$ gravity. We surprisingly found that the no DM power-law f(R) case fits them well, performing much better than $Λ$CDM Dark Matter halo models. The level of this unexpected success can be a boost for $R^n$ gravity.

astro-ph.GA↗