The relation between galaxy stellar mass and gas-phase metallicity is a sensitive diagnostic of the main processes that drive galaxy evolution, namely cosmological gas inflow, metal production in ...stars, and gas outflow via galactic winds. We employed the direct method to measure the metallicities of ~200,000 star-forming galaxies from the Sloan Digital Sky Survey that were stacked in bins of (1) stellar mass and (2) both stellar mass and star formation rate (SFR) to significantly enhance the signal-to-noise ratio of the weak OIII lambda4363 and OII lambdalambda7320, 7330 auroral lines required to apply the direct method. These metallicity measurements span three decades in stellar mass from log(Mlow */M sub(middot in circle)) = 7.4-10.5, which allows the direct method mass-metallicity relation to simultaneously capture the high-mass turnover and extend a full decade lower in mass than previous studies that employed more uncertain strong line methods. The direct method mass-metallicity relation rises steeply at low mass (O/H is proportional to Mlow * super(1/2)) until it turns over at log(Mlow */M sub(middot in circle)) = 8.9 and asymptotes to 12 + log(O/H) = 8.8 at high mass. The direct method mass-metallicity relation has a steeper slope, a lower turnover mass, and a factor of two to three greater dependence on SFR than strong line mass-metallicity relations. Furthermore, the SFR-dependence appears monotonie with stellar mass, unlike strong line mass-metallicity relations. We also measure the N/O abundance ratio, an important tracer of star formation history, and find the clear signature of primary and secondary nitrogen enrichment. N/O correlates tightly with oxygen abundance, and even more so with stellar mass.
We present new analytic solutions for one-zone (fully mixed) chemical evolution models that incorporate a realistic delay time distribution for Type Ia supernovae (SNe Ia) and can therefore track the ...separate evolution of -elements produced by core collapse supernovae (CCSNe) and iron peak elements synthesized in both CCSNe and SNe Ia. Our solutions allow constant, exponential, or linear-exponential ( ) star formation histories, or combinations thereof. In generic cases, and iron abundances evolve to an equilibrium at which element production is balanced by metal consumption and gas dilution, instead of continuing to increase over time. The equilibrium absolute abundances depend principally on supernova yields and the outflow mass loading parameter , while the equilibrium abundance ratio depends mainly on yields and secondarily on star formation history. A stellar population can be metal-poor either because it has not yet evolved to equilibrium or because high outflow efficiency makes the equilibrium abundance itself low. Systems with ongoing gas accretion develop metallicity distribution functions (MDFs) that are sharply peaked, while "gas starved" systems with rapidly declining star formation, such as the conventional "closed box" model, have broadly peaked MDFs. A burst of star formation that consumes a significant fraction of a system's available gas and retains its metals can temporarily boost by 0.1-0.3 dex, a possible origin for rare, -enhanced stars with intermediate age and/or high metallicity. Other sudden transitions in system properties can produce surprising behavior, including backward evolution of a stellar population from high to low metallicity.
Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, ...outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in O/Fe-Fe/H and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in O/Fe-Fe/H unlike the observed bimodality (separate high- and low- sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present X/Fe-Fe/H tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of -elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.
We use direct method oxygen abundances in combination with strong optical emission lines, stellar masses (M
⋆), and star formation rates (SFRs) to recalibrate the N2, O3N2, and N2O2 oxygen abundance ...diagnostics. We stack spectra of ∼200 000 star-forming galaxies from the Sloan Digital Sky Survey in bins of M
⋆ and SFR offset from the star-forming main sequence (
$ {\Delta \log (SSFR)}$
) to measure the weak emission lines needed to apply the direct method. All three new calibrations are reliable to within ±0.10 dex from log (M
⋆/M⊙) ∼ 7.5–10.5 and up to at least 200 M⊙ yr−1 in SFR. The N2O2 diagnostic is the least subject to systematic biases. We apply the diagnostics to galaxies in the local Universe and investigate the M
⋆–Z–SFR relation. The N2 and O3N2 diagnostics suggest the SFR dependence of the M
⋆–Z–SFR relation varies with both M
⋆ and
${\Delta \log (SSFR)}$
, whereas the N2O2 diagnostic suggests a nearly constant dependence on SFR. We apply our calibrations to a sample of high-redshift galaxies from the literature, and find them to be metal-poor relative to local galaxies with similar M
⋆ and SFR. The calibrations do reproduce direct method abundances of the local analogues. We conclude that the M
⋆–Z–SFR relation evolves with redshift.
The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is currently acquiring integral-field spectroscopy for the largest sample of galaxies to date. By 2020, the MaNGA Survey-which ...is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV)-will have observed a statistically representative sample of 104 galaxies in the local universe (z 0.15). In addition to a robust data-reduction pipeline (DRP), MaNGA has developed a data-analysis pipeline (DAP) that provides higher-level data products. To accompany the first public release of its code base and data products, we provide an overview of the MaNGA DAP, including its software design, workflow, measurement procedures and algorithms, performance, and output data model. In conjunction with our companion paper (Belfiore et al.), we also assess the DAP output provided for 4718 observations of 4648 unique galaxies in the recent SDSS Data Release 15 (DR15). These analysis products focus on measurements that are close to the data and require minimal model-based assumptions. Namely, we provide stellar kinematics (velocity and velocity dispersion), emission-line properties (kinematics, fluxes, and equivalent widths), and spectral indices (e.g., D4000 and the Lick indices). We find that the DAP provides robust measurements and errors for the vast majority (>99%) of analyzed spectra. We summarize assessments of the precision and accuracy of our measurements as a function of signal-to-noise. We also provide specific guidance to users regarding the limitations of the data. The MaNGA DAP software is publicly available and we encourage community involvement in its development.
Abstract
We present new evidence for AGN feedback in a subset of 69 quenched low-mass galaxies (M⋆ ≲ 5 × 109 M⊙, Mr > −19) selected from the first 2 yr of the Sloan Digital Sky Survey-IV Mapping ...Nearby Galaxies at APO (SDSS-IV MaNGA) survey. The majority (85 per cent) of these quenched galaxies appear to reside in a group environment. We find six galaxies in our sample that appear to have an active AGN that is preventing on-going star formation; this is the first time such a feedback mechanism has been observed in this mass range. Interestingly, five of these six galaxies have an ionized gas component that is kinematically offset from their stellar component, suggesting the gas is either recently accreted or outflowing. We hypothesize these six galaxies are low-mass equivalents to the ‘red geysers’ observed in more massive galaxies. Of the other 63 galaxies in the sample, we find 8 do appear for have some low level, residual star formation, or emission from hot, evolved stars. The remaining galaxies in our sample have no detectable ionized gas emission throughout their structures, consistent with them being quenched. This work shows the potential for understanding the detailed physical properties of dwarf galaxies through spatially resolved spectroscopy.
ABSTRACT Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is an optical fiber-bundle integral-field unit (IFU) spectroscopic survey that is one of three core programs in the ...fourth-generation Sloan Digital Sky Survey (SDSS-IV). With a spectral coverage of 3622-10354 and an average footprint of ∼500 arcsec2 per IFU the scientific data products derived from MaNGA will permit exploration of the internal structure of a statistically large sample of 10,000 low-redshift galaxies in unprecedented detail. Comprising 174 individually pluggable science and calibration IFUs with a near-constant data stream, MaNGA is expected to obtain ∼100 million raw-frame spectra and ∼10 million reduced galaxy spectra over the six-year lifetime of the survey. In this contribution, we describe the MaNGA Data Reduction Pipeline algorithms and centralized metadata framework that produce sky-subtracted spectrophotometrically calibrated spectra and rectified three-dimensional data cubes that combine individual dithered observations. For the 1390 galaxy data cubes released in Summer 2016 as part of SDSS-IV Data Release 13, we demonstrate that the MaNGA data have nearly Poisson-limited sky subtraction shortward of ∼8500 and reach a typical 10 limiting continuum surface brightness = 23.5 AB arcsec−2 in a five-arcsecond-diameter aperture in the g-band. The wavelength calibration of the MaNGA data is accurate to 5 km s−1 rms, with a median spatial resolution of 2.54 arcsec FWHM (1.8 kpc at the median redshift of 0.037) and a median spectral resolution of = 72 km s−1.
Abstract
Mapping Nearby Galaxies at Apache Point Observatory provides the opportunity to make precise spatially resolved measurements of the IMF slope in galaxies owing to its unique combination of ...spatial resolution, wavelength coverage, and sample size. We derive radial gradients in age, element abundances, and IMF slope analysing optical and near-infrared absorption features from stacked spectra out to the half-light radius of 366 early-type galaxies with masses 9.9–10.8 log M/M⊙. We find flat gradients in age and α/Fe ratio, as well as negative gradients in metallicity, consistent with the literature. We further derive significant negative gradients in the Na/Fe ratio with galaxy centres being well enhanced in Na abundance by up to 0.5 dex. Finally, we find a gradient in IMF slope with a bottom-heavy IMF in the centre (typical mass excess factor of 1.5) and a Milky Way-type IMF at the half-light radius. This pattern is mass dependent with the lowest mass galaxies in our sample featuring only a shallow gradient around a Milky Way IMF. Our results imply the local IMF–σ relation within galaxies to be even steeper than the global relation and hint towards the local metallicity being the dominating factor behind the IMF variations. We also employ different stellar population models in our analysis and show that a radial IMF gradient is found independently of the stellar population model used. A similar analysis of the Wing-Ford band provides inconsistent results and further evidence of the difficulty in measuring and modelling this particular feature.
Abstract
In this paper, we investigate 2727 galaxies observed by MaNGA as of 2016 June to develop spatially resolved techniques for identifying signatures of active galactic nuclei (AGNs). We ...identify 303 AGN candidates. The additional spatial dimension imposes challenges in identifying AGNs due to contamination from diffuse ionized gas, extraplanar gas and photoionization by hot stars. We show that the combination of spatially resolved line diagnostic diagrams and additional cuts on H α surface brightness and H α equivalent width can distinguish between AGN-like signatures and high-metallicity galaxies with low-ionization nuclear emission-line regions-like spectra. Low-mass galaxies with high specific star formation rates are particularly difficult to diagnose and routinely show diagnostic line ratios outside of the standard star formation locus. We develop a new diagnostic – the distance from the standard diagnostic line in the line-ratio space – to evaluate the significance of the deviation from the star formation locus. We find 173 galaxies that would not have been selected as AGN candidates based on single-fibre spectral measurements but exhibit photoionization signatures suggestive of AGN activity in the Mapping Nearby Galaxies at APO resolved observations, underscoring the power of large integral field unit surveys. A complete census of these new AGN candidates is necessary to understand their nature and probe the complex co-evolution of supermassive black holes and their hosts.
ABSTRACT
We derive ages, metallicities, and individual element abundances of early- and late-type galaxies (ETGs and LTGs) out to 1.5 Re. We study a large sample of 1900 galaxies spanning 8.6–11.3 ...log M/M⊙ in stellar mass, through key absorption features in stacked spectra from the SDSS-IV/MaNGA survey. We use mock galaxy spectra with extended star formation histories to validate our method for LTGs and use corrections to convert the derived ages into luminosity- and mass-weighted quantities. We find flat age and negative metallicity gradients for ETGs and negative age and negative metallicity gradients for LTGs. Age gradients in LTGs steepen with increasing galaxy mass, from −0.05 ± 0.11 log Gyr/Re for the lowest mass galaxies to −0.82 ± 0.08 log Gyr/Re for the highest mass ones. This strong gradient–mass relation has a slope of −0.70 ± 0.18. Comparing local age and metallicity gradients with the velocity dispersion σ within galaxies against the global relation with σ shows that internal processes regulate metallicity in ETGs but not age, and vice versa for LTGs. We further find that metallicity gradients with respect to local σ show a much stronger dependence on galaxy mass than radial metallicity gradients. Both galaxy types display flat C/Fe and Mg/Fe, and negative Na/Fe gradients, whereas only LTGs display gradients in Ca/Fe and Ti/Fe. ETGs have increasingly steep Na/Fe gradients with local σ reaching 6.50 ± 0.78 dex/log km s−1 for the highest masses. Na/Fe ratios are correlated with metallicity for both galaxy types across the entire mass range in our sample, providing support for metallicity-dependent supernova yields.
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