We produced a spectral index catalog matching specially re-processed images from two radio surveys at different frequencies: NVSS and TGSS. These surveys were chosen because they are the most sensitive metre and centimetre wavelength surveys currently available, they both cover a large fraction of the sky, and their separation in frequency provides a large lever arm for spectral index calculation. The resulting catalogue includes >1.4 million entries, making it the largest collection of spectral index information to date. Furthermore, we provide the community a spectral index map of 80% of the sky that can be used to classify radio sources.
Sources in the catalog are classified into categories:
The final spectral index catalogue has 1 396 515 entries, of which 503,647 (36%) are full detections (source type: S, C, or M), 845,459 (61%) are lower limits (L), and 6,386 (<1%) are upper limits (U). Entries marked as island (I) are 41,023 (3%). The high number of lower limits is due to the higher sensitivity of NVSS with respect to TGSS.
The spectral index catalog can be downloaded here:
|RA||degree||S,M,C,I: weighted average of NVSS and TGSS detections|
|DEC||degree||S,M,C,I: weighted average of NVSS and TGSS detections|
|Total_flux_NVSS||Jy||I: sum of detections fluxes; U: set to 0|
|E_Total_flux_NVSS||Jy||I: quadratic mean of detections' errors; U: set to 0|
|Peak_flux_NVSS||Jy/beam||I: maximum of detections peak fluxes; U: set to 0|
|E_Peak_flux_NVSS||Jy/beam||I: error relative to the maximum of detections peak fluxes; U: set to 0|
|Rms_NVSS||Jy/beam||Local rms noise|
|Total_flux_TGSS||Jy||I: sum of detections fluxes; L: set to 0|
|E_Total_flux_TGSS||Jy||I: quadratic mean of detections' error; L: set to 0|
|Peak_flux_TGSS||Jy/beam||I: maximum of detections peak fluxes; L: set to 0|
|E_Peak_flux_TGSS||Jy/beam||I: error relative to the maximum of detections peak fluxes; L: set to 0|
|Rms_TGSS||Jy/beam||Local rms noise|
|E_Spidx||–||L,U: set to 0|
|s2n||–||Peak_flux over Island Rms|
|S_code||S,M,C,L,U,I||Source code as described above|
|Num_match||–||Number of matched sources in the same island|
|Num_unmatch_NVSS||–||Number of NVSS unmatched sources in the same island|
|Num_unmatch_TGSS||–||Number of TGSS unmatched sources in the same island|
|Isl_id||–||Island identification number|
|Source_id||–||Unique source identification number|
Some notes are valid only for specific entry types as saved in the S_code column.
We produced a spectral index map that covers in total 80% of the sky (Dec>-40 deg). The map has been created by extracting a pixel by pixel spectral index value from the NVSS and TGSS images used for the spectral index catalogue. From these images, we retained only those pixels that were at least three times above the noise in both surveys. The output of the process are two maps:
Direct access through the web-based Aladin lite tool (limited functionality; pre-loaded images):
Alternatively, download and run the Aladin Desktop tool (full functionality)
Then use menu File→Open URL and enter the following links:
Fits files are available here.
Two examples of the radio spectral index map produced matching pixel-by-pixel the NVSS and the TGSS maps. Left is the NVSS image, right the TGSS image, at the centre we show the spectral index map:
If you use resources listed in this page, please reference the paper: de Gasperin, Intema & Frail, MNRAS, 474, 5008 (2018).