Spectral Range and Resolution

Spectral Range and Resolution

Huan Lin

Fermilab

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• Wavelengths 5500 Å 6000 Å 10000 Å

• Emission line redshifts

• [OII] 3727 0.48 0.61 1.68

• [OIII] 5007 0.10 0.20 1.00

• H 6563 N/A N/A 0.52

• For nominal 6000-10000 Å spectral range, the emission line galaxy redshift coverage is z = 0-0.52 with H and z = 0.61-1.68 with [OII] 3727

• Gap from z = 0.52-0.61 can be partly filled using [OIII] 5007 for strong emission line galaxies (as [OIII] 5007 is a weaker line in general)

• Absorption line redshifts

• Ca H+K 3950 0.39 0.52 1.53

• G band 4300 0.28 0.40 1.33

• Mg 5170 0.06 0.16 0.93

• Na 5892 N/A 0.02 0.70

• LRG redshift coverage is about z = 0.52-1.33 using both Ca H+K and G band

• Lower redshifts can be reached by Mg and Na features, but in detail will use simulations to assess redshift success rates

Wavelength range and redshift coverage

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Wavelength range vs. emission line redshift coverage

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Wavelength range vs. absorption line redshift coverage

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• High-resolution (R 45000) night sky spectral atlas (Hanuschik 2003) derived from echelle spectroscopy using the UVES instrument on VLT

• Wavelength coverage 3140-10430 Å

• Data restricted to dark sky conditions

• Resolution much higher than for DESpec and so good for S/N forecasts

• Before had used Mauna Kea night sky spectrum from Gemini website, but that looks like it’s effectively very low resolution (tens of Å?), even though it’s tabulated with spacing of a few Å

• Not good for forecasts at full DESpec resolution

Night Sky Spectra

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UVES/VLT night sky spectrum (Hanuschik 2003)

R 45000

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UVES sky resolution comparison

R 9000 at 9000 Å

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UVES sky resolution comparison

R 3600 at 9000 Å

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UVES sky resolution comparison

R 2200 at 9000 Å (~SDSS)

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• Consider simple cases of

• Galaxy with constant AB mag = 21.5 continuum

• Unresolved emission line with flux = 1.0 x 10-17 erg/s/cm2

• S/N calculation assumptions

• 2-arcsec diameter fiber, with 70% of light entering fiber (based on galaxy sizes in DECam image simulations)

• Throughput simply taken as 50% of DECam (for now), at airmass = 1.3

• 30 min exposure time

• UVES night sky spectrum

• S/N calculated in fixed resolution element bins of 2.5 Å, corresponding to resolution R = 3600 at 9000 Å

• Working on IDL simulation package (C. Cunha & H. Lin) that simulates 1D extracted spectra, based on input mock galaxy catalogs and template spectra, throughput components, resolution, and night sky data

• Will compute S/N using outputs, as well as run cross-correlations using IRAF rvsao package to compute redshift success rates in detail as functions of galaxy magnitude, color, redshift, and emission line strength

Example S/N calculations

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S/N for continuum w/ constant AB mag = 21.5

R 3600 at 9000 Å

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S/N for emission line with flux = 1.0x10-17 erg/s/cm2

R 3600 at 9000 Å