Astronomy

Observational astronomy group headed by Prof. Finoguenov has been involved in 35 publications in 2014, with a number of topics covered. We continue our survey science by publishing a newly established algorithm for cluster identification (RedMapper), and pursue identification of galaxy groups and clusters in the prominent surveys  SDSS and  CFHTLS (Rykoff et al; Mirkazemi et al; Gozaliasl et al.). We continue our work on understanding the properties of galaxy cluster for the use in cosmological studies, using weak lensing to measure the cluster mass (Kettula et al.; Mulroy et al.). In the studies led by Dr Allevato we use the spatial clustering to shed light on the halo occupation of AGNs. One of the important results obtained is on early growth of black holes.

Another important topic covered by the publications in 2014 concerns the importance of galaxy groups in the star-formation at high-redshift Universe (Popesso et al. - two publications; Betherman et al.; Ziparo et al.; Mok et al.; Balogh et al.; Erfanianfar et al.). Extensive work on the properties of nearby groups under ZENS project has also been completed.

Research of interstellar medium continued with the analysis of Herschel and Planck satellite data. The final version of the Planck Galactic Cold Clump catalogue (PGCC) was completed and will be made public in early 2015. The catalogue contains some 13000 objects. These are dense clumps in Galactic interstellar clouds that represent an early stage in the process of star formation. A number of Planck fields have been investigated further with Herschel sub-millimetre observations, studies ranging from the large scale properties of interstellar cloud filaments to star formation in individual sources. Further studies have been made into interstellar extinction, light scattering, dust physics, and the chemistry of cold pre-stellar cloud cores.


    Ophiuchus-Herschel

Figure 13: Part of the Ophiuchus molecular cloud as seen by Herschel (Herschel Gould Belt Survey, P. André et al.). The cross marks a star forming core that, according to chemical models of H2D+ spectral lines, is least one million years old (Brünken, Sipilä et al. 2014, Nature 516, 219)

The major emphasis of the research on stellar magnetic activity was to combine observational studies with direct numerical magnetohydrodynamic (DNS-MHD) simulations. The research group continued to collect and analyse photometric, spectroscopic and spectropolarimetric observations of magnetically active late-type stars. The Nordic Optical Telescope and European Southern Observatory remained the most important sources for this data. Analysis of stellar spot activity in the stars DI Psc, LQ Hya, II Peg, sigma Gem, AF Lep, and V352 CMa was reported in refereed scientific articles. Important results included a confirmation of the drift of the active longitude in II Peg. By DNS-MHD using similar angular rotation velocity as in II Peg, an azimuthal dynamo wave was confirmed to be the most likely cause of this drift (Cole et al. 2014). This is an analogue to the latitudinal dynamo wave causing the butterfly diagram of sunspots.

The research was conducted by three senior scientists and four doctoral students in close cooperation with the ReSoLVE Center of Excellence, NORDITA, AIP (Potsdam), Tartu Observatory, CSC - IT Center for Science, and the Finnish Centre of Astronomy with ESO.

    Radial magnetic field - rapidly rotating star

Figure 14: Radial magnetic field near the surface of the star in a simulation of rapidly rotating convection. See also an associated video showing the azimuthal propagation of the large-scale non-axisymmetric field (http://www.youtube.com/watch?v=u55sAtN2Fqs).

In the theoretical extragalactic group our focus is on studying the formation and evolution of galaxies using numerical simulations run on high-performance computing facilities. Highlights for 2014 include running the first adaptive-mesh-refinement simulations that include radiative transfer. This simulation technique was used to model the collapse of massive gas clouds in the very early Universe and we demonstrated that this process can directly produce massive black holes with masses of the order of 100 000 solar masses. In addition we participated in observational studies of local interacting galaxies and used our numerical simulations to aid in the interpretation of the observational data. We also continued our investigations on the origin and ultimate faith of elliptical galaxies using both semi-analytic techniques and full cosmological simulations. 

2collapsingclouds

Figure 15: The two panels compare the temperature (left panels) and density (right panels) structure of two collapsing gas clouds, as a function of the intensity of the background ultraviolet radiation field. In the top panels the intensity of the UV field is 100x larger than in the bottom panels.  (Regan, Johansson, Wise, 2014, Astrophysical Journal, 795, 137)

In planetary system research, our focus is on asteroids and comets as well as on small particles in regoliths and atmospheres, including the atmosphere of the Earth. In 2014, our activity has culminated in the organization of the international conference entitled "Asteroids, Comets, Meteors 2014" in Helsinki on June 30 - July 4, 2014 (http://www.helsinki.fi/acm2014/). With almost 500 participants from more than 40 countries, the conference turned out to be a complete success. According to the participant feedback, a new standard was set for the ACM conferences regularly held since 1983.

Studies on electromagnetic scattering by small particles and random media composed of such particles have continued with funding from the ERC Advanced Grant project entitled "Scattering and absorption of electromagnetic waves in particulate media" (SAEMPL) and the Academy of Finland Consortium project entitled "Electromagnetic Wave Scattering in Complex random Media".

The primary goal of the SAEMPL project is theoretical, that is, the development of an unprecedented numerical method for multiple scattering by close-packed media of small particles. For the validation of the method, the SAEMPL project includes an experimental component including the development of a nano-mechanical device for scattering measurements for single particles and media of such particles.

In more detail, we have discussed the spectral properties of the volume integral equation for electromagnetic scattering by a dielectric object. The analysis shows that the spectrum of the volume-integral operator depends on the material parameter, and it explains the poor convergence of the iterative solution when the permittivity function is strongly discontinuous.  We further introduce a higher-order discretization procedure for the electric-current volume-integral equation. Numerical results show that the proposed technique increases the accuracy of the solution compared with the standard discretization, without deteriorating the stability of the method. A review of integral equations and their discretizations by the method of moments in computational electromagnetics was published.
In studies of coherent backscattering by media of spherical particles, we were able to map the evolution of the light scattering response from that of finite media of particles to an essentially infinite regolith of particles. A comparison of the so-called discrete exterior calculus method (DEC) and the discrete-dipole approximation method (DDA) for electromagnetic scattering was published, validating the novel DEC method.
We pioneered a stereogrammetric method to model the shapes of micron-sized mineral dust particles for light-scattering computations. They showed that traditionally used, simplified shape models are not versatile enough to capture the true variability in both the shapes and scattering properties of real dust particles.
Astronomical observations have been carried out using the Hubble Space Telescope for Comet ISON as well as the Rosetta mission target comet 67P/Churyumov-Gerasimenko. As to ESA’s astrometry mission Gaia (launch in December 20, 2013), our software for statistical inversion of asteroid orbits has been successfully utilized to real Gaia data in fall 2014, constituting a major operational achievement. We continue our involvement in the BepiColombo mission to planet Mercury. We also assess the risk of near-Earth asteroid collisions and participate in the Canadian NEOSSat mission as well as in the proposed ESA main-belt comet mission Castalia. In the StreakDet project funded by ESA, we have developed automated pattern recognition methods and software for the analysis of space-debris streaks in both ground-based and space-based imaging data.

In laboratory experiments, we focused on the simulations of space weathering and its effects on the spectrum of reflected light, the physical properties of meteorites, and the internal structure of the cosmic dust particles.  As a result of space weathering simulations, it was found that space weathering progresses logarithmically with time. This explains the observed rapid onset of space weathering on fresh planetary surfaces, while old mature planetary surfaces are saturated and do not show substantial spectral changes.  The meteorite physical properties investigations were focused on the Chelyabinsk and Košice meteorite falls. While the Košice meteorites are homogeneous, the Chelyabinsk meteorites show variations in their shock level. While the light-colored meteorites are of low shock level, the dark-colored meteorites are heavily shocked with signs of partial or complete melting. Such a shock is caused by a collision of the Chelyabinsk parent body with another asteroid during the early evolution of the Solar System. Investigations of cosmic dust using X-ray microtomography revealed changes in the internal structure during the high-velocity atmospheric entry. At low entry velocities, no changes are observed. At high entry velocities, partial melting of the dust particles occurs during deceleration associated with temporary increase in porosity followed by subsequent complete melting and porosity reduction. 

Tomographysection

Figure 16: Tomography section of a partially molten porous cosmic dust particle (approximately 170 micrometers in size).