ABSTRACT We report on high resolution CO(1-0), CS(2-1), and 3 mm continuum Combined Array for Research in Millimeter Astronomy (CARMA) observations of the molecular outflow host and nearest quasar ...Markarian 231. We use the CS(2-1) measurements to derive a dense gas mass within Mrk 231 of , consistent with previous measurements. The CS(2-1) data also seem to indicate that the molecular disk of Mrk 231 is forming stars at about normal efficiency. The high resolution CARMA observations were able to resolve the CO(1-0) outflow into two distinct lobes, allowing for a size estimate to be made and further constraining the molecular outflow dynamical time, further constraining the molecular gas escape rate. We find that 15% of the molecular gas within the Mrk 231 outflow actually exceeds the escape velocity in the central kiloparsec. Assuming that molecular gas is not constantly being accelerated, we find the depletion timescale of molecular gas in Mrk 231 to be 49 Myr, rather than 32 Myr, more consistent with the poststarburst stellar population observed in the system.
Galactic archaeology based on star counts is instrumental to reconstruct the past mass assembly of Local Group galaxies. The development of new observing techniques and data reduction, coupled with ...the use of sensitive large field of view cameras, now allows us to pursue this technique in more distant galaxies exploiting their diffuse low surface brightness (LSB) light. As part of the ATLAS3D project, we have obtained with the MegaCam camera at the Canada–France–Hawaii Telescope extremely deep, multiband images of nearby early-type galaxies (ETGs). We present here a catalogue of 92 galaxies from the ATLAS3D sample, which are located in low- to medium-density environments. The observing strategy and data reduction pipeline, which achieve a gain of several magnitudes in the limiting surface brightness with respect to classical imaging surveys, are presented. The size and depth of the survey are compared to other recent deep imaging projects. The paper highlights the capability of LSB-optimized surveys at detecting new prominent structures that change the apparent morphology of galaxies. The intrinsic limitations of deep imaging observations are also discussed, among those, the contamination of the stellar haloes of galaxies by extended ghost reflections, and the cirrus emission from Galactic dust. The detection and systematic census of fine structures that trace the present and past mass assembly of ETGs are one of the prime goals of the project. We provide specific examples of each type of observed structures – tidal tails, stellar streams and shells – and explain how they were identified and classified. We give an overview of the initial results. The detailed statistical analysis will be presented in future papers.
We study the volume-limited and nearly mass-selected (stellar mass M
stars 6 × 109 M) ATLAS3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). We construct detailed ...axisymmetric dynamical models (Jeans Anisotropic MGE), which allow for orbital anisotropy, include a dark matter halo and reproduce in detail both the galaxy images and the high-quality integral-field stellar kinematics out to about 1R
e, the projected half-light radius. We derive accurate total mass-to-light ratios (M/L)
e
and dark matter fractions f
DM, within a sphere of radius
centred on the galaxies. We also measure the stellar (M/L)stars and derive a median dark matter fraction f
DM = 13 per cent in our sample. We infer masses M
JAM ≡ L × (M/L)
e
2 × M
1/2, where M
1/2 is the total mass within a sphere enclosing half of the galaxy light. We find that the thin two-dimensional subset spanned by galaxies in the
coordinates system, which we call the Mass Plane (MP) has an observed rms scatter of 19 per cent, which implies an intrinsic one of 11 per cent. Here,
is the major axis of an isophote enclosing half of the observed galaxy light, while σ
e
is measured within that isophote. The MP satisfies the scalar virial relation
within our tight errors. This show that the larger scatter in the Fundamental Plane (FP) (L, σ
e
, R
e) is due to stellar population effects including trends in the stellar initial mass function (IMF). It confirms that the FP deviation from the virial exponents is due to a genuine (M/L)
e
variation. However, the details of how both R
e and σ
e
are determined are critical in defining the precise deviation from the virial exponents. The main uncertainty in masses or M/L estimates using the scalar virial relation is in the measurement of R
e. This problem is already relevant for nearby galaxies and may cause significant biases in virial mass and size determinations at high redshift. Dynamical models can eliminate these problems. We revisit the (M/L)
e
-σ
e
relation, which describes most of the deviations between the MP and the FP. The best-fitting relation is
(r band). It provides an upper limit to any systematic increase of the IMF mass normalization with σ
e
. The correlation is more shallow and has smaller scatter for slow rotating systems or for galaxies in Virgo. For the latter, when using the best distance estimates, we observe a scatter in (M/L)
e
of 11 per cent, and infer an intrinsic one of 8 per cent. We perform an accurate empirical study of the link between σ
e
and the galaxies circular velocity V
circ within 1R
e (where stars dominate) and find the relation max (V
circ) 1.76 × σ
e
, which has an observed scatter of 7 per cent. The accurate parameters described in this paper are used in the companion Paper XX (Cappellari et al.) of this series to explore the variation of global galaxy properties, including the IMF, on the projections of the MP.
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.
Abstract
How do galaxies transform from blue, star-forming spirals to red, quiescent early-type galaxies? To answer this question, we analyzed a set of 26 gas-rich, shocked post-starburst galaxies ...with Hubble Space Telescope (HST) imaging in
B
,
I
, and
H
bands and Sloan Digital Sky Survey (SDSS)
i
-band imaging of similar depth but lower resolution. We found that post-starbursts in our sample have intermediate morphologies between disk- and bulge-dominated (Sérsic
n
=
1.7
−
0.0
+
0.3
) and have red bulges, likely due to dust obscuration in the cores. A majority of galaxies in our sample are more morphologically disturbed than regular galaxies (88%, corresponding to >3
σ
significance) when observed with HST, with asymmetry and Sérsic residual flux fraction being the most successful measures of disturbance. Most disturbances are undetected at the lower resolution of SDSS imaging. Although ∼27% galaxies are clear merger remnants, we found that disturbances in another ∼30% of the sample are internal, caused by small-scale perturbations or dust substructures rather than tidal features, and require high-resolution imaging to detect. We found 2.8
σ
evidence that asymmetry features fade on timescales ∼200 Myr, and may vanish entirely after ∼750 Myr, so we do not rule out a possible merger origin of all post-starbursts given that asymmetric features may have already faded. This work highlights the importance of small-scale disturbances, detected only in high-resolution imaging, in understanding structural evolution of transitioning galaxies.
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, Δh
3≈Δh
4≈ 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.
The morphology-density relationship states that dense cosmic environments such as galaxy clusters have an overabundance of quiescent elliptical galaxies, but it is unclear at which redshift this ...relationship is first established. We study the morphology of four clusters with 1.2 < z < 1.8 using Hubble Space Telescope imaging and the morphology computation code statmorph. By comparing the median morphology of cluster galaxies to CANDELS field galaxies using Monte Carlo analysis, we find that two out of four clusters (at z = 1.19 and 1.75) have an established morphology-density relationship with more than 3 significance. Approximately 50% of the galaxies in these clusters are bulge-dominated, compared to ∼30% in the field, and they are significantly more compact. This result is more significant for low-mass galaxies with , showing that low-mass galaxies are affected the most in clusters. We also find an intriguing system of two z 1.45 clusters at a unusually small 2D separation of 3′ and 3D separation of 73 Mpc that exhibit no morphology-density relationship but have enhanced merger signatures. We conclude that the environmental mechanism responsible for the morphology-density relationship is (1) already active as early as z = 1.75; (2) forms compact, bulge-dominated galaxies; and (3) affects primarily low-mass galaxies. However, there is a significant degree of intracluster variance that may depend on the larger cosmological environment in which the cluster is embedded.
Super spirals are the most massive star-forming disk galaxies in the universe. We measured rotation curves for 23 massive spirals with the Southern African Large Telescope (SALT) and found a wide ...range of fast rotation speeds (240-570 km s−1), indicating enclosed dynamical masses of (0.6−4) × 1012M . Super spirals with mass in stars log M stars M > 11.5 break from the baryonic Tully-Fisher relation (BTFR) established for lower-mass galaxies. The BTFR power-law index breaks from 3.75 0.11 to 0.25 0.41 above a rotation speed of ∼340 km s−1. Super spirals also have very high specific angular momenta that break from the Fall relation. These results indicate that super spirals are undermassive for their dark matter halos, limited to a mass in stars of log M stars M < 11.8 . Most giant elliptical galaxies also obey this fundamental limit, which corresponds to a critical dark halo mass of log M halo M 12.7 . Once a halo reaches this mass, its gas can no longer cool and collapse in a dynamical time. Super spirals survive today in halos as massive as log M halo M 13.6 , continuing to form stars from the cold baryons they captured before their halos reached critical mass. The observed high-mass break in the BTFR is inconsistent with the Modified Newtonian Dynamics theory.
We use interferometric 12CO(1-0) observations to compare and contrast 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 scalelengths. Amongst ETGs, we find that the extent of the gas is independent of its kinematic misalignment (with respect to the stars), but does depend on the environment, with Virgo cluster ETGs having less extended molecular gas reservoirs, further emphasizing that cluster ETGs follow different evolutionary pathways from those in the field. 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. These galaxies often have a low mass, and either have disturbed molecular gas or are in the Virgo cluster, suggesting that recent mergers, ram pressure stripping and/or the presence of hot gas can compress/truncate the gas. 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 ionized gas velocities. We confirm that the molecular gas reaches beyond the turnover of the circular velocity curve in 70 per cent of our CO-rich ATLAS3D ETGs, validating previous work on the CO Tully-Fisher relation. In general we find that in most galaxies the molecular gas is dynamically cold, and the observed CO rotation matches well model predictions of the circular velocity. In the galaxies with the largest molecular masses, dust obscuration and/or population gradients can cause model predictions of the circular velocity to disagree with observations of the molecular gas rotation; however, these effects are confined to the most star forming systems. Bars and non-equilibrium conditions can also make the gas deviate from circular orbits. In both these cases, one expects the model circular velocity to be higher than the observed CO velocity, in agreement with our observations. Molecular gas is a better direct tracer of the circular velocity than the ionized gas, justifying its use as a kinematic tracer for Tully-Fisher and similar analyses.
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.
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