Sains Malaysiana 51(4)(2022): 1271-1282

http://doi.org/10.17576/jsm-2022-5104-25

Analyzing Interferometric CO (3-2) Observations of NGC 4039

(Menganalisis Interferometrik CO (3-2) Pemerhatian NGC 4039)

JAZEEL H. AZEEZ^1,*, ZAMRI ZAINAL ABIDIN², SADEEM ABBAS FADHIL¹ & CHORNG-YUAN HWANG³

¹Al-Nahrain University, Faculty of Science, Physics Department, Baghdad 10072, Iraq

²Physics Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

³National Central University, Graduate Institute of Astronomy, Chung-Li, 32054, Taiwan

Received: 12 August 2021/Accepted: 25 October 2021

Abstract

Starburst merging galaxies are important in the history of galaxy evolution timeline. For this work, we have chosen the Antennae galaxy (NGC4039), which is one of the most famous starburst merging galaxies. We analyzed the CO (3–2) interferometric observations for the southern mosaic of the NGC 4039, together with the CO (2–1) data taken from Atacama Large Millimeter/Sub-millimeter Array (ALMA). Using the galactic CO luminosity to H₂ mass conversion factor, we found molecular gas mass range in this galaxy to be (0.8–2.92) × 10⁸ M_ʘ. Line emissions at CO (2–1) and CO (3–2) were detected at selected regions in the nucleus of NGC 4039. The CO (3–2) / CO (2–1) ratio for this galaxy was calculated to be approximately 0.62. In addition, we found a significant correlation between the brightness temperature ratio and IR luminosity for this galaxy. We used a new model to interpret the rotation curve and found that the most important factor is related to gas mass distribution. The disturbance in the gas distribution may be caused by the merging process. We have also analyzed the spatially resolved star formation law in this galaxy up to 345 parsec. We found a breakdown of the Kennicutt–Schmidt law at this scale. The results are consistent with the previous findings that there is a possibility of sub-thermally excited widespread gas in the neighborhood of denser regions, which causes the flatter star formation law.

Keywords: Galaxy evolution; NGC 4039; rotation curve; starburst; star formation

Abstrak

Galaksi percantuman ledakan bintang adalah penting dalam sejarah garis masa evolusi galaksi. Dalam kajian ini, kami memilih galaksi Antennae (NGC4039) yang merupakan salah satu galaksi percantuman ledakan bintang yang terkenal. Kami menganalisis hasil cerapan interferometer CO (3-2) bagi mozek selatan NGC4039, bersama-sama dengan data CO (2-1) yang diambil daripada Atacama Large Millimeter/Sub-millimeter Array (ALMA). Dengan menggunakan faktor penggubah kecerahan CO untuk galaksi kepada jisim H₂, kami mendapati bahawa julat jisim gas molekul adalah (0.8–2.92) × 10⁸ M_ʘ. Nisbah CO (3–2)/CO (2–1) untuk galaksi ini telah dihitung sebagai lebih kurang 0.62. Tambahan pula, kami mendapati hubungan ketara antara nisbah suhu kecerahan dan IR kelumenan bagi galaksi ini. Kami menggunakan suatu model baharu bagi menginterpretasi lengkung putaran dan mendapati bahawa faktor terpenting bagi model ini berkait dengan pembahagian jisim gas. Sebarang gangguan dalam pembahagian gas mungkin disebabkan oleh proses percantuman. Kami juga telah menganalisis hukum kejadian bintang reruang terlerai dalam galaksi ini sehingga 345 parsec. Kami mendapati hukum Kennicutt–Schmidt gagal pada skala ini. Keputusan kajian ini adalah tekal dengan keputusan sebelum ini yang berkemungkinan terdapat gas tersebar teruja secara sub-terma dalam kawasan kejiranan yang lebih padat dan ini akan menjadikan hukum kejadian bintang yang lebih rata.

Kata kunci: Evolusi galaksi; ledakan bintang; lengkuk putaran; NGC 4039; pembentukan bintang

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^*Corresponding author; email: jazeelhussein@yahoo.com