arXiv subjects

Soojong Pak

Publications and source records attributed to Soojong Pak.

At least 19 recordsLinked to original sources

arXiv2025

The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82

We present observations of HCN J=4-3 and HCO^+ J=4-3 lines obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey, combined with archival HCN J=1-0 and HCO^+ J=1-0 data from the Green Bank Telescope, to study the spatial distribution and excitation conditions of dense molecular gas in the disk of M82. We detect HCN J=4-3 and HCO^+ J=4-3 emission within the central region (< 500 pc) of the galaxy, while the J=1-0 emission lines exhibit a more extended spatial distribution (> 700 pc). The dense gas shows a clear double-lobed structure in both spatial distribution and kinematics, with the HCN and HCO^+ J=4-3 lines in the southwest lobe blueshifted by ~ 40 km/s relative to the J=1-0 lines. The HCN J=4-3/1-0 and HCO^+ J=4-3/1-0 line-luminosity ratios range from 0.09 to 0.53 and from 0.14 to 0.87, respectively, with mean values of 0.18 +/- 0.04 and 0.36 +/- 0.06. The HCN ratio is lower than the typical average observed in nearby star-forming galaxies, whereas the HCO^+ ratio is comparatively higher, suggesting that the high-J HCN emission in M82 is significantly sub-thermally excited. Spatially, the peak values of the J=4-3/1-0 ratios are found in the northwest region of M82, coinciding with the galaxy-scale outflow. Elevated HCN/HCO^+ ratios are also detected in roughly the same area, potentially tracing local excitation enhancements driven by the outflow. The HCN/HCO^+ J=4-3 ratio across all detected regions ranges from 0.19 to 1.07 with a mean value of 0.41 +/- 0.11, which is significantly lower than the average J=1-0 ratio of 0.76 +/- 0.08. Both ratios are significantly lower than the average values observed in nearby star-forming galaxies, which could be related to the relatively low gas density and the presence of an extended photo-dissociation region in M82.

astro-ph.GA↗

arXiv2025

10 Years of Archival High-Resolution NIR Spectra: The Raw and Reduced IGRINS Spectral Archive (RRISA)

The Immersion GRating INfrared Spectrometer (IGRINS) is a compact, high-resolution (R~45,000) near-infrared spectrograph spanning 1.45 to 2.45 um in a single exposure. We introduce the Raw and Reduced IGRINS Spectral Archive (RRISA), which provides public data access for all non-proprietary IGRINS data taken at McDonald Observatory's Harlan J. Smith Telescope, the Lowell Discovery Telescope (formerly Discovery Channel Telescope), and Gemini South. RRISA provides access to raw files, reduced data products, and cross-matched IGRINS targets with the SIMBAD, 2MASS, Gaia DR3, APOGEE2 DR17, and PASTEL catalogs. We also introduce version 3 of the IGRINS data reduction pipeline, IGRINS PLP v3, which implements an improved cosmic ray correction, pattern noise removal, and a new flexure correction that reduces telluric residuals. RRISA and supporting information can be found at http://igrinscontact.github.io.

astro-ph.IM↗

arXiv2024

Telescope control software and proto-model siderostat for the SDSS-V Local Volume Mapper

The fifth Sloan Digital Sky Survey (SDSS-V) Local Volume Mapper (LVM) is a wide-field integral field unit (IFU) survey that uses an array of four 160 mm fixed telescopes with siderostats to minimize the number of moving parts. Individual telescope observes the science field or calibration field independently and is synchronized with the science exposure. We developed the LVM Acquisition and Guiding Package (LVMAGP) optimized telescope control software program for LVM observations, which can simultaneously control four focusers, three K-mirrors, one fiber selector, four mounts (siderostats), and seven guide cameras. This software is built on a hierarchical architecture and the SDSS framework and provides three key sequences: autofocus, field acquisition, and autoguide. We designed and fabricated a proto-model siderostat to test the telescope pointing model and LVMAGP software. The mirrors of the proto-model were designed as an isogrid open-back type, which reduced the weight by 46% and enabled reaching thermal equilibrium quickly. Additionally, deflection due to bolting torque, self-gravity, and thermal deformation was simulated, and the maximum scatter of the pointing model induced by the tilt of optomechanics was predicted to be $4'.4$, which can be compensated for by the field acquisition sequence. We performed a real sky test of LVMAGP with the proto-model siderostat and obtained field acquisition and autoguide accuracies of $0''.38$ and $1''.5$, respectively. It met all requirements except for the autoguide specification, which will be resolved by more precise alignment among the hardware components at Las Campanas Observatory.

astro-ph.IM↗

arXiv2024

Maunakea Spectroscopic Explorer exposure time calculator for end-to-end simulator: to optimizing spectrograph design and observing simulation

The Maunakea Spectroscopic Explorer (MSE) project will provide multi-object spectroscopy in the optical and near-infrared bands using an 11.25-m aperture telescope, repurposing the original Canada-France-Hawaii Telescope (CFHT) site. MSE will observe 4,332 objects per single exposure with a field of view of 1.5 square degrees, utilizing two spectrographs with low-moderate (R$\sim$3,000, 6,000) and high (R$\approx$30,000) spectral resolution. In general, an exposure time calculator (ETC) is used to estimate the performance of an observing system by calculating a signal-to-noise ratio (S/N) and exposure time. We present the design of the MSE exposure time calculator (ETC), which has four calculation modes (S/N, exposure time, S/N trend with wavelength, and S/N trend with magnitude) and incorporates the MSE system requirements as specified in the Conceptual Design. The MSE ETC currently allows for user-defined inputs of target AB magnitude, water vapor, airmass, and sky brightness AB magnitude (additional user inputs can be provided depending on computational mode). The ETC is built using Python 3.7 and features a graphical user interface that allows for cross-platform use. The development process of the ETC software follows an Agile methodology and utilizes the Unified Modeling Language (UML) diagrams to visualize the software architecture. We also describe the testing and verification of the MSE ETC.

astro-ph.IM↗

arXiv2022

The Infrared Medium-deep Survey. IX. Discovery of Two New $z\sim6$ Quasars and Space Density down to $M_{1450}\sim-23.5$ mag

We present the result of the Infrared Medium-deep Survey (IMS) $z\sim6$ quasar survey, using the combination of the IMS near-infrared images and the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) optical images. The traditional color-selection method results in 25 quasar candidates over $86$ deg$^{2}$. We introduce the corrected Akaike Information Criterion (AICc) with the high-redshift quasar and late-type star models to prioritize the candidates efficiently. Among the color-selected candidates, seven plausible candidates finally passed the AICc selection of which three are known quasars at $z\sim6$. The follow-up spectroscopic observations for the remaining four candidates were carried out, and we confirmed that two out of four are $z\sim6$ quasars. With this complete sample, we revisited the quasar space density at $z\sim6$ down to $M_{1450}\sim-23.5$ mag. Our result supports the low quasar space density at the luminosity where the quasar's ultraviolet ionizing emissivity peaks, favoring a minor contribution of quasars to the cosmic reionization.

astro-ph.GA↗

arXiv2021

The IGRINS YSO Survey I. Stellar parameters of pre-main sequence stars in Taurus-Auriga

We present fundamental parameters for 110 canonical K- & M-type (1.3$-$0.13$M_\odot$) Taurus-Auriga young stellar objects (YSOs). The analysis produces a simultaneous determination of effective temperature ($T_{\rm eff}$), surface gravity ($\log$ g), magnetic field strength (B), and projected rotational velocity ($v \sin i$). Our method employed synthetic spectra and high-resolution (R$\sim$45,000) near-infrared spectra taken with the Immersion GRating INfrared Spectrometer (IGRINS) to fit specific K-band spectral regions most sensitive to those parameters. The use of these high-resolution spectra reduces the influence of distance uncertainties, reddening, and non-photospheric continuum emission on the parameter determinations. The median total (fit + systematic) uncertainties were 170 K, 0.28 dex, 0.60 kG, 2.5 km s$^{-1}$ for $T_{\rm eff}$, $\log$ g, B, and $v \sin i$, respectively. We determined B for 41 Taurus YSOs (upper limits for the remainder) and find systematic offsets (lower $T_{\rm eff}$, higher $\log$ g and $v \sin i$) in parameters when B is measurable but not considered in the fit. The average $\log$ g for the Class II and Class III objects differs by 0.23$\pm$0.05dex, which is consistent with Class III objects being the more evolved members of the star-forming region. However, the dispersion in $\log$ g is greater than the uncertainties, which highlights how the YSO classification correlates with age ($\log$ g), yet there are exceptionally young (lower $\log$ g) Class III YSOs and relatively old (higher $\log$ g) Class II YSOs with unexplained evolutionary histories. The spectra from this work are provided in an online repository along with TW Hydrae Association (TWA) comparison objects and the model grid used in our analysis.

astro-ph.SR↗

arXiv2020

Medium-band observation of the neutrino emitting blazar, TXS 0506+056

TXS 0506+056 is a blazar that has been recently identified as the counterpart of the neutrino event IceCube-170922A. Understanding blazar type of TXS 0506+056 is important to constrain the neutrino emission mechanism, but the blazar nature of TXS 0506+056 is still uncertain. As an attempt to understand the nature of TXS 0506+056, we report the medium-band observation results of TXS 0506+056, covering the wavelength range of 0.575 to 1.025 $\mu$m. The use of the medium-band filters allow us to examine if there were any significant changes in its spectral shapes over the course of one month and give a better constraint on the peak frequency of synchrotron radiation with quasi-simultaneous datasets. The peak frequency is found to be $10^{14.28}$ Hz, and our analysis shows that TXS 0506+056 is not an outlier from the blazar sequence. As a way to determine the blazar type, we also analyzed if TXS 0506+056 is bluer-when-brighter (BL Lac type and some flat spectrum radio quasars, FSRQs) or redder-when-brighter (found only in some FSRQs). Even though we detect no significant variability in the spectral shape larger than observational error during our medium-band observation period, the comparison with a dataset taken at 2012 shows a possible redder-when-brighter behavior of FSRQs. Our results demonstrate that medium-band observations with small to moderate-sized telescopes can be an effective way to trace the spectral evolution of transients such as TXS 0506+056.

astro-ph.HE↗

arXiv2020

The Infrared Medium-deep Survey. VIII. Quasar Luminosity Function at $z\sim5$

Faint $z\sim5$ quasars with $M_{1450}\sim-23$ mag are known to be the potentially important contributors to the ultraviolet ionizing background in the post-reionization era. However, their number density has not been well determined, making it difficult to assess their role in the early ionization of the intergalactic medium (IGM). In this work, we present the updated results of our $z\sim5$ quasar survey using the Infrared Medium-deep Survey (IMS), a near-infrared imaging survey covering an area of 85 deg$^{2}$. From our spectroscopic observations with the Gemini Multi-Object Spectrograph (GMOS) on the Gemini-South 8 m Telescope, we discovered eight new quasars at $z\sim5$ with $-26.1\leq M_{1450} \leq -23.3$. Combining our IMS faint quasars ($M_{1450}>-27$ mag) with the brighter Sloan Digital Sky Survey (SDSS) quasars ($M_{1450}<-27$ mag), we derive the $z\sim5$ quasar luminosity function (QLF) without any fixed parameters down to the magnitude limit of $M_{1450}=-23$ mag. We find that the faint-end slope of the QLF is very flat ($\alpha=-1.2^{+1.4}_{-0.6}$), with a characteristic luminosity of $M^{*}_{1450}=-25.8^{+1.4}_{-1.1}$ mag. The number density of $z\sim5$ quasars from the QLF gives an ionizing emissivity at 912 $\unicode{x212B}$ of $\epsilon_{912}=(3.7$--$7.1)\times10^{23}$ erg s$^{-1}$ Hz$^{-1}$ Mpc$^{-3}$ and an ionizing photon density of $\dot{n}_{\rm ion}=(3.0$--$5.7)\times10^{49}$ Mpc$^{-3}$ s$^{-1}$. These results imply that quasars are responsible for only 10-20% (up to 50% even in the extreme case) of the photons required to completely ionize the IGM at $z\sim5$, disfavoring the idea that quasars alone could have ionized the IGM at $z\sim5$.

astro-ph.GA↗

arXiv2020

Flight model characterization of the wide-field off-axis telescope for the MATS satellite

We present optical characterization, calibration, and performance tests of the Mesospheric Airglow/Aerosol Tomography Spectroscopy (MATS) satellite, which for the first time for a satellite applies a linear-astigmatism-free confocal off-axis reflective optical design. Mechanical tolerances of the telescope were investigated using Monte-Carlo methods and single-element perturbations. The sensitivity analysis results indicate that tilt errors of the tertiary mirror and a surface RMS error of the secondary mirror mainly degrade optical performance. From the Monte-Carlo simulation, the tolerance limits were calculated to $\pm$0.5 mm, $\pm$1 mm, and $\pm$0.15$^\circ$ for decenter, despace, and tilt, respectively. We performed characterization measurements and optical tests with the flight model of the satellite. Multi-channel relative pointing, total optical system throughput, and distortion of each channel were characterized for end-users. Optical performance was evaluated by measuring modulation transfer function (MTF) and point spread function (PSF). The final MTF performance is 0.25 MTF at 20 lp/mm for the ultraviolet channel (304.5 nm), and 0.25 - 0.54 MTF at 10 lp/mm for infrared channels. The salient fact of the PSF measurement of this system is that there is no noticeable linear astigmatism detected over wide field of view (5.67$^\circ$ $\times$ 0.91$^\circ$). All things considered, the design method showed great advantages in wide field of view observations with satellite-level optical performance.

astro-ph.IM↗

arXiv2020

Transformable Reflective Telescope for optical testing and education

We propose and experimentally demonstrate the Transformable Reflective Telescope (TRT) Kit for educational purposes and for performing various optical tests with a single kit. The TRT Kit is a portable optical bench setup suitable for interferometry, spectroscopy, measuring stray light, and developing adaptive optics, among other uses. Supplementary modules may be integrated easily thanks to the modular design of the TRT Kit. The Kit consists of five units; a primary mirror module, a secondary mirror module, a mounting base module, a baffle module, and an alignment module. Precise alignment and focusing are achieved using a precision optical rail on the alignment module. The TRT Kit transforms into three telescope configurations: Newtonian, Cassegrain, and Gregorian. Students change telescope configurations by exchanging the secondary mirror. The portable design and the aluminum primary mirror of the TRT Kit enable students to perform experiments in various environments. The minimized baffle design utilizes commercial telescope tubes, allowing users to look directly into the optical system while suppressing stray light down to $\sim$10$^{-8}$ point source transmittance (PST). The TRT Kit was tested using a point source and field images. Point source measurement of the Newtonian telescope configuration resulted in an 80\% encircled energy diameter (EED) of 23.8 $\mu$m.

physics.ed-ph↗

arXiv2020

The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at $z \sim 5$ in the ELAIS-N1 Field

The intergalactic medium (IGM) at $z\sim$ 5 to 6 is largely ionized, and yet the main source for the IGM ionization in the early universe is uncertain. Of the possible contributors are faint quasars with $-26 \lesssim M_{\rm 1450} \lesssim -23$, but their number density is poorly constrained at $z\sim5$. In this paper, we present our survey of faint quasars at $z\sim5$ in the European Large-Area {\it ISO} Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg$^2$ and examine if such quasars can be the dominant source of the IGM ionization. We use the deep optical/near-infrared data of the ELAIS-N1 field as well as the additional medium-band observations to find $z \sim 5$ quasars through a two-step approach using the broadband color selection, and SED fitting with the medium-band information included. Adopting Bayesian information criterion, we identify ten promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at $z\sim5$ and supporting the reliability of the quasar selection. Using the promising candidates, we derive the $z\sim5$ quasar luminosity function at $-26 \lesssim M_{\rm 1450} \lesssim -23$. The number density of faint $z\sim5$ quasars in the ELAIS-N1 field is consistent with several previous results that quasars are not the main contributors to the IGM-ionizing photons at $z\sim5$

astro-ph.GA↗

arXiv2020

Development of Linear Astigmatism Free -- Three Mirror System (LAF-TMS)

We present the development of Linear Astigmatism Free - Three Mirror System (LAF-TMS). This is a prototype of an off-axis telescope that enables very wide field of view (FoV) infrared satellites that can observe Paschen-$\alpha$ emission, zodiacal light, integrated star light, and other infrared sources. It has the entrance pupil diameter of 150 mm, the focal length of 500 mm, and the FoV of 5.5$^\circ$ $\times$ 4.1$^\circ$. LAF-TMS is an obscuration-free off-axis system with minimal out-of-field baffling and no optical support structure diffraction. This optical design is analytically optimized to remove linear astigmatism and to reduce high-order aberrations. Sensitivity analysis and Monte-Carlo simulation reveal that tilt errors are the most sensitive alignment parameters that allow $\sim$1$^\prime$. Optomechanical structure accurately mounts aluminum mirrors, and withstands satellite-level vibration environments. LAF-TMS shows optical performance with 37 $\mu$m FWHM of the point source image satisfying Nyquist sampling requirements for typical 18 $\mu$m pixel Infrared array detectors. The surface figure errors of mirrors and scattered light from the tertiary mirror with 4.9 nm surface micro roughness may affect the measured point spread function (PSF). Optical tests successfully demonstrate constant optical performance over wide FoV, indicating that LAF-TMS suppresses linear astigmatism and high-order aberrations.

astro-ph.IM↗

arXiv2020

IGRINS Slit-Viewing Camera Software

We have developed observation control software for the Immersion GRating INfrared Spectrometer (IGRINS) slit-viewing camera module, which maintains the position of an astronomical target on the spectroscopic slit. It is composed of several packages that monitor and control the system, acquire the images, and compensate for the tracking error by sending tracking feedback information to the telescope control system. For efficient development and maintenance of each software package, we have applied software engineering methods, i.e., a spiral software development with model-based design. It is not trivial to define the shape and center of astronomical object point spread functions (PSFs), which do not have symmetric Gaussian profiles in short exposure (<4 s) guiding images. Efforts to determine the PSF centroid are additionally complicated by the core saturation of bright guide stars. We have applied both a two-dimensional Gaussian fitting algorithm (2DGA) and center balancing algorithm (CBA) to identify an appropriate method for IGRINS in the near-infrared K-band. The CBA derives the expected center position along the slit-width by referencing the spillover flux ratio of the PSF wings on both sides of the slit. In this research, we have compared the accuracy and reliability of the CBA to the 2DGA by using data from IGRINS commissioning observations at McDonald Observatory. We find that the performance of each algorithm depends on the brightness of the targets and the seeing conditions, with the CBA performing better in typical observing scenarios. The algorithms and test results we present can be utilized with future spectroscopic slit observations in various observing conditions and for a variety of spectrograph designs.

astro-ph.IM↗

arXiv2019

Intensive Monitoring Survey of Nearby Galaxies (IMSNG)

Intensive Monitoring Survey of Nearby Galaxies (IMSNG) is a high cadence observation program monitoring nearby galaxies with high probabilities of hosting supernovae (SNe). IMSNG aims to constrain the SN explosion mechanism by inferring sizes of SN progenitor systems through the detection of the shock-heated emission that lasts less than a few days after the SN explosion. To catch the signal, IMSNG utilizes a network of 0.5-m to 1-m class telescopes around the world and monitors the images of 60 nearby galaxies at distances D < 50 Mpc to a cadence as short as a few hours. The target galaxies are bright in near-ultraviolet (NUV) with M_NUV < -18.4 AB mag and have high probabilities of hosting SNe (0.06 SN/yr per galaxy). With this strategy, we expect to detect the early light curves of 3.4 SNe per year to a depth of R ~ 19.5 mag, enabling us to detect the shock-heated emission from a progenitor star with a radius as small as 0.1 R_sun. The accumulated data will be also useful for studying faint features around the target galaxies and other science projects. So far, 18 SNe have occurred in our target fields (16 in IMSNG galaxies) over 5 years, confirming our SN rate estimate of 0.06 SN/yr per galaxy.

astro-ph.GA↗

arXiv2018

The Infrared Medium-deep Survey. VI. Discovery of Faint Quasars at $z\sim5$ with a Medium-band-based Approach

The faint quasars with $M_{1450}>-24$ mag are known to hold the key to the determination of the ultraviolet emissivity for the cosmic re-ionization. But only a few have been identified so far because of the limitations on the survey data. Here, we present the first results of the $z\sim5$ faint quasar survey with the Infrared Medium-deep Survey (IMS), which covers $\sim100$ deg$^{2}$ areas in $J$-band to the depths of $J_{\rm AB}\sim23$ mag. To improve selection methods, the medium-band follow-up imaging has been carried out using the SED camera for QUasars in Early uNiverse (SQUEAN) on the Otto Struve 2.1 m Telescope. The optical spectra of the candidates were obtained with 8-m class telescopes. We newly discovered 10 quasars with $-25<M_{1450}<-23$ at $z\sim5$, among which three have been missed in a previous survey using the same optical data over the same area, implying the necessity for improvements in high redshift faint quasars selection. We derived photometric redshifts from the medium-band data, and find that they have high accuracies of $\langle|\Delta z|/(1+z)\rangle=0.016$. The medium-band-based approach allows us to rule out many of the interlopers that contaminate $\gtrsim20~\%$ of the broad-band-selected quasar candidates. These results suggest that the medium-band-based approach is a powerful way to identify $z\sim5$ quasars and measure their redshifts at high accuracy (1-2 %). It is also a cost-effective way to understand the contribution of quasars to the cosmic re-ionization history.

astro-ph.GA↗

arXiv2018

The Infrared Medium-deep Survey. IV. Low Eddington Ratio of A Faint Quasar at $z\sim6$: Not Every Supermassive Black Hole is Growing Fast in the Early Universe

To date, most of the luminous quasars known at $z\sim6$ have been found to be in maximal accretion with the Eddington ratios, $\lambda_{\rm{Edd}}\sim1$, 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 on faint quasars that are more likely to harbor SMBHs with low $\lambda_{\rm{Edd}}$. To gain a better understanding on 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 have been identified at $z\sim6$. From the redshifted C IV $\lambda 1549$ emission line in the NIR spectrum, we find that IMS J2204+0112 harbors a SMBH with about a billion solar mass and $\lambda_{\rm{Edd}} \sim 0.1$, but with a large uncertainty in both quantities (0.41 dex). IMS J2204+0112 has one of the lowest Eddington ratios among quasars at $z\sim6$, but a common value among quasars at $z\sim2$. Its low $\lambda_{\rm{Edd}}$ 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 ($\sim10^{5}\,M_{\odot}$) with Eddington-limited accretion. NIR spectra of more faint quasars are needed to better understand the accretion activities of SMBHs at $z \sim 6$.

astro-ph.GA↗

arXiv2017

Inner warm disk of ESO H$\alpha$ 279A revealed by NA I and CO overtone emission lines

We present analysis of near-infrared, high-resolution spectroscopy towards the Flat-spectrum YSO (Young Stellar Object) ESO H$\alpha$ 279a (1.5 solar mass) in the Serpens star forming region, at the distance of 429 pc. Using the Immersion GRating INfrared Spectrometer (IGRINS, R=45,000), we detect emission lines originating from the accretion channel flow, jet, and inner disk. Specifically, we identify hydrogen Brackett series recombination, [Fe II], [Fe III], [Fe IV], Ca I, Na I, H2, H2O and CO overtone emission lines. By modeling five bands of CO overtone emission lines, and the symmetric double-peaked line profile for Na I emission lines, we find that ESO H$\alpha$ 279a has an actively accreting Keplerian disk. From our Keplerian disk model, we find that Na I emission lines originate between 0.04 AU and 1.00 AU, while CO overtone emission lines are from the outer part of disk, in the range between 0.22 AU and 3.00 AU. It reveals that the neutral atomic Na gas is a good tracer of the innermost region of the actively accreting disk. We derive a mass accretion rate of 2-10x10^{-7} M_solar/yr from the measured Br_gamma emission luminosity of 1.78(+-0.31)x10^{31} erg/s.

astro-ph.SR↗

arXiv2017

The Infrared Medium-deep Survey. III. Survey of Luminous Quasars at 4.7 $\leq$ z $\leq$ 5.4

We present our first results of the survey for high redshift quasars at $5 \lesssim {\rm z} \lesssim 5.7$. The search for quasars in this redshift range has been known to be challenging due to limitations of filter sets used in previous studies. We conducted a quasar survey for two specific redshift ranges, 4.60 $\leq$ z $\leq$ 5.40 and 5.50 $\leq$ z $\leq$ 6.05, using multi-wavelength data that include observations using custom-designed filters, $is$ and $iz$. Using these filters and a new selection technique, we were able to reduce the fraction of interlopers. Through optical spectroscopy, we confirmed seven quasars at 4.7 $\leq$ z $\leq$ 5.4 with $-27.4 < M_{1450} < -26.4$ which were discovered independently by another group recently. We estimated black hole masses and Eddington ratios of four of these quasars from optical and near-infrared spectra, and found that these quasars are undergoing nearly Eddington-limited accretion which is consistent with the rapid growth of supermassive black holes in luminous quasars at z $\sim$ 5.

astro-ph.GA↗