分类： 天文学 >> 天文学 提交时间： 2023-02-19
Marco Castellano
Adriano Fontana
Tommaso Treu
Emiliano Merlin
Paola Santini
Pietro Bergamini
Claudio Grillo
Piero Rosati
Ana Acebron
Nicha Leethochawalit
Diego Paris
Andrea Bonchi
Davide Belfiori
Antonello Calabrò
Matteo Correnti
Mario Nonino
Gianluca Polenta
Michele Trenti
Kristan Boyett
G. Brammer
摘要： We report the detection of a high density of redshift $z\approx 10$ galaxies behind the foreground cluster Abell 2744, selected from imaging data obtained recently with NIRCam onboard JWST by three programs -- GLASS-JWST, UNCOVER, and DDT-2756. To ensure robust estimates of the lensing magnification $\mu$, we use an improved version of our model that exploits the first epoch of NIRCam images and newly obtained MUSE spectra, and avoids regions with $\mu>5$ where the uncertainty may be higher. We detect seven bright $z\approx 10$ galaxies with demagnified rest-frame $-22 \lesssim M_{\rm UV}\lesssim -19$ mag, over an area of $\sim37$ sq. arcmin. Taking into account photometric incompleteness and the effects of lensing on luminosity and cosmological volume, we find that the density of $z\approx 10$ galaxies in the field is about $10\times$ ($3\times$) larger than the average at $M_{UV}\approx -21 (-20)$ mag reported so far. The density is even higher when considering only the GLASS-JWST data, which are the depeest and the least affected by magnification and incompleteness. The GLASS-JWST field contains 5 out of 7 galaxies, distributed along an apparent filamentary structure of 2 Mpc in projected length, and includes a close pair of candidates with $M_{\rm UV}< -20$ mag having a projected separation of only 16 kpc. These findings suggest the presence of a $z\approx 10$ overdensity in the field. In addition to providing excellent targets for efficient spectroscopic follow-up observations, our study confirms the high density of bright galaxies observed in early JWST observations, but calls for multiple surveys along independent lines of sight to achieve an unbiased estimate of their average density and a first estimate of their clustering.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Benedetta Vulcani
Tommaso Treu
Antonello Calabro
Jacopo Fritz
Bianca Poggianti
Pietro Bergamini
Andrea Bonchi
Kit Boyett
Gabriel Caminha
Marco Castellano
Alan Dressler
Adriano Fontana
Karl Glazebrook
Claudio Grillo
Matthew Malkan
Sara Mascia
Amata Mercurio
Emiliano Merlin
Benjamin Metha
Takahiro Morishita
摘要： We combine the superior JWST/NIRCam imaging and MUSE data to characterize the properties of galaxies in different environmental conditions in the cluster Abell2744 (z=0.3064) and in its immediate surroundings. Our most striking result is the discovery of a ``red-excess'' population in F200W-F444W colors both in the cluster regions and the field. These galaxies have normal F115W-F150W colors, but are up to 0.8 mag redder than red sequence galaxies in F200W-F444W. They also have rather blue rest frame B-V colors. Galaxies with the largest color deviations are found in the field and at the cluster virial radius, suggesting that mechanisms taking place in these regions might be more effective in producing these colors. Looking at their morphology, many cluster galaxies show signatures consistent with ram pressure stripping, while field galaxies have features resembling interactions and mergers. Our hypothesis is that these galaxies are characterized by dust enshrouded star formation: a JWST/NIRSpec spectrum for one of the galaxies is dominated by a strong PAH at 3.3mu m, suggestive of dust obscured star formation. Larger spectroscopic samples are needed to understand if the color excess is due exclusively to dust-obscured star formation, and the role of environment in triggering it.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Guido Roberts-Borsani
Tommaso Treu
Wenlei Chen
Takahiro Morishita
Eros Vanzella
Adi Zitrin
Pietro Bergamini
Marco Castellano
Adriano Fontana
Claudio Grillo
Patrick L. Kelly
Emiliano Merlin
Diego Paris
Piero Rosati
Ana Acebron
Andrea Bonchi
Kit Boyett
Marusa Bradac
Tom Broadhurst
Antonello Calabro
摘要： The appearance of galaxies over the first billion years after the Big Bang is believed to be responsible for the last dramatic change in the state of the Universe. Ultraviolet photons from galaxies within this time period - the Epoch of Reionization - ionized intergalactic Hydrogen, rendering the Universe transparent to UV radiation and ending the so-called cosmic Dark Ages, sometime after redshift $z\sim8$. The majority of ionizing photons in the first few hundred Myrs of cosmic history are thought to derive from galaxies significantly fainter than the characteristic luminosity $L^{*}$. These faint galaxies are thought to be surrounded by sufficient neutral gas to prevent the escape of the Lyman-$\alpha$ photons that would allow confirmation with current observatories. Here we demonstrate the power of the recently commissioned James Webb Space Telescope to transform our understanding of the sources of reionization, by reporting the first spectroscopic confirmation of a very low luminosity ($\sim0.05 L^{*}$) galaxy at $z=9.76$, observed 480 Myr after the Big Bang, via the detection of the Lyman-break and redward continuum with the NIRSpec and NIRCam instruments. The galaxy JD1 is gravitationally magnified by a factor of $\mu\sim13$ by the foreground cluster A2744. The power of JWST and lensing allows us to peer deeper than ever before into the cosmic Dark Ages, revealing the compact ($\sim$150 pc) and complex morphology and physical properties of an ultrafaint galaxy ($M_{\rm UV}=-17.45$).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Takahiro Morishita
Guido Roberts-Borsani
Tommaso Treu
Gabriel Brammer
Charlotte A. Mason
Michele Trenti
Benedetta Vulcani
Xin Wang
Ana Acebron
Yannick Bahé
Pietro Bergamini
Kristan Boyett
Marusa Bradac
Antonello Calabrò
Marco Castellano
Wenlei Chen
Gabriella De Lucia
Alexei V. Filippenko
Adriano Fontana
Karl Glazebrook
摘要： We present the spectroscopic confirmation of a protocluster at $z=7.88$ behind the galaxy cluster Abell2744 (hereafter A2744-z7p9OD). Using JWST NIRSpec, we find seven galaxies within a projected radius of 60kpc. Although the galaxies reside in an overdensity around $>20\times$ greater than a random volume, they do not show strong Lyman-alpha emission. We place 2-$\sigma$ upper limits on the rest-frame equivalent width $ 0.45$ (68% CI). Using an empirical $M_{\rm UV}$-$M_{\rm halo}$ relation for individual galaxies, we estimate that the total halo mass of the system is $\gtrsim 4\times10^{11}\,M_\odot$. Likewise, the line of sight velocity dispersion is estimated to be $1100 \pm 200$km/s. Using an empirical relation, we estimate the present-day halo mass of A2744-z7p9OD to be $\sim2\times10^{15}\,M_\odot$, comparable to the Coma cluster. A2744-z7p9OD is the highest redshift spectroscopically confirmed protocluster to date, demonstrating the power of JWST to investigate the connection between dark-matter halo assembly and galaxy formation at very early times with medium-deep observations at $<20$hrs total exposure time. Follow-up spectroscopy of the remaining photometric candidates of the overdensity will further refine the features of this system and help characterize the role of such overdensities in cosmic reionization.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Tucker Jones
Ryan Sanders
Yuguang Chen
Xin Wang
Takahiro Morishita
Guido Roberts-Borsani
Tommaso Treu
Alan Dressler
Emiliano Merlin
Diego Paris
Paola Santini
Pietro Bergamini
Erin Huntzinger
Themiya Nanayakkara
Kristan Boyett
Marusa Bradac
Gabriel Brammer
Antonello Calabro
Karl Glazebrook
Kathryn Grasha
摘要： The abundance of carbon relative to oxygen (C/O) is a promising probe of star formation history in the early universe, as these elements are produced on different timescales. We present a measurement of $\log{\mathrm{(C/O)}} = -1.01\pm0.12$ (stat) $\pm0.10$ (sys) in a $z=6.23$ galaxy observed as part of the GLASS-JWST Early Release Science Program. Notably, we achieve good precision thanks to the detection of the rest-frame ultraviolet O III], C III], and C IV emission lines delivered by JWST/NIRSpec. The C/O abundance is $\sim$0.8 dex lower than the solar value and is consistent with the expected yield from core-collapse supernovae, indicating negligible carbon enrichment from intermediate-mass stars. This in turn implies rapid buildup of a young stellar population with age $\lesssim$100 Myr in a galaxy seen $\sim$900 million years after the Big Bang. Our chemical abundance analysis is consistent with spectral energy distribution modeling of JWST/NIRCam photometric data, which indicates a current stellar mass $\log\,\mathrm{M}_* / \mathrm{Msun} = 8.4^{+0.4}_{-0.2}$ and specific star formation rate sSFR $\simeq 20$ Gyr$^{-1}$. These results showcase the value of chemical abundances and C/O in particular to study the earliest stages of galaxy assembly.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Guido Roberts-Borsani
Takahiro Morishita
Tommaso Treu
Gabriel Brammer
Victoria Strait
Xin Wang
Marusa Bradac
Ana Acebron
Pietro Bergamini
Kristan Boyett
Antonello Calabró
Marco Castellano
Adriano Fontana
Karl Glazebrook
Claudio Grillo
Alaina Henry
Tucker Jones
Matthew Malkan
Danilo Marchesini
Sara Mascia
摘要： We present the first search for $z\geqslant7$, continuum-confirmed sources with NIRISS/WFS spectroscopy over the Abell 2744 Frontier Fields cluster, as part of the GLASS-JWST ERS survey. With $\sim15$ hrs of pre-imaging and multi-angle grism exposures in the F115W, F150W, and F200W filters, we describe the general data handling (i.e., reduction, cleaning, modeling, and extraction processes) and analysis for the GLASS-JWST survey. We showcase the power of JWST to peer deep into reionization, when most intergalactic hydrogen is neutral, by confirming two galaxies at $z=8.04\pm0.15$ and $z=7.90\pm0.13$ by means of their Lyman breaks. Fainter continuum spectra are observed in both the F150W and F200W bands, indicative of blue ($-1.69$ and $-1.33$) UV slopes and moderately-bright absolute magnitudes ($-20.37$ and $-19.68$ mag). We do not detect strong Ly$\alpha$ in either galaxy, but do observe tentative ($\sim2.7-3.8\sigma$) HeII$\lambda$1640 A, OIII]$\lambda\lambda$1661,1666 A, and NIII]$\lambda\lambda$1747,1749 A line emission in one, suggestive of low metallicity, star-forming systems with possible non-thermal contributions. These novel observations provide a first look at the extraordinary potential of JWST/NIRISS for confirming representative samples of bright $z\geqslant7$ sources in the absence of strong emission lines, and gain unprecedented insight into their contributions towards cosmic reionization.
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