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DISCOVERY OF A FAINT QUASAR AT <i>z</i> ∼ 6 AND IMPLICATIONS FOR COSMIC REIONIZATION
Kim, Yongjung,Im, Myungshin,Jeon, Yiseul,Kim, Minjin,Choi, Changsu,Hong, Jueun,Hyun, Minhee,Jun, Hyunsung David,Karouzos, Marios,Kim, Dohyeong,Kim, Duho,Kim, Jae-Woo,Kim, Ji Hoon,Lee, Seong-Kook,Pak, IOP Publishing 2015 ASTROPHYSICAL JOURNAL LETTERS - Vol.813 No.2
<P>Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars (M-1450 > -24 mag) at z greater than or similar to 6, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z similar to 6 in a 12.5 deg(2) region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at similar to 8443 angstrom, with emission lines redshifted to z = 5.944 +/- 0.002 and rest-frame ultraviolet continuum magnitude M-1450 = -23.59 +/- 0.10 AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z similar to 6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars. This suggests that the number of M-1450 similar to 23 mag quasars at z similar to 6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.</P>
Kim, Yongjung,Im, Myungshin,Jeon, Yiseul,Kim, Minjin,Hyun, Minhee,Kim, Dohyeong,Kim, Jae-Woo,Taak, Yoon Chan,Yoon, Yongmin,Choi, Changsu,Hong, Jueun,Jun, Hyunsung David,Karouzos, Marios,Kim, Duho,Kim, American Astronomical Society 2018 The Astrophysical journal Vol.855 No.2
<P>To date, most of the luminous quasars known at z similar to 6 have been found to be in maximal accretion with the Eddington ratios, lambda(Edd) similar to 1, suggesting enhanced nuclear activities in the early universe. However, this may not be the whole picture of supermassive black hole (SMBH) growth, since previous studies have not reached faint quasars that are more likely to harbor SMBHs with low lambda(Edd). To gain a better understanding of the accretion activities in quasars in the early universe, we obtained a deep near-infrared (NIR) spectrum of a quasar, IMS J220417.92+011144.8 (hereafter IMS J2204+0112), one of the faintest quasars that has been identified at z similar to 6. From the redshifted C IV lambda 1549 emission line in the NIR spectrum, we find that IMS J2204+0112 harbors a SMBH with a solar mass of about a billion and lambda(Edd) similar to 0.1, but with a large uncertainty in both quantities (0.41 dex). IMS J2204+0112 has one of the lowest Eddington ratios among quasars at z similar to 6, but a common value among quasars at z similar to 2. Its low lambda(Edd) can be explained with two scenarios; the SMBH growth from a stellar-mass black hole through short-duration super-Eddington accretion events or from a massive black hole seed (similar to 10(5) M-circle dot) with Eddington-limited accretion. NIR spectra of more faint quasars are needed to better understand the accretion activities of SMBHs at z similar to 6.</P>
Discovery of a Faint Quasar at z ~ 6 and Implications for Cosmic Reionization
Yongjung Kim,Myungshin Im,Yiseul Jeon,Minjin Kim,Changsu Choi,Jueun Hong,Minhee Hyun,Hyunsung David Jun,Marios Karouzos,Dohyeong Kim,Duho Kim,Jae-Woo Kim,Ji Hoon Kim,Seong-Kook Lee,Soojong Pak,Won-Kee 한국천문학회 2016 天文學會報 Vol.41 No.1
Are Quasars Growing Fast in the Early Universe?: The Lowest Eddington Ratio Quasar at z~6
Yongjung Kim,Myungshin Im,Yiseul Jeon,Minjin Kim,Minhee Hyun,Dohyeong Kim,Jae-Woo Kim,Yoon Chan Taak,Yongmin Yoon,Changsu Choi,Jueun Hong,Hyunsung David Jun,Marios Karouzos,Duho Kim,Ji Hoon Kim,Seong- 한국천문학회 2017 天文學會報 Vol.42 No.2
Comparative study of chemical tolerance between Drosophila melanogaster and Drosophila suzukii
YiSeul Kim,Sungho Lee,YeongHo Kim,Young Ho Kim 한국응용곤충학회 2018 한국응용곤충학회 학술대회논문집 Vol.2018 No.04
Drosophila melanogaster and Drosophila suzukii are the species of the family Drosophilidae. Although these two fruit flies are taxonomically close species, D. suzukii is thought to be evolutionally adapted to the flesh or maturing fruits, whereas D. melanogaster is adapted to more fermented environments. According to the previous studies, several environmental toxins, such as acetic acid, ethanol, methanol and phenylacetate, ect., have been identified from rotten fruit and fermentation procedures. Considering the differences of distinct habitat between two flies, D. melanogaster is hypothesized to exhibit higher tolerance to the chemical toxins than D. suzukii. Therefore, in this study, we compared the tolerance and susceptibility of two fruit flies to three chemicals (acetic acid, ethanol, 2-phenlyethano).
Yiseul Kim, Ki-Myung Chung, Kyung-Nyun Kim, Young Kyung Cho 충북대학교 동물의학연구소 2013 Journal of Biomedical and Translational Research Vol.14 No.1
Taste receptors of the anterior tongue are innervated by the chorda tympani (CT) branch of the facial (VIIth) nerve. The CT nerve transmits information on taste to the ipsilateral nucleus of the solitary tract (NST), which is the first taste central nucleus in the medulla. Taste information is known to be transferred ipsilaterally along the taste pathway in the central nervous system. Some patients with unilateral CT damage often retain their ability to sense taste. This phenomenon is not explained by the unilateral taste pathway. We examined whether neurons in the NST receive information on taste from the contralateral side of the tongue by measuring c-Fos-like Immunoreactivity (cFLI) following taste stimulation of the contralateral side of the tongue in the anesthetized rats. We used four basic taste stimuli, 1.0 M sucrose, 0.3 M NaCl, 0.01 M citric acid, 0.03 M QHCl, and distilled water. Stimulation of one side of the tongue with taste stimuli induced cFLI in the NST bilaterally. The mean number of cFLI ranged from 23.28 ± 2.46 by contralateral QHCl to 30.28 ± 2.26 by ipsilateral NaCl stimulation. The difference between the number of cFLI in the ipsilaterl and contralateral NST was not significant. The result of the current study suggests that neurons in the NST receive information on taste not only from the ipsilateral but also the contralateral side of the tongue.