環境如何影響星系的AGN活動？我們選擇了AKARI North Ecliptic Pole寬
場中紅移為0 < z 1.2的1210個星系，以不受消光影響(extinction-free) 的方法研究這個問題。相較於其他紅外衛星在中紅外範圍內只有4-5個濾鏡(filter)，AKARI 衛星的獨特之處是其涵括了連續9個波段的中紅外濾光片(filter)，為我們提供了前所未有、包含了數千個星系的中紅外光SED的大樣本。藉由充分運用AKARI的9個中紅外濾光片(filter)，我們首次得以在探索擬合出的SED時，同時考量紅位移/光度、環境和AGN比例(AGN fraction)。我們發現星系環境（常態化局部密度）不會大幅影響我們星系樣本中的AGN比例(AGN fraction)。有趣的是，我們發現了超亮紅外星系(ULIRGs)的不同表現。在我們最高的紅移區間(0.7 ≲ z ≲ 1.2)，AGN比例(AGN fraction)與環境密度成正比；但在中度紅移區間(0.3 ≲ z ≲ 0.7)，則觀察到相反的現象。我們的研究結果顯示，要決定環境對中紅外光AGN 活動的影響，宿主星系的特性和/或紅移(epoch)至關重要。

How does the environment affect the active galactic nucleus (AGN) activity of galaxies? We investigated this question in an extinction-free way, by selecting 1210 galaxies in the AKARI North Ecliptic Pole Wide field in the redshift range 0 Ÿ I 1.2. A unique feature of the AKARI satellite is its continuous 9-band mid-infrared filter coverage, providing us with an unprecedentedly large sample of mid-infrared
spectral energy distributions (SEDs) of galaxies, while other infrared satellites only had 4-5 filters in the mid-infrared range. Taking advantage of AKARI’s 9 mid-infrared filters, for the first time, we explored the AGN activity derived from SEDs as a function of redshift, luminosity, and environment. We found that galaxy
environment (normalised local density) does not greatly affect the AGN fraction of our galaxy sample. Interestingly, we found a different behavior for ultra-luminous infrared galaxies (ULIRGs). At our highest redshift bin (0.7 ≲ z ≲ 1.2), their AGN fraction increases with denser environments, but at the intermediate redshift bin (0.3 ≲ z ≲ 0.7), the opposite is observed. Our results suggest that host galaxy
properties and/or epoch are crucial to determine the environmental effects on midinfrared AGN activity.

1. Introduction--------------------------------------------------1
1.1 Active Galactic Nucleus--------------------------------------1
1.2 Galaxy Environment-------------------------------------------1
1.3 Environmental Effects on AGN Activity------------------------3
1.4 Studying the MIR regime with AKARI---------------------------6

2. Data and Analysis---------------------------------------------9
2.1 Sample Selection---------------------------------------------9
2.2 Estimation of Galaxy Physical Properties--------------------12
2.3 Density Estimation------------------------------------------19

3. Results------------------------------------------------------22
3.1 Binning of MIR-FIR Sample Distribution----------------------24
3.2 AGN activity vs. Normalised Local Density-------------------24

4. Discussion
4.1 Selection bias----------------------------------------------28
4.2 Difference between our work and previous works--------------29
4.3 Reversal of ULIRGs' AGN activity-Local Environment relation-33
4.4 Possible Explanations for Reversal of AGN activity-environment
trend for ULIRGs------------------------------------------------35
4.5 Limitations and Future Prospects----------------------------36

5. Conclusion---------------------------------------------------37
Reference-------------------------------------------------------39
Appendix--------------------------------------------------------46

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