Higher‐order Balmer line indices in α/Fe‐enhanced stellar population models

By D. Thomas, C. Maraston, A. Korn. 2004

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We have computed the higher-order Balmer absorption line indices Hγ and Hδ for stellar population models with variable element ratios. The response of these indices to abundance ratio variations is taken from detailed line formation and model atmosphere calculations. We find that Hγ and Hδ, unlike Hβ, are very sensitive to α/Fe ratio changes at super-solar metallicities. Both line indices increase significantly with increasing α/Fe ratio. This effect cannot be neglected when these line indices are used to derive the ages of metal-rich, unresolved stellar populations such as early-type galaxies. We re-analyze the elliptical galaxy sample of Kuntschner, and show that consistent age estimates from Hβ and Hγ are obtained only if the effect of α/Fe enhancement on Hγ is taken into account in the models. This result rectifies a problem currently present in the literature, namely that Hγ and Hδ have up to now led to significantly younger ages for early-type galaxies than Hβ. Our work particularly impacts on the interpretation of intermediate- to high-redshift data, for which only the higher-order Balmer lines are accessible observationally.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ce710a6d6ba36550b6ebe2f3d53b2f4d570089f5

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Citations in the corpus

A census of metals and baryons in stars in the local universe (2007, methodology): “First of all, for a stellar population with abundance ratio [α/Fe] = 0.3, we determine the offset between the expected (true) parameters and those derived with a model library with [α/Fe] = 0, using the predictions from Thomas et al. (2004) simple stellar population (SSP) models.”
The SAURON project - IV. The mass-to-light ratio, the virial mass estimator and the Fundamental Plane of elliptical and lenticular galaxies (2005, methodology): “A similar approach was adopted by us and by other groups to measure the black hole (BH) masses in galaxy nuclei or to analyse the stellar orbital distribution (e.g. Cretton et al. 1999; Cappellari et al. 2002; Verolme et al. 2002; Gebhardt et al. 2003; Valluri et al. 2004; Thomas et al. 2004).”
EARLY-TYPE GALAXY ARCHEOLOGY: AGES, ABUNDANCE RATIOS, AND EFFECTIVE TEMPERATURES FROM FULL-SPECTRUM FITTING (2013, methodology): “The results from T10 are based on the SPS models of Thomas et al. (2003b) and Thomas et al. (2004).”
Observational evidence for AGN feedback in early-type galaxies (2007, methodology): “We derive luminosity-weighted SSP ages and metallicities byχ2 fitting the Thomas et al. (2003, 2004) models to the 25 Lick absorption line indices and compute a second probability distribution through the comparison of these quantities with theV -luminosity weighted ages and metallicities of the…”
VLT spectroscopy of globular cluster systems - II. Spectroscopic ages, metallicities and [α/Fe] ratios of globular clusters in early-type galaxies (2005, methodology): “It is worth noting that some of these values are only valid for our data quality in combination with the SSP models of Thomas et al. (2003, 2004).”
Environment and self-regulation in galaxy formation (2009, methodology): “By means of the stellar population models of Thomas et al. (2003, 2004), the stellar population parameters age, metallicity and α/Fe ratio are derived using a minimized χ 2 technique.”
SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs (2016, methodology): “The stellar population models are the same as those predicting absorption-line indices including abundance-ratio effects, which are required to describe the absorption spectra of old galaxies and bulges (Thomas et al. 2004, 2011).”
NOAO Fundamental Plane Survey. II. Age and Metallicity along the Red Sequence from Line-Strength Data (2005, methodology): “Thomas et al. (2004a) quote ages, metallicities and αenhancements for 54 early-type galaxies in high-density environments.”
The ages and metallicities of galaxies in the local universe (2005, methodology): “…the potential error on our metallicity and age estimates for galaxies with enhanced α/Fe relative to solar, we compared the predictions of the Thomas et al. (2004) stellar populations models at solar element abundance ratio, α/Fe = 0, with those for α/Fe = 0.3 (a typical ratio for massive…”
Fitting the integrated spectral energy distributions of galaxies (2010, background): “Much work has gone into optimizing the set of available indices, as well in terms of coverage, as well as in terms of model precision (e.g. Rose 1984; Worthey et al. 1994; Trager et al. 1998; Tripicco and Bell 1995; Cenarro et al. 2002; Thomas et al. 2004; Lee et al. 2009b, and references therein).”
The Origin of Dwarf Ellipticals in the Virgo Cluster (2008, background): “…(Hα emission line; Kennicutt 1998; Boselli et al. 2001) and past (Hβ absorption line14; Poggianti & Barbaro 1997; Poggianti et al. 2001a, 2001b; Thomas et al. 2004) star formation activity and the FUV − H color index are expected to evolve after a ram pressure stripping event for galaxies…”
SPIDER VIII - constraints on the stellar initial mass function of early-type galaxies from a variety of spectral features (2013, methodology): “…ages is a well-known issue, whose explanation might involve the stronger sensitivity of high-order (relative to Hβ) Balmer lines to (i) [α/Fe] (Thomas et al. 2004; Thomas & Davies 2006), (ii) single element abundance ratios (Serven & Worthey 2007), and (iii) fraction of young stars…”
Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters (2006, methodology): “…library (Gorgas et al. 1993; Worthey et al. 1994), which contains about 430 stars in the spectral range λλ4000–6200 Å. Examples of population models using this library are those of Bruzual & Charlot (1993), Worthey (1994a), Vazdekis et al. (1996), Thomas et al. (2003) and Thomas et al. (2004).”
Evolutionary population synthesis: models, analysis of the ingredients and application to high‐z galaxies (2004, background): “At high redshifts when galaxies are dominated by∼ 1 Gyr old populations as inferred from the ages and element ratios of local early-type galaxies (Thomas et al. 2004), the TP-AGB signature in the rest-frame near-IR must show up, with e.g. the rest-frame V − K colour mapping into the observedK − 10…”
Galaxy Masses: A Review (2013, background): “The dimensionality equivalence between the observables and the DF explains why one can uniquely recover the DF from the data, when all other model parameters are known (Thomas et al. 2004b; Krajnović et al. 2005; van de Ven et al. 2008; Morganti & Gerhard 2012).”
Stellar populations of early-type galaxies in different environments - II. Ages and metallicities (2006, background): “Thomas et al. (2004) did not find a significant trend between the age and the velocity dispersion in either their sample of high- or low-density environment galaxies.”