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2MASS Photometric Redshift catalogue (2MPZ)

The archive also hosts the 2MASS Photometric Redshift catalogue (2MPZ), constructed by cross-matching 2MASS XSC, WISE and SuperCOSMOS all-sky samples and employing the artificial neural network approach (the ANNz algorithm, Collister & Lahav 2004), trained on several redshift surveys (2MRS, SDSS, 6dFGS, 2dFGRS and ZCAT). The derived photometric redshifts have errors nearly independent of distance, with an all-sky accuracy of σz = 0.015, and a very small percentage of outliers. These redshift estimates have a typical precision of 12% for all the 2MASS XSC galaxies that lack spectroscopy. The resulting 2MPZ sample contains almost 1 million galaxies with a median redshift of z=0.07. This catalogue is described in Bilicki et al. 2014, ApJS, 210, 9. The arXiv version can be found, here. Please reference this paper and acknowledge the Wide Field Astronomy Unit (WFAU) when using these data.

The arrangement of the data is simple: all the data is in the twompzPhotoz table. The table is linked to the 3 input photometric tables through the twomassID, which links to the TWOMASS twomass_xsc ext_key, the scosID, which links to the SSA Source objID and the wiseID, which links to the WISE wise_allskysc cntr. It is much faster to match through the integer IDs rather than the designations. Matching is possible to previous releases of UKIDSS and VISTA and OSA ATLAS surveys through the existing neighbour tables to twomass_xsc. Future releases of these surveys will be matched directly to the 2MASS Photometric Redshift catalogue (2MPZ).

2MPZ uses SuperCOSMOS gCorMag magnitudes from the SSA Source table, but have applied some important corrections:
1) There is a small offset between the UKST plates in the Southern hemispere and the POSS-II plates in the Northern hemisphere (found by comparison with SDSS) that was corrected by changing the Southern hemisphere (δ1950<2.5):

  • BScorr=B-0.03(B-R)2+0.03(B-R)-0.01
  • RScorr=R-0.04(B-R)2+0.08(B-R)-0.02
  • IScorr=I-0.02(R-I)2-0.07(R-I)+0.01
  • 2) All of the magnitudes were corrected for Galactic extinction using the Schlegel et al. 1998, ApJ, 500, 525 dust maps. In the case of SuperCOSMOS, the A_λ/E(B-V) coefficients were hemisphere-dependent: ANB=4.165 and ANR=2.773 in the North (δ1950>2.5), ASB=4.011 and ANR=2.778 in the South (δ1950<2.5), and AI=2.016 for the entire sky. 2MASS J/H/K_m_k20fe magnitudes use A_λ/E(B-V) from Cardelli et al. (1989), whereas for WISE w?mpro magnitudes the coefficients are AW1/EBV=0.231 and AW2/EBV=0.194 (Flaherty et al. 2007).

    What is released

    The current version, 1.1, of the 2MPZ catalogue includes all the 2MASS extended sources that fulfil the following criteria:

    1. Their Ks-band magnitudes are brighter than Ks=13.9 mag (extinction-corrected);
    2. Their J-Ks colour is positive (J-Ks > 0, extinction-corrected);
    3. They have all the 8 magnitudes B,R,I,J,H,Ks,W1,W2 measured in SuperCOSMOS, 2MASS and WISE, respectively;
    4. The Galactic extinction from Schlegel et al. maps and the local 2MASS stellar density at a given position are respectively EBV<1.5 and log(density)<4.0.
      This catalogue includes 928,352 sources.
    Note 1: All the sources in the 2MPZ catalogue have photometric redshift estimates. However, in high extinction, large stellar density or low Galactic latitude regions, the photo-z's are likely to be biased (usually underestimated). See Bilicki et al. 2014 for details.

    Note 2: The 2MPZ catalogue will be updated on an irregular basis, so please always check this webpage for the latest version.

    20160606: 5823 supplimental sources have been added, which have matches in WISE allwise_sc, rather than WISE wise_allskysc.

    For more information concerning the dataset and how to explore it and download it, please see the 2MPZ, in the SQL Cookbook. The schema for this dataset is available in the Schema Browser. Please contact Maciej Bilicki maciek@ast.uct.ac.za for scientific questions, and mar@roe.ac.uk for technical questions.



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    WFAU, Institute for Astronomy,
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    mar@roe.ac.uk
    18/6/2016