arXiv subjects

M. Vika

Publications and source records attributed to M. Vika.

5 recordsLinked to original sources

arXiv2019

Multi-wavelength structure analysis of local cluster galaxies. The WINGS project

We present a multi-wavelength analysis of the galaxies in nine clusters selected from the WINGS dataset, examining how galaxy structure varies as a function of wavelength and environment using the state of the art software GALAPAGOSII. We simultaneously fit single Sérsic functions on three optical (u, B and V) and two near-infrared (J and K) bands thus creating a wavelength-dependent model of each galaxy. We measure the magnitudes, effective radius ($R_{e}$) the Sérsic index ($n$), axis ratio and position angle in each band. The sample contains 790 cluster members (located close to the cluster center < 0.64 R$_{200}$ and 254 non-member galaxies that we further separate based on their morphology into ellipticals, lenticulars and spirals. We find that the Sérsic index of all galaxies inside clusters remains nearly constant with wavelength while $R_{e}$ decreases as wavelength increases for all morphological types. We do not observe a significant variation on n and $R_{e}$ as a function of projected local density and distance from the clusters center. Comparing the n and $R_{e}$ of bright cluster galaxies with a subsample of non-member galaxies we find that bright cluster galaxies are more concentrated (display high $n$ values) and are more compact (low $R_{e}$). Moreover, the light profile ($\mathcal{N}$) and size ($\mathcal{R}$) of bright cluster galaxies does not change as a function of wavelength in the same manner as non-member galaxies.

astro-ph.GA↗

arXiv2019

DustPedia - the relationships between stars, gas and dust for galaxies residing in different environments

We use a sub-set of the DustPedia galaxy sample (461 galaxies) to investigate the effect the environment has had on galaxies. We consider Virgo cluster and field samples and also assign a density contrast parameter to each galaxy, as defined by the local density of SDSS galaxies. We consider their chemical evolution (using M_{Dust}/M_{Baryon} and M_{Gas}/M_{Baryon}), their specific star formation rate (SFR/M_{Stars}), star formation efficiency (SFR/M_{Gas}), stars-to-dust mass ratio (M_{Stars}/M_{Dust}), gas-to-dust mass ratio (M_{Gas}/M_{Dust}) and the relationship between star formation rate per unit mass of dust and dust temperature (SFR/M_{Dust} and T_{Dust}). Late type galaxies (later than Sc) in all of the environments can be modelled using simple closed box chemical evolution and a simple star formation history (SFR(t) \propto t\exp{-t/τ}). For earlier type galaxies the physical mechanisms that give rise to their properties are clearly much more varied and require a more complicated model (mergers, gas in or outflow). However, we find little or no difference in the properties of galaxies of the same morphological type within the cluster, field or with different density contrasts. It appears that it is morphology, how and whenever this is laid down, and consistent internal physical processes that primarily determine the derived properties of galaxies in the DustPedia sample and not processes related to differences in the local environment.

astro-ph.GA↗

arXiv2018

Dust emission profiles of DustPedia galaxies

Most radiative transfer models assume that dust in spiral galaxies is distributed exponentially. In this paper our goal is to verify this assumption by analysing the two-dimensional large-scale distribution of dust in galaxies from the DustPedia sample. For this purpose, we make use of Herschel imaging in five bands, from 100 to 500μm, in which the cold dust constituent is primarily traced and makes up the bulk of the dust mass in spiral galaxies. For a subsample of 320 disc galaxies, we successfully perform a simultaneous fitting with a single Sérsic model of the Herschel images in all five bands using the multiband modelling code GALFITM. We report that the Sérsic index $n$, which characterises the shape of the Sérsic profile, lies systematically below 1 in all Herschel bands and is almost constant with wavelength. The average value at 250μm is $0.67\pm0.37$ (187 galaxies are fitted with $n_{250}\leq0.75$, 87 galaxies have $0.75 1.25$). Most observed profiles exhibit a depletion in the inner region (at $r<0.3-0.4$ of the optical radius $r_{25}$ ) and are more or less exponential in the outer part. We also find breaks in the dust emission profiles at longer distances $(0.5-0.6)r_{25}$ which are associated with the breaks in the optical and near-infrared. We assume that the observed deficit of dust emission in the inner galaxy region is related to the depression in the radial profile of the HI surface density in the same region because the atomic gas reaches high enough surface densities there to be transformed into molecular gas. If a galaxy has a triggered star formation in the inner region (for example, because of a strong bar instability, which transfers the gas inwards to the centre, or a pseudobulge formation), no depletion or even an excess of dust emission in the centre is observed.

astro-ph.GA↗

arXiv2016

DustPedia - A Definitive Study of Cosmic Dust in the Local Universe

The European Space Agency has invested heavily in two cornerstones missions; Herschel and Planck. The legacy data from these missions provides us with an unprecedented opportunity to study cosmic dust in galaxies so that we can answer fundamental questions about, for example: the origin of the chemical elements, physical processes in the interstellar medium (ISM), its effect on stellar radiation, its relation to star formation and how this relates to the cosmic far infrared background. In this paper we describe the DustPedia project, which is enabling us to develop tools and computer models that will help us relate observed cosmic dust emission to its physical properties (chemical composition, size distribution, temperature), to its origins (evolved stars, super novae, growth in the ISM) and the processes that destroy it (high energy collisions and shock heated gas). To carry out this research we will combine the Herschel/Planck data with that from other sources of data, providing observations at numerous wavelengths (< 41) across the spectral energy distribution, thus creating the DustPedia database. To maximise our spatial resolution and sensitivity to cosmic dust we limit our analysis to 4231 local galaxies (v < 3000 km/s) selected via their near infrared luminosity (stellar mass). To help us interpret the data we have developed a new physical model for dust (THEMIS), a new Bayesian method of fitting and interpreting spectral energy distributions (HerBIE) and a state-of-the-art Monte Carlo photon tracing radiative transfer model (SKIRT). In this the first of the DustPedia papers we describe the project objectives, data sets used and provide an insight into the new scientific methods we plan to implement.

astro-ph.GA↗

arXiv2015

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

Aims. This work investigates the potential of using the wavelength-dependence of galaxy structural parameters (Sérsic index, n, and effective radius, Re) 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 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. N can therefore 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 Re 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.

astro-ph.GA↗