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Register a new userSDSS-IV MaNGA: Radial Gradients in Stellar Population Properties of Early-Type and Late-Type Galaxies
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We derive ages, metallicities, and individual element abundances of early- and late-type galaxies (ETGs and LTGs) out to 1.5 R$_e$. We study a large sample of 1900 galaxies spanning $8.6 - 11.3 log M/M_{odot}$ 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 $-0.05pm0.11~log$ Gyr/R$_e$ for the lowest mass galaxies to $-0.82pm0.08~log$ Gyr/R$_e$ for the highest mass ones. This strong gradient-mass relation has a slope of $-0.70pm0.18$. Comparing local age and metallicity gradients with the velocity dispersion $sigma$ within galaxies against the global relation with $sigma$ 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 $sigma$ 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 $sigma$ reaching $6.50pm0.78$ dex/$log$ km/s 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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Bars in galaxies are thought to stimulate both inflow of material and radial mixing along them. Observational evidence for this mixing has been inconclusive so far however, limiting the evaluation of the impact of bars on galaxy evolution. We now use results from the MaNGA integral field spectroscopic survey to characterise radial stellar age and metallicity gradients along the bar and outside the bar in 128 strongly barred galaxies. We find that age and metallicity gradients are flatter in the barred regions of almost all barred galaxies when compared to corresponding disk regions at the same radii. Our results re-emphasize the key fact that by azimuthally averaging integral field spectroscopic data one loses important information from non-axisymmetric galaxy components such as bars and spiral arms. We interpret our results as observational evidence that bars are radially mixing material in galaxies of all stellar masses, and for all bar morphologies and evolutionary stages.
We study the internal radial gradients of the stellar populations in a sample comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney- AAO Multi-object Integral field spectrograph) Galaxy Survey. We stack the spectra of individual spaxels in radial bins, and derive basic stellar population properties: total metallicity ([Z/H]), [Mg/Fe], [C/Fe] and age. The radial gradient ($ abla$) and central value of the fits (evaluated at R$_e$/4) are compared against a set of six possible drivers of the trends. We find that velocity dispersion ($sigma$) - or, equivalently gravitational potential - is the dominant driver of the chemical composition gradients. Surface mass density is also correlated with the trends, especially with stellar age. The decrease of $ abla$[Mg/Fe] with increasing $sigma$ is contrasted by a rather shallow dependence of $ abla$[Z/H] with $sigma$ (although this radial gradient is overall rather steep). This result, along with a shallow age slope at the massive end, imposes stringent constraints on the progenitors of the populations that contribute to the formation of the outer envelopes of ETGs. The SAMI sample is split between a field sample and a cluster sample. Only weak environment-related differences are found, most notably a stronger dependence of central total metallicity ([Z/H]$_{e4}$) with $sigma$, along with a marginal trend of $ abla$[Z/H] to steepen in cluster galaxies, a result that is not followed by [Mg/Fe]. The results presented here serve as constraints on numerical models of the formation and evolution of ETGs.
The mean stellar alpha-to-iron abundance ratio ([$alpha$/Fe]) of a galaxy is an indicator of galactic star formation timescale. It is important for understanding the star formation history of early-type galaxies (ETGs) as their star formation processes have basically stopped. Using the model templates which are made by Vazdekis et al., we apply the pPXF based spectral fitting method to estimate the [$alpha$/Fe] of 196 high signal-to-noise ratio ETGs from the MaNGA survey. The velocity dispersions within 1R$_e$ ($sigma_{e}$) range from 27 to 270 km/s. We find a flat relation between the mean [$alpha$/Fe] within the 1R$_e^{maj}$ ellipses and log($sigma_{e}$), even if limiting to the massive sample with log($sigma_{e}$/km s$^{-1}$)$>$1.9. However, the relation becomes positive after we exclude the Mg$_1$ feature in our fits, which agrees with the results from the previous work with other stellar population models, albeit with relatively large scatter. It indicates that the spectral fits with Vazdekis models could give basically the consistent predictions of [$alpha$/Fe] with previous studies when the Mg$_b$ index is used, but do not work well at the Mg$_1$ band when their $alpha$-enhanced version is employed in the metal-rich regime. We suggest avoiding this rather wide index, which covers 471AA, as it might suffer from other effects such as flux-calibration issues. For reference, we also measure the stellar population radial gradients within 1R$_e^{maj}$ ellipses. Due to the low resolution of age estimations for old objects and the Mg$_1$ issue, the uncertainties of these gradients cannot be neglected.
By applying spectroscopic decomposition methods to a sample of MaNGA early-type galaxies, we separate out spatially and kinematically distinct stellar populations, allowing us to explore the similarities and differences between galaxy bulges and discs, and how they affect the global properties of the galaxy. We find that the components have interesting variations in their stellar populations, and display different kinematics. Bulges tend to be consistently more metal rich than their disc counterparts, and while the ages of both components are comparable, there is an interesting tail of younger, more metal poor discs. Bulges and discs follow their own distinct kinematic relationships, both on the plane of the stellar spin parameter, lambda_R, and ellipticity, and in the relation between stellar mass and specific angular momentum, j, with the location of the galaxy as a whole on these planes being determined by how much bulge and disc it contains. As a check of the physical significance of the kinematic decompositions, we also dynamically model the individual galaxy components within the global potential of the galaxy. The resulting components exhibit kinematic parameters consistent with those from the spectroscopic decomposition, and though the dynamical modelling suffers from some degeneracies, the bulges and discs display systematically different intrinsic dynamical properties. This work demonstrates the value in considering the individual components of galaxies rather than treating them as a single entity, which neglects information that may be crucial in understanding where, when and how galaxies evolve into the systems we see today.
We study the internal radial gradients of stellar population properties within $1.5;R_{rm e}$ and analyse the impact of galaxy environment. We use a representative sample of 721 galaxies with masses ranging between $10^{9};M_{odot}$ to $10^{11.5};M_{odot}$ from the SDSS-IV survey MaNGA. We split this sample by morphology into early-type and late-type galaxies. Using the full spectral fitting code FIREFLY, we derive the light and mass-weighted stellar population properties age and metallicity, and calculate the gradients of these properties. We use three independent methods to quantify galaxy environment, namely the $N^{th}$ nearest neighbour, the tidal strength parameter $Q$ and distinguish between central and satellite galaxies. In our analysis, we find that early-type galaxies generally exhibit shallow light-weighted age gradients in agreement with the literature and mass-weighted median age gradients tend to be slightly positive. Late-type galaxies, instead, have negative light-weighted age gradients. We detect negative metallicity gradients in both early and late-type galaxies that correlate with galaxy mass, with the gradients being steeper and the correlation with mass being stronger in late-types. We find, however, that stellar population gradients, for both morphological classifications, have no significant correlation with galaxy environment for all three characterisations of environment. Our results suggest that galaxy mass is the main driver of stellar population gradients in both early and late-type galaxies, and any environmental dependence, if present at all, must be very subtle.
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