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We describe the \"overlight\" test that was done for JWST's Teledyne H2RG HgCdTe near-infrared detector arrays. We projected many very bright λ = 632.8 nm spots onto one flight representative, substrate-removed, HgCdTe 5 μm cutoff detector array. We allowed individual spots to \"burn in\" for as long as ≈1000 s before turning off the laser. We did not detect any permanent change in detector performance for extreme over illuminations as bright as 320 μW pixel-1 (≤ 1 μW μm-2) after the array had been returned to ambient laboratory temperature and pressure. The brightest individual spot contained roughly 4 mW of power spread over a 100 μm diameter circular area. This is brighter than the brightest lasers that are planned for use during JWST integration and testing. It is also ≈103× brighter than any 632.8 nm astronomical source in the night sky.

We present narrow band, continuum subtracted H α , [S ii ], H β , [O iii ] and [O ii ] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.

The Space Telescope Imaging Spectrograph (STIS) was designed as a versatile spectrograph for the HST capable of maintaining or exceeding the spectroscopic capabilities of first-generation HST instruments primarily through the use of large areal detectors in both the UV and visible regions of the spectrum. Simultaneous spatial and spectral coverage is provided through long-slit or slitless spectroscopy of extended sources. A substantial spectral multiplexing advantage is achieved for UV echelle spectroscopy. This paper will focus on the key issue of S/N performance with the STIS UV detectors. Spectra obtained during the first few months of operation illustrate that high S/N spectra can be obtained while exploiting STIS's multiplexing advantage. From analysis of a single spectrum of GD 153, with count statistics of 165, a S/N of 130 is achieved per spectral resolution element in the far-UV for a flat-fielded spectrum. In the near-UV, a single spectrum of GRW +705824, with count statistics of 200, yields an S/N of 150 per spectral resolution element for the flat-fielded spectrum. Without flat-fielding, a S/N of 100 is achieved. An even higher S/N capability is illustrated through the use of the fixed pattern split slits in the medium-resolution echelle modes. These results verify that STIS is capable of achieving a S/N in excess of 100:1 per spectral resolution element in both the first-order and echelle modes. (Author)

The most massive galaxies and the richest clusters are believed to have emerged from regions with the largest enhancements of mass density 1 , 2 , 3 , 4 relative to the surrounding space. Distant radio galaxies may pinpoint the locations of the ancestors of rich clusters, because they are massive systems associated with ‘overdensities’ of galaxies that are bright in the Lyman-α line of hydrogen 5 , 6 , 7 . A powerful technique for detecting high-redshift galaxies is to search for the characteristic ‘Lyman break’ feature in the galaxy colour, at wavelengths just shortwards of Lyα, which is due to absorption of radiation from the galaxy by the intervening intergalactic medium. Here we report multicolour imaging of the most distant candidate 7 , 8 , 9 protocluster, TN J1338–1942 at a redshift z ≈ 4.1. We find a large number of objects with the characteristic colours of galaxies at that redshift, and we show that this excess is concentrated around the targeted dominant radio galaxy. Our data therefore indicate that TN J1338–1942 is indeed the most distant cluster progenitor of a rich local cluster, and that galaxy clusters began forming when the Universe was only ten per cent of its present age.

A technique involving 55Fe Fe 55 X-rays provides a straightforward method to measure the response of a detector. The detector’s response can lead directly to a calculation of the conversion gain ( e -ADU-1 e - ADU - 1 ), as well as aid detector design and performance studies. We calibrate the 55Fe Fe 55 X-ray energy response and pair production energy of HgCdTe using 8HSTWFC3 1.7 μm flight grade detectors. The results show that each Kα X-ray generates2273 ± 137 2273 ± 137 electrons, which corresponds to a pair-production energy of2.61 ± 0.16 eV 2.61 ± 0.16     eV . The uncertainties are dominated by our knowledge of the conversion gain. In future studies, we plan to eliminate this uncertainty by directly measuring conversion gain at very low light levels.