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courses:ast403:lyman-break-technique [2026/03/26 06:34] – [Advantages and Limitations] shuvocourses:ast403:lyman-break-technique [2026/03/26 07:49] (current) – [Advantages and Limitations] shuvo
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 If a galaxy is at a redshift of $z = 3$, the Lyman break is shifted from $912 \mathring{A}$ to roughly $3648 \mathring{A}$, moving it out of the extreme UV and into the visible part of the spectrum. If a galaxy is at a redshift of $z = 3$, the Lyman break is shifted from $912 \mathring{A}$ to roughly $3648 \mathring{A}$, moving it out of the extreme UV and into the visible part of the spectrum.
  
 +[{{ :courses:ast403:highz_galaxy.jpeg?600 | Fig 1: The shift of Lyman$\alpha$ from UV to IR at $z=11$. }}]
 ===== The "Dropout" Observation Method =====  ===== The "Dropout" Observation Method ===== 
 Astronomers do not usually have the time to take detailed spectra of every single point of light in the sky to see where this break occurs. Instead, they use a highly efficient shortcut called broadband photometry.  Astronomers do not usually have the time to take detailed spectra of every single point of light in the sky to see where this break occurs. Instead, they use a highly efficient shortcut called broadband photometry. 
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-[{{ :courses:ast403:dropout.jpg?600 | Fig 1: Dropout technique.}}]+[{{ :courses:ast403:dropout.jpg?600 | Fig 2: Dropout technique to find high-redshift galaxies.}}]
  
  
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 **Efficiency:** It allows astronomers to survey thousands of galaxies in a single image. By simply comparing brightness across a few filters, they can isolate a reliable list of high-redshift candidates without needing time-consuming spectroscopy for every object.\\ **Efficiency:** It allows astronomers to survey thousands of galaxies in a single image. By simply comparing brightness across a few filters, they can isolate a reliable list of high-redshift candidates without needing time-consuming spectroscopy for every object.\\
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 +[{{ :courses:ast403:dropout_photo.png?600 | Fig 3: Dropout technique with HST filters showing photometric data.}}]
 **Targeting:** It helps optimize expensive telescope time. Once astronomers identify a list of dropouts, they can point massive spectrographs (like those on the Keck or VLT telescopes) exactly at those targets to confirm their exact redshift. **Targeting:** It helps optimize expensive telescope time. Once astronomers identify a list of dropouts, they can point massive spectrographs (like those on the Keck or VLT telescopes) exactly at those targets to confirm their exact redshift.
  
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 +[{{ :courses:ast403:interloopers.jpg?600 | Fig 4: Color-color diagram for LBGs at z ~ 3 (light grey shaded zone). Black dots are the complete sample of galaxies in the SDSS photometric catalog. Red filled dots represent the sample of LBGs spectroscopically confirmed to be}}]
courses/ast403/lyman-break-technique.1774528447.txt.gz · Last modified: by shuvo
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