Nuclear angular momentum of early-type galaxies hosting nuclear star clusters

Nucleation is a common phenomenon in all types of galaxies and at least 70% of them host nuclear star clusters (NSCs) in their centres. Many of the NSCs co-habit with super-massive black holes and follow similar scaling relations with host galaxy properties. NSCs, unlike black holes, preserve the signature of their evolutionary path imprinted onto their kinematics and stellar populations. Thus their study provides us with important information about the formation of galactic nuclei. In this paper we explored the angular momentum of the nuclei of six intermediate mass (9.7 > log(Mdyn/M_sun) > 10.6) early-type galaxies in the Fornax cluster that host NSCs. Our goal was to derive a link between the nuclear angular momentum and the proposed formation scenarios of NSCs. We used Adaptive Optics assisted IFU observations with VLT/SINFONI to derive the spatially resolved stellar kinematics of the galaxy nuclei. We measured their specific stellar angular momenta ($\lambda_\mathrm{Re}$), and compared these with Milky Way globular clusters and N-body simulations of NSC formation. We found that all studied nuclei exhibit varied stellar kinematics. Their specific stellar angular momenta and ellipticities are similar to Milky Way globular clusters (GCs). Five out of six galaxy nuclei are consistent with the $\lambda_\mathrm{Re} - \epsilon_\mathrm{e}$ of simulated NSCs embedded in a contaminating nuclear bulge that have formed via the in-spiralling and merging of GCs. It has previously been suggested that the NSCs in higher mass galaxies, like the ones studied in this paper, form via dissipational sinking of gas onto the galactic nuclei with hints that some might also involve the merger of GCs. Here we showed that we cannot exclude the pure GC merging scenario as a viable path for the formation of NSCs.Comment: 8 pages, 3 figures, accepted for publication in A&

Towards calibrating stellar population models in the near-IR

This thesis presents a study of the near-IR spectral properties of six globular clusters (GCs) and 21 early-type galaxies in the local Universe, 10 of which are in low density environments and 11 are in the Fornax cluster of galaxies. Our observations were acquired using integral field unit (IFU) and long-slit spectrographs. The common goal of the various projects was to verify the predictions of current stellar population models in the near-IR using GCs and early-type galaxies data. We provide the first spectral library of the integrated near-IR light of globular clusters with ages > 1 Gyr. Using VLT/SINFONI we obtained integrated luminosity weighted spectra of six GCs in the Large Magellanic Cloud (LMC). Three of them are old > 10 Gyr) and metal poor ([Z/H]~-1.4), the other three have intermediate ages (1< age < 3 Gyr) and higher metallicity ([Z/H]~-0.4). We have measured the strength of the near-IR K-band features Na I, Ca I and 12CO(2-0) and compared the Dco index, used to measure the strength of 12CO(2-0), with the predictions of the stellar population models of Maraston (2005). We find reasonable agreement between the data and the model predictions for old and metal poor GCs. For intermediate age and half solar metallicity GCs we find a marked disagreement with the models. While the models predict an increase of the index with younger ages, we find a strong drop of index strength at ~1 Gyr. We consider that this is due to the different spectral properties of galactic carbon rich AGB stars, used to empirically calibrate the models, and the ones present in LMC globular clusters. This conclusion is based on the different Dco index strength that we measure for the carbon stars in our LMC sample and the galactic carbon stars for a given (J-K) colour. Our study of early-type galaxies in low density environments and in the Fornax cluster reveals that the near-IR Na I and Dco indices follow similar index-sigma scaling relations as optical metallicity indices. The Na I index shows a good positive correlation with the metallicity at old ages and additionally increases for younger ages in contrast to the behaviour of optical metal indices. We derive an empirical calibration for the Na I index as function of metallicity and suggest that a diagnostic diagram, based on the optical hydrogen Balmer index and the near-IR Na I index, will be a good age-metallicity estimator once more detailed SSP models in the near-IR become available. The Dco index exhibits similar trends with metallicity, albeit with a shallower slope and more complex behaviour at young ages. We find evidence of saturation of the Dco index above twice solar metallicity. Utilising the superb spatial resolution of adaptive optics assisted IFU observations in the near-IR we observed the centre of the Fornax cD galaxy NGC 1399. We confirm the presence of a central velocity dispersion drop within r<0.2" and reveal drops in the Na I and Dco index with the same extent and location. We suggest that the centre of NGC 1399 harbours a cold subsystem with a distinct stellar population, which is either more metal poor, or younger and more metal poor than the main body of the galaxy. We detect a negative gradient of the Na I index within r<1.4". Using our calibration of Na I vs. metallicity we derive a metallicity gradient, which appears to be shallower than the typical metallicity gradients measured at larger radii in other early-type galaxies

The inner mass distribution of late-type spiral galaxies from SAURON stellar kinematic maps

We infer the central mass distributions within 0.4-1.2 disc scale lengths of 18 late-type spiral galaxies using two different dynamical modelling approaches - the Asymmetric Drift Correction (ADC) and axisymmetric Jeans Anisotropic Multi-gaussian expansion (JAM) model. ADC adopts a thin disc assumption, whereas JAM does a full line-of-sight velocity integration. We use stellar kinematics maps obtained with the integral-field spectrograph SAURON to derive the corresponding circular velocity curves from the two models. To find their best-fit values, we apply Markov Chain Monte Carlo (MCMC) method. ADC and JAM modelling approaches are consistent within 5% uncertainty when the ordered motions are significant comparable to the random motions, i.e, $\overline{v_{\phi}}/\sigma_R$ is locally greater than 1.5. Below this value, the ratio $v_\mathrm{c,JAM}/v_\mathrm{c,ADC}$ gradually increases with decreasing $\overline{v_{\phi}}/\sigma_R$, reaching $v_\mathrm{c,JAM}\approx 2 \times v_\mathrm{c,ADC}$. Such conditions indicate that the stellar masses of the galaxies in our sample are not confined to their disk planes and likely have a non-negligible contribution from their bulges and thick disks.Comment: 44 pages, 60 figures, MNRAS accepted. The ADC-MCMC and JAM-MCMC python codes are available at: https://github.com/Kalinova/Dyn_models. The Multi-Gaussian Expansion (MGE) results are also available in the Appendi

The Panchromatic High-Resolution Spectroscopic Survey of Local Group Star Clusters - I. General Data Reduction Procedures for the VLT/X-shooter UVB and VIS arm

Our dataset contains spectroscopic observations of 29 globular clusters in the Magellanic Clouds and the Milky Way performed with VLT/X-shooter. Here we present detailed data reduction procedures for the VLT/X-shooter UVB and VIS arm. These are not restricted to our particular dataset, but are generally applicable to different kinds of X-shooter data without major limitation on the astronomical object of interest. ESO's X-shooter pipeline (v1.5.0) performs well and reliably for the wavelength calibration and the associated rectification procedure, yet we find several weaknesses in the reduction cascade that are addressed with additional calibration steps, such as bad pixel interpolation, flat fielding, and slit illumination corrections. Furthermore, the instrumental PSF is analytically modeled and used to reconstruct flux losses at slit transit and for optimally extracting point sources. Regular observations of spectrophotometric standard stars allow us to detect instrumental variability, which needs to be understood if a reliable absolute flux calibration is desired. A cascade of additional custom calibration steps is presented that allows for an absolute flux calibration uncertainty of less than ten percent under virtually every observational setup provided that the signal-to-noise ratio is sufficiently high. The optimal extraction increases the signal-to-noise ratio typically by a factor of 1.5, while simultaneously correcting for resulting flux losses. The wavelength calibration is found to be accurate to an uncertainty level of approximately 0.02 Angstrom. We find that most of the X-shooter systematics can be reliably modeled and corrected for. This offers the possibility of comparing observations on different nights and with different telescope pointings and instrumental setups, thereby facilitating a robust statistical analysis of large datasets.Comment: 22 pages, 18 figures, Accepted for publication in Astronomy & Astrophysics; V2 contains a minor change in the abstract. We note that we did not test X-shooter pipeline versions 2.0 or later. V3 contains an updated referenc

CALIFA reveals Prolate Rotation in Massive Early-type Galaxies: A Polar Galaxy Merger Origin?

We present new evidence for eight early-type galaxies (ETGs) from the CALIFA Survey that show clear rotation around their major photometric axis ("prolate rotation"). These are LSBCF560-04, NGC 0647, NGC 0810, NGC 2484, NGC 4874, NGC 5216, NGC 6173 and NGC 6338. Including NGC 5485, a known case of an ETG with stellar prolate rotation, as well as UGC 10695, a further possible candidate for prolate rotation, we report ten CALIFA galaxies in total that show evidence for such a feature in their stellar kinematics. Prolate rotators correspond to ~9% of the volume-corrected sample of CALIFA ETGs, a fraction much higher than previously reported. We find that prolate rotation is more common among the most massive ETGs. We investigate the implications of these findings by studying N-body merger simulations, and show that a prolate ETG with rotation around its major axis could be the result of a major polar merger, with the amplitude of prolate rotation depending on the initial bulge-to-total stellar mass ratio of its progenitor galaxies. Additionally, we find that prolate ETGs resulting from this formation scenario show a correlation between their stellar line-of-sight velocity and higher order moment h_3, opposite to typical oblate ETGs, as well as a double peak of their stellar velocity dispersion along their minor axis. Finally, we investigate the origin of prolate rotation in polar galaxy merger remnants. Our findings suggest that prolate rotation in massive ETGs might be more common than previously expected, and can help towards a better understanding of their dynamical structure and formation origin.Comment: accepted for publication in A&

A dynamical view on stellar metallicity gradient diversity across the Hubble sequence with CALIFA

We analyze radial stellar metallicity and kinematic profiles out to 1Re in 244 CALIFA galaxies ranging from morphological type E to Sd, to study the evolutionary mechanisms of stellar population gradients. We find that linear metallicity gradients exhibit a clear correlation with galaxy morphological type - with early type galaxies showing the steepest gradients. We show that the metallicity gradients simply reflect the local mass-metallicity relation within a galaxy. This suggests that the radial stellar population distribution within a galaxys effective radius is primarily a result of the \emph{in-situ} local star formation history. In this simple picture, the dynamically derived stellar surface mass density gradient directly predicts the metallicity gradient of a galaxy. We show that this correlation and its scatter can be reproduced entirely by using independent empirical galaxy structural and chemical scaling relations. Using Schwarzschild dynamical models, we also explore the link between a galaxys local stellar populations and their orbital structures. We find that galaxies angular momentum and metallicity gradients show no obvious causal link. This suggests that metallicity gradients in the inner disk are not strongly shaped by radial migration, which is confirmed by the lack of correlation between the metallicity gradients and observable probes of radial migration in the galaxies, such as bars and spiral arms. Finally, we find that galaxies with positive metallicity gradients become increasingly common towards low mass and late morphological types - consistent with stellar feedback more efficiently modifying the baryon cycle in the central regions of these galaxies.Comment: 20 pages, 13 figure

MRK 1216 & NGC 1277 - An orbit-based dynamical analysis of compact, high velocity dispersion galaxies

We present a dynamical analysis to infer the structural parameters and properties of the two nearby, compact, high velocity dispersion galaxies MRK1216 & NGC1277. Combining deep HST imaging, wide-field IFU stellar kinematics, and complementary long-slit spectroscopic data out to 3 R_e, we construct orbit-based models to constrain their black hole masses, dark matter content and stellar mass-to-light ratios. We obtain a black hole mass of log(Mbh/Msun) = 10.1(+0.1/-0.2) for NGC1277 and an upper limit of log(Mbh/Msun) = 10.0 for MRK1216, within 99.7 per cent confidence. The stellar mass-to-light ratios span a range of Upsilon_V = 6.5(+1.5/-1.5) in NGC1277 and Upsilon_H = 1.8(+0.5/-0.8) in MRK1216 and are in good agreement with SSP models of a single power-law Salpeter IMF. Even though our models do not place strong constraints on the dark halo parameters, they suggest that dark matter is a necessary ingredient in MRK1216, with a dark matter contribution of 22(+30/-20) per cent to the total mass budget within 1 R_e. NGC1277, on the other hand, can be reproduced without the need for a dark halo, and a maximal dark matter fraction of 13 per cent within the same radial extent. In addition, we investigate the orbital structures of both galaxies, which are rotationally supported and consistent with photometric multi-S\'ersic decompositions, indicating that these compact objects do not host classical, non-rotating bulges formed during recent (z <= 2) dissipative events or through violent relaxation. Finally, both MRK 1216 and NGC 1277 are anisotropic, with a global anisotropy parameter delta of 0.33 and 0.58, respectively. While MRK 1216 follows the trend of fast-rotating, oblate galaxies with a flattened velocity dispersion tensor in the meridional plane of the order of beta_z = delta, NGC 1277 is highly tangentially anisotropic and seems to belong kinematically to a distinct class of objects.Comment: 27 pages, 15 figures and 4 tables. Accepted for publication in MNRA

The complex nature of the nuclear star cluster in FCC 277

Recent observations have shown that compact nuclear star clusters (NSCs) are present in up to 80% of galaxies. However, detailed studies of their dynamical and chemical properties are confined mainly to spiral galaxy hosts, where they are more easily observed. In this paper we present our study of the NSC in FCC 277, a nucleated elliptical galaxy in the Fornax cluster. We use a combination of adaptive optics assisted near-infrared integral field spectroscopy, Hubble Space Telescope imaging, and literature long slit data. We show that while the NSC does not appear to rotate within our detection limit of ~6 km/s, rotation is detected at larger radii, where the isophotes appear to be disky, suggesting the presence of a nuclear disk. We also observe a distinct central velocity dispersion drop that is indicative of a dynamically cold rotating sub-system. Following the results of orbit-based dynamical modelling, co-rotating as well as counter-rotating stellar orbits are simultaneously needed to reproduce the observed kinematics. We find evidence for varying stellar populations, with the NSC and nuclear disk hosting younger and more metal rich stars than the main body of the galaxy. We argue that gas dissipation and some level of merging have likely played an important role in the formation of the nucleus of this intermediate-mass galaxy. This is in contrast to NSCs in low-mass early- type galaxies, which may have been formed primarily through the infall of star clusters.Comment: 10 pages, 11 figures, MNRAS in press, changes to this version: co-author adde