J-PLUS Data Release DR2

The J-PLUS DR2 Data Release (July 2020) (J-PLUS-DR2) comprises 1088 J-PLUS fields observed in twelve optical bands amounting to 2176deg2. J-PLUS DR2 is based on images collected from November 2015 to February 2020 by the JAST/T80 telescope.

For quick access to the archive and the User's Manual, you can use the following links.

Scope

Total area covered 2176 deg2 (~1941 deg2 after masking)
Image size 9500x9500 pixels (~2 deg2)
Image pixel scale 0.555 arcsec
Total number of fields 1088
Number of objects in dual catalogue ~31.5 million (~19.5 million with MAG_AUTO(rSDSS)≤21)
Number of objects with estimations of photo-z (with their full PDFs) ~30.7 million
Number of detections in single catalogue ~223.6 million
Size of the database ~221 GB
Number of Single Frames 42307
Tile Images Total Size (compressed) ~625.4 GB
Single Frames Total Size (compressed) ~2.9 TB
DR2 Footprint

Figure 1. Footprint of the pointings observed in this J-PLUS DR2.

Main differences with respect to the DR1

The main differences with respect to the DR1 are the following:

  • Data processing:
    • Improved the background determination and subtraction of the single frames before their coaddition.
    • Implemented the background subtraction related with the illumination correction as developed for mini-JPAS images.
    • Improvements in the generation of master flat fields and master fringing.
    • Implemented a new overscan correction after discovering that the behaviour of the overscan regions depends on the exposure time. Once this dependence is taken into account, the behaviour is quite stable with time. This new correction is based on the computation of master OVSC images using overscan areas of hundreds of images with similar exposure times in order to recover the shape of the overscan regions (of each amplifier independently) with high signal-to-noise. The actual overscan correction of a given single frame is based on the correspoding master OSCV given its exposure time which is normalized to the overall level of the actual overscan region of the single frame.
    • Used of single frames compressed with fpack to construct the final coadded images. In order to allow the reproducibility of our final images, we are now constructing the final coadded images using single frame images that have been previously compressed with fpack. Although this compression is lossy (this means that pixels are slightly changed), preliminary checks show that the changes in photometry are under the photometric error (although more tests will be needed). Besides, and even if it could seem unrelated, this compression was the way to solve the problem commented above regarding the background of images with low sky levels.
  • Photometric calibration:
    • The reference photometric calibration now is the Stellar and White Dwarf Loci procedure developed by C. López-Sanjuan (see article). We improved the large scale systematics in the calibration by including the metallicity information from LAMOST DR5 in the stellar locus estimation. We greatly thanks H. Yuan for his collaboration on this regards and for enlightening discussions. The calibration statistical errors in DR2 are similar to those in DR1, and we believe that systematic errors are now below 10 mmag in all the filters.
  • Morphological star/galaxy classification:
    • We provide the Bayesian compact/extended classification as in DR1. The only change is the update in the galaxy locus variation with magnitude. It was assumed as constant in DR1, and now it approaches asymptotically to the stellar locus at faint (r > 20) magnitudes following the results obtained in the deeper mini-JPAS data.
  • Photometric redshift computation:
    • In this DR2, we provide only photo-z's computed with a modified version of the code LePhare.
    • A new set of templates has been constructed.
    • Full PDFs of the photo-z's are provided with a better compression procedure.
  • Data access:
    • A cross-match wih J-PLUS DR1 is provided in table jplus.xmatch_jplus_dr1.
    • Access to individual frames. We provide access to all the individual frames used to construct the coadded images and the main information of these frames is stored in the main database.
    • Access to PDFs of the photo-z's.
    • Access to the PSF models either in PSFEx format or as a FITS image in any position of any coadded frame.
    • Apart from the previous ones, you can have direct HTML access to many other services (Direct Download Services).
    • Some statistical functions have been added to ADQL.
    • You can check all the changes clicking on the version ID of the Catalogues Web Portal located in the bottom right corner of the window.

Specific caveats and known issues of this DR

Except the issues related with the calibration and the galactic extinction now solved with the SWDL calibration procedure, most of the caveats presented in DR1 (see DR1 caveats) are still present since they are related on how the data is taken.

Apart from this, this is a list of known issues of this DR2:

  • Coadded images have been constructed using lossy compressed images. No significant effects on the photometry have been detected, however, this could have some impact for specific objects.
  • Some images are affected by issues like clouds (sometimes evident other not so much), bad seeing or reflections. Instead of removing these data we provide some information about known problems in the table TileImageWithFlag.

Data Quality Overview

In this section we show a couple of figures summarizing the data quality of this DR2.

Figure 2 shows the distribution of the average stellar FWHM measured from single-mode catalogues for each image.

Distribution of the mean stellar FWHM of each single coadded image

Figure 2. Distribution of the mean stellar FWHM of each single coadded image.

Figure 3 shows the theoretical photometric depth (mlim) of each individual image computed from the standard deviation of the background noise (σbg) within an aperture of 3" and considering a flux threshold of 5σbg.

Distribution of the theoretical photometric depth of each single coadded image

Figure 3. Distribution of the theoretical photometric depth of each single coadded image.