Sains Malaysiana 44(3)(2015): 457–462
The
Nonlinear Least Square Fitting for Rotation Curve of Orion Dwarf Spiral
(Penyuaian Kuasa Dua Terkecil Tak Linear bagi Putaran Lengkung Orion
Kerdil Berpilin)
N. HASHIM1*, Z.Z. ABIDIN2, U.F.S.U. IBRAHIM1, M.S.R. HASSAN2, Z.S. HAMIDI2, R. UMAR4 & Z.A. IBRAHIM3
1Centre for Foundation
Studies in Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
2Radio Cosmology
Research Lab, Physics Department, Faculty of Science, Universiti Malaya
50603 Kuala Lumpur, Malaysia
3Faculty of Applied
Sciences, Universiti Teknologi MARA (UiTM), 40450
Shah Alam, Selangor Darul Ehsan, Malaysia
4Astronomy Unit,
Universiti Sultan Zainal Abidin, 21300 Kuala Terengganu, Terengganu
Darul Iman, Malaysia
Diserahkan: 15 Januari 2014/Diterima: 21 Ogos 2014
ABSTRACT
The basis of the nonlinear least square fitting is to fit the
nonlinear rotation curve model with the observed rotation curve of the Orion
dwarf galaxy. It has been the most powerful tool to study the distribution of dark
matter in galaxies where it is used to obtain the proper mass model of a
galaxy. In this paper, we present the rotation curve fit of Orion dwarf galaxy,
corrected for asymmetric drift by using the gradient method of nonlinear least
square. Our results showed an excellent agreement between the mass models of
cored halo profile with the observed rotation curve. Thus, we can estimate the
value of disk mass, MD; the core radius, r0 and
core density, roof the galaxy with 1-s of
uncertainty. We finally indicated the dark matter halo distribution as cored
dark matter halo with density, 3.9 × 106MŸ kpc-3.
Keywords: Dwarf spiral - rotation curve - dark matter; fitting;
galaxies; gradient method
ABSTRAK
Asas kepada penyuaian kuasa dua terkecil tak
linear adalah menyuaikan model putaran lengkung dengan cerapan putaran lengkung
galaksi Orion kerdil. Ia telah menjadi kaedah yang paling berkuasa dalam kajian taburan
jirim gelap di dalam galaksi dan ia digunakan untuk
mendapatkan model jisim yang bersesuaian untuk suatu galaksi. Di dalam artikel ini, kami mempersembahkan suaian putaran lengkung
bagi galaksi Orion kerdil yang telah dibetulkan pecutan asimetri dengan
menggunakan kaedah kecerunan daripada kuasa dua terkecil tak linear. Keputusan yang kami peroleh menunjukkan keselarian yang cemerlang antara model
jisim profil halo teras dengan cerapan putaran lengkung. Justeru,
kami boleh menganggarkan nilai jisim cakera, MD; jejari teras, r0 dan
ketumpatan teras, ro bagi suatu galaksi di bawah 1-s
ketidakpastian. Kami juga akhirnya menunjukkan bahawa taburan halo jirim
gelap adalah halo jirim gelap berteras dengan ketumpatan, 3.9 × 106MŸ kpc-3.
Kata kunci: Galaksi; kaedah
kecerunan; kerdil berpilin - putaran lengkung - jirim gelap; penyuaian
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*Pengarang
untuk surat-menyurat; email: norsiahashim@um.edu.my
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