Sophie Maurogordato - Academia.edu (original) (raw)

Papers by Sophie Maurogordato

Astronomy & Astrophysics, 1988

The authors present multicolor surface photometry of a sample of blue compact galaxies with reces... more The authors present multicolor surface photometry of a sample of blue compact galaxies with recession velocities close to 1000 km s-1. These galaxies are dwarfs undergoing strong star formation activity. They may be genuine young galaxies. It is been found that the star formation knots are close to the centers of these galaxies and sequentially ordered in space from the

Multicolor surface photometry performed on a selected sample of nearby (V ≡ 1000 km/s) blue compa... more Multicolor surface photometry performed on a selected sample of nearby (V ≡ 1000 km/s) blue compact galaxies shows that this galaxy class contains very different objects: interacting galaxies, irregular, or elliptical-like galaxies. Only some of them have small sizes (<2 kpc) and can be suspected to be genuine young galaxies. In the largest ones, in addition to the previously known

The analysis of the Southern Sky Redshift Survey 2 has shown that the galaxy correlation length i... more The analysis of the Southern Sky Redshift Survey 2 has shown that the galaxy correlation length increases with galaxy luminosity for L > L*. The correlation length of Very Luminous Galaxies (defined as MB 4L*), r0 ~ 16± 2h-1 Mpc, is even comparable to r0 of clusters. Nevertheless, we have shown that most VLGs are not early type galaxies in clusters, and that in many cases they appear to interact with nearby fainter galaxies. Visual inspection of fields around VLGs suggests that many VLGs are the brightest members of systems with much fainter galaxies; this seems an effective way of identifying galaxy systems which cannot be selected by traditional group finding algorithms. The study of VLGs may contribute to our understanding of the halo-galaxy connection and galaxy evolution. Here we resumetyheir main properties and present some results from our observations of a few VLG systems.

Astronomy and Astrophysics, Mar 1, 2000

We present the results of a dynamical analysis of the rich X-Ray luminous galaxy cluster Abell 52... more We present the results of a dynamical analysis of the rich X-Ray luminous galaxy cluster Abell 521, and discuss the nature of the arc-like structure first noted by Maurogordato et al. (1996). Our study is based on radial velocities for 41 cluster members, measured from spectra obtained at the European Southern Observatory and the Canada-France-Hawaii Telescope. Based on statistical analyses performed with the ROSTAT package, we find that Abell 521 is an intermediate-redshift cluster (C BI = 74132 +202 −250 km/s) with a rather high apparent value of the velocity dispersion S BI = 1386 +206 −139 km/s. There are many indications that this cluster is presently undergoing strong dynamical evolution: a) the high value of the velocity dispersion, which cannot be explained by trivial projection effects, b) signific ant clumping in the two-dimensional projected positions of the galaxies in the cluster, quantified by a mixture-model three-group partition significant at 99 % level, c) the extreme value of the velocity dispersion (σ ∼ 2000 km/s) in a central high density NE/SW structure, d) a strong increase of the velocity dispersion as determined from the reddest and bluest galaxies, suggesting that cluster spirals are not yet virialized; e) the presence of multiple nuclei in the core of the brightest cluster galaxy , one of which has a statistically significant velocity offset from the rest of the cluster members, and f) an apparently different stellar population for the various knots of the arc candidate which changes along the structure. The two brightest knots of the giant arc candidate are shown to be at the velocity of the cluster. This makes the

arXiv: Cosmology and Nongalactic Astrophysics, 2019

Modern galaxy cluster science is a multi-wavelength endeavor with cornerstones provided by X-ray,... more Modern galaxy cluster science is a multi-wavelength endeavor with cornerstones provided by X-ray, optical/IR, mm, and radio measurements. In combination, these observations enable the construction of large, clean, complete cluster catalogs, and provide precise redshifts and robust mass calibration. The complementary nature of these multi-wavelength data dramatically reduces the impact of systematic effects that limit the utility of measurements made in any single waveband. The future of multi-wavelength cluster science is compelling, with cluster catalogs set to expand by orders of magnitude in size, and extend, for the first time, into the high-redshift regime where massive, virialized structures first formed. Unlocking astrophysical and cosmological insight from the coming catalogs will require new observing facilities that combine high spatial and spectral resolution with large collecting areas, as well as concurrent advances in simulation modeling campaigns. Together, future mul...

arXiv: Instrumentation and Methods for Astrophysics, 2020

MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction... more MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 micron wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue.

arXiv: Astrophysics of Galaxies, 2020

The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity... more The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity, broad simultaneous spectral coverage (from optical to near-infrared bands), large patrol area and high fibre density. These properties provide the unprecedented potential of enabling, for the very first time, SDSS-like surveys around Cosmic Noon (z~1-2.5), when the star formation rate in the Universe peaked. The high-quality spectra delivered by MOONS will sample the same nebular and stellar diagnostics observed in extensive surveys of local galaxies, providing an accurate and consistent description of the evolution of various physical properties of galaxies, and hence a solid test of different scenarios of galaxy formation and transformation. Most importantly, by spectroscopically identifying hundreds of thousands of galaxies at high redshift, the MOONS surveys will be capable of determining the environments in which primeval galaxies lived and will reveal how such environments affect...

Astronomy & Astrophysics, 2017

Context. The next generation of galaxy surveys will provide cluster catalogues probing an unprece... more Context. The next generation of galaxy surveys will provide cluster catalogues probing an unprecedented range of scales, redshifts, and masses with large statistics. Their analysis should therefore enable us to probe the spatial distribution of clusters with high accuracy and derive tighter constraints on the cosmological parameters and the dark energy equation of state. However, for the majority of these surveys, redshifts of individual galaxies will be mostly estimated by multiband photometry which implies nonnegligible errors in redshift resulting in potential difficulties in recovering the real-space clustering. Aims. We investigate to which accuracy it is possible to recover the real-space two-point correlation function of galaxy clusters from cluster catalogues based on photometric redshifts, and test our ability to detect and measure the redshift and mass evolution of the correlation length r 0 and of the bias parameter b(M, z) as a function of the uncertainty on the cluster redshift estimate. Methods. We calculate the correlation function for cluster sub-samples covering various mass and redshift bins selected from a 500 deg 2 light-cone limited to H < 24. In order to simulate the distribution of clusters in photometric redshift space, we assign to each cluster a redshift randomly extracted from a Gaussian distribution having a mean equal to the cluster cosmological redshift and a dispersion equal to σ z. The dispersion is varied in the range σ (z=0) = σz 1+zc = 0.005, 0.010, 0.030 and 0.050, in order to cover the typical values expected in forthcoming surveys. The correlation function in real-space is then computed through estimation and deprojection of w p (r p). Four mass ranges (from M halo > 2 × 10 13 h −1 M to M halo > 2 × 10 14 h −1 M) and six redshift slices covering the redshift range [0, 2] are investigated, first using cosmological redshifts and then for the four photometric redshift configurations. Results. From the analysis of the light-cone in cosmological redshifts we find a clear increase of the correlation amplitude as a function of redshift and mass. The evolution of the derived bias parameter b(M, z) is in fair agreement with theoretical expectations. We calculate the r 0 − d relation up to our highest mass, highest redshift sample tested (z = 2, M halo > 2 × 10 14 h −1 M). From our pilot sample limited to M halo > 5 × 10 13 h −1 M (0.4 < z < 0.7), we find that the real-space correlation function can be recovered by deprojection of w p (r p) within an accuracy of 5% for σ z = 0.001 × (1 + z c) and within 10% for σ z = 0.03 × (1 + z c). For higher dispersions (besides σ z > 0.05 × (1 + z c)), the recovery becomes noisy and difficult. The evolution of the correlation in redshift and mass is clearly detected for all σ z tested, but requires a large binning in redshift to be detected significantly between individual redshift slices when increasing σ z. The best-fit parameters (r 0 and γ) as well as the bias obtained from the deprojection method for all σ z are within the 1σ uncertainty of the z c sample.

Astronomy & Astrophysics, 2017

Measurement of the gas velocity distribution in galaxy clusters provides insight into the physics... more Measurement of the gas velocity distribution in galaxy clusters provides insight into the physics of mergers, through which large scale structures form in the Universe. Velocity estimates within the intracluster medium (ICM) can be obtained via the Sunyaev-Zel’dovich (SZ) effect, but its observation is challenging both in term of sensitivity requirement and control of systematic effects, including the removal of contaminants. In this paper we report resolved observations, at 150 and 260 GHz, of the SZ effect toward the triple merger MACS J0717.5+3745 (z = 0.55), using data obtained with the NIKA camera at the IRAM 30 m telescope. Assuming that theSZ signal is the sum of a thermal (tSZ) and a kinetic (kSZ) component and by combining the two NIKA bands, we extract for the first time a resolved map of the kSZ signal in a cluster. The kSZ signal is dominated by a dipolar structure that peaks at −5.1 and + 3.4σ, corresponding to two subclusters moving respectively away and toward us and ...

Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are i... more Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are interesting per se, since their detailed analysis allows us to understand how galaxies form and evolve in various environments and second, they play an important part in cosmology because their number as a function of redshift gives constraints on cosmological parameters. Aims. We have searched for galaxy clusters in the Stripe 82 region of the Sloan Digital Sky Survey, and analysed various properties of the cluster galaxies. Methods. Based on a recent photometric redshift (hereafter photo−z) galaxy catalogue, we built a cluster catalogue by applying the Adami & MAzure Cluster FInder (AMACFI). Extensive tests were made to fine-tune the AMACFI parameters and make the cluster detection as reliable as possible. The same method was applied to the Millennium simulation to estimate our detection efficiency and the approximate masses of the detected clusters. Considering all the cluster galaxies (i.e. within a 1 Mpc radius of the cluster to which they belong and with a photo−z differing by less than ±0.05 from that of the cluster), we stacked clusters in various redshift bins to derive colour-magnitude diagrams and galaxy luminosity functions (GLFs). For each galaxy brighter than M r < −19.0, we computed the disk and spheroid components by applying SExtractor, and by stacking clusters we determined how the disk-to-spheroid flux ratio varies with cluster redshift and mass. Results. We detected 3663 clusters in the redshift range 0.15 ≤ z ≤ 0.70, with estimated mean masses between ∼ 10 13 and a few 10 14 M. We cross-matched our catalogue of candidate clusters with various catalogues extracted from optical and/or X-ray data. The percentages of redetected clusters are at most 40% because in all cases we detect relatively massive clusters, while other authors detect less massive structures. By stacking the cluster galaxies in various redshift bins, we find a clear red sequence in the (g − r) versus r colour-magnitude diagrams, and the GLFs are typical of clusters, though with a possible contamination from field galaxies. The morphological analysis of the cluster galaxies shows that the fraction of late-type to early-type galaxies shows an increase with redshift (particularly in 9σ clusters) and a decrease with detection level, i.e. cluster mass. Conclusions. From the properties of the cluster galaxies, the majority of the candidate clusters detected here seem to be real clusters with typical cluster properties.

Astronomy & Astrophysics, 2016

Context. This article belongs to the first series of XXL publications. It presents multifibre spe... more Context. This article belongs to the first series of XXL publications. It presents multifibre spectroscopic observations of three 0.55 deg 2 fields in the XXL Survey, which were selected on the basis of their high density of X-ray-detected clusters. The observations were obtained with the AutoFib2+WYFFOS (AF2) wide-field fibre spectrograph mounted on the 4.2 m William Herschel Telescope. Aims. The paper first describes the scientific rationale, the preparation, the data reduction, and the results of the observations, and then presents a study of active galactic nuclei (AGN) within three superclusters. Methods. To determine the redshift of galaxy clusters and AGN, we assign high priority to a) the brightest cluster galaxies (BCGs), b) the most probable cluster galaxy candidates, and c) the optical counterparts of X-ray point-like sources. We use the outcome of the observations to study the projected (2D) and the spatial (3D) overdensity of AGN in three superclusters. Results. We obtained redshifts for 455 galaxies in total, 56 of which are counterparts of X-ray point-like sources. We were able to determine the redshift of the merging supercluster XLSSC-e, which consists of six individual clusters at z ∼ 0.43, and we confirmed the redshift of supercluster XLSSC-d at z ∼ 0.3. More importantly, we discovered a new supercluster, XLSSC-f, that comprises three galaxy clusters also at z ∼ 0.3. We find a significant 2D overdensity of X-ray point-like sources only around the supercluster XLSSC-f. This result is also supported by the spatial (3D) analysis of XLSSC-f, where we find four AGN with compatible spectroscopic redshifts and possibly one more with compatible photometric redshift. In addition, we find two AGN (3D analysis) at the redshift of XLSSC-e, but no AGN in XLSSC-d. Comparing these findings with the optical galaxy overdensity we conclude that the total number of AGN in the area of the three superclusters significantly exceeds the field expectations. All of the AGN found have luminosities below 7 × 10 42 erg s −1. Conclusions. The difference in the AGN frequency between the three superclusters cannot be explained by the present study because of small number statistics. Further analysis of a larger number of superclusters within the 50 deg 2 of the XXL is needed before any conclusions on the effect of the supercluster environment on AGN can be reached.

Proceedings of the International Astronomical Union, 2004

We present the analysis and results of a new spectroscopic and photometric survey of the central ... more We present the analysis and results of a new spectroscopic and photometric survey of the central 1.5 Mpc 2 region of the galaxy cluster A3921 (z=0.094). We detect the presence of two dominant clumps of galaxies with a mass ratio of ∼4-5: a main cluster centered on the BCG (A3921-A), and a NW sub-cluster (A3921-B) hosting the second brightest cluster object. By comparing optical results to the X-ray analysis of XMM observations (Belsole et al. 2004), we find that A3921-B is tangentially traversing the main cluster along a SW/NE direction. The analysis of stellar populations of more than one hundred cluster members reveals that the merger event has probably affected the kinematics and spectral properties of the active galaxies in A3921.

Astronomy from Wide-Field Imaging, 1994

We present preliminary results of a galaxy redshift survey we are accomplishing as an ESO Key Pro... more We present preliminary results of a galaxy redshift survey we are accomplishing as an ESO Key Project over about 40 square degrees in a region near the South Galactic Pole, to a limiting magnitude bj = 19.4. Up to now ~ 50% of the survey has been completed, providing about 2000 galaxy redshifts.

Astronomy & Astrophysics, 2015

Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are i... more Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are interesting per se, since their detailed analysis allows us to understand how galaxies form and evolve in various environments and second, they play an important part in cosmology because their number as a function of redshift gives constraints on cosmological parameters. Aims. We have searched for galaxy clusters in the Stripe 82 region of the Sloan Digital Sky Survey, and analysed various properties of the cluster galaxies. Methods. Based on a recent photometric redshift (hereafter photo-z) galaxy catalogue, we built a cluster catalogue by applying the Adami & MAzure Cluster FInder (AMACFI). Extensive tests were made to fine-tune the AMACFI parameters and make the cluster detection as reliable as possible. The same method was applied to the Millennium simulation to estimate our detection efficiency and the approximate masses of the detected clusters. Considering all the cluster galaxies (i.e. within a 1 Mpc radius of the cluster to which they belong and with a photo-z differing by less than ±0.05 from that of the cluster), we stacked clusters in various redshift bins to derive colour-magnitude diagrams and galaxy luminosity functions (GLFs). For each galaxy brighter than M r < −19.0, we computed the disk and spheroid components by applying SExtractor, and by stacking clusters we determined how the disk-to-spheroid flux ratio varies with cluster redshift and mass. Results. We detected 3663 clusters in the redshift range 0.15 ≤ z ≤ 0.70, with estimated mean masses between ∼10 13 and a few 10 14 M. We cross-matched our catalogue of candidate clusters with various catalogues extracted from optical and/or X-ray data. The percentages of redetected clusters are at most 40% because in all cases we detect relatively massive clusters, while other authors detect less massive structures. By stacking the cluster galaxies in various redshift bins, we find a clear red sequence in the (g − r) versus r colour−magnitude diagrams, and the GLFs are typical of clusters, though with a possible contamination from field galaxies. The morphological analysis of the cluster galaxies shows that the fraction of late-type to early-type galaxies shows an increase with redshift (particularly in 9σ clusters) and a decrease with detection level, i.e. cluster mass. Conclusions. From the properties of the cluster galaxies, the majority of the candidate clusters detected here seem to be real clusters with typical cluster properties.

Observational Cosmology, 1987

Recent results concerning the galaxy distribution at scales < 100 h"" 1 Mpc (H Q = 100 h kms" Mpc... more Recent results concerning the galaxy distribution at scales < 100 h"" 1 Mpc (H Q = 100 h kms" Mpc") show a number of characteristics which cannot be described by conventional statistical models. Correlation functions, for instance, can in no way give account of the presence of voids of the cellular (or spongy) appearance of the local galaxy distribution (M. Geller, this conference). There is clearly a need for new kinds of statistical models and statistical indicators. Among those we wish to emphasize the advantages of the void probability function (VPF), and its particular convenience for studying

The Astronomical Journal, 1998

Recent analysis of the SSRS2 data based on cell-counts and two-point correlation function has sho... more Recent analysis of the SSRS2 data based on cell-counts and two-point correlation function has shown that very luminous galaxies are much more strongly clustered than fainter galaxies. In fact, the amplitude of the correlation function of very luminous galaxies (L > L *) asymptotically approaches that of R ≥ 0 clusters. In this paper we investigate the properties of the most luminous galaxies, with blue absolute magnitude M B ≤ −21. We find that: 1) the population mix is comparable to that in other ranges of absolute magnitudes; 2) only a small fraction are located in bona fide clusters; 3) the bright galaxy-cluster cross-correlation function is significantly higher on large scales than that measured for fainter galaxies; 4) the correlation length of galaxies brighter than M B ∼ −20.0, expressed as a function of the mean interparticle distance, appears to follow the universal dimensionless correlation function found for clusters and radio galaxies; 5) a large fraction of the bright galaxies are in interacting pairs, others show evidence for tidal distortions, while some appear to be surrounded by faint satellite galaxies. We conclude that very luminous optical galaxies differ from the normal population of galaxies both in the clustering and other respects. We speculate that this population is highly biased tracers of mass, being associated to dark halos with masses more comparable to clusters than typical loose groups.

Astronomy & Astrophysics, 1998

We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescr... more We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescribed by Pietronero and collaborators, to check their claim that the galaxy distribution is fractal at all scales, and we discuss and explain the reasons of some controversial points, through tests on both galaxy samples and simulations. We confirm that the amplitude of the two-point

We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescr... more We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescribed by Pietronero and collaborators, to check their claim that the galaxy distribution is fractal at all scales, and we discuss and explain the reasons of some controversial points, through tests on both galaxy samples and simulations. We confirm that the amplitude of the two-point correlation function does not depend on the sample depth, but increases with luminosity. We find that there is no contradiction between the results of standard and non-standard statistical analysis; moreover, such results are consistent with theoretical predictions derived from standard CDM models of galaxy formation, and with the hypothesis of homogeneity at large scale ($\sim 100$ \h). However, for our SSRS2 volume-limited subsamples we show that the first zero-point of the autocorrelation function xi(s)\xi(s)xi(s) increases linearly with the sample depth, and that its value is comparable to the radius of the maxim...

The Astrophysical Journal, 1995

We analyse the two{dimensional all{sky distribution of rich Abell and ACO galaxy clusters by usin... more We analyse the two{dimensional all{sky distribution of rich Abell and ACO galaxy clusters by using counts in cells and measuring the high{order area{averaged angular correlation functions. Con rming previous results, we nd a well de ned hierarchical relation between the two and three{point correlation functions, remarkably constant with scale. In the angular range 2 4 , the southern sample, limited at b II 40 and including both Abell and ACO clusters, shows a remarkable hierarchical behavior up to the sixth order, while northern Abell clusters give positive correlations in the same range only up to the fourth order. The inferred deprojected values of the 3{D coe cients S J , where S J = J = J 1 2 , are similar to those measured for the galaxy distribution, and consistent with theoretical predictions. These results are con rmed to the 4th order by our analysis of a 3{D sample of Abell and ACO clusters. Assuming that selection e ects and / or the absence of a cluster fair sample are the reason of the di erence between the two galactic hemispheres, and between Abell and ACO clusters, our results indicate that the statistical properties of the cluster distribution originate from the underlying galaxy distribution and show that the biasing between clusters and galaxies is non{linear.

Astronomy & Astrophysics, 1988

The authors present multicolor surface photometry of a sample of blue compact galaxies with reces... more The authors present multicolor surface photometry of a sample of blue compact galaxies with recession velocities close to 1000 km s-1. These galaxies are dwarfs undergoing strong star formation activity. They may be genuine young galaxies. It is been found that the star formation knots are close to the centers of these galaxies and sequentially ordered in space from the

Multicolor surface photometry performed on a selected sample of nearby (V ≡ 1000 km/s) blue compa... more Multicolor surface photometry performed on a selected sample of nearby (V ≡ 1000 km/s) blue compact galaxies shows that this galaxy class contains very different objects: interacting galaxies, irregular, or elliptical-like galaxies. Only some of them have small sizes (<2 kpc) and can be suspected to be genuine young galaxies. In the largest ones, in addition to the previously known

The analysis of the Southern Sky Redshift Survey 2 has shown that the galaxy correlation length i... more The analysis of the Southern Sky Redshift Survey 2 has shown that the galaxy correlation length increases with galaxy luminosity for L > L*. The correlation length of Very Luminous Galaxies (defined as MB 4L*), r0 ~ 16± 2h-1 Mpc, is even comparable to r0 of clusters. Nevertheless, we have shown that most VLGs are not early type galaxies in clusters, and that in many cases they appear to interact with nearby fainter galaxies. Visual inspection of fields around VLGs suggests that many VLGs are the brightest members of systems with much fainter galaxies; this seems an effective way of identifying galaxy systems which cannot be selected by traditional group finding algorithms. The study of VLGs may contribute to our understanding of the halo-galaxy connection and galaxy evolution. Here we resumetyheir main properties and present some results from our observations of a few VLG systems.

Astronomy and Astrophysics, Mar 1, 2000

We present the results of a dynamical analysis of the rich X-Ray luminous galaxy cluster Abell 52... more We present the results of a dynamical analysis of the rich X-Ray luminous galaxy cluster Abell 521, and discuss the nature of the arc-like structure first noted by Maurogordato et al. (1996). Our study is based on radial velocities for 41 cluster members, measured from spectra obtained at the European Southern Observatory and the Canada-France-Hawaii Telescope. Based on statistical analyses performed with the ROSTAT package, we find that Abell 521 is an intermediate-redshift cluster (C BI = 74132 +202 −250 km/s) with a rather high apparent value of the velocity dispersion S BI = 1386 +206 −139 km/s. There are many indications that this cluster is presently undergoing strong dynamical evolution: a) the high value of the velocity dispersion, which cannot be explained by trivial projection effects, b) signific ant clumping in the two-dimensional projected positions of the galaxies in the cluster, quantified by a mixture-model three-group partition significant at 99 % level, c) the extreme value of the velocity dispersion (σ ∼ 2000 km/s) in a central high density NE/SW structure, d) a strong increase of the velocity dispersion as determined from the reddest and bluest galaxies, suggesting that cluster spirals are not yet virialized; e) the presence of multiple nuclei in the core of the brightest cluster galaxy , one of which has a statistically significant velocity offset from the rest of the cluster members, and f) an apparently different stellar population for the various knots of the arc candidate which changes along the structure. The two brightest knots of the giant arc candidate are shown to be at the velocity of the cluster. This makes the

arXiv: Cosmology and Nongalactic Astrophysics, 2019

Modern galaxy cluster science is a multi-wavelength endeavor with cornerstones provided by X-ray,... more Modern galaxy cluster science is a multi-wavelength endeavor with cornerstones provided by X-ray, optical/IR, mm, and radio measurements. In combination, these observations enable the construction of large, clean, complete cluster catalogs, and provide precise redshifts and robust mass calibration. The complementary nature of these multi-wavelength data dramatically reduces the impact of systematic effects that limit the utility of measurements made in any single waveband. The future of multi-wavelength cluster science is compelling, with cluster catalogs set to expand by orders of magnitude in size, and extend, for the first time, into the high-redshift regime where massive, virialized structures first formed. Unlocking astrophysical and cosmological insight from the coming catalogs will require new observing facilities that combine high spatial and spectral resolution with large collecting areas, as well as concurrent advances in simulation modeling campaigns. Together, future mul...

arXiv: Instrumentation and Methods for Astrophysics, 2020

MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction... more MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 micron wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue.

arXiv: Astrophysics of Galaxies, 2020

The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity... more The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity, broad simultaneous spectral coverage (from optical to near-infrared bands), large patrol area and high fibre density. These properties provide the unprecedented potential of enabling, for the very first time, SDSS-like surveys around Cosmic Noon (z~1-2.5), when the star formation rate in the Universe peaked. The high-quality spectra delivered by MOONS will sample the same nebular and stellar diagnostics observed in extensive surveys of local galaxies, providing an accurate and consistent description of the evolution of various physical properties of galaxies, and hence a solid test of different scenarios of galaxy formation and transformation. Most importantly, by spectroscopically identifying hundreds of thousands of galaxies at high redshift, the MOONS surveys will be capable of determining the environments in which primeval galaxies lived and will reveal how such environments affect...

Astronomy & Astrophysics, 2017

Context. The next generation of galaxy surveys will provide cluster catalogues probing an unprece... more Context. The next generation of galaxy surveys will provide cluster catalogues probing an unprecedented range of scales, redshifts, and masses with large statistics. Their analysis should therefore enable us to probe the spatial distribution of clusters with high accuracy and derive tighter constraints on the cosmological parameters and the dark energy equation of state. However, for the majority of these surveys, redshifts of individual galaxies will be mostly estimated by multiband photometry which implies nonnegligible errors in redshift resulting in potential difficulties in recovering the real-space clustering. Aims. We investigate to which accuracy it is possible to recover the real-space two-point correlation function of galaxy clusters from cluster catalogues based on photometric redshifts, and test our ability to detect and measure the redshift and mass evolution of the correlation length r 0 and of the bias parameter b(M, z) as a function of the uncertainty on the cluster redshift estimate. Methods. We calculate the correlation function for cluster sub-samples covering various mass and redshift bins selected from a 500 deg 2 light-cone limited to H < 24. In order to simulate the distribution of clusters in photometric redshift space, we assign to each cluster a redshift randomly extracted from a Gaussian distribution having a mean equal to the cluster cosmological redshift and a dispersion equal to σ z. The dispersion is varied in the range σ (z=0) = σz 1+zc = 0.005, 0.010, 0.030 and 0.050, in order to cover the typical values expected in forthcoming surveys. The correlation function in real-space is then computed through estimation and deprojection of w p (r p). Four mass ranges (from M halo > 2 × 10 13 h −1 M to M halo > 2 × 10 14 h −1 M) and six redshift slices covering the redshift range [0, 2] are investigated, first using cosmological redshifts and then for the four photometric redshift configurations. Results. From the analysis of the light-cone in cosmological redshifts we find a clear increase of the correlation amplitude as a function of redshift and mass. The evolution of the derived bias parameter b(M, z) is in fair agreement with theoretical expectations. We calculate the r 0 − d relation up to our highest mass, highest redshift sample tested (z = 2, M halo > 2 × 10 14 h −1 M). From our pilot sample limited to M halo > 5 × 10 13 h −1 M (0.4 < z < 0.7), we find that the real-space correlation function can be recovered by deprojection of w p (r p) within an accuracy of 5% for σ z = 0.001 × (1 + z c) and within 10% for σ z = 0.03 × (1 + z c). For higher dispersions (besides σ z > 0.05 × (1 + z c)), the recovery becomes noisy and difficult. The evolution of the correlation in redshift and mass is clearly detected for all σ z tested, but requires a large binning in redshift to be detected significantly between individual redshift slices when increasing σ z. The best-fit parameters (r 0 and γ) as well as the bias obtained from the deprojection method for all σ z are within the 1σ uncertainty of the z c sample.

Astronomy & Astrophysics, 2017

Measurement of the gas velocity distribution in galaxy clusters provides insight into the physics... more Measurement of the gas velocity distribution in galaxy clusters provides insight into the physics of mergers, through which large scale structures form in the Universe. Velocity estimates within the intracluster medium (ICM) can be obtained via the Sunyaev-Zel’dovich (SZ) effect, but its observation is challenging both in term of sensitivity requirement and control of systematic effects, including the removal of contaminants. In this paper we report resolved observations, at 150 and 260 GHz, of the SZ effect toward the triple merger MACS J0717.5+3745 (z = 0.55), using data obtained with the NIKA camera at the IRAM 30 m telescope. Assuming that theSZ signal is the sum of a thermal (tSZ) and a kinetic (kSZ) component and by combining the two NIKA bands, we extract for the first time a resolved map of the kSZ signal in a cluster. The kSZ signal is dominated by a dipolar structure that peaks at −5.1 and + 3.4σ, corresponding to two subclusters moving respectively away and toward us and ...

Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are i... more Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are interesting per se, since their detailed analysis allows us to understand how galaxies form and evolve in various environments and second, they play an important part in cosmology because their number as a function of redshift gives constraints on cosmological parameters. Aims. We have searched for galaxy clusters in the Stripe 82 region of the Sloan Digital Sky Survey, and analysed various properties of the cluster galaxies. Methods. Based on a recent photometric redshift (hereafter photo−z) galaxy catalogue, we built a cluster catalogue by applying the Adami & MAzure Cluster FInder (AMACFI). Extensive tests were made to fine-tune the AMACFI parameters and make the cluster detection as reliable as possible. The same method was applied to the Millennium simulation to estimate our detection efficiency and the approximate masses of the detected clusters. Considering all the cluster galaxies (i.e. within a 1 Mpc radius of the cluster to which they belong and with a photo−z differing by less than ±0.05 from that of the cluster), we stacked clusters in various redshift bins to derive colour-magnitude diagrams and galaxy luminosity functions (GLFs). For each galaxy brighter than M r < −19.0, we computed the disk and spheroid components by applying SExtractor, and by stacking clusters we determined how the disk-to-spheroid flux ratio varies with cluster redshift and mass. Results. We detected 3663 clusters in the redshift range 0.15 ≤ z ≤ 0.70, with estimated mean masses between ∼ 10 13 and a few 10 14 M. We cross-matched our catalogue of candidate clusters with various catalogues extracted from optical and/or X-ray data. The percentages of redetected clusters are at most 40% because in all cases we detect relatively massive clusters, while other authors detect less massive structures. By stacking the cluster galaxies in various redshift bins, we find a clear red sequence in the (g − r) versus r colour-magnitude diagrams, and the GLFs are typical of clusters, though with a possible contamination from field galaxies. The morphological analysis of the cluster galaxies shows that the fraction of late-type to early-type galaxies shows an increase with redshift (particularly in 9σ clusters) and a decrease with detection level, i.e. cluster mass. Conclusions. From the properties of the cluster galaxies, the majority of the candidate clusters detected here seem to be real clusters with typical cluster properties.

Astronomy & Astrophysics, 2016

Context. This article belongs to the first series of XXL publications. It presents multifibre spe... more Context. This article belongs to the first series of XXL publications. It presents multifibre spectroscopic observations of three 0.55 deg 2 fields in the XXL Survey, which were selected on the basis of their high density of X-ray-detected clusters. The observations were obtained with the AutoFib2+WYFFOS (AF2) wide-field fibre spectrograph mounted on the 4.2 m William Herschel Telescope. Aims. The paper first describes the scientific rationale, the preparation, the data reduction, and the results of the observations, and then presents a study of active galactic nuclei (AGN) within three superclusters. Methods. To determine the redshift of galaxy clusters and AGN, we assign high priority to a) the brightest cluster galaxies (BCGs), b) the most probable cluster galaxy candidates, and c) the optical counterparts of X-ray point-like sources. We use the outcome of the observations to study the projected (2D) and the spatial (3D) overdensity of AGN in three superclusters. Results. We obtained redshifts for 455 galaxies in total, 56 of which are counterparts of X-ray point-like sources. We were able to determine the redshift of the merging supercluster XLSSC-e, which consists of six individual clusters at z ∼ 0.43, and we confirmed the redshift of supercluster XLSSC-d at z ∼ 0.3. More importantly, we discovered a new supercluster, XLSSC-f, that comprises three galaxy clusters also at z ∼ 0.3. We find a significant 2D overdensity of X-ray point-like sources only around the supercluster XLSSC-f. This result is also supported by the spatial (3D) analysis of XLSSC-f, where we find four AGN with compatible spectroscopic redshifts and possibly one more with compatible photometric redshift. In addition, we find two AGN (3D analysis) at the redshift of XLSSC-e, but no AGN in XLSSC-d. Comparing these findings with the optical galaxy overdensity we conclude that the total number of AGN in the area of the three superclusters significantly exceeds the field expectations. All of the AGN found have luminosities below 7 × 10 42 erg s −1. Conclusions. The difference in the AGN frequency between the three superclusters cannot be explained by the present study because of small number statistics. Further analysis of a larger number of superclusters within the 50 deg 2 of the XXL is needed before any conclusions on the effect of the supercluster environment on AGN can be reached.

Proceedings of the International Astronomical Union, 2004

We present the analysis and results of a new spectroscopic and photometric survey of the central ... more We present the analysis and results of a new spectroscopic and photometric survey of the central 1.5 Mpc 2 region of the galaxy cluster A3921 (z=0.094). We detect the presence of two dominant clumps of galaxies with a mass ratio of ∼4-5: a main cluster centered on the BCG (A3921-A), and a NW sub-cluster (A3921-B) hosting the second brightest cluster object. By comparing optical results to the X-ray analysis of XMM observations (Belsole et al. 2004), we find that A3921-B is tangentially traversing the main cluster along a SW/NE direction. The analysis of stellar populations of more than one hundred cluster members reveals that the merger event has probably affected the kinematics and spectral properties of the active galaxies in A3921.

Astronomy from Wide-Field Imaging, 1994

We present preliminary results of a galaxy redshift survey we are accomplishing as an ESO Key Pro... more We present preliminary results of a galaxy redshift survey we are accomplishing as an ESO Key Project over about 40 square degrees in a region near the South Galactic Pole, to a limiting magnitude bj = 19.4. Up to now ~ 50% of the survey has been completed, providing about 2000 galaxy redshifts.

Astronomy & Astrophysics, 2015

Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are i... more Context. The discovery of new galaxy clusters is important for two reasons. First, clusters are interesting per se, since their detailed analysis allows us to understand how galaxies form and evolve in various environments and second, they play an important part in cosmology because their number as a function of redshift gives constraints on cosmological parameters. Aims. We have searched for galaxy clusters in the Stripe 82 region of the Sloan Digital Sky Survey, and analysed various properties of the cluster galaxies. Methods. Based on a recent photometric redshift (hereafter photo-z) galaxy catalogue, we built a cluster catalogue by applying the Adami & MAzure Cluster FInder (AMACFI). Extensive tests were made to fine-tune the AMACFI parameters and make the cluster detection as reliable as possible. The same method was applied to the Millennium simulation to estimate our detection efficiency and the approximate masses of the detected clusters. Considering all the cluster galaxies (i.e. within a 1 Mpc radius of the cluster to which they belong and with a photo-z differing by less than ±0.05 from that of the cluster), we stacked clusters in various redshift bins to derive colour-magnitude diagrams and galaxy luminosity functions (GLFs). For each galaxy brighter than M r < −19.0, we computed the disk and spheroid components by applying SExtractor, and by stacking clusters we determined how the disk-to-spheroid flux ratio varies with cluster redshift and mass. Results. We detected 3663 clusters in the redshift range 0.15 ≤ z ≤ 0.70, with estimated mean masses between ∼10 13 and a few 10 14 M. We cross-matched our catalogue of candidate clusters with various catalogues extracted from optical and/or X-ray data. The percentages of redetected clusters are at most 40% because in all cases we detect relatively massive clusters, while other authors detect less massive structures. By stacking the cluster galaxies in various redshift bins, we find a clear red sequence in the (g − r) versus r colour−magnitude diagrams, and the GLFs are typical of clusters, though with a possible contamination from field galaxies. The morphological analysis of the cluster galaxies shows that the fraction of late-type to early-type galaxies shows an increase with redshift (particularly in 9σ clusters) and a decrease with detection level, i.e. cluster mass. Conclusions. From the properties of the cluster galaxies, the majority of the candidate clusters detected here seem to be real clusters with typical cluster properties.

Observational Cosmology, 1987

Recent results concerning the galaxy distribution at scales < 100 h"" 1 Mpc (H Q = 100 h kms" Mpc... more Recent results concerning the galaxy distribution at scales < 100 h"" 1 Mpc (H Q = 100 h kms" Mpc") show a number of characteristics which cannot be described by conventional statistical models. Correlation functions, for instance, can in no way give account of the presence of voids of the cellular (or spongy) appearance of the local galaxy distribution (M. Geller, this conference). There is clearly a need for new kinds of statistical models and statistical indicators. Among those we wish to emphasize the advantages of the void probability function (VPF), and its particular convenience for studying

The Astronomical Journal, 1998

Recent analysis of the SSRS2 data based on cell-counts and two-point correlation function has sho... more Recent analysis of the SSRS2 data based on cell-counts and two-point correlation function has shown that very luminous galaxies are much more strongly clustered than fainter galaxies. In fact, the amplitude of the correlation function of very luminous galaxies (L > L *) asymptotically approaches that of R ≥ 0 clusters. In this paper we investigate the properties of the most luminous galaxies, with blue absolute magnitude M B ≤ −21. We find that: 1) the population mix is comparable to that in other ranges of absolute magnitudes; 2) only a small fraction are located in bona fide clusters; 3) the bright galaxy-cluster cross-correlation function is significantly higher on large scales than that measured for fainter galaxies; 4) the correlation length of galaxies brighter than M B ∼ −20.0, expressed as a function of the mean interparticle distance, appears to follow the universal dimensionless correlation function found for clusters and radio galaxies; 5) a large fraction of the bright galaxies are in interacting pairs, others show evidence for tidal distortions, while some appear to be surrounded by faint satellite galaxies. We conclude that very luminous optical galaxies differ from the normal population of galaxies both in the clustering and other respects. We speculate that this population is highly biased tracers of mass, being associated to dark halos with masses more comparable to clusters than typical loose groups.

Astronomy & Astrophysics, 1998

We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescr... more We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescribed by Pietronero and collaborators, to check their claim that the galaxy distribution is fractal at all scales, and we discuss and explain the reasons of some controversial points, through tests on both galaxy samples and simulations. We confirm that the amplitude of the two-point

We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescr... more We perform a fractal analysis of the Southern Sky Redshift Survey 2, following the methods prescribed by Pietronero and collaborators, to check their claim that the galaxy distribution is fractal at all scales, and we discuss and explain the reasons of some controversial points, through tests on both galaxy samples and simulations. We confirm that the amplitude of the two-point correlation function does not depend on the sample depth, but increases with luminosity. We find that there is no contradiction between the results of standard and non-standard statistical analysis; moreover, such results are consistent with theoretical predictions derived from standard CDM models of galaxy formation, and with the hypothesis of homogeneity at large scale ($\sim 100$ \h). However, for our SSRS2 volume-limited subsamples we show that the first zero-point of the autocorrelation function xi(s)\xi(s)xi(s) increases linearly with the sample depth, and that its value is comparable to the radius of the maxim...

The Astrophysical Journal, 1995

We analyse the two{dimensional all{sky distribution of rich Abell and ACO galaxy clusters by usin... more We analyse the two{dimensional all{sky distribution of rich Abell and ACO galaxy clusters by using counts in cells and measuring the high{order area{averaged angular correlation functions. Con rming previous results, we nd a well de ned hierarchical relation between the two and three{point correlation functions, remarkably constant with scale. In the angular range 2 4 , the southern sample, limited at b II 40 and including both Abell and ACO clusters, shows a remarkable hierarchical behavior up to the sixth order, while northern Abell clusters give positive correlations in the same range only up to the fourth order. The inferred deprojected values of the 3{D coe cients S J , where S J = J = J 1 2 , are similar to those measured for the galaxy distribution, and consistent with theoretical predictions. These results are con rmed to the 4th order by our analysis of a 3{D sample of Abell and ACO clusters. Assuming that selection e ects and / or the absence of a cluster fair sample are the reason of the di erence between the two galactic hemispheres, and between Abell and ACO clusters, our results indicate that the statistical properties of the cluster distribution originate from the underlying galaxy distribution and show that the biasing between clusters and galaxies is non{linear.