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Richard S Ellis - One of the best experts on this subject based on the ideXlab platform.
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the z 6 luminosity function fainter than 15 mag from the hubble frontier fields the impact of Magnification uncertainties
The Astrophysical Journal, 2017Co-Authors: R J Bouwens, P A Oesch, G D Illingworth, Richard S Ellis, Mauro StefanonAbstract:We use the largest sample of $z\sim 6$ galaxies to date from the first four Hubble Frontier Fields clusters to set constraints on the shape of the $z\sim 6$ luminosity functions (LFs) to fainter than ${M}_{\mathrm{UV},{AB}}=-14$ mag. We quantify, for the first time, the impact of Magnification uncertainties on LF results and thus provide more realistic constraints than other recent work. Our simulations reveal that, for the highly magnified sources, the systematic uncertainties can become extremely large fainter than −14 mag, reaching several orders of magnitude at 95% confidence at approximately −12 mag. Our new forward-modeling formalism incorporates the impact of Magnification uncertainties into the LF results by exploiting the availability of many independent Magnification models for the same cluster. One public Magnification model is used to construct a mock high-redshift galaxy sample that is then analyzed using the other Magnification models to construct an LF. Large systematic errors occur at high Magnifications ($\mu \gtrsim 30$) because of differences between the models. The volume densities we derive for faint (gsim−17 mag) sources are ~3–4× lower than one recent report and give a faint-end slope $\alpha =-1.92\pm 0.04$, which is 3.0–3.5σ shallower (including or not including the size uncertainties, respectively). We introduce a new curvature parameter δ to model the faint end of the LF and demonstrate that the observations permit (at 68% confidence) a turn-over at $z\sim 6$ in the range of −15.3 to −14.2 mag, depending on the assumed lensing model. The present consideration of Magnification errors and new size determinations raise doubts about previous reports regarding the form of the LF at $\gt -14\,\mathrm{mag}$. We discuss the implications of our turn-over constraints in the context of recent theoretical predictions.
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A Keck Survey for Gravitationally Lensed Ly? Emitters in the Redshift Range 8.5
The Astrophysical Journal, 2007Co-Authors: Daniel P. Stark, Richard S Ellis, Johan Richard, Jean-paul Kneib, Graham P. Smith, Michael R. SantosAbstract:We discuss new observational constraints on the abundance of faint high-redshift Ly? emitters secured from a deep Keck near-infrared spectroscopic survey that utilizes the strong Magnification provided by lensing galaxy clusters. In each of nine clusters, we have undertaken a systematic ``blind'' search for line emission with NIRSPEC in the J band within carefully selected regions that offer very high Magnifications (>~10×-50×) for background sources with redshifts z~=10. The high Magnification enables the detection of emission at unprecedented flux limits (1041-1042 ergs s-1). As the comoving volumes probed are small, our survey is designed to address the important question of whether low-luminosity galaxies could provide the dominant ionizing flux at z~10. Our survey has yielded six promising (>5 ?) candidate Ly? emitters that lie between z=8.7 and z=10.2. We carefully discuss the validity of our detections and the likelihood that the detected line is Ly? in light of earlier, apparently false, claims. Lower redshift line interpretations can be excluded, with reasonable assumptions, through the nondetection of secondary emission in further spectroscopy undertaken with LRIS and NIRSPEC. Nonetheless, as a result of our tests, we argue that at least two of our candidates are likely to be at z~=10. Given the small survey volume, this suggests there is a large abundance of low-luminosity star-forming sources at z~=8-10. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z~=10 universe suggests that low-luminosity star-forming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization.
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A Keck Survey for Gravitationally-Lensed Lyman-alpha Emitters in the Redshift Range 8.5
2007Co-Authors: Daniel P. Stark, Richard S Ellis, Johan Richard, Jean-paul Kneib, Graham P. Smith, Michael R. SantosAbstract:We discuss new observational constraints on the abundance of faint high redshift Lyman-alpha emitters secured from a deep Keck near-infrared spectroscopic survey which utilizes the strong Magnification provided by lensing galaxy clusters at intermediate redshift (z=0.2-0.5). In each of 9 clusters we have undertaken a systematic `blind' search for line emission with NIRSPEC in the J-band within carefully-selected regions which offer very high Magnifications (>10-50x) for background sources with redshifts z~10. The high Magnification enables the detection of emission at unprecedented limits (10^41 - 10^42 erg/s), much fainter than those of conventional narrow band imaging and other spectroscopic searches. As the comoving volumes probed are small, our survey is designed to address the important question of whether intrinsically feeble star forming galaxies could provide the dominant ionizing flux at z~10. Our survey has yielded six promising (>5 sigma) candidate Lyman-alpha emitters which lie between z=8.7 and z=10.2. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z~10 Universe suggests that low luminosity star-forming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization. [Abridged]
Michael R. Santos - One of the best experts on this subject based on the ideXlab platform.
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A Keck Survey for Gravitationally Lensed Ly? Emitters in the Redshift Range 8.5
The Astrophysical Journal, 2007Co-Authors: Daniel P. Stark, Richard S Ellis, Johan Richard, Jean-paul Kneib, Graham P. Smith, Michael R. SantosAbstract:We discuss new observational constraints on the abundance of faint high-redshift Ly? emitters secured from a deep Keck near-infrared spectroscopic survey that utilizes the strong Magnification provided by lensing galaxy clusters. In each of nine clusters, we have undertaken a systematic ``blind'' search for line emission with NIRSPEC in the J band within carefully selected regions that offer very high Magnifications (>~10×-50×) for background sources with redshifts z~=10. The high Magnification enables the detection of emission at unprecedented flux limits (1041-1042 ergs s-1). As the comoving volumes probed are small, our survey is designed to address the important question of whether low-luminosity galaxies could provide the dominant ionizing flux at z~10. Our survey has yielded six promising (>5 ?) candidate Ly? emitters that lie between z=8.7 and z=10.2. We carefully discuss the validity of our detections and the likelihood that the detected line is Ly? in light of earlier, apparently false, claims. Lower redshift line interpretations can be excluded, with reasonable assumptions, through the nondetection of secondary emission in further spectroscopy undertaken with LRIS and NIRSPEC. Nonetheless, as a result of our tests, we argue that at least two of our candidates are likely to be at z~=10. Given the small survey volume, this suggests there is a large abundance of low-luminosity star-forming sources at z~=8-10. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z~=10 universe suggests that low-luminosity star-forming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization.
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A Keck Survey for Gravitationally-Lensed Lyman-alpha Emitters in the Redshift Range 8.5
2007Co-Authors: Daniel P. Stark, Richard S Ellis, Johan Richard, Jean-paul Kneib, Graham P. Smith, Michael R. SantosAbstract:We discuss new observational constraints on the abundance of faint high redshift Lyman-alpha emitters secured from a deep Keck near-infrared spectroscopic survey which utilizes the strong Magnification provided by lensing galaxy clusters at intermediate redshift (z=0.2-0.5). In each of 9 clusters we have undertaken a systematic `blind' search for line emission with NIRSPEC in the J-band within carefully-selected regions which offer very high Magnifications (>10-50x) for background sources with redshifts z~10. The high Magnification enables the detection of emission at unprecedented limits (10^41 - 10^42 erg/s), much fainter than those of conventional narrow band imaging and other spectroscopic searches. As the comoving volumes probed are small, our survey is designed to address the important question of whether intrinsically feeble star forming galaxies could provide the dominant ionizing flux at z~10. Our survey has yielded six promising (>5 sigma) candidate Lyman-alpha emitters which lie between z=8.7 and z=10.2. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z~10 Universe suggests that low luminosity star-forming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization. [Abridged]
D L Wilson - One of the best experts on this subject based on the ideXlab platform.
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image quality evaluation of flat panel and image intensifier digital Magnification in x ray fluoroscopy
Medical Physics, 2002Co-Authors: Yogesh Srinivas, D L WilsonAbstract:Interventional devices used in radiology often have dimensions on the order of a pixel, and radiologists resort to image Magnification to better visualize such small devices. Traditional image intensifier (II) systems use analog Magnification with x-ray exposure inversely proportional to the area of field of view (FOV) so as to maintain light output for the camera. Analog Magnification is impossible with flat panel (FP) detectors, and images must be magnified using digital interpolation that does not reduce the pixel partial area effect for small devices. We quantitatively investigated image quality of digital and analog Magnification using a clinically relevant task of detecting a partially deployed stent in x-rayfluoroscopyimage sequences that were created using realistic detector models. Using the standard exposure strategy for II analog Magnification, exposure was increased from a nominal 43.65 nGy (5.0 μR) per frame at 23 cm FOV to 79.9 nGy (9.15 μR) per frame and 117.81 nGy (13.49 μR) per frame at 17 cm and 14 cm FOV, respectively. Contrast sensitivity improved significantly (p by 43.5±6.5% and 64.1±7.3% with the 17 cm and 14 cm FOV, respectively. Exposure for digitally magnified images was varied in an adaptive forced choice experiment so as to match performance with II analog Magnification. For digital Magnification, bilinear interpolation was used to give magnified stents sizes equivalent to those in the analog magnified images. For equivalent image quality, FP required 34.87±2.59, 80.16±5.37, and 84.08±5.59 nGy per frame at normal, and the two Magnification modes, respectively. Hence, FP with digital Magnification gives significant (p dose savings of 20±6% and 27±5% at the normal and highest Magnification modes, respectively. Digitally magnified II images required exposures of 110.85±8.07 and 103.34±5.90 nGy per frame for the two Magnifications levels, respectively, giving no significant (p>0.1) dose savings. A spatiotemporal human observer model based on signal detection theory successfully predicted the human data and was used to predict other conditions associated with image Magnification. Model predictions quantitatively showed that Magnification is most useful when signal size is relatively small and that FP digital Magnification can improve image quality for the stent deployment task without increasing exposure. In conclusion, the results show that FP digital Magnification can be useful and dose efficient as compared to analog Magnification.
Dan, Coe - One of the best experts on this subject based on the ideXlab platform.
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Illuminating a Dark Lens : A Type Ia Supernova Magnified by the Frontier Fields Galaxy Cluster Abell 2744
The Astrophysical Journal, 2015Co-Authors: Steven A., Rodney, Brandon, Patel, Daniel, Scolnic, Ryan J., Foley, Alberto, Molino, Gabriel, Brammer, Mathilde, Jauzac, Maruša, Bradač, Tom, Broadhurst, Dan, CoeAbstract:SN HFF14Tom is a Type Ia SN discovered at z=1.3457+/- 0.0001 behind the galaxy cluster Abell 2744 (z = 0.308). In a cosmology-independent analysis, we find that HFF14Tom is 0.77 ± 0.15 mag brighter than unlensed Type Ia SNe at similar redshift, implying a lensing Magnification of {μ }{obs}=2.03+/- 0.29. This observed Magnification provides a rare opportunity for a direct empirical test of galaxy cluster lens models. Here we test 17 lens models, 13 of which were generated before the SN Magnification was known, qualifying as pure “blind tests.” The models are collectively fairly accurate: 8 of the models deliver median Magnifications that are consistent with the measured μ to within 1σ. However, there is a subtle systematic bias: the significant disagreements all involve models overpredicting the Magnification. We evaluate possible causes for this mild bias, and find no single physical or methodological explanation to account for it. We do find that model accuracy can be improved to some extent with stringent quality cuts on multiply imaged systems, such as requiring that a large fraction have spectroscopic redshifts. In addition to testing model accuracies as we have done here, Type Ia SN Magnifications could also be used as inputs for future lens models of Abell 2744 and other clusters, providing valuable constraints in regions where traditional strong- and weak-lensing information is unavailable.
Daniel P. Stark - One of the best experts on this subject based on the ideXlab platform.
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A Keck Survey for Gravitationally Lensed Ly? Emitters in the Redshift Range 8.5
The Astrophysical Journal, 2007Co-Authors: Daniel P. Stark, Richard S Ellis, Johan Richard, Jean-paul Kneib, Graham P. Smith, Michael R. SantosAbstract:We discuss new observational constraints on the abundance of faint high-redshift Ly? emitters secured from a deep Keck near-infrared spectroscopic survey that utilizes the strong Magnification provided by lensing galaxy clusters. In each of nine clusters, we have undertaken a systematic ``blind'' search for line emission with NIRSPEC in the J band within carefully selected regions that offer very high Magnifications (>~10×-50×) for background sources with redshifts z~=10. The high Magnification enables the detection of emission at unprecedented flux limits (1041-1042 ergs s-1). As the comoving volumes probed are small, our survey is designed to address the important question of whether low-luminosity galaxies could provide the dominant ionizing flux at z~10. Our survey has yielded six promising (>5 ?) candidate Ly? emitters that lie between z=8.7 and z=10.2. We carefully discuss the validity of our detections and the likelihood that the detected line is Ly? in light of earlier, apparently false, claims. Lower redshift line interpretations can be excluded, with reasonable assumptions, through the nondetection of secondary emission in further spectroscopy undertaken with LRIS and NIRSPEC. Nonetheless, as a result of our tests, we argue that at least two of our candidates are likely to be at z~=10. Given the small survey volume, this suggests there is a large abundance of low-luminosity star-forming sources at z~=8-10. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z~=10 universe suggests that low-luminosity star-forming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization.
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A Keck Survey for Gravitationally-Lensed Lyman-alpha Emitters in the Redshift Range 8.5
2007Co-Authors: Daniel P. Stark, Richard S Ellis, Johan Richard, Jean-paul Kneib, Graham P. Smith, Michael R. SantosAbstract:We discuss new observational constraints on the abundance of faint high redshift Lyman-alpha emitters secured from a deep Keck near-infrared spectroscopic survey which utilizes the strong Magnification provided by lensing galaxy clusters at intermediate redshift (z=0.2-0.5). In each of 9 clusters we have undertaken a systematic `blind' search for line emission with NIRSPEC in the J-band within carefully-selected regions which offer very high Magnifications (>10-50x) for background sources with redshifts z~10. The high Magnification enables the detection of emission at unprecedented limits (10^41 - 10^42 erg/s), much fainter than those of conventional narrow band imaging and other spectroscopic searches. As the comoving volumes probed are small, our survey is designed to address the important question of whether intrinsically feeble star forming galaxies could provide the dominant ionizing flux at z~10. Our survey has yielded six promising (>5 sigma) candidate Lyman-alpha emitters which lie between z=8.7 and z=10.2. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z~10 Universe suggests that low luminosity star-forming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization. [Abridged]
