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

Abstract

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 $\rm \langle SNR \rangle \sim 4$, but we find that for iAB < 21 all direct D4000 measurements have $\rm SNR>3$. The CIGALE D4000n has $\rm \langle SNR \rangle \sim 20$, 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.

Predicting the Spectroscopic Features of Galaxies by Applying Manifold Learning on Their Broadband Colors: Proof of Concept and Potential Applications for Euclid, Roman, and Rubin LSST

“…The D4000-stellar mass relation measured for our blue galaxies is comparable to the relations reported in Haines et al (2017), who measured a slope of 0.12-0.14 for the D4000-stellar mass relation for their blue galaxies with little to no redshift dependence at 0.5 < z < 1.1, based on data for ∼65,000 galaxies from the VIMOS Public Extragalactic Redshift Survey (Guzzo et al 2014). Renard et al (2022) also measured a slope of ∼0.09-0.12 for blue clouds based on D4000 measured from narrowband photometry for ∼17,000…”

“…galaxies at 0.5 < z < 1 in the Physics of the Accelerating Universe Survey (Benítez et al 2009). However, both of these studies measured a steeper slope for their red-sequence galaxies, ∼0.23 in Haines et al (2017) and 0.25-0.32 in Renard et al (2022). One potential source of larger discrepancy in the measured relation for the red population can arise from the wider redshift range of our sample as well as the fact that these samples are magnitude limited and therefore are not mass complete, leaving us with the most massive and bluer galaxies at higher-redshift bins and a low fraction of red galaxies in general.…”

“…In this section, we use our predicted D4000 features based on SOMs to study the D4000-stellar mass relation for the galaxies in our sample. This relation has been studied in the literature based on D4000 features from spectroscopy and narrowband photometry (Haines et al 2017;Siudek et al 2017;Kim et al 2018;Renard et al 2022). These studies observed a bimodal distribution of galaxies on the D4000-stellar mass plane, where they found blue cloud and red-sequence galaxies differentiated from each other.…”

“…By taking advantage of this model-free SED grouping, we then use the physical features measured for a subsample of galaxies in each cell to predict that feature for the rest of the galaxies in that cell. To investigate this approach and its potential, we estimate the 4000 Å break for our sample in Section 4, which classically requires spectroscopy or narrowband photometry for proper estimation (Stothert et al 2018;Renard et al 2022).…”

A Dynamic Galaxy: Stellar Age Patterns across the Disk of M101

“…Another alternative to broadband photometry is narrowband photometry, particularly observations targeting age-diagnostic absorption features like the Balmer lines, the 4000 Å break, or metallic lines such as Mg b. Pioneering narrowband work has been performed for spiral galaxies (Beauchamp & Hardy 1997;Mollá et al 1999;Ryder et al 2005), and modern narrowband photometry can measure absorption line strengths that are compatible with spectroscopy (Stothert et al 2018;Angthopo et al 2020;Renard et al 2022). Absorption line equivalent widths (EWs) are largely insensitive to dust effects (MacArthur 2005) and, combined with stellar population synthesis modeling, have been used to investigate luminosityweighted stellar ages in integrated stellar populations (e.g., Fisher et al 1995;Ganda et al 2007;Sánchez-Blázquez et al 2014a, 2014b.…”