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Register a new userMagnetic fields and star formation in galaxies of different morphological types
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Authors
Marita Krause
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From our radio continuum and polarization observations of a sample of spiral galaxies with different morphological types, inclinations, and star formation rates (SFR) we found that galaxies with low SFR have higher thermal fractions/ smaller synchrotron fractions than those with normal or high SFR. Adopting an equipartition model, we concluded from our observations that the nonthermal radio emission and the total magnetic field strength grow nonlinearly with SFR. We also studied the magnetic field structure and disk thicknesses in highly inclined (edge-on) galaxies. We found in five galaxies that - despite their different radio appearance - the vertical scale heights for both, the thin and thick disk/halo, are about equal (0.3/1.8kpc), independently of their different SFR. They also show a similar large-scale magnetic field configuration, parallel to the midplane and X-shaped further away from the disk plane, independent of Hubble type and SFR in the disk. Hence we conclude that the amplification and formation of the large-scale magnetic field structure is independent of SFR.
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We study interstellar dust evolution in various environments by means of chemical evolution models for galaxies of different morphological types. We start from the formalism developed by Dwek (1998) to study dust evolution in the solar neighbourhood and extend it to ellipticals and dwarf irregular galaxies, showing how the evolution of the dust production rates and of the dust fractions depend on the galactic star formation history. The observed dust fractions observed in the solar neighbourhood can be reproduced by assuming that dust destruction depends the condensation temperatures T_c of the elements. In elliptical galaxies, type Ia SNe are the major dust factories in the last 10 Gyr. With our models, we successfully reproduce the dust masses observed in local ellipticals (~10^6 M_sun) by means of recent FIR and SCUBA observations. We show that dust is helpful in solving the iron discrepancy observed in the hot gaseous halos surrounding local ellipticals. In dwarf irregulars, we show how a precise determination of the dust depletion pattern could be useful to put solid constraints on the dust condensation efficiencies. Our results will be helpful to study the spectral properties of dust grains in local and distant galaxies.
The main observational results from radio continuum and polarization observations about the magnetic field strength and large-scale pattern for face-on and edge-on spiral galaxies are summarized and compared within our sample of galaxies of different morphological types, inclinations, and star formation rates (SFR). We found that galaxies with low SFR have higher thermal fractions/smaller synchrotron fractions than those with normal or high SFR. Adopting an equipartition model, we conclude that the nonthermal radio emission and the emph{total magnetic field} strength grow nonlinearly with SFR, while the regular magnetic field strength does not seem to depend on SFR. We also studied the magnetic field structure and disk thicknesses in highly inclined (edge-on) galaxies. We found in four galaxies that - despite their different radio appearance - the vertical scale heights for both, the thin and thick disk/halo, are about equal (0.3/1.8 kpc at 4.75 GHz), independently of their different SFR. This implies that all these galaxies host a galactic wind, in which the bulk velocity of the cosmic rays (CR) is determined by the total field strength within the galactic disk. The galaxies in our sample also show a similar large-scale magnetic field configuration, parallel to the midplane and X-shaped further away from the disk plane, independent of Hubble type and SFR in the disk. Hence we conclude that also the large-scale magnetic field pattern does not depend on the amount of SFR.
We study populations of soft and super-soft X-ray sources in nearby galaxies of various morphological types with the special emphasis on characterizing populations of stable nuclear burning accreting WDs. Analysing the content of Chandra archive we assembled a sample of nearby galaxies suitable for studying populations of super-soft X-ray sources. Our sample includes 4 spiral galaxies, 2 lenticular galaxies and 3 ellipticals with stellar mass exceeding $10^{10}$ $M_odot$ and X-ray sensitivity of the order of a ${rm few}times 10^{36}$ erg/s. We used combination of hardness ratio and median energy to pre-select X-ray sources with soft spectra, and temperature - X-ray luminosity diagram to identify super-soft X-ray sources - likely nuclear burning accreting white dwarfs. For spiral galaxies, there is a distinct and rare population of super-soft sources, largely detached from the rest of sources on the $kT_{bb}-L_X$ plane. The boundary between these sources and the much more numerous population of harder (but still soft) sources is consistent with the boundary of stable hydrogen burning on the white dwarf surface. Combined spectrum of soft sources located outside this boundary, shows clear emission lines of Mg and S, which equivalent width is similar to that in the combined spectrum of a large number of confirmed supernova remnants in M83. This confirms earlier suggestions that the vast majority of so called quasi-soft sources are supernova remnants. In early-type galaxies, populations of super-soft sources are about a factor of $approx 8$ less abundant, in broad agreement with the population synthesis calculations. Specific frequencies of super-soft sources are: (2.08$pm$0.46)$times10^{-10}$ M$_{odot}^{-1}$ in spiral galaxies and (2.47$pm$1.34)$times10^{-11}$ M$_{odot}^{-1}$ in lenticular and elliptical galaxies, with the ratio of the latter to the former of $0.12pm0.05$.
Radio continuum and polarization observations of several nearby galaxies allowed to determine their vertical scaleheights, magnetic field strengths and large-scale magnetic field patterns. They all show a similar large-scale magnetic field pattern, which is parallel to the galactic disk along the midplane and X-shaped further away from the disk plane, indepenent of their Hubble type or star formation in the disk or nuclear region. We conclude that - though a high star formation rate (SFR) in the disk increases the total magnetic field strength in the disk and the halo - the SFR does not significantly change the global field configuration nor influence the global scale heights of the radio emission. The observed similar scale heights indicate that star formation regulates the galactic wind velocities. The galactic wind itself may be essential for an effective dynamo action.
Stars and their exoplanets evolve together. Depending on the physical characteristics of these systems, such as age, orbital distance and activity of the host stars, certain types of star-exoplanet interactions can dominate during given phases of the evolution. Identifying observable signatures of such interactions can provide additional avenues for characterising exoplanetary systems. Here, I review some recent works on star-planet interactions and discuss their observability at different wavelengths across the electromagnetic spectrum.
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