-
Timothy A. Davis,
Katherine Alatalo,
Martin Bureau,
Michele Cappellari,
Nicholas Scott,
Lisa M. Young,
Leo Blitz,
Alison F. Crocker,
Estelle Bayet,
Maxime Bois, [......],
Davor Krajnović,
Harald Kuntschner, Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Paolo Serra,
Anne-Marie Weijmans
[show abstract]
[hide abstract]
ABSTRACT: We use interferometric CO observations to compare the extent, surface
brightness profiles and kinematics of the molecular gas in CO-rich Atlas3D
early-type galaxies (ETGs) and spiral galaxies. We find that the molecular gas
extent is smaller in absolute terms in ETGs than in late-type galaxies, but
that the size distributions are similar once scaled by the galaxies
optical/stellar characteristic scale-lengths. Virgo cluster ETGs have less
extended molecular gas reservoirs than field counterparts. Approximately half
of ETGs have molecular gas surface brightness profiles that follow the stellar
light profile. These systems often have relaxed gas out to large radii,
suggesting they are unlikely to have had recent merger/accretion events. A
third of the sample galaxies show molecular gas surface brightness profiles
that fall off slower than the light, and sometimes show a truncation. We
suggest that ram pressure stripping and/or the presence of hot gas has
compressed/truncated the gas in these systems. The remaining galaxies have
rings, or composite profiles, that we argue can be caused by the effects of
bars. We investigated the kinematics of the molecular gas using
position-velocity diagrams, and compared the observed kinematics with dynamical
model predictions, and the observed stellar and ionised gas velocities. We
confirm that the molecular gas reaches beyond the turnover of the circular
velocity curve in ~70% of our CO-rich Atlas3D ETGs. In general we find that in
most galaxies the molecular gas is relaxed and dynamically cold. Molecular gas
is a better direct tracer of the circular velocity than the ionised gas,
justifying its use as a kinematic tracer for Tully-Fisher and similar analyses.
(abridged)
11/2012;
-
Katherine Alatalo,
Timothy A. Davis,
Martin Bureau,
Lisa M. Young,
Leo Blitz,
Alison F. Crocker,
Estelle Bayet,
Maxime Bois,
Frédéric Bournaud,
Michele Cappellari, [......],
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Richard M. McDermid,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans
[show abstract]
[hide abstract]
ABSTRACT: We present the Combined Array for Research in Millimeter Astronomy (CARMA)
ATLAS3D molecular gas imaging survey, a systematic study of the distribution
and kinematics of molecular gas in CO-rich early-type galaxies. Our full sample
of 40 galaxies (30 newly mapped and 10 taken from the literature) is complete
to a 12CO(1-0) integrated flux of 18.5 Jy km/s, and it represents the largest,
best-studied sample of its type to date. A comparison of the CO distribution of
each galaxy to the g-r color image (representing dust) shows that the molecular
gas and dust distributions are in good agreement and trace the same underlying
interstellar medium. The galaxies exhibit a variety of CO morphologies,
including discs (50%), rings (15%), bars+rings (10%), spiral arms (5%), and
mildly (12.5%) and strongly (7.5%) disrupted morphologies. There appear to be
weak trends between galaxy mass and CO morphology, whereby the most massive
galaxies in the sample tend to have molecular gas in a disc morphology. We
derive a lower limit to the total accreted molecular gas mass across the sample
of 2.48x10^10 Msuns, or approximately 8.3x10^8 Msuns per minor merger within
the sample, consistent with minor merger stellar mass ratios.
10/2012;
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Paolo Serra,
Baerbel Koribalski,
Pierre-Alain Duc,
Tom Oosterloo,
Richard M. McDermid,
Leo Michel-Dansac,
Eric Emsellem,
Jean-Charles Cuillandre,
Katherine Alatalo,
Leo Blitz, [......],
Sadegh Khochfar,
Davor Krajnovic,
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Thorsten Naab,
Marc Sarzi,
Nicholas Scott,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: 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.
09/2012;
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Timothy A. Davis,
Davor Krajnovic,
Richard M. McDermid,
Martin Bureau,
Marc Sarzi,
Kristina Nyland,
Katherine Alatalo,
Estelle Bayet,
Leo Blitz,
Maxime Bois, [......],
Sadegh Khochfar,
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: 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.
07/2012;
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Pierre-Yves Lablanche,
Michele Cappellari,
Eric Emsellem,
Frederic Bournaud,
Leo Michel-Dansac,
Katherine Alatalo,
Leo Blitz,
Maxime Bois,
Martin Bureau,
Roger L. Davies, [......],
Harald Kuntschner,
Raffaella Morganti,
Richard M. McDermid,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: 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]
06/2012;
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Michele Cappellari,
Richard M McDermid,
Katherine Alatalo,
Leo Blitz,
Maxime Bois,
Frédéric Bournaud,
M Bureau,
Alison F Crocker,
Roger L Davies,
Timothy A Davis, [......],
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans,
Lisa M Young
[show abstract]
[hide abstract]
ABSTRACT: Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars, which depends on the present number of each type of star in the galaxy. The present number depends on the stellar initial mass function (IMF), which describes the distribution of stellar masses when the population formed, and knowledge of it is critical to almost every aspect of galaxy evolution. More than 50 years after the first IMF determination, no consensus has emerged on whether it is universal among different types of galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot both be universal, but they could not convincingly discriminate between the two possibilities. Only recently were indications found that massive elliptical galaxies may not have the same IMF as the Milky Way. Here we report a study of the two-dimensional stellar kinematics for the large representative ATLAS(3D) sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass, using detailed dynamical models. We find a strong systematic variation in IMF in early-type galaxies as a function of their stellar mass-to-light ratios, producing differences of a factor of up to three in galactic stellar mass. This implies that a galaxy's IMF depends intimately on the galaxy's formation history.
Nature 04/2012; 484(7395):485-8. · 36.28 Impact Factor
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Maxime Bois,
Eric Emsellem,
Frédéric Bournaud,
Katherine Alatalo,
Leo Blitz,
Martin Bureau,
Michele Cappellari,
Roger L. Davies,
Timothy A. Davis,
P. T. de Zeeuw, [......], Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: 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.
01/2012;
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Alison Crocker,
Melanie Krips,
Martin Bureau,
Lisa M. Young,
Timothy A. Davis,
Estelle Bayet,
Katherine Alatalo,
Leo Blitz,
Maxime Bois,
Frédéric Bournaud, [......],
Harald Kuntschner, Pierre-Yves Lablanche,
Rchard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans
[show abstract]
[hide abstract]
ABSTRACT: Surveying eighteen 12CO-bright galaxies from the ATLAS3D early-type galaxy
sample with the Institut de Radio Astronomie Millim\'etrique (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.
12/2011;
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Paolo Serra,
Tom Oosterloo,
Raffaella Morganti,
Katherine Alatalo,
Leo Blitz,
Maxime Bois,
Frederic Bournaud,
Martin Bureau,
Michele Cappellari,
Alison F. Crocker, [......],
Davor Krajnovic,
Harald Kuntschner, Pierre-Yves Lablanche,
Richard M. McDermid,
Thorsten Naab,
Marc Sarzi,
Nicholas Scott,
Scott C. Trager,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: 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.
11/2011;
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Timothy A. Davis,
Katherine Alatalo,
Marc Sarzi,
Martin Bureau,
Lisa M. Young,
Leo Blitz,
Paolo Serra,
Alison F. Crocker,
Davor Krajnović,
Richard M. McDermid, [......],
P. Tim de Zeeuw,
Eric Emsellem,
Sadegh Khochfar,
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Nicholas Scott,
Anne-Marie Weijmans
[show abstract]
[hide abstract]
ABSTRACT: We make use of interferometric CO and H i observations, and optical integral-field spectroscopy from the ATLAS3D survey, to probe the origin of the molecular and ionized interstellar medium (ISM) in local early-type galaxies. We find that 36 ± 5 per cent of our sample of fast-rotating early-type galaxies have their ionized 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, ionized 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 early-type galaxies 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 (presumably stellar mass loss). In the field, however, kinematic misalignments between the stellar and gaseous components indicate that at least 42 ± 5 per cent of local fast-rotating early-type galaxies have their gas supplied from external sources. When one also considers evidence of accretion present in the galaxies’ atomic gas distributions, ≳46 per cent of fast-rotating field ETGs are likely to have acquired a detectable amount of ISM from accretion and mergers. We discuss several scenarios which could explain the environmental dichotomy, including preprocessing in galaxy groups/cluster outskirts and the morphological transformation of spiral galaxies, but we 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 (MK≲−24 mag; stellar mass of ≈8 × 1010 M⊙) always having kinematically aligned gas. This mass dependence appears to be independent of environment, suggesting it is caused by a separate physical mechanism.
Monthly Notices of the Royal Astronomical Society 10/2011; 417(2):882 - 899. · 4.90 Impact Factor
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Sadegh Khochfar,
Eric Emsellem,
Paolo Serra,
Maxime Bois,
Katherine Alatalo,
R. Bacon,
Leo Blitz,
Frédéric Bournaud,
M. Bureau,
Michele Cappellari, [......],
Harald Kuntschner, Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: We propose a simple model for the origin of fast and slow rotator early-type galaxies (ETG) within the hierarchical Λcold dark matter (ΛCDM) 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 λR. Within our model we reproduce the fraction of fast and slow rotators as a function of magnitude in the ATLAS3D survey, assuming that fast-rotating ETGs have at least 10 per cent of their total stellar mass in a disc component. In agreement with ATLAS3D observations we find that slow rotators are predominantly galaxies with M* > 1010.5 M⊙ contributing ∼20 per cent 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 ∼50 and 90 per cent of their stellar mass from satellites and their most massive progenitors have on average up to three major mergers during their evolution. Fast rotators in contrast accrete less than 50 per cent 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 stop, 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 λR into the slow rotator regime.On average, the last gas-rich major merger interaction in slow rotators happens at z > 1.5, followed by a series of minor mergers. These results support the idea that kinematically decoupled cores (KDC) form during gas-rich major mergers at high z followed by minor mergers, which build-up the outer layers of the remnant, and make remnants that are initially too flat compared to observations become rounder. Fast rotators are less likely to form such KDCs due to the fact that they have on average less than one major merger in their past.Fast rotators in our model have different formation paths. The majority, 78 per cent, has bulge-to-total stellar mass ratios (B/T) > 0.5 and managed to grow stellar discs due to continued gas cooling or bulges due to frequent minor mergers. The remaining 22 per cent live in high-density environments and consist of low B/T galaxies with gas fractions below 15 per cent, that have exhausted their cold gas reservoir and have no hot halo from which gas can cool. These fast rotators most likely resemble the flattened disc-like fast rotators in the ATLAS3D survey.Our results predict that ETGs can change their state from fast to slow rotator and vice versa, while the former is taking place predominantly at low z (z < 2), the latter is occurring during cosmic epochs when cooling times are short and galaxies gas-rich. We predict that the ratio of the number density of slow to fast rotators is a strong function of redshift, with massive (>1010 M⊙) fast rotators being more than one order of magnitude more frequent at z∼ 2.
Monthly Notices of the Royal Astronomical Society 10/2011; 417(2):845 - 862. · 4.90 Impact Factor
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Maxime Bois,
Eric Emsellem,
Frédéric Bournaud,
Katherine Alatalo,
Leo Blitz,
Martin Bureau,
Michele Cappellari,
Roger L. Davies,
Timothy A. Davis,
P. T. de Zeeuw, [......], Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: We study the formation of early-type galaxies (ETGs) through mergers with a sample of 70 high-resolution (softening length <60 pc and 12 × 106 particles) numerical simulations of binary mergers of disc galaxies (with 10 per cent of gas) 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 and high central baryonic angular momentum. 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 λR parameter – ATLAS3D Paper III): they preserve the structure of the input fast rotating spiral progenitors. They have intrinsic ellipticities larger than 0.5, cover intrinsic λR values between 0.2 and 0.6, within the range of observed fast rotators. The distribution of the observed fastest rotators does in fact coincide with the distribution of our disc progenitors. 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 ε 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 kiloparsec: these KDCs are built from the stellar components of the progenitors. However, these remnants are still very flat with ε often larger than 0.45 and sometimes as high as 0.65. Besides a handful of specific observed systems – the counter-rotating discs (2σ galaxies, ATLAS3D Paper II) – these therefore cannot reproduce the observed population of slow rotators in the nearby Universe. This sample of simulations supports the notion of slow and fast rotators: these two families of ETGs present distinct characteristics in term of their angular momentum content (at all radii) and intrinsic properties – the slow rotators are not simply velocity-scaled down versions of fast rotators. 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. We also study remergers of these merger remnants: these produce relatively round fast rotators or systems near the threshold for slow rotators. In such cases, the orbital angular momentum dominates the central region, and these systems no longer exhibit a KDC, as KDCs are destroyed during the remergers and do not re-form in these relatively dry events.
Monthly Notices of the Royal Astronomical Society 09/2011; 416(3):1654 - 1679. · 4.90 Impact Factor
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Sadegh Khochfar,
Eric Emsellem,
Paolo Serra,
Maxime Bois,
Katherine Alatalo,
Roland Bacon,
Leo Blitz,
Frederic Bournaud,
Martin Bureau,
Michele Cappellari, [......],
Harald Kuntschner, Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: We propose a simple model for the origin of fast and slow rotator early-type
galaxies (ETG) within the hierarchical $\Lambda$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 $\lambda_R$. 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 $\lambda_R$
into the slow rotator regime. Abridged...
07/2011;
-
Davor Krajnović,
Eric Emsellem,
Michele Cappellari,
Katherine Alatalo,
Leo Blitz,
Maxime Bois,
Frédéric Bournaud,
Martin Bureau,
Roger L. Davies,
Timothy A. Davis, [......], Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Paolo Serra,
Anne-Marie Weijmans,
Lisa M. Young
[show abstract]
[hide abstract]
ABSTRACT: 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.
Monthly Notices of the Royal Astronomical Society 07/2011; 414(4):2923 - 2949. · 4.90 Impact Factor
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Timothy A. Davis,
Katherine Alatalo,
Marc Sarzi,
Martin Bureau,
Lisa M. Young,
Leo Blitz,
Paolo Serra,
Alison F. Crocker,
Davor Krajnović,
Richard M. McDermid, [......],
P. Tim de Zeeuw,
Eric Emsellem,
Sadegh Khochfar,
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Nicholas Scott,
Anne-Marie Weijmans
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ABSTRACT: 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)
06/2011;
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Pierre-Alain Duc,
Jean-Charles Cuillandre,
Paolo Serra,
Leo Michel-Dansac,
Etienne Ferriere,
Katherine Alatalo,
Leo Blitz,
Maxime Bois,
Frederic Bournaud,
Martin Bureau, [......],
Harald Kuntschner, Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Anne-Marie Weijmans,
Lisa M. Young
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ABSTRACT: 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).
05/2011;
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Michele Cappellari,
Eric Emsellem,
Davor Krajnović,
Richard M. McDermid,
Nicholas Scott,
G. A. Verdoes Kleijn,
Lisa M. Young,
Katherine Alatalo,
R. Bacon,
Leo Blitz, [......],
Pierre-Alain Duc,
Sadegh Khochfar,
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Paolo Serra,
Anne-Marie Weijmans
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ABSTRACT: 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 (H i), molecular (CO) and ionized gas (Hβ, [O iii] and [N i]), together with the kinematics and population of the stars (Hβ, Fe5015 and Mg b), for a carefully selected, volume-limited (1.16 × 105 Mpc3) 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 < 42 Mpc, |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 < −21.5 mag (stellar mass M★≳ 6 ×109 M⊙). 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≈ 6 km s−1, Δσ≈ 7 km s−1, Δh3≈Δh4≈ 0.03 in the mean velocity, the velocity dispersion and Gauss–Hermite (GH) moments for galaxies with effective dispersion σe≳ 120 km s−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.
Monthly Notices of the Royal Astronomical Society 05/2011; 413(2):813 - 836. · 4.90 Impact Factor
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Michele Cappellari,
Eric Emsellem,
Davor Krajnovic,
Richard M. McDermid,
Paolo Serra,
Katherine Alatalo,
Leo Blitz,
Maxime Bois,
Frederic Bournaud,
M. Bureau, [......],
Sadegh Khochfar,
Harald Kuntschner, Pierre-Yves Lablanche,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Nicholas Scott,
Anne-Marie Weijmans,
Lisa M. Young
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ABSTRACT: 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)
04/2011;
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Katherine Alatalo,
Leo Blitz,
Lisa M. Young,
Timothy A. Davis,
Martin Bureau,
Laura A. Lopez,
Michele Cappellari,
Nicholas Scott,
Kristen L. Shapiro,
Alison F. Crocker, [......],
Davor Krajnovic,
Harald Kuntschner, Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Paolo Serra,
Anne-Marie Weijmans
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ABSTRACT: 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.
04/2011;
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Timothy A. Davis,
Martin Bureau,
Lisa M. Young,
Katherine Alatalo,
Leo Blitz,
Michele Cappellari,
Nicholas Scott,
Maxime Bois,
Frederic Bournaud,
Roger L. Davies, [......],
Davor Krajnovic,
Harald Kuntschner, Pierre-Yves Lablanche,
Richard M. McDermid,
Raffaella Morganti,
Thorsten Naab,
Tom Oosterloo,
Marc Sarzi,
Paolo Serra,
Anne-Marie Weijmans
[show abstract]
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ABSTRACT: 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 of early-type galaxies. We compare the Tully-Fisher relations 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-fit 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 Tully-Fisher (CO-TF) relation
is offset from the CO-TF of spirals by 0.98 \pm 0.22 magnitude at Ks-band, in
line with other results. The intrinsic scatter of the relation is found to be
\approx 0.4 magnitudes, similar to the level found in the spiral galaxy
population. Next generation facilities such as the Large Millimeter Telescope
(LMT) and the Atacama Large Millimeter/Sub-millimeter Array (ALMA) 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.
02/2011;
