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Register a new userSDSS-IV MaNGA: Uncovering the Angular Momentum Content of Central and Satellite Early-type Galaxies
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We study 379 central and 159 satellite early-type galaxies with two-dimensional kinematics from the integral-field survey Mapping Nearby Galaxies at APO (MaNGA) to determine how their angular momentum content depends on stellar and halo mass. Using the Yang et. al. (2007) group catalog, we identify central and satellite galaxies in groups with halo masses in the range 10^12.5 h^-1 M_sun < M_200b < 10^15 h^-1 M_sun. As in previous work, we see a sharp dependence on stellar mass, in the sense that ~ 70% of galaxies with stellar mass M_* > 10^11 h^-2 M_sun tend to have very little rotation, while nearly all galaxies at lower mass show some net rotation. The ~ 30% of high-mass galaxies that have significant rotation do not stand out in other galaxy properties except for a higher incidence of ionized gas emission. Our data are consistent with recent simulation results suggesting that major merging and gas accretion have more impact on the rotational support of lower-mass galaxies. When carefully matching the stellar mass distributions, we find no residual differences in angular momentum content between satellite and central galaxies at the 20% level. Similarly, at fixed mass, galaxies have consistent rotation properties across a wide range of halo mass. However, we find that errors in classification of centrals and satellites with group finders systematically lowers differences between satellite and central galaxies at a level that is comparable to current measurement uncertainties. To improve constraints, the impact of group finding methods will have to be forward modeled via mock catalogs.
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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 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.
We study the radial acceleration relation (RAR) for early-type galaxies (ETGs) in the SDSS MaNGA MPL5 dataset. The complete ETG sample show a slightly offset RAR from the relation reported by McGaugh et al. (2016) at the low-acceleration end; we find that the deviation is due to the fact that the slow rotators show a systematically higher acceleration relation than the McGaughs RAR, while the fast rotators show a consistent acceleration relation to McGaughs RAR. There is a 1sigma significant difference between the acceleration relations of the fast and slow rotators, suggesting that the acceleration relation correlates with the galactic spins, and that the slow rotators may have a different mass distribution compared with fast rotators and late-type galaxies. We suspect that the acceleration relation deviation of slow rotators may be attributed to more galaxy merger events, which would disrupt the original spins and correlated distributions of baryons and dark matter orbits in galaxies.
MaNGA 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 $9.9 - 10.8;log M/M_{odot}$. We find flat gradients in age and [$alpha$/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-$sigma$ 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.
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