arXiv subjects

G. Rodighiero

Publications and source records attributed to G. Rodighiero.

At least 19 recordsLinked to original sources

arXiv2026

Multi-tracer exploration of molecular gas in main sequence galaxies at z~4.5

Molecular gas masses in high-z galaxies are inferred from indirect tracers, whose respective reliability remains poorly constrained. In particular, the bright [CII] 158$\mu$m line is now widely used as a molecular gas tracer at z>4, yet direct observational tests against CO remain scarce. We search for CO(4-3), CO(5-4), and [CI](1-0) lines in three of the most [CII]-luminous galaxies at z~4.5 from the ALPINE survey to assess the detectability of these lines in high-z main-sequence (MS) galaxies and to test the reliability of [CII] emission as a molecular gas tracer through the cross-comparison of molecular gas masses inferred from six tracers: CO(4-3), CO(5-4), [CI](1-0), [CII], dust continuum, and [CII]-based dynamical mass, adopting standard calibrations and conversion factors. We detect CO(4-3) and CO(5-4) lines at high significance in the near-solar metallicity galaxy DC873756, obtain a tentative CO(4-3) detection in the merging system DC818760, and detect no CO emission in the half-solar metallicity galaxy VC5110377875. [CI] remains undetected in all three galaxies. In DC873756 the molecular gas masses inferred from the six considered tracers agree within their uncertainties despite different systematics inherent to each tracer. The agreement suggests that, at least for some near-solar metallicity MS galaxies at z~4.5, the CO SLED and Milky Way CO-to-H2 conversion factor adopted for MS galaxies at cosmic noon remain applicable and that mid-J CO transitions trace a substantial fraction of the molecular gas reservoir. The CO non-detection in VC5110377875 is consistent with the reduced CO detectability expected at lower metallicities. In DC818760 we find an inconsistency between the [CII]-based molecular gas mass and masses derived from the other tracers, indicating a [CII] excess possibly reflecting enhanced emission from shocks and/or diffuse ionized gas in merger-driven conditions.

astro-ph.GA↗

arXiv2026

Euclid Quick Data Release (Q1). Searching for radio-selected \Euclid-dark galaxies in the EDF-N

We present and investigate the properties of a sample of radio-selected, Euclid-dark galaxies, identified from LOFAR HBA observations at 144 MHz within the Euclid Deep Field-North (EDF-N). Starting from radio sources lacking optical counterparts in previous surveys, but detected with Spitzer/IRAC, we identified 166 galaxies with no emission at a more than $3\sigma$ level in Euclid Quick Release 1 (Q1) images, and no matches in the Euclid Q1 catalogue. To minimise contamination from nearby sources, we selected a sub-sample of 88 isolated galaxies. By exploiting multi-band images and catalogues available for the EDF-N, we inferred the physical properties of our sample via SED fitting. The resulting redshift distribution spans $0.4 \leq z_\mathrm{ph} \leq 5.0$. We used recent sub-arcsecond imaging from the International LOFAR Telescope to constrain the nature of the compact radio emission through brightness temperature estimates. By combining this information with the radio excess relative to the infrared/radio correlation (IRRC), we searched for possible active galactic nuclei (AGN) activity. Approximately 40% of our sources show evidence of AGN activity. The Euclid-dark sources detected in the far-infrared are consistent with a population of heavily obscured, massive star-forming galaxies with high star formation rates. Their location above the star-forming main sequence is consistent with similar near-infrared-dark galaxy populations reported in the literature. We also performed a UV-to-radio median stacking analysis, finding that the two subsamples exhibit similar global physical properties and differ primarily in their radio emission. These preliminary results indicate that the wide area covered by Euclid enables the identification of a higher fraction of systems in which intense star formation and AGN activity coexist, likely capturing a key phase of galaxy--black hole co-evolution.

astro-ph.GA↗

arXiv2026

Globular Clusters in the Time of the JWST. I. Survey Design and First Results on Multiple Populations and Beyond

Globular clusters (GCs) host multiple stellar populations with distinct chemical compositions, but their properties among very low-mass stars remain poorly constrained. The James Webb Space Telescope (JWST) enables precise infrared studies that are highly sensitive to abundance variations in cool stars. We initiate a homogeneous survey of Galactic GCs, based primarily on deep JWST GO-8960 observations and complemented by archival JWST and Hubble Space Telescope data, to characterize multiple populations across a wide range of cluster properties. In this first paper, we present the survey and initial NIRCam results. We analyze eleven GCs, deriving high-precision photometry and astrometry to measure proper motions. Multiple populations are detected among low-mass stars in all clusters, with diverse behaviors. We find discrete main sequences in NGC 288, NGC 6723, and NGC 2808, and more continuous distributions in NGC 104 and the Type II clusters NGC 1851 and NGC 6656. The bulge clusters NGC 6528, NGC 6553, and NGC 6440 show patterns consistent with varying helium and oxygen abundances that do not scale simply with cluster mass. In Terzan 5 and Liller 1, we identify populations spanning different ages and helium variations within the old population of Terzan 5. We also detect an M-dwarf gap in NGC 104 around 0.35 solar masses, consistent with the Jao Gap of field stars and open clusters. This work establishes the foundation for a homogeneous JWST survey of Galactic GCs and provides a valuable dataset for studies of cluster evolution, Galactic stellar populations, and background extragalactic sources.

astro-ph.GA↗

arXiv2026

No Blue without Red: Evolutionary Properties of Super-Early Galaxies

The discovery of numerous luminous, super-early galaxies at $z>10$ by JWST has revealed a striking diversity in their ultraviolet (UV) properties, ranging from extremely blue, dust-poor systems to a smaller population of significantly reddened sources. We investigate the physical origin of this diversity within the framework of the Attenuation-Free Model (AFM), in which radiation-driven outflows redistribute dust to large galactic radii, reducing the effective attenuation. Applying the model to a sample of 32 spectroscopically confirmed super-early galaxies, we derive their key physical properties, including halo mass, star formation efficiency, metallicity, and outflow extent. We find that these systems reside in massive halos ($\log M/M_\odot \sim 10.7$) and exhibit moderate ($0.01 \lesssim \epsilon_* \lesssim 0.05$) star formation efficiencies, while frequently reaching super-Eddington conditions that trigger powerful outflows. Within this framework, we propose an evolutionary sequence in which galaxies transition from a dust-obscured ``Red Monster'' phase to a UV-bright ``Blue Monster'' phase as outflows clear their central regions. The recently confirmed red galaxy EGS-z11-R0 at $z=11.45$ is naturally interpreted as a system observed during this obscured phase. Compact ($r_e \lesssim 150$ pc) sources are instead difficult to reconcile within AFM; we speculate that their emission is dominated by an AGN. Our results provide a unified interpretation of super-early galaxy properties and highlight the key role of radiation-driven outflows in shaping galaxy evolution at cosmic dawn. Future observations with JWST and ALMA will be essential to test these predictions and further constrain the nature of the earliest galaxies.

astro-ph.GA↗

arXiv2026

An X-ray and optical spectral study of the changing-look narrow-line Seyfert 1 2MASX J0413-0050

Active galactic nuclei (AGN) showing dramatic spectral and flux variations, either due to changes in the accretion rate (changing-state, CS-AGN) of the supermassive black hole or in the line-of-sight column density (changing-obscuration, CO-AGN), have been classified as changing-look (CL) AGN. Here we present a peculiar source, 2MASX J0413-0050, first identified as a narrow-line Seyfert 1 (NLS1s) galaxy in 2004. When re-observed twice in 2021, it showed a transition in the spectral type (towards a Seyfert 1.9) and the complete and mysterious disappearance of the Hbeta line while source was in a high accretion state. In the meantime, the X-ray flux decreased between observations taken in 2020 and 2022, and again in the most recent spectrum of 2023. Shortly after this, another optical spectrum revealed the re-emergence of both the narrow and broad Hbeta components (Seyfert 1.8). Despite the fact that it was not possible to retrieve the line-of-sight column density from the X-ray spectra, which would have helped in assessing whether this event could be attributed to a CO AGN scenario, the observational evidence does not necessarily support such an interpretation. J0413-0050 may have undergone several switch-on switch-off phases over the past 20 years, on an unknown timescale, which could have affected the accretion power and, consequently, the optical continuum and so the emission lines coming from the broad-line region (BLR). For these reasons, it is reasonable to classify this source as a CS-AGN. The case of J0413-0050 supports the hypothesis that NLS1s can indeed experience CL phenomena.

astro-ph.HE↗

arXiv2026

Euclid: Scaled-up little red dots and other sources with v-shaped spectral energy distributions at z>4

Little Red Dots (LRDs) are some the most intriguing galaxy populations recently identified at z>~4 with JWST. They constitute the most extreme class of a more abundant population of sources with `V-shaped' spectral energy distributions (SEDs) and compact morphologies, which includes also Little Blue Dots (LBDs). Finding brighter analogues to these sources requires surveying sky areas which are significantly larger than those covered with JWST. Euclid deep images are ideally suited for this purpose. We make use of Euclid near-infrared images, complemented by Spitzer Infrared Array Camera (IRAC) data, over 0.75 sq. deg. of the COSMOS field to select a sample of 233 sources with `V-shaped' SEDs at z>4. Out of those, we identify 16 sources with compactness >1sigma above the median of all z>4 galaxies, which we consider robust LRD/LBD candidates in our sample. The stellar masses of these 16 sources are in the range 10^{8.5} - 10^{10.5} Msun, so they are significantly more massive than typical JWST-selected LRDs/LBDs. Interestingly, half of them are about as old as the Universe at their redshifts. In addition, we find that the median photometric properties of the Euclid LRDs/LBDs are similar to those of the so-called Blue Dust-Obscured Galaxies (Blue DOGs). Less than 10% of all our `V-shaped' SED sources, including only one of the Euclid LBDs, correspond to known AGN. The latter mostly constitute a population disjoint to the `V-shaped' SED sources. Spectroscopic follow up of the Euclid LRDs/LBD candidates remains necessary to probe whether they host BLAGN as fainter analogues do and whether constitute a transition phase from these fainter sources to standard AGN.

astro-ph.GA↗

arXiv2026

JWST Reveals Two Overmassive Black Hole Candidates in Dwarf Galaxies at z $\approx$ 0.7: Pushing Black Hole Searches into the Dwarf-Galaxy Regime

We report the discovery and characterization of two compact galaxies, Pelias and Neleus, at z ~ 0.71 and z ~ 0.75, identified in MACS J0416.1-2403 and GOODS-North. Both exhibit unusual spectral energy distributions (SEDs), with very blue rest-frame UV-optical emission and a steep rise toward near- and mid-infrared wavelengths. JWST/NIRISS and JWST/NIRSpec spectroscopy show strong rest-frame optical lines ([O III] 4959,5007 and Halpha) with extreme equivalent widths (>= 1000 Angstrom), indicating young burst-dominated populations with low metallicities (Z ~ 0.1-0.4 Zsun), low dust attenuation (Av ~ 0.2 mag), and stellar masses of Mstar ~ 10^7 Msun. Nonetheless, JWST/MIRI photometry reveals a strong mid-infrared excess that cannot be explained by stellar populations or star-formation-heated dust alone, requiring a hot-dust component most naturally associated with a deeply embedded active galactic nucleus (AGN). SED modelling yields log10(Lbol [erg/s]) ~ 43.7-44.0, implying black hole masses of log10(MBH [Msun]) ~ 5.7-6.7 under the assumption of Eddington-limited accretion. Given the very low stellar masses of the hosts, this corresponds to black-hole-to-stellar mass ratios of about 6-60%, well above the extrapolation of local scaling relations. The lack of X-ray detections suggests that the accretion may be either heavily obscured or intrinsically X-ray weak. Their SEDs also resemble those of Blue Excess Hot Dust Obscured Galaxies and show the characteristic V-shaped continuum seen in Little Red Dots, although with the inflection occurring at redder wavelengths.

astro-ph.GA↗

arXiv2026

First Sardinia Radio Telescope detection of the Sunyaev-Zel'dovich effect at 18.6 GHz

Galaxy clusters imprint a distinctive signature on the cosmic microwave background through the thermal Sunyaev-Zel'dovich (SZ) effect, which enables to study the intracluster plasma distribution and makes them powerful cosmological probes. We present the first Sardinia Radio Telescope (SRT) detection of the SZ effect in the galaxy cluster MACS J1752+4440 at 18.6 GHz, with a resolution of 0.9'. We detected a decrement in brightness toward the cluster centre, which we attributed to the thermal SZ effect. We modelled the signal using a spherically symmetric $\beta$ model for the electron density distribution and we employed a Bayesian retrieval to estimate the core radius, central electron density, and $\beta$ parameter of the cluster. We found values consistent with expectations for a galaxy cluster of the mass of MACS J1752+4440: a core radius of ($160 \pm 30$) kpc, a central electron density of ($2.5^{+0.7}_{-0.5} \cdot 10^{-3}$) cm$^{-3}$, and $\beta$=$0.6\pm0.1$. The mean Compton-$y$ parameter within a radius of 3.5' is $(2.6 \pm 0.3) \cdot 10^{-5}$, higher than the value reported by Planck, which is coherent considering the different resolution of the instruments and the modelling adopted. This work demonstrates the potential of the SRT to detect the onset of the SZ decrement at low frequencies, providing higher angular resolution than current all-sky surveys and enabling an improved reconstruction of the SZ decrement profile and the plasma distribution in the intracluster medium.

astro-ph.CO↗

arXiv2025

HELM's deep: Highly Extincted Low-Mass galaxies seen by JWST

The dust content of star-forming galaxies is generally positively correlated with their stellar mass. However, some recent JWST studies have shown the existence of a population of dwarf galaxies with an unexpectedly large dust attenuation. Using the Cosmic Evolution Early Release Science Survey (CEERS) data, we identified a sample of 1361 highly extincted low-mass (HELM) galaxies, defined as dwarf galaxies ($M_*<10^{8.5}$) with Av>1mag or more massive galaxies with an exceptionally high dust attenuation given their stellar mass (i.e., $Av>1.6log_{10}(M_*/Mo)-12.6$). The selection is performed using the multiparameter distribution obtained through a comprehensive spectral energy distribution fitting analysis, based on optical to near-infrared data. After excluding possible contaminants, like brown dwarfs, little red dots, high-z (z>8.5) and ultra-high-z (z>15) galaxies, the sample mainly includes sources at z<1, with a tail extending up to z=7.2. The sample has a median stellar mass of $10^7$ Mo and a median dust attenuation of Av=2mag. We analysed the morphology, environment and star-formation rate of these sources to investigate the reason of their large dust attenuation. In particular, HELM sources have sizes (effective radii, Re) similar to non-dusty dwarf galaxies and no correlation is visible between the axis ratios (b/a) and the dust attenuation. This findings indicate that it is unlikely that the large dust attenuation is due to projection effects, but a prolate or a disk-on oblate geometry are still possible, at least for a subsample of the sources. We have found that the distribution of HELM sources is slightly skewed toward more clustered environments than non-dusty dwarfs and tend to be slightly less star forming. This finding, if confirmed by spectroscopic follow-up, indicates that HELM sources could be going through some environmental processes, such as galaxy interactions.

astro-ph.GA↗

arXiv2025

Euclid: The first statistical census of dusty and massive objects in the ERO/Perseus field

Our comprehension of the history of star formation at $z>3$ relies on rest-frame UV observations, yet this selection misses the most dusty and massive sources, yielding an incomplete census at early times. Infrared facilities such as Spitzer and the James Webb Space Telescope have revealed a hidden population at $z=3$-$6$ with extreme red colours, named HIEROs (HST-to-IRAC extremely red objects), identified by the criterion $H_{\mathrm{E}}-\mathrm{ch2}>2.25$. Recently, Euclid Early Release Observations (ERO) have made it possible to further study such objects by comparing Euclid data with ancillary Spitzer/IRAC imaging. We investigate a $232$ arcmin$^2$ area in the Perseus field using VIS and NISP photometry, complemented by the four Spitzer channels and ground-based MegaCam bands ($u$, $g$, $r$, ${\rm H}\alpha$, $i$, $z$). Applying the colour cut yields $121$ HIEROs; after removing globular clusters, brown dwarfs, and unreliable cases through visual inspection of multiband cutouts, we obtain a final sample of $42$ robust HIEROs. Photometric redshifts and physical properties are estimated with the SED-fitting code Bagpipes. From the resulting $z_{\mathrm{phot}}$ and $M_*$ values, we compute the galaxy stellar mass function at $3.5<z<5.5$. Even after excluding possible AGN hosts or systems where the stellar mass may be overestimated, the high-mass end remains comparable to previous determinations, suggesting the true abundance could be higher. These results highlight the importance of further study of this obscured population to assess its role in the cosmic star-formation rate density and its consistency with galaxy-formation models, demonstrating Euclid's capability to advance our understanding of dust-hidden star formation across early epochs.

astro-ph.GA↗

arXiv2025

Euclid Quick Data Release (Q1): Identification of massive galaxy candidates at the end of the Epoch of Reionisation

Probing the presence and properties of massive galaxies at high redshift is one of the most critical tests for galaxy formation models. In this work, we search for galaxies with stellar masses M* > 10^10.25 Msun at z in [5,7], i.e., towards the end of the Epoch of Reionisation, over a total of ~23 deg^2 in two of the Euclid Quick Data Release (Q1) fields: the Euclid Deep Field North and Fornax (EDF-N and EDF-F). In addition to the Euclid photometry, we incorporate Spitzer Infrared Camera (IRAC) and ground-based optical data to perform spectral energy distribution (SED) fitting, obtaining photometric redshifts and derived physical parameters. After applying rigorous selection criteria, we identify a conservative sample of 145 candidate massive galaxies with M* > 10^10.25 Msun at z in [5,7], including 5 objects with M* > 10^11 Msun. This makes for a surface density of about 6.3 deg^-2 at z in [5,7], which should be considered a lower limit because of the current depth of the Euclid data (H_E < 24, 5 sigma in Q1). We find that the inferred stellar masses are consistent with galaxy formation models with standard star-formation efficiencies. These massive galaxies have colour excess E(B-V) values up to 0.75, indicating significant dust attenuation in some of them. In addition, half of the massive galaxies have best-fit ages comparable to the age of the Universe at those redshifts, which suggests that their progenitors were formed very early in cosmic time. About 78% of the massive galaxies lie on the star-forming main sequence (MS) in the SFR-M* plane, ~12% are found in the starburst region, and 10% in the transition zone between the MS and starbursts. We find no significant evidence for outshining or AGN contamination that could account for the elevated specific star-formation rates (sSFR) observed in the ~12% of galaxies classified as starbursts.

astro-ph.GA↗

arXiv2025

Atomic hydrogen reservoirs in quiescent galaxies at z = 0.4

Context. Based on Local Universe observations, quiescent galaxies (QGs) host lower to no HI compared to star-forming galaxies (SFGs), but no constraints have been derived so far at higher redshift (z>0.1). Understanding whether QGs can retain significant HI reservoirs at higher z is crucial to refine quenching and gas accretion models and to constrain overall star formation efficiency at different epochs. Aims. We aim to probe HI in candidate QGs at intermediate redshifts (z=0.36) and to understand whether there exists a class of QGs retaining consistent HI reservoirs and which parameters (dust content, stellar mass, Dn4000, morphology, environment) effectively capture HI-rich QGs. Methods. We perform 21-cm spectral line stacking on MIGHTEE-HI data at z=0.36, targeting two different samples of QGs, defined by means of a color-selection criterion and a spectroscopic criterion based on Dn4000, respectively. We also perform stacking on subsamples of the spectroscopically-selected quiescent sample to investigate the correlation between the HI content and other galaxy properties. Results. We find that QGs with an IR counterpart (i.e., dusty galaxies) are found to host a substantial HI content, on average just 40% lower than SFGs. In contrast, color-selected QGs still hold HI, but lower than SFGs by a factor 3. Among dusty objects, we find morphology to have a mild impact on the atomic gas content, with spirals hosting approximately 15-30% more HI than spheroids. Environmental effects are also present, with low-density regions hosting galaxies that are HI-richer than in high-density ones, by approximately 30% for spirals and 60% for spheroids. We suggest that, in general, HI content is driven by several factors, including quenching mechanisms and ISM enrichment processes. Also, quiescent galaxies - and especially dusty systems - seem to yield HI more consistently than in the Local Universe.

astro-ph.GA↗

arXiv2025

Euclid: The potential of slitless infrared spectroscopy: A z=5.4 quasar and new ultracool dwarfs

We demonstrate the potential of Euclid's slitless spectroscopy to discover high-redshift (z>5) quasars and their main photometric contaminant, ultracool dwarfs. Sensitive infrared spectroscopy from space is able to efficiently identify both populations, as demonstrated by Euclid Near-Infrared Spectrometer and Photometer Red Grism (NISP RGE) spectra of the newly discovered z=5.404 quasar EUCL J181530.01+652054.0, as well as several ultracool dwarfs in the Euclid Deep Field North and the Euclid Early Release Observation field Abell 2764. The ultracool dwarfs were identified by cross-correlating their spectra with templates. The quasar was identified by its strong and broad CIII] and MgII emission lines in the NISP RGE 1206-1892 nm spectrum, and confirmed through optical spectroscopy from the Large Binocular Telescope. The NISP Blue Grism (NISP BGE) 926-1366 nm spectrum confirms CIV and CIII] emission. NISP RGE can find bright quasars at z~5.5 and z>7, redshift ranges that are challenging for photometric selection due to contamination from ultracool dwarfs. EUCL J181530.01+652054.0 is a high-excitation, broad absorption line quasar detected at 144 MHz by the LOw-Frequency Array (L144=4e25 W/Hz). The quasar has a bolometric luminosity of 3e12 Lsun and is powered by a 3.4e9 Msun black hole. The discovery of this bright quasar is noteworthy as fewer than one such object was expected in the ~20 deg2 surveyed. This finding highlights the potential and effectiveness of NISP spectroscopy in identifying rare, luminous high-redshift quasars, previewing the census of these sources that Euclid's slitless spectroscopy will deliver over about 14,000 deg2 of the sky.

astro-ph.GA↗

arXiv2025

Pushing JWST to the extremes: search and scrutiny of bright galaxy candidates at z$\simeq$15-30

We designed customized Lyman-break color selection techniques to identify galaxy candidates in the redshift ranges $15 \leq z \leq 20$ and $20 \leq z \leq 28$. The selection was performed on the ASTRODEEP-JWST multi-band catalogs of the CEERS, Abell-2744, JADES, NGDEEP, and PRIMER survey fields, covering a total area of $\sim0.2$ sq. deg. We identify five candidates at $15 \leq z \leq 20$, while no objects are found based on the $z\gtrsim20$ color selection criteria. Despite exhibiting a $>$1.5 mag break, all the objects display multimodal redshift probability distributions across different SED-fitting codes and methodologies. The alternative solutions correspond to poorly understood populations of low-mass quiescent or dusty galaxies at z$\sim$3-7. This conclusion is supported by the analysis of five F200W-dropout objects that we find to be interlopers on the basis of NIRSpec PRISM spectra: four dusty star-forming galaxies at z$\sim$2.2-6.6, and a passive galaxy at z=4.91 with log$(M_{\rm star}/{\rm M}_{\odot}) \lesssim$ 9. We measured the UV luminosity function under different assumptions on the contamination level within our sample. We find that if even a fraction of the candidates is indeed at $z\gtrsim15$, the resulting UV LF points to a very mild evolution compared to estimates at $z<15$, implying a significant tension with existing theoretical models. In particular, confirming our bright ($M_{\text{UV}}<-21$) candidates would require substantial revisions to the theoretical framework. In turn, if all these candidates will be confirmed to be interlopers, we conclude that future surveys may need ten times wider areas to select $M_{\text{UV}}\lesssim-20$ galaxies at $z>15$. Observations in the F150W and F200W filters at depths comparable to those in the NIRCam LW bands are also required to mitigate contamination from rare red objects at z$\lesssim$8.

astro-ph.GA↗

arXiv2025

Euclid Quick Data Release (Q1). A first view of the star-forming main sequence in the Euclid Deep Fields

The star-forming main sequence (SFMS) is a tight relation observed between stellar masses and star formation rates (SFR) in a population of galaxies. This relation is observed at different redshifts, in various morphological, and environmental domains, and is key to understanding the underlying relations between a galaxy budget of cold gas and its stellar content. Euclid Quick Data Release 1 (Q1) gives us the opportunity to investigate this fundamental relation in galaxy formation and evolution. We complement the Euclid release with public IRAC observations of the Euclid Deep Fields, improving the quality of recovered photometric redshifts, stellar masses, and SFRs, as is shown both with simulations and a comparison with available spectroscopic redshifts. From Q1 data alone, we recover more than $\sim 30\,\mathrm{k}$ galaxies with $\log_{10} (M_\ast/M_\odot) > 11$, giving a precise constraint of the SFMS at the high-mass end. We investigated the SFMS, in a redshift interval between $0.2$ and $3.0$, comparing our results with the existing literature and fitting them with a parameterisation taking into account the presence of a bending of the relation at the high-mass end, depending on the bending mass, $M_0$. We find good agreement with previous results in terms of $M_0$ values, and an increasing trend for the relation scatter at higher stellar masses. We also investigate the distribution of physical (e.g. dust absorption, $A_V$, and formation age) and morphological properties (e.g., S\'ersic index and radius) in the SFR--stellar mass plane, and their relation with the SFMS. These results highlight the potential of Euclid in studying the fundamental scaling relations that regulate galaxy formation and evolution in anticipation of the forthcoming Data Release 1.

astro-ph.GA↗

arXiv2025

Euclid Quick Data Release (Q1). An investigation of optically faint, red objects in the Euclid Deep Fields

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. Recently, infrared data from Spitzer and the James Webb Space Telescope (JWST) have revealed a hidden population at $z\sim$3-6 with extreme red colours. Taking advantage of the overlap between imaging in the Euclid Deep Fields (EDFs), covering $\sim$ 60 deg$^2$, and ancillary Spitzer observations, we identified 27000 extremely red objects with $H_E-{\rm IRAC}2>2.25$ (dubbed HIEROs) down to a $10\sigma$ completeness magnitude limit of IRAC2 $=$ 22.5 AB. After a visual inspection to discard artefacts and objects with troubling photometry, we ended up with a final sample of 3900 candidates. We retrieved the physical parameter estimates for these objects from the SED-fitting tool CIGALE. Our results confirm that HIERO galaxies may populate the high-mass end of the stellar mass function at $z>3$, with some reaching extreme stellar masses ($M_*>10^{11}M_\odot$) and exhibiting high dust attenuation ($A_V>3$). However, we consider stellar mass estimates unreliable for $z>3.5$, favouring a lower-z solution. The challenges faced by SED-fitting tools in characterising these objects highlight the need for further studies, incorporating shorter-wavelength 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 understanding galaxy evolution. This work demonstrates Euclid's potential to provide statistical samples of rare, massive, dust-obscured galaxies at $z>3$, which will be prime targets for JWST, ALMA, and ELT.

astro-ph.GA↗

arXiv2025

Euclid Quick Data Release (Q1). Extending the quest for little red dots to z<4

Recent James Webb Space Telescope (JWST) observations have revealed a population of sources with a compact morphology and a characteristic `v-shaped' continuum, namely blue at rest-frame $\lambda<4000$A and red at longer wavelengths. The nature of these sources, called `little red dots' (LRDs), is still debated, as it is unclear if they host active galactic nuclei (AGN) and their number seems to drastically drop at z<4. We take advantage of the $63 \deg^2$ covered by the quick Euclid Quick Data Release (Q1) to extend the search for LRDs to brighter magnitudes and to lower redshifts than what has been possible with JWST. The selection is 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 both the rest-frame optical and UV slopes consistently over a large redshift range (i.e, z<7.6). We exclude extended objects and possible line emitters, and perform a careful visual inspection to remove any imaging artefacts. The final selection includes 3341 LRD candidates at z=0.33-3.6, with 29 detected also 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-z down to z=1.5-2.5 and decreases at lower z. However, less evolution is apparent focusing on the subsample of more robust LRD candidates having IRAC detections, which however has low statistics and limited by the IRAC resolution. The comparison with previous quasar (QSO) UV luminosity functions shows that LRDs are not the dominant AGN population at z<4 and $M_{\rm UV}<-21$. Follow-up studies of these LRD candidates are pivotal to confirm their nature, probe their physical properties and check for their compatibility with JWST sources, given the different spatial resolution and wavelength coverage of Euclid and JWST.

astro-ph.GA↗

arXiv2025

Ultra High-Redshift or Closer-by, Dust-Obscured Galaxies? Deciphering the Nature of Faint, Previously Missed F200W-Dropouts in CEERS

The James Webb Space Telescope (JWST) is revolutionizing our understanding of the Universe by unveiling faint, near-infrared dropouts previously beyond our reach, ranging from exceptionally dusty sources to galaxies up to redshift $z \sim 14$. In this paper, we identify F200W-dropout objects in the Cosmic Evolution Early Release Science (CEERS) survey which are absent from existing catalogs. Our selection method can effectively identify obscured low-mass ($\log \text{M}_* \leq 9$) objects at $z \leq 6$, massive dust-rich sources up to $z \sim 12$, and ultra-high-redshift ($z > 15$) candidates. Primarily relying on NIRCam photometry from the latest CEERS data release and supplementing with Mid-Infrared/(sub-)mm data when available, our analysis pipeline combines multiple SED-fitting codes, star formation histories, and CosMix - a novel tool for astronomical stacking. Our work highlights three $2 15$, with best-fit masses compatible with $\Lambda$CDM and a standard baryons-to-star conversion efficiency. Their bi-modal redshift probability distributions suggest they could also be $z<1.5$ dwarf galaxies with extreme dust extinction. We also identify a strong line emitter galaxy at $z \sim 5$ mimicking the near-infrared emission of a $z \sim 13$ galaxy. Our sample holds promising candidates for future follow-ups. Confirming ultra high-redshift galaxies or lower-z dusty dwarfs will offer valuable insights into early galaxy formation, evolution with their central black holes and the nature of dark matter, and/or cosmic dust production mechanisms in low-mass galaxies, and will help us to understand degeneracies and contamination in high-z object searches.

astro-ph.GA↗