We present the "VIMOS Public Extragalactic Redshift Survey" (VIPERS). We discuss the present status of the survey, the data which are already open to the public, and review first scientific results of the project

Krywult, Janusz

Małek, Katarzyna

Pollo, Agnieszka

Solarz, Aleksandra

Jagiellonian Univeristy Repository

VIPERS: in search for the solution of theriddle of dark energy (and many others)Agnieszka Pollo1·2, Janusz Krywult3, Katarzyna Ma lek2·4,Aleksandra Solarz4 and The VIPERS Team51. Astronomical Observatory, Jagiellonian University, Orla 171, Cracow, Poland2. National Centre for Nuclear Research, Hoz˙a 69, Warszawa, Poland3. Institute of Physics, Jan Kochanowski University, S´wi ↪etokrzyska 15, Kielce, Poland4. Department of Particle and Astrophysical Science, Nagoya University, Furo-cho,Chikusa-ku, 464-8602 Nagoya, Japan5. The VIPERS Team coauthors are presented at the end of this proceedingsWe present the ”VIMOS Public Extragalactic Redshift Survey” (VIPERS). Wediscuss the present status of the survey, the data which are already open to thepublic, and review first scientific results of the project.1 IntroductionThe ”VIMOS Public Extragalactic Redshift Survey” (VIPERS) is an ongoing ESOLarge Program. Its main goal is to provide a detailed map of the the spatial distribu-tion of galaxies over a very large volume of the z ∼ 1 Universe. VIPERS makes use ofthe multispectrograph VIMOS, which is installed at Melipal - one of the Very LargeTelescope (VLT) units on Mount Paranal in Chile. VIPERS is aiming at measuring100,000 redshifts for galaxies in the redshift range 0.5 < z < 1.2 and red magnituderange 17.5 < IAB < 22.5. The survey at the end will cover an area of 24 square de-grees on the sky, in only two separate fields. These fields are located inside two fieldsof the Canada-France-Hawaii Telescope Legacy Survey Wide catalogue (CFHTLS-Wide) which allowed to base the selection of the galaxy target sample on the 5-bandCFHTLS photometric data.The pre-selection was first based on the combination of the measurement of theobject’s apparent size and the Spectral Energy Distribution (SED) fitting to elimi-nate stars, and then on a robust color-based pre-selection in order to eliminate low-zgalaxies. A resultant sample proved to be 98% complete at z > 0.6, with a contam-ination of 5% of low-redshift interlopers and 3.22% stars. A small number of AGNcandidates was also added to the target sample. This pre-selection allowed for a veryhigh - above 40% - target sampling rate of the resultant catalogue (Guzzo et al., 2014,see also http://vipers.inaf.it).At redshift z ∼ 1, a large covered area together with a high sampling rate makeVIPERS unique among galaxy surveys. When completed, it will probe a volume of5∗107 h−3 Mpc3 (assuming Hubble constant H0 = 100h km/s/Mpc) which will makeVIPERS a statistically worthy equivalent of the local (z ≤ 0.2) galaxy surveys.The main scientific goal of VIPERS is the establishment of cosmological param-eters and measurements of the large-scale structure at an epoch when the Universepta.edu.pl/proc/36pta/v1p41 PTA Proceedings ? December, 2014 ? vol. 1 ? 41Agnieszka Pollo, et al.was about half of its today’s age. At the same time, the survey will allow to mea-sure physical properties of galaxies with unprecedented statistical accuracy at theseredshifts, and relate galaxy evolution with the evolution of the cosmic structure itself.Until now, more than 70,000 targets were observed, more than 75% of the plannedarea covered by observations, and more than 66,00 redshifts measured (the differenceis related to the fact that for a small percentage of spectra a sufficiently secure redshiftmeasurement is not possible). Further observations are on-going. In the beginning of2013 the first scientific results, based on more than a half of planned final data, werepublished. The submission of the scientific articles was followed by the public releaseof the redshifts used to obtained these results.2 Publicly released data: VIPERS PD-1On 4 October 2013 the VIPERS team publicly released the first spectroscopic mea-surements for 57,204 objects, including 54,756 galaxies and 2,448 stars. The relateddata files, separately for fields W1 and W4, can be freely downloaded from the fol-lowing link: http://vipers.inaf.it/rel-pdr1.html. They are accompanied by the surveymasks and weights, as well as photometric ancillary data from the CFHTLS, whichare necessary, e.g., for clustering measurements. A map of cone W1 and redshift his-tograms of the released data from both fields are presented in Figure 1. The publicrelease of the related spectra is foreseen in 2014. Detailed information on the datacan be found in Garilli et al. (2014) and Guzzo et al. (2014).Fig. 1: Left: Depth (in redshift and comoving distance, computed for the ΛCDM modelwith the value of ΩΛ,0 = 0.7) of VIPERS cones in both fields: W1 and W2, compared to theSDSS (from VIPERS public materials). Right: Redshift histogram for galaxies with reliableredshift measurements for both VIPERS fields.3 Epoch 1 Results3.1 Source classificationDealing with huge databases of present-day sky surveys, we encounter a number ofstatistical problems. One of them is the classification of sources and selection of42 ? PTA Proceedings ? December, 2014 ? vol. 1 pta.edu.pl/proc/36pta/v1p41VIPERS: in search for the solution of the riddle of dark energycertain classes of objects based on the existing, usually incomplete, information. Asthe first attempt to deal ”blindly” with VIPERS data Marchetti et al. (2013) appliedthe principal component analysis (PCA) to classify and repair galaxy spectra.Ma lek et al. (2013) applied the support vector machine (SVM) based method todesign a classifier able to distinguish galaxies, active galactic nuclei (AGNs) and starsfrom the photometric data only. As explained above, the pre-selection techniquesused in VIPERS are effective but not perfect: a certain number of stars escapes apre-selection, and the distinction between AGNs, stars, and galaxies always posesa tricky problem. As demonstrated in the left panel of Figure 2, all these classesoverlap in a large part in classical color-color diagrams. SVM-based classifier operatesin a multi-color (in general, multi-parameter space) and allows to draw a hyperplanedividing all three populations in these multidimensional space. Ma lek et al. (2013)has demonstrated a very good performance of the so-obtained classifier; as shown inthe right panel of Figure 2, a classifier using optical colors only has a performanceabove 90% in selecting galaxies brighter than i′ ∼ 21 and above 85% for fainter ones;the performance of the classifier can be significantly (above 95%) enhanced by addingnear-infrared data to the color space.This kind of classifiers can be used for pre-selecting targets for the future, yetlarger and more complex surveys. After fine-tuning, they can also be used for selectingcertain classes of sources, e.g. narrow-line AGNs, from VIPERS (or other surveys)for the subsequent more detailed analysis (Ma lek et al. 2014, in prep.).Fig. 2: Left: Representative color–color plot for VIPERS galaxies (pink x-es), AGNs (bluecircles) and stars (open black squares) with redshift security level ≥ 99%, and with theapparent magnitude 19 < i′ < 22.5. Right: Accuracy of optical (blue dashed line) andoptical+NIR (black solid line) SVM-based classifiers for VIPERS galaxies, as a function ofi′ apparent magnitude. See Ma lek et al. (2013) for details.3.2 Galaxy clustering and what is behindThe central topic of VIPERS science is the determination of cosmological parametersand the recovery of the cosmic large scale structure at z ∼ 1. The structure emergingfrom the first-epoch observations, presented in Figure 3, looks strikingly similar totoday’s one: there are clear overdensities (i.e. clusters and groups of galaxies), voids,walls and filaments in between. Moreover, the location of galaxies in this cosmic webis strongly correlated with their rest-frame colors: very similarly to what is observedpta.edu.pl/proc/36pta/v1p41 PTA Proceedings ? December, 2014 ? vol. 1 ? 43Agnieszka Pollo, et al.in the local Universe, red galaxies are located in the ”nodes” of the cosmic net -the strongest overdensities, while the blue objects are mostly field galaxies. Theintermediate green population is located in the areas of the intermediate densities.Fig. 3: VIPERS galaxies in the field W1 and their ”physical” colors: blue star-forminggalaxies are marked in blue, red passive galaxies – in red, and the intermediate green valleypopulation is marked by green dots (VIPERS public materials).This picture seen ”by eye” can be, however, deceptive. The comparison betweentoday’s large scale structure and those revealed by VIPERS, which can allow forcosmological conclusions, requires deeper statistical analysis and taking into accountall the observational biases and incompletnesses, including geometrical biases (relatedto the photometric and spectroscopic masks, as well as the target selection procedurewhich leaves a pattern of spectroscopic slits in the data), color-based selection, effectsof apparent magnitude limits (which turn into different rest-frame magnitude limitsfor different z) and so on. These effects superimpose on the actual physical effects:the evolution of the large scale structure on one side, and the evolution of galaxiesthemselves on the other side. Since we try to probe the evolution of the large scalestructure probing the evolving - in the environmentally dependent way - populationof galaxies, the problem becomes multifold.Taking these biases into account, de la Torre et al. (2013) provided a first mea-surement of the galaxy clustering and redshift space distortions from VIPERS, andrecovered from them growth rate of structure at z = 0.8: fσ8 = 0.47±0.08. This valueis consistent with the predictions of standard cosmological models based on Einsteingravity; the standard cosmological constant Λ remains the most likely interpretationof the accelerated expansion of the Universe. However, this measurement alone doesnot yet discriminate between different gravity models and does not rule out all thealternatives. More accurate theoretical modelling of the redshift space distortions willbe necessary to reduce the uncertainties.Marulli et al. (2013) measured the two-point correlation function for VIPERSgalaxies as a function of the B-band absolute magnitude, stellar mass, and redshift.It was confirmed that the relation between the luminosity and stellar mass in z ∼ 144 ? PTA Proceedings ? December, 2014 ? vol. 1 pta.edu.pl/proc/36pta/v1p41VIPERS: in search for the solution of the riddle of dark energygalaxies is in fact quite complex; some of the differences between clustering propertiesof luminosity-selected and mass-selected populations might be related to processesoccurring in galaxies mostly at high z.An interesting attempt to constrain the cosmological model through a measure-ment of the galaxy clustering ratio ηg,R was presented by Bel et al. (2014). Combiningtwo measurements at z ∼ 0.3 and z ∼ 0.9 allowed for a very precise estimate of thedensity parameter Ωm,0 = 0.274±0.017, well consistent with other other cosmologicalprobes, but obtained by an independent method.Another way to probe large scale structure properties is the direct measurementof the galaxy density field. Cucciati et al. (2014) tested seven different methods torecover the VIPERS density field and concluded that the performance of all thesemethods is similar. Results do not differ significantly, and methods with the small-est random errors can be more affected by systematic errors than others and viceversa. Thus, it is not possible to chose the clearly best method. However, in spite ofsystematic effects, it should be possible to reconstruct the lowest and highest densityenvironments on scales ∼ 5h−1 Mpc at redshifts and volumes covered by the VIPERS.3.3 Galaxy properties and their evolutionThe reliability of the large scale structure measurements at high z strongly dependson how well we understand the evolution of galaxy properties and its environementaldependence. Using VIPERS data, Davidzon et al. (2013) presented the evolution ofthe galaxy stellar mass function from z = 1.3 to z = 0.5, finding that high mass redgalaxies evolve more slowly with redshift, when compared to lower mass red galaxies.Additionally, a population of similarly massive blue galaxies was found, and suchgalaxies are no longer detectable below z = 0.7. These results may suggest a mass-dependent quenching of star formation in galaxies at z ∼ 1.Fritz et al. (2014) analysed the evolution of the colour–magnitude relation andluminosity function in VIPERS and found that most massive red galaxies have ap-parently experienced a sharp quenching of star formation at z ∼ 1, and mergingplayed only a limited role in their evolution. In contrast, less massive red galaxiesexperienced a mix of the truncation of star formation and minor mergers which to-gether led to the formation of low- and intermediate-mass red galaxies observed atlater epochs.In the local Universe, galaxies are classified primarily according to their shapes(elliptical vs spiral galaxies). Moving to higher z, determination of galaxy morpholo-gies from images becomes more difficult and most classifications rely rather on galaxycolors. Krywult et al. 2014 (in prep.; see also Krywult et al. 2014, in this issue)used CFHTLS images of VIPERS z ∼ 1 galaxies to fit their Se´rsic profiles and selectspheroidal, disk-like and immediate populations using the Se´rsic index n. So-definedgalaxy types are well consistent with color-based types, and preliminary results indi-cate that the sizes and shapes of the red population evolved after z ∼ 1 much lessthan those of the blue population, and that the strength of this effect depends ongalaxy sizes and stellar masses.Next works should allow to reveal the links between the evolution of the galaxiesand cosmic structure with an even greater accuracy.1The VIPERS Team coauthors: U. Abbas5, C. Adami4, S. Arnouts6, J. Bel7, M. Bolzonella9,D. Bottini3, E. Branchini10·28·29, A. Cappi9, J. Coupon12, O. Cucciati9, I. Davidzon9·17,G. De Lucia13, S. de la Torre14, A. Fritz3, P. Franzetti3, M. Fumana3, B. Garilli3·4,B. R. Granett2, L. Guzzo2·27, O. Ilbert4, A. Iovino2, V. Le Brun4, O. Le Fe`vre4, D. Maccagni3,pta.edu.pl/proc/36pta/v1p41 PTA Proceedings ? December, 2014 ? vol. 1 ? 45Agnieszka Pollo, et al.Acknowledgements. We acknowledge the support from the National Science Centre (UMO-2012/07/B/ST9/04425; UMO-2013/09/D/ST9/04030), and the European Associated Labo-ratory Astrophysics Poland-France HECOLS. The VIPERS website is vipers.inaf.it.ReferencesBel, J., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). Ωm0 from thegalaxy clustering ratio measured at z ∼ 1, A&A 563, A37 (2014)Cucciati, O., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). Nevermind the gaps: comparing techniques to restore homogeneous sky coverage, A&A 565,A67 (2014)Davidzon, I., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). A precisemeasurement of the galaxy stellar mass function and the abundance of massive galaxies atredshifts 0.5 < z < 1.3, A&A 558, A23 (2013)de la Torre, S., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). Galaxyclustering and redshift-space distortions at z∼0.8 in the first data release, A&A 557, A54(2013)Fritz, A., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). A quiescentformation of massive red-sequence galaxies over the past 9 Gyr, A&A 563, A92 (2014)Garilli, B., et al., The VIMOS Public Extragalactic Survey (VIPERS). First Data Release of57 204 spectroscopic measurements, A&A 562, A23 (2014)Guzzo, L., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). An unprece-dented view of galaxies and large-scale structure at 0.5 < z < 1.2, A&A 566, A108 (2014)Ma lek, K., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). A supportvector machine classification of galaxies, stars, and AGNs, A&A 557, A16 (2013)Marchetti, A., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS): spectralclassification through principal component analysis, MNRAS 428, 1424 (2013)Marulli, F., et al., The VIMOS Public Extragalactic Redshift Survey (VIPERS). Luminosityand stellar mass dependence of galaxy clustering at 0.5 < z < 1.1, A&A 557, A17 (2013)F. Marulli17·18·9, H. J. McCracken19, L. Paioro3, M. Polletta3, H. Schlagenhaufer24·20,M. Scodeggio3, L. A. .M. Tasca4, R. Tojeiro11, D. Vergani25·9, A. Zanichelli26, A. Burden11,C. Di Porto9, A. Marchetti1·2, C. Marinoni7, Y. Mellier19, L. Moscardini17·18·9, R. C. Nichol11,J. A. Peacock14, W. J. Percival11, S. Phleps20, M. Wolk19, G. Zamorani9[1] Universita` degli Studi di Milano; [2] INAF - Osservatorio Astronomico di Brera; [3] INAF -Istituto di Astrofisica Spaziale e Fisica Cosmica Milano; [4] Aix Marseille Universite´, CNRS, LAM(Laboratoire d’Astrophysique de Marseille); [5] INAF - Osservatorio Astronomico di Torino; [6]Canada-France-Hawaii Telescope; [7] Centre de Physique The´orique, UMR 6207 CNRS-Universite´de Provence; [8] Universite´ de Lyon; [9] INAF - Osservatorio Astronomico di Bologna; [10] Dipar-timento di Matematica e Fisica, Universita` degli Studi Roma Tre; [11] Institute of Cosmology andGravitation, University of Portsmouth; [12] Institute of Astronomy and Astrophysics, AcademiaSinica; [13] INAF - Osservatorio Astronomico di Trieste; [14] SUPA, Institute for Astronomy, Uni-versity of Edinburgh, Royal Observatory; [16] Department of Particle and Astrophysical Science,Nagoya University; [17] Dipartimento di Fisica e Astronomia - Universita` di Bologna; [18] INFN,Sezione di Bologna; [19] Institute d’Astrophysique de Paris, UMR7095 CNRS, Universite´ Pierreet Marie Curie; [20] Max-Planck-Institut fu¨r Extraterrestrische Physik; [24] Universita¨tssternwarteMu¨nchen, Ludwig-Maximillians Universita¨t; [25] INAF - Istituto di Astrofisica Spaziale e Fisica Cos-mica Bologna; [26] INAF - Istituto di Radioastronomia; [27] Dipartimento di Fisica, Universita` diMilano-Bicocca; [28] INFN, Sezione di Roma Tre; [29] INAF - Osservatorio Astronomico di Roma46 ? PTA Proceedings ? December, 2014 ? vol. 1 pta.edu.pl/proc/36pta/v1p41

VIPERS : in search for the solution of the riddle of dark energy (and many others)

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