arXiv subjects

Eric Emsellem

Publications and source records attributed to Eric Emsellem.

At least 199 records · Page 11Linked to original sources

arXiv2012

Discovery of a giant HI tail in the galaxy group HCG 44

We report the discovery of a giant HI tail in the intra-group medium of HCG 44 as part of the Atlas3D survey. The tail is ~300 kpc long in projection and contains ~5x10^8 M_sun of HI. We detect no diffuse stellar light at the location of the tail down to ~28.5 mag/arcsec^2 in g band. We speculate that the tail might have formed as gas was stripped from the outer regions of NGC 3187 (a member of HCG 44) by the group tidal field. In this case, a simple model indicates that about 1/3 of the galaxy's HI was stripped during a time interval of <1 Gyr. Alternatively, the tail may be the remnant of an interaction between HCG 44 and NGC 3162, a spiral galaxy now ~650 kpc away from the group. Regardless of the precise formation mechanism, the detected HI tail shows for the first time direct evidence of gas stripping in HCG 44. It also highlights that deep HI observations over a large field are needed to gather a complete census of this kind of events in the local Universe.

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arXiv2012

Gemini GMOS and WHT SAURON integral-field spectrograph observations of the AGN driven outflow in NGC 1266

We use the SAURON and GMOS integral field spectrographs to observe the active galactic nucleus (AGN) powered outflow in NGC 1266. This unusual galaxy is relatively nearby (D=30 Mpc), allowing us to investigate the process of AGN feedback in action. We present maps of the kinematics and line strengths of the ionised gas emission lines Halpha, Hbeta, [OIII], [OI], [NII] and [SII], and report on the detection of Sodium D absorption. We use these tracers to explore the structure of the source, derive the ionised and atomic gas kinematics and investigate the gas excitation and physical conditions. NGC 1266 contains two ionised gas components along most lines of sight, tracing the ongoing outflow and a component closer to the galaxy systemic, the origin of which is unclear. This gas appears to be disturbed by a nascent AGN jet. We confirm that the outflow in NGC 1266 is truly multiphase, containing radio plasma, atomic, molecular and ionised gas and X-ray emitting plasma. The outflow has velocities up to \pm900 km/s away from the systemic velocity, and is very likely to be removing significant amounts of cold gas from the galaxy. The LINER-like line-emission in NGC 1266 is extended, and likely arises from fast shocks caused by the interaction of the radio jet with the ISM. These shocks have velocities of up to 800 km/s, which match well with the observed velocity of the outflow. Sodium D equivalent width profiles are used to set constraints on the size and orientation of the outflow. The ionised gas morphology correlates with the nascent radio jets observed in 1.4 GHz and 5 GHz continuum emission, supporting the suggestion that an AGN jet is providing the energy required to drive the outflow.

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arXiv2012

The Atlas3D project - XII. Recovery of the mass-to-light ratio of simulated early-type barred galaxies with axisymmetric dynamical models

We investigate the accuracy in the recovery of the stellar dynamics of barred galaxies when using axisymmetric dynamical models. We do this by trying to recover the mass-to-light ratio (M/L) and the anisotropy of realistic galaxy simulations using the Jeans Anisotropic Multi-Gaussian Expansion (JAM) method. However, given that the biases we find are mostly due to an application of an axisymmetric modeling algorithm to a non-axisymmetric system and in particular to inaccuracies in the de-projected mass model, our results are relevant for general axisymmetric modelling methods. We run N-body collisionless simulations to build a library with various luminosity distribution, constructed to mimic real individual galaxies, with realistic anisotropy. The final result of our evolved library of simulations contains both barred and unbarred galaxies. The JAM method assumes an axisymmetric mass distribution, and we adopt a spatially constant M/L and anisotropy beta_z=1-sigma_z^2/sigma_R^2 distributions. The models are fitted to two-dimensional maps of the second velocity moments V_rms=sqrt(V^2+sigma^2) of the simulations for various viewing angles (position angle of the bar and inclination of the galaxy). We find that the inclination is generally well recovered by the JAM models, for both barred and unbarred simulations. For unbarred simulations the M/L is also accurately recovered, with negligible median bias and with a maximum one of just Delta(M/L)<1.5% when the galaxy is not too close to face on. At very low inclinations (i<30 deg) the M/L can be significantly overestimated (9% in our tests, but errors can be larger for very face-on views). For barred simulations the M/L is on average (when PA=45 deg) essentially unbiased, but we measure an over/under estimation of up to Delta(M/L)=15% in our tests. The sign of the M/L bias depends on the position angle of the bar as expected. [Abridged]

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arXiv2012

The SAURON project-XXI. The spatially-resolved UV-line strength relations of early-type galaxies

The unexpected rising flux of early-type galaxies at decreasing ultraviolet (UV) wavelengths is a long-standing mystery. One important observational constraint is the correlation between UV-optical colours and Mg2 line strengths found by Burstein et al. (1988). The simplest interpretation of this phenomenon is that the UV strength is related to the Mg line strength. Under this assumption, we expect galaxies with larger Mg gradients to have larger UV colour gradients. By combining UV imaging from GALEX, optical imaging from MDM and SAURON integral-field spectroscopy, we investigate the spatially-resolved relationships between UV colours and stellar population properties of 34 early-type galaxies from the SAURON survey sample. We find that galaxies with old stellar populations show tight correlations between the FUV colours (FUV-V and FUV-NUV) and the Mgb index, Hβ index and metallicity [Z/H]. The equivalent correlations for the Fe5015 index, α-enhancement [α/Fe] and age are present but weaker. We have also derived logarithmic internal radial colour, measured line strength and derived stellar population gradients for each galaxy and again found a strong dependence of the FUV-V and FUV-NUV colour gradients on both the Mg b line strength and the metallicity gradients for galaxies with old stellar populations. In particular, global gradients of Mg b and [Z/H] with respect to the UV colour across galaxies are consistent with their local gradients within galaxies, suggesting that the global correlations also hold locally. From a simple model based on multi-band colour fits of UV upturn and UV-weak galaxies, we have identified a plausible range of parameters that reproduces the observed radial colour profiles. In these models, the centers of elliptical galaxies, where the UV flux is strong, are enhanced in metals by roughly 60% compared to UV-weak regions.

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arXiv2012

A systematic variation of the stellar initial mass function in early-type galaxies

Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars. It depends on the stellar initial mass function (IMF) describing the distribution of stellar masses when the population formed. Consequently knowledge of the IMF is critical to virtually every aspect of galaxy evolution. More than half a century after the first IMF determination, no consensus has emerged on whether it is universal in different galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot be both universal, but they could not break the degeneracy between the two effects. Only recently indications were found that massive elliptical galaxies may not have the same IMF as our Milky Way. Here we report unambiguous evidence for a strong systematic variation of the IMF in early-type galaxies as a function of their stellar mass-to-light ratio, producing differences up to a factor of three in mass. This was inferred from detailed dynamical models of the two-dimensional stellar kinematics for the large Atlas3D representative sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass. Our finding indicates that the IMF depends intimately on a galaxy's formation history.

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arXiv2012

Simulations of binary galaxy mergers and the link with Fast Rotators, Slow Rotators, and Kinematically Distinct Cores

We study the formation of early-type galaxies (ETGs) through mergers with a sample of 70 high-resolution numerical simulations of binary mergers of disc galaxies. These simulations encompass various mass ratios, initial conditions and orbital parameters. We find that binary mergers of disc galaxies with mass ratios of 3:1 and 6:1 are nearly always classified as Fast Rotators according to the Atlas3D criterion: they preserve the structure of the input fast rotating spiral progenitors. Major disc mergers (mass ratios of 2:1 and 1:1) lead to both Fast and Slow Rotators. Most of the Slow Rotators hold a stellar Kinematically Distinct Core (KDC) in their 1-3 central kilo-parsec: these KDCs are built from the stellar components of the progenitors. The mass ratio of the progenitors is a fundamental parameter for the formation of Slow Rotators in binary mergers, but it also requires a retrograde spin for the progenitor galaxies with respect to the orbital angular momentum. The importance of the initial spin of the progenitors is also investigated in the library of galaxy mergers of the GalMer project.

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arXiv2011

A Magellan-IMACS-IFU Search for Dynamical Drivers of Nuclear Activity. I. Reduction Pipeline and Galaxy Catalog

Using the Inamori Magellan Areal Camera and Spectrograph (IMACS) integral-field unit (IFU) on the 6.5m Magellan telescope, we have designed the first statistically significant investigation of the two-dimensional distribution and kinematics of ionized gas and stars in the central kiloparsec regions of a well-matched sample of Seyfert and inactive control galaxies selected from the Sloan Digital Sky Survey. The goals of the project are to use the fine spatial sampling (0.2 arcsec/pixel) and large wavelength coverage (4000-7000A) of the IMACS-IFU to search for dynamical triggers of nuclear activity in the central region where active galactic nucleus (AGN) activity and dynamical timescales become comparable, to identify and assess the impact of AGN-driven outflows on the host galaxy and to provide a definitive sample of local galaxy kinematics for comparison with future three-dimensional kinematic studies of high-redshift systems. In this paper, we provide the first detailed description of the procedure to reduce and calibrate data from the IMACS-IFU in `long mode' to obtain two-dimensional maps of the distribution and kinematics of ionized gas and stars. The sample selection criteria are presented, observing strategy described and resulting maps of the sample galaxies presented along with a description of the observed properties of each galaxy and the overall observed properties of the sample.

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arXiv2011

The Atlas3D Project -- XI. Dense molecular gas properties of CO-luminous early-type galaxies

Surveying eighteen 12CO-bright galaxies from the ATLAS3D early-type galaxy sample with the Institut de Radio Astronomie Millimétrique (IRAM) 30m telescope, we detect 13CO(1-0) and 13CO(2-1) in all eighteen galaxies, HCN(1-0) in 12/18 and HCO+(1-0) in 10/18. We find that the line ratios 12CO(1-0)/13CO(1-0) and 12CO(1-0)/HCN(1-0) are clearly correlated with several galaxy properties: total stellar mass, luminosity-weighted mean stellar age, molecular to atomic gas ratio, dust temperature and dust morphology. We suggest that these correlations are primarily governed by the optical depth in the 12CO lines; interacting, accreting and/or starbursting early-type galaxies have more optically thin molecular gas while those with settled dust and gas discs host optically thick molecular gas. The ranges of the integrated line intensity ratios generally overlap with those of spirals, although we note some outliers in the 12CO(1- 0)/13CO(1-0), 12CO(2-1)/13CO(2-1) and HCN/HCO+(1-0) ratios. In particular, three galaxies are found to have very low 12CO(1-0)/13CO(1-0) and 12CO(2-1)/13CO(2-1) ratios. Such low ratios may signal particularly stable molecular gas which creates stars less efficiently than 'normal' (i.e. below Schmidt-Kennicutt prediction), consistent with the low dust temperatures seen in these galaxies.

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arXiv2011

The Atlas3D project -- XIII. Mass and morphology of HI in early-type galaxies as a function of environment

We present the Atlas3D HI survey of 166 nearby early-type galaxies (ETGs) down to M(HI)~10^7 M_sun. We detect HI in ~40% of all ETGs outside the Virgo cluster and in ~10% of all ETGs inside it. This demonstrates that it is common for non-cluster ETGs to host HI. The HI morphology varies from regular discs/rings (the majority of the detections) to unsettled gas distributions. The former are either small discs (M(HI)<10^8 M_sun) confined within the stellar body and sharing the same kinematics of the stars, or large discs/rings (M(HI) up to 5x10^9 M_sun) extending to tens of kpc from the host galaxy and frequently kinematically decoupled from the stars. Neutral hydrogen provides material for star formation in ETGs. Galaxies with central HI exhibit signatures of star formation in ~70% of the cases, ~5 times more frequently than galaxies without central HI. The central ISM is dominated by molecular gas. In ETGs with a small gas disc the conversion of HI into H_2 is as efficient as in spirals. The ETG HI mass function has M*~2x10^9 M_sun and slope=-0.7. ETGs host much less HI than spirals as a family. However, a significant fraction of them is as HI-rich as spirals. The main difference between ETGs and spirals is that the former lack the high-column-density HI typical of the bright stellar disc of the latter. We find an envelope of decreasing M(HI) with increasing environment density. The gas-richest ETGs live in the poorest environments (where star-formation is more common), galaxies in the centre of Virgo have the lowest HI content, and the cluster outskirts are a transition region. We find an HI morphology-density relation. At low environment density HI is mostly distributed on large discs/rings. More disturbed HI morphologies dominate environment densities typical of rich groups, confirming the importance of processes occurring on a galaxy-group scale for the evolution of ETGs.

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arXiv2011

The SAURON Project - XX. The Spitzer [3.6] - [4.5] colour in early-type galaxies: colours, colour gradients and inverted scaling relations

We investigate the [3.6] - [4.5] Spitzer-IRAC colour behaviour of the early-type galaxies of the SAURON survey, a representative sample of 48 nearby ellipticals and lenticulars. We investigate how this colour, which is unaffected by dust extinction, can be used to constrain the stellar populations in these galaxies. We find a tight relation between the [3.6]-[4.5] colour and effective velocity dispersion, a good mass-indicator in early-type galaxies. Contrary to other colours in the optical and near-infrared, we find that the colours become bluer for larger galaxies. The relations are tighter when using the colour inside r_e, rather than the much smaller r_e/8 aperture, due to the presence of young populations in the central regions. We also obtain strong correlations between the [3.6]-[4.5] colour and 3 strong absorption lines (H beta, Mg b and Fe 5015). Comparing our data with the models of Marigo et al., which show that more metal rich galaxies are bluer, we can explain our results in a way consistent with results from the optical, by stating that larger galaxies are more metal rich. The blueing is caused by a strong CO absorption band, whose line strength increases strongly with decreasing temperature and which covers a considerable fraction of the 4.5 micron filter. In galaxies that contain a compact radio source, the [3.6]-[4.5] colour is generally slightly redder than in the other galaxies, indicating small amounts of either hot dust, non-thermal emission, or young stars near the center. We find that the large majority of the galaxies show redder colours with increasing radius. abbreviated...

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arXiv2011

The ATLAS3D Project-- VIII: Modelling the Formation and Evolution of Fast and Slow Rotator Early-Type Galaxies within $Λ$CDM

We propose a simple model for the origin of fast and slow rotator early-type galaxies (ETG) within the hierarchical $Λ$CDM scenario, that is based on the assumption that the mass fraction of stellar discs in ETGs is a proxy for the specific angular momentum expressed via $λ_R$. Within our model we reproduce the fraction of fast and slow rotators as a function of magnitude in the \atl survey, assuming that fast rotating ETGs have at least 10% of their total stellar mass in a disc component. In agreement with \atl observations we find that slow rotators are predominantly galaxies with $ M_* > 10^{10.5}$ M$_{\odot}$ contributing $\sim 20%$ to the overall ETG population. We show in detail that the growth histories of fast and slow rotators are different, supporting the classification of ETGs into these two categories. Slow rotators accrete between $\sim 50% -90%$ of their stellar mass from satellites and their most massive progenitors have on average up to 3 major mergers during their evolution. Fast rotators in contrast, accrete less than 50% and have on average less than one major merger in their past. We find that the underlying physical reason for the different growth histories is the slowing down and ultimately complete shut-down of gas cooling in massive galaxies. Once cooling and associated star formation in disc stops, galaxies grow via infall from satellites. Frequent minor mergers thereby, destroy existing stellar discs via violent relaxation and also tend to lower the specific angular momentum of the main stellar body, lowering $λ_R$ into the slow rotator regime. Abridged...

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arXiv2011

The Atlas3D project - X. On the origin of the molecular and ionised gas in early-type galaxies

We make use of interferometric CO and HI observations, and optical integral-field spectroscopy to probe the origin of the molecular and ionised interstellar medium (ISM) in local early-type galaxies (ETGs). We find that 36\pm5% of our sample of fast rotating ETGs have their ionised gas kinematically misaligned with respect to the stars, setting a strong lower limit on the importance of externally acquired gas (e.g. from mergers and cold accretion). Slow rotators have a flat distribution of misalignments, indicating that the dominant source of gas is external. The molecular, ionised and atomic gas in all the detected galaxies are always kinematically aligned, even when they are misaligned from the stars, suggesting that all these three phases of the ISM share a common origin. In addition, we find that the origin of the cold and warm gas in fast-rotating ETGs is strongly affected by environment, despite the molecular gas detection rate and mass fractions being fairly independent of group/cluster membership. Galaxies in dense groups and the Virgo cluster nearly always have their molecular gas kinematically aligned with the stellar kinematics, consistent with a purely internal origin. In the field, however, kinematic misalignments between the stellar and gaseous components indicate that >46% of local fast-rotating ETGs have their gas supplied from external sources. We discuss several scenarios which could explain the environmental dichotomy, but find it difficult to simultaneously explain the kinematic misalignment difference and the constant detection rate. Furthermore, our results suggest that galaxy mass may be an important independent factor associated with the origin of the gas, with the most massive fast-rotating galaxies in our sample (M_K<-24 mag; stellar mass of >8x10^10 Msun) always having kinematically aligned gas. (abridged)

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arXiv2011

The Atlas-3D project - IX. The merger origin of a fast and a slow rotating Early-Type Galaxy revealed with deep optical imaging: first results

The mass assembly of galaxies leaves imprints in their outskirts, such as shells and tidal tails. The frequency and properties of such fine structures depend on the main acting mechanisms - secular evolution, minor or major mergers - and on the age of the last substantial accretion event. We use this to constrain the mass assembly history of two apparently relaxed nearby Early-Type Galaxies (ETGs) selected from the Atlas-3D sample, NGC 680 and NGC 5557. Our ultra deep optical images obtained with MegaCam on the Canada-France-Hawaii Telescope reach 29 mag/arcsec^2 in the g-band. They reveal very low-surface brightness (LSB) filamentary structures around these ellipticals. Among them, a gigantic 160 kpc long tail East of NGC 5557 hosts gas-rich star-forming objects. NGC 680 exhibits two major diffuse plumes apparently connected to extended HI tails, as well as a series of arcs and shells. Comparing the outer stellar and gaseous morphology of the two ellipticals with that predicted from models of colliding galaxies, we argue that the LSB features are tidal debris, the star-forming objects near NGC 5557, long lived Tidal Dwarf Galaxies and that each of the two ETGs was assembled during a relatively recent, major wet merger, which likely occurred at a redshift below z = 0.5. The inner kinematics of NGC 680 is typical for fast rotators which make the bulk of nearby ETGs in the Atlas-3D sample. NGC 5557 belongs to the poorly populated class of massive, round, slow rotators that are predicted by semi-analytic models and cosmological simulations to be the end-product of a complex mass accretion history, involving ancient major mergers and more recent minor mergers. Our observations suggest that under specific circumstances a single binary merger may dominate the formation history of such objects and thus that at least some massive ETGs may form at relatively low redshift (abridged).

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arXiv2011

The Atlas3D Project - VI. Simulations of binary galaxy mergers and the link with Fast Rotators, Slow Rotators, and Kinematically Distinct Cores

We study the formation of early-type galaxies through mergers with a sample of 70 high-resolution (softening length < 60 pc and 12*10^6 particles) numerical simulations of binary mergers of disc galaxies and 16 simulations of ETG remergers. These simulations, designed to accompany observations and models conducted within the Atlas3D project, encompass various mass ratios (from 1:1 to 6:1), initial conditions and orbital parameters. The progenitor disc galaxies are spiral-like with bulge to disc ratios typical of Sb and Sc galaxies. We find that binary mergers of disc galaxies with mass ratios of 3:1 and 6:1 are nearly always classified as Fast Rotators according to the Atlas3D criterion (based on the lambda_R parameter): they preserve the structure of the input fast rotating spiral progenitors. They have intrinsic ellipticities larger than 0.5, cover intrinsic lambda_R values between 0.2 and 0.6, within the range of observed Fast Rotators. Major disc mergers (mass ratios of 2:1 and 1:1) lead to both Fast and Slow Rotators. Most of the Fast Rotators produced in major mergers have intermediate flattening, with ellipticities between 0.4 and 0.6. Most Slow Rotators formed in these binary disc mergers hold a stellar Kinematically Distinct Core (KDC) in their 1-3 central kilo-parsec: these KDCs are built from the stellar components of the progenitors. Besides a handful of specific observed systems -- the counter-rotating discs (2-sigma galaxies) -- these therefore cannot reproduce the observed population of Slow Rotators in the nearby Universe. The mass ratio of the progenitors is a fundamental parameter for the formation of Slow Rotators in these binary mergers, but it also requires a retrograde spin for the earlier-type (Sb) progenitor galaxy with respect to the orbital angular momentum. (Abridged)

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arXiv2011

The Atlas3D project - VII. A new look at the morphology of nearby galaxies: the kinematic morphology-density relation

We look at the morphology of fast and slow rotator early-type galaxies. Edge-on fast rotators are lenticular galaxies. They appear like spiral galaxies with the gas and dust removed, and in some cases are flat ellipticals with disky isophotes. Fast rotators are often barred and span the same full range of bulge fractions as spiral galaxies. The slow rotators are rounder and are generally consistent with being genuine, namely spheroidal-like, elliptical galaxies. We propose a revision to the tuning-fork diagram by Hubble as it gives a misleading description of ETGs. We study for the first time the kinematic morphology-density T-Sigma relation using fast and slow rotators to replace lenticulars and ellipticals. We find that our relation is cleaner than using classic morphology. Slow rotators are nearly absent at the lowest density environments [f(SR)<2%] and generally constitute a small fraction [f(SR)~4%] of the total galaxy population in the environments explored by our survey, with the exception of the densest core of the Virgo cluster [f(SR)~20%]. We find a clean log-linear relation between the fraction f(Sp) of spiral galaxies and the local galaxy surface density. The existence of a smooth kinematic T-Sigma relation in the field excludes processes related to the cluster environment as main contributors to the apparent conversion of spirals into fast-rotators in low-density environments. It shows that the segregation is driven by local effects at the small-group scale. Only at the largest densities in the Virgo core does the f(Sp) relation break down and steepens sharply, while the fraction of slow-rotators starts to significantly increase. This suggests that a different mechanism is at work there. (Abridged)

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arXiv2011

Discovery of an AGN-Driven Molecular Outflow in the Local Early-Type Galaxy NGC 1266

We report the discovery of a powerful molecular wind from the nucleus of the non-interacting nearby S0 field galaxy NGC 1266. The single-dish CO profile exhibits emission to +/- 400 km/s and requires a nested Gaussian fit to be properly described. Interferometric observations reveal a massive, centrally- concentrated molecular component with a mass of 1.1x10^9 Msuns and a molecular outflow with a molecular mass of 2.4x10^7 Msuns. The molecular gas close to the systemic velocity consists of a rotating, compact nucleus with a mass of about 4.1x108 Msuns within a radius of approximately 60 pc. This compact molecular nucleus has a surface density of \approx 2.7 \times 10^4 Msuns/pc^2, more than two orders of magnitude larger than that of giant molecular clouds in the disk of the Milky Way, and it appears to sit on the Kennicutt-Schmidt relation despite its extreme kinematics and energetic activity. We interpret this nucleus as a disk that confines the outflowing wind. A mass outflow rate of 13 Msuns/yr leads to a depletion timescale of about 85 Myr. The star formation in NGC 1266 is insufficient to drive the outflow, and thus it is likely driven by the active galactic nucleus (AGN). The concentration of the majority of the molecular gas in the central 100 pc requires an extraordinary loss of angular momentum, but no obvious companion or interacting galaxy is present to enable the transfer. NGC 1266 is the first known outflowing molecular system that does not show any evidence of a recent interaction.

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arXiv2011

The Planetary Nebulae Population in the Central Regions of M32: the SAURON view

Extragalactic Planetary Nebulae (PNe) are not only useful as distance signposts or as tracers of the dark-matter content of their host galaxies, but constitute also good indicators of the main properties of their parent stellar populations. Yet, so far, the properties of PNe in the optical regions of galaxies where stellar population gradients can be more extreme have remained largely unexplored, mainly because the detection of PNe with narrow-band imaging or slit-less spectroscopy is considerably hampered by a strong stellar background. Integral-field spectroscopy (IFS) can overcome this limitation, and here we present a study of the PN population in the nearby compact elliptical M32. Using SAURON data taken with just two 10-minutes-long pointings we have doubled the number of known PNe within the effective radius of M32, detecting PNe five times fainter than previously found in narrow-band images that collected nearly the same number of photons. Furthermore, by carefully accounting for the incompleteness of our survey we could conclude, despite having only 15 sources, that the central PNe population of M32 is consistent with the generally adopted shape for the PNe Luminosity Function and its typical normalization observed in early-type galaxies. Finally, owing to the proximity of M32 and to UV images taken with HST, we could identify the most likely candidates for the central star of a subset of our detected PNe and conclude that these stars are affected by substantial amounts of circumstellar dust extinction, a finding that could reconcile the intriguing discrepancy previously reported in M32 between model predictions and observations for the later stages of stellar evolution. Considering the modest time investment on a 4m-class telescope that delivered these results, this work illustrates the potential of future IFS studies for the central PNe population of early-type galaxies.

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arXiv2011

The ATLAS3D project - II. Morphologies, kinemetric features and alignment between photometric and kinematic axes of early-type galaxies

[Abridged] We use the ATLAS3D sample of 260 early-type galaxies (ETGs) to study the apparent kinematic misalignment angle, Psi, defined as the angle between the photometric and kinematic major axis. We find that 71% of nearby ETGs are strictly aligned systems (Psi > 5 deg), an additional 14% have 5 < Psi < 10 deg and 90% of galaxies have Psi < 15 deg. Taking into account measurement uncertainties, 90% of galaxies can be considered aligned to better than 5 deg, suggesting that only a small fraction of early-type galaxies (~10%) are not consistent with axisymmetry within the projected half-light radius. We identify morphological features such as bars and rings (30%), dust structures (16%), blue nuclear colours (6%) and evidence of interactions (8%). We use kinemetry to analyse the mean velocity maps and separate galaxies in two broad types of regular and non-regular rotators. We find 82% of regular rotators and 17% non-regular rotators, with 2 galaxies that we were not able to classify due to data quality. The non-regular rotators are typically found in dense regions and are massive. The majority of galaxies do not have any specific kinemetric features, but we highlight here the frequency of the kinematically distinct cores (7%) and the aligned double peaks in the velocity dispersion maps (4%). Most of the galaxies that are misaligned have complex kinematics and are non-regular rotators. While the trends are weak, there is a tendency that large values of Psi are found in galaxies at intermediate environmental densities and among the most massive galaxies in the sample. We suggest that the most common formation mechanism for ETGs preserves the axisymmetry of the disk progenitors. Less commonly, the formation process results in a triaxial galaxy with much lower net angular momentum.

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