Affiliation: Università degli Studi di Padova, INAF-OAPd

Contribution: Oral

Title: Euclid ERO: a pilot investigation of the HIEROs physical properties found in the Perseus cluster

Abstract: Our comprehension of the cosmic star formation history at z>3 strongly relies on rest-frame UV observations, which allow to individuate the so called Lyman-break galaxies. Nevertheless, this selection systematically misses the most dusty and massive sources, resulting in an incomplete census at earlier times. However, Near- to Mid-Infrared data from Spitzer and JWST have shed light to a hidden population lying at z∼3−6 characterized by extreme red colors, named HIEROs by Wang et al. (2016) and individuated through a two-color criterion, H − 4.5 > 2.25. Nowadays, Euclid Early Release Observations (ERO) have opened the possibility to further search for this kind of objects, exploiting the overlap with ancillary Spitzer/IRAC observations. Thus, the aim of this work is to conduct a preliminary investigation, on a small area of ∼ 230 arcmin^2, to prove the effectiveness of this synergy in identifying and subsequently analyze this extremely red population. We used the Perseus official catalogues by the ERO team and the IRAC images of two different pointings, where the sources have been detected by SExtractor. After applying
the HIERO color selection, the sample has been cleaned by checking for the presence of globular
cluster and inspecting by eye the multi-band cutouts of each source. The photometric redshifts
and the physical properties of the final sample have been estimated by Bagpipes, finding two main
categories: one representing a low-z population and another a high-z , in which we are interested. We also used a set of brown dwarf templates trying to fit our objects, in order to compare the goodness of the fits and remaining with robust candidates. We selected the galaxies associated to a photo-z between 3.5−7.5 and from their estimated physical properties we computed the Mass Function in four different redshift bins. Our selection allowed us to end up with some very massive candidates, with M∗>10^12 Msun, resulting in very high Mass Functions, lying above the results found in previous literature based on selections at wavelength less than 2μm. Our completeness is good only at the very high mass end of the MFs, thus representing only a lower limit for stellar masses below ∼10^12 Msun. Given the amount of HIEROs individuated in such a small area, the expected numbers once the Euclid deep fields (50 deg^2) will be released are significant, highlighting the importance of a deeper study on this still mysterious population, with particular interest in assessing its contribution to the cosmic star formation rate density and its agreement with current galaxy evolution and formation models. Indeed, these early results are showing Euclid’s capabilities to push the boundaries of our understanding regarding the obscured star formation beyond the edge of the Universe.

This contribution can be found here (pdf).