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James Webb (télescope spatial)

Résumé

Le James Webb (JWST, pour l'anglais James Webb Space Telescope) est un télescope spatial servant d'observatoire fonctionnant principalement dans l'infrarouge, développé par la NASA avec la participation de l'Agence spatiale européenne (ESA) et de l'Agence spatiale canadienne (ASC). Plus grand et plus onéreux télescope spatial à son lancement, le JWST est conçu pour poursuivre les travaux du télescope spatial Hubble, en effectuant toutefois ses observations dans des longueurs d'onde plus longues. Son lancement a lieu le et la première image de qualité scientifique produite par le télescope est publiée en . Les observations du JWST sont centrées sur l'infrarouge proche et moyen, tout en incluant une partie du spectre située dans le domaine du visible (longueurs d'onde allant de ). Par sa résolution, sa surface collectrice et la bande spectrale couverte, il surpasse largement Hubble pour l'observation dans l'infrarouge, mais, contrairement à celui-ci, il ne peut observer ni l'ultravio

Source officielle

https://fr.wikipedia.org/wiki/James_Webb_(t%C3%A9lescope_spatial)

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, , , ,

We use deep Hubble Space Telescope imaging of the Frontier Fields to accurately measure the galaxy rest-frame ultraviolet luminosity function (UV LF) in the redshift range z similar to 6-8. We combine observations in three lensing clusters, A2744, MACS 0416, and MACS 0717, and their associated parallel. fields to select high-redshift dropout candidates. We use the latest lensing models to estimate the flux magnification and the effective survey volume in combination with completeness simulations performed in the source plane. We report the detection of 227 galaxy candidates at z = 6-7 and 25 candidates at z similar to 8. While the total survey area is about 4 arcmin(2) in each parallel field, it drops to about 0.6-1 arcmin(2) in the cluster core fields because of the strong lensing. We compute the UV LF at z similar to 7 using the combined galaxy sample and perform Monte Carlo simulations to determine the best-fit Schechter parameters. We are able to reliably constrain the LF down to an absolute magnitude of M-UV = -15.25, which corresponds to 0.005 L-star. More importantly, we find that the faint-end slope remains steep down to this magnitude limit with alpha = -2.04(-0.17)(+0.13). We find a characteristic magnitude of M-star = -20.89(-0.72)(+0.60) and log (phi(star)) = -3.54(-0.45)(+0.48). Our results confirm the most recent results in deep blank fields but extend the LF measurements more than two magnitudes deeper. The UV LF at z similar to 8 is not very well constrained below M-UV = -18 owing to the small number statistics and incompleteness uncertainties. To assess the contribution of galaxies to cosmic reionization, we derive the UV luminosity density at z similar to 7 by integrating the UV LF down to an observational limit of M-UV = -15. We show that our determination of log(rho(UV)) = 26.2 +/- 0.13 (erg s(-1) Hz(-1) Mpc(-3)) can be sufficient to maintain reionization with an escape fraction of ionizing radiation of f(esc) = 10%-15%. Future Hubble Frontier Fields observations will certainly improve the constraints on the UV LF at the epoch of reionization, paving the way to more ambitious programs using cosmic telescopes with the next generation of large aperture telescopes such as the James Webb Space Telescope and the European Extremely Large Telescope.

Iop Publishing Ltd2015

Chargement

Molecular gas in radio galaxies in dense megaparsec-scale environments at z=0.4-2.6

Gianluca Castignani

Context. Low luminosity radio galaxies (LLRGs) typically reside in dense megaparsec-scale environments and are often associated with brightest cluster galaxies (BCGs). They are an excellent tool to study the evolution of molecular gas reservoirs in giant ellipticals, even close to the active galactic nucleus. Aims. We investigate the role of dense megaparsec-scale environment in processing molecular gas in LLRGs in the cores of galaxy (proto-)clusters. To this aim we selected within the COSMOS and DES surveys a sample of five LLRGs at z = 0.4-2.6 that show evidence of ongoing star formation on the basis of their far-infrared (FIR) emission. Methods. We assembled and modeled the FIR-to-UV spectral energy distributions (SEDs) of the five radio sources to characterize their host galaxies in terms of stellar mass and star formation rate. We observed the LLRGs with the IRAM-30m telescope to search for CO emission. We then searched for dense megaparsec-scale overdensities associated with the LLRGs using photometric redshifts of galaxies and the Poisson Probability Method, which we have upgraded using an approach based on the wavelet-transform (wPPM), to ultimately characterize the overdensity in the projected space and estimate the radio galaxy miscentering. Color-color and colormagnitude plots were then derived for the fiducial cluster members, selected using photometric redshifts. Results. Our IRAM-30m observations yielded upper limits to the CO emission of the LLRGs, at z = 0 : 39, 0.61, 0.91, 0.97, and 2.6. For the most distant radio source, COSMOS-FRI 70 at z = 2 : 6, a hint of CO(7 -> 6) emission is found at 2.2 sigma. The upper limits found for the molecular gas content M(H-2) = M-star< 0 : 11, 0.09, 1.8, 1.5, and 0.29, respectively, and depletion time tau(dep) less than or similar to (0.2-7) Gyr of the five LLRGs are overall consistent with the corresponding values of main sequence field galaxies. Our SED modeling implies large stellar-mass estimates in the range log(M-star/M-Theta) = 10.9-11.5, typical for giant ellipticals. Both our wPPM analysis and the cross-matching of the LLRGs with existing cluster/group catalogs suggest that the megaparsec-scale overdensities around our LLRGs are rich (less than or similar to 10(14) M-Theta) groups and show a complex morphology. The color-color and color-magnitude plots suggest that the LLRGs are consistent with being star forming and on the high-luminosity tail of the red sequence. The present study thus increases the still limited statistics of distant cluster core galaxies with CO observations. Conclusions. The radio galaxies of this work are excellent targets for ALMA as well as next-generation telescopes such as the James Webb Space Telescope.

EDP SCIENCES S A2019

Chargement

Molecular gas in distant brightest cluster galaxies

Gianluca Castignani

The mechanisms governing the stellar mass assembly and star formation history of brightest cluster galaxies (BCGs) are still being debated. By means of new and archival molecular gas observations we investigate the role of dense megaparsec-scale environments in regulating the fueling of star formation in distant BCGs, through cosmic time. We observed in CO with the IRAM 30 m telescope two star-forming BCGs belonging to SpARCS clusters, namely, 3C 244.1 (z=0.4) and SDSS J161112.65+550823.5 (z=0.9), and compared their molecular gas and star formation properties with those of a compilation of similar to 100 distant cluster galaxies from the literature, including nine additional distant BCGs at z similar to 0.4-3.5. We set robust upper limits of M-H2< 1.0x10(10) M-circle dot and < 2.8x10(10) M-circle dot to their molecular gas content, respectively, and to the ratio of molecular gas to stellar mass M(H-2)/M-star less than or similar to 0.2 and depletion time tau(dep)less than or similar to 40 Myr of the two targeted BCGs. They are thus among the distant cluster galaxies with the lowest gas fractions and shortest depletion times. The majority (64%+/- 15% and 73%+/- 18%) of the 11 BCGs with observations in CO have lower M(H-2)/M-star values and tau(dep), respectively, than those estimated for main sequence galaxies. Statistical analysis also tentatively suggests that the values of M(H-2)/M-star and tau(dep) for the 11 BCGs deviates, with a significance of similar to 2 sigma, from those of the comparison sample of cluster galaxies. A morphological analysis for a subsample of seven BCGs with archival HST observations reveals that 71%+/- 17% of the BCGs are compact or show star-forming components or substructures. Our results suggest a scenario where distant star-forming BCGs assemble a significant fraction similar to 16% of their stellar mass on the relatively short timescale similar to tau(dep), while environmental mechanisms might prevent the replenishment of gas feeding the star formation. We speculate that compact components also favor the rapid exhaustion of molecular gas and ultimately help to quench the BCGs. Distant star-forming BCGs are excellent targets for ALMA and for next-generation telescopes such as the James Webb Space Telescope.

2020

Chargement

Molecular gas in distant brightest cluster galaxies

Gianluca Castignani

2020

Molecular gas in radio galaxies in dense megaparsec-scale environments at z=0.4-2.6

Gianluca Castignani

EDP SCIENCES S A2019

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Iop Publishing Ltd2015