A New Approach to Galaxy Morphology. I. Analysis of the Sloan Digital Sky Survey Early Data Release

Abraham, Roberto; Bergh, Sidney van den; Nair, Preethi

doi:10.1086/373919

Cited by 400 publications

(453 citation statements)

References 52 publications

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“…Values span the range 0-1 and larger values correspond to higher intensity of the residuals; The Gini coefficient was first introduced in Abraham et al (2003). It provides a quantitative measure of the inequality with which galaxy's light is distributed among its constituent pixels.…”

Section: The Morphological Classificationmentioning

confidence: 99%

The zCOSMOS redshift survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z ~ 1

Tasca

Kneib²,

Iovino

et al. 2009

A&A

149

146

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Context. For more than two decades we have known that galaxy morphological segregation is present in the Local Universe. It is important to see how this relation evolves with cosmic time. Aims. To investigate how galaxy assembly took place with cosmic time, we explore the evolution of the morphology-density relation up to redshift z ∼ 1 using about 10 000 galaxies drawn from the zCOSMOS Galaxy Redshift Survey. Taking advantage of accurate HST/ACS morphologies from the COSMOS survey, of the well-characterised zCOSMOS 3D environment, and of a large sample of galaxies with spectroscopic redshift, we want to study here the evolution of the morphology-density relation up to z ∼ 1 and its dependence on galaxy luminosity and stellar mass. The multi-wavelength coverage of the field also allows a first study of the galaxy morphological segregation dependence on colour. We further attempt to disentangle between processes that occurred early in the history of the Universe or late in the life of galaxies. Methods. The zCOSMOS field benefits of high-resolution imaging in the F814W filter from the Advanced Camera for Survey (ACS). We use standard morphology classifiers, optimised for being robust against band-shifting and surface brightness dimming, and a new, objective, and automated method to convert morphological parameters into early, spiral, and irregular types. We use about 10 000 galaxies down to I AB = 22.5 with a spectroscopic sampling rate of 33% to characterise the environment of galaxies up to z ∼ 1 from the 100 kpc scales of galaxy groups up to the 100 Mpc scales of the cosmic web. The evolution of the morphology-density relation in different environments is then studied for luminosity and stellar-mass selected, volume-limited samples of galaxies. The trends are described and related to the various physical processes that could play a relevant role in the build-up of the morphology-density relation. Results. We confirm that the morphological segregation is present up to z ∼ 1 for luminosity-selected, volume-limited samples. The behaviour of the morphology-density relation gets flatter at fixed masses expecially above 10 10.6 M . We suggest the existence of a critical mass above which the physical processes governing galaxy stellar mass also determine the shaping of the galaxy more than its environment. We finally show that at a fixed morphology there is still a residual variation in galaxy colours with density. Conclusions. The observed evolution with redshift of the morphology-density relation offers an opportunity to trace the effect of nature and nurture as a function of environment. Even though it is based mainly on a biased view, the environmental dependence of the morphological evolution for luminosity-selected, volume-limited samples seems to indicate that nurture is in play. On the other hand, the lack of evolution observed for earlytype and spiral galaxies that are more massive than 10 10.8 M independents of the environment indicates that nature has imprinted these properties early in the life of...

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Section: The Morphological Classificationmentioning

confidence: 99%

The zCOSMOS redshift survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z ~ 1

Tasca

Kneib²,

Iovino

et al. 2009

A&A

149

146

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“…The classification is made in a 10-D volume with a Radial Basis Function Kernel (see Paper I for more details). The measured parameters include 6 morphological parameters: Asymmetry, Concentration (Conselice et al 2000;and Abraham et al 1996, definitions), Gini (Abraham et al 2003), M20 (Lotz et al 2004), Smoothness (Conselice et al 2003), a distance parameter (photometric redshift), a shape parameter (elongation), 2 luminosity parameters (surface brightness and magnitude). See Paper I for details on how these parameters are calculated.…”

Section: Classification Proceduresmentioning

confidence: 99%

A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images

Huertas-Company¹,

Tasca

Rouan³

et al. 2009

A&A

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Context. Morphology is the most accessible tracer of galaxies physical structure, but its interpretation in the framework of galaxy evolution still remains problematic. Its quantification at high redshift requires deep high-angular resolution imaging, which is why space data (HST) are usually employed. At z > 1, the HST visible cameras however probe the UV flux, which is dominated by the emission of young stars, which could bias the estimated morphologies towards late-type systems. Aims. In this paper we quantify the effects of this morphological k-correction at 1 < z < 2 by comparing morphologies measured in the K and I-bands in the COSMOS area. The Ks-band data indeed have the advantage of probing old stellar populations in the rest frame for z < 2, enabling determination of galaxy morphological types unaffected by recent star formation. Methods. In Paper I we presented a new non-parametric method of quantifying morphologies of galaxies on seeing-limited images based on support vector machines. Here we use this method to classify ∼50 000 Ks selected galaxies in the COSMOS area observed with WIRCam at CFHT. We use a 10-dimensional volume, including 5 morphological parameters, and other characteristics of galaxies such as luminosity and redshift. The obtained classification is used to investigate the redshift distributions and number counts per morphological type up to z ∼ 2 and to compare them to the results obtained with HST/ACS in the I-band on the same objects. We associate to every galaxy with Ks < 21.5 and z < 2 a probability between 0 and 1 of being late-type or early-type. We use this value to assess the accuracy of our classification as a function of physical parameters of the galaxy and to correct for classification errors. Results. The classification is found to be reliable up to z ∼ 2. The mean probability is p ∼ 0.8. It decreases with redshift and with size, especially for the early-type population, but remains above p ∼ 0.7. The classification globally agrees with the one obtained using HST/ACS for z < 1. Above z ∼ 1, the I-band classification tends to find less early-type galaxies than the Ks-band one by a factor ∼1.5, which might be a consequence of morphological k-correction effects. Conclusions. We argue therefore that studies based on I-band HST/ACS classifications at z > 1 could be underestimating the elliptical population. Using our method in a K s ≤ 21.5 magnitude-limited sample, we observe that the fraction of the early-type population is (21.9% ± 8%) at z ∼ 1.5−2 and (32.0% ± 5%) at the present time. We will discuss the evolution of the fraction of galaxies in types from volume-limited samples in a forthcoming paper.

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“…As an example, they are used for galaxy morphology classification in the analysis of the HST and SDSS galaxy surveys (Abraham et al 2003;Conselice 2003;Lotz et al 2004;Zamojski et al 2007;Holwerda et al 2011a;Wang et al 2012). Abraham et al (2003), Lotz et al (2004), andWang et al (2012) also revealed the inter-relation between Gini, concentration and M 20 , as well as the possible inter-change between the concentration and Gini parameter for high-z galaxies. This encouraged us to investigate these parameters in more detail in order to characterise the dynamical state of galaxy clusters, particularly at high-z.…”

Section: Introduction Of Morphology Parametersmentioning

confidence: 99%

Morphology parameters: substructure identification in X-ray galaxy clusters

Parekh

Heyden

Ferrari

et al. 2015

A&A

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Context. In recent years multi-wavelength observations have shown the presence of substructures related to merging events in a large proportion of galaxy clusters. Clusters can be roughly grouped into two categories -relaxed and non-relaxed -and a proper characterisation of the dynamical state of these systems is crucial for both astrophysical and cosmological studies. Aims. In this paper we investigate the use of a number of morphological parameters (Gini, M 20 , concentration, asymmetry, smoothness, ellipticity, and Gini of the second-order moment, G M ) introduced to automatically classify clusters as relaxed or dynamically disturbed systems. Methods. We apply our method to a sample of clusters at different redshifts extracted from the Chandra archive and investigate possible correlations between morphological parameters and other X-ray gas properties. Results. We conclude that a combination of the adopted parameters is a very useful tool for properly characterising the X-ray cluster morphology. According to our results, three parameters -Gini, M 20 , and concentration -are very promising for identifying cluster mergers. The Gini coefficient is a particularly powerful tool, especially at high redshift, because it is independent of the choice of the position of the cluster centre. We find that high Gini (>0.65), high concentration (>1.55), and low M 20 (<-2.0) values are associated with relaxed clusters, while low Gini (<0.4), low concentration (<1.0), and high M 20 (>-1.4) characterise dynamically perturbed systems. We also estimate the X-ray cluster morphological parameters in the case of radio loud clusters. Since they are in excellent agreement with previous analyses we confirm that diffuse intracluster radio sources are associated with major mergers.

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A New Approach to Galaxy Morphology. I. Analysis of the Sloan Digital Sky Survey Early Data Release

Cited by 400 publications

References 52 publications

The zCOSMOS redshift survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z ~ 1

The zCOSMOS redshift survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z ~ 1

A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images

Morphology parameters: substructure identification in X-ray galaxy clusters

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