Characterization of instrumental noise in 2D images and determination of galaxy
distances
Martin Eriksen, IFAE-PIC
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The PAU survey
- The PAU Survey is an astronomical survey.
- Use PAUCam, a unique instrument which has 40 narrow redshift bands.
- Aim is to determine galaxy
distances with 10x higher precision than other photometric surveys.
- Opening up a hitherto uncharted regime of deep, wide, and dense galaxy survey
- Unique insights into the formation, evolution and clustering of galaxies
Installed at the William Herschel Telescope (WHT).
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Determining redshifts
PAUCam filters - One observe galaxies in different
photometric bands.
- Narrow bands enable measuring sharp features.
- 10x better reconstruction of distances for brighter galaxies.
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Deepz: Photometric redshifts with deep learning
- State-of-the-art PAUS photo-z results use template fitting (Eriksen 2019).
- The modelling started to
become increasingly complex.
- Using a neural network, including transfer learning, improves the precisions.
- For 100% at i<22.5, the
sigma68 is Deepz 0.77% and
BCNz 0.86%.
Measure of precision.Imag - Measure of brightness (high value - less light) 4
Correction of scattered light
- PAUCam is suffering from additional noise in the images.
- “The PAU Survey: Background estimation method with deep
learning techniques.” Cabayol et.al.
- Detailed study on how to correct for this effect in software.
- Main method use a convolutional neural network.
Left: Image taken in NB685 with a scattered light pattern on the edges.
Middle: The image after correcting with the sky flat.
Right:The sky flat generated with equation (1) considering all images taken the same
observation night as the original image. 5
Results of the background network
Results on data
Results on simulations
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Infrastructure
● Interested in discussing what infrastructure others use for ML.
● By now 3 GTX1050 + 1 Titan-V.
● In the process of purchasing more.
● Effort at PIC to create an
environment usable for multiple users sharing GPUs.
https://zero-to-jupyterhub.readthedocs.io/e
n/latest/ 7
Questions?
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