PROBING STAR FORMATION IN ULTRALUMINOUS INFRARED GALAXIES USING AKARI NEAR-INFRARED SPECTROSCOPY

다국어 초록 (Multilingual Abstract)

We performed systematic observations of the \ion{H}{i} Br$\alpha$ line (4.05 $\mu$m)in 51 nearby (z<0.3) ultraluminous infrared galaxies(ULIRGs), using AKARI near-infrared spectroscopy.
The Br$\alpha$ line is predicted to be the brightest among the \ion{H}{i} recombination linesin ULIRGs with visual extinction higher than 15 mag.
We detected the Br$\alpha$ line in 33 ULIRGs.
In these galaxies, the relative contribution ofstarburst to the total infrared luminosity ($L_\mathrm{IR}$)is estimated on the basis of the ratio ofthe Br$\alpha$ line luminosity ($L_{\mathrm{Br}\alpha}$) to $L_\mathrm{IR}$.
The mean $L_{\mathrm{Br}\alpha}/L_\mathrm{IR}$ ratioin LINERs or Seyfertsis significantly lower (~ 50%)than that in \ion{H}{ii} galaxies. This result indicates that active galactic nuclei contributesignificantly (~ 50%) to $L_\mathrm{IR}$ in LINERs,as well as Seyferts.
We also estimate the absolutecontribution of starburst to $L_\mathrm{IR}$ using the ratio of star formation rates (SFRs)derived from $L_{\mathrm{Br}\alpha}$ (SFR$_{\mathrm{Br}\alpha}$) and those neededto explain $L_\mathrm{IR}$ (SFR$_\mathrm{IR}$). The mean SFR$_{\mathrm{Br}\alpha}/$SFR$_\mathrm{IR}$ratio is only 0.33 even in\ion{H}{ii} galaxies,where starburst is supposed to dominate the luminosity.
We attribute this apparently low SFR$_{\mathrm{Br}\alpha}/$SFR$_\mathrm{IR}$ratio to the absorption ofionizing photons by dust within \ion{H}{ii} regions.

참고문헌 (Reference)

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