1 / 17

Radio continuum observations of the Sombrero galaxy NGC4594 (M104) and other edge-on spirals

Radio continuum observations of the Sombrero galaxy NGC4594 (M104) and other edge-on spirals. Marita Krause MPIfR, Bonn Michael Dumke ESO, Chile Richard Wielebinski MPIfR, Bonn. Outline

nadda
Télécharger la présentation

Radio continuum observations of the Sombrero galaxy NGC4594 (M104) and other edge-on spirals

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Radio continuum observations of the Sombrero galaxy NGC4594 (M104) and other edge-on spirals Marita Krause MPIfR, Bonn Michael Dumke ESO, Chile Richard Wielebinski MPIfR, Bonn

  2. Outline • Introduction of M104 and the new observations in the radio polarization and • sub-mm observations • How can we observe the magnetic field by radio polarization? • Some examples of the large-scale magnetic field in some face-on spiral galaxies • What are the results of radio polarization observations for edge-on galaxies? • Presentation and discussion of the results for M104

  3. M104: Sa galaxy HI ring/spiral arm at ± 140 ″,170″ d = 8.9 Mpc CO at ± 140 ″ nucleus is LINER, inner disk < r=15’’, central BH with 109 M☼ i = 84 º p.a. = 90 º HST image 3kpc=70“

  4. Emsellem (1995): spatial photometric model → not only extinction, but also light scattering by dust → galaxy would appear dust free if viewed face-on, significant cold dust expected in M104 which should be detectable in mm / sub-mm wavelength range i = 84 º p.a. = 90 º HST image

  5. PIis uneffected by reversals of B RM is sensitive to direction of B

  6. Sombrero galaxy M104: Linear polarization at λ = 6.2 cm (VLA) λ = 3.6 cm (100-m Effelsberg) Sub-mm continuum at λ =870 μm (HHT, Arizona) Is M104 a `normal´ spiral galaxy? Where does the huge bulge come from? Comparison with other edge-on galaxies like NGC891, NGC4631, NGC3628, NGC5907, NGC4565

  7. Magnetic field strength from synchrotron intensities • Assumtions: • Equipartitionbetween the average energy densities of cosmic rays and magnetic field • Results: • Average strength of total field (74 spirals): 9 ± 3 µG • Average strength of regular field: 1-5 µG • Maximum strength of total field in spiral arms: • 25 µG (NGC6946), 35 µG (M51) • Strength of regular field in interarm regions: • 10 µG (NGC6946), 15 µG (M51)

  8. Dumke, Krause et al., 1995

  9. Plane-parallel B-field is expected by the dynamo theory for differential rotation. • Thin disk (300 pc) and thick disk (1.8 kpc), except for NGC 4631 Dumke, Krauseet al.1995

  10. Edge-on Galaxies • Most galaxies have a magnetic field configuration parallelto the disk. • NGC891, NGC3628, NGC4565 and NGC5907 have all similar exponential scale heights for the thinandthickdisk/halo (0.3 / 1.8 kpc) resp., despite their different star forming activties. NGC4631 has only about 50% larger scale heights. • NGC4631 has a vertical magnetic field in the central ~7 kpc, M82, NGC4666 and NGC5775 have also vertical fields.

  11. M104 HST image

  12. M104 VLA 6cm 23“HPBW • First detection of large-scale • magnetic field in an Sa galaxy • Increasing vrot up to r = 8 kpc (180 “) • Gaussian z-distribution with scale heights of about 1.4 kpc in TP and PI (thin disk inside • huge mass distribution, the huge bulge)

  13. RM < ± 100 rad/m² for most points → M104 B-vectors • B is parallel to disk in midplane • significant vertical components at higher z • Bt = 6 ± 1 μG, Breg = 3 ± 1 μG • → magnetic field in M104 is similar to that of other edge-on galaxies

  14. HHT observations at λ870μm Where does the huge bulge comes from? Is Emsellem‘s dust model correct? • Detection in the nuclear region with • S 870μm = 230 ± 35 mJy • Upper limit fo extended emission of • (r.m.s. = 40 mJy/beam at 40”HPBW) • S 870μm≤ 200 mJy → with T = 22 K: M cold dust ≤ 1.2 107 M☼ (Emsellem: M cold dust ≥ 8 106 M☼)

  15. Where does the huge bulge comes from? • Simulations of galaxy evolution revealed that bars form and dissolve. • A spherical bulge can evolve while the bar starts to decrease. • →The bulge in M104 may be due to a dissolving bar(first proposed by • Emsellem, 1995) • A dissolving of a bar is a relatively short-living period compared to a galaxy‘s lifetime → This evolutionary phase should be observable only in a few number of galaxies. • The large-scale magnetic field seems to have persisted during the galaxy‘s evolution.

  16. Conclusions: • Our dust observations support Emsellem‘s dust model (i.e. M104 would look dust free if viewed face-on). • We have detected a large scale magnetic field in M104 with a typical configuration for spiral galaxies seen edge-on. • The idea that the bulge is due to a dissolving bar (in a short-living evolutionary phase) also explains the outstanding appearance of M104 (as observable with present telescopes) → M104 seems to be a ‘normal‘ early type galaxy in a special (short-living) evolutionary phase.

  17. Thank you

More Related