Publications by Michele Cappellari


The ATLAS<sup>3D</sup> project - II. Morphologies, kinemetric features and alignment between photometric and kinematic axes of early-type galaxies

Monthly Notices of the Royal Astronomical Society 414 (2011) 2923-2949

D Krajnović, E Emsellem, M Cappellari, K Alatalo, L Blitz, M Bois, F Bournaud, M Bureau, RL Davies, TA Davis, PT de Zeeuw, S Khochfar, H Kuntschner, PY Lablanche, RM Mcdermid, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, P Serra, AM Weijmans, LM Young

We use the ATLAS3D sample of 260 early-type galaxies to study the apparent kinematic misalignment angle, Ψ, defined as the angle between the photometric and kinematic major axes. We find that 71 per cent of nearby early-type galaxies are strictly aligned systems (Ψ≤ 5°), an additional 14 per cent have 5° < Ψ≤ 10° and 90 per cent of galaxies have Ψ≤ 15°. Taking into account measurement uncertainties, 90 per cent of galaxies can be considered aligned to better than 5°, suggesting that only a small fraction of early-type galaxies (∼10 per cent) are not consistent with the axisymmetry within the projected half-light radius. We identify morphological features such as bars and rings (30 per cent), dust structures (16 per cent), blue nuclear colours (6 per cent) and evidence of interactions (8 per cent) visible on ATLAS3D galaxies. We use kinemetry to analyse the mean velocity maps and separate galaxies into two broad types of regular and non-regular rotators. We find 82 per cent of regular rotators and 17 per cent of non-regular rotators, with two galaxies that we were not able to classify due to the poor data quality. The non-regular rotators are typically found in dense regions and are massive. We characterize the specific features in the mean velocity and velocity dispersion maps. The majority of galaxies do not have any specific features, but we highlight here the frequency of the kinematically distinct cores (7 per cent of galaxies) and the aligned double peaks in the velocity dispersion maps (4 per cent of galaxies). We separate galaxies into five kinematic groups based on the kinemetric features, which are then used to interpret the (Ψ-ε) diagram. Most of the galaxies that are misaligned have complex kinematics and are non-regular rotators. In addition, some show evidence of the interaction and might not be in equilibrium, while some are barred. While the trends are weak, there is a tendency that large values of Ψ are found in galaxies at intermediate environmental densities and among the most massive galaxies in the sample. Taking into account the kinematic alignment and the kinemetric analysis, the majority of early-type galaxies have velocity maps more similar to that of the spiral discs than to that of the remnants of equal-mass mergers. We suggest that the most common formation mechanism for early-type galaxies preserves the axisymmetry of the disc progenitors and their general kinematic properties. Less commonly, the formation process results in a triaxial galaxy with much lower net angular momentum. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Investigating the merger origin of early-type galaxies using ultra-deep optical images

Proceedings of the International Astronomical Union 6 (2010) 238-241

PA Duc, JC Cuillandre, K Alatalo, L Blitz, M Bois, F Bournaud, M Bureau, M Cappellari, P Côté, RL Davies, TA Davis, PT De Zeeuw, E Emsellem, L Ferrarese, E Ferriere, S Gwyn, S Khochfar, D Krajnovic, H Kuntschner, PY Lablanche, L MacArthur, RM McDermid, L Michel-Dansac, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, P Serra, A Weijmans, LM Young

The mass assembly of galaxies leaves various imprints on their surroundings, such as shells, streams and tidal tails. The frequency and properties of these fine structures depend on the mechanism driving the mass assembly: e.g. a monolithic collapse, rapid cold-gas accretion followed by violent disk instabilities, minor mergers or major dry/wet mergers. Therefore, by studying the outskirts of galaxies, one can learn about their main formation mechanism. I present here our on-going work to characterize the outskirts of Early-Type Galaxies (ETGs), which are powerful probes at low redshift of the hierarchical mass assembly of galaxies. This work relies on ultra-deep optical images obtained at CFHT with the wide-field of view MegaCam camera of field and cluster ETGs obtained as part of the ATLAS3D and NGVS projects. State of the art numerical simulations are used to interpret the data. The images reveal a wealth of unknown faint structures at levels as faint as 29 mag arcsec-2 in the g-band. Initial results for two galaxies are presented here. © Copyright International Astronomical Union 2011.


Molecular gas and star formation in local early-type galaxies

Proceedings of the International Astronomical Union 6 (2010) 55-58

M Bureau, TA Davis, K Alatalo, AF Crocker, L Blitz, LM Young, F Combes, M Bois, F Bournaud, M Cappellari, RL Davies, PT De Zeeuw, PA Duc, E Emsellem, S Khochfar, D Krajnović, H Kuntschner, PY Lablanche, RM McDermid, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, P Serra, A Weijmans

The molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the ATLAS 3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation, following the standard Schmidt-Kennicutt law but not the far infrared-radio correlation. This may suggest a greater diversity in star formation processes than observed in disk galaxies. Using multiple molecular tracers, we are thus starting to probe the physical conditions of the cold gas in early-types. © Copyright International Astronomical Union 2011.


The ATLAS<sup>3D</sup> project - III. A census of the stellar angular momentum within the effective radius of early-type galaxies: Unveiling the distribution of fast and slow rotators

Monthly Notices of the Royal Astronomical Society 414 (2011) 888-912

E Emsellem, M Cappellari, D Krajnović, K Alatalo, L Blitz, M Bois, F Bournaud, M Bureau, RL Davies, TA Davis, PT de Zeeuw, S Khochfar, H Kuntschner, PY Lablanche, RM Mcdermid, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, P Serra, G van de Ven, AM Weijmans, LM Young

We provide a census of the apparent stellar angular momentum within one effective radius of a volume-limited sample of 260 early-type galaxies (ETGs) in the nearby Universe, using the integral-field spectroscopy obtained in the course of the ATLAS3D project. We exploit the λR parameter (previously used via a constant threshold value of 0.1) to characterize the existence of two families of ETGs: slow rotators which exhibit complex stellar velocity fields and often include stellar kinematically distinct cores, and fast rotators which have regular velocity fields. Our complete sample of 260 ETGs leads to a new criterion to disentangle fast and slow rotators which now includes a dependency on the apparent ellipticity ε. It separates the two classes significantly better than the previous prescription and better than a criterion based on V/σ: slow rotators and fast rotators have λR lower and larger than, respectively, where kFS= 0.31 for measurements made within an effective radius Re. We show that the vast majority of ETGs are fast rotators: these have the regular stellar rotation, with aligned photometric and kinematic axes (Paper II of this series), include discs and often bars and represent 86 ± 2 per cent (224/260) of all ETGs in the volume-limited ATLAS3D sample. Fast rotators span the full range of apparent ellipticities from ε= 0 to 0.85, and we suggest that they cover intrinsic ellipticities from about 0.35 to 0.85, the most flattened having morphologies consistent with spiral galaxies. Only a small fraction of ETGs are slow rotators representing 14 ± 2 per cent (36/260) of the ATLAS3D sample of ETGs. Of all slow rotators, 11 per cent (4/36) exhibit two counter-rotating stellar disc-like components and are rather low-mass objects (Mdyn < 1010.5M⊙). All other slow rotators (32/36) appear relatively round on the sky (εe < 0.4), tend to be massive (Mdyn > 1010.5M⊙), and often (17/32) exhibit kinematically distinct cores. Slow rotators dominate the high-mass end of ETGs in the ATLAS3D sample, with only about one-fourth of galaxies with masses above 1011.5M⊙ being fast rotators. We show that the a4 parameter which quantifies the isophote's disciness or boxiness does not seem to be simply related to the observed kinematics, while our new criterion based on λR and ε is nearly independent of the viewing angles. We further demonstrate that the classification of ETGs into ellipticals and lenticulars is misleading. Slow and fast rotators tend to be classified as ellipticals and lenticulars, respectively, but the contamination is strong enough to affect results solely based on such a scheme: 20 per cent of all fast rotators are classified as ellipticals, and more importantly 66 per cent of all ellipticals in the ATLAS3D sample are fast rotators. Fast and slow rotators illustrate the variety of complex processes shaping galactic systems, such as secular evolution, disc instabilities, interaction and merging, gas accretion, stripping and harassment, forming a sequence from high to low (stellar) baryonic angular momentum. Massive slow rotators represent the extreme instances within the red sequence of galaxies which might have suffered from significant merging without being able to rebuild a fast-rotating component within one effective radius. We therefore argue for a shift in the paradigm for ETGs, where the vast majority of ETGs are galaxies consistent with nearly oblate systems (with or without bars) and where only a small fraction of them (less than 12 per cent) have central (mildly) triaxial structures. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


The ATLAS<sup>3D</sup> project - IV. The molecular gas content of early-type galaxies

Monthly Notices of the Royal Astronomical Society 414 (2011) 940-967

LM Young, M Bureau, TA Davis, F Combes, RM Mcdermid, K Alatalo, L Blitz, M Bois, F Bournaud, M Cappellari, RL Davies, PT de Zeeuw, E Emsellem, S Khochfar, D Krajnović, H Kuntschner, PY Lablanche, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, P Serra, AM Weijmans

We have carried out a survey for CO J= 1-0 and J= 2-1 emission in the 260 early-type galaxies of the volume-limited ATLAS3D sample, with the goal of connecting their star formation and assembly histories to their cold gas content. This is the largest volume-limited CO survey of its kind and is the first to include many Virgo cluster members. Sample members are dynamically hot galaxies with a median stellar mass ∼3 × 1010 M⊙; they are selected by their morphology rather than colour, and the bulk of them lie on the red sequence. The overall CO detection rate is 56/259 = 0.22 ± 0.03, with no dependence on the K luminosity and only a modest dependence on the dynamical mass. There are a dozen CO detections among the Virgo cluster members; statistical analysis of their H2 mass distributions and their dynamical status within the cluster shows that the cluster's influence on their molecular masses is subtle at best, even though (unlike spirals) they seem to be virialized within the cluster. We suggest that the cluster members have retained their molecular gas through several Gyr residences in the cluster. There are also a few extremely CO-rich early-type galaxies with H2 masses ≳109 M⊙ and these are in low-density environments. We do find a significant trend between the molecular content and stellar specific angular momentum. The galaxies of low angular momentum also have low CO detection rates, suggesting that their formation processes were more effective at destroying the molecular gas or preventing its re-accretion. We speculate on the implications of these data for the formation of various subclasses of early-type galaxies. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


The ATLAS<sup>3D</sup> project - V. The CO Tully-Fisher relation of early-type galaxies

Monthly Notices of the Royal Astronomical Society 414 (2011) 968-984

TA Davis, M Bureau, LM Young, K Alatalo, L Blitz, M Cappellari, N Scott, M Bois, F Bournaud, RL Davies, PT de Zeeuw, E Emsellem, S Khochfar, D Krajnović, H Kuntschner, PY Lablanche, RM Mcdermid, R Morganti, T Naab, T Oosterloo, M Sarzi, P Serra, AM Weijmans

We demonstrate here using both single-dish and interferometric observations that CO molecules are an excellent kinematic tracer, even in high-mass galaxies, allowing us to investigate for the first time the CO Tully-Fisher relation (CO-TFR) of early-type galaxies. We compare the TFRs produced using both single-dish and interferometric data and various inclination estimation methods, and evaluate the use of the velocity profile shape as a criterion for selecting galaxies in which the molecular gas extends beyond the peak of the rotation curve. We show that the gradient and zero-point of the best-fitting relations are robust, independent of the velocity measure and inclination used, and agree with those of relations derived using stellar kinematics. We also show that the early-type CO-TFR is offset from the CO-TFR of spirals by 0.98 ± 0.22 mag at Ks band, in line with other results. The intrinsic scatter of the relation is found to be ≈0.4 mag, similar to the level found in the spiral galaxy population. Next-generation facilities such as the Large Millimeter Telescope and the Atacama Large Millimeter/Sub-millimeter Array should allow this technique to be used in higher redshift systems, providing a simple new tool to trace the mass-to-light ratio evolution of the most massive galaxies over cosmic time. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


The ATLAS<sup>3D</sup> project - IX. The merger origin of a fast- and a slow-rotating early-type galaxy revealed with deep optical imaging: First results

Monthly Notices of the Royal Astronomical Society 417 (2011) 863-881

PA Duc, JC Cuillandre, P Serra, L Michel-Dansac, E Ferriere, K Alatalo, L Blitz, M Bois, F Bournaud, M Bureau, M Cappellari, RL Davies, TA Davis, PT de Zeeuw, E Emsellem, S Khochfar, D Krajnović, H Kuntschner, PY Lablanche, RM McDermid, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, AM Weijmans, LM Young

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 ATLAS3D sample, NGC 680 and 5557. Our ultra-deep optical images obtained with MegaCam on the Canada-France-Hawaii Telescope reach 29 magarcsec-2 in thegband. They reveal very low surface brightness (LSB) filamentary structures around these ellipticals. Among them, a gigantic 160kpc long, narrow, tail east of NGC 5557 hosts three gas-rich star-forming objects, previously detected in Hi with the Westerbork Synthesis Radio Telescope and in UV withGALEX. 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 and that each of these two ETGs was assembled during a relatively recent, major wet merger, which most likely occurred after the redshiftz≃ 0.5 epoch. Had these mergers been older, the tidal features should have already fallen back or be destroyed by more recent accretion events. However, the absence of molecular gas and of a prominent young stellar population in the core region of the galaxies indicates that the merger is at least 1-2 Gyr old: the memory of any merger-triggered nuclear starburst has indeed been lost. The star-forming objects found towards the collisional debris of NGC 5557 are then likely tidal dwarf galaxies. Such recycled galaxies here appear to be long-lived and continue to form stars while any star formation activity has stopped in their parent galaxy. The inner kinematics of NGC 680 is typical for fast rotators which make the bulk of nearby ETGs in the ATLAS3D sample. On the other hand, 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. Whether the two galaxies studied here are representative of their own sub-class of ETGs is still an open question that will be addressed by an on-going deep optical survey of ATLAS3D galaxies. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


THE FUNDAMENTAL PLANE OF EARLY-TYPE GALAXIES

CRAL-2010: A UNIVERSE OF DWARF GALAXIES 48 (2011) 411-+

J Falcon-Barroso, G van de Ven, R Bacon, M Bureau, M Cappellari, RL Davies, PT de Zeeuw, E Emsellem, D Krajnovic, H Kuntschner, RM McDermid, RF Peletier, M Sarzi, RCE van den Bosch


The ATLAS 3D project - VII. A new look at the morphology of nearby galaxies: The kinematic morphology-density relation

Monthly Notices of the Royal Astronomical Society 416 (2011) 1680-1696

M Cappellari, E Emsellem, D Krajnović, RM McDermid, P Serra, K Alatalo, L Blitz, M Bois, F Bournaud, M Bureau, RL Davies, TA Davis, PT de Zeeuw, S Khochfar, H Kuntschner, P-Y Lablanche, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, A-M Weijmans, LM Young


The ATLAS 3D project - VI. Simulations of binary galaxy mergers and the link with fast rotators, slow rotators and kinematically distinct cores

Monthly Notices of the Royal Astronomical Society 416 (2011) 1654-1679

M Bois, E Emsellem, F Bournaud, K Alatalo, L Blitz, M Bureau, M Cappellari, RL Davies, TA Davis, PT de Zeeuw, P-A Duc, S Khochfar, D Krajnović, H Kuntschner, P-Y Lablanche, RM McDermid, R Morganti, T Naab, T Oosterloo, M Sarzi, N Scott, P Serra, A-M Weijmans, LM Young


The SAURON project - XIX. Optical and near-infrared scaling relations of nearby elliptical, lenticular and Sa galaxies

Monthly Notices of the Royal Astronomical Society (2011)

J Falcón-Barroso, G Van de Ven, RF Peletier, M Bureau, H Jeong, R Bacon, M Cappellari, RL Davies, PT De Zeeuw, E Emsellem, D Krajnović, H Kuntschner, RM Mcdermid, M Sarzi, KL Shapiro, RCE Van Den Bosch, G Van Der Wolk, A Weijmans, S Yi


The SAURON project - XVIII. The integrated UV-line-strength relations of early-type galaxies

Monthly Notices of the Royal Astronomical Society (2011)

M Bureau, H Jeong, SK Yi, K Schawinski, RCW Houghton, RL Davies, R Bacon, M Cappellari, PT de Zeeuw, E Emsellem, J Falcón-Barroso, D Krajnović, H Kuntschner, RM Mcdermid, RF Peletier, M Sarzi, Y-J Sohn, D Thomas, RCE van den Bosch, G van de Ven


The ATLAS<sup>3D</sup> project - I. A volume-limited sample of 260 nearby early-type galaxies: Science goals and selection criteria

Monthly Notices of the Royal Astronomical Society 413 (2011) 813-836

M Cappellari, E Emsellem, D Krajnović, RM Mcdermid, N Scott, GA Verdoes Kleijn, LM Young, K Alatalo, R Bacon, L Blitz, M Bois, F Bournaud, M Bureau, RL Davies, TA Davis, PT de Zeeuw, PA Duc, S Khochfar, H Kuntschner, PY Lablanche, R Morganti, T Naab, T Oosterloo, M Sarzi, P Serra, AM Weijmans

The ATLAS3D project is a multiwavelength survey combined with a theoretical modelling effort. The observations span from the radio to the millimetre and optical, and provide multicolour imaging, two-dimensional kinematics of the atomic (Hi), molecular (CO) and ionized gas (Hβ, [Oiii] and [Ni]), together with the kinematics and population of the stars (Hβ, Fe5015 and Mg b), for a carefully selected, volume-limited (1.16 × 105Mpc3) sample of 260 early-type (elliptical E and lenticular S0) galaxies (ETGs). The models include semi-analytic, N-body binary mergers and cosmological simulations of galaxy formation. Here we present the science goals for the project and introduce the galaxy sample and the selection criteria. The sample consists of nearby (D < 42Mpc, |δ- 29°| < 35°, |b| > 15°) morphologically selected ETGs extracted from a parent sample of 871 galaxies (8 per cent E, 22 per cent S0 and 70 per cent spirals) brighter than MK < -21.5mag (stellar mass M{black star}≳ 6 ×109M⊙). We analyse possible selection biases and we conclude that the parent sample is essentially complete and statistically representative of the nearby galaxy population. We present the size-luminosity relation for the spirals and ETGs and show that the ETGs in the ATLAS3D sample define a tight red sequence in a colour-magnitude diagram, with few objects in the transition from the blue cloud. We describe the strategy of the SAURON integral field observations and the extraction of the stellar kinematics with the ppxf method. We find typical 1σ errors of ΔV≈ 6kms-1, Δσ≈ 7kms-1, Δh3≈Δh4≈ 0.03 in the mean velocity, the velocity dispersion and Gauss-Hermite (GH) moments for galaxies with effective dispersion σe≳ 120kms-1. For galaxies with lower σe (≈40 per cent of the sample) the GH moments are gradually penalized by ppxf towards zero to suppress the noise produced by the spectral undersampling and only V and σ can be measured. We give an overview of the characteristics of the other main data sets already available for our sample and of the ongoing modelling projects. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Discovery of an active galactic nucleus driven molecular outflow in the local early-type galaxy NGC 1266

Astrophysical Journal 735 (2011)

K Alatalo, L Blitz, LM Young, TA Davis, M Bureau, LA Lopez, M Cappellari, N Scott, KL Shapiro, AF Crocker, S Martín, M Bois, F Bournaud, RL Davies, PT De Zeeuw, PA Duc, E Emsellem, J Falcón-Barroso, S Khochfar, D Krajnović, H Kuntschner, PY Lablanche, RM McDermid, R Morganti, T Naab, T Oosterloo, M Sarzi, P Serra, A Weijmans

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 400kms-1 and requires a nested Gaussian fit to be properly described. Interferometric observations reveal a massive, centrally concentrated molecular component with a mass of 1.1 × 109 M and a molecular outflow with a molecular mass of 2.4 × 107 M . The molecular gas close to the systemic velocity consists of a rotating, compact nucleus with a mass of about 4.1 × 108 M within a radius of 60pc. This compact molecular nucleus has a surface density of 2.7 × 104 M 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 M yr-1 leads to a depletion timescale of ≲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. The concentration of the majority of the molecular gas in the central 100pc 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. © 2011. The American Astronomical Society. All rights reserved..


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

Monthly Notices of the Royal Astronomical Society (2011)

RF Peletier, E Kutdemir, G van der Wolk, J Falcón-Barroso, R Bacon, M Bureau, M Cappellari, RL Davies, PT de Zeeuw, E Emsellem, D Krajnović, H Kuntschner, RM Mcdermid, M Sarzi, N Scott, KL Shapiro, RCE van den Bosch, G van de Ven


The SAURON project - XVIII. The integrated UV-line-strength relations of early-type galaxies

Monthly Notices of the Royal Astronomical Society 414 (2011) 1887-1902

M Bureau, H Jeong, SK Yi, K Schawinski, RCW Houghton, RL Davies, R Bacon, M Cappellari, PT de Zeeuw, E Emsellem, J Falcón-Barroso, D Krajnović, H Kuntschner, RM McDermid, RF Peletier, M Sarzi, YJ Sohn, D Thomas, RCE van den Bosch, G van de Ven

Using far-ultraviolet (FUV) and near-ultraviolet (NUV) photometry from guest investigator programmes on the Galaxy Evolution Explorer (GALEX) satellite, optical photometry from the MDM Observatory and optical integral-field spectroscopy from SAURON, we explore the UV-line-strength relations of the 48 nearby early-type galaxies in the SAURON sample. Identical apertures are used for all quantities, avoiding aperture mismatch. We show that galaxies with purely old stellar populations show well-defined correlations of the integrated FUV -V and FUV - NUV colours with the integrated Mg b and Hβ absorption line-strength indices, strongest for FUV - NUV. Correlations with the NUV -V colour, Fe5015 index and stellar velocity dispersion σ are much weaker. These correlations put stringent constraints on the origin of the UV-upturn phenomenon in early-type galaxies and highlight its dependence on age and metallicity. In particular, despite recent debate, we recover the negative correlation between FUV -V colour and Mg line strength originally publicized by Burstein et al., which we refer to as the 'Burstein relation', suggesting a positive dependence of the UV upturn on metallicity. We argue that the scatter in the correlations is real and present mild evidence that a strong UV excess is preferentially present in slow-rotating galaxies. We also demonstrate that most outliers in the correlations are galaxies with current or recent star formation, some at very low levels. We believe that this sensitivity to weak star formation, afforded by the deep and varied data available for the SAURON sample, explains why our results are occasionally at odds with other recent but shallower surveys. This is supported by the analysis of a large, carefully crafted sample of more distant early-type galaxies from the Sloan Digital Sky Survey (SDSS), more easily comparable with current and future large surveys. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


The SAURON project - XVII. Stellar population analysis of the absorption line strength maps of 48 early-type galaxies

Monthly Notices of the Royal Astronomical Society 408 (2010) 97-132

H Kuntschner, E Emsellem, R Bacon, M Cappellari, RL Davies, PT De Zeeuw, J Falcón-Barroso, D Krajnović, RM McDermid, RF Peletier, M Sarzi, KL Shapiro, RCE Van Den Bosch, G Van De Ven

We present a stellar population analysis of the absorption line strength maps for 48 early-type galaxies from the SAURON sample. Using the line strength index maps of Hβ, Fe5015 and Mg b, measured in the Lick/IDS system and spatially binned to a constant signal-to-noise ratio, together with predictions from up-to-date stellar population models, we estimate the simple stellar population-equivalent (SSP-equivalent) age, metallicity and abundance ratio [alpha;/Fe] over a two-dimensional field extending up to approximately one effective radius. A discussion of calibrations and differences between model predictions is given. Maps of SSP-equivalent age, metallicity and abundance ratio [alpha;/Fe] are presented for each galaxy. We find a large range of SSP-equivalent ages in our sample, of which ~40 per cent of the galaxies show signs of a contribution from a young stellar population. The most extreme cases of post-starburst galaxies, with SSP-equivalent ages of ≤3 Gyr observed over the full field-of-view, and sometimes even showing signs of residual star formation, are restricted to low-mass systems (σe≤ 100 km s-1 or ~2 × 1010 M.). Spatially restricted cases of young stellar populations in circumnuclear regions can almost exclusively be linked to the presence of star formation in a thin, dusty disc/ring, also seen in the near-UV or mid-IR on top of an older underlying stellar population.The flattened components with disc-like kinematics previously identified in all fast rotators are shown to be connected to regions of distinct stellar populations. These range from the young, still star-forming circumnuclear discs and rings with increased metallicity preferentially found in intermediate-mass fast rotators, to apparently old structures with extended disc-like kinematics, which are observed to have an increased metallicity and mildly depressed [alpha;/Fe] ratio compared to the main body of the galaxy. The slow rotators, often harbouring kinematically decoupled components (KDC) in their central regions, generally show no stellar population signatures over and above the well-known metallicity gradients in early-type galaxies and are largely consistent with old (≥10 Gyr) stellar populations.Using radially averaged stellar population gradients we find in agreement with Spolaor et al. a mass-metallicity gradient relation where low-mass fast rotators form a sequence of increasing metallicity gradient with increasing mass. For more massive systems (above ~3.5 × 1010 M.) there is an overall downturn such that metallicity gradients become shallower with increased scatter at a given mass leading to the most massive systems being slow rotators with relatively shallow metallicity gradients. The observed shallower metallicity gradients and increased scatter could be a consequence of the competition between different star formation and assembly scenarios following a general trend of diminishing gas fractions and more equal-mass mergers with increasing mass, leading to the most massive systems being devoid of ordered motion and signs of recent star formation. © 2010 The Authors. Journal compilation © 2010 RAS.


Early-type galaxies in different environments: An H-i view

Monthly Notices of the Royal Astronomical Society 409 (2010) 500-514

T Oosterloo, R Morganti, A Crocker, E Jütte, M Cappellari, T De Zeeuw, D Krajnovic, R McDermid, H Kuntschner, M Sarzi, AM Weijmans

We present an analysis of deep Westerbork Synthesis Radio Telescope observations of the neutral hydrogen in 33 nearby early-type galaxies selected from a representative sample studied earlier at optical wavelengths with the SAURON integral-field spectrograph. This is the deepest homogeneous set of H-i imaging data available for this class of objects. The sample covers both field environments and the Virgo cluster. Our analysis shows that gas accretion plays a role in the evolution of field early-type galaxies, but less so for those in clusters.The H-i properties of SAURON early-type galaxies strongly depend on environment. For detection limits of a few times 106- M-, H-i is detected in about 2/3 of the field galaxies, while <10 per cent of the Virgo objects are detected. In about half of the detections, the H-i forms a regularly rotating disc or ring. In many galaxies unsettled tails and clouds are seen. All H-i discs have counterparts of ionized gas, and inner H-i discs are also detected in molecular gas. The cold interstellar medium (ISM) in the central regions is dominated by molecular gas (). Assuming our sample is representative, we conclude that accretion of H-i is very common for field early-type galaxies, but the amount of material involved is usually small and the effects on the host galaxy are, at most, subtle. Cluster galaxies appear not to accrete H-i, or the accreted material gets removed quickly by environmental effects. The relation between H-i and stellar population is complex. The few galaxies with a significant young sub-population all have inner gas discs, but for the remaining galaxies there is no trend between stellar population and H-i properties. A number of early-type galaxies are very gas rich, but only have an old population. The stellar populations of field galaxies are typically younger than those in Virgo. This is likely related to differences in accretion history. There is no obvious overall relation between gas H-i content and global dynamical characteristics except that the fastest rotators all have an H-i disc. This confirms that if fast and slow rotators are the result of different evolution paths, this is not strongly reflected in the current H-i content. In about 50 per cent of the galaxies we detect a central radio continuum source. In many objects this emission is from a low-luminosity active galactic nucleus (AGN), and in some it is consistent with the observed star formation. Galaxies with H-i in the central regions are more likely detected in continuum. This is due to a higher probability for star formation to occur in such galaxies and not to H-i-related AGN fuelling. © 2010 The Authors. Journal compilation © 2010 RAS.


Weighing black holes using open-loop focus corrections for LGS-AO observations of galaxy nuclei at Gemini Observatory

Proceedings of SPIE - The International Society for Optical Engineering 7736 (2010)

RM McDermid, D Krajnovic, M Cappellari, C Trujillo, J Christou, RL Davies

We present observations of early-type galaxies with laser guide star adaptive optics (LGS AO) obtained at Gemini North telescope using the NIFS integral field unit (IFU). We employ an innovative technique where the focus compensation due to the changing distance to the sodium layer is made 'open loop', allowing the extended galaxy nucleus to be used only for tip-tilt correction. The purpose of these observations is to determine high spatial resolution stellar kinematics within the nuclei of these galaxies to determine the masses of the super-massive black holes. The resulting data have spatial resolution of 0.2" FWHM or better. This is sufficient to positively constrain the presence of the central black hole in even low-mass early-type galaxies, suggesting that larger samples of such objects could be observed with this technique in the future. The open-loop focus correction technique is a supported queue-observing mode at Gemini, significantly extending the sky coverage in particular for faint, extended guide sources. We also provide preliminary results from tests combining tip/tilt correction from the Gemini peripheral guider with on-axis LGS. The current test system demonstrates feasibility of this mode, providing about a factor 2-3 improvement over natural seeing. With planned upgrades to the peripheral wave-front sensor, we hope to provide close to 100% sky coverage with low Strehl corrections, or 'improved seeing', significantly increasing flux concentration for deep field and extended object studies. © 2010 SPIE.


The Tully-Fisher relations of early-type spiral and S0 galaxies

Monthly Notices of the Royal Astronomical Society 409 (2010) 1330-1346

MJ Williams, M Bureau, M Cappellari

We demonstrate that the comparison of Tully-Fisher relations (TFRs) derived from global H-i linewidths to TFRs derived from the circular-velocity profiles of dynamical models (or stellar kinematic observations corrected for asymmetric drift) is vulnerable to systematic and uncertain biases introduced by the different measures of rotation used. We therefore argue that to constrain the relative locations of the TFRs of spiral and S0 galaxies, the same tracer and measure must be used for both samples. Using detailed near-infrared imaging and the circular velocities of axisymmetric Jeans models of 14 nearby edge-on Sa-Sb spirals and 14 nearby edge-on S0s drawn from a range of environments, we find that S0s lie on a TFR with the same slope as the spirals, but are on average 0.53 ± 0.15-mag fainter at KS band at a given rotational velocity. This is a significantly smaller offset than that measured in earlier studies of the S0 TFR, which we attribute to our elimination of the bias associated with using different rotation measures and our use of earlier-type spirals as a reference. Since our measurement of the offset avoids systematic biases, it should be preferred to previous estimates. A spiral stellar population in which star formation is truncated would take ≈1-Gyr to fade by 0.53-mag at KS band. If S0s are the products of a simple truncation of star formation in spirals, then this finding is difficult to reconcile with the observed evolution of the spiral/S0 fraction with redshift. Recent star formation could explain the observed lack of fading in S0s, but the offset of the S0 TFR persists as a function of both stellar and dynamical mass. We show that the offset of the S0 TFR could therefore be explained by a systematic difference between the total mass distributions of S0s and spirals, in the sense that S0s need to be smaller or more concentrated than spirals. © 2010 The Authors. Journal compilation © 2010 RAS.

Pages