arXiv subjects

M. Capaccioli

Publications and source records attributed to M. Capaccioli.

At least 73 records · Page 4Linked to original sources

arXiv2010

Stellar population gradients from cosmological simulations: dependence on mass and environment in local galaxies

The age and metallicity gradients for a sample of group and cluster galaxies from N-body+hydrodynamical simulation are analyzed in terms of galaxy stellar mass. Dwarf galaxies show null age gradient with a tail of high and positive values for systems in groups and cluster outskirts. Massive systems have generally zero age gradients which turn to positive for the most massive ones. Metallicity gradients are distributed around zero in dwarf galaxies and become more negative with mass; massive galaxies have steeper negative metallicity gradients, but the trend flatten with mass. In particular, fossil groups are characterized by a tighter distribution of both age and metallicity gradients. We find a good agreement with both local observations and independent simulations. The results are also discussed in terms of the central age and metallicity, as well as the total colour, specific star formation and velocity dispersion.

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arXiv2010

Color and stellar population gradients in galaxies. Correlation with mass

We analyze the color gradients (CGs) of ~50000 nearby SDSS galaxies. From synthetic spectral models based on a simplified star formation recipe, we derive the mean spectral properties, and explain the observed radial trends of the color as gradients of the stellar population age and metallicity (Z). The most massive ETGs (M_* > 10^{11} Msun) have shallow CGs in correspondence of shallow (negative) Z gradients. In the stellar mass range 10^(10.3-10.5) < M_* < 10^(11) Msun, the Z gradients reach their minimum of ~ -0.5 dex^{-1}. At M_* ~ 10^{10.3-10.5} Msun, color and Z gradient slopes suddenly change. They turn out to anti-correlate with the mass, becoming highly positive at the very low masses. We have also found that age gradients anti-correlate with Z gradients, as predicted by hierarchical cosmological simulations for ETGs. On the other side, LTGs have gradients which systematically decrease with mass (and are always more negative than in ETGs), consistently with the expectation from gas infall and SN feedback scenarios. Z is found to be the main driver of the trend of color gradients, especially for LTGs, but age gradients are not negligible and seem to play a significant role too. We have been able to highlight that older galaxies have systematically shallower age and Z gradients than younger ones. Our results for high-mass galaxies are in perfect agreement with predictions based on the merging scenario, while the evolution of LTGs and younger and less massive ETGs seems to be mainly driven by infall and SN feedback. (Abridged)

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arXiv2009

Extending the Hubble diagram by gamma ray bursts

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arXiv2009

Testing Dark Energy models vs $Λ$CDM Cosmology by Supernovae and Gamma Ray Bursts

A new method to constrain the cosmological equation of state is proposed by using combined samples of gamma-ray bursts (GRBs) and supernovae (SNeIa). The Chevallier-Polarski-Linder parameterization is adopted for the equation of state in order to find out a realistic approach to achieve the deceleration/acceleration transition phase of dark energy models. As results, we find that GRBs, calibrated by SNeIa, could be, at least, good distance indicators capable of discriminating cosmological models with respect to $Λ$CDM at high redshift. Besides, GRBs+SNeIa combined redshift-distance diagram puts better in evidence the change of slope around redshift $z\sim 0.5$ which is usually addressed as the "signature" of today observed acceleration. This feature could be interpreted, in more standard way, by the red sequence in galaxy clusters.

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arXiv2009

Sersic galaxy with Sersic halo models of early-type galaxies: a tool for N-body simulations

We present spherical, non-rotating, isotropic models of early-type galaxies with stellar and dark-matter components both described by deprojected Sersic density profiles, and prove that they represent physically admissible stable systems. Using empirical correlations and recent results of N-body simulations, all the free parameters of the models are expressed as functions of one single quantity: the total (B-band) luminosity of the stellar component. We analyze how to perform discrete N-body realizations of Sersic models. To this end, an optimal smoothing length is derived, defined as the softening parameter minimizing the error on the gravitational potential for the deprojected Sersic model. It is shown to depend on the Sersic index $n$ and on the number of particles of the N-body realization. A software code allowing the computations of the relevant quantities of one- and two-component Sersic models is provided. Both the code and the results of the present work are primarily intended as tools to perform N-body simulations of early-type galaxies, where the structural non-homology of these systems (i.e. the variation of the shape parameter along the galaxy sequence) might be taken into account.

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arXiv2009

On the origin of the scatter around the Fundamental Plane: correlations with stellar population parameters

We present a fundamental plane (FP) analysis of 141 early-type galaxies in the Shapley supercluster at z=0.049 based on spectroscopy from the AAOmega spectrograph at the AAT and photometry from the WFI on the ESO/MPI 2.2m telescope. The key feature of the survey is its coverage of low-mass galaxies down to sigma_0~50km/s. We obtain a best-fitting FP relation log r_e=1.06 log sigma_0 - 0.82 log < I >_e + cst in the R band. The shallow exponent of sigma_0 is a result of the extension of our sample to low velocity dispersions. We investigate the origin of the intrinsic FP scatter, using estimates of age, metallicity and alpha/Fe. We find that the FP residuals anti-correlate (>3sigma) with the mean stellar age in agreement with previous work. However, a stronger (>4sigma) correlation with alpha/Fe is also found. These correlations indicate that galaxies with effective radii smaller than those predicted by the FP have stellar populations systematically older and with alpha over-abundances larger than average, for their sigma_0. Including alpha/Fe as a fourth parameter in the FP, the total scatter decreases from 0.088 dex to 0.075 dex and the estimated intrinsic scatter decreases from 0.068 dex to 0.049 dex. Thus, variations in alpha/Fe account for >> 30% of the total variance around the FP, and >> 50% of the estimated intrinsic variance. This result indicates that the distribution of galaxies around the FP are tightly related to the enrichment, and hence to the timescale of star-formation. Our results appear to be consistent with the merger hypothesis for the formation of ellipticals which predicts that a significant fraction of the scatter is due to variations in the importance of dissipation in forming merger remnants of a given mass.

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arXiv2009

Central mass-to-light ratios and dark matter fractions in early-type galaxies

Dynamical studies of local ETGs and the Fundamental Plane point to a strong dependence of M/L ratio on luminosity (and stellar mass) with a relation of the form $M/L \propto L^γ$. The "tilt" $γ$ may be caused by various factors, including stellar population properties, IMF, rotational support, luminosity profile non-homology and dark matter (DM) fraction. We evaluate the impact of all these factors using a large uniform dataset of local ETGs from Prugniel & Simien (1997). We take particular care in estimating the stellar masses, using a general star formation history, and comparing different population synthesis models. We find that the stellar M/L contributes little to the tilt. We estimate the total M/L using simple Jeans dynamical models, and find that adopting accurate luminosity profiles is important but does not remove the need for an additional tilt component, which we ascribe to DM. We survey trends of the DM fraction within one effective radius, finding it to be roughly constant for galaxies fainter than $M_B \sim -20.5$, and increasing with luminosity for the brighter galaxies; we detect no significant differences among S0s and fast- and slow-rotating ellipticals. We construct simplified cosmological mass models and find general consistency, where the DM transition point is caused by a change in the relation between luminosity and effective radius. A more refined model with varying galaxy star formation efficiency suggests a transition from total mass profiles (including DM) of faint galaxies distributed similarly to the light, to near-isothermal profiles for the bright galaxies. These conclusions are sensitive to various systematic uncertainties which we investigate in detail, but are consistent with the results of dynamics studies at larger radii.

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arXiv2008

White dwarfs in the Capodimonte deep field

In this article we describe the search for white dwarfs (WDs) in the multi-band photometric data of the Capodimonte deep field survey. The WD candidates were selected through the V-R_C vs B-V color-color diagram. For two bright objects, the WD nature has been confirmed spectroscopically, and the atmospheric parameters (Teff and logg) have been determined. We have computed synthetic stellar population models for the observed field and the expected number of white dwarfs agrees with the observations. The possible contamination by turn-off and horizontal branch halo stars has been estimated. The quasar (QSO) contamination has been determined by comparing the number of WD candidates in different color bins with state-of-the-art models and previous observations. The WD space density is measured at different distances from the Sun. The total contamination (non-degenerate stars + QSOs) in our sample is estimated to be around 30%. This work should be considered a small experiment in view of more ambitious projects to be performed in the coming years in larger survey contexts.

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arXiv2008

Kinematic properties of early-type galaxy haloes using planetary nebulae

We present new planetary nebulae (PNe) positions, radial velocities, and magnitudes for 6 early-type galaxies obtained with the Planetary Nebulae Spectrograph, their two-dimensional velocity and velocity dispersion fields. We extend this study to include an additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, to obtain a broader description of the outer-halo kinematics in early-type galaxies. These data extend the information derived from stellar kinematics to typically up to ~8 Re. The combination of photometry, stellar and PNe kinematics shows: i) good agreement between the PNe number density and the stellar surface brightness in the region where the two data sets overlap; ii) good agreement between PNe and stellar kinematics; iii) that the mean rms velocity profiles fall into two groups: with of the galaxies characterized by slowly decreasing profiles and the remainder having steeply falling profiles; iv) a larger variety of velocity dispersion profiles; v) that twists and misalignments in the velocity fields are more frequent at large radii, including some fast rotators; vi) that outer haloes are characterised by more complex radial profiles of the specific angular momentum-related lambda_R parameter than observed within 1Re; vii) that many objects are more rotationally dominated at large radii than in their central parts; and viii) that the halo kinematics are correlated with other galaxy properties, such as total luminosity, isophotal shape, total stellar mass, V/sigma, and alpha parameter, with a clear separation between fast and slow rotators.

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arXiv2008

Probing the kinematics of early-type galaxy halos using planetary nebulae

We present first results of a study of the halo kinematics for a sample of early type galaxies using planetary nebulae (PNe) as kinematical tracers. PNe allow to extend up to several effective radii (Re) the information from absorption line kinematics (confined to within 1 or 2 Re), providing valuable information and constraints for merger simulations and galaxy formation models. We find that the specific angular momentum per unit mass has a more complex radial dependence when the halo region is taken into account and that the halo velocity dispersion is related to the total galaxy luminosity, isophotal shape, and number of PNe per unit of luminosity

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arXiv2008

The PN.S Elliptical Galaxy Survey: the dark matter in NGC 4494

We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 PNe out to 7 effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the PNe agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside 1 Re. The velocity dispersion profile declines with radius, though not very steeply, down to ~70 km/s at the last data point. We have constructed spherical dynamical models of the system, including Jeans analyses with multi-component LCDM-motivated galaxies as well as logarithmic potentials. These models include special attention to orbital anisotropy, which we constrain using fourth-order velocity moments. Given several different sets of modelling methods and assumptions, we find consistent results for the mass profile within the radial range constrained by the data. Some dark matter (DM) is required by the data; our best-fit solution has a radially anisotropic stellar halo, a plausible stellar mass-to-light ratio, and a DM halo with an unexpectedly low central density. We find that this result does not substantially change with a flattened axisymmetric model. Taken together with other results for galaxy halo masses, we find suggestions for a puzzling pattern wherein most intermediate-luminosity galaxies have very low concentration halos, while some high-mass ellipticals have very high concentrations. We discuss some possible implications of these results for DM and galaxy formation.

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arXiv2008

Gauging the dark matter fraction in a $L_*$ S0 galaxy at z=0.47 through gravitational lensing from deep HST/ACS imaging

We analyze a new gravitational lens, OAC-GL J1223-1239, serendipitously found in a deep I-band image of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). The lens is a L_*, edge-on S0 galaxy at z=0.4656. The gravitational arc has a radius of 0.42 arcsec. We have determined the total mass and the dark matter (DM) fraction within the Einstein radius as a function of the lensed source redshift, which is presently unknown. For z ~ 1.3, which is in the middle of the redshift range plausible for the source according to some external constraints, we find the central velocity dispersion to be ~180 km/s. With this value, close to that obtained by means of the Faber-Jackson relation at the lens redshift, we compute a 30% DM fraction within the Einstein radius (given the uncertainty in the source redshift, the allowed range for the DM fraction is 25-35 % in our lensing model). When compared with the galaxies in the local Universe, the lensing galaxy, OAC-GL J1223-1239 seems to fall in the transition regime between massive DM dominated galaxies and lower-mass, DM deficient systems.

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arXiv2008

CMB Anisotropy Induced by a Moving Straight Cosmic String

We showed that the part of strings could be detected by optical method is only 20% from the total available amount of such objects, therefore the gravitational lensing method has to be "completed" by CMB one. We found the general structure of the CMB anisotropy generated by a cosmic string for simple model of straight string moving with constant velocity. For strings with deficit angle 1-2 arcsec the amplitude of generated anisotropy has to be 15-30 muK (the corresponding string linear density is (G mu) ~ 10^{-7} and energy is GUT one, 10^{15} GeV). To use both radio and optical methods the deficit angle has to be from 0.1 arcsec to 5-6 arcsec. If cosmic string can be detected by optical method, the length of corresponding brightness spot of anisotropy has to be no less than 100 degrees.

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arXiv2008

The evolution of the galaxy Red Sequence in simulated clusters and groups

N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a LambdaCDM cosmology are used in order to follow the building-up of the colour-magnitude relation in two clusters and in 12 groups. We have found that galaxies, starting from the more massive, move to the Red Sequence (RS) as they get aged over times and eventually set upon a ``dead sequence'' (DS) once they have stopped their bulk star formation activity. Fainter galaxies keep having significant star formation out to very recent epochs and lie broader around the RS. Environment plays a role as galaxies in groups and cluster outskirts hold star formation activity longer than the central cluster regions. However galaxies experiencing infall from the outskirts to the central parts keep star formation on until they settle on to the DS of the core galaxies. Merging contributes to mass assembly until z~1, after which major events only involve the brightest cluster galaxies. The emerging scenario is that the evolution of the colour-magnitude properties of galaxies within the hierarchical framework is mainly driven by star formation activity during dark matter halos assembly. Galaxies progressively quenching their star formation settle to a very sharp ``red and dead'' sequence, which turns out to be universal, its slope and scatter being almost independent of the redshift (since at least z~1.5) and environment. Differently from the DS, the operatively defined RS evolves more evidently with z, the epoch when it changes its slope being closely corresponding to that at which the passive galaxies population takes over the star forming one: this goes from z~1 in clusters down to 0.4 in normal groups.

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arXiv2008

Dearth of dark matter or massive dark halo? Mass-shape-anisotropy degeneracies revealed by NMAGIC dynamical models of the elliptical galaxy NGC 3379

Recent results from the Planetary Nebula Spectrograph (PN.S) survey have revealed a rapidly falling velocity dispersion profile in the nearby elliptical galaxy NGC 3379, casting doubts on whether this intermediate-luminosity galaxy has the kind of dark matter halo expected in LambdaCDM cosmology. We present a detailed dynamical study of this galaxy, combining long-slit spectroscopy, SAURON integral-field data, and PN.S velocities, reaching to more than seven effective radii (R_e). We construct spherical and axisymmetric dynamical models for these data with the flexible made-to-measure NMAGIC code, in a sequence of gravitational potentials with varying dark halo mass. We find that the data are consistent both with near-isotropic spherical systems dominated by the stellar mass, and with models in massive halos with strongly radially anisotropic outer parts (beta >~ 0.8 at 7R_e). Formal likelihood limits would exclude (at 1 sigma) the model with stars only, as well as halo models with v_circ(7R_e) >~ 250 km/s. A sequence of more realistic axisymmetric models of different inclinations and a small number of triaxial tests confirm the spherical results. All valid models fitting all the data are dynamically stable over Gyrs, including the most anisotropic ones. NGC 3379 may well have a dark matter halo as predicted by recent merger models within LambdaCDM cosmology, provided its outer envelope is strongly radially anisotropic. (abridged)

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arXiv2008

2DPHOT: A Multi-purpose Environment for the Two-dimensional Analysis of Wide-field Images

We describe 2DPHOT, a general purpose analysis environment for source detection and analysis in deep wide-field images. 2DPHOT is an automated tool to obtain both integrated and surface photometry of galaxies in an image, to perform reliable star-galaxy separation with accurate estimates of contamination at faint flux levels, and to estimate completeness of the image catalog. We describe the analysis strategy on which 2DPHOT is based, and provide a detailed description of the different algorithms implemented in the package. This new environment is intended as a dedicated tool to process the wealth of data from wide-field imaging surveys. To this end, the package is complemented by 2DGUI, an environment that allows multiple processing of data using a range of computing architectures.

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arXiv2008

Global Properties of the Rich Cluster ABCG 209 at z~0.2. Spectroscopic and Photometric Catalogue

This paper is aimed at giving an overview of the global properties of the rich cluster of galaxies ABCG 209. This is achieved by complementing the already available data with new medium resolution spectroscopy and NIR photometry which allow us to i) analyse in detail the cluster dynamics, distinguishing among galaxies belonging to different substructures and deriving their individual velocity distributions, using a total sample of 148 galaxies in the cluster region, of which 134 belonging to the cluster; ii) derive the cluster NIR luminosity function; iii) study the Kormendy relation and the photometric plane of cluster early-type galaxies (ETGs). Finally we provide an extensive photometric (optical and NIR) and spectroscopic dataset for such a complex system to be used in further analyses investigating the nature, formation and evolution of rich clusters of galaxies. The observational scenario confirms that ABCG 209 is presently undergoing strong dynamical evolution with the merging of two or more subclumps. This interpretation is also supported by the detection of a radio halo (Giovannini et al. 2006) suggesting that there is a recent or ongoing merging. Cluster ETGs follow a Kormendy relation whose slope is consistent with previous studies both at optical and NIR wavelengths. We investigate the origin of the intrinsic scatter of the photometric plane due to trends of stellar populations, using line indices as indicators of age, metallicity and alpha/Fe enhancement. We find that the chemical evolution of galaxies could be responsible for the intrinsic dispersion of the Photometric Plane.

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arXiv2007

Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023

We investigate the manner in which lenticular galaxies are formed by studying their stellar kinematics: an S0 formed from a fading spiral galaxy should display similar cold outer disc kinematics to its progenitor, while an S0 formed in a minor merger should be more dominated by random motions. In a pilot study to attempt to distinguish between these scenarios, we have measured the planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the Planetary Nebula Spectrograph, we have detected and measured the line-of-sight velocities of 204 candidate PNe in the field of this galaxy. Out to intermediate radii, the system displays the kinematics of a normal rotationally-supported disc system. After correction of its rotational velocities for asymmetric drift, the galaxy lies just below the spiral galaxy Tully-Fisher relation, as one would expect for a fading system. However, at larger radii the kinematics undergo a gradual but major transition to random motion with little rotation. This transition does not seem to reflect a change in the viewing geometry or the presence of a distinct halo component, since the number counts of PNe follow the same simple exponential decline as the stellar continuum with the same projected disc ellipticity out to large radii. The galaxy's small companion, NGC 1023A, does not seem to be large enough to have caused the observed modification either. This combination of properties would seem to indicate a complex evolutionary history in either the transition to form an S0 or in the past life of the spiral galaxy from which the S0 formed. More data sets of this type from both spirals and S0s are needed in order to definitively determine the relationship between these types of system.

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