MegaMorph – multiwavelength measurement of galaxy structure: physically meaningful bulge–disc decomposition of galaxies near and far

Vika, Marina; Bamford, Steven P.; Häußler, Boris; Rojas, A.

doi:10.1093/mnras/stu1696

Cited by 55 publications

(68 citation statements)

References 52 publications

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“…Although some differences were found in V14, they are less significant than those for N . The narrower wavelength range we are considering here may further reduce the observed variation in R. In Vika et al (2014) we showed that, for the sample considered in this paper, all galaxies, regardless of morphology, have a similar bulge-to-disk effective radius ratio (R e,b /R e,d ∼ 0.3) that changes little with wavelength. However, it is currently unclear why the above arguments for N do not translate into similar behaviour for R. We are continuing to explore the behaviour and physical interpretation of N and R, using the sample of V14 (Kennedy et al, in prep.…”

Section: Discussionmentioning

confidence: 65%

“…Column 1: Hubble type, Col. 2: total number of galaxies in each Hubble type after applying the following cuts: M r < −18.7 and z < 0.01, Col. 3: mean n r from V13, Col. 4: mean B/T from Vika et al (2014), Cols. 5, 6: number of galaxies selected in each cut for the original sample.…”

Section: Resultsmentioning

confidence: 99%

“…Sérsic index and bulge fraction (from Vika et al 2014) for each morphology. Table 2 lists the number of galaxies in the remaining three quadrants.…”

Section: Resultsmentioning

confidence: 99%

“…This is possibly an effect of late-types possessing a bluer disk, which contrasts with a redder bulge, while early-types are dominated by a spheroid at all wavelengths, and/or their bulge and disk components have similarly red colours. A detailed analysis of the component colours can be found in Vika et al (2014) where we present the results of the bulge-disk decomposition of a sample of 163 nearby galaxies.…”

Section: Introductionmentioning

confidence: 99%

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MegaMorph: classifying galaxy morphology using multi-wavelength Sérsic profile fits

Vika

Vulcani

Bamford

et al. 2015

A&A

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Aims. This work investigates the potential of using the wavelength-dependence of galaxy structural parameters (Sérsic index, n, and effective radius, R e ) to separate galaxies into distinct types. Methods. A sample of nearby galaxies with reliable visual morphologies is considered, for which we measure structural parameters by fitting multi-wavelength single-Sérsic models. Additionally, we use a set of artificially redshifted galaxies to test how these classifiers behave when the signal-to-noise ratio decreases. Results. We show that the wavelength-dependence of n may be employed to separate visually-classified early-and late-type galaxies in a manner similar to the use of colour and n. Furthermore, we find that the wavelength variation of n can recover galaxies that are misclassified by these other morphological proxies. Roughly half of the spiral galaxies that contaminate an early-type sample selected using (u − r) versus n can be correctly identified as late-types by N , the ratio of n measured in two different bands. Using a set of artificially redshifted images, we show that this technique remains effective up to z ∼ 0.1. Therefore, N can be used to achieve purer samples of early-types and more complete samples of late-types than using a colour-n cut alone. We also study the suitability of R, the ratio of R e in two different bands, as a morphological classifier, but find that the average sizes of both early-and late-type galaxies do not change substantially over optical wavelengths.

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Section: Discussionmentioning

confidence: 65%

Section: Resultsmentioning

confidence: 99%

“…Sérsic index and bulge fraction (from Vika et al 2014) for each morphology. Table 2 lists the number of galaxies in the remaining three quadrants.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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MegaMorph: classifying galaxy morphology using multi-wavelength Sérsic profile fits

Vika

Vulcani

Bamford

et al. 2015

A&A

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“…This strategy allows us to directly compare sizes, Sérsic indices, axial ratios and colour gradients, while minimizing uncertainties due to k-and e-corrections which often affect field studies where structural parameters are determined in several different rest-frame bands (cf. the discussion in Cassata et al 2013 andVika et al 2014 on the dependence of structural parameters on bandpass). All data were retrieved as fully drizzled frames from the Hubble Legacy Archive.…”

Section: Photometry and Cluster Membershipmentioning

confidence: 99%

Morphological evolution of cluster red sequence galaxies in the past 9 Gyr

Propris¹,

Bremer²,

Phillipps³

2016

Mon. Not. R. Astron. Soc.

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Galaxies arrive on the red sequences of clusters at high redshift (z > 1) once their star formation is quenched and evolve passively thereafter. However, we have previously found that cluster red sequence galaxies (CRSGs) undergo significant morphological evolution subsequent to the cessation of star formation, at some point in the past 9-10 Gyr. Through a detailed study of a large sample of cluster red sequence galaxies spanning 0.2 < z < 1.4 we elucidate the details of this evolution. Below z ∼ 0.5 − 0.6 (in the last 5-6 Gyr) there is little or no morphological evolution in the population as a whole, unlike in the previous 4-5 Gyrs. Over this earlier time (i) disklike systems with Sérsic n < 2 progressively disappear, as (ii) the range of their axial ratios similarly decreases, removing the most elongated systems (those consistent with thin disks seen at an appreciable inclination angle), and (iii) radial colour gradients (bluer outwards) decrease in an absolute sense from significant age-related gradients to a residual level consistent with the metallicity-induced gradients seen in low redshift cluster members. The distribution of their effective radii shows some evidence of evolution, consistent with growth of at most a factor < 1.5 between z ∼ 1.4 and z ∼ 0.5, significantly less than for comparable field galaxies, while the distribution of their central (< 1kpc) bulge surface densities shows no evolution at least at z < 1. A simple model involving the fading and thickening of a disk component after comparatively recent quenching (after z ∼ 1.5) around an otherwise passively evolving older spheroid component is consistent with all of these findings.

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Multi-band morpho-Spectral Component Analysis Deblending Tool (MuSCADeT): Deblending colourful objects

Joseph¹,

Courbin²,

Starck³

2016

A&A

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We introduce a new algorithm for colour separation and deblending of multi-band astronomical images called MuSCADeT which is based on Morpho-spectral Component Analysis of multi-band images. The MuSCADeT algorithm takes advantage of the sparsity of astronomical objects in morphological dictionaries such as wavelets and their differences in spectral energy distribution (SED) across multi-band observations. This allows us to devise a model independent and automated approach to separate objects with different colours. We show with simulations that we are able to separate highly blended objects and that our algorithm is robust against SED variations of objects across the field of view. To confront our algorithm with real data, we use HST images of the strong lensing galaxy cluster MACS J1149+2223 and we show that MuSCADeT performs better than traditional profile-fitting techniques in deblending the foreground lensing galaxies from background lensed galaxies. Although the main driver for our work is the deblending of strong gravitational lenses, our method is fit to be used for any purpose related to deblending of objects in astronomical images. An example of such an application is the separation of the red and blue stellar populations of a spiral galaxy in the galaxy cluster Abell 2744. We provide a python package along with all simulations and routines used in this paper to contribute to reproducible research efforts.

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MegaMorph – multiwavelength measurement of galaxy structure: physically meaningful bulge–disc decomposition of galaxies near and far

Cited by 55 publications

References 52 publications

MegaMorph: classifying galaxy morphology using multi-wavelength Sérsic profile fits

MegaMorph: classifying galaxy morphology using multi-wavelength Sérsic profile fits

Morphological evolution of cluster red sequence galaxies in the past 9 Gyr

Multi-band morpho-Spectral Component Analysis Deblending Tool (MuSCADeT): Deblending colourful objects

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