Euclid

Abstract:

Our understanding of cosmic star formation at z > 3 used to largely rely on rest-frame UV observations. However, these observations overlook dusty and massive sources, resulting in an incomplete census of early star-forming galaxies. Recent infrared data from Spitzer and the James Webb Space Telescope (JWST) have revealed a hidden population at z ∼ 3 − 6 with extreme red colours. Taking advantage of the overlap between imaging of the Euclid Deep Fields (EDFs), covering about 60 deg 2 , and ancillary Spitzer observations, we identified 27 000 extremely red objects with H E − IRAC2 > 2.25 (dubbed HIEROs) down to a 10 σ completeness magnitude limit of IRAC2 = 22.5 AB. After a visual investigation to discard artefacts and any objects with troubling photometry, we were left with a final sample of 3900 candidates. We retrieved the physical parameter estimates for these objects from the spectral energy distribution-fitting tool CIGALE . Our results confirm that HIERO galaxies can populate the high-mass end of the stellar mass function at z > 3, with some sources reaching extreme stellar masses ( M * > 10 11 M ⊙ ) and exhibiting high dust attenuation values ( A V > 3). However, we consider the stellar mass estimates unreliable for sources at z > 3.5. For this reason, we favour a more conservative lower- z solution. The challenges faced by spectral energy distribution-fitting tools in accurately characterising these objects underscore the need for further studies that incorporate both observations at shorter wavelengths and spectroscopic data. Euclid spectra will help resolve degeneracies and better constrain the physical properties of the brightest galaxies. Given the extreme nature of this population, characterising these sources is crucial for building a comprehensive picture of galaxy evolution and stellar mass assembly across most of the history of the Universe. This work demonstrates Euclid ’s potential to provide statistical samples of rare objects, such as massive, dust-obscured galaxies at z > 3, which will be prime targets for JWST and the Atacama Large Millimeter/submillimeter Array (ALMA).

Abstract:

This paper describes the near-infrared processing function (NIR PF) that processes NIR images from the Near-Infrared Spectrometer and Photometer (NISP) instrument on board the Euclid satellite. NIR PF consists of three main components: (i) a common pre-processing stage for both photometric (NIR) and spectroscopic (SIR) data to remove instrumental effects; (ii) astrometric and photometric calibration of NIR data, along with catalogue extraction; and (iii) resampling and stacking. The necessary calibration products are generated using dedicated pipelines that process observations from both the early performance verification (PV) phase in 2023 and the nominal survey operations. After outlining the pipelineś structure and algorithms, we describe its application to Euclid Q1 images. For Q1, we achieved an astrometric accuracy of 5–8 mas, a relative photometric accuracy of 5 mmag, along with an absolute flux calibration limited by the 1% uncertainty of the Hubble Space Telescope (HST) CALSPEC database. We characterised the point spread function (PSF), which we found to be very stable across the focal plane. Finally, we discuss current limitations of NIR PF that will be improved upon for future data releases.

Abstract:

Strong gravitational-lensing systems with multiple source planes are powerful tools for probing the density profiles and dark matter substructure of galaxies. The ratio of the Einstein radii is related to the dark energy equation of state through the cosmological scaling factor β . Galaxy-scale double-source-plane lenses (DSPLs) are extremely rare, however. We report the discovery of four new galaxy-scale DSPL candidates in the Euclid Quick Release 1 (Q1) data. These systems were initially identified through a combination of machine-learning lens-finding models and subsequent visual inspection from citizens and experts. We applied the widel -used LensPop lens-forecasting model to predict that the full Euclid survey will discover 1700 DSPLs. This scales to 6 ± 3 DSPLs in 63 deg 2 , which is the area of Q1. The number of discoveries in this work is broadly consistent with this forecast. We present lens models for each DSPL and infer their β values. Our initial Q1 sample demonstrates that Euclid promises to discover these rare objects.

Abstract:

Recent observations with the James Webb Space Telescope (JWST) have revealed an interesting population of sources with a compact morphology and a characteristic v-shaped continuum, namely blue at a rest frame λ < 4000 Å and red at longer wavelengths. The nature of these sources, which are called little red dots (LRDs), is still highly debated because it is unclear whether they host active galactic nuclei (AGNs) and their number seems to drop drastically at z < 4. We took advantage of the 63 deg 2 covered by the Euclid Quick Data Release (Q1) to extend the search for LRDs to brighter magnitudes and lower redshifts than what was possible with JWST. This is fundamental for a broader view of the evolution of this peculiar galaxy population. The selection was performed by fitting the available photometric data ( Euclid , the Spitzer Infrared Array Camera (IRAC), and ground-based griz data) with two power laws to retrieve the rest-frame optical and UV slopes consistently over a wide redshift range (i.e. z < 7.6). We then excluded extended objects and possible line emitters and inspected the data visually to remove any imaging artefacts. The final selection included 3341 LRD candidates from z = 0.33 to z = 3.6, 29 of which were also detected in IRAC. The resulting rest-frame UV luminosity function, in contrast with previous JWST studies, shows that the number density of LRD candidates increases from high redshift to z = 1.5–2.5 and decreases at even lower redshifts. The subsample of more robust LRD candidates that are also detected with IRAC show a weaker evolution, however, which is affected by low statistics and limited by the IRAC resolution. The comparison with previous quasar UV luminosity functions shows that LRDs are not the dominant AGN population at z < 4 and M UV < −21. Follow-up studies of these LRD candidates are pivotal to confirm their nature, probe their physical properties, and determine whether they are compatible with JWST sources because the different spatial resolution and wavelength coverage of Euclid and JWST might select different samples of compact sources.

Abstract:

Galaxy morphologies and shape orientations are expected to correlate with their large-scale environments, since they grow by accreting matter from the cosmic web and are subject to interactions with other galaxies. We extracted cosmic filaments in projection from the Euclid Quick Data Release 1 (covering 63.1 deg 2 ) at 0.5 < z < 0.9 in tomographic slices of 170 comoving h −1 Mpc using photometric redshifts. Galaxy morphologies are accurately retrieved thanks to the excellent imaging resolution of the visible camera (VIS) of Euclid . The distribution of massive galaxies ( M * > 10 10 M ⊙ ) in the projected cosmic web is analysed as a function of morphology measured from VIS data. Specifically, the 2D alignment of galaxy shapes with large-scale filaments is quantified as a function of Sérsic indices and masses. We find the known trend that more massive galaxies are closer to filament spines. At fixed stellar masses, morphologies correlate both with densities and distances to large-scale filaments. In addition, the large volume of this data set allows us to detect a signal indicating that there is a preferential alignment of the major axis of massive early-type galaxies along projected cosmic filaments. Overall, these results demonstrate our capabilities to carry out detailed studies of galaxy environments with Euclid , which will be extended to higher redshift and lower stellar masses with the future Euclid Deep Survey.