The study of strongly star-forming galaxies: their physical characteristics as a function of morphology and IR-luminosity
Kimani, Naftali Kagiri
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The Infrared Astronomical Satellite (IRAS) all-sky survey i.e. 96% of the sky in the thermal infrared observing in four. bands 12, 25, 60 and 1OOJ-Lm detected a very large number of extragalactic sources that were bright at mid/far infrared from less than 106L0 to about 1013L0 up to a redshift z '" 0.3. The observed galaxies generated a lot of interest due to their immense luminosities, dusty nature and their large numbers at high redshifts. Later studies have indicated that more than 70% of these objects are involved in interactions. These interactions are a common process in the evolution of galaxies in the distance universe. They are difficult to study in detail due to the distances involved. This study focussed on strongly star forming galaxies in the nearby universe at a redshift 0.003 ~ z ~ 0.010 having Far-Infrared emission of 1010.22L0 to 1Oll.31 L0 using longslit optical spectroscopy. Data collection was done using 1.9m Radcliffe Telescope mounted at Sutherland, South Africa. SITe1 Charge-coupled Detector (CCD) chip was used to record data which were then read out and stored in multi-extension FITS file. IRAF and Python softwares were used in data reduction, analysis and presentation. The total visual dust extinction (Av) and Ho dust extinction (AHa) obtained were in the range 0.75 - 3.54 and 0.56 - 2.65 respectively attributed to the presence of dust in the interstellar medium (ISM). However, all the strongly star forming galaxies in the sample were metal-rich (8.43' ~ 12+log(O/H) ~ 8.81) indicating they have undergone massive chemical evolution. The Ho star-formation rate in this sample was in the range 0.04 - 2.4M0yr-l. The emission line ratios suggested HII regions of purely star-forming regions and shock-heating mechanism. The derived molecular gas masses were in the range (0.2 - 4.9) x 1Q6M0, the total dust masses ranging between 3.6 x 105 - 3.4 x 107M0' while the nuclear galaxy masses interior of the maximum rotational velocity was in the range of 3.1 x 106 - 7.2 x 108M0. The overall galaxy masses were in the range between 6.0 x 107 - 3.2 x 1OlOM0. The sample was observed to have a strong correlation between SFR and color excess, total dust mass, total galaxy mass and Ho luminosity. The same correlation was identified between galaxy mass and maximum rotational velocity and also between Mdust!Mgas ratio and metallicities.