Galaxies and AGN - Clusters of galaxies

 Nearby Clusters: WINGS

1. THE SURVEY

 A3395

 Fig.1: Portion of WFI(ESO2.2) image of Abell 3395 

 The WIde-field Nearby Galaxy-cluster Survey (WINGS) is a comprehensive survey of clusters and cluster galaxies in the local Universe (0.04<z<0.07).

WINGS is an international collaboration, including astronomers from Italy (PD,TS), Spain, Denmark, USA and Australia, but it is coordinated and mostly carried out by Italian INAF astronomers in Padova.

 The WINGS sample consists of a complete, X-ray flux-limited selection of 77 clusters in the redshift interval 0.04-0.07, with a wide range of X-ray and optical properties. WINGS entailed a huge observational effort, including optical imaging (B- and V-band, see Fig.1) and spectroscopy, near-IR (J- and K-band) and U-band imaging, using wide-field cameras and spectrographs at 8 different telescopes in both hemispheres, for a total of 120 observing nights allocated so far.

 

 WINGS spectra

 Fig.2: examples of WINGS spectra in the southern sample

 

Up to now WINGS has produced: 

  • integrated and aperture photometry in the optical (B,V; 400,000 galaxies), NIR(J,K; 700,000 galaxies) and (150,000 galaxies) bands;
  • surface photometry (V-, B- and K-band) and morphology of 45,000 galaxies;
  • redshift, line-widths and Lick-indices of 7,000 galaxies (see Fig.2).

Most of the presently available WINGS database (imaging, spectroscopy and catalogues) is already at the astronomical community's disposal, both from the CDS and through a friendly, purposely devised query interface, while plenty of more material will be released in the near future, as soon as it will be ready for publication. Detailes about the survey (observations and catalogs) can be found in the survey web site.

Moreover, in the framework of the WINGS project, a dedicated database has been carried out and three software packages have been purposely devised to obtain:

  • the automatic surface photometry of galaxies (GASPHOT);
  • the automatic morphological type estimation (MORPHOT, see Fig.3);
  • the fitting of galaxy spectra through stellar population synthesismodels including a reliable guess of the Star Formation History.

 A3395 map

 Fig.3: MORPHOT classification map for the portion of Abell 3395 reported in Fig.1. Red, green, cyan and blue symbols refer to ellipticals, S0s, early and late spirals, respectively. White circles are stars and small dots are unclassified galaxies.

 

 2. OMEGA-WINGS

 Because of the limited FOV (~35’x35’), the WINGS survey covers only the cluster cores: the maximum clustercentric distance reached in (almost) all clusters is only 0.6 times the virial radius. Crucially, what is missing is coverage out to at least the virial radius and into the outer regions, to link clusters with the surrounding population and the field. The OMEGA-WINGS programme has been developed to extend the WINGS project to the outer regions of our target clusters.

OMEGA-WINGS is an imaging survey carried out with OMEGACAM, the wide-field imager for the Cassegrain focus of the VLT Survey Telescope (VST) at Cerro Paranal. We were granted a total of 60hr of ESO GTO observing time to obtain B, V and u’ photometry for all 59 WINGS cluster observable from the Paranal Observatory. Operations started in late 2011 and the project will be completed at the end of 2014. Up to now we have gathered imaging of 44 and 10 clusters in the optical (B,V) and u’ bands, respectively.

In parallel with the wide-field (1ox1o) OMEGACAM imaging we are also gathering multifiber spectroscopy of southern WINGS clusters with the new wide-field (2dF) spectrograph AAOMEGA@AAO.

 

3. SCIENCE

The main goal of WINGS is to carry out a systematic study of the cluster galaxy populations as a function of the global and local environment. The large field-of-view and the complementarity of the different sets of observations allow for the first time a detailed study of galaxy masses, morphologies and star formation histories from the densest regions in the cluster cores to the low-density outskirts of clusters and infalling groups and filaments. WINGS will provide a reliable zero point reference for studies of galaxies at higher redshifts, thus representing the local benchmark for evolutionary studies.

Scientific highlights from the WINGS survey up to 2011 can be found here.

Most recent results concern: 1) the superdense massive galaxies (SDGs); 2) the shape of the brightest cluster galaxies (BCGs); 3) the red sequence of galaxies in clusters; 4) the stellar mass function and its dependence on morphology, environment and redshift; 5) the origin of the ‘tilt’ of the Fundamental Plane (FP) of early-type galaxies.

1) At variance with previous claims, we discover in the WINGS clusters a significant population of superdense massive galaxies with masses and sizes comparable to those observed at high redshift (Valentinuzzi et al. 2010, see Fig.4). They approximately represent 22% of all cluster galaxies more massive than 3×1010M. We find a relation between mass, effective radius, and luminosity-weighted age in our cluster galaxies, which can mimic the claimed evolution of the radius with redshift, if not properly taken into account (see also Poggianti et al. 2013).

SuperDense

Fig.4: Stellar mass surface density and equivalent radius at the effective isophote as a function of the total stellar mass for galaxies in the WINGS clusters (red and blue dots) compared with high redshift galaxy samples (big symbols). The red full dots are the galaxies classified as superdense in the WINGS clusters. 

 

2) We compare the apparent axial ratio distributions of the brightest cluster galaxies (BCGs) and normal ellipticals (Es)the WINGS clusters (Fasano et al. 2010). We find the BCGs to have triaxial shape with tendency towards prolateness much stronger than in the case of Es. Such a strong prolateness appears entirely due to the sizeable (dominant) component of cDs inside the WINGS sample of BCGs (see Fig.5). In fact, while the `normal' (non-cD) BCGs do not differ from Es, as far as the shape distribution is concerned, the axial ratio distribution of cD galaxies is found to support quite prolate shapes, in agreement with N-body simulation of cluster-sized dark matter haloes. 

     WINGS BCG1          WINGS BCG2

Fig.5: Probability distributions ψ(β,γ) of the intrinsic axial ratios (γβ≤1) obtained deprojecting, in blind mode (initial guess ψ0const.) with the Lucy algorithm, the ellipticity distributions of normal Es (top-left), BCGs (bottom-left), cDs (top-right) and normal (non cD) BCGs (bottom-right) in the WINGS clusters. T=(1-β2)(1-γ2) is the triaxiality parameter, spanning the range from 0 (β=1; oblate shape) to 1 (β=γ; prolate shape). The curves on the top and right of each plot show the marginal distributions of β and γ, respectively. Note that Es and normal (non cDs) BCGs have quite similar (triaxial) distributions, while cDs and the global BCGs (cD dominated) population show a marked prolateness.

 

3) We have studied the color-magnitude red sequence (RS) of galaxies in the WINGS clusters, searching for correlations between the characteristics of the RS and the environment. No correlations with global properties of clusters are found. The properties of the RS, instead, depend strongly on local galaxy density (see Fig.6). Higher density regions have a smaller RS scatter, a higher luminous-to-faint ratio, a lower blue fraction, and a lower spiral fraction on the RS. Our results clearly illustrate the prominent effect of the local density in setting the epoch when galaxies become passive and join the RS (Valentinuzzi et al. 2011).

WINGS RS

Fig.6Red-Sequence slope and scatter, luminous-to-faint ratio and blue fraction vs. galaxy local density.

 

4) Using the WINGS and the EDISCS databases for the local and distant galaxies, we investigate the stellar mass function of cluster galaxies and find that it evolves noticeably with redshift (Vulcani et al. 2011). The shape at M*>1011 M does not evolve, but below M*1010.8M the mass function at high redshift is flat, while in the local Universe it flattens out at lower masses. The population of M*=1010.2-1010.8M galaxies must have grown significantly between z=0.8 and z=0. We examine how the proportion of galaxies of different morphological types changes with galaxy mass, finding that it strongly depends on redshift (see Fig.7). At both redshifts, 40% of the stellar mass is in elliptical galaxies. Another 43% of the mass is in S0 galaxies in local clusters, while it is in late types in distant clusters. Our results lead to the conclusion that mass growth due to star formation must play a crucial role in driving the evolution. It has to be accompanied by infall of galaxies on to clusters, and the mass distribution of infalling galaxies might be different from that of cluster galaxies. We also analyse the galaxy stellar mass distribution as a function of local density in mass-limited samples, in the field and in clusters from low to high redshift (Vulcani et al. 2012 , see also Calvi et al. 2013). We find that at all redshifts and in all environments, local density plays a role in shaping the mass distribution. In the field, it regulates the shape of the mass function at any mass above the mass limits. In clusters, it seems to be important only at low masses.

WINGS MF

Fig.7Comparison of the mass function of EDisCS (blue filled squares) and WINGS (black crosses) galaxies, for the different morphological types. Mass distributions are normalized to the WINGS total number of objects with logM∗/M≥11. Errors are defined as Poissonian errors. The cumulative distributions are shown in the insets. Each morphological type has a mass distribution that depends on redshift. In WINGS there are always proportionally more less-massive galaxies than in EDisCS.

 

 

 

5) By exploiting the database of early-type galaxy members of the WINGS survey, we have addressed the long debated question of the origin and shape of the Fundamental Plane (FP). Our data suggest that different physical mechanisms concur in shaping and `tilting' the FP with respect to the virial plane expectation. In particular, a `hybrid solution' in which the structure of galaxies and their stellar population are the main contributors to the FP tilt seems to be favoured (see Fig.8). We find that the bulk of the tilt should be attributed to structural non-homology, while stellar population effects play an important but less crucial role (D’Onofrio et al. 2013).

WINGS FP

Fig.8: Distance from the Virial plane (ΔFP=FP_tilt) in the V-band as a function of log(M∗/M), log(M∗/LV), log(n=Sersic_index) and ε=(1-b/a) for ETGs in the WINGS clusters. Ellipticals and S0 galaxies are indicated by red and green dots, respectively. The straight lines illustrate the best-fitting regressions, while the crosses located aside in the plots report the median uncertainties of the two variables.

 

 


 

People of the Padova ObservatoryD. Bettoni, G. Fasano, M. Gullieuszik, P. Marziani, A. Omizzolo, A. Paccagnella, B.M. Poggianti.

Collaboration: M. D'Onofrio, A. Moretti (Padova Univ.), J. Fritz (UGENT,BE), R. Calvi, B. Vulcani (IPMU,JP) , T. Valentinuzzi, M. Ramella, A. Biviano (INAF OA Trieste), M. Moles, J. Varela (CEFCA,ES) A. Cava, R. Janssen (IAC,ES), P. Kjaergaard (Copenhagen Univ., DK), W. Couch, D. Woods (NSW Univ. Sydney,AU), A. Dressler (Carnegie Inst. Pasadena,USA).

 

Recent Publications   Valentinuzzi et al. (2010), ApJ 712,226; Fasano et al. (2010), MNRAS 404,1490; D'Onofrio et al. (2011), ApJ 727,L6; Fritz et al. (2011), A&A 526,45; Bettoni et al. (2011), AN 332,299; Vulcani et al. (2011), MNRAS 412,246; Vulcani et al. (2011), MNRAS 413,921; Valentinuzzi et al. (2012), A&A 536,34; Calvi et al. (2012), MNRAS 419,L14; Fasano et al. (2012), MNRAS 420,926; Vulcani et al. (2011), MNRAS 420,1481; Poggianti et al. (2013), ApJ 762,77; D’Onofrio et al. (2013), AN 334,373; Marziani et al. (2013), AN 334,412; Calvi et al. (2013), MNRAS 432,3141; D’Onofrio et al. (2013), MNRAS 435,45; Omizzolo et al. (2013), A&A in press.

 

 

 

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