1Center for the Exploration of the Origin of the Universe (CEOU)
2Astronomy Program, Dept. of Physics & Astronomy, Seoul National University (SNU)
3LOCOOP, Inc
4Korea Astronomy and Space Science Institute (KASI)
5University of Science and Technology (UST)

Image Credit: ESO/M. Kornmesser (http://www.eso.org/public/images/eso1122a/)

High-redshift Quasars• High-redshift (z>5) Quasars• Quasars are energetic sources in the universe• Through surveys of them suggest

MBH• Significant fraction of intergalactic medium (IGM) is reionized• Formation of ~108-10 Msun SMBHs just ~1 Gyr after Big Bang

Fan+06

redshift

Jun+15
1/13

High-redshift Quasars• Unsolved Issues on High-redshift Quasars• How did high-redshift quasars contribute to cosmic reionization?
• Main contributors (Giallongo+15) or not (Willott+10b; Kashikawa+15)
X-ray AGNs

Optical/NIR Quasars

UV Emissivity
𝜖 ∝ 𝜙×𝐿
𝜙: QLF L: luminosity

Maximum at
M1450 ~ -23.5 mag

Lack of Quasars!

Giallongo+15
2/13

High-redshift Quasars• Unsolved Issues on High-redshift Quasars• Are high-redshift quasars growing fast? Or simply a tip of iceberg?
• High Eddington ratio (λEdd) of high-redshift quasars• Key to solve theoretical challenges on the growth to 109 Msun?
• Result of bias?

LbolHigh-z Quasars

Low-z Quasars

MBHWu+15

Willott+10a
3/13

[1]
How Did High-redshift Quasars
Contribute to Cosmic Reionization?
[2]
Are High-redshift Quasars Growing Fast?

4/13

Infrared Medium-deep Survey (IMS)• Description of IMS• Imaging survey at JAB<23 mag, 120 deg2 (+Y-band data)• UKIRT WFCAM observation (2009-2013)• CFHT Legacy Survey optical data (ugriz, ~25 mag)• Discovery of high-z quasars, galaxy clusters, and transients□ CFHTLS
□ IMS
□ DXS

5/13

Discovery of High-redshift Quasars• Color Selection Method• Red colors due to Lyman break with Intergalactic Medium (IGM) attenuation• (i-z) for z~6 quasars, and (r-i) for z~5 quasars• Robust sample from broad-band data (CFHTLS + IMS)

grizJ selection by McGreer+13

No detection in u,g,r bands +Kim Y.+15
6/13

Discovery of High-redshift Quasars• Color Selection Method• Follow-up medium-band observations• SQUEAN (SED camera for QUasars in the Early Universe; Kim S.+15)• On Otto Struve 2.1m Telescope, McDonald Observatory, TX• Improve identification rates from 60% (broad band) to 90%

Kim S.+15

Jeon+16
7/13

Discovery of High-redshift Quasars• Spectroscopic Identification of Quasars

Supported by• GMOS/Gemini 8 m Telescope• IMACS/Magellan Baade 6.5 m Telescope• Discovered Quasars with IMS So Far• 3 quasars at z~6 (a quasar newly discovered)• ~30 quasars at z~5 (~10 quasars newly discovered)

Quasar Model

Kim Y.+15

Kim Y., in prep
8/13

Discovery of High-redshift Quasars• Constraints on Cosmic Reionization at z~6• Expected number of quasars in SA22
• Fraction of required UV photons for Reionization• It is likely to be <15% of ionizing photons

Many Quasars:
Ionizing Sources

Few Quasars:
Not main contributors
Discovery of more faint quasars
is consistent with this result(e.g., Matsuoka+17)
Kim Y.+15
9/13

BH Growth in the Early Universe• Deep NIR Spectroscopy of IMS J2204+0112• IMS J2204+0112: One of the Faint quasars at z~6 (Lbol~1046 erg/s)• FIRE on Magellan Baade 6.5 m Telescope• 5.0 hrs exposures for CIV λ1549 detection

MBH=109.09±0.40 Msun
Kim Y., submitted
10/13

BH Growth in the Early Universe• The lowest Eddington Ratio (λEdd) Quasar at z~6• λEdd ~ 0.1 of IMS J2204+0112• Only chance of 0.03% (3.5σ) with the intrinsic λEdd distribution from Willott+10CIV

MgII

Willott+10a
Kim Y., submitted
11/13

BH Growth in the Early Universe• What is the Intrinsic λEdd Distribution of z~6 Quasars?
• 2D fitting for density map on MBH-Lbol plane• QLF-adapted observations vs. Mock 106 quasars• λEdd at z~6 could be lower than before,
but still slightly higher (0.35 dex)
than λEdd at z~2• Implications for SMBH Evolution?
• For ~102 Msun seed BH,• Episodic high super-Eddington accretion(λEdd > 10) within short time scale• For ~105 Msun seed BH,• Eddington-limited accretion until z~7,
and then reduces to λEdd ~ 0.2 at z~6Generated from
Luminosity-matchedz~2 SDSS Quasars

Kim Y., submitted
12/13

Summary• Faint High-redshift Quasars• IGM ionization source• SMBH growth probe• Survey with IMS• We discovered one z~6 quasar and ~10 of z~5• MBH & λEdd measurements• High-redshift Quasars for Cosmic Reionization?
• They are probably too few to fully account for the IGM ionization at z ~ 6• High-redshift Quasars for Early SMBH Growth?
• Not all quasars are accreting materials at maximal rates

13/13