The PAU survey: measurements of the 4000 Å spectral break with narrow-band photometry

Pablo Renard*, Malgorzata Siudek*, Martin B. Eriksen, Laura Cabayol, Zheng Cai*, Jorge Carretero, Ricard Casas, Francisco J. Castander, Enrique Fernandez, Juan García-Bellido, Enrique Gaztanaga, Henk Hoekstra, Benjamin Joachimi, Ramon Miquel, David Navarro-Girones, Cristóbal Padilla, Eusebio Sanchez, Santiago Serrano, Pau Tallada-Crespí, Juan De VicenteAnna Wittje, Angus H. Wright

*Corresponding author for this work

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The D4000 spectral break index is one of the most important features in the visible spectrum, as it is a proxy for stellar ages and is also used in galaxy classification. However, its direct measurement has always been reserved to spectroscopy. Here, we present a general method to directly measure the D4000 with narrow-band (NB) photometry; it has been validated using realistic simulations, and then evaluated with PAUS NBs, cross-matched with VIPERS spectra (iAB < 22.5, 0.562 < z < 0.967). We also reconstruct the D4000 with the SED-fitting code cigale; the use of PAUS NBs instead of broad-bands significantly improves the SED fitting results. For D4000n, the direct measurement has [SNR]∼ 4, but we find that for iAB < 21 all direct D4000 measurements have [SNR]> 3. The cigale D4000n has [SNR ]∼ 20, but underestimates the error by >50 per cent. Furthermore, the direct method recreates well the D4000-SFR relation, as well as the D4000-mass relation for blue galaxies (for red galaxies, selection effects impact the results). On the other hand, cigale accurately classifies galaxies into red and blue populations. We conclude that the direct measurement of D4000 with narrow-band photometry is a promising tool to determine average properties of galaxy samples, with results compatible with spectroscopy.

Original languageEnglish
Pages (from-to)146-166
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date14 Jul 2022
Publication statusPublished - 1 Sept 2022


  • Galaxies: evolution

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