Are currency crises self-fulfilling? The case of Argentina

This paper analyzes the 2002 Argentine crisis using the Jeanne and Masson (2000) model with sunspots. Testing this model empirically through a Markov-switching model suggests that self-sulfilling prophecies is a reasonable explanation for the devaluation of the peso

Extragalactic planetary nebulae as mass tracers: biases in the estimate of dynamical quantities

Planetary Nebulae (PNe) are very important kinematical tracers of the outer regions of early-type galaxies, where the integrated light techniques fail. Under ad hoc assumptions, they allow measurements of rotation velocity and velocity dispersion profile from descrete radial velocity fields. We present the results on the precision allowed by different set of radial velocity samples, discuss the hypotheses in the analysis of descrete velocity fields and their impact on the inferred kinematics of the stellar population.Comment: 4 pages, 2 figures. To appear on ``Galaxy Dynamics: from Early Universe to the Present'', ASP Conf. Ser., F. Combes, G.A. Mamon and V. Charmandaris (eds.

Mass-to-light ratios of ellipticals in LCDM

We use the mass-to-light gradients in early-type galaxies to infer the global dark matter fraction, f_d=M_d/M_*, for these systems. We discuss implications about the total star formation efficiency in dark-matter halos and show that the trend of $f_{\rm d}$ with mass produces virial mass-to-light ratios which are consistent with semi-analitical models. Preliminary kurtosis analysis of the quasi-constant M/L galaxies in Romanowsky et al. seems at odd with Dekel et al. simulations.Comment: 5 pages, 4 figures. To appear in Proceedings of XXIst IAP Colloquium, "Mass Profiles & Shapes of Cosmological Structures" (Paris, 4-9 July 2005), eds G. A. Mamon, F. Combes, C. Deffayet, B. Fort (Paris: EDP Sciences). Figure enlarged with respect the proceeding format, minor changes. Collaboration website at http://www.astro.rug.nl/~pns/pns_team.htm

Dark Matter and IMF normalization in Virgo dwarf early-type galaxies

In this work we analyze the dark matter (DM) fraction, $f_{DM}$, and mass-to-light ratio mismatch parameter, $\delta_{IMF}$ (computed with respect to a Milky-Way-like IMF), for a sample of 39 dwarf early-type galaxies (dEs) in the Virgo cluster. Both $f_{DM}$ and $\delta_{IMF}$ are estimated within the central (one effective radius) galaxy regions, with a Jeans dynamical analysis that relies on galaxy velocity dispersions, structural parameters, and stellar M/L ratios from the SMAKCED survey. In this first attempt to constrain, simultaneously, the IMF normalization and the DM content, we explore the impact of different assumptions on the DM model profile. On average, for a NFW profile, the $\delta_{IMF}$ is consistent with a Chabrier-like normalization ($\delta_{IMF} \sim 1$), with $f_{DM} \sim 0.35$. One of the main results of the present work is that for at least a few systems the $\delta_{IMF}$ is heavier than the MW-like value (i.e. either top- or bottom-heavy). When introducing tangential anisotropy, larger $\delta_{IMF}$ and smaller $f_{DM}$ are derived. Adopting a steeper concentration-mass relation than that from simulations, we find lower $\delta_{IMF}$ ($< 1$) and larger $f_{DM}$. A constant M/L profile with null $f_{DM}$ gives the heaviest $\delta_{IMF}$ ($\sim 2$). In the MONDian framework, we find consistent results to those for our reference NFW model. If confirmed, the large scatter of $\delta_{IMF}$ for dEs would provide (further) evidence for a non-universal IMF in early-type systems. On average, our reference $f_{DM}$ estimates are consistent with those found for low-$\sigma_{e}$ ($\rm \sim 100 \, \rm km s^{-1}$) early-type galaxies (ETGs). Furthermore, we find $f_{DM}$ consistent with values from the SMAKCED survey, and find a double-value behavior of $f_{DM}$ with stellar mass, which mirrors the trend of dynamical M/L and global star formation efficiency with mass.Comment: 11 pages, 3 figures, 1 table, published on MNRAS. Figure 1 has been updated with respect to version 1, including the range of values found if the S\'ersic index, n, is varied from 0.5 to 2 (dark-green curves

Central dark matter content of early-type galaxies: scaling relations and connections with star formation histories

We examine correlations between masses, sizes and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar population models. We confirm an anticorrelation between the size and stellar age and go on to survey for trends with the central content of dark matter (DM). An average relation between the central DM density and galaxy size of 〈ρDM〉∝R−2eff provides the first clear indication of cuspy DM haloes in these galaxies – akin to standard Λ cold dark matter haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as expected, deviating from suggestions of a universal halo profile for dwarf and late-type galaxies. We introduce a new fundamental constraint on galaxy formation by finding that the central DM fraction decreases with stellar age. This result is only partially explained by the size–age dependencies, and the residual trend is in the opposite direction to basic DM halo expectations. Therefore, we suggest that there may be a connection between age and halo contraction and that galaxies forming earlier had stronger baryonic feedback, which expanded their haloes, or lumpier baryonic accretion, which avoided halo contraction. An alternative explanation is a lighter initial mass function for older stellar populations

Colour gradients of high-redshift Early-Type Galaxies from hydrodynamical monolithic models

We analyze the evolution of colour gradients predicted by the hydrodynamical models of early type galaxies (ETGs) in Pipino et al. (2008), which reproduce fairly well the chemical abundance pattern and the metallicity gradients of local ETGs. We convert the star formation (SF) and metal content into colours by means of stellar population synthetic model and investigate the role of different physical ingredients, as the initial gas distribution and content, and eps_SF, i.e. the normalization of SF rate. From the comparison with high redshift data, a full agreement with optical rest-frame observations at z < 1 is found, for models with low eps_SF, whereas some discrepancies emerge at 1 < z < 2, despite our models reproduce quite well the data scatter at these redshifts. To reconcile the prediction of these high eps_SF systems with the shallower colour gradients observed at lower z we suggest intervention of 1-2 dry mergers. We suggest that future studies should explore the impact of wet galaxy mergings, interactions with environment, dust content and a variation of the Initial Mass Function from the galactic centers to the peripheries.Comment: 13 pages, 7 figures, 1 table, accepted for publication on MNRA

Testing Verlinde's emergent gravity in early-type galaxies

Verlinde derived gravity as an emergent force from the information flow, through two-dimensional surfaces and recently, by a priori postulating the entanglement of information in 3D space, he derived the effect of the gravitational potential from dark matter (DM) as the entropy displacement of dark energy by baryonic matter. In Emergent Gravity (EG) this apparent DM depends only on the baryonic mass distribution and the present-day value of the Hubble parameter. In this paper we test the EG proposition, formalized by Verlinde for a spherical and isolated mass distribution, using the central velocity dispersion, $\sigma$ and the light distribution in a sample of 4260 massive and local early-type galaxies (ETGs) from the SPIDER sample. Our results remain unaltered if we consider the sample of 807 roundest field galaxies. We derive the predictions by EG for the stellar mass-to-light ratio (M/L) and the Initial Mass Function (IMF), and compare them with the same inferences derived from a) DM-based models, b) MOND and c) stellar population models. We demonstrate that, consistently with a classical Newtonian framework with a DM halo component, or alternative theories of gravity as MOND, the central dynamics can be fitted if the IMF is assumed non-universal. The results can be interpreted with a IMF lighter than a standard Chabrier at low-$\sigma$, and bottom-heavier IMFs at larger $\sigma$. We find lower, but still acceptable, stellar M/L in EG theory, if compared with the DM-based NFW model and with MOND. The results from EG are comparable to what is found if the DM haloes are adiabatically contracted and with expectations from spectral gravity-sensitive features. If the strain caused by the entropy displacement would be not maximal, as adopted in the current formulation, then the dynamics of ETGs could be reproduced with larger M/L. (abridged)Comment: 12 pages, 2 figures, submitted to MNRAS. The updated manuscript presents significantly altered conclusions, after discovering an internal bug in an older version of the Mathematica package, leading to incorrect numerical results when calculating the derivatives of Gamma function

MOND and IMF variations in early-type galaxies from ATLAS3D

MOdified Newtonian dynamics (MOND) represents a phenomenological alternative to dark matter (DM) for the missing mass problem in galaxies and clusters of galaxies. We analyze the central regions of a local sample of $\sim 220$ early-type galaxies from the $\rm ATLAS^{3D}$ survey, to see if the data can be reproduced without recourse to DM. We estimate dynamical masses in the MOND context through Jeans analysis, and compare to $\rm ATLAS^{3D}$ stellar masses from stellar population synthesis. We find that the observed stellar mass--velocity dispersion relation is steeper than expected assuming MOND with a fixed stellar initial mass function (IMF) and a standard value for the acceleration parameter $a_{\rm 0}$. Turning from the space of observables to model space, a) fixing the IMF, a universal value for $a_{\rm 0}$ cannot be fitted, while, b) fixing $a_{\rm 0}$ and leaving the IMF free to vary, we find that it is "lighter" (Chabrier-like) for low-dispersion galaxies, and "heavier" (Salpeter-like) for high dispersions. This MOND-based trend matches inferences from Newtonian dynamics with DM, and from detailed analysis of spectral absorption lines, adding to the converging lines of evidence for a systematically-varying IMF.Comment: 6 pages, 3 figures, accepted for publication on MNRAS Letters, typos corrected and further references adde