J-PLUS: On the identification of new cluster members in the double galaxy cluster A2589 and A2593 using PDFs

Abstract

Aims. We aim to use multiband imaging from the Phase-3 Verification Data of the J-PLUS survey to derive accurate photometric redshifts (photo-z) and look for potential new members in the surroundings of the nearby galaxy clusters A2589 (z=0.0414) & A2593 (z=0.0440), using redshift probability distribution functions (PDF). The ultimate goal is to demonstrate the usefulness of a 12-band filter system in the study of largescale structure in the local universe. Methods. We present an optimized pipeline for the estimation of photometric redshifts in clusters of galaxies. This pipeline includes a PSF-corrected photometry, specific photometric apertures capable of enhancing the integrated signal in the bluest filters, a careful recalibration of the photometric uncertainties and accurate upper-limit estimations for faint detections. To foresee the expected precision of our photo-z beyond the spectroscopic sample, we designed a set of simulations in which real cluster galaxies are modeled and reinjected inside the images at different signal-to-noise ratio (S/N) levels, recomputing their photometry and photo-z estimates. Results. We tested our photo-z pipeline with a sample of 296 spectroscopically confirmed cluster members with an averaged magnitude of < r >= 16.6 and redshift < z >=0.041. The combination of seven narrow and five broadband filters with a typical photometricdepth of r ∼ 21.5 provides δ z /(1+z)=0.01 photo-z estimates. A precision of δ z /(1+z)=0.005 is obtained for the 177 galaxies brighter than magnitude r <17. Based on simulations, a δ z /(1+z)=0.02 and δ z /(1+z)=0.03 is expected at magnitudes < r >= 18 and < r >= 22, respectively. Complementarily, we used SDSS/DR12 data to derive photo-z estimates for the same galaxy sample. This exercise demonstrates that the wavelength-resolution of the J-PLUS data can double the precision achieved by SDSS data for galaxies with a high S/N. Based on the Bayesian membership analysis carried out in this work, we find as much as 170 new candidates across the entire field (∼5deg 2 ). The spatial distribution of these galaxies may suggest an overlap between the systems with no evidence of a clear filamentary structure connecting the clusters. This result is supported by X-ray Rosat All-Sky Survey observations suggesting that a hypothetical filament may have low density contrast on diffuse warm gas. Conclusions. We prove that the addition of the seven narrow-band filters make the J-PLUS data deeper in terms of photo-z-depth than other surveys of a similar photometric-depth but using only five broadbands. These preliminary results show the potential of J-PLUS data to revisit membership of groups and clusters from nearby galaxies, important for the determination of luminosity and mass functions and environmental studies at the intermediate and low-mass regime.

The search for galaxy cluster members with deep learning of panchromatic HST imaging and extensive spectroscopy

“…In recent years, the selection of CLMs has been addressed in several ways: via the classical identification of the members' red-sequence in colour-magnitude diagrams, aided by spectroscopic measurements (e.g. Caminha et al 2019 for strong lensing applications); by measuring photometric redshifts with a Bayesian method (Molino et al 2017(Molino et al , 2019; by exploiting an ML approach based on the so-called multi-layer perceptron trained by a quasi-Newton approximation (Biviano et al 2013;Cavuoti et al 2015;Brescia et al 2013); or by fitting a multivariate normal distribution to the colour distribution of both spectroscopic members and field galaxies (Grillo et al 2015). All these methods require accurate photometric measurements, which are difficult to obtain with standard photometric techniques in galaxy clusters, due to the strong contamination from bright cluster galaxies, including the brightest cluster galaxies (BSGs), and the intra-cluster light (Molino et al 2017).…”

The miniJPAS survey: A preview of the Universe in 56 colors

“…MAG_PSFCOR: This photometry is performed following the approach of Molino et al (2019) (see also Molino et al 2014Molino et al , 2017 with the aim of applying corrections object by object in the images with worst PSF to correct for the differences in PSF among different bands. To increase the robustness of the color determination, instead of total magnitude estimators such as MAG_AUTO or MAG_ISO, the fluxes are measured within an aperture with the same shape as the Kron aperture and a semimajor axis equal to the KRON_RADIUS.…”

“…To increase the robustness of the color determination, instead of total magnitude estimators such as MAG_AUTO or MAG_ISO, the fluxes are measured within an aperture with the same shape as the Kron aperture and a semimajor axis equal to the KRON_RADIUS. These magnitudes are also called restricted magnitudes (Molino et al 2017(Molino et al , 2019. Being smaller than the aperture of MAG_AUTO, the signal-to-noise ratio (S/N) is higher and, therefore, color measurements, which are key in spectral analysis such as photo-z determination, are more robust.…”

The Southern Photometric Local Universe Survey (S-PLUS): improved SEDs, morphologies, and redshifts with 12 optical filters

“…In particular, accurate PDFs can play a key role in the identification of groups and galaxy clusters from photometric data (e.g. Molino et al 2019). In this regard, the S-PLUS will be used to construct the most accurate photo-z nearbygalaxy catalogue yet produced over a large area of the Southern sky.…”