Partial/missing bricks in DR9 phot/pz sweeps

[Zack Hutchens]

Hi there,

A hopefully quick question --- I am looking at using LS DR9 data within a particular footprint on the sky, roughly 130-240 deg in RA by 0-50 deg in Dec. I have downloaded all the photometry sweep catalogs for DR9 and notice that there are several missing or partially complete bricks at approximately declination +35-40 deg through this RA range (see figure below). Is this due to incompleteness in coverage where the LS is transition from DECaLS to MzLS/BASS imaging? I am sure this must be documented somewhere on the LS website or papers, but I am having trouble pinpointing the explanation; any insight would be greatly appreciated.

Best wishes,

Zack Hutchens

[David Schlegel]

Zack,

Could you point us to exactly which files you’re using?

We definitely have targets (and spectra) in those regions,

so I’m wondering if this is a version of the sweep files not

used for targeting.

-David

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[Zack Hutchens]

Hi David,

Many thanks for the quick response. I used the sweep files located here:

North: https://portal.nersc.gov/cfs/cosmo/data/legacysurvey/dr9/north/sweep/9.0/

South: https://portal.nersc.gov/cfs/cosmo/data/legacysurvey/dr9/south/sweep/9.0/

I downloaded all the files from the two directories with a simple wget script. I have 662 sweep files overall. This link is a .txt file listing out the filenames.
https://drive.google.com/file/d/1PFtclxhlkCA03qhpHisAP4HlJcG-QmKt/view?usp=sharing

Thanks again,

Zack

[Dustin Lang]

For DESI targeting, we switch from south to north at Dec = 32.375 deg.

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[Zack Hutchens]

Thanks Dustin -- so that switch from south to north wouldn't explain the partial/missing bricks I see at higher decl., right?

-Zack

[David Schlegel]

Zack,

I just read in + plotted the coordinates for all the sources in those files,

which doesn’t show any gaps.

I’m guessing that you’ve overwritten some files from “north” and “south”

that have the same file names.  Re-fetch those files in separate directories

and you should have everything.  There should be 283 in the north, 455

in the south.

The imaging in the north is from different telescopes than in the south.

We intentionally have some overlap between the two, and then as Dustin

notes select from “south" for objects at dec < +32.375 and from “north”

for decades > +32.375.

-David

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