分类： 天文学 >> 天文学 提交时间： 2023-02-19
Daniel Lazarz
Renbin Yan
Ronald Wilhelm
Yanping Chen
Lewis Hill
Jon A. Holtzman
Julie Imig
Claudia Maraston
Szabolcs Mészáros
Guy S. Stringfellow
Daniel Thomas
Timothy C. Beers
Dmitry Bizyaev
Niv Drory
Richard R. Lane
Christian Nitschelm
摘要： We present a stellar parameter catalog built to accompany the MaStar Stellar Library, which is a comprehensive collection of empirical, medium-resolution stellar spectra. We constructed this parameter catalog by using a multicomponent $\chi^{2}$ fitting approach to match MaStar spectra to models generated by interpolating the ATLAS9-based BOSZ model spectra. The total $\chi^{2}$ for a given model is defined as the sum of components constructed to characterize narrow-band features of observed spectra (e.g., absorption lines) and the broadband continuum shape separately. Extinction and systematics due to flux calibration were taken into account in the fitting. The $\chi^{2}$ distribution for a given region of model space was sampled using a Markov Chain Monte Carlo (MCMC) algorithm, the data from which were then used to extract atmospheric parameter estimates ($T_{eff}$, log g, [Fe/H], and [$\alpha$/Fe]), their corresponding uncertainties, and direct extinction measurements. Two methods were used to extract parameters and uncertainties: one that accepts the MCMC's prescribed minimum-$\chi^{2}$ result, and one that uses Bayesian inference to compute a likelihood-weighted mean from the $\chi^{2}$ distribution sampled by the MCMC. Results were evaluated for internal consistency using repeat observations where available and by comparing them with external data sets (e.g., APOGEE-2 and Gaia DR2). Our spectral-fitting exercise reveals possible deficiencies in current theoretical model spectra, illustrating the potential power of MaStar spectra for helping to improve the models. This paper represents an update to the parameters that were originally presented with SDSS-IV DR17. The MaStar parameter catalog containing our BestFit results is available on the SDSS-IV DR17 website as part of version 2 of the MaStar stellar parameter value-added catalog.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Lorenza Nanni
Daniel Thomas
James Trayford
Claudia Maraston
Justus Neumann
David R. Law
Lewis Hill
Annalisa Pillepich
Renbin Yan
Yanping Chen
Dan Lazarz
摘要： To test the current theory on galaxy formation and evolution, it is essential to strengthening the synergy between simulations and observations. For this reason, in our previous paper of this series, we presented a method to mock SDSS-IV/MaNGA integral-field spectroscopic galaxy observations from cosmological simulations of galaxy formation. Here we present the resulting mock galaxy catalogue. This catalogue consists of 1,000 unique galaxies in TNG50 falling into the SDSS-IV/MaNGA-Primary target footprint, defined in the redshift and i-band absolute magnitude space, i.e. the iMaNGA sample. In this paper, we describe the general characteristics of the catalogue, in terms of morphology, kinematics, and stellar population properties. We also investigate our ability to recover the galaxy characteristics, as given by the simulations, analysing the synthetic spectra. We demonstrate that the `intrinsic' and recovered stellar kinematics, and stellar age and metallicity are consistent with zero within the 1$-{\sigma}$ level, for all the $\sim 8$ million tassels in the iMaNGA sample presented in this paper. We also compare `intrinsic' and recovered star formation histories, noting a strong resemblance. Therefore, our mocking and spectral fitting processes do not distort `intrinsic' galaxy properties, hence we can use these results for scientific analysis. In the future papers of this series, we will present a comprehensive comparison and scientific analysis of TNG50 simulations with MaNGA observational results.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jianhui Lian
Gail Zasowski
Sten Hasselquist
Jon A. Holtzman
Nicholas Boardman
Katia Cunha
José G. Fernández-Trincado
Peter M. Frinchaboy
D. A. Garcia-Hernandez
Christian Nitschelm
Richard R. Lane
Daniel Thomas
Kai Zhang
摘要： Stellar radial migration plays an important role in reshaping a galaxy's structure and the radial distribution of stellar population properties. In this work, we revisit reported observational evidence for radial migration and quantify its strength using the age--[Fe/H] distribution of stars across the Milky Way with APOGEE data. We find a broken age--[Fe/H] relation in the Galactic disc at $r>6$ kpc, with a more pronounced break at larger radii. To quantify the strength of radial migration, we assume stars born at each radius have a unique age and metallicity, and then decompose the metallicity distribution function (MDF) of mono-age young populations into different Gaussian components that originated from various birth radii at $r_{\rm birth}<13$ kpc. We find that, at ages of 2 and 3 Gyr, roughly half the stars were formed within 1 kpc of their present radius, and very few stars ($<5$%) were formed more than 4 kpc away from their present radius. These results suggest limited short distance radial migration and inefficient long distance migration in the Milky Way during the last 3 Gyr. In the very outer disc beyond 15~kpc, the observed age--[Fe/H] distribution is consistent with the prediction of pure radial migration from smaller radii, suggesting a migration origin of the very outer disc. We also estimate intrinsic metallicity gradients at ages of 2 and 3 Gyr of $-0.061$ dex kpc$^{-1}$ and $-0.063$ dex kpc$^{-1}$, respectively.
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