Recovering galaxy star formation and metallicity histories from spectra using VESPA

Aims. We provide an easy-to-use full-spectrum fitting package and explore its applications to (i) the determination of the stellar atmospheric parameters and (ii) the study of the history of stellar populations. Methods. We developed ULySS, a package to fit spectroscopic observations against a linear combination of non-linear model components convolved with a parametric line-of-sight velocity distribution. The minimization can be either local or global, and determines all the parameters in a single fit. We use χ 2 maps, convergence maps and Monte-Carlo simulations to study the degeneracies, local minima and to estimate the errors. Results. We show the importance of determining the shape of the continuum simultaneously to the other parameters by including a multiplicative polynomial in the model (without prior pseudo-continuum determination, or rectification of the spectrum). We also stress the usefulness of using an accurate line-spread function, depending on the wavelength, so that the line-shape of the models properly matches the observation. For simple models, i.e., to measure the atmospheric parameters or the age/metallicity of a singleage stellar population, there is often a unique minimum, or when local minima exist they can be recognized unambiguously. For more complex models, Monte-Carlo simulations are required to assess the validity of the solution. Conclusions. The ULySS package is public, simple to use and flexible. The full spectrum fitting makes optimal use of the signal.

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“…formation because of the degeneracies and the finite quality of the models and observation (see also Tojeiro et al 2007). …”

Section: History Of Stellar Populationsmentioning

confidence: 99%

ULySS: a full spectrum fitting package

Koleva

Prugniel

Bouchard

et al. 2009

A&A

482

526

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“…This number, with certain caveats (discussed later), contains all the information about the parameter contained in the full data. The method has been successfully applied in the fields of CMB analysis (Bond et al 1998), medical image registration 2 and galaxy shape fitting (Tojeiro et al 2007). A complete background of the development of the MOPED algorithm can be found in Tegmark et al (1997, hereafter T97), Heavens et al (2000, hereafter H00) and Panter et al (2003).…”

Section: Introductionmentioning

confidence: 99%

Stellar atmosphere parameters with MAχ, a MAssive compression ofχ²for spectral fitting

Jofré¹,

Panter

Hansen

et al. 2010

A&A

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MAχ is a new tool to estimate parameters from stellar spectra. It is based on the maximum likelihood method, with the likelihood compressed in a way that the information stored in the spectral fluxes is conserved. The compressed data are given by the size of the number of parameters, rather than by the number of flux points. The optimum speed-up reached by the compression is the ratio of the data set to the number of parameters. The method has been tested on a sample of low-resolution spectra from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey for the estimate of metallicity, effective temperature and surface gravity, with accuracies of 0.24 dex, 130 K and 0.5 dex, respectively. Our stellar parameters and those recovered by the SEGUE Stellar Parameter Pipeline agree reasonably well. A small sample of high-resolution VLT-UVES spectra is also used to test the method and the results were compared to a more classical approach. The speed and multi-resolution capability of MAχ combined with its performance compared with other methods indicates that it will be a useful tool for the analysis of upcoming spectral surveys.

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“…The PSS approach saw its inception with the works by Morgan (1956), Wood (1966), and Faber (1972) and has over the years been subject to significant development (e.g. Bica 1988;Pelat 1997Pelat , 1998Moultaka et al 2004;Heavens, Jimenez & Lahav 2000;Heavens et al 2004;Ocvirk et al 2006a,b;Tojeiro et al 2007;MacArthur et al 2009;Koleva et al 2009). In the last two decades, spectral synthesis has transitioned from the modelling of a few observables, such as colours, fluxes, and/or equivalent widths (EWs) of absorption lines (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Wood 1966;Faber 1972;Worthey 1994;Kauffmann et al 2003) to the more powerful pixel-by-pixel (λ-by-λ) fitting technique that exploits the full information in current medium-to high-resolution spectroscopic data (e.g. Cid Koleva et al 2009;Tojeiro et al 2007). …”

Section: Introductionmentioning

confidence: 99%

Impact of an AGN featureless continuum on estimation of stellar population properties

Cardoso

Gomes

Papaderos

2017

A&A

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The effect of the featureless power-law (PL) continuum of an active galactic nucleus (AGN) on the estimation of physical properties of galaxies with optical population spectral synthesis (PSS) remains largely unknown. With the goal of a quantitative examination of this issue, we fit synthetic galaxy spectra representing a wide range of galaxy star formation histories (SFHs) and including distinct PL contributions of the form F ν ∝ ν −α with the PSS code Starlight to study to which extent various inferred quantities (e.g. stellar mass, mean age, and mean metallicity) match the input. The synthetic spectral energy distributions (SEDs) computed with our evolutionary spectral synthesis code include an AGN PL component with 0.5 ≤ α ≤ 2 and a fractional contribution 0.2 ≤ x AGN ≤ 0.8 to the monochromatic flux at 4020 Å. At the empirical AGN detection threshold x AGN 0.26 that we previously inferred in a pilot study on this subject, our results show that the neglect of a PL component in spectral fitting can lead to an overestimation by ∼2 dex in stellar mass and by up to ∼1 and ∼4 dex in the light-and mass-weighted mean stellar age, respectively, whereas the light-and mass-weighted mean stellar metallicity are underestimated by up to ∼0.3 and ∼0.6 dex, respectively. These biases, which become more severe with increasing x AGN , are essentially independent of the adopted SFH and show a complex behaviour with evolutionary time and α. Other fitting set-ups including either a single PL or multiple PLs in the base reveal, on average, much lower unsystematic uncertainties of the order of those typically found when fitting purely stellar SEDs with stellar templates, however, reaching locally up to ∼1, 3 and 0.4 dex in mass, age and metallicity, respectively. Our results underscore the importance of an accurate modelling of the AGN spectral contribution in PSS fits as a minimum requirement for the recovery of the physical and evolutionary properties of stellar populations in active galaxies. In particular, this study draws attention to the fact that the neglect of a PL in spectral modelling of these systems may lead to substantial overestimates in stellar mass and age, thereby leading to potentially significant biases in our understanding of the co-evolution of AGN with their galaxy hosts.

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Recovering galaxy star formation and metallicity histories from spectra using VESPA

Cited by 250 publications

References 37 publications

ULySS: a full spectrum fitting package

ULySS: a full spectrum fitting package

Stellar atmosphere parameters with MAχ, a MAssive compression ofχ²for spectral fitting

Impact of an AGN featureless continuum on estimation of stellar population properties

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Recovering galaxy star formation and metallicity histories from spectra using VESPA

Cited by 250 publications

References 37 publications

ULySS: a full spectrum fitting package

ULySS: a full spectrum fitting package

Stellar atmosphere parameters with MAχ, a MAssive compression ofχ2for spectral fitting

Impact of an AGN featureless continuum on estimation of stellar population properties

Contact Info

Product

Resources

About

Stellar atmosphere parameters with MAχ, a MAssive compression ofχ²for spectral fitting