arXiv subjects

D. A. Gadotti

Publications and source records attributed to D. A. Gadotti.

At least 37 records · Page 2Linked to original sources

arXiv2020

The kinematics of young and old stellar populations in nuclear rings of MUSE TIMER galaxies

Studying the stellar kinematics of galaxies is a key tool in the reconstruction of their evolution. However, the current measurements of the stellar kinematics are complicated by several factors, including dust extinction and the presence of multiple stellar populations. We use integral field spectroscopic data of four galaxies from the TIMER survey to explore and compare the kinematics measured in different spectral regions that are sensitive to distinct stellar populations. We derive the line-of-sight velocity and velocity dispersion of both a young (<2 Gyr) and an old stellar population from the spectral regions around the H$β$ line and the Ca II Triplet. In addition we obtain colour excess, mean age, and metallicity. We report a correlation of the colour excess with the difference in the kinematic parameters of the H$β$ line and the Ca II Triplet range, which are dominated by young and old stellar populations, respectively. Young stellar populations, located primarily in nuclear rings, have higher velocity dispersions than old ones. These differences in the rings are typically 10 km/s in velocity dispersion, but up to a mean value of 24 km/s in the most extreme case. Trends with age exist in the nuclear rings but are less significant than those with dust extinction. We report different degrees of correlation of these trends among the galaxies in the sample, which are related to the size of the Voronoi bins in their rings. No clear trends for the difference of line-of-sight velocity are observed. The absence of these trends can be explained as a consequence of the masking process of the H$β$ line during the kinematic extraction, as confirmed by dedicated simulations. Our study demonstrates that kinematic differences caused by different stellar populations can be identified in the central regions of nearby galaxies even from intermediate resolution spectroscopy.

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arXiv2020

The Fornax 3D project: Globular clusters tracing kinematics and metallicities

Globular clusters (GCs) are found ubiquitously in massive galaxies and due to their old ages, they are regarded as fossil records of galaxy evolution. Spectroscopic studies of GC systems are often limited to the outskirts of galaxies, where GCs stand out against the galaxy background and serve as bright tracers of galaxy assembly. In this work, we use the capabilities of the Multi Unit Explorer Spectrograph (MUSE) to extract a spectroscopic sample of 722 GCs in the inner regions ($\lesssim 3 R_\text{eff}$) of 32 galaxies in the Fornax cluster. These galaxies were observed as part of the Fornax 3D project, a MUSE survey that targets early and late-type galaxies within the virial radius of Fornax. After accounting for the galaxy background in the GC spectra, we extracted line-of-sight velocities and determined metallicities of a sub-sample of 238 GCs. We found signatures of rotation within GC systems, and comparing the GC kinematics and that of the stellar body shows that the GCs trace the spheroid of the galaxies. While the red GCs prove to closely follow the metallicity profile of the host galaxy, the blue GCs show a large spread of metallicities but they are generally more metal-poor than the host.

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arXiv2020

The Fornax 3D project: Non-linear colour-metallicity relation of globular clusters

Globular cluster (GC) systems of massive galaxies often show a bimodal colour distribution. This has been interpreted as a metallicity bimodality, created by a two-stage galaxy formation where the red, metal-rich GCs were formed in the parent halo and the blue metal-poor GCs were accreted. This interpretation, however, crucially depends on the assumption that GCs are exclusively old stellar systems with a linear colour-metallicity relation (CZR). The shape of the CZR and range of GC ages are currently under debate, because their study requires high quality spectra to derive reliable stellar population properties. We determined metallicities with full spectral fitting from a sample of 187 GCs with high spectral signal-to-noise ratio in 23 galaxies of the Fornax cluster that were observed as part of the Fornax 3D project. The derived CZR from this sample is non-linear and can be described by a piecewise linear function with a break point at ($g - z$) $\sim$ 1.1 mag. The less massive galaxies in our sample ($M_\ast < 10^{10} M_\odot$) appear to have slightly younger GCs, but the shape of the CZR is insensitive to the GC ages. Although the least massive galaxies lack red, metal-rich GCs, a non-linear CZR is found irrespective of the galaxy mass, even in the most massive galaxies ($M_\ast \geq 10^{11} M_\odot$). Our CZR predicts narrow unimodal GC metallicity distributions for low mass and broad unimodal distributions for very massive galaxies, dominated by a metal-poor and metal-rich peak, respectively, and bimodal distributions for galaxies with intermediate masses (10$^{10}$ $\leq$ $M_\ast < 10^{11} M_\odot$) as a consequence of the relative fraction of red and blue GCs. The diverse metallicity distributions challenge the simple differentiation of GC populations solely based on their colour.

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arXiv2019

The sequence of spiral arm classes: Observational signatures of persistent spiral density waves in grand-design galaxies

We investigate how the properties of spiral arms relate to other fundamental galaxy properties. To this end, we use previously published measurements of those properties, and our own measurements of arm-interarm luminosity contrasts for a large sample of galaxies, using 3.6$μ$m images from the Spitzer Survey of Stellar Structure in Galaxies. Flocculent galaxies are clearly distinguished from other spiral arm classes, especially by their lower stellar mass and surface density. Multi-armed and grand-design galaxies are similar in most of their fundamental parameters, excluding some bar properties and the bulge-to-total luminosity ratio. Based on these results, we discuss dense, classical bulges as a necessary condition for standing spiral wave modes in grand-design galaxies. We further find a strong correlation between bulge-to-total ratio and bar contrast, and a weaker correlation between arm and bar contrasts.

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arXiv2019

The Fornax3D project: Tracing the assembly history of the cluster from the kinematic and line-strength maps

The 31 brightest galaxies (m_B < 15 mag) inside the virial radius of the Fornax cluster were observed from the centres to the outskirts with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. These observations provide detailed high-resolution maps of the line-of-sight kinematics and line strengths of the stars and ionised gas reaching 2-3 Re for 21 early-type galaxies and 1-2 Re for 10 late-type galaxies. The majority of the galaxies are regular rotators, with eight hosting a kinematically distinct core. Only two galaxies are slow rotators. The mean age, total metallicity, and [Mg/Fe] abundance ratio in the bright central region inside 0.5 Re and in the galaxy outskirts are presented. Extended emission-line gas is detected in 13 galaxies, most of them are late-type objects with wide-spread star formation. The measured structural properties are analysed in relation to the galaxies' position in the projected phase space of the cluster. This shows that the Fornax cluster appears to consist of three main groups of galaxies inside the virial radius: the old core; a clump of galaxies, which is aligned with the local large-scale structure and was accreted soon after the formation of the core; and a group of galaxies that fell in more recently.

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arXiv2019

The GIST Pipeline: A Multi-Purpose Tool for the Analysis and Visualisation of (Integral-field) Spectroscopic Data

We present a convenient, all-in-one framework for the scientific analysis of fully reduced, (integral-field) spectroscopic data. The GIST pipeline (Galaxy IFU Spectroscopy Tool) is entirely written in Python3 and conducts all steps from the preparation of input data, over the scientific analysis to the production of publication-quality plots. In its basic setup, it extracts stellar kinematics, performs an emission-line analysis and derives stellar population properties from full spectral fitting as well as via the measurement of absorption line-strength indices by exploiting the well-known pPXF and GandALF routines, where the latter has now been implemented in Python. The pipeline is not specific to any instrument or analysis technique and provides easy means of modification and further development, as of its modular code architecture. An elaborate, Python-native parallelisation is implemented and tested on various machines. The software further features a dedicated visualization routine with a sophisticated graphical user interface. This allows an easy, fully-interactive plotting of all measurements, spectra, fits, and residuals, as well as star formation histories and the weight distribution of the models. The pipeline has successfully been applied to both low and high-redshift data from MUSE, PPAK (CALIFA), and SINFONI, as well as to simulated data for HARMONI@ELT and WEAVE and is currently being used by the TIMER, Fornax3D, and PHANGS collaborations. We demonstrate its capabilities by applying it to MUSE TIMER observations of NGC 1433.

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arXiv2019

The Fornax 3D project: Thick disks in a cluster environment

We used deep MUSE observations to perform a stellar-kinematic and population analysis of FCC 153 and FCC 177, two edge-on S0 galaxies in the Fornax cluster. The geometrical definition of the different structural components of these two galaxies allows us to describe the nature of their thick disks. These are both old, relatively metal poor and [Mg/Fe]-enhanced, and their star formation history (SFH) reveals a minor younger component whose chemical properties suggest its later accretion. Moreover, the outer regions of these geometrically defined thick disks show higher values of metallicity and lower values of [Mg/Fe]. These stars probably formed in the thin-disk region and they were dynamically heated to form the flares present in these two galaxies. We propose different formation scenarios for the three populations of these thick disks: in-situ formation, accretion and disk heating. A clear distinction in age is found between the metal poor and [Mg/Fe]-enhanced thick disks (old, $\sim 12-13$ Gyr), and the metal rich and less [Mg/Fe]-enhanced thin disks (young, $\sim 4-5$ Gyr). These two galaxies show signs of relatively recent star formation in their thin disks and nuclear regions. While the thin disks show more continuous SFHs, the nuclei display a rather bursty SFH. These two galaxies are located outside of the densest region of the Fornax cluster where FCC 170 resides. This other edge-on S0 galaxy was studied by \citet{Pinna2019}. We compare and discuss our results with this previous study. The differences between these three galaxies, at different distances from the cluster center, suggest that the environment can have a strong effect on the galaxy evolutionary path.

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arXiv2019

The Fornax 3D project: a two-dimensional view of the stellar initial mass function in the massive lenticular galaxy FCC 167

The stellar initial mass function (IMF) regulates the baryonic cycle within galaxies, and is a key ingredient to translate observations into physical quantities. Although for decades it was assumed to be universal, there is now growing observational evidence showing that the center of massive early-type galaxies host an enhanced population of low-mass stars compared to the expectations from the Milky Way. Moreover, these variations in the IMF have been found to be related to the radial metallicity variations in massive galaxies. We present here a two-dimensional stellar population analysis of the massive lenticular galaxy FCC 167 (NGC 1380) as part of the Fornax3D project. Using a newly developed stellar population fitting scheme, we derive a full two-dimensional IMF map of an early-type galaxy. This two-dimensional analysis allows us go further than a radial analysis, showing how the metallicity changes along a disc-like structure while the IMF follows a distinct, less disky distribution. Thus, our findings indicate that metallicity cannot be the sole driver of the observed radial IMF variations. In addition, a comparison with the orbital decomposition shows suggestive evidence of a coupling between stellar population properties and the internal dynamical structure of FCC 167, where metallicity and IMF maps seem to track the distribution of cold and warm orbits, respectively.

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arXiv2019

Clocking the assembly of double-barred galaxies with the MUSE TIMER project

The formation of two stellar bars within a galaxy has proved challenging for numerical studies. It is yet not clear whether the inner bar is born via a star formation process promoted by gas inflow along the outer bar, or whether it is dynamically assembled from instabilities in a small-scale stellar disc. Observational constraints to these scenarios are scarce. We present a thorough study of the stellar content of two double-barred galaxies observed by the MUSE TIMER project, NGC 1291 and NGC 5850, combined with a two-dimensional multi-component photometric decomposition performed on the 3.6μm images from S4G. Our analysis confirms the presence of σ-hollows appearing in the stellar velocity dispersion distribution at the ends of the inner bars. Both galaxies host inner discs matching in size with the inner bars, suggestive of a dynamical formation for the inner bars from small-scale discs. The analysis of the star formation histories for the structural components shaping the galaxies provides constraints on the epoch of dynamical assembly of the inner bars, which took place >6.5 Gyr ago for NGC 1291 and >4.5 Gyr ago for NGC 5850. This implies that inner bars are long-lived structures.

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arXiv2019

The Fornax 3D project: unveiling the thick disk origin in FCC 170: signs of accretion?

We present and discuss the stellar kinematics and populations of the S0 galaxy FCC 170 (NGC 1381) in the Fornax cluster, using deep MUSE data from the Fornax 3D survey. We show the maps of the first four moments of the stellar line-of-sight velocity distribution and of the mass-weighted mean stellar age, metallicity and [Mg/Fe] abundance ratio. The high-quality MUSE stellar kinematic measurements unveil the structure of this massive galaxy: a nuclear disk, a bar seen as a boxy bulge with a clear higher-velocity-dispersion X shape, a fast-rotating and flaring thin disk and a slower rotating thick disk. Whereas their overall old age makes it difficult to discuss differences in the formation epoch between these components, we find a clear-cut distinction between metal-rich and less [Mg/Fe]-enhanced populations in the thin-disk, boxy-bulge and nuclear disk, and more metal-poor and [Mg/Fe]-enhanced stars in the thick disk. Located in the densest region of the Fornax cluster, where signs of tidal stripping have been recently found, the evolution of FCC 170 might have been seriously affected by its environment. We discuss the possibility of its "pre-processing" in a subgroup before falling into the present-day cluster, which would have shaped this galaxy a long time ago. The thick disk displays a composite star formation history, as a significant fraction of younger stars co-exist with the main older thick-disk population. The former sub-population is characterized by even lower-metallicity and higher-[Mg/Fe] values, suggesting that these stars formed later and faster in a less chemically evolved satellite, which was subsequently accreted. Finally, we discuss evidence that metal-rich and less [Mg/Fe]-enhanced stars were brought in the outer parts of the thick disk by the flaring of the thin disk.

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arXiv2018

The Fornax 3D project: dust mix and gas properties in the center of early-type galaxy FCC 167

Galaxies continuously reprocess their interstellar material. One can therefore expect changing dust grain properties in galaxies which have followed different evolutionary pathways. Determining the intrinsic dust grain mix of a galaxy helps in reconstructing its evolutionary history. Early-type galaxies occasionally display regular dust lanes in their central regions. Due to the relatively simple geometry and composition of their stellar bodies, these galaxies are ideal to disentangle dust mix variations from geometric effects. We therefore model the various components of such a galaxy (FCC 167). We reconstruct its recent history, and investigate the possible fate of the dust lane. MUSE and ALMA observations reveal a nested ISM structure. An ionised-gas disk pervades the central regions of FCC 167, including those occupied by the main dust lane. Inward of the dust lane, we also find a disk/ring of cold molecular gas where stars are forming and HII regions contribute to the ionised-gas emission. Further in, the gas ionisation points towards an active galactic nucleus and the fuelling of a central supermassive black hole from its surrounding ionised and molecular reservoir. Observational constraints and radiative transfer models suggest the dust and gas are distributed in a ring-like geometry and the dust mix lacks small grains. The derived dust destruction timescales from sputtering in hot gas are short and we conclude that the dust must be strongly self-shielding and clumpy, or will quickly be eroded and disappear. Our findings show how detailed analysis of individual systems can complement statistical studies of dust-lane ETGs.

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arXiv2018

Inner bars also buckle. The MUSE TIMER view of the double-barred galaxy NGC 1291

Double bars are thought to be important features for secular evolution in the central regions of galaxies. However, observational evidence about their origin and evolution is still scarce. We report on the discovery of the first Box-Peanut (B/P) structure in an inner bar detected in the face-on galaxy NGC 1291. We use the integral field data obtained from the MUSE spectrograph within the TIMER project. The B/P structure is detected as bi-symmetric minima of the $h_4$ moment of the line-of-sight velocity distribution along the major axis of the inner bar, as expected from numerical simulations. Our observations demonstrate that inner bars can follow a similar evolutionary path as outer bars, undergoing buckling instabilities. They also suggest that inner bars are long-lived structures, thus imposing tight constraints to their possible formation mechanisms

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arXiv2018

The Fornax3D project: overall goals, galaxy sample, MUSE data analysis and initial results

The Fornax cluster provides a uniquely compact laboratory to study the detailed history of early-type galaxies and the role played by environment in driving their evolution and their transformation from late-type galaxies. Using the superb capabilities of the Multi Unit Spectroscopic Explorer on the Very Large Telescope, high-quality integral-field spectroscopic data were obtained for the inner regions of all the bright ($m_B\leq15$) galaxies within the virial radius of Fornax. The stellar haloes of early-type galaxies are also covered out to about four effective radii. State-of-the-art stellar dynamical and population modelling allows to aim in particular at better characterising the disc components of fast-rotating early-type galaxies, constraining radial variations in the stellar initial-mass functions and measuring the stellar age, metallicity, and $α$-element abundance of stellar haloes in cluster galaxies. This paper describes the sample selection, observations, and overall goals of the survey, and provides initial results based on the spectroscopic data, including the detailed characterisation of stellar kinematics and populations to large radii; decomposition of galaxy components directly via their orbital structure; the ability to identify globular clusters and planetary nebulae, and derivation of high-quality emission-line diagnostics in the presence of complex ionised gas.

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arXiv2017

A combined photometric and kinematic recipe for evaluating the nature of bulges using the CALIFA sample

Understanding the nature of bulges in disc galaxies can provide important insights into the formation and evolution of galaxies. For instance, the presence of a classical bulge suggests a relatively violent history, in contrast, the presence of simply an inner disc (also referred to as a "pseudobulge") indicates the occurrence of secular evolution processes in the main disc. However, we still lack criteria to effectively categorise bulges, limiting our ability to study their impact on the evolution of the host galaxies. Here we present a recipe to separate inner discs from classical bulges by combining four different parameters from photometric and kinematic analyses: The bulge Sérsic index $n_\mathrm{b}$, the concentration index $C_{20,50}$, the Kormendy (1977) relation and the inner slope of the radial velocity dispersion profile $\nablaσ$. With that recipe we provide a detailed bulge classification for a sample of 45 galaxies from the integral-field spectroscopic survey CALIFA. To aid in categorising bulges within these galaxies, we perform 2D image decomposition to determine bulge Sérsic index, bulge-to-total light ratio, surface brightness and effective radius of the bulge and use growth curve analysis to derive a new concentration index, $C_{20,50}$. We further extract the stellar kinematics from CALIFA data cubes and analyse the radial velocity dispersion profile. The results of the different approaches are in good agreement and allow a safe classification for approximately $95\%$ of the galaxies. In particular, we show that our new "inner" concentration index performs considerably better than the traditionally used $C_{50,90}$ when yielding the nature of bulges. We also found that a combined use of this index and the Kormendy (1977) relation gives a very robust indication of the physical nature of the bulge.

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arXiv2016

Morphology and environment of galaxies with disc breaks in the S4G and NIRS0S

We study the surface brightness profiles of disc galaxies in the 3.6 micron images from the Spitzer Survey of Stellar Structure in Galaxies (S4G) and K_s-band images from the Near Infrared S0-Sa galaxy Survey (NIRS0S). We particularly connect properties of single exponential (type I), downbending double exponential (type II), and upbending double exponential (type III) disc profile types, to structural components of galaxies by using detailed morphological classifications, and size measurements of rings and lenses. We also study how the local environment of the galaxies affects the profile types by calculating parameters describing the environmental density and the tidal interaction strength. We find that in majority of type II profiles the break radius is connected with structural components such as rings, lenses, and spirals. The exponential disc sections of all three profile types, when considered separately, follow the disc scaling relations. However, the outer discs of type II, and the inner discs of type III, are similar in scalelength to the single exponential discs. Although the different profile types have similar mean environmental parameters, the scalelengths of the type III profiles show a positive correlation with the tidal interaction strength.

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arXiv2016

Comparing the properties of the X-shaped bulges of NGC 4710 and the Milky Way with MUSE

We used the new ESO VLT instrument MUSE to obtain spectral and imaging coverage of NGC 4710. The wide area and excellent sampling of the MUSE integral field spectrograph allows us to investigate the dynamical properties of the X-shaped bulge of NGC 4710 and compare it with the properties of the Milky Way's own X-shaped bulge. We measured the radial velocities, velocity dispersion, and stellar populations using a penalized pixel full spectral fitting technique adopting simple stellar populations models, on a 1' x 1' area centred on the bulge of NGC 4710. We have constructed the velocity maps of the bulge of NGC 4710 and we investigated the presence of vertical metallicity gradients. These properties were compared to those of the Milky Way bulge and as well as to a simulated galaxy with boxy/peanut bulge. We find the line-of-sight velocity maps and 1D rotation curves of the bulge of NGC 4710 to be remarkably similar to those of the Milky Way bulge. Some specific differences that were identified are in good agreement with the expectations from variations in the bar orientation angle. The bulge of NGC 4710 has a boxy-peanut morphology with a pronounced X-shape, showing no indication of any additional spheroidally distributed bulge population, in which we measure a vertical metallicity gradient of 0.35 dex/kpc. The general properties of NGC 4710 are very similar to those observed in the MW bulge. However, it has been suggested that the MW bulge has an additional component that is comprised of the oldest, most metal-poor stars and which is not part of the boxy-peanut bulge structure. Such a population is not observed in NGC 4710, but could be hidden in the integrated light we observed.

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arXiv2015

Central enhancement of the nitrogen-to-oxygen abundance ratio in barred galaxies

Bar-induced gas inflows towards the galaxy centres are recognized as a key agent for the secular evolution of galaxies. One immediate consequence is the accumulation of gas in the centre of galaxies where it can form stars and alter the chemical and physical properties. We use a sample of nearby face--on disc galaxies with available SDSS spectra to study whether the properties of the ionised gas in the central parts (radii <~0.6-2.1 kpc) of barred galaxies are altered by the presence of a bar, and whether the bar effect is related to bar and/or parent galaxy properties. The distributions of all parameters analysed are different for barred and unbarred galaxies, except for the R23 metallicity tracer and the oxygen abundance (from photoionisation models). The median values point towards (marginally) larger dust content, star formation rate per unit area, electron density and ionisation parameter in the centres of barred galaxies than in the unbarred counterpart. The most remarkable barred/unbarred difference appears in the [NII]6583/Ha line ratio, which is on average ~25% larger in barred galaxies, due to a larger N/O in the centres of these galaxies. We observe an enhancement of the central gas differences in later-type galaxies or galaxies with less massive bulges. However the bar seems to have a lower impact on the central gas properties for galaxies with more massive bulges (M_bulge > 10^10 M_sun) or galaxies with total stellar mass above ~ 10^10.8 M_sun. In conclusion, we find observational evidence that the presence of a galactic bar affects the central ionised gas properties of disc galaxies, where the most striking effect is an enhancement in the N/O abundance ratio, which can be qualitatively interpreted as due to a different origin or evolutionary processes for less and more massive bulges, with the gaseous phase of the former having currently a closer relation with bars.

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arXiv2015

ARRAKIS: Atlas of Resonance Rings As Known In the S4G

Resonance rings are the consequence of secular evolution processes that redistribute material and angular momentum in discs. We produced a Catalogue and an Atlas of the rings detected in the Spitzer Survey of Stellar Structure in Galaxies (S4G) and to conduct a statistical study of the data in the Catalogue. We traced the contours of rings previously identified by Buta et al. (in preparation) and fitted them with ellipses. We found the orientation of bars by studying the galaxy ellipse fits from S4G's Pipeline 4. We used the galaxy orientation data obtained by S4G's Pipeline 4 to obtain intrinsic ellipticities and orientations of rings and the bars. ARRAKIS contains data on 724 ringed galaxies in the S4G. The frequency of resonance rings in the S4G is of 16+-1% and 35+-1% for outer and inner features, respectively. Outer rings are mostly found in Hubble stages -1<=T<=4. Inner rings are found in a distribution that covers the range -1<=T<=7. We confirm that outer rings have two preferred orientations, parallel and perpendicular to the bar. We confirm a tendency for inner rings to be oriented parallel to the bar, but we find that a significant fraction (~50%) of them have random orientations with respect to the bar. These misaligned inner rings are mostly found in late-type galaxies (T>=4). This may be due to spiral modes decoupled from the bar dominating the Fourier amplitude spectrum at the radius of the inner ring. We find that the fraction of barred galaxies hosting outer (inner) rings is ~1.7 times (~1.3 times) that in unbarred galaxies. The fact that rings are only mildly favoured by bars suggests that those in unbarred galaxies either formed due to weak departures from the axisymmetry of the galactic potential or that they are born because of bars that have been destroyed after the ring formation.

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