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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>
SOMANGNET: SMALL TELESCOPE NETWORK OF KOREA
MYUNGSHIN IM,Yonggi Kim,이충욱,이희원,박수종,Hyunjin Shim,Hyun-Il Sung,Wonseok Kang,Taewoo Kim,Jeong-Eun Heo,HINSE TOBIAS CORNELIUS,Masateru Ishiguro,임구,Cuc T. K. Lý,Gregory S. H. Paek,서진국,Joh-Na Yoon,우종학,안호재 한국천문학회 2021 Journal of The Korean Astronomical Society Vol.54 No.3
Even in an era where 8-meter class telescopes are common, small telescopes are considered very valuable research facilities since they are available for rapid follow-up or long term monitoring observations. To maximize the usefulness of small telescopes in Korea, we established the SomangNet, a network of 0.4-1.0 m class optical telescopes operated by Korean institutions, in 2020. Here, we give an overview of the project, describing the current participating telescopes, its scientific scope and operation mode, and the prospects for future activities. SomangNet currently includes 10 telescopes that are located in Australia, USA, and Chile as well as in Korea. The operation of many of these telescopes currently relies on operators, and we plan to upgrade them for remote or robotic operation. The latest SomangNet science projects include monitoring and follow-up observational studies of galaxies, supernovae, active galactic nuclei, symbiotic stars, solar system objects, neutrino/gravitational-wave sources, and exoplanets.
Distance and Properties of NGC 4993 as the Host Galaxy of the Gravitational-wave Source GW170817
Im, Myungshin,Yoon, Yongmin,Lee, Seong-Kook J.,Lee, Hyung Mok,Kim, Joonho,Lee, Chung-Uk,Kim, Seung-Lee,Troja, Eleonora,Choi, Changsu,Lim, Gu,Ko, Jongwan,Shim, Hyunjin American Astronomical Society 2017 ASTROPHYSICAL JOURNAL LETTERS - Vol.849 No.1