Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey

Ilbert, O.; Arnouts, S.; McCracken, H. J.; Bolzonella, M.; Bertin, E.; Fèvre, O. Le; Mellier, Y.; Zamorani, G.; Pelló, R.; Iovino, A.; Tresse, L.; Brun, V. Le; Bottini, D.; Garilli, B.; Maccagni, D.; Picat, J. P.; Scaramella, R.; Scodeggio, M.; Vettolani, G.; Zanichelli, A.; Adami, C.; Bardelli, S.; Cappi, A.; Charlot, S.; Ciliegi, P.; Contini, T.; Cucciati, O.; Foucaud, Sylvie; Franzetti, P.; Gavignaud, I.; Guzzo, L.; Marano, B.; Marinoni, C.; Mazure, A.; Meneux, B.; Merighi, R.; Paltani, S.; Pollo, A.; Pozzetti, L.; Radovich, M.; Zucca, E.; Bondì, M.; Bongiorno, A.; Busarello, G.; Torre, S. de la; Gregorini, L.; Lamareille, F.; Mathez, G.; Merluzzi, P.; Ripepi, V.; Rizzo, D.; Vergani, D.

doi:10.1051/0004-6361:20065138

Cited by 1,330 publications

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“…Our photometric redshift estimates are made with two different techniques: Le Phare (LPZ) 15 and Bayesian Photometric Redshifts (BPZ) 16 . LPZ photometric redshifts are based on a template fitting procedure with a maximum likelihood (χ 2 ) estimate.…”

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confidence: 99%

A magnified young galaxy from about 500 million years after the Big Bang

Zheng

Postman

Zitrin

et al. 2012

Nature

306

341

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The early Universe at redshift z∼6-11 marks the reionization of the intergalactic medium, following the formation of the first generation of stars. However, those young galaxies at a cosmic age of < ∼ 500 million years (Myr, at z > ∼ 10) remain largely unexplored as they are at or beyond the sensitivity limits of current large telescopes. Gravitational lensing by galaxy clusters enables the detection of high-redshift galaxies that are fainter than what otherwise could be found in the deepest images of the sky. We report the discovery of an object found in the multi-band observations of the cluster MACS1149+22 that has a high probability of being a gravitationally magnified object from the early universe. The object is firmly detected (12σ) in the two reddest bands of HST/WFC3, and not detected below 1.2 µm, matching the characteristics of z∼9 objects. We derive a robust photometric redshift of z = 9.6 ± 0.2, corresponding to a cosmic age of 490 ± 15 Myr (i.e., 3.6% of the age of the Universe).The large number of bands used to derive the redshift estimate make it one of the most accurate estimates ever obtained for such a distant object. The significant magnification by cluster lensing (a factor of ∼15) allows us to analyze the object's ultra-violet and optical luminosity in its rest-2 frame, thus enabling us to constrain on its stellar mass, star-formation rate and age. If the galaxy is indeed at such a large redshift, then its age is less than 200 Myr (at the 95% confidence level), implying a formation redshift of z f < ∼ 14. The object is the first z>9 candidate that is bright enough for detailed spectroscopic studies with JWST, demonstrating the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts.Observational cosmology has established that the age of the Universe is 13.7 billion years, and the reionization of the vast intergalactic medium (IGM) started around redshift z ∼ 11, 1 as the result of radiation from the first generation of stars. The task of probing the most distant Universe is progressively challenging: While more than 10 5 quasars have been found, only one is at z > 7; 2 while thousands of gamma-ray burst events have been recorded, only one 3 is confirmed at z=8.3; and while thousands of galaxy candidates have been found at z ∼ 6, only one has been reported at z ∼ 10, 4 which is based on a single-band detection. Galaxies at z ∼ 10 are expected to be at a magnitude of ∼ 29 (in the AB system, used hereafter) 4, 5 , near the detection limits of the deepest fields observed by Hubble Space Telescope (HST), and beyond the spectroscopic capability of even the next generation of large telescopes.In this Letter we report the discovery of a gravitationally lensed source whose most likely redshift is z ∼ 9.6. The source, hereafter called MACS1149-JD1, is selected from a near-infrared detection image at significance of 22σ. MACS1149-JD1 has a unique flux distribution characterized by a) no detection at Galaxy clusters are the largest r...

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confidence: 99%

A magnified young galaxy from about 500 million years after the Big Bang

Zheng

Postman

Zitrin

et al. 2012

Nature

306

341

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“…We use the standard SED fitting method, adopting the software Le PHARE (Arnouts et al 1999;Ilbert et al 2006). KiDS observed magnitudes are matched with those predicted from a set of spectral energy distributions (SEDs).…”

Section: Le Phare Sed Fittingmentioning

confidence: 99%

“…The basic COSMOS library is composed by nine galaxy templates from Polletta et al (2007), which includes three SEDs of elliptical galaxies (E) and five templates of spiral galaxies (S0, Sa, Sb, Sc, Sd). These models are generated using the code GRASIL (Silva et al 1998), providing a better joining of UV and mid-IR than those by Coleman et al (1980) used in Ilbert et al (2006). Moreover, to reproduce very blue colors not accounted by the Polletta et al (2007) models, 12 additional templates using Bruzual & Charlot (2003) models with starburst (SB) ages ranging from 3 to 0.03 Gyr are added.…”

Section: Le Phare Sed Fittingmentioning

confidence: 99%

“…Finally, they also require a detailed understanding of how external factors, such as intergalactic and galactic extinctions, affect the final result. The templates are then shifted to any redshift in a given range and convolved with the transmission curves of the filters to create a template set for the redshift estimators (Koo 1999;Massarotti et al 2001a,b;Csabai et al 2003;Ilbert et al 2006). Photometric redshifts can then be obtained by comparing observed galaxy fluxes in the i th photometric band with the library of reference fluxes, depending on (bounded by) redshift z and on a set of parameters T , that account for galaxy spectral type.…”

Section: Introductionmentioning

confidence: 99%

“…In this work we apply five different photo-z techniques to the same KiDS dataset: a) three empirical methods, namely: the above mentioned MLPQNA, the Random Forest (RF; Breiman 2001), and an optimization network based on the Levenberg-Marquardt learning rule (LEMON; Nocedal and Wright 2006); b) the Le PHARE SED template fitting (Arnouts et al 1999;Ilbert et al 2006); c) the Bayesian Photometric Redshift model (Benitez 2000). The final goal being to analyze the possibility to use these models in a cooperative way, in order to optimize the accuracy of photo-z estimation.…”

Section: Introductionmentioning

confidence: 99%

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A cooperative approach among methods for photometric redshifts estimation: an application to KiDS data

Cavuoti

Tortora

Brescia

et al. 2016

Mon. Not. R. Astron. Soc.

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Photometric redshifts (photo-z's) are fundamental in galaxy surveys to address different topics, from gravitational lensing and dark matter distribution to galaxy evolution. The Kilo Degree Survey (KiDS), i.e. the ESO public survey on the VLT Survey Telescope (VST), provides the unprecedented opportunity to exploit a large galaxy dataset with an exceptional image quality and depth in the optical wavebands. Using a KiDS subset of about 25, 000 galaxies with measured spectroscopic redshifts, we have derived photo-z's using i) three different empirical methods based on supervised machine learning, ii) the Bayesian Photometric Redshift model (or BPZ), and iii) a classical SED template fitting procedure (Le PHARE). We confirm that, in the regions of the photometric parameter space properly sampled by the spectroscopic templates, machine learning methods provide better redshift estimates, with a lower scatter and a smaller fraction of outliers. SED fitting techniques, however, provide useful information on the galaxy spectral type which can be effectively used to constrain systematic errors and to better characterize potential catastrophic outliers. Such classification is then used to specialize the training of regression machine learning models, by demonstrating that a hybrid approach, involving SED fitting and machine learning in a single collaborative framework, can be effectively used to improve the accuracy of photo-z estimates.

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A Panchromatic View of Galaxies

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Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey

Cited by 1,330 publications

References 42 publications

A magnified young galaxy from about 500 million years after the Big Bang

A magnified young galaxy from about 500 million years after the Big Bang

A cooperative approach among methods for photometric redshifts estimation: an application to KiDS data

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