A z=1.85 galaxy group in CEERS: evolved, dustless, massive intra-halo light and a brightest group galaxy in the making

We present CEERS JWST/NIRCam imaging of a massive galaxy group at z=1.85, to explore the early JWST view on massive group formation in the distant Universe. The group contains >16 members (including 6 spectros. confirmations) down to log10(Mstar/Msun)=8.5, including the brightest group galaxy (BGG) in the process of actively assembling at this redshift. The BGG is comprised of multiple merging components extending ~3.6" (30kpc) across the sky. The BGG contributes 69% of the group's total galactic stellar mass, with one of the merging components containing 76% of the total mass of the BGG and a SFR>1810Msun/yr. Most importantly, we detect intra-halo light (IHL) in several HST and JWST/NIRCam bands, allowing us to construct a state-of-the-art rest-frame UV-NIR Spectral Energy Distribution of the IHL for the first time at this high redshift. This allows stellar population characterisation of both the IHL and member galaxies, as well as the morphology distribution of group galaxies vs. their star-formation activity when coupled with Herschel data. We create a stacked image of the IHL, giving us a sensitivity to extended emission of 28.5 mag/arcsec2 at rest-frame 1um. We find that the IHL is extremely dust poor (Av~0), containing an evolved stellar population of log10(t50/yr)=8.8, corresponding to a formation epoch for 50% of the stellar material 0.63Gyr before z=1.85. There is no evidence of ongoing star-formation in the IHL. The IHL in this group at z=1.85 contributes ~10% of the total stellar mass, comparable with what is observed in local clusters. This suggests that the evolution of the IHL fraction is more self-similar with redshift than predicted by some models, challenging our understanding of IHL formation during the assembly of high-redshift clusters. JWST is unveiling a new side of group formation at this redshift, which will evolve into Virgo-like structures in the local Universe.Comment: 14 pages + appendix, 11 figures, 4 tables. Accepted to A&A on 15th May 202

CEERS: 7.7 μ{\mu}m PAH Star Formation Rate Calibration with JWST MIRI

We test the relationship between UV-derived star formation rates (SFRs) and the 7.7 ${\mu}$m polycyclic aromatic hydrocarbon (PAH) luminosities from the integrated emission of galaxies at z ~ 0 - 2. We utilize multi-band photometry covering 0.2 - 160 ${\mu}$m from HST, CFHT, JWST, Spitzer, and Herschel for galaxies in the Cosmic Evolution Early Release Science (CEERS) Survey. We perform spectral energy distribution (SED) modeling of these data to measure dust-corrected far-UV (FUV) luminosities, $L_{FUV}$, and UV-derived SFRs. We then fit SED models to the JWST/MIRI 7.7 - 21 ${\mu}$m CEERS data to derive rest-frame 7.7 ${\mu}$m luminosities, $L_{770}$, using the average flux density in the rest-frame MIRI F770W bandpass. We observe a correlation between $L_{770}$ and $L_{FUV}$, where log $L_{770}$ is proportional to (1.27+/-0.04) log $L_{FUV}$. $L_{770}$ diverges from this relation for galaxies at lower metallicities, lower dust obscuration, and for galaxies dominated by evolved stellar populations. We derive a "single-wavelength" SFR calibration for $L_{770}$ which has a scatter from model estimated SFRs (${{\sigma}_{{\Delta}SFR}}$) of 0.24 dex. We derive a "multi-wavelength" calibration for the linear combination of the observed FUV luminosity (uncorrected for dust) and the rest-frame 7.7 ${\mu}$m luminosity, which has a scatter of ${{\sigma}_{{\Delta}SFR}}$ = 0.21 dex. The relatively small decrease in ${\sigma}$ suggests this is near the systematic accuracy of the total SFRs using either calibration. These results demonstrate that the rest-frame 7.7 ${\mu}$m emission constrained by JWST/MIRI is a tracer of the SFR for distant galaxies to this accuracy, provided the galaxies are dominated by star-formation with moderate-to-high levels of attenuation and metallicity.Comment: 20 pages, 11 figures, 2 tables, submitted to Ap

JWST CEERS probes the role of stellar mass and morphology in obscuring galaxies

A population of massive galaxies invisible or very faint in deep optical/near-infrared surveys, but brighter at longer wavelengths has been uncovered in the past years. However, the nature of these optically dark/faint galaxies (OFGs, among other nomenclatures) is highly uncertain. In this work, we investigate the drivers of dust attenuation in the JWST era. Particularly, we study the role of stellar mass, size, and orientation in obscuring star-forming galaxies (SFGs) at $3 < z < 7.5$, focusing on understanding why galaxies like OFGs are so faint at optical/near-infrared wavelengths. We find that stellar mass is the primary proxy of dust attenuation among those studied. Effective radius and axis ratio do not show a clear link with dust attenuation, with the effect of orientation close to random. However, there is a subset of highly dust attenuated ($A_V > 1$, typically) SFGs, of which OFGs are a specific case. For this subset, we find that the key distinctive feature is their compact size (for massive systems with $\log (M_{*}/M_{\odot}) > 10$), exhibiting 30% smaller effective radius than the average SFGs at the same stellar mass and redshift. On the contrary, they do not exhibit a preference for low axis ratios (i.e., edge-on disks). The results in this work show stellar mass as a primary proxy of dust attenuation and compact stellar light profiles behind thick dust columns obscuring typical massive SFGs.Comment: Submitted to A&A. 13 pages, 9 figure

JWST : De l'élaboration d'un catalogue infrarouge à l'étude des galaxies poussiéreuses lointaines

On Christmas Day 2021, the most powerful space telescope ever built by mankind was sent into space. This telescope, the James Webb, with its huge mirror and high sensitivity in the infrared promised to revolutionize our understanding of the distant Universe. Within the framework of the CEERS collaboration led by S. Finkelstein, and in order to be fully prepared for the reception of the first images of the telescope, I built a catalog of bright sources in the far infrared (24μm - 1.1mm). To achieve this, I applied the state-of-the-art "super-deblending" method developed by E. Daddi, D. Liu and S. Jin. This method relies on an active selection of priors to fit based on predictions from spectral energy distribution (SED) fitting of each galaxy. Thus, by measuring fluxes in more and more confused images, I was able to select only the sources that I knew would be the brightest. In order to measure the most realistic fluxes, I performed Monte-Carlo simulations to correct the measurement bias and obtain Gaussian uncertainties. To build this catalog, I exploited all the images taken by different space-based and ground-based IR telescopes, namely Spitzer, Herschel, JCMT, LMT and the VLA for the radio allowing a better selection of priors, especially at high redshift.Based on this catalog, which is the deepest existing far-infrared catalog in the EGS field (which is the field of interest in this manuscript), I selected the brightest sources around cosmic noon (1.5 < z < 3) in order to study them through the eye of the James Webb Space Telescope.I investigated the morphology and physical properties of a sample of 22 IR-selected dusty star-forming galaxies (DSFGs) at Cosmic Noon (z ≈ 2), using JWST Near Infra-Red Camera images obtained in the EGS field for the CEERS survey.The exceptional resolution of the NIRCam images allowed me to spatially resolve these galaxies up to 4.4μm and identify their bulge/core even when very extinguished by dust.Based on red-green-blue images using the F115W, F200W and F444W filters, I divided each galaxy in several uniformly colored regions, fitted their respective SED and measured dust attenuations, stellar masses, star formation rates and ages. After classifying each region as star-forming or quiescent, I assigned galaxies to three classes, depending on whether active star-formation was located in the core, in the disk or in both. The main results are:(i) ≈ 70% of my DSFGs have a compact highly dust attenuated star-forming core that can contain up to 80% of the star-formation of the galaxy but only 20-30% of its stellar mass, and is always surrounded by a larger, less attenuated massive disk (no blue nuggets);(ii) 64% (27%) of disks are significantly (strongly) lopsided, likely due to asymmetric cold gas accretion, major mergers and/or large scale instabilities; (iii) 23% of galaxies have a star-forming core embedded in a quiescent disk, they are undergoing outside-in quenching, often facilitated by their strong lopsidedness inducing small and large scale instabilities; (iv) some galaxies host highly heterogeneous disks in terms of RGB colors: these are driven by in-homogeneous dust attenuation; and (v) I found surprising evidence for clump-like substructures being quiescent and/or residing in quiescent regions.The work carried out as part of this thesis demonstrates the incredible power of the JWST and its impact, as it enables for the first time to probe distant galaxies in the infrared and resolve them spatially, revealing the complexity of their formation and evolution.Le jour de Noël 2021, le télescope spatial le plus puissant jamais construit par l'humanité a été envoyé dans l'espace. Ce télescope, le James Webb, avec son immense miroir et sa grande sensibilité dans l'infrarouge, promettait de révolutionner notre compréhension de l'Univers. Dans le cadre de la collaboration CEERS dirigée par S. Finkelstein, et afin d'être prêts dès la réception des premières images du télescope, j'ai construit un catalogue de sources brillantes dans l'infrarouge lointain (24μm - 1.1mm). Pour ce faire, j'ai appliqué la méthode de pointe du "super-débruitage" développée par E. Daddi, D. Liu et S. Jin. Cette méthode repose sur une sélection active des sources à fitter basée sur des prédictions issues du fit de la distribution spectrale d'énergie (SED) de chaque galaxie. Ainsi, en mesurant des flux dans des images de plus en plus confuses, j'ai pu sélectionner les sources que je savais être les plus brillantes. Afin de mesurer les flux les plus réalistes possible, j'ai effectué des simulations de type Monte-Carlo pour corriger les biais de mesure et obtenir des incertitudes quasi-gaussiennes. Pour construire ce catalogue, j'ai exploité toutes les images prises par différents télescopes IR spatiaux et terrestres, à savoir Spitzer, Herschel, JCMT, LMT et le VLA, ce dernier permet une meilleure sélection des sources, en particulier à grand redshift.Sur la base de ce catalogue, qui est le catalogue infrarouge lointain le plus profond existant dans le champ EGS, j'ai sélectionné les sources les plus brillantes afin de les étudier à travers l'œil du JWST.J'ai étudié la morphologie et les propriétés physiques d'un échantillon de 22 galaxies poussiéreuses formant activement des étoiles (DSFG) sélectionnées dans l'IR au midi cosmique (z ≈ 2), en utilisant les images de la caméra proche infrarouge du JWST obtenues dans le champ EGS pour CEERS.La résolution des images NIRCam m'a permis de résoudre spatialement ces galaxies jusqu'à 4.4μm et d'identifier leur bulbe/noyau même lorsqu'elles étaient très éteintes par la poussière.Sur la base d'images rouge-vert-bleues utilisant les filtres F115W, F200W et F444W, j'ai divisé chaque galaxie en plusieurs régions uniformément colorées, fitté leur SED respective et mesuré leurs atténuations due à la poussière, leur masses stellaires, leur taux de formation d'étoiles et leurs âges. Après avoir classé chaque région comme étant active ou passive, j'ai réparti les galaxies en trois classes, selon que la formation active d'étoiles était située dans le noyau, dans le disque ou dans les deux. Les principaux résultats sont les suivants :(i) ≈ 70% de mes DSFGs ont un noyau actif compact fortement atténué par la poussière et qui peut contenir jusqu'à 80% de la formation d'étoiles de la galaxie mais seulement 20-30% de sa masse stellaire, et qui est toujours entouré d'un disque massif plus grand et moins atténué ;(ii) 64 % (27 %) des disques sont significativement (fortement) désaxés, probablement en raison d'une accrétion asymétrique de gaz froid, de fusions majeures et/ou d'instabilités à grande échelle ; (iii) 23% des galaxies ont un cœur actif au sein d'un disque éteint, elles subissent une extinction de l'extérieur vers l'intérieur, souvent facilitée par leur forte asymétrie qui induit des instabilités à petite et à grande échelle ; (iv) certaines galaxies abritent des disques très hétérogènes en termes de couleurs RVB : ces disparités sont le résultat d'une atténuation inhomogène de la poussière ; et (v) j'ai trouvé des preuves surprenantes de l'existence de sous-structures en forme d'amas globulaire dans des régions éteintes.Le travail réalisé dans le cadre de cette thèse démontre l'incroyable puissance du JWST ainsi que son impact, puisqu'il permet pour la première fois de sonder les galaxies lointaines dans l'infrarouge et de les résoudre spatialement, permettant ainsi de révéler la complexité de leur formation et de leur évolution

JWST CEERS probes the role of stellar mass and morphology in obscuring galaxies

In recent years, observations have uncovered a population of massive galaxies that are invisible or very faint in deep optical/near-infrared (near-IR) surveys but brighter at longer wavelengths. However, the nature of these optically dark or faint galaxies (OFGs; one of several names given to these objects) is highly uncertain. In this work, we investigate the drivers of dust attenuation in the JWST era. In particular, we study the role of stellar mass, size, and orientation in obscuring star-forming galaxies (SFGs) at 3'., '., 1, typically) SFGs, of which OFGs are a specific case. For this subset, we find that the key distinctive feature is their compact size (for massive systems with log(M∗/M™ ) > 10); OFGs exhibit a 30% smaller effective radius than the average SFG at the same stellar mass and redshift. On the contrary, OFGs do not exhibit a preference for low axis ratios (i.e., edge-on disks). The results in this work show that stellar mass is the primary proxy for dust attenuation and compact stellar light profiles behind the thick dust columns obscuring typical massive SFGs.</p

CEERS Key Paper. VII. JWST/MIRI reveals a faint population of galaxies at cosmic noon unseen by Spitzer

The Cosmic Evolution Early Release Science program observed the Extended Groth Strip (EGS) with the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) in 2022. In this paper, we discuss the four MIRI pointings that observed with longer-wavelength filters, including F770W, F1000W, F1280W, F1500W, F1800W, and F2100W. We compare the MIRI galaxies with the Spitzer/MIPS 24 μm population in the EGS field. We find that MIRI can observe an order of magnitude deeper than MIPS in significantly shorter integration times, attributable to JWST's much larger aperture and MIRI’s improved sensitivity. MIRI is exceptionally good at finding faint (L IR </p

A z = 1.85 galaxy group in CEERS: Evolved, dustless, massive intra-halo light and a brightest group galaxy in the making

International audienceWe present CEERS JWST/NIRCam imaging of a massive galaxy group at z = 1.85, to explore the early JWST view on massive group formation in the distant Universe. The group contains ≳16 members (including six spectroscopic confirmations) down to log 10 ( M ⋆ / M ⊙ ) = 8.5, including the brightest group galaxy (BGG) in the process of actively assembling at this redshift. The BGG is comprised of multiple merging components extending ∼3.6″ (30 kpc) across the sky. The BGG contributes 69% of the group’s total galactic stellar mass, with one of the merging components containing 76% of the total mass of the BGG and a star formation rate > 1810 M ⊙ yr −1 . Most importantly, we detected intra-halo light (IHL) in several HST and JWST/NIRCam bands, allowing us to construct a state-of-the-art rest-frame UV-NIR spectral energy distribution of the IHL for the first time at this high redshift. This allows stellar population characterisation of both the IHL and member galaxies, as well as the morphology distribution of group galaxies versus their star formation activity when coupled with Herschel data. We created a stacked image of the IHL, giving us a sensitivity to extended emission of 28.5 mag arcsec −2 at rest-frame 1 μm. We find that the IHL is extremely dust poor ( A v ∼ 0), containing an evolved stellar population of log 10 ( t 50 /yr) = 8.8, corresponding to a formation epoch for 50% of the stellar material 0.63 Gyr before z = 1.85. There is no evidence of ongoing star formation in the IHL. The IHL in this group at z = 1.85 contributes ∼10% of the total stellar mass, comparable with what is observed in local clusters. This suggests that the evolution of the IHL fraction is more self-similar with redshift than predicted by some models, challenging our understanding of IHL formation during the assembly of high-redshift clusters. JWST is unveiling a new side of group formation at this redshift, which will evolve into Virgo-like structures in the local Universe