arXiv subjects

Roberto De Propris

Publications and source records attributed to Roberto De Propris.

At least 91 records · Page 5Linked to original sources

arXiv2004

Substructure Analysis of Selected Low Richness 2dFGRS Clusters of Galaxies

Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure in clusters of galaxies are applied to recently obtained data from the 2dF Galaxy Redshift Survey. The sample of 25 clusters used in this study includes 16 clusters not previously investigated for substructure. Substructure is detected at or greater than the 99% CL level in at least one test for 21 of the 25 clusters studied here. From the results, it appears that low richness clusters commonly contain subclusters participating in mergers. About half of the clusters have two or more components within 0.5 h^{-1} Mpc of the cluster centroid, and at least three clusters (Abell 1139, Abell 1663, and Abell S333) exhibit velocity-position characteristics consistent with the presence of possible cluster rotation, shear, or infall dynamics. The geometry of certain features is consistent with influence by the host supercluster environments. In general, our results support the hypothesis that low richness clusters relax to structureless equilibrium states on very long dynamical time scales (if at all).

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arXiv2004

The 2dF Galaxy Redshift Survey: The blue galaxy fraction and implications for the Butcher-Oemler effect

We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift. The value of the blue fraction is observed to depend on the luminosity limit adopted, cluster-centric radius and, more generally, local galaxy density, but it does not depend on cluster properties. Changes in the blue fraction are due to variations in the relative proportions of red and blue galaxies but the star formation rate for these two galaxy groups remains unchanged. Our results are most consistent with a model where the star formation rate declines rapidly and the blue galaxies tend to be dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused by processes specific to the cluster environment.

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arXiv2004

Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS

We analyse the observed correlation between galaxy environment and H-alpha emission line strength, using volume-limited samples and group catalogues of 24968 galaxies drawn from the 2dF Galaxy Redshift Survey (Mb<-19.5) and the Sloan Digital Sky Survey (Mr<-20.6). We characterise the environment by 1) Sigma_5, the surface number density of galaxies determined by the projected distance to the 5th nearest neighbour; and 2) rho1.1 and rho5.5, three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 Mpc and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterised by their H-alpha equivalent width, EW(Ha). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of EW(Ha) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, rho5.5, which is likely independent of the trend with local density, rho1.1. We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for sigma=200-1000 km/s. Even in the lowest density environments, no more than ~70 per cent of galaxies show significant H-alpha emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-timescale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.

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arXiv2003

The 2dF Galaxy Redshift Survey: Wiener Reconstruction of the Cosmic Web

We reconstruct the underlying density field of the 2 degree Field Galaxy Redshift Survey (2dFGRS) for the redshift range 0.035<z<0.200 using the Wiener Filtering method. The Wiener Filter suppresses shot noise and accounts for selection and incompleteness effects. The method relies on prior knowledge of the 2dF power spectrum of fluctuations and the combination of matter density and bias parameters however the results are only slightly affected by changes to these parameters. We present maps of the density field in two different resolutions: 5 Mpc/h and 10 Mpc/h. We identify all major superclusters and voids in the survey. In particular, we find two large superclusters and two large local voids. A version of this paper with full set of colour maps can be found at http://www.ast.cam.ac.uk/~pirin.

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arXiv2003

Local redshift surveys and galaxy evolution

We present observations of galaxy environmental dependencies using data from the 2dF Galaxy Redshift Survey. From a combined analysis of the luminosity function, Butcher-Oemler effect and trends in H$α$ line strengths we find support for a model where galaxy properties are mainly set by initial conditions at the time of their formation.

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arXiv2003

Clustering studies with the 2dF galaxy redshift survey

The 2dF Galaxy Redshift Survey has now been completed and has mapped the three-dimensional distribution, and hence clustering, of galaxies in exquisite detail over an unprecedentedly large ($\sim 10^{8} h^{-3}$ Mpc$^{3}$) volume of the local Universe. Here we highlight some of the major results to come from studies of clustering within the survey: galaxy correlation function and power spectrum analyses and the constraints they have placed on cosmological parameters; the luminosity functions of rich galaxy clusters, their dependence on global cluster properties and galaxy type, and how they compare with the field; and the variation of galactic star formation activity with environment, both within clusters and in galaxy groups.

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arXiv2003

The K-selected Butcher-Oemler Effect

[abridged] We investigate the Butcher-Oemler effect in a sample of K-selected galaxies in 33 clusters at 0.15 < z < 0.92. We attempt to duplicate the original Butcher-Oemler analysis as closely as possible given the characteristics of our data. We find that the infrared selected blue fractions are lower than those measured in the optical and that the trend with redshift is much weaker. Comparison with optical data in clusters in common with Butcher & Oemler (1984) shows that infrared selection is the primary difference between our study and optically selected samples. We suggest that the Butcher-Oemler effect is in large part due to a population of star-forming low mass galaxies which will evolve into dwarf galaxies. These early results point to the need for larger and deeper infrared samples of cluster galaxies to address this issue

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arXiv2003

The 2dF Galaxy Redshift Survey: Final Data Release

The 2dF Galaxy Redshift Survey (2dFGRS) has obtained spectra for 245591 sources, mainly galaxies, brighter than a nominal extinction-corrected magnitude limit of b_J=19.45. Reliable redshifts were measured for 221414 galaxies. The galaxies are selected from the extended APM Galaxy Survey and cover an area of approximately 1500 square degrees in three regions: an NGP strip, an SGP strip and random fields scattered around the SGP strip. This paper describes the 2dFGRS final data release of 30 June 2003 and complements Colless et al. (2001), which described the survey and the initial 100k data release. The 2dFGRS database and full documentation are available on the WWW at http://www.mso.anu.edu.au/2dFGRS/

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arXiv2002

The 2dF Galaxy Redshift Survey: the luminosity function of cluster galaxies

We have determined the composite luminosity function (LF) for galaxies in 60 clusters from the 2dF Galaxy Redshift Survey. The LF spans the range $-22.5<M_{b_{\rm J}}<-15$, and is well-fitted by a Schechter function with ${M_{b_{\rm J}}}^{*}=-20.07\pm0.07$ and $α=-1.28\pm0.03$ ($H_0$=100 km s$^{-1}$ Mpc$^{-1}$, $Ω_M$=0.3, $Ω_Λ$=0.7). It differs significantly from the field LF of \cite{mad02}, having a characteristic magnitude that is approximately 0.3 mag brighter and a faint-end slope that is approximately 0.1 steeper. There is no evidence for variations in the LF across a wide range of cluster properties. However the LF of early-type galaxies in clusters is both brighter and steeper than its field counterpart. The differences between the field and cluster LFs for the various spectral types can be qualitatively explained by the suppression of star formation in the dense cluster environment, together with mergers to produce the brightest early-type galaxies.

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arXiv2002

The Global, Local and Cluster Galaxy Luminosity Function

We review selected measurements of the galaxy luminosity function including the global field, the local group, the local sphere, nearby clusters (Virgo, Coma and Fornax) and clusters in general. We conclude that the overall cluster luminosity function is consistent with the global luminosity function over the magnitude range in common (-22 < M_B -5logh_0.68 < -17). We find that only in the core regions of clusters (r < 300 kpc) does the overall form of the luminosity function show significant variation. However when the luminosity function is subdivided by spectral type some further variations are seen. We argue that these results imply: substantial late infall, efficient star-formation suppression, and the confinement of mass-changing evolutionary processes to the core regions only.

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arXiv2002

Parameter constraints for flat cosmologies from CMB and 2dFGRS power spectra

We constrain flat cosmological models with a joint likelihood analysis of a new compilation of data from the cosmic microwave background (CMB) and from the 2dF Galaxy Redshift Survey (2dFGRS). Fitting the CMB alone yields a known degeneracy between the Hubble constant h and the matter density Omega_m, which arises mainly from preserving the location of the peaks in the angular power spectrum. This `horizon-angle degeneracy' is considered in some detail and shown to follow a simple relation Omega_m h^{3.4} = constant. Adding the 2dFGRS power spectrum constrains Omega_m h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant h=0.665 +/- 0.047, the matter density Omega_m=0.313 +/- 0.055, and the physical CDM and baryon densities Omega_c h^2 = 0.115 +/- 0.009, Omega_b h^2 = 0.022 +/- 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set a upper limit to the tensor-to-scalar ratio of r<0.7 at 95% confidence. We then show how these data can be used to constrain the equation of state of the vacuum, and find w<-0.52 at 95% confidence. The preferred cosmological model is thus very well specified, and we discuss the precision with which future CMB data can be predicted, given the model assumptions. The 2dFGRS power-spectrum data and covariance matrix, and the CMB data compilation used here, are available from http://www.roe.ac.uk/~wjp/

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arXiv2002

The 2dF Galaxy Redshift Survey: The amplitudes of fluctuations in the 2dFGRS and the CMB, and implications for galaxy biasing

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey and by the latest measurements of the Cosmic Microwave Background anisotropies. By combining the 2dFGRS and CMB data we find the linear-theory rms mass fluctuations in 8 Mpc/h spheres to be sigma_8 = 0.73 +-0.05 (after marginalization over the matter density parameter Omega_m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scale-independent bias parameter of present-epoch L_s = 1.9L_* APM-selected galaxies to be b(L_s,z=0) = 1.10 +- 0.08 on comoving scales of 0.02 < k < 0.15 h/Mpc. If luminosity segregation operates on these scales, L_* galaxies would be almost un-biased, b(L_*,z=0) = 0.96. These results are derived by assuming a flat Lambda-CDM Universe, and by marginalizing over other free parameters and fixing the spectral index n=1 and the optical depth due to reionization tau=0. We also study the best fit pair (Omega_m,b), and the robustness of the results to varying n and tau. Various modelling corrections can each change the resulting b by 5-15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the SDSS, cluster abundance and cosmic shear.

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arXiv2002

Optical and Near-Infrared Photometry of Distant Galaxy Clusters

We present optical and near-infrared photometry of 45 clusters of galaxies at 0.1 < z < 1.3. Galaxy catalogs in each cluster were defined at the longest wavelenth available, generally the K-band, down to approximately two magnitudes below M*. We include finding chart images of the band used for catalog definition. The photometry has been used in previously published papers to examine the origin and evolution of galaxies in distant clusters.

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arXiv2002

The 2dF Galaxy Redshift Survey: The environmental dependence of galaxy star formation rates near clusters

We have measured the equivalent width of the H-alpha emission line for 11006 galaxies brighter than M_b=-19 (LCDM) at 0.05<z<0.1 in the 2dF Galaxy Redshift Survey (2dF), in the fields of seventeen known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace mustar, the star formation rate normalized to Lstar, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of mustar steadily skews toward larger values with increasing distance from the cluster centre, converging to the field distribution at distances greater than ~3 times the virial radius. A correlation between star formation rate and local projected density is also found, which is independent of cluster velocity dispersion and disappears at projected densities below ~1 galaxy (brighter than M_b=-19) per Mpc^2. This characteristic scale corresponds approximately to the mean density at the cluster virial radius. The same correlation holds for galaxies more than two virial radii from the cluster centre. We conclude that environmental influences on galaxy properties are not restricted to cluster cores, but are effective in all groups where the density exceeds this critical value. The present day abundance of such systems, and the strong evolution of this abundance, makes it likely that hierarchical growth of structure plays a significant role in decreasing the global average star formation rate. Finally, the low star formation rates well beyond the virialised cluster rule out severe physical processes, such as ram pressure stripping of disk gas, as being completely responsible for the variations in galaxy properties with environment.

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arXiv2002

Spectrophotometric evolution of spiral galaxies with truncated star formation: An evolutionary link between spirals and S0s in distant clusters

A one-zone chemo-spectro-photometric model is used to investigate the time evolution of disk galaxies whose star formation is truncated, and to determine the dependence of this evolution on the previous star formation history and the truncation epoch. Truncated spirals show red colors $\sim 1$ Gyr after truncation, and evolve spectrally from an e(b) type, down through the e(a), a+k, and k+a classes, to finally become a k type. The exact behavior in this phase depends on the truncation epoch and the star formation history prior to truncation. For example, earlier type disks show redder colors and do not show a+k-type spectra after truncation of star formation. We also discuss a possible evolutionary link between the k-type galaxies with spiral morphology found in distant clusters, and present-day S0s, by investigating whether truncated spirals reproduce the infrared color-magnitude relation of Coma galaxies. We suggest that only less luminous, later-type disk galaxies whose star formation is truncated at intermediate and high redshifts can reproduce the red $I-K$ colors observed for S0s in the Coma cluster.

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arXiv2002

The 2dF Galaxy Redshift Survey: The Number and Luminosity Density of Galaxies

We present the bivariate brightness distribution (BBD) for the 2dF Galaxy Redshift Survey (2dFGRS) based on a preliminary subsample of 45,000 galaxies. The BBD is an extension of the galaxy luminosity function incorporating surface brightness information. It allows the measurement of the local luminosity density, j_B, and the galaxy luminosity and surface brightness distributions while accounting for surface brightness selection biases. The recovered 2dFGRS BBD shows a strong surface brightness-luminosity relation (M_B~2.4μ_e). The luminosity-density is dominated by normal galaxies and the luminosity-density peak lies away from the selection boundaries implying that the 2dFGRS is complete and that luminous low surface brightness galaxies are rare. The final value we derive for the local luminosity-density, inclusive of surface brightness corrections, is: j_B=2.49+/-0.20x10^8 h L_solar Mpc^-3. Representative Schechter function parameters are: M*=-19.75+/-0.05, phi*=2.02+/-0.02x10^-2 and alpha=-1.09+/-0.03. Extending the conventional methodology to incorporate surface brightness selection effects has resulted in an increase in the luminosity-density of 37%.

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arXiv2002

The 2dF Galaxy Redshift Survey: A targeted study of catalogued clusters of galaxies

We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information has been used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10%, whereas the APM catalogue suffers only 5% contamination. If we use the original catalog centroids, the level of contamination rises to approximately 15% for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at $z \sim 0.05$ that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive an upper limit to the space density of $σ> 1000 \kms$ clusters of $3.6 \times 10^{-6} \hdens$. This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum.

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arXiv2001

The 2dF Galaxy Redshift Survey: Near Infrared Galaxy Luminosity Functions

We combine the 2MASS extended source catalogue and the 2dFGRS to produce an IR selected galaxy catalogue with 17,173 measured redshifts. We use this extensive dataset to estimate the J and K-band galaxy luminosity functions. The LFs are fairly well fit by Schechter functions with J: M*-5log h= -22.36+/-0.02, alpha= -0.93+/-0.04, Phi=0.0104+/-0.0016 h^3/Mpc^3 and K: M*-5log h= -23.44+/-0.03, alpha=-0.96+/-0.05, Phi=0.0108+/-0.0016 h^3/Mpc^3 (2MASS Kron magnitudes). These parameters assume a cosmological model with Omega=0.3 and Lambda=0.7. With datasets of this size, systematic rather than random errors are the dominant source of uncertainty in the determination of the LF. We carry out a careful investigation of possible systematic effects in our data. The surface brightness distribution of the sample shows no evidence that significant numbers of low surface brightness or compact galaxies are missed by the survey. We estimate the present-day distributions of B-K and J-K colours as a function of absolute magnitude and use models of the galaxy stellar populations, constrained by the observed optical and infrared colours, to infer the galaxy stellar mass function. Integrated over all galaxy masses, this yields a total mass fraction in stars (in units of the critical mass density) of Omega_*.h= (1.6+/-0.24)/10^3 for a Kennicutt IMF and Omega_*.h= (2.9+/-0.43)/10^3 for a Salpeter IMF. These values agree with those inferred from observational estimates of the star formation history of the universe provided that dust extinction corrections are modest.

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