1. University of Mauritius
GMRT observations of a sample of extragalactic radio sources at 618 MHz
Assoc. Prof Somanah R
University of Mauritius
Dr. Oozeer Nadeem
HartRAO

2. Outline Low frequency survey The Mauritius Radio Telescope Our sample
GMRT observations
Preliminary Analysis & Results
Conclusion

4. Low frequency survey
utility in identifying classes of objects that can be observed at other wavelengths
less affected by optical depth and beaming
provides samples with an isotropic source distribution.
particular interest for finding radio galaxies, especially those at large redshifts.

5. AGN

6. Analytical model of FRII source
Q - energy supplied per unit time
U - energy density
r - distance frome core
Assume density IGM = k r - α

7. The Mauritius Radio Telescope (MRT)‏
T-shaped Fourier synthesis non- coplanar array
2048 m long East-West (EW) arm
880 m long North-South (NS) arm
operating at Mhz.
EW fixed helices arranged in 32 groups at the same height but the different groups are at not co-planar.

8. Elements – Helical antenna

9. MRT layout

10. DATA processing steps at MRT
Data Selection
Calibration
Fourier Transform
Deconvolution
Source extraction

11. Dirty Image

12. CLEANed image

13. Galactic centre at MHz

14. SNRs in the galactic plane

15. VELA SNR

17. Extragalactic radio sources from MRT survey

18. Spectra

19. Giant Metre wave radio Telescope
Pune India
30 parabolic mesh grid dish of 45m diameter each
Y-shaped
Shortest spacing 60m (central square)‏
Longest spacing 25 km

20. GMRT follow up Sample
selected from the MRC using similar criteria as the MRC/1Jy sample
14h04m < RA < 20h20m
-30o < dec < -20o
No of sources 117 sources
Frequency 618 Mhz
Snapshots 3 x 15 min each

21. Sample Region

22. MRC MRC

23. MRC MRC

24. Spectra of some sources

25. Results
By considering the spectral index a of the sources in the MRC/1Jy-B sample (107 sources), between MHz and the 408 MHz:
27.3% of the sources show ultra steep spectrum
67.3% show steep spectrum features and
remaining, 4.6% were flat spectrum sources.

26. Morphology 41% - singles or unresolved,
49% - apparent double structures
5% - triple sources
5% - complex structures.

27. MRC