Papers by Ana Laura Serra
We explore the possibility of measuring the mass accretion rate (MAR) of galaxy clusters from the... more We explore the possibility of measuring the mass accretion rate (MAR) of galaxy clusters from their mass profiles beyond the virial radius R_200. We derive the accretion rate from the mass of a spherical shell whose inner radius is 2R_200, whose thickness changes with redshift, and whose infall velocity is assumed to be equal to the mean infall velocity of the spherical shells of dark matter halos extracted from N-body simulations. This approximation is rather crude in hierarchical clustering scenarios where both smooth accretion and aggregation of smaller dark matter halos contribute to the mass accretion of clusters.Nevertheless, in the redshift range z=[0,2], our prescription returns an average MAR within 20-40 % of the average rate derived from the merger trees of dark matter halos extracted from N-body simulations. The MAR of galaxy clusters has been the topic of numerous detailed numerical and theoretical investigations, but so far it has remained inaccessible to measurements ...
Using the caustic method, we identify the member stars of five dwarf spheroidal (dSph) galaxies o... more Using the caustic method, we identify the member stars of five dwarf spheroidal (dSph) galaxies of the Milky Way, the smallest dark matter (DM) dominated systems in the Universe. After our interloper rejection, we compute line-of-sight velocity dispersion profiles that are substantially smoother than previous results. Moreover, two dSphs have line-of-sight velocity dispersions 20% smaller than previous calculations suggested. Our Jeans modelling confirms that the DM content interior to 300pc is roughly constant with satellite luminosity. Finally, if we assume that MOND provides the true law of gravity, our identification of interlopers implies that four dSphs have mass-to-light ratios in agreement with stellar population synthesis models, whereas Carina still has a mass-to-light ratio a factor of two too large and remains a problem for MOND.
The Astrophysical Journal, 2018
Astronomy & Astrophysics, 2016
The Astrophysical Journal, 2016
The Astrophysical Journal, 2015
EAS Publications Series, 2014
Although the thick disk in our Galaxy was revealed more than thirty years ago, the formation scen... more Although the thick disk in our Galaxy was revealed more than thirty years ago, the formation scenario is still unclear. Recently, several studies of in-situ thick disk stars have evidenced a positive kinematicmetallicity correlation, dVphi/d[Fe/H] = 40-50 km/s/dex. Such a finding appears consistent with a mild positive radial metallicity gradient, d[Fe/H]/dR, for thick disk stars, which, differently from thin disk stars, show lower chemical abundances towards the inner disk. Here, we discuss these results with respect to the expected evolution of a primordial disk population, as deduced through high resolution N-body simulations of a Milky Way-like disk galaxy. In particular, we analyse how the presence of a central bar may affect the disk evolution from the spatial and chemo-kinematical point of view. Bar vs. disk velocity distribution Our simulations show that the bar produce a thickening in the inner-disk and a flaring in the outer disk (Spagna et al 2015, in preparation). These results are not completely consistent with studies published by other authors (e.g.
Proceedings of the International Astronomical Union, 2014
We examine the evolution induced by secular processes of an initial, cosmologically motivated, ra... more We examine the evolution induced by secular processes of an initial, cosmologically motivated, radial chemical distribution, in a barred and an unbarred disk.
Monthly Notices of the Royal Astronomical Society: Letters, 2014
The Astrophysical Journal, 2013
The caustic technique measures the mass of galaxy clusters in both their virial and infall region... more The caustic technique measures the mass of galaxy clusters in both their virial and infall regions and, as a byproduct, yields the list of cluster galaxy members. Here we use 100 galaxy clusters with mass M 200 ≥ 10 14 h −1 M ⊙ extracted from a cosmological N-body simulation of a ΛCDM universe to test the ability of the caustic technique to identify the cluster galaxy members. We identify the true threedimensional members as the gravitationally bound galaxies. The caustic technique uses the caustic location in the redshift diagram to separate the cluster members from the interlopers. We apply the technique to mock catalogs containing 1000 galaxies in the field of view of 12h −1 Mpc on a side at the cluster location. On average, this sample size roughly corresponds to 180 real galaxy members within 3r 200 , similar to recent redshift surveys of cluster regions. The caustic technique yields a completeness, the fraction of identified true members, f c = 0.95 ± 0.03 within 3r 200. The contamination, the fraction of interlopers in the observed catalog of members, increases from f i = 0.020 +0.046 −0.015 at r 200 to f i = 0.08 +0.11 −0.05 at 3r 200. No other technique for the identification of the members of a galaxy cluster provides such large completeness and small contamination at these large radii. The caustic technique assumes spherical symmetry and the asphericity of the cluster is responsible for most of the spread of the completeness and the contamination. By applying the technique to an approximately spherical system obtained by stacking the individual clusters, the spreads decrease by at least a factor of two. We finally estimate the cluster mass within 3r 200 after removing the interlopers: for individual clusters, the mass estimated with the virial theorem is unbiased and within 30% of the actual mass; this spread decreases to less than 10% for the spherically symmetric stacked cluster.
The Astrophysical Journal, 2014
The Astrophysical Journal, 2013
Context. The cores of clusters at 0 z 1 are dominated by quiescent early-type galaxies, whereas t... more Context. The cores of clusters at 0 z 1 are dominated by quiescent early-type galaxies, whereas the field is dominated by star-forming late-type galaxies. Clusters grow through the accretion of galaxies/groups from the surrounding field, which implies that galaxy properties, notably the star formation ability, are altered as they fall into overdense regions. The critical issues to understand this evolution are how the truncation of star formation is connected to the morphological transformation and what physical mechanism is responsible for these changes. The GaLAxy Cluster Evolution Survey (GLACE) is conducting a thorough study on the variation of galaxy properties (star formation, AGN activity and morphology) as a function of environment in a representative and well-studied sample of clusters. Aims. To address these questions, the GLACE survey is performing a deep panoramic survey of emission line galaxies (ELG), mapping a set of optical lines [O ii], [O iii], Hβ and Hα/[N ii] when possible) in several galaxy clusters at z ∼ 0.40, 0.63 and 0.86.
In this letter we examine the evolution of the radial metallicity gradient induced by secular pro... more In this letter we examine the evolution of the radial metallicity gradient induced by secular processes, in the disk of an N-body Milky Way-like galaxy. We assign a [Fe/H] value to each particle of the simulation according to an initial, cosmologically motivated, radial chemical distribution and let the disk dynamically evolve for 6 Gyr. This direct approach allows us to take into account only the effects of dynamical evolution and to gauge how and to what extent they affect the initial chemical conditions. The initial [Fe/H] distribution increases with R in the inner disk up to R ~ 10 kpc and decreases for larger R. We find that the initial chemical profile does not undergo major transformations after 6 Gyr of dynamical evolution. The final radial chemical gradients predicted by the model in the solar neighborhood are positive and of the same order of those recently observed in the Milky Way thick disk.
We conclude that: 1) the spatial chemical imprint at the time of disk formation is not washed out by secular dynamical processes, and 2) the observed radial gradient may be the dynamical relic of a thick disk originated from a stellar population showing a positive chemical radial gradient in the inner regions.
We present a new deep determination of the spectroscopic LF within the virial radius of the nearb... more We present a new deep determination of the spectroscopic LF within the virial radius of the nearby and massive Abell\,85 (A85) cluster down to the dwarf regime (M* + 6) using VLT/VIMOS spectra for ∼2000 galaxies with mr≤21 mag and ⟨μe,r⟩≤24 mag arcsec−2. The resulting LF from 438 cluster members is best modelled by a double Schechter function due to the presence of a statistically significant upturn at the faint-end. The amplitude of this upturn (αf=−1.58+0.19−0.15), however, is much smaller than that of the SDSS composite photometric cluster LF by Popesso et al. 2006, αf∼ -2. The faint-end slope of the LF in A85 is consistent, within the uncertainties, with that of the field. The red galaxy population dominates the LF at low luminosities, and is the main responsible for the upturn. The fact that the slopes of the spectroscopic LFs in the field and in a cluster as massive as A85 are similar suggests that the cluster environment does not play a major role in determining the abundance of low-mass galaxies.
The caustic technique measures the mass of galaxy clusters in both their virial and infall region... more The caustic technique measures the mass of galaxy clusters in both their virial and infall regions and, as a byproduct, yields the list of cluster galaxy members. Here we use 100 galaxy clusters with mass M200>=1E14 Msun/h extracted from a cosmological N-body simulation of a LambdaCDM universe to test the ability of the caustic technique to identify the cluster galaxy members. We identify the true three-dimensional members as the gravitationally bound galaxies. The caustic technique uses the caustic location in the redshift diagram to separate the cluster members from the interlopers. We apply the technique to mock catalogues containing 1000 galaxies in the field of view of 12 Mpc/h on a side at the cluster location. On average, this sample size roughly corresponds to 180 real galaxy members within 3r200, similar to recent redshift surveys of cluster regions. The caustic technique yields a completeness, the fraction of identified true members, fc=0.95 (+- 0.03) within 3r200. The contamination increases from fi=0.020 (+0.046;-0.015) at r200 to fi=0.08 (+0.11;-0.05) at 3r200. No other technique for the identification of the members of a galaxy cluster provides such large completeness and small contamination at these large radii. The caustic technique assumes spherical symmetry and the asphericity of the cluster is responsible for most of the spread of the completeness and the contamination. By applying the technique to an approximately spherical system obtained by stacking the individual clusters, the spreads decrease by at least a factor of two. We finally estimate the cluster mass within 3r200 after removing the interlopers: for individual clusters, the mass estimated with the virial theorem is unbiased and within 30 per cent of the actual mass; this spread decreases to less than 10 per cent for the spherically symmetric stacked cluster.
Cluster mass profiles are tests of models of structure formation. Only two current observational ... more Cluster mass profiles are tests of models of structure formation. Only two current observational methods of determining the mass profile, gravitational lensing and the caustic technique, are independent of the assumption of dynamical equilibrium. Both techniques enable determination of the extended mass profile at radii beyond the virial radius. For 19 clusters, we compare the mass profile based on the caustic technique with weak lensing measurements taken from the literature. This comparison offers a test of systematic issues in both techniques. Around the virial radius, the two methods of mass estimation agree to within about 30%, consistent with the expected errors in the individual techniques. At small radii, the caustic technique overestimates the mass as expected from numerical simulations. The ratio between the lensing profile and the caustic mass profile at these radii suggests that the weak lensing profiles are a good representation of the true mass profile. At radii larger than the virial radius, the lensing mass profile exceeds the caustic mass profile possibly as a result of contamination of the lensing profile by large-scale structures within the lensing kernel. We highlight the case of the closely neighboring clusters MS0906+11 and A750 to illustrate the potential seriousness of contamination of the the weak lensing signal by unrelated structures.
Monthly Notices of The Royal Astronomical Society, 2011
The nature of the dominant component of galaxies and clusters remains unknown. While the astrophy... more The nature of the dominant component of galaxies and clusters remains unknown. While the astrophysics community supports the cold dark matter (CDM) paradigm as a clue factor in the current cosmological model, no direct CDM detections have been performed. Faber & Visser have suggested a simple method for measuring the dark matter equation of state that combines kinematic and gravitational lensing data to test the widely adopted assumption of pressureless dark matter. Following this formalism, we have measured the dark matter equation of state for the first time using improved techniques. We have found that the value of the equation-of-state parameter is consistent with pressureless dark matter within the errors. Nevertheless, the measured value is lower than expected because, typically, the masses determined with lensing are larger than those obtained through kinematic methods. We have tested our techniques using simulations and we have also analysed possible sources of error that could invalidate or mimic our results. In light of this result, we can now suggest that understanding the nature of requires a complete general relativistic analysis.
Astronomy & Astrophysics, 2009
Using the caustic method, we identify the member stars of five dwarf spheroidal (dSph) galaxies o... more Using the caustic method, we identify the member stars of five dwarf spheroidal (dSph) galaxies of the Milky Way, the smallest dark matter (DM) dominated systems in the Universe. After our interloper rejection, we compute line-of-sight velocity dispersion profiles that are substantially smoother than previous results. Moreover, two dSphs have line-of-sight velocity dispersions 20% smaller than previous calculations suggested. Our Jeans modelling confirms that the DM content interior to 300pc is roughly constant with satellite luminosity. Finally, if we assume that MOND provides the true law of gravity, our identification of interlopers implies that four dSphs have mass-to-light ratios in agreement with stellar population synthesis models, whereas Carina still has a mass-to-light ratio a factor of two too large and remains a problem for MOND.
Monthly Notices of The Royal Astronomical Society, 2011
The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profile... more The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic technique to clusters with mass M_200>=10^{14}h^{-1} M_sun extracted from a cosmological hydrodynamic simulation of a LambdaCDM universe. With a few tens of redshifts per squared comoving megaparsec within the cluster, the caustic technique, on average, recovers the profile of the escape velocity from the cluster with better than 10 percent accuracy up to r~4 r_200. The caustic technique also recovers the mass profile with better than 10 percent accuracy in the range (0.6-4) r_200, but it overestimates the mass up to 70 percent at smaller radii. This overestimate is a consequence of neglecting the radial dependence of the filling function F_beta(r). The 1-sigma uncertainty on individual escape velocity profiles increases from ~20 to ~50 percent when the radius increases from r~0.1 r_200 to ~4 r_200. Individual mass profiles have 1-sigma uncertainty between 40 and 80 percent within the radial range (0.6-4) r_200. We show that the amplitude of these uncertainties is completely due to the assumption of spherical symmetry, which is difficult to drop. Alternatively, we can apply the technique to synthetic clusters obtained by stacking individual clusters: in this case, the 1-sigma uncertainty on the escape velocity profile is smaller than 20 percent out to 4 r_200. The caustic technique thus provides reliable average profiles which extend to regions difficult or impossible to probe with other techniques.
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Papers by Ana Laura Serra
We conclude that: 1) the spatial chemical imprint at the time of disk formation is not washed out by secular dynamical processes, and 2) the observed radial gradient may be the dynamical relic of a thick disk originated from a stellar population showing a positive chemical radial gradient in the inner regions.
We conclude that: 1) the spatial chemical imprint at the time of disk formation is not washed out by secular dynamical processes, and 2) the observed radial gradient may be the dynamical relic of a thick disk originated from a stellar population showing a positive chemical radial gradient in the inner regions.