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Register a new userStellar Population Synthesis with Distinct Kinematics: Multi-Age Asymmetric Drift in SDSS-IV MaNGA Galaxies
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We present the first asymmetric drift (AD) measurements for unresolved stellar populations of different characteristic ages above and below 1.5 Gyr. These measurements sample the age-velocity relation (AVR) in galaxy disks. In this first paper we develop two efficient algorithms to extract AD on a spaxel-by-spaxel basis from optical integral-field spectroscopic (IFS) data-cubes. The algorithms apply different spectral templates, one using simple stellar populations and the other a stellar library; their comparison allows us to assess systematic errors in derived multi-component velocities, such as template-mismatch. We test algorithm reliability using mock spectra and Monte Carlo Markov Chains on real data from the MaNGA survey in SDSS-IV. We quantify random and systematic errors in AD as a function of signal-to-noise and stellar population properties with the aim of applying this technique to large subsets of the MaNGA galaxy sample. As a demonstration of our methods, we apply them to an initial sample of seven galaxies with comparable stellar mass and color to the Milky Way. We find a wide range of distinct AD radial profiles for young and old stellar populations.
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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 present a study on the stellar age and metallicity distributions for 1105 galaxies using the STARLIGHT software on MaNGA integral field spectra. We derive age and metallicity gradients by fitting straight lines to the radial profiles, and explore their correlations with total stellar mass M*, NUV-r colour and environments, as identified by both the large scale structure (LSS) type and the local density. We find that the mean age and metallicity gradients are close to zero but slightly negative, which is consistent with the inside-out formation scenario. Within our sample, we find that both the age and metallicity gradients show weak or no correlation with either the LSS type or local density environment. In addition, we also study the environmental dependence of age and metallicity values at the effective radii. The age and metallicity values are highly correlated with M* and NUV-r and are also dependent on LSS type as well as local density. Low-mass galaxies tend to be younger and have lower metallicity in low-density environments while high-mass galaxies are less affected by environment.
We present the kinematics and stellar population properties of a sample of 53 galaxies (50 are Early-Type galaxies, ETGs) with Counter-Rotating Disks (CRD) extracted from a sample of about 4000 galaxies of all morphological types in the MaNGA survey (DR16). The kinematic maps were used to select galaxies based on evidence of counter-rotation in the velocity maps or two peaks in the velocity dispersion maps. For about 1/3 of the sample, the counter-rotating components can also be separated spectroscopically. We then produced the age and metallicity maps, and compared the stellar population properties to those of the general ETGs population. We found that CRDs have similar trends in age and metallicity, but they are generally less metallic at low masses. The metallicity gradients are similar; instead, age gradients are typically flatter and confined within a smaller range of values. We compared the velocity fields of the ionized gas and the stars, and found that in 25 cases the gas corotates with either the inner (13 cases) or the outer (12 cases) disk, and in 9 cases the gaseous and stellar disks are misaligned. With one exception, all misaligned cases have stellar masses less than $3 times 10^{10}$M$_odot$. We also compared stellar and gaseous disks with age maps and found that in most cases the gas corotates with the younger disk. We looked for evidences of multimodality in the stellar populations, and found it in 25 galaxies, plus 11 cases with evidences of ongoing star formation, and the latter are the youngest and least massive galaxies; 13 galaxies, instead, exhibit unimodality, and are the oldest and most massive CRDs. As a general result, our work supports different formation scenarios for the kinematic class of counter-rotators.
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 investigate the effects of Active Galactic Nuclei (AGN) on the gas kinematics of their host galaxies, using MaNGA data for a sample of 62 AGN hosts and 109 control galaxies (inactive galaxies). We compare orientation of the line of nodes (kinematic Position Angle - PA) measured from the gas and stellar velocity fields for the two samples. We found that AGN hosts and control galaxies display similar kinematic PA offsets between gas and stars. However, we note that AGN have larger fractional velocity dispersion $sigma$ differences between gas and stars [$sigma_{frac}=(sigma_{rm gas}-sigma_{stars})/sigma_{rm stars}$] when compared to their controls, as obtained from the velocity dispersion values of the central (nuclear) pixel (2.5 diameter). The AGN have a median value of $sigma_{rm frac}$ of $<sigma_{frac}>_{rm AGN}=0.04$, while the the median value for the control galaxies is $<sigma_{frac}>_{rm CTR}=-0.23$. 75% of the AGN show $sigma_{frac}>-0.13$, while 75% of the normal galaxies show $sigma_{rm frac}<-0.04$, thus we suggest that the parameter $sigma_{rm frac}$ can be used as an indicative of AGN activity. We find a correlation between the [OIII]$lambda$5007 luminosity and $sigma_{frac}$ for our sample. Our main conclusion is that the AGN already observed with MaNGA are not powerful enough to produce important outflows at galactic scales, but at 1-2 kpc scales, AGN feedback signatures are always present on their host galaxies.
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