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Search Results: 1 - 10 of 542408 matches for " C. M. Carollo "
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Spiral galaxies with WFPC2: III. Nuclear Cusp Slopes
C. M. Carollo,M. Stiavelli
Physics , 1998, DOI: 10.1086/300373
Abstract: In this paper, the third of a series dedicated to the investigation of the nuclear properties of spiral galaxies, we have (i) modelled the WFPC2 F606W nuclear surface brightness profiles of 41 spiral galaxies presented in Carollo et al. 1997c, 1998 with the analytical law introduced by Lauer et al. 1995, and (ii) deprojected these surface brightness profiles and their analytical fits, so as to estimate the nuclear stellar densities of bulges of spiral galaxies. We find that the nuclear stellar cusps (quantified by the average logarithmic slope of the surface brightness profiles within 0.1''-0.5'') are significantly different for R^1/4-law and exponential bulges. The former have nuclear properties similar to those of early-type galaxies, i.e. similar values of nuclear cusps for comparable luminosities, and increasingly steeper stellar cusps with decreasing luminosity. By contrast, exponential bulges have (underlying the light contribution from photometrically distinct, central compact sources) comparative shallower stellar cusps, and likely lower nuclear densities, than R^1/4-law bulges.
Spiral galaxies with WFPC2: II. The Nuclear Properties of 40 objects
C. M. Carollo,M. Stiavelli,J. Mack
Physics , 1998, DOI: 10.1086/300407
Abstract: We report the analysis of HST WFPC2 F606W images of 40 spirals belonging to the sample introduced in Carollo et al. (paper I), where 35 other targets were discussed. We describe the optical morphology of the new 40 galaxies, derive the surface brightness profiles for 25 of them, and present the results of photometric decompositions of these profiles into a ``bulge'' (R^1/4 or exponential) and a disk component. The analysis of the sample of 75 galaxies puts on a statistically more solid ground the main results presented in paper I. Furthermore, the analysis of the sample of 75 objects shows that: A. Several of the non-classical inner structures are well fitted by an exponential profile. These ``exponential bulges'' are fainter than R^1/4 bulges for given total galaxy luminosity and (catalog) Hubble type later than Sab. B. Irregular/exponential bulges typically host central compact sources. C. The central sources are present in all types of disk galaxies, starting with systems as early as S0a. About 60 % of Sb to Sc galaxies host a central compact source. Many of the galaxies which host compact sources contain a barred structure. D. Galaxies with apparent nuclear star formation and the brightest compact sources, are preferentially the early- and intermediate- type (S0a-Sb) systems. E. None of the features depends on environment: isolated and not isolated galaxies show indistinguishable properties. Independently from the physical nature of the non-classical inner structures, our main conclusion is that a significant fraction of galaxies classified from the ground as relatively early-type shows a rich variety of central properties, and little or no morphological/photometric evidence for a smooth, R^1/4-law bulge.
Dynamical Constraints on the Formation of Elliptical Galaxies
P. T. de Zeeuw,C. M. Carollo
Physics , 1995,
Abstract: Recent work on the construction of spherical, Axisymmetric and triaxial dynamical models for elliptical galaxies is reviewed briefly, including their role in providing evidence for dark halos and central black holes. The different orbital structures and shapes of low-mass and giant elliptical galaxies provide essential constraints on scenarios of galaxy formation.
The Hubble Sequence in Groups: The Birth of the Early-Type Galaxies
R. Feldmann,C. M. Carollo,L. Mayer
Physics , 2010, DOI: 10.1088/0004-637X/736/2/88
Abstract: The physical mechanisms and timescales that determine the morphological signatures and the quenching of star formation of typical (~L*) elliptical galaxies are not well understood. To address this issue, we have simulated the formation of a group of galaxies with sufficient resolution to track the evolution of gas and stars inside about a dozen galaxy group members over cosmic history. Galaxy groups, which harbor many elliptical galaxies in the universe, are a particularly promising environment to investigate morphological transformation and star formation quenching, due to their high galaxy density, their relatively low velocity dispersion, and the presence of a hot intragroup medium. Our simulation reproduces galaxies with different Hubble morphologies and, consequently, enables us to study when and where the morphological transformation of galaxies takes place. The simulation does not include feedback from active galactic nuclei showing that it is not an essential ingredient for producing quiescent, red elliptical galaxies in galaxy groups. Ellipticals form, as suspected, through galaxy mergers. In contrast with what has often been speculated, however, these mergers occur at z>1, before the merging progenitors enter the virial radius of the group and before the group is fully assembled. The simulation also shows that quenching of star formation in the still star-forming elliptical galaxies lags behind their morphological transformation, but, once started, is taking less than a billion years to complete. As long envisaged the star formation quenching happens as the galaxies approach and enter the finally assembled group, due to quenching of gas accretion and (to a lesser degree) stripping. A similar sort is followed by unmerged, disk galaxies, which, as they join the group, are turned into the red-and-dead disks that abound in these environments.
Holonomic Quantum Computation
Angelo C. M. Carollo,Vlatko Vedral
Physics , 2005,
Abstract: In this brief review we describe the idea of holonomic quantum computation. The idea of geometric phase and holonomy is introduced in a general way and we provide few examples that should help the reader understand the issues involved.
Geometric phases and criticality in spin systems
Jiannis K. Pachos,Angelo C. M. Carollo
Physics , 2006, DOI: 10.1098/rsta.2006.1894
Abstract: A general formalism of the relation between geometric phases produced by circularly evolving interacting spin systems and their criticality behavior is presented. This opens up the way for the use of geometric phases as a tool to study regions of criticality without having to undergo a quantum phase transition. As a concrete example a spin-1/2 chain with XY interactions is presented and the corresponding geometric phases are analyzed. The generalization of these results to the case of an arbitrary spin system provides an explanation for the existence of such a relation.
The Metallicity of 0.5
C. M. Carollo,S. J. Lilly
Physics , 2000, DOI: 10.1086/319104
Abstract: We have measured the emission line ratios in a sample of 34 CFRS star-forming galaxies with redshifts between 0.5 < z < 1.0, and computed their metallicities by means of the empirically-calibrated R_23 metallicity estimator introduced by Pagel et al. (1979). The current analysis concentrates on the 15 galaxies with L_Hbeta > 1.2x10^41 erg s-1. Although our results can only be regarded as preliminary until near-IR spectroscopy of Halpha and [NII]6583 are available, the metallicities of these galaxies appear to be remarkably similar to those of local galaxies selected in the same way, and there appears to have been little change in the relationship between metallicity and line- and continuum-luminosity from z~1 to today. At this stage our results do not support the idea that these galaxies, known to be generally small and with late-type morphologies, are dwarf galaxies brightened by large bursts of star-formation, as had been suggested from previous studies. Rather, our findings are more consistent with a picture in which these systems are the progenitors of today's massive metal-rich galaxies.
Geometric phases and criticality in spin chain systems
Angelo C. M. Carollo,Jiannis K. Pachos
Physics , 2005, DOI: 10.1103/PhysRevLett.95.157203
Abstract: A relation between geometric phases and criticality of spin chains is established. As a result, we show how geometric phases can be exploited as a tool to detect regions of criticality without having to undergo a quantum phase transition. We analytically evaluate the geometric phase that correspond to the ground and excited states of the anisotropic XY model in the presence of a transverse magnetic field when the direction of the anisotropy is adiabatically rotated. Ultra-cold atoms in optical lattices are presented as a possible physical realization.
Triaxial Haloes and Particle Dark Matter Detection
N. W. Evans,C. M. Carollo,P. T. de Zeeuw
Physics , 2000, DOI: 10.1046/j.1365-8711.2000.03787.x
Abstract: This paper presents the properties of a family of scale-free triaxial haloes. We adduce arguments to suggest that the velocity ellipsoids of such models are aligned in conical coordinates. We provide an algorithm to find the set of conically aligned velocity second moments that support a given density against the gravity field of the halo. The case of the logarithmic ellipsoidal model -- the simplest triaxial generalisation of the familiar isothermal sphere -- is examined in detail. The velocity dispersions required to hold up the self-consistent model are analytic. The velocity distribution of the dark matter can be approximated as a triaxial Gaussian with semiaxes equal to the velocity dispersions. There are roughly twenty experiments worldwide that are searching for evidence of scarce interactions between weakly-interacting massive-particle dark matter (WIMPs) and detector nuclei. The annual modulation signal, caused by the Earth's rotation around the Sun, is a crucial discriminant between WIMP events and the background. The greatest rate is in June, the least in December. We compute the differential detection rate for energy deposited by the rare WIMP-nucleus interactions in our logarithmic ellipsoidal halo models. Triaxiality and velocity anisotropy change the total rate by up to 40 %, and have a substantial effect on the amplitude of the annual modulation signal. The overall rate is greatest, but the amplitude of the modulation is weakest, in our radially anisotropic halo models. Even the sign of the signal can be changed. Restricting attention to low energy events, the models predict that the maximum rate occurs in December, and not in June.
On the relation between sSFR and metallicity
A. Pipino,S. J. Lilly,C. M. Carollo
Physics , 2014,
Abstract: In this paper we present an exact general analytic expression $Z(sSFR)=y/\Lambda(sSFR)+I(sSFR)$ linking the gas metallicity Z to the specific star formation rate (sSFR), that validates and extends the approximate relation put forward by Lilly et al. (2013, L13), where $y$ is the yield per stellar generation, $\Lambda(sSFR)$ is the instantaneous ratio between inflow and star formation rate expressed as a function of the sSFR, and $I$ is the integral of the past enrichment history, respectively. We then demonstrate that the instantaneous metallicity of a self-regulating system, such that its sSFR decreases with decreasing redshift, can be well approximated by the first term on the right-hand side in the above formula, which provides an upper bound to the metallicity. The metallicity is well approximated also by the L13 ideal regulator case, which provides a lower bound to the actual metallicity. We compare these approximate analytic formulae to numerical results and infer a discrepancy <0.1 dex in a range of metallicities and almost three orders of magnitude in the sSFR. We explore the consequences of the L13 model on the mass-weighted metallicity in the stellar component of the galaxies. We find that the stellar average metallicity lags 0.1-0.2 dex behind the gas-phase metallicity relation, in agreement with the data. (abridged)
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