Olga Melnyk

Angular correlation functions of X-ray point-like sources in the full exposure XMM-LSS field

Aims. Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. Methods. We measure the two-point angular correlation function of ∼5700 and 2500 X-ray point-like sources over the ∼11 sq. deg. XMM-LSS field in the soft (0.5–2 keV) and hard (2–10 keV) bands. For the conversion from the angular to the spatial correlation function we used the Limber integral equation and the luminosity-dependent density evolution model of the AGN X-ray luminosity function. Results. We have found significant angular correlations with the power-law parameters γ = 1.81 ± 0.02, θ0 = 1.3 �� ± 0.2 �� for the soft, and γ = 2.00 ± 0.04, θ0 = 7.3 �� ± 1.0 �� for the hard bands. The amplitude of the correlation function w(θ) is higher in the hard than in the soft band for fx < 10 −14 erg s −1 cm −2 and lower above this flux limit. We confirm that the clustering strength θ0 grows with the flux limit of the sample, a trend which is also present in the amplitude of the spatial correlation function, but only for the soft band. In the hard band, it remains almost constant with r0 � 10 h −1 Mpc, irrespective of the flux limit. Our analysis of AGN subsamples with different hardness ratios shows that the sources with a hard-spectrum are more clustered than soft-spectrum ones. This result may be a hint that the two main types of AGN populate different environments. Finally, we find that our clustering results correspond to an X-ray selected AGN bias factor of ∼2.5 for the soft band sources (at a median ¯ � 1.1) and ∼3.3 for the hard band sources (at a median ¯ ,

Catalog of Isolated Galaxies Selected from the 2MASS Survey

We search for isolated galaxies based on the automatic identification of isolated sources from the Two Micron All-Sky Survey (2MASS) followed by a visual inspection of their surroundings. We use the modified Karachentseva criterion to compile a catalog of 3227 isolated galaxies (2MIG), which contains 6% of 2MASS Extended Sources Catalog (or 2MASX) sources brighter than Ks = 12m with angular diameters aK ≥ 30″. The catalog covers the entire sky and has an effective depth of z ∼ 0.02. The 2493 very isolated objects of the catalog, which we include into the 2MVIG catalog, can be used as a reference sample to investigate the effects of the environment on the structure and evolution of galaxies located in regions with extremely low density of matter.

Low-density structures in the Local Universe. II. Nearby cosmic voids

We present the results of the search for spherical volumes containing no galaxies with luminosities brighter than the Magellanic Clouds in the Local Supercluster and its vicinity. Within a distance of 40 Mpc from us, 89 cosmic voids were discovered with the diameters of 24 to 12 Mpc, containing no galaxies with absolute magnitudes brighter than MK < −18.4. A list of these voids and the sky distribution maps are given. It was found that 93% of spherical voids overlap, forming three more extended percolated voids (hypervoids). The largest of them, HV1, has 56 initial spherical cells and extends in a horseshoe shape, enveloping the Local Volume and the Virgo cluster. The Local Void (Tully, 1988) in the Hercules-Aquila region is the closest part of the HV1. Another hypervoid, HV2, contains 22 spherical voids in the Eridanus constellation, and the third compact hypervoid (HV3) comprises 6 spherical cells in the Bootes. The total volume of these voids incorporates about 30% of the Local Universe. Among 2906 dwarf galaxies excluded from the original sample (n = 10502) in the search for spherical volumes, only 68 are located in the voids we have discovered. They are characterized by late morphological types (85% are Ir, Im, BCD, Sm), absolute magnitudes MB ranging from −13.0 to −16.7, moderate star formation rates (log SSFR ∼ −10 M⊙ yr−1L−1⊙) and gas reserves per luminosity unit twice to three times larger than in the other dwarf galaxies located in normal environments. The dwarf population of the voids shows a certain tendency to sit shallow near the surfaces of cosmic voids.

Faint companions of isolated 2MIG galaxies

We present the results of a search for companions around the isolated galaxies from the 2MIG catalog. Among 3227 2MIG galaxies we detected 125 objects with a total of 214 neighbors having radial velocity differences of ΔV < 500 km/s and projected separations of Rp < 500 kpc relative to the 2MIG galaxies. The median luminosity of the companions is 1/25 of the luminosity of catalog galaxies, which has little effect on the dynamic isolation of the latter. The median ratio of the orbital mass to the K-luminosity determined from 60 companions of E and S0 2MIG galaxies, 63M⊙/L⊙, is significantly greater than that found from the spiral galaxy companions (17M⊙/L⊙). We note that a fraction of 2MIG galaxies with companions may be a part of low-contrast diffuse structures: clouds and filaments.

Star formation in nearby isolated galaxies

I. D. Karachentsev, 2 V. E. Karachentseva, O. V. Melnyk, 5 and H. M. Courtois Special Astrophysical Observatory of the Russian AS, Nizhnij Arkhyz 369167, Russia Leibniz-Institut für Astrophysik (AIP), Potsdam, D-14482 Germany Main Astronomical Observatory, National Academy of Sciences, Kiev, 03680 Ukraine Astronomical Observatory, Taras Shevchenko Kiev National University, Kiev, 04053 Ukraine Institut d’Astrophysique et de Géophysique, Université de Liège, B5C Belgique Université de Lyon, Institut de Physique Nucléaire de Lyon, Villeurbanne, 69100 France (Received April 23, 2013; Revised June 3, 2013)We use the FUV fluxes measured with the GALEX to study the star formation properties of galaxies collected in the “Local Orphan Galaxies” catalog (LOG). Among 517 LOG galaxies having radial velocities VLG < 3500 km/s and Galactic latitudes |b| > 15°, 428 objects have been detected in FUV. We briefly discuss some scaling relations between the specific star formation rate (SSFR) and stellar mass, HI-mass, morphology, and surface brightness of galaxies situated in extremely low density regions of the Local Supercluster. Our sample is populated with predominantly late-type, gas-rich objects with the median morphological type of Sdm. Only 5% of LOG galaxies are classified as early types: E, S0, S0/a, however, they systematically differ from normal E and S0 galaxies by lower luminosity and presence of gas and dust. We find that almost all galaxies in our sample have their SSFR below 0.4 [Gyr−1]. This limit is also true even for a sample of 270 active star-burst Markarian galaxies situated in the same volume. The existence of such a quasi-Eddington limit for galaxies seems to be a key factor which characterizes the transformation of gas into stars at the current epoch.

Search for gravitational lens candidates in the XMM-LSS/CFHTLS common field

Our aim was to identify gravitational lens candidates among some 5500 optical counterparts of the X-ray point-like sources in the medium-deep ~11 sq. deg. XMM-LSS survey. We have visually inspected the optical counterparts of each QSOs/AGN using CFHTLS T006 images. We have selected compact pairs and groups of sources which could be multiply imaged QSO/AGN. We have measured the colors and characterized the morphological types of the selected sources using the multiple PSF fitting technique. We found three good gravitational lens candidates: J021511.4-034306, J022234.3-031616 and J022607.0-040301 which consist of pairs of point-like sources having similar colors. On the basis of a color-color diagram and X-ray properties we could verify that all these sources are good QSO/AGN candidates rather than stars. Additional secondary gravitational lens candidates are also reported.

Low density structures in the local universe. I. Diffuse agglomerates of galaxies

This paper is the first of a series considering the properties of distribution of nearby galaxies in the low density regions. Among 7596 galaxies with radial velocities VLG < 3500 km/s, absolute magnitudes MK < −18ṃ4, and Galactic latitudes |b| > 15° there are 3168 field galaxies (i.e. 42%) that do not belong to pairs, groups or clusters in the Local universe. Applying to this sample the percolation method with a radius of r0 = 2.8Mpc, we found 226 diffuse agglomerates with n ≥ 4 number of members. The structures of eight most populated objects among them (n ≥ 25) are discussed. These non-virialized agglomerates are characterized by amedian dispersion of radial velocities of about 170 km/s, the linear size of around 6 Mpc, integral K-band luminosity of 3 × 1011L⊙, and a formal virial-mass-to-luminosity ratio of about 700M⊙/L⊙. The mean density contrast for the considered agglomerates is only

Colours of isolated galaxies selected from the Two-Micron All-Sky Survey

\left\langle {\Delta n/\bar n} \right\rangle

Predicted multiply imaged X-ray AGNs in the XXL survey

∼ 5, and their crossing time is about 30–40 Gyr.

3-D Voronoi's Tessellation as a Tool for Identifying Galaxy Groups

The properties of isolated galaxies are mainly driven by intrinsic evolution and not by the external influence of their environments. Therefore the isolated galaxy sample may be considered as a reference sample to study different environmental effects. We made detailed comparisons between the near-infrared (2MASS) and optical (SDSS) colours of the 2MASS XSC selected sample of isolated 2MIG galaxies and with other objects from the wide range of denser environments (field, groups/clusters, triplets and pairs). We found that early type galaxies show similar (J-H)rest and (g-r)rest colours practically in all types of environments. Exception is for the massive early type galaxies located in compact pairs with high velocity difference (dV~180 km/s), which are significantly redder and brighter than isolated galaxies. We assume that these pairs are located in the centres of more populated groups and clusters. In general, galaxies in groups and pairs of spiral and late morphological types have redder near-infrared colours (J-H)rest than 2MIG isolated galaxies. The (g-r)rest colours of galaxies in groups and pairs with high velocity difference are also significantly redder than corresponding colours of 2MIG galaxies. On the contrary, the members of most compact pairs (dV~50 km/s, R~30 kpc) show the same (g-r)rest colour and even tend to be bluer than 2MIG galaxies. In summary, our results show that the colours of galaxies are strongly depend on the external factors.