SDSS-IV MaStar: [α/Fe] for the MaNGA Stellar Library from synthetic model spectra
ABSTRACT

We calculate the α-enhancement ratio [α/Fe] for the Mapping Nearby Galaxies at APO (MaNGA) Stellar Library (MaStar) while also fitting for the fundamental atmospheric parameters effective temperature, surface gravity, and metallicity – Teff, log g, [Fe/H]. This approach builds upon a previous catalogue of stellar parameters, whereby only the fundamental atmospheric parameters are fit with solar-scaled models. Here, we use the same Markov Chain Monte Carlo method with the additional free parameter [α/Fe]. Using the full spectral fitting code pPXF, we are able to fit multiple lines sensitive to [α/Fe] for a more robust measurement. Quality flags based on the convergence of the sampler, errors in [α/Fe] and a cut in the χ2 of the model fit are used to clean the final catalogue, returning 17 214 spectra and values in the range of −0.25 < [α/Fe] < 0.48. Comparing our calculated [α/Fe] with literature values reveals a degeneracy in cool stars with log g ≥ ∼4; this comparison is then used to create an alternative and calibrated parameter set. We also plot the final catalogue in an [Fe/H] versus [α/Fe] diagram and recover the expected result of increasing [α/Fe] with decreasing [Fe/H] for Milky Way disc-halo stars. We apply more »

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
NSF-PAR ID:
10378155
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
517
Issue:
3
Page Range or eLocation-ID:
p. 4275-4290
ISSN:
0035-8711
Publisher:
Oxford University Press
3. Abstract We present a joint analysis of rest-UV and rest-optical spectra obtained using Keck/LRIS and Keck/MOSFIRE for a sample of 62 star-forming galaxies at z ∼ 2.3. We divide our sample into two bins based on their location in the [OIII]5007/Hβ vs. [NII]6584/Hα BPT diagram, and perform the first differential study of the rest-UV properties of massive ionizing stars as a function of rest-optical emission-line ratios. Fitting BPASS stellar population synthesis models, including nebular continuum emission, to our rest-UV composite spectra, we find that high-redshift galaxies offset towards higher [OIII]λ5007/Hβ and [NII]λ6584/Hα have younger ages ($\log (\textrm {~Age/yr})=7.20^{+0.57}_{-0.20}$) and lower stellar metallicities ($Z_*=0.0010^{+0.0011}_{-0.0003}$) resulting in a harder ionizing spectrum, compared to the galaxies in our sample that lie on the local BPT star-forming sequence ($\log (\textrm {Age/yr})=8.57^{+0.88}_{-0.84}$, $Z_*=0.0019^{+0.0006}_{-0.0006}$). Additionally, we find that the offset galaxies have an ionization parameter of $\log (U)=-3.04^{+0.06}_{-0.11}$ and nebular metallicity of ($12+\log (\textrm {~O/H})=8.40^{+0.06}_{-0.07}$), and the non-offset galaxies have an ionization parameter of $\log (U)=-3.11^{+0.08}_{-0.08}$ and nebular metallicity of $12+\log (\textrm {~O/H})=8.30^{+0.05}_{-0.06}$. The stellar and nebular metallicities derived for our sample imply that the galaxies offset from the local BPT relation are more α-enhanced ($7.28^{+2.52}_{-2.82}\textrm {~O/Fe}_{\odot }$) compared to those consistent with the local sequencemore »