arXiv subjects

P. Nurmi

Publications and source records attributed to P. Nurmi.

23 records · Page 2Linked to original sources

arXiv2007

The richest superclusters. II. Galaxy populations

We study the morphology of galaxy populations of the richest superclusters from the catalogue of superclusters of galaxies in the 2dF Galaxy Redshift Survey using the luminosity density distribution and Minkowski functional V3. We compare the properties of grouped and isolated galaxies in regions of different density in superclusters. We find that in high-density cores of rich superclusters there is an excess of early type, passive galaxies, among galaxies in groups and clusters, as well as among those which do not belong to groups, while in lower density outer regions there are more blue, star-forming galaxies both in groups and among those galaxies which do not belong to groups. This also shows that the galaxy content of groups depends on the environment where the groups reside in. The density distributions and the behaviour of the Minkowski functional V3 for different superclusters show that substructures in superclusters as traced by different populations of galaxies are very different. Our results show that both local (group/cluster) and global (supercluster) environments are important in forming galaxy morphologies and star formation activity. The presence of a high density core with X-ray clusters and a relatively small fraction of star-forming galaxies in the supercluster SCL126 may be an indication that this supercluster has started its evolution earlier than the supercluster SCL9.

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arXiv2007

The richest superclusters. I. Morphology

We study the morphology of the richest superclusters from the catalogues of superclusters of galaxies in the 2dF Galaxy Redshift Survey and compare the morphology of real superclusters with model superclusters in the Millennium Simulation. We use Minkowski functionals and shapefinders to quantify the morphology of superclusters: their sizes, shapes, and clumpiness. We generate empirical models of simple geometry to understand which morphologies correspond to the supercluster shapefinders. We show that rich superclusters have elongated, filamentary shapes with high-density clumps in their core regions. The clumpiness of superclusters is determined using the fourth Minkowski functional $V_3$. In the $K_1$-$K_2$ shapefinder plane the morphology of superclusters is described by a curve which is characteristic to multi-branching filaments. We also find that the differences between the fourth Minkowski functional $V_3$ for the bright and faint galaxies in observed superclusters are larger than in simulated superclusters.

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arXiv2006

Subhaloes in $Λ$CDM cosmological simulations: I. Masses and abundances

If the concordance $Λ$CDM model is a true description of the universe, it should also properly predict the properties and structure of dark matter haloes, where galaxies are born. Using N-body simulations with a broad scale of mass and spatial resolution, we study the structure of dark matter haloes, the distribution of masses and the spatial distribution of subhaloes within the main haloes. We carry out three $Λ$CDM simulations with different resolutions using the AMIGA code. Dark matter haloes are identified using an algorithm that is based on the adaptive grid structure of the simulation code. The haloes we find encompass the mass scales from $10^8\mathrm{M}_{\sun}$ to $10^{15}\mathrm{M}_{\sun}$. We find that if we have to study the halo structure (search for subhaloes), the haloes have to contain at least $10^4$ particles. For such haloes, where we can resolve substructure, we determined the subhalo mass function and found that it is close to a power law with the slope -0.9 (at present time), consistent with previous studies. This slope depends slightly on the redshift and it is approximately the same for main haloes. The subhalo mass fraction ($M_{\s subH}/M_{\s MH}$) is between 0.08 and 0.2, increasing slightly with redshift and with the mass of the main halo. Its distribution is approximated using the Weibull distribution at different epochs. The mean values of subhalo mass are independent of the main halo mass. The spatial density of subhaloes, scaled to the virial radius of the main halo ($r_{\s vir}$), is independent of redshift and follows the $r^{1/3}$ rule.

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arXiv2006

Computing secular motion under slowly rotating quadratic perturbation

We consider secular perturbations of nearly Keplerian two-body motion under a perturbing potential that can be approximated to sufficient accuracy by expanding it to second order in the coordinates. After averaging over time to obtain the secular Hamiltonian, we use angular momentum and eccentricity vectors as elements. The method of variation of constants then leads to a set of equations of motion that are simple and regular, thus allowing efficient numerical integration. Some possible applications are briefly described.

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arXiv2001

Optical and radio variability of the BL Lac object AO 0235+16: a possible 5-6 year periodicity

New optical and radio data on the BL Lacertae object AO 0235+16 have been collected in the last four years by a wide international collaboration, which confirm the intense activity of this source. The optical data also include the results of the Whole Earth Blazar Telescope (WEBT) first-light campaign organized in November 1997. The optical spectrum is observed to basically steepen when the source gets fainter. We have investigated the existence of typical variability time scales and of possible correlations between the optical and radio emissions by means of visual inspection, Discrete Correlation Function analysis, and Discrete Fourier Transform technique. The major radio outbursts are found to repeat quasi-regularly with a periodicity of about 5.7 years; this period is also in agreement with the occurrence of some of the major optical outbursts, but not all of them.

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