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

By D. Krajnovi'c, Eric Emsellem, M. Cappellari, K. Alatalo, L. Blitz, M. Bois, Frédéric Bournaud, M. Bureau, Roger Davies, T. Davis and 13 more. 2011

347 citations recorded by the source corpus.

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-ɛ) 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/711faf6e49bfc9c8bd3970314c28a96ad4c11190

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In Astronomy and Astrophysics

1. M. Cappellari
2. P. Hopkins
3. L. Hernquist
4. T. Naab
5. C. Conroy
6. R. Somerville
7. Thomas J. Cox
8. M. Sarzi

In Instrumentation

1. M. Cappellari
2. P. Hopkins
3. T. Naab
4. L. Hernquist
5. M. Sarzi
6. Eric Emsellem
7. C. Conroy
8. M. Bureau

Citations in the corpus

• The SLUGGS Survey: kinematics for over 2500 globular clusters in 12 early-type galaxies (2012, background): “An eventual position angle misalignment might contain information about the triaxiality of the system (Krajnović et al. 2011).”
• The ATLAS3D Project – XXX. Star formation histories and stellar population scaling relations of early-type galaxies (2015, methodology): “In Krajnović et al. (2011), we have shown that, applying the Fourier analysis technique of kinemetry (Krajnović et al. 2006), we can further classify the velocity fields of galaxies, giving ‘regular’ rotators (corresponding very closely to the fast rotators, which show disc-like rotation), and…”
• The SAMI Galaxy Survey: Instrument specification and target selection (2014, background): “SAMI’s angular scale elements are expected to average ∼ 2.1 arcsec due to seeing, while ATLAS3D has on-average 1.5 arcsec seeing (Krajnović et al. 2011) and CALIFA has a median angular resolution of 2.5 arcsec (Garćıa-Benito et al. 2014).”
• A REVISED PARALLEL-SEQUENCE MORPHOLOGICAL CLASSIFICATION OF GALAXIES: STRUCTURE AND FORMATION OF S0 AND SPHEROIDAL GALAXIES (2011, result): “…good agreement between the above dichotomy and the results of the SAURON and ATLAS3D surveys (e. g., de Zeeuw et al. 2002; Emsellem et al. 2004, 2007, 2011; Cappellari et al. 2007, 2011a, b; Krajnović et al. 2008, 2011; McDermid et al. 2006): 3 PARALLEL-SEQUENCE GALAXY CLASSIFICATION Vol. 00 A –”
• Galaxy Masses: A Review (2013, background): “Still, the large majority of the galaxies in the Universe are to first order axisymmetric (except for spiral arms and bars) and possess disks even for ETGs (McDonald et al. 2011; Krajnović et al. 2011).”
• The ATLAS3D 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 (2011, background): “A number of galaxies in our sample exhibit strong bars (e.g. NGC 936 and 6548, see Krajnović et al. 2011, hereinafter Paper II).”
• The ATLAS3D project - XIII. Mass and morphology of H I in early-type galaxies as a function of environment (2011, background): “We find that as many as 80 per cent of all ETGs in the nearby Universe consist of nearly axisymmetric, fast rotating stellar systems (Krajnović et al. 2011, hereafter Paper II; Emsellem et al. 2011, hereafter Paper III), most of which resemble spiral galaxies with the arms removed (Cappellari et…”
• DISCOVERY OF AN ACTIVE GALACTIC NUCLEUS DRIVEN MOLECULAR OUTFLOW IN THE LOCAL EARLY-TYPE GALAXY NGC 1266 (2011, background): “It is a fast rotator with regular stellar kinematics (Krajnović et al. 2011), and is of normal metallicity.”
• TRACING OUTFLOWS AND ACCRETION: A BIMODAL AZIMUTHAL DEPENDENCE OF Mg ii ABSORPTION (2012, neutral): “We modeled all galaxy morphological types since 86% of early-types have regular stellar rotation (14% exhibit slow r - tation), spanning the full range of apparent ellipticities, with 90% being kinematically and photometrically aligned (see Emsellem et al. 2011; Krajnović et al. 2011).”
• The ATLAS3D Project – XXVIII. Dynamically driven star formation suppression in early-type galaxies (2014, background): “…for stellar luminosity, the offsets aboveand below the line defined in Equation 1 for the CO non-detected sample do not correlate with stellar kinematic quantities (Krajnović et al. 2011; Emsellem et al. 2011), ionised-gas quantities,or measures of galaxy environment (Cappellari et al. 2011b).”
• Structure and Kinematics of Early-Type Galaxies from Integral Field Spectroscopy (2016, methodology): “The fields are oriented in such a way that PAphot, measured around 3Re in Krajnović et al. (2011), is horizontal.”
• The ATLAS3D project – IV. The molecular gas content of early-type galaxies (2011, background): “Krajnović et al. (2011) (hereinafter Paper II) present a morphological classification of the internal stellar kinematic structure of the galaxies and Emsellem et al. (2011) (hereinafter Paper III) analyse the stellar specific angular momentum proxy λR for the galaxies.”