In this paper we present the results of our search for and study of z 6 galaxy candidates behind the third Frontier Fields (FF) cluster, MACSJ0717.5+3745, and its parallel field, combining data from Hubble and Spitzer. We select 39 candidates using the Lyman Break technique, for which the clear non-detection in optical make the extreme mid-z interlopers hypothesis unlikely. We also take benefit from z 6 samples selected using previous Frontier Fields datasets of Abell 2744 and MACS0416 to improve the constraints on the properties of very high-redshift objects. We compute the redshift and the physical properties, such emission lines properties, star formation rate, reddening, and stellar mass for all Frontier Fields objects from their spectral energy distribution using templates including nebular emission lines. We study the relationship between several physical properties and confirm the trend already observed in previous surveys for evolution of star formation rate with galaxy mass, and between the size and the UV luminosity of our candidates. The analysis of the evolution of the UV Luminosity Function with redshift seems more compatible with an evolution of density. Moreover, no robust z ≥8.5 object is selected behind the cluster field, and few z∼9 candidates have been selected in the two previous datasets from this legacy survey, suggesting a strong evolution in the number density of galaxies between z∼8 and 9. Thanks to the use of the lensing cluster, we study the evolution of the star formation rate density produced by galaxies with L>0.03L , and confirm the strong decrease observed between z∼8 and 9.

We searched for z7 Lyman-break galaxies in the optical-to-mid-infrared Hubble Frontier Field and associated parallel field observations of the strong-lensing cluster MACS J0416−2403. We discovered 22 candidates, of which 6 lie at z9 and 1 lies at z10. Based on the Hubble and Spitzer photometry, all have secure photometric redshifts and a negligible probability of being at lower redshifts according to their peak-probability ratios, . This substantial increase in the number of known high-redshift galaxies allows a solid determination of the luminosity function (LF) at z8. The number of high-z candidates in the parallel field is considerably higher than that in the Abell 2744 parallel field. Our candidates have median stellar masses of * ~-+ M log 8.44 0.31 0.55 ( ) M e , star formation rates (SFRs) of ~-+ 1.8 0.4 0.5 M e yr −1 , and SFR-weighted ages of  -+ 300 Myr 140 70. Finally, we are able to put strong constraints on the z=7, 8, 9, and 10 LFs. One of the objects in the cluster field is a z ; 10 candidate, with a magnification of μ∼20±13. This object is likely the faintest z∼10 object known to date, allowing a first look into the extreme faint end (L∼0.04 L * ) of the z∼10 LF (It is named "Tayna" in the Aymara language).

We use the EAGLE simulations to study the effects of the intra-cluster medium (ICM) on the spatially resolved star-formation activity in galaxies. We study three cases of galaxy asymmetry dividing each galaxy in two halves using the plane (i) perpendicular to the velocity direction, differentiating the galaxy part approaching to the cluster center, hereafter dubbed as the "leading half", and the opposite one "trailing half", (ii) perpendicular to the radial position of the satellite to the centre of the cluster, (iii) that maximizes the star-formation rate (SFR) difference between the two halves. For (i), we find an enhancement of the SFR, star formation efficiency (SFE), and interstellar medium pressure in the leading half with respect to the trailing one and normal star-forming galaxies in the EAGLE simulation, and a clear overabundance of gas particles in their trailing. These results suggest that ram pressure (RP) is boosting the star formation by gas compression in the leading half, and transporting the gas to the trailing half. This effect is more pronounced in satellites of intermediate stellar masses 10 9.5−10.5 M , with gas masses above 10 9 M , and located within one virial radius or in the most massive clusters. In (iii) we find an alignment between the velocity and the vector perpendicular to the plane that maximizes the SFR difference between the two halves. It suggests that finding this plane in real galaxies can provide insights into the velocity direction.

Context. The Hubble and Spitzer Space Telescope surveys of the Frontier Fields provide extremely deep images around six massive, strong-lensing clusters of galaxies. The ALMA Frontier Fields survey aims to cover the same fields at 1.1 mm, with maps reaching (unlensed) sensitivities of <70 µJy, in order to explore the properties of background dusty star-forming galaxies. Aims. We report on the multi-wavelength photometric analysis of all 12 significantly detected (>5σ) sources in the first three Frontier Fields clusters observed by ALMA, based on data from Hubble and Spitzer, the Very Large Telescope and the Herschel Space Observatory. Methods. We measure the total photometry in all available bands and determine the photometric redshifts and the physical properties of the counterparts via SED-fitting. In particular, we carefully estimate the far-infrared (FIR) photometry using 1.1 mm priors to limit the misidentification of blended FIR counterparts, which strongly affect some flux estimates in previous FIR catalogs. Due to the extremely red nature of these objects, we used a large range of parameters (e.g. 0.0 < A v < 20.0) and templates (including AGNs and ULIRGs models). Results. We identify robust near-infrared (NIR) counterparts for all 11 sources with K s detection, the majority of which are quite red, with eight having F814W − K s 4 and five having F160W − [4.5] 3. From the FIR point of view, all our objects have z phot ∼ 1-3, whereas based on the optical SED one object prefers a high-z solution (z ≥ 7). Five objects among our sample have spectroscopic redshifts from the GLASS survey for which we can reproduce their SEDs with existing templates. This verification confirms the validity of our photometric redshift methodology. The mean redshift of our sample is z phot = 1.99 ± 0.27. All 1.1 mm selected objects are massive (10.0 < log[M (M)] < 11.5), with high star formation rates (log[SFR(M /yr)] ≈ 1.6) and high dust contents (8.1 < log[M dust (M)] < 8.8), consistent with previous ALMA surveys.