分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Using the first epoch of four-band NIRCam observations obtained by the James Webb Space Telescope (JWST) Prime Extragalactic Areas for Reionization and Lensing Science Program in the Spitzer IRAC Dark Field, we search for F150W and F200W dropouts. In 14.2 arcmin^2, we have found eight F150W dropouts and eight F200W dropouts, all brighter than 27.5 mag (the brightest being ~24 mag) in the band to the red side of the break. As they are detected in multiple bands, these must be real objects. Their nature, however, is unclear, and characterizing their properties is important for realizing the full potential of JWST. If the observed color decrements are due to the Lyman break, these objects should be at z >~ 11.7 and z >~ 15.4, respectively. The color diagnostics show that at least four F150W dropouts are far away from the usual contaminators encountered in dropout searches (red galaxies at much lower redshifts or brown dwarf stars). While the diagnostics of the F200W dropouts are less certain due to the limited number of passbands, at least one of them is likely not a known type of contaminant, and the rest are consistent with either high-redshift galaxies with evolved stellar populations or old galaxies at z ~ 3 to 8. If a significant fraction of our dropouts are indeed at z ~ 12, we have to face the severe problem of explaining their high luminosities and number densities. Spectroscopic identifications of such objects are urgently needed.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The massive galaxy cluster El Gordo ($z=0.87$) imprints multitudes of gravitationally lensed arcs onto James Webb Space Telescope (JWST) Near-Infrared Camera (NIRCam) images. Eight bands of NIRCam imaging were obtained in the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) program (GTO #1176). PSF-matched photometry across a suite of Hubble Space Telescope (HST) and NIRCam filters gives new photometric redshifts. We confirm 54 known image multiplicities and find two new ones and construct a lens model based on the light-traces-mass method. The mass within 500kpc estimated from the lens model is $\sim$$7.0\times10^{14}$M$_{\odot}$ with a mass ratio between the southeastern and northwestern components of $\sim$unity, similar to recent works. A statistical search for substructures recovers only these two components, which are each tightly bound kinematically and are separated in radial velocity by ~300 km s$^{-1}$. We identify a candidate member of a known 4-member $z=4.32$ galaxy overdensity by its model-predicted and photometric redshifts. These five members span a physical extent of $\sim$60 kpc and exhibit multiple components consistent with satellite associations. Thirteen additional candidates selected by spectroscopic/photometric constraints are small and faint, with a mean apparent brightness corrected for lensing magnification that is $\sim$2.2 mag fainter than M*. NIRCam imaging admits a wide range of brightnesses and morphologies for these candidates, suggesting a more diverse galaxy population may be underlying this rare view of a strongly-lensed galaxy overdensity.