arXiv subjects

G. Chincarini

Publications and source records attributed to G. Chincarini.

At least 163 records · Page 9Linked to original sources

arXiv2003

SN 2002lt and GRB 021211: a SN/GRB Connection at z = 1

We present spectroscopic and photometric observations of the afterglow of GRB 021211 and the discovery of its associated supernova, SN 2002lt. The spectrum shows a broad feature (FWHM = 150 A), around 3770 A (in the rest-frame of the GRB), which we interpret as Ca H+K blueshifted by 14400 km/s. Potential sources of contamination due to the host galaxy and/or residuals of telluric absorption have been analyzed and ruled out. Overall, the spectrum shows a suggestive resemblance with the one of the prototypical type-Ic SN 1994I. This might indicate that GRBs are produced also by standard type-Ic supernovae.

astro-ph↗

arXiv2003

Dust and dark Gamma-Ray Bursts: mutual implications

In a cosmological context dust has been always poorly understood. That is true also for the statistic of GRBs so that we started a program to understand its role both in relation to GRBs and in function of z. This paper presents a composite model in this direction. The model considers a rather generic distribution of dust in a spiral galaxy and considers the effect of changing some of the parameters characterizing the dust grains, size in particular. We first simulated 500 GRBs distributed as the host galaxy mass distribution, using as model the Milky Way. If we consider dust with the same properties as that we observe in the Milky Way, we find that due to absorption we miss about 10% of the afterglows assuming we observe the event within about 1 hour or even within 100s. In our second set of simulations we placed GRBs randomly inside giants molecular clouds, considering different kinds of dust inside and outside the host cloud and the effect of dust sublimation caused by the GRB inside the clouds. In this case absorption is mainly due to the host cloud and the physical properties of dust play a strong role. Computations from this model agree with the hypothesis of host galaxies with extinction curve similar to that of the Small Magellanic Cloud, whereas the host cloud could be also characterized by dust with larger grains. To confirm our findings we need a set of homogeneous infrared observations. The use of coming dedicated infrared telescopes, like REM, will provide a wealth of cases of new afterglow observations.

astro-ph↗

arXiv2003

Comparison of two optical cluster finding algorithms for the new generation of deep galaxy surveys

We present a comparison between two optical cluster finding methods: a matched filter algorithm using galaxy angular coordinates and magnitudes, and a percolation algorithm using also redshift information. We test the algorithms on two mock catalogues. The first mock catalogue is built by adding clusters to a Poissonian background, while the other is derived from N-body simulations. Choosing the physically most sensible parameters for each method, we carry out a detailed comparison and investigate advantages and limits of each algorithm, showing the possible biases on final results. We show that, combining the two methods, we are able to detect a large part of the structures, thus pointing out the need to search for clusters in different ways in order to build complete and unbiased samples of clusters, to be used for statistical and cosmological studies. In addition, our results show the importance of testing cluster finding algorithms on different kinds of mock catalogues to have a complete assessment of their behaviour.

astro-ph↗

arXiv2003

The Luminosity Function of Cluster Galaxies. III

We investigated the optical properties of 7 clusters of galaxies observed in three colors over the range of absolute magnitudes -24 < M < -12. Our aim is to estimate the Luminosity Function and the total cluster luminosity of our sample in order to have information about the formation and the evolution of galaxies in clusters. In this paper, we present the main points of our analysis and give the formal parameters obtained by fitting the data using the maximum likelihood algorithm. We find consistency between our results and other works in literature confirming the bimodal nature of the luminosity function of cluster galaxies. More important, we find that the relation L_opt/ L_X versus L_X is color dependent: Low X ray Luminosity clusters have a bluer galaxy population.

astro-ph↗

arXiv2003

Evidence for Supernova Signatures in the Spectrum of the Late-time Bump of the Optical Afterglow of GRB 021211

We present photometric and spectroscopic observations of the gamma-ray burst GRB 021211 obtained during the late stages of its afterglow. The light curve shows a rebrightening occurring ~25 days after the GRB. The analysis of a VLT spectrum obtained during the bump (27 days after the GRB) reveals a suggestive resemblance with the spectrum of the prototypical type-Ic SN 1994I, obtained about ~10 days past maximum light. Particularly we have measured a strong, broad absorption feature at 3770 A, which we have identified with Ca II blueshifted by ~14400 km/s, thus indicating that a supernova (SN) component is indeed powering the `bump' in the afterglow decay. Assuming SN 1994I as a template, the spectroscopic and photometric data together indicate that the SN and GRB explosions were at most separated by a few days. Our results suggest that GRBs might be associated also to standard type-Ic supernovae.

astro-ph↗

arXiv2002

Halpha rotation curves: the soft core question

We present high resolution Halpha rotation curves of 4 late-type dwarf galaxies and 2 low surface brightness galaxies (LSB) for which accurate HI rotation curves are available from the literature. Observations are carried out at Telescopio Nazionale Galileo (TNG). For LSB F583-1 an innovative dispersing element was used, the Volume Phase Holographic (VPH) with a dispersion of about 0.35 A/pxl. We find good agreement between the Halpha data and the HI observations and conclude that the HI data for these galaxies suffer very little from beam smearing. We show that the optical rotation curves of these dark matter dominated galaxies are best fitted by the Burkert profile. In the centers of galaxies, where the N-body simulations predict cuspy cores and fast rising rotation curves, our data seem to be in better agreement with the presence of soft cores.

astro-ph↗

arXiv2002

The REM Telescope: Detecting the Near Infra-Red Counterparts of Gamma-Ray Bursts and the Prompt Behaviour of Their Optical Continuum

Observations of the prompt afterglow of Gamma Ray Burst events are unanimously considered of paramount importance for GRB science and related cosmology. Such observations at NIR wavelengths are even more promising allowing one to monitor high-z Ly-alpha absorbed bursts as well as events occurring in dusty star-forming regions. In these pages we present REM (Rapid Eye Mount), a fully robotized fast slewing telescope equipped with a high throughput NIR (Z', J, H, K') camera dedicated to detecting the prompt IR afterglow. REM can discover objects at extremely high red-shift and trigger large telescopes to observe them. The REM telescope will simultaneously feed ROSS (REM Optical Slitless spectrograph) via a dichroic. ROSS will intensively monitor the prompt optical continuum of GRB afterglows. The synergy between REM-IR cam and ROSS makes REM a powerful observing tool for any kind of fast transient phenomena.

astro-ph↗

arXiv2001

Dark Matter in the center of galaxies and galaxy clusters: ruling out the CDM scenario?

This work is focused on the preliminary results of the observations of Hαrotation curves for some of the late type dwarf and LSB galaxies carried out at the TNG telescope. In light of the observational data and of the N-body simulations we have performed recently, we discuss some of the implications on the nature of the DM particles and the formation of the dark haloes.

astro-ph↗

arXiv2001

Soft Cores in Late-Type Dwarf and LSB Galaxies from HαObservations

We present high spatial resolution Hαrotation curves of late-type dwarf and LSB galaxies. From our analysis we find good agreement between our Hαdata and the HI observations taken from the literature, concluding that the HI rotation curves for these galaxies suffer very little from beam smearing. A preliminary analysis of our data rules out the CDM model in the inner regions of these galaxies.

astro-ph↗

arXiv2001

The REFLEX Galaxy Cluster Survey IV: The X-ray Luminosity Function

The X-ray galaxy cluster sample from the REFLEX Cluster Survey, which covers the X-ray brightest galaxy clusters detected in the ROSAT All-Sky Survey in the southern sky, is used to construct the X-ray luminosity function of clusters in the local Universe. With 452 clusters detected above an X-ray flux-limit of 3 10^(-12) erg s^(-1) cm^(-2) in 4.24 sr of the sky, this sample is the most comprehensive X-ray cluster sample with a well documented selection function, providing the best current census of the local X-ray galaxy cluster population. In this paper we discuss the construction of the luminosity function, the effects of flux measurement errors and of variations with sample region and we compare the results to those from previous surveys.

astro-ph↗

arXiv2001

The VIRMOS-VLT Deep Survey

The aim of the VIRMOS VLT Deep Survey (VVDS) is to study of the evolution of galaxies, large scale structures and AGNs from a sample of more than 150,000 galaxies with measured redshifts in the range 0<z<5+. The VVDS will rely on the VIMOS and NIRMOS wide field multi-object spectrographs, which the VIRMOS consortium is delivering to ESO. Together, they offer unprecedented multiplex capability in the wavelength range 0.37-1.8microns, allowing for large surveys to be carried out. The VVDS has several main aspects: (1) a deep multi-color imaging survey over 18deg^2 of more than one million galaxies, (2) a "wide" spectroscopic survey with more than 130,000 redshifts measured for objects brighter than IAB=22.5 over 18deg^2, (3) a "deep" survey with 50,000 redshifts measured to IAB=24, (4) ultra-deep" surveys with several thousand redshifts measured to IAB=25, (5) multi-wavelength observations with the VLA and XMM.

astro-ph↗

arXiv2000

The ROSAT-ESO Flux Limited X-Ray (REFLEX) Galaxy Cluster Survey I: The Construction of the Cluster Sample

We describe the construction of an X-ray flux-limited sample of galaxy clusters, the REFLEX survey catalogue, to be used for cosmological studies. The survey is based on the ROSAT All-Sky Survey and on extensive follow-up observations conducted in the frame of an ESO key program. In the paper we document the process by which the primary cluster candidate catalogue is constructed prior to the optical follow-up observations. We describe the reanalysis of the RASS source catalogue which enables us to impose a proper flux limit cut to the X-ray source list without introducing a severe bias against extended sources. We discuss the correlation of the X-ray and optical (COSMOS) data to find galaxy density enhancements at the RASS X-ray source positions and the further evaluation of the nature of these cluster candidates. Based also on the results of the follow-up observations we provide a statistical analysis of the completeness and contamination of the final cluster sample and show results on the cluster number counts. The final sample of identified X-ray clusters reaches a flux limit of 3e-12 erg s-1 cm-2 in the 0.1 - 2.4 keV band and comprises 452 clusters. The results imply a completeness of the REFLEX cluster sample well in excess of 90% and a contamination by non-cluster X-ray sources of less than 9%, an accuracy sufficient for the use of this cluster sample for cosmological tests.

astro-ph↗

arXiv2000

Modelling Self-Interacting CDM Haloes with a Cosmological Boltzmann Code

We investigate the density profiles and evolution of weakly self-interacting cold dark matter haloes using a numerical code based on the collisional Boltzmann equation. This approach is alternative to N-body techniques in following the dynamical evolution of haloes in the cosmological context and taking into account particle self-interaction. The physical case with a cross section inversely proportional to the relative velocity of the colliding particles is modelled with an unprecedented resolution, spanning five orders of magnitude on the radius for each halo. The modelled haloes cover a mass range from dwarf galaxies to galaxy clusters. We find that for σv_{100} \approx 10^{-24} cm^2/GeV, where σis the cross section per unit mass and v_{100} is the collision velocity in units of 100 km/s, soft cores in good agreement with observations on galactic as well as on galaxy cluster scales are obtained. Remarkably, the observed nearly invariance of the halo central density with mass is reproduced.

astro-ph↗

arXiv2000

Constraints on dark matter physics from dwarf galaxies through galaxy cluster haloes

One of the predictions of the standard CDM is that dark haloes have centrally divergent density profiles. An extensive body of rotation curve observations of dwarf and low surface brightness galaxies shows the dark haloes of those systems to be characterized by soft constant density central cores. Several physical processes have been proposed to produce soft cores in dark haloes, each one with different scaling properties. With the aim of discriminating among them we have examined the rotation curves of dark matter dominated dwarf and low surface brightness galaxies and the inner mass profiles of two clusters of galaxies lacking a central cD galaxy and with evidence of soft cores in the centre. The core radii and central densities of these haloes scale in a well defined manner with the depth of their potential wells, as measured through the maximum circular velocity. As a result of our analysis we identify self-interacting CDM as a viable solution to the core problem, where a non-singular isothermal core is formed in the halo center surrounded by a Navarro, Frenk, & White profile in the outer parts. We show that this particular physical situation predicts core radii in agreement with observations. Furthermore, using the observed scalings, we derive an expression for the minimum cross section (σ) which has an explicit dependence with the halo dispersion velocity (v). If m_x is the mass of the dark matter particle: σ/m_x ~4 10^-25 (v/100 km s^-1)^-1 cm^2/Gev.

astro-ph↗

arXiv2000

The ROSAT-ESO Flux Limited X-ray (REFLEX) Galaxy Cluster Survey II: The Spatial Correlation Function

We report the results of the spatial two-point correlation function xi(r) for the new X-ray galaxy cluster survey REFLEX, which comprises of 452 X-ray selected clusters (449 with redshifts) detected by the ROSAT satellite during the ROSAT All-Sky-Survey. The REFLEX cluster sample is flux limited to 3x10^{-12} erg s^{-1} cm^{-2} in the ROSAT energy band (0.1-2.4 keV) and spans 3 decades in X-ray luminosity (10^{42} - 10^{45} h^{-2} erg s^{-1}), containing galaxy groups and rich clusters out to a redshift z~0.3. Covering a contiguous area of 4.24 sr REFLEX is the largest X-ray cluster sample to date for which spatial clustering has been analysed. Correlation studies using clusters selected on the basis of their X-ray emission are particularly interesting as they are largely free from the projection biases inherent to optical studies. For the entire flux-limited sample we find that the correlation length (the scale at which the correlation amplitude passes through unity) r_0~20 h^{-1}Mpc. For example, if a power-law fit is made to xi(r) over the range 4-40 h^{-1} Mpc then r_0=18.8+-0.9. An indication of the robustness of this result comes from the high degree of isotropy seen in the clustering pattern on scales close to the correlation length. On larger scales xi(r) deviates from a power-law, crossing zero at ~45h^{-1} Mpc. From an examination of 5 volume-limited cluster sub-samples we find no significant trend of r_0 with limiting X-ray luminosity. A comparison with recent model predictions for the clustering properties of X-ray flux-limited samples, indicates that Cold Dark Matter models with the matter density Omega_m=1 fail to produce sufficient clustering to account for the data, while Omega_m~0.3 models provide an excellent fit.

astro-ph↗

arXiv2000

Interpreting the optical data of the Hubble Deep Field South: colors, morphological number counts and photometric redshifts

We present an analysis of the optical data of the Hubble Deep Field South. We derive F300W(AB), F450W(AB), F606W(AB) and F814W(AB) number counts for galaxies in all four bands. The slope is steeper at shortest wavelengths: we estimated gamma(F300W(AB))=0.47, gamma(F450W(AB))=0.35, gamma(F606W(AB))=0.28 and gamma(F814W(AB))=0.28. Morphological number counts are actually dominated by late type galaxies, while early type galaxies show a decreasing slope at faint magnitudes. Combining this information with photometric redshifts, we notice that galaxies contributing with a steep slope to morphological number counts (i.e. spiral and irregular galaxies) have z>1, suggesting a moderate merging. However we emphasize that any cut in apparent magnitude at optical wavelengths results in samples biased against elliptical galaxies, affecting as a consequence the redshift distributions and the implications on the evolution of galaxies along the Hubble sequence.

astro-ph↗

arXiv2000

EISily looking for distant clusters of galaxies - - a new algorithm and its application to the EIS-wide data

We present a new algorithm to search for distant clusters of galaxies on catalogues deriving from imaging data, as those of the ESO Imaging Survey. Our algorithm is a matched filter one, similar to that adopted by Postman et al. (1996), aiming at identifying cluster candidates by using positional and photometric data simultaneously. The main novelty of our approach is that spatial and luminosity filter are run separately on the catalogue and no assumption is made on the typical size nor on the typical M* for clusters, as these parameters intervene in our algorithm as typical angular scale (sigma) and typical apparent magnitude m*. Moreover we estimate the background locally for each candidate, allowing us to overcome the hazards of inhomogeneous datasets. As a consequence our algorithm has a lower contamination rate - without loss of completeness - in comparison to other techniques, as tested through extensive simulations. We provide catalogues of galaxy cluster candidates as the result of applying our algorithm to the I-band data of the EIS-wide patches A and B.

astro-ph↗

arXiv2000

Evidence of self-interacting cold dark matter from galactic to galaxy cluster scales

Within the framework of the cold dark matter (CDM) cosmogony, a central cusp in the density profiles of virialized dark haloes is predicted. This prediction disagrees with the soft inner halo mass distribution inferred from observations of dwarf and low surface brightness galaxies, and some clusters of galaxies. By analysing data for some of these objects, we find that the halo central density is nearly independent of the mass from galactic to galaxy cluster scales with an average value of around 0.02 M_sun/pc^3. We show that soft cores can be produced in the CDM haloes by introducing a lower cut-off in the power spectra of fluctuations and assuming high orbital thermal energies during halo formation. However, the scale invariance of the halo central density is not reproduced in these cases. The introduction of self-interaction in the CDM particles offers the most attractive alternative to the core problem. We propose gravothermal expansion as a possible mechanism to produce soft cores in the CDM haloes with self-interacting particles. A global thermodynamical equilibrium can explain the central density scale invariance. We find a minimum cross section capable of establishing isothermal cores in agreement with the observed shallow cores. If σand m_x are the cross section and mass of the dark matter particle, and v is the halo velocity dispersion, then (σ/m_x) \~ 4 10^{-25} (100 km s^{-1}/v) cm^2/GeV.

astro-ph↗