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arXiv 2103.08287astro-ph.HEastro-ph.GA
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切伦科夫望远镜阵新探测邻近成星星系的前景

Prospects of newly detecting nearby star-forming galaxies by the Cherenkov Telescope Array

Naoya Shimono, Tomonori Totani, Takahiro Sudoh

摘要:

讨论了切伦科夫望远镜阵列(CTA)在研究邻近恒星形成星系甚高能γ射线辐射方面的应用前景。在以前的工作中,我们建立了一个模型来计算宇宙射线与星际介质(ISM)相互作用产生的π衰变γ射线发射的光度和能谱,从四个物理量星系[恒星形成率(SFR),气体质量,恒星质量和有效半径]。该模型与观测到的几个邻近星系的GeV-TeV辐射符合得很好。应用这个模型尚未检测到的TeV(主要是从KINGFISH目录)附近的星系,它们的强子伽马射线光度和光谱进行了预测。我们确定了CTA检测机会最高的星系,包括NGC 5236,M33,NGC 6946和IC 342。关于伽马射线光谱,NGC 1482是特别有趣的,因为我们的模型预测,这个星系接近量热极限和它的伽马射线光谱指数GeV-TeV接近宇宙射线质子注入ISM。因此,即使它的GeV通量低于{ \it Fermi}大区域望远镜的灵敏度极限,CTA也可以探测到这个星系。在TeV的制度,大多数星系是不是在量热极限,和预测的TeV流量是低于假设之间的TeV光度和SFR的M82和NGC 253的简单关系,通常由一个因素的15。这意味着需要一个超越量热极限假设的更复杂的模型来研究恒星形成星系的TeV辐射。

英文摘要:

Prospects of the Cherenkov Telescope Array (CTA) for the study of very high energy gamma-ray emission from nearby star-forming galaxies are investigated. In the previous work, we constructed a model to calculate luminosity and energy spectrum of pion-decay gamma-ray emission produced by cosmic-ray interaction with the interstellar medium (ISM), from four physical quantities of galaxies [star formation rate (SFR), gas mass, stellar mass, and effective radius]. The model is in good agreement with the observed GeV--TeV emission of several nearby galaxies. Applying this model to nearby galaxies that are not yet detected in TeV (mainly from the KINGFISH catalog), their hadronic gamma-ray luminosities and spectra are predicted. We identify galaxies of the highest chance of detection by CTA, including NGC 5236, M33, NGC 6946, and IC 342. Concerning gamma-ray spectra, NGC 1482 is particularly interesting because our model predicts that this galaxy is close to the calorimetric limit and its gamma-ray spectral index in GeV--TeV is close to that of cosmic-ray protons injected into ISM. Therefore this galaxy may be detectable by CTA even though its GeV flux is below the {\it Fermi} Large Area Telescope sensitivity limit. In the TeV regime, most galaxies are not in the calorimetric limit, and the predicted TeV flux is lower than that assuming a simple relation between the TeV luminosity and SFR of M82 and NGC 253, typically by a factor of 15. This means that a more sophisticated model beyond the calorimetric limit assumption is necessary to study TeV emission from star-forming galaxies.

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