Specifics and general query on using DR10 data products for science purposes

[Rajnil Mukherjee]

Hi,

Greetings. So, I was just getting started with a project which requires me to study some outflow features in a few galactic sources, and I was thinking of using the data provided by the LS team. One way I saw is that I can use the cutout service to get source-centric images, but I am kind of worried about the resolution of the images changing if I try to increase the pixel size of the image in order to achieve a greater FOV. Also one of my colleagues/seniors was warning me that in DESI data, as far as he remembers, as you increase the pixel size,  since the cutouts get "binned", in the process larger objects tend to become point-ier objects as you try to increase the pixel size of the image, thus leading to a loss in resolution and may lead to me losing minute features. This I don't want since the whole point of my project is to observe minute features. Although, going from this conversation (https://groups.google.com/g/decam-legacy-survey/c/hfivp_jYY3U/m/gF-iRNd-BAAJ) I think that perhaps this used to be the case before, but after introducing the "pixel-scale" feature in the wget commands, this problem should no longer occur i.e this tradeoff between FOV and resolution by trying to increase the pixel size? Could somebody quickly confirm/add something to this? 

Also, in case I wanted to use the tractor files, how should I go about using them in case I want to study a particular galaxy at a particular location, apart from using the cutouts? I am sorry if all of this sounds kind of naive but I am a bit new to this thing.

Thanks,

Rajnil

[Dustin Lang]

Hi,

The 'pixscale' argument (in arcseconds per pixel) does the right thing.  The native pixel scale of the images is 0.262"/pixel, so if you request that, you will be getting the full resolution available.

You can specify the width and height of the cutout using width= and height= arguments, eg:

    https://www.legacysurvey.org/viewer/cutout.jpg?ra=11.9748&dec=19.5966&layer=ls-dr9&pixscale=0.262&width=750&height=500

For catalogs / tractor files: one option is to use the NOIRLab Astro Data Lab, which provides a database style query interface.

https://datalab.noirlab.edu/

Another option (probably only useful if you're just looking at a handful of objects) is to use the viewer - click on the map to get the pop-up dialog box, and follow the "Data" link.  At the top of that page, there is a "Catalog" link, which will give you a FITS table containing all the tractor catalog objects within the field of view shown in the viewer; the URL is like

    https://www.legacysurvey.org/viewer/ls-dr9/cat.fits?ralo=11.727600&rahi=12.222600&declo=19.468500&dechi=19.725000

OR, turn on the "Imaging catalogs -> Legacy Surveys DR10 Catalog" overlay, and cilck on individual objects to get a pop-up with their details;

    https://www.legacysurvey.org/viewer/?ra=11.9757&dec=19.5967&layer=ls-dr9&zoom=16&sources-dr10

and if you click on the "objid" in the popup, you'll get a page with details like

    https://www.legacysurvey.org/viewer/ls-dr10/cat?ralo=11.974091692674792&rahi=11.97609169267479&declo=19.59590339165473&dechi=19.597903391654732&objid=5302

cheers,

dustin

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[Rajnil Mukherjee]

Thanks a lot for the quick reply! I will get back to you if I face any further issues! :D

Regards,

Rajnil