Marina Ramón Pérez, Miguel Cerviño Saavedra, Ángel Manuel Bongiovanni, Carmen Pilar Padilla Torres, Jakub Nadolny
E. Alfaro (IAA); B. Altieri, D. Coia, L Metcalfe, A.M. Pérez-García, R.M. Pérez-Martínez, I. Valtchanov (ESAC), M. Sánchez-Portal, B. Vila (ESO, Chile), I. Pintos Castro (U. Toronto); H. Castañeda (IPN, México); J. Gallego (UCM); I. González-Serrano (IFCA-UNICAN); J.A. de Diego, J. González, A. Lara-López (IA-UNAM, México); I. Oteo (ESO, Germany)
Galaxy evolution is a crucial topic in modern extragalactic astrophysics, linking cosmology to the Local Universe. Their study requires collecting statistically significant samples of galaxies of different luminosities at different distances. Cosmological surveys normally cover either very wide areas of sky (e.g. SDSS, 2dFGRS), or a comparatively small region of sky at higher depth (e.g. HUDF, GOODS). It is, however, a quite difficult discipline from both the physical bases, and the techniques required. It involves knowledge and testing of a variety of fundamental astrophysical theories and models, from stellar formation and evolution, to the accretion on a super-massive black hole. Also, the observational study of galaxy evolution has to deal with faint objects (either intrinsically or because of their distance) in order to avoid observational biases, and requires the use of different techniques (imaging, spectroscopy, and synthesis imaging, among others), and with the need of observing at different wavelengths (literally from the centimetre regime to gamma-rays) both for comprehensively tackling different physical processes, and for constraining the spectral energy distribution of the targets. Moreover, cosmological distance causes the same spectral feature to be shifted at different wavelengths according to the redshift, reinforcing the need to use different facilities at different wavelengths to homogeneously study objects that are at different distances.
Relatively recently, narrow band filters have been successfully used to isolate emission lines in order to very efficiently find high redshift galaxies, and trace the star formation evolution. The tunable filters of OSIRIS at GTC (the largest optical fully-steerable telescope of the world) have been mostly thought for this scope, with the additional advantage of providing a way to obtain data cubes in the low resolution spectral domain, but using simple photometric techniques. Alternatively, the forthcoming J-PAS survey will combine fixed narrow band filters with large sky coverage at an unprecedented depth.
The present project is aimed at dealing with a wide set of deep multi-wavelength data, for building a unique legacy-dataset, the "Evolution Survey", that fulfils the strong observational requirements for efficiently tackling hot topics in galaxy evolution. It is composed of several coordinated imaging surveys, including unique FIR data from HERSCHEL observatory, and enriched with multiple object optical and near infrared spectroscopy. This survey will be the deepest polichromatic emission line survey, and will remain so during years to come. Evolución will provide, for thousands of galaxies, the emission line fluxes of different elements together with their morphologies and continuum in the optical, NIR, FIR and X-ray, from redshifts ranging from z = 0.24 up to 7.0. A parallel survey of clusters using the same techniques and wavelengths, will allow studying the evolution of their galaxies, and to compare it with that derived from field ones. With these surveys the team will tackle several critical aspects of galaxy evolution such as the evolution of star formation rate (SFR), metallicity, bolometric luminosity, extinction, and the accretion power of active galactic nuclei, among others, with cosmic time and environmental density, for even the faintest or the more distant galaxies observable with the currently existing facilities. Also, the combination of deep observations at different wavelengths, will allow shedding light on the relations among the different objects of the zoo observed at high redshift, which is still largely at stake.
The data will be obtained through three own surveys which take advantage of either guaranteed time on OSIRIS/GTC, or already awarded ESO-GTC time to the project team: OTELO, GLACE and Lockman SpReSO. OTELO and GLACE will use the OSIRIS tunable filters, while Lockman SpReSO will exploit the multiple spectroscopy mode. The former and the latter will study field galaxies using the guaranteed time reserved for the instrument builders, while GLACE will use open, guaranteed and ESO-GTC time to study selected galaxy clusters. Most of the team researchers are also members of the PEP survey (a guaranteed-time key-program with the Herschel Space Observatory, operating in the far infrared). Complementary data from known public databases will be used as well, together with ALHAMBRA and J-PAS surveys, in which the team members are also engaged, and ALMA follow-ups. OSIRIS/GTC, HERSCHEL and ALMA are unique, state-of-the-art facilities, which are already providing and will certainly provide more, fresh views on the subject of galaxy evolution.
OSIRIS and its tunable filters, allow obtaining narrow-band imaging at any optical wavelengths (from 365-960 nm) with the possibility to select different full widths at half maximum at each wavelength (from 0.4 to 3 nm). These filters, used in a high transmission instrument such as OSIRIS, installed in a 10m-class telescope, placed in an excellent site such as the Observatorio del Roque de Los Muchachos, will allow implementing and pushing to the limit the tunable tomography techniques applied to surveys: i.e. obtaining the deepest possible set of images at the same pointing, each image at different but contiguous wavelengths, thus providing low resolution 3D spectroscopy of any object in the field of view. This is a very powerful tool to detect very faint or very low equivalent width (EW) emission line objects.
OTELO survey (OSIRIS Tunable Emission Line Object survey, P.I.: Jordi Cepa), is the backbone of the Evolution Survey, covering the main optical emission lines from Lyα to Hα at different redshifts, by observing a wavelength window in the atmospheric OH sky line forest at 925 nm. Given the low equivalent widths (EW) that can achieve, it will allow, for the first time in this kind of surveys, observing all spirals and most emission line E/S0 (at the typical emission line luminosities of E galaxies OTELO can observe EWs as low as 0.2), and determining the faint end luminosity function of Lyα emitters (LAEs).
GLACE is an innovative narrow band imaging survey of emission-line galaxies and AGNs in a well-studied and well-defined sample of galaxy clusters in three redshift windows at z=0.40, ~0.63 and 0.89, targeting several emission lines (Hα/[NII], Hβ, [OII], [OIII]) by means of the TF of the OSIRIS instrument. The redshift windows have been selected in such a way that the observed lines lay within windows in the OH sky lines forest and sample the cosmic time at 8.9, 7.6 and 6.0 Gyr. This redshift range is extremely interesting since there are indications of a strong evolution from blue, star forming galaxies, into the red sequence. Indeed, across this interval, the cosmic SFR declines by a factor 2.5. The GLACE project was approved as a large ESO/GTC programme (PI Sánchez-Portal) that started in 2011.
LOCKMAN SpReSO (P.I.: Jordi Cepa y Jesús González) will devote more than 200 hours of OSIRIS guaranteed time, for gathering intermediate resolution MOS, from 365 through 1000nm, of a thousand Herschel sources in the inner Lockman field up to a magnitude 24.5 AB. Also, NIR MOS will be obtained for a subsample of selected targets using EMIR at GTC.
PEP (PACS Extragalactic Probe, P.I. D. Lutz, Co-I: Jordi Cepa) The fields and clusters selected for the previous surveys are coincident with a fraction of the ones surveyed from 60 through 600 µm by PACS and SPIRE instruments aboard HERSCHEL observatory. Then targets’ optical counterparts could be identified and studied in the FIR. Part of the project participants are members of the PACS scientific team, and have access to the reduced and calibrated data obtained using guaranteed time, in the framework of HERSCHEL guaranteed time Key Projects.
These surveys represent a unique database for tackling the study of emission line galaxies up to redshift 7.0. The proposed project is aimed at completing and scientifically exploiting them.
Obtaining the final OTELO catalogue corresponding to the first pointing, has been a milestone for the project. This catalogue represents the deepest extragalactic emission line survey so far obtained, and includes astrometry, and correlated ancillary data ranging from X-Rays to radio (cm). Deriving photometric redshifts and morphologies (using HST/ACS data) will allow the team to tackle the scientific exploitation of this survey. A Lyman-α candidate at a redshift larger than 6 is shown in the image below.