Fingerprints of stellar populations in the near-infrared: an optimized set of spectral indices in the <i>JHK</i> bands 0

Eftekhari, Elham; Vazdekis, Alexandre; Barbera, F. La

doi:10.1093/mnras/stab976

Cited by 11 publications

(10 citation statements)

References 75 publications

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“…Note that, for all spectra, we measured CO spectral indices (see Sec. 4), when they lie within the available spectral range and are considered to be safe for the stellar population analysis, according to the criteria given in Eftekhari et al (2021) (see their section 4.8).…”

Section: Samplesmentioning

confidence: 99%

“…the individual XSGs, while the median-stacked spectrum is shown in black. The wavelength definitions of CO indices, from Eftekhari et al (2021), are shown with shaded grey and orange areas corresponding to indices bandpass and pseudo-continua bands, respectively. In the same figure, we also show a fiducial model (pink) corresponding to an E-MILES simple stellar population (SSP) with an age of 11 Gyr (mean age of the XSGs as derived from optical indices), solar chemical abundance pattern, and a bimodal IMF of logarithmic slope 1.3 (corresponding to a MW-like IMF).…”

Section: O R I Gmentioning

confidence: 99%

“…The model and observed spectra have been convolved to a common resolution of 𝜎 = 360 km s −1 , as this is the highest velocity dispersion in the sample of La Barbera et al (2019). The central bandpasses of CO indices, as well as the blue and red pseudo-continua, are from Eftekhari et al (2021) and are shown as grey and orange areas, respectively. All spectra have been normalised to the mean flux within pseudo-continua bands.…”

Section: Co Vs Metallicitymentioning

confidence: 99%

“…2, shows measurements for the same CO feature as for D CO , but using the index definition, named CO2.30, from Eftekhari et al (2021). While D CO measures the absorption at ∼ 2.30 𝜇m as a generic discontinuity, defined as the ratio between the average fluxes in the pseudo-continua and in the absorption bands, the CO2.30 index follows a Lick-style definition, with a blue and red pseudo-continua and the absorption bandpass (see figure A3 in Eftekhari et al 2021 for a comparison of the two definitions). Note that the red bandpass of CO2.30 is not covered by the S08 and M09 spectra and, therefore, these samples are not included in the upperright panel of Fig.…”

Section: Other K-band Co Indicesmentioning

confidence: 99%

“…Since Stellar Population Synthesis (SPS) models are an essential tool to constrain the stellar content of galaxies, a detailed assessment of their validity and limitations is crucial to determine the physical and evolutionary properties of these systems. While spectral synthesis modelling at optical wavelengths is now a mature field of research and optical galaxy spectra can be accurately matched with SPS models, there is still a long road ahead for Near-Infrared (NIR) SPS models to consistently agree with observations (Riffel et al 2019;Eftekhari et al 2021). For example, only in the last decade, the problem of matching strong sodium absorption lines of massive Early-Type Galaxies (ETGs) has been scrutinized in the NIR.…”

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confidence: 99%

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Strong CO absorption features in massive ETGs

Eftekhari¹,

Barbera²,

Vazdekis³

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Massive Early-Type Galaxies (ETG) in the local Universe are believed to be the most mature stage of galaxy evolution. Their stellar population content reveals the evolutionary history of these galaxies. However, while state-of-the-art Stellar Population Synthesis (SPS) models provide an accurate description of observed galaxy spectra in the optical range, the modelling in the Near-Infrared (NIR) is still in its infancy. Here we focus on NIR CO absorption features to show, in a systematic and comprehensive manner, that for massive ETGs, all CO indices, from H through to K band, are significantly stronger than currently predicted by SPS models. We explore and discuss several possible explanations of this ‘CO mismatch’, including the effect of intermediate-age, AGB-dominated, stellar populations, high metallicity populations, non-solar abundance ratios and the initial mass function. While none of these effects is able to reconcile models and observations, we show that ad-hoc ‘empirical’ corrections, taking into account the effect of CO-strong giant stars in the low-temperature regime, provide model predictions that are closer to the observations. Our analysis points to the effect of carbon abundance as the most likely explanation of NIR CO line-strengths, indicating possible routes for improving the SPS models in the NIR.

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Section: Samplesmentioning

confidence: 99%

Section: O R I Gmentioning

confidence: 99%

Section: Co Vs Metallicitymentioning

confidence: 99%

Section: Other K-band Co Indicesmentioning

confidence: 99%

mentioning

confidence: 99%

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Strong CO absorption features in massive ETGs

Eftekhari¹,

Barbera²,

Vazdekis³

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Modelling simple stellar populations in the near-ultraviolet to near-infrared with the X-shooter Spectral Library (XSL)

Verro

Trager

Peletier

et al. 2022

A&A

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We present simple stellar population models based on the empirical X-shooter Spectral Library (XSL) from near-ultraviolet (NUV) to near-infrared (NIR) wavelengths. The unmatched characteristics of the relatively high resolution and extended wavelength coverage (350–2480 nm, R ∼ 10 000) of the XSL population models bring us closer to bridging optical and NIR studies of intermediate-age and old stellar populations. It is now common to find good agreement between observed and predicted NUV and optical properties of stellar clusters due to our good understanding of the main-sequence and early giant phases of stars. However, NIR spectra of intermediate-age and old stellar populations are sensitive to cool K and M giants. The asymptotic giant branch, especially the thermally pulsing asymptotic giant branch, shapes the NIR spectra of 0.5–2 Gyr old stellar populations; the tip of the red giant branch defines the NIR spectra of older populations. We therefore construct sequences of the average spectra of static giants, variable O-rich giants, and C-rich giants to be included in the models separately. The models span the metallicity range −2.2 < [Fe/H] < +0.2 and ages above 50 Myr, a broader range in the NIR than in other models based on empirical spectral libraries. We focus on the behaviour of colours and absorption-line indices as a function of age and metallicity. Our models can reproduce the integrated optical colours of the Coma cluster galaxies at the same level as other semi-empirical models found in the literature. In the NIR, there are notable differences between the colours of the models and Coma cluster galaxies. Furthermore, the XSL models expand the range of predicted values of NIR indices compared to other models based on empirical libraries. Our models make it possible to perform in-depth studies of colours and spectral features consistently throughout the optical and the NIR range to clarify the role of evolved cool stars in stellar populations.

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Radial gradients of CO absorptions and abundance ratios in the bulge of M31

La Barbera,

Vazdekis,

Pasquali

et al. 2024

A&A

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We present new H- and K-band spectroscopy for the bulge of M31, taken with the LUCI spectrograph at the Large Binocular Telescope (LBT). We studied radial trends of CO absorption features (namely and ) in the bulge of M31, out to a galactocentric distance of $ 380$ pc). We find that most COs do not exhibit a strong radial gradient, despite the strong metallicity gradient inferred from the optical spectral range, except for showing a steep increase in the center. We compared the observed line strengths to predictions of different state-of-the-art stellar population models, including an updated version of EMILES models, which also uses the extended IRTF spectral library. The observed COs are close to models' predictions, but in some models they turn out to be underestimated. We find that the lack of radial gradients is due to the combination of increasing CO strength with metallicity and C abundance, and decreasing CO strength with IMF slope and O abundance. We speculate that the steep gradient of might be due to Na overabundance. Remarkably, we were able to fit, at the same time, optical indices and all the NIR COs (except for CO1.68) leaving abundance ratios (i.e. and ) as free-fitting parameters, imposing age and metallicity constraints from the optical spectral range with no significant contribution from intermediate-age populations ($ 1$ Gyr-old). For the majority of the bulge, we find 0.15$ dex larger than (by $ 0.1$ dex), and C abundance consistent with that of Mg. In the central (few arcsec) region, we still find an enhancement of O and Mg, but significantly lower . We find that the COs' line strengths of the bulge are significantly lower than those of massive galaxies, possibly because of a difference in carbon abundance, as well as, to some extent, total metallicity.

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Fingerprints of stellar populations in the near-infrared: an optimized set of spectral indices in the JHK bands 0

Cited by 11 publications

References 75 publications

Strong CO absorption features in massive ETGs

Strong CO absorption features in massive ETGs

Modelling simple stellar populations in the near-ultraviolet to near-infrared with the X-shooter Spectral Library (XSL)

Radial gradients of CO absorptions and abundance ratios in the bulge of M31

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