Extremely Large Telescope

Abstract:

Three basic ingredients are required to generate a simple stellar population (SSP) library, i.e. an initial mass function (IMF), a stellar evolution model/isochrones, and an empirical/theoretical stellar spectral library. However, there are still some uncertainties to the determination and understanding of these ingredients. We perform the spectral fitting to test the relative parameter offsets between these uncertainties using two different stellar population models, two different empirical stellar libraries, two different isochrones, and the Salpeter and Chabrier IMFs. Based on these setups, we select five SSP libraries generated with the Galaxev/STELIB and Vazdekis/MILES models, and apply them to the pPXF full-spectrum fitting of both MaNGA and mock spectra. We find that: (1) Compared to the Galaxev/STELIB model, spectral fitting qualities with the Vazdekis/MILES model have significant improvements for those metal-rich (especially oversolar) spectra, which cause better reduced χ 2 distributions and more precisely fitted absorption lines. This might due to the lack of metal-rich stars in the empirical STELIB library, or code improvement of the Vazdekis model. (2) When applying the Vazdekis/MILES model for spectral fitting, the IMF variation will lead to not only a systematic offset in M ∗ /L r , but also offsets in age and metallicity, and these offsets increase with increasing stellar population ages. However, the IMF variation caused metallicity offsets disappear in the case of Galaxev/STELIB based libraries. (3) The Padova2000 model provides a better match to the MaNGA galaxy spectra at [M/H] L < −1.0, while the BaSTI model match the local galaxy spectra better at [M/H] L > −1.0. Current tests suggest that spectral fitting with the Vazdekis/MILES + BaSTI combination would be a better choice for local galaxies.

Abstract:

Twenty years have passed since first light for the Sloan Digital Sky Survey (SDSS). Here, we release data taken by the fourth phase of SDSS (SDSS-IV) across its first three years of operation (2014 July–2017 July). This is the third data release for SDSS-IV, and the 15th from SDSS (Data Release Fifteen; DR15). New data come from MaNGA—we release 4824 data cubes, as well as the first stellar spectra in the MaNGA Stellar Library (MaStar), the first set of survey-supported analysis products (e.g., stellar and gas kinematics, emission-line and other maps) from the MaNGA Data Analysis Pipeline, and a new data visualization and access tool we call "Marvin." The next data release, DR16, will include new data from both APOGEE-2 and eBOSS; those surveys release no new data here, but we document updates and corrections to their data processing pipelines. The release is cumulative; it also includes the most recent reductions and calibrations of all data taken by SDSS since first light. In this paper, we describe the location and format of the data and tools and cite technical references describing how it was obtained and processed. The SDSS website (www.sdss.org) has also been updated, providing links to data downloads, tutorials, and examples of data use. Although SDSS-IV will continue to collect astronomical data until 2020, and will be followed by SDSS-V (2020–2025), we end this paper by describing plans to ensure the sustainability of the SDSS data archive for many years beyond the collection of data.