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Igor Chilingarian

Publications and source records attributed to Igor Chilingarian.

At least 73 records · Page 4Linked to original sources
arXiv2011

Lessons learnt in building VO resources: binding together several VO standards into an operational service

The International Virtual Observatory Alliance (IVOA) developed numerous interoperability standards during the last several years. Most of them are quite simple to implement from the technical point of view and even contain "SIMPLE" in the title. Does it mean that it is also simple to build a working VO resource using those standards? Yes and no. "Yes" because the standards are indeed simple, and "no" because usually one needs to implement a lot more than it was thought in the beginning of the project so the time management of the team becomes difficult. In our presentation we will start with a basic case of a simple spectral data collection. Then we will describe several examples of small" technologically advanced VO resources built in CDS and VO-Paris and will show that many standards are hidden from managers' eyes at the initial stage of the project development. The projects will be: (1) the GalMer database providing access to the results of numerical simulations of galaxy interactions; (2) the full spectrum fitting service that allows one to extract internal kinematics and stellar populations from spectra of galaxies available in the VO. We conclude that: (a) with the existing set of IVOA standards one can already build very advanced VO-enabled archives and tools useful for scientists; (b) managers have to be very careful when estimating the project development timelines for VO-enabled resources.

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arXiv2011

Evolution of the IVOA Characterisation Data Model

The Characterisation data model is a standard of the International Virtual Observatory Alliance (IVOA) that describes observational datasets in the multi-dimensional parameter space. Defining three properties: coverage, resolution, and sampling along different physical axes (e.g. spatial, spectral, flux) with variable level of details for the description, this model has been used in several IVOA contexts: Simple Spectral Access Protocol, Spectrum Data Model, ObsTAP (Table Access Protocol for the Core Components of the Observation Data Model. Here we propose a new version which addresses more completely the most detailed level of description (level 4) dealing with variation maps of coverage, resolution, and sampling. It also introduces new specific axes in order to cover various photometric measurements, velocity and polarimetry. Special care is given for composed data sets. These improvements and add-ons follow the evolution of needs expressed to the uptake of VO tools in various observation domains for data discovery but also for data analysis requirements. This is also introduced to tackle use-cases designed to analyse scientifically datasets in the V0 context together with calibration/provenance information.

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arXiv2011

IVOA Recommendation: Observation Data Model Core Components and its Implementation in the Table Access Protocol Version 1.0

This document defines the core components of the Observation data model that are necessary to perform data discovery when querying data centers for observations of interest. It exposes use-cases to be carried out, explains the model and provides guidelines for its implementation as a data access service based on the Table Access Protocol (TAP). It aims at providing a simple model easy to understand and to implement by data providers that wish to publish their data into the Virtual Observatory. This interface integrates data modeling and data access aspects in a single service and is named ObsTAP. It will be referenced as such in the IVOA registries. There will be a separate document to cover the full Observation data model. In this document, the Observation Data Model Core Components (ObsCoreDM) defines the core components of queryable metadata required for global discovery of observational data. It is meant to allow a single query to be posed to TAP services at multiple sites to perform global data discovery without having to understand the details of the services present at each site. It defines a minimal set of basic metadata and thus allows for a reasonable cost of implementation by data providers. The combination of the ObsCoreDM with TAP is referred to as an ObsTAP service. As with most of the VO Data Models, ObsCoreDM makes use of STC, Utypes, Units and UCDs. The ObsCoreDM can be serialized as a VOTable. ObsCoreDM can make reference to more complete data models such as ObsProvDM (the Observation Provenance Data Model, to come), Characterisation DM, Spectrum DM or Simple Spectral Line Data Model (SSLDM).

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arXiv2011

IVOA Recommendation: Data Model for Astronomical DataSet Characterisation

This document defines the high level metadata necessary to describe the physical parameter space of observed or simulated astronomical data sets, such as 2D-images, data cubes, X-ray event lists, IFU data, etc.. The Characterisation data model is an abstraction which can be used to derive a structured description of any relevant data and thus to facilitate its discovery and scientific interpretation. The model aims at facilitating the manipulation of heterogeneous data in any VO framework or portal. A VO Characterisation instance can include descriptions of the data axes, the range of coordinates covered by the data, and details of the data sampling and resolution on each axis. These descriptions should be in terms of physical variables, independent of instrumental signatures as far as possible. Implementations of this model has been described in the IVOA Note available at: http://www.ivoa.net/Documents/latest/ImplementationCharacterisation.html Utypes derived from this version of the UML model are listed and commented in the following IVOA Note: http://www.ivoa.net/Documents/latest/UtypeListCharacterisationDM.html An XML schema has been build up from the UML model and is available at: http://www.ivoa.net/xml/Characterisation/Characterisation-v1.11.xsd

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arXiv2011

A universal ultraviolet-optical colour-colour-magnitude relation of galaxies

Although the optical colour-magnitude diagram of galaxies allows one to select red sequence objects, neither can it be used for galaxy classification without additional observational data such as spectra or high-resolution images, nor to identify blue galaxies at unknown redshifts. We show that adding the near ultraviolet colour to the optical CMD reveals a tight relation in the three-dimensional colour-colour-magnitude space smoothly continuing from the "blue cloud" to the "red sequence". We found that 98 per cent of 225,000 low-redshift (Z<0.27) galaxies follow a smooth surface g-r=F(M,NUV-r) with a standard deviation of 0.03-0.07 mag making it the tightest known galaxy photometric relation. There is a strong correlation between morphological types and integrated NUV-r colours. Rare galaxy classes such as E+A or tidally stripped systems become outliers that occupy distinct regions in the 3D parameter space. Using stellar population models for galaxies with different SFHs, we show that (a) the (NUV-r, g-r) distribution is formed by objects having constant and exponentially declining SFR with different characteristic timescales; (b) colour evolution for exponentially declining models goes along the relation suggesting its weak evolution up-to a redshift of 0.9; (c) galaxies with truncated SFHs have very short transition phase offset from the relation thus explaining the rareness of E+A galaxies. This relation can be used as a powerful galaxy classification tool when morphology remains unresolved. Its mathematical consequence is the photometric redshift estimates from 3 broad-band photometric points. This approach works better than most existing photometric redshift techniques applied to multi-colour datasets. Therefore, the relation can be used as an efficient selection technique for galaxies at intermediate redshifts (0.3<Z<0.8) using optical imaging surveys.

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arXiv2011

Large scale nested stellar discs in NGC 7217

NGC7217 is an unbarred early-type spiral galaxy having a multi-segment exponential light profile and a system of starforming rings of the unknown origin; it also possesses a circumnuclear gaseous polar disc. We analysed new long slit spectroscopic data for NGC7217 and derived the radial distributions of its stellar population parameters and stellar and gaseous kinematics up to the radius of r~100 arcsec (~8 kpc). We performed the dynamical analysis of the galaxy by recovering its velocity ellipsoid at different radii, and estimated the scaleheights of its two exponential discs. The inner exponential stellar disc of NGC7217 appears to be thin and harbours intermediate age stars (t(SSP) ~ 5 Gyr). The outer stellar disc seen between the radii of 4 and 7 kpc is very thick (z0 = 1...3 kpc), metal-poor, [Fe/H]<-0.4 dex, and has predominantly young stars, t(SSP) = 2 Gyr. The remnants of minor mergers of gas-rich satellites with an early-type giant disc galaxy available in the GalMer database well resemble different structural components of NGC7217, suggesting two minor merger events in the past responsible for the formation of the inner polar gaseous disc and large outer starforming ring. Another possibility to form the outer ring is the re-accretion of the tidal streams created by the first minor merger.

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arXiv2010

The True Bottleneck of Modern Scientific Computing in Astronomy

We discuss what hampers the rate of scientific progress in our exponentially growing world. The rapid increase in technologies leaves the growth of research result metrics far behind. The reason for this lies in the education of astronomers lacking basic computer science aspects crucially important in the data intensive science era.

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arXiv2010

Dynamical versus Stellar Masses of Ultracompact Dwarf Galaxies in the Fornax Cluster

The origin of ultracompact dwarf (UCD) galaxies, compact extragalactic stellar systems, is still a puzzle for present galaxy formation models. We present the comprehensive analysis of high resolution multi-object spectroscopic data for a sample of 24 Fornax cluster UCDs obtained with VLT FLAMES. It comprises previously published data for 19 objects (Mieske et al. 2008) which we re-analysed, including 13 with available HST photometric data. Using Virtual Observatory technologies we found archival HST images for two more UCDs and then determined their structural properties. For all objects we derived internal velocity dispersions, stellar population parameters, and stellar mass-to-light ratios (M/L)* by fitting individual simple stellar population (SSP) synthetic spectra convolved with a Gaussian against the observed spectra using the NBursts full spectral fitting technique. For 14 objects we estimated dynamical masses suggesting no dark matter (DM) in 12 of them and no more than 40 per cent DM mass fraction in the remaining two, in contrast to findings for several UCDs in the Virgo cluster. Some Fornax UCDs even have too high values of (M/L)* estimated using the Kroupa stellar initial mass function (IMF) resulting in negative formally computed DM mass fractions. The objects with too high (M/L)* ratios compared to the dynamical ones have relatively short dynamical relaxation timescales, close to the Hubble time or below. We therefore suggest that their lower dynamical ratios (M/L)dyn are caused by low-mass star depletion due to dynamical evolution. Overall, the observed UCD characteristics suggest at least two formation channels: tidal threshing of nucleated dwarf galaxies for massive UCDs (~10^8 M_sun), and a classical scenario of red globular cluster formation for lower-mass UCDs (< 10^7 M_sun).

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arXiv2010

Virtual Observatory based identification of AX J194939+2631 as a new cataclysmic variable

We report the discovery of a new cataclysmic variable (CV) among unidentified objects from the ASCA Galactic Plane Survey made using the Virtual Observatory data mining. First, we identified AX J194939+2631 with IPHAS J194938.39+263149.2, the only prominent H-alpha emitter among 400 sources in a 1 arcmin field of the IPHAS survey, then secured as a single faint X-ray source found in an archival Chandra dataset. Spectroscopic follow-up with the 3.5-m Calar Alto telescope confirmed its classification as a CV, possibly of magnetic nature. Our analysis suggests that AX J194939+2631 is a medium distance system (d ~ 0.6 kpc) containing a late-K or early-M type dwarf as a secondary component and a partially disrupted accretion disc revealed by the double-peaked H-alpha line. However, additional deep observations are needed to confirm our tentative classification of this object as an intermediate polar.

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arXiv2010

The GalMer database: Galaxy Mergers in the Virtual Observatory

We present the GalMer database, a library of galaxy merger simulations, made available to users through tools compatible with the Virtual Observatory (VO) standards adapted specially for this theoretical database. To investigate the physics of galaxy formation through hierarchical merging, it is necessary to simulate galaxy interactions varying a large number of parameters: morphological types, mass ratios, orbital configurations, etc. On one side, these simulations have to be run in a cosmological context, able to provide a large number of galaxy pairs, with boundary conditions given by the large-scale simulations, on the other side the resolution has to be high enough at galaxy scales, to provide realistic physics. The GalMer database is a library of thousands simulations of galaxy mergers at moderate spatial resolution and it is a compromise between the diversity of initial conditions and the details of underlying physics. We provide all coordinates and data of simulated particles in FITS binary tables. The main advantages of the database are VO access interfaces and value-added services which allow users to compare the results of the simulations directly to observations: stellar population modelling, dust extinction, spectra, images, visualisation using dedicated VO tools. The GalMer value-added services can be used as virtual telescope producing broadband images, 1D spectra, 3D spectral datacubes, thus making our database oriented towards the usage by observers. We present several examples of the GalMer database scientific usage obtained from the analysis of simulations and modelling their stellar population properties, including: (1) studies of the star formation efficiency in interactions; (2) creation of old counter-rotating components; (3) reshaping metallicity profiles in elliptical galaxies; (4) orbital to internal angular momentum transfer; (5) reproducing observed colour bimodality of galaxies.

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arXiv2010

SDSSJ150634.27+013331.6: the second compact elliptical galaxy in the NGC5846 group

We report the discovery of the second compact elliptical (cE) galaxy SDSSJ150634.27+013331.6 in the nearby NGC5846 group by the Virtual Observatory (VO) workflow . This object (M_B = -15.98 mag, R_e = 0.24 kpc) becomes the fifth cE where the spatially-resolved kinematics and stellar populations can be obtained. We used archival HST WFPC2 images to demonstrate that its light profile has a two-component structure, and integrated photometry from GALEX, SDSS, UKIDSS, and Spitzer to build the multi-wavelength SED to constraint the star formation history (SFH). We observed this galaxy with the PMAS IFU spectrograph at the Calar-Alto 3.5m telescope and obtained two-dimensional maps of its kinematics and stellar population properties using the full-spectral fitting technique. Its structural, dynamical and stellar population properties suggest that it had a massive progenitor heavily tidally stripped by NGC5846.

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arXiv2010

Analytical approximations of K-corrections in optical and near-infrared bands

To compare photometric properties of galaxies at different redshifts, the fluxes need to be corrected for the changes of effective rest-frame wavelengths of filter bandpasses, called K-corrections. Usual approaches to compute them are based on the template fitting of observed spectral energy distributions (SED) and, thus, require multi-colour photometry. Here, we demonstrate that, in cases of widely used optical and near-infrared filters, K-corrections can be precisely approximated as two-dimensional low-order polynomials of only two parameters: redshift and one observed colour. With this minimalist approach, we present the polynomial fitting functions for K-corrections in SDSS ugriz, UKIRT WFCAM YJHK, Johnson-Cousins UBVR_cI_c, and 2MASS JHK_s bands for galaxies at redshifts Z<0.5 based on empirically-computed values obtained by fitting combined optical-NIR SEDs of a set of 10^5 galaxies constructed from SDSS DR7 and UKIDSS DR5 photometry using the Virtual Observatory. For luminous red galaxies we provide K-corrections as functions of their redshifts only. In two filters, g and r, we validate our solutions by computing K-corrections directly from SDSS DR7 spectra. We also present a K-corrections calculator, a web-based service for computing K-corrections on-line.

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arXiv2010

Transparent scientific usage as the key to success of the Virtual Observatory

Nowadays, Virtual Observatory standards, resources, and services became powerful enough to help astronomers making real science on everyday basis. The key to the VO success is its entire transparency for a scientific user. This allows an astronomer to combine "online" VO-enabled parts with "offline" research stages including dedicated data processing and analysis, observations, numerical simulations; and helps to overpass one of the major issues that most present-day VO studies do not go further than data mining. Here we will present three VO-powered research projects combining VO and non-VO blocks, all of them resulted in peer-reviewed publications.

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arXiv2009

A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory

Compact elliptical galaxies are characterized by small sizes and high stellar densities. They are thought to form through tidal stripping of massive progenitors. However, only a handful of them were known, preventing us from understanding the role played by this mechanism in galaxy evolution. We present a population of 21 compact elliptical galaxies gathered with the Virtual Observatory. Follow-up spectroscopy and data mining, using high-resolution images and large databases, show that all the galaxies exhibit old metal-rich stellar populations different from those of dwarf elliptical galaxies of similar masses but similar to those of more massive early-type galaxies, supporting the tidal stripping scenario. Their internal properties are reproduced by numerical simulations, which result in compact dynamically hot remnants resembling the galaxies in our sample.

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arXiv2009

NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics and stellar populations

Lenticular galaxies are believed to form by a combination of environmental effects and secular evolution. We study the nearby disc-dominated S0 galaxy NGC 6340 photometrically and spectroscopically to understand the mechanisms of S0 formation and evolution in groups. We use SDSS images to build colour maps and light profile of NGC 6340 which we decompose using a three-component model including Sersic and two exponential profiles. We also use Spitzer images to study the morphology of regions containing warm ISM and dust. Then, we re-process and re-analyse deep long-slit spectroscopic data for NGC 6340 and recover its stellar and gas kinematics, distribution of age and metallicity with the NBursts full spectral fitting. We obtain the profiles of internal kinematics, age, and metallicity out to >2 half-light radii. The three structural components of NGC 6340 are found to have distinct kinematical and stellar population properties. We see a kinematical misalignment between inner and outer regions of the galaxy. We confirm the old metal-rich centre and a wrapped inner gaseous polar disc (r~1 kpc) having weak ongoing star formation, counter-rotating in projection with respect to the stars. The central compact pseudo-bulge of NGC 6340 looks very similar to compact elliptical galaxies. In accordance with the results of numerical simulations, we conclude that properties of NGC 6340 can be explained as the result of a major merger of early-type and spiral galaxies which occurred about 12 Gyr ago. The intermediate exponential structure might be a triaxial pseudo-bulge formed by a past bar structure. The inner compact bulge could be the result of a nuclear starburst triggered by the merger. The inner polar disc appeared recently, 1/3-1/2 Gyr ago as a result of another minor merger or cold gas accretion.

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arXiv2009

Virtual Observatory for Astronomers: Where Are We Now?

After several years of intensive technological development Virtual Observatory resources have reached a level of maturity sufficient for their routine scientific exploitation. The Virtual Observatory is starting to be used by astronomers in a transparent way. In this article I will review several research projects making use of the VO at different levels of importance. I will present two projects going further than data mining: (1) studies of environmental effects on galaxy evolution, where VO resources and services are used in connection with dedicated observations using a large telescope and numerical simulations, and (2) a study of optical and near-infrared colours of nearby galaxies complemented by the spectroscopic data.

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arXiv2008

Evolution of dwarf early-type galaxies I. Spatially resolved stellar populations and internal kinematics of Virgo cluster dE/dS0 galaxies

Understanding the origin and evolution of dwarf early-type galaxies remains an important open issue in modern astrophysics. Internal kinematics of a galaxy contains signatures of violent phenomena which may have occurred, e.g. mergers or tidal interactions, while stellar population keeps a fossil record of the star formation history, therefore studying connection between them becomes crucial for understanding galaxy evolution. Here, in the first paper of the series, we present the data on spatially resolved stellar populations and internal kinematics for a large sample of dwarf elliptical (dE) and lenticular (dS0) galaxies in the Virgo cluster. We obtained radial velocities, velocity dispersions, stellar ages and metallicities out to 1--2 half-light radii by re-analysing already published long-slit and integral-field spectroscopic datasets using the {\sc NBursts} full spectral fitting technique. Surprisingly, bright representatives of the dE/dS0 class ($M_B = -18.0 ... -16.0$ mag) look very similar to intermediate-mass and giant lenticulars and ellipticals: (1) their nuclear regions often harbour young metal-rich stellar populations always associated with the drops in the velocity dispersion profiles; (2) metallicity gradients in the main discs/spheroids vary significantly from nearly flat profiles to -0.9 dex $r_e^{-1}$, i.e. somewhat 3 times steeper than for typical bulges; (3) kinematically decoupled cores were discovered in 4 galaxies, including two with very little, if any, large scale rotation. These results suggest similarities in the evolutionary paths of dwarf and giant early-type galaxies and call for reconsidering the role of major mergers in the dE/dS0 evolution.

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