Kinemetry: a generalization of photometry to the higher moments of the line-of-sight velocity distribution

By D. Krajnovi'c, M. Cappellari, P. de Zeeuw, Y. Copin. 2005

391 citations recorded by the source corpus.

We present a generalization of surface photometry to the higher-order moments of the line-of-sight velocity distribution of galaxies observed with integral-field spectrographs. The generalization follows the approach of surface photometry by determining the best-fitting ellipses along which the profiles of the moments can be extracted and analysed by means of harmonic expansion. The assumption for the odd moments (e.g. mean velocity) is that the profile along an ellipse satisfies a simple cosine law. The assumption for the even moments (e.g. velocity dispersion) is that the profile is constant, as it is used in surface photometry. We test the method on a number of model maps and discuss the meaning of the resulting harmonic terms. We apply the method to the kinematic moments of an axisymmetric model elliptical galaxy and probe the influence of noise on the harmonic terms. We also apply the method to SAURON observations of NGC 2549, NGC 2974, NGC 4459 and NGC 4473 where we detect multiple co- and counter-rotating (NGC 2549 and NGC 4473, respectively) components. We find that velocity profiles extracted along ellipses of early-type galaxies are well represented by the simple cosine law (with 2 per cent accuracy), while possible deviations are carried in the fifth harmonic term which is sensitive to the existence of multiple kinematic components, and has some analogy to the shape parameter of photometry. We compare the properties of the kinematic and photometric ellipses and find that they are often very similar, but a study on a larger sample is necessary. Finally, we offer a characterization of the main velocity structures based only on the kinemetric parameters which can be used to quantify the features in velocity maps.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/034eaa2676d15115032c5f8b3d6d4ea7c5b657f2

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In Astronomy and Astrophysics

1. M. Cappellari
2. P. Hopkins
3. L. Hernquist
4. T. Naab
5. P. V. van Dokkum
6. A. Dekel
7. R. Dav'e
8. Roger Davies

Citations in the corpus

• The ATLAS3D project - XIV. The extent and kinematics of the molecular gas in early-type galaxies (2012, background): “…can detect non-circular motions by the effect they have on the observed molecular gas velocity fields (see e.g. Schoenmakers, Franx & de Zeeuw 1997; Krajnović et al. 2006), however our modest spatial resolution limits our ability to do this with the current data set. c© 2011 RAS, MNRAS 000,…”
• Structure and Kinematics of Early-Type Galaxies from Integral Field Spectroscopy (2016, methodology): “…one assumes there is no dark matter and the gravitational potential is produced by the stars alone, still, also a basic parameter like the galaxy inclination, or equivalently its shape, is virtually unconstrained by the IFS data (Krajnović et al. 2005; van den Bosch & van de Ven 2009; Figure 8).”
• The SAURON project – IX. A kinematic classification for early‐type galaxies (2007, methodology): “Note that the photometric PA is derived using the large-scale MDM data, but the kinematic PA via a global measurement on theSAURON velocity maps as described in Appendix C of Krajnović et al. (2006).”
• The SAURON project – XII. Kinematic substructures in early-type galaxies: evidence for discs in fast rotators (2008, methodology): “Krajnović et al. (2006) presented kinemetry, as a quantitative approach to analysis of maps of kinematic moments.”
• RESULTS OF THE LICK OBSERVATORY SUPERNOVA SEARCH FOLLOW-UP PHOTOMETRY PROGRAM: BVRI LIGHT CURVES OF 165 TYPE Ia SUPERNOVAE (2010, methodology): “Using algorithms developed by Krajnović et al. (2006), we determined the isophote along the position of the SN.6 Artificial stars with the same PSF as the SN were injected along the isophote in each data image, and the image was then reprocessed by our pipeline.”
• The Sydney-AAO Multi-object Integral field spectrograph (2011, methodology): “Kinematic information from integral field spectroscopy can be used to differentiate between quiescent galaxies and those undergoing a merger (e.g. Shapiro et al. 2008), using procedures such as kinemetry (Krajnović et al. 2006).”
• The SAURON project – X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/σ, ɛ) diagram with integral‐field stellar kinematics (2007, methodology): “(20) The PAkin is defined as the PA at which the observedSAURON velocity field is best approximated by a bi-antisymmetric version of it and was measured as described in Appendix C of Krajnović et al. (2006).”
• The ATLAS3D project - X. On the origin of the molecular and ionized gas in early-type galaxies (2011, methodology): “The molecular and ionisedgas kinematic PAs are presented here for the first time, and are measurd using the same method (theFIT KINEMATIC PA routine§ described in Appendix C of Krajnović et al. 2006).”
• THE KMOS3D SURVEY: DESIGN, FIRST RESULTS, AND THE EVOLUTION OF GALAXY KINEMATICS FROM 0.7 ⩽ z ⩽ 2.7 (2014, methodology): “Disk sample Distinguishing rotationally-supported galaxies from other kinematic classes is ideally done though a quantitative analysis, such as kinemetry (e.g. Krajnović et al. 2006).”
• Neutral hydrogen in nearby elliptical and lenticular galaxies: the continuing formation of early-type galaxies (2006, methodology): “We have traced the position angle and the absolute rotation as function of radius using the harmonicexpansion method for analysing two-dimensional velocity maps of Krajnović et al. (2006).”
• CONSTRAINTS ON THE ASSEMBLY AND DYNAMICS OF GALAXIES. I. DETAILED REST-FRAME OPTICAL MORPHOLOGIES ON KILOPARSEC SCALE OF z ∼ 2 STAR-FORMING GALAXIES (2010, background): “…to distinguish reliably between disks and mergers as a function of the degree of symmetry of velocity fields and velocity dispersion maps (e.g., Krajnovíc et al. 2006; Flores et al. 2006; Shapiro et al. 2008; Épinat et al. 2010), and to determine the main source of dynamical support from the…”
• The SAURON project – XVII. Stellar population analysis of the absorption line strength maps of 48 early-type galaxies (2010, methodology): “…dispersion maps using kinemetry, a generalization of surface photometry to the higher order moments of the line-of-sightvelocity distribution (Krajnović et al. 2006) and found that 74 per cent of Es and 92 per cent of S0s in theSAURON sample exhibit rotation, which can be well-described by…”
• ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED (2012, positive): “There is also a connection here to the “kinemetric” methods of modeling data from integral-field spectrographs, where the two-dimensional kinematics are expanded in a Fourier series (Krajnović et al. 2006; Krajnović et al. 2008).”
• The SAURON project – VIII. OASIS/CFHT integral-field spectroscopy of elliptical and lenticular galaxy centres (2006, methodology): “To quantify the structures found in our stellar velocity fields, we employ the so-called ‘kinemetry’ method of Krajnović et al. (2006).”