arXiv subjects

Myungshin Im

Publications and source records attributed to Myungshin Im.

At least 37 records · Page 2Linked to original sources

arXiv2025

GECKO Follow-up Observation of the Binary Neutron Star-Black Hole Merger Candidate S230518h

The gravitational wave (GW) event S230518h is a potential binary neutron star-black hole merger (NSBH) event that was detected during engineering run 15 (ER15), which served as the commissioning period before the LIGO-Virgo-KAGRA (LVK) O4a observing run. Despite its low probability of producing detectable electromagnetic emissions, we performed extensive follow-up observations of this event using the GECKO telescopes in the southern hemisphere. Our observation covered 61.7\% of the 90\% credible region, a $\rm 284\:deg^2$ area accessible from the southern hemisphere, reaching a median limiting magnitude of $R=21.6$ mag. In these images, we conducted a systematic search for an optical counterpart of this event by combining a CNN-based classifier and human verification. We identified 128 transient candidates, but no significant optical counterpart was found that could have caused the GW signal. Furthermore, we provide feasible KN properties that are consistent with the upper limits of observation. Although no optical counterpart was found, our result demonstrates both GECKO's efficient wide-field follow-up capabilities and usefulness for constraining properties of kilonovae from NSBH mergers at distances of $\sim 200$ Mpc.

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arXiv2025

Multiwavelength Afterglow Analysis of GRB 221009A: Unveiling the Evolution of a Cooling Break in a Wind-like Medium

Gamma-ray bursts (GRBs) are the most energetic explosions in the universe, and their afterglow emission provides an opportunity to probe the physics of relativistic shock waves in an extreme environment. Several key pieces for completing the picture of the GRB afterglow physics are still missing, including jet properties, emission mechanism, and particle acceleration. Here we present a study of the afterglow emission of GRB 221009A, the most energetic GRB ever observed. Using optical, X-ray, and gamma-ray data up to approximately two days after the trigger, we trace the evolution of the multi-wavelength spectrum and the physical parameters behind the emission process. The broadband spectrum is consistent with the synchrotron emission emitted by relativistic electrons with its index of $p = 2.29\pm 0.02$. We identify a break energy at keV and an exponential cutoff at GeV in the observed multi-wavelength spectrum. The break energy increases in time from $16.0_{-4.9}^{+7.1}$ keV at 0.65 days to $46.8_{-15.5}^{+25.0}$ keV at 1.68 days, favoring a stellar wind-like profile of the circumburst medium with $k=2.4\pm0.1$ as in $ρ(r) \propto r^{-k}$. The high-energy attenuation at around 0.4 to 4 GeV is attributed to the maximum of the particle acceleration in the relativistic shock wave. This study confirms that the synchrotron process can explain the multi-wavelength afterglow emission and its evolution.

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arXiv2024

Test of Cosmic Web-feeding Model for Star Formation in Galaxy Clusters in the COSMOS Field

It is yet to be understood how large-scale environments influence star formation activity in galaxy clusters. One recently proposed mechanism is that galaxy clusters can remain star-forming when fed by infalling groups and star-forming galaxies from large-scale structures surrounding them (the \textit{``web-feeding model"}). Using the COSMOS2020 catalog that has half a million galaxies with high accuracy ($σ_{Δz /1+z} \sim 0.01$) photometric redshifts, we study the relationship between star formation activities in galaxy clusters and their surrounding environment to test the web-feeding model. We first identify $68$ cluster candidates at $0.3 \leq z \leq 1.4$ with halo masses at $10^{13.0} - 10^{14.5}$ \SI{}{M_{\odot}}, and the surrounding large-scale structures (LSSs) with the friends-of-friends algorithm. We find that clusters with low fractions of quiescent galaxies tend to be connected with extended LSSs as expected in the web-feeding model. We also investigated the time evolution of the web-feeding trend using the IllustrisTNG cosmological simulation. Even though no clear correlation between the quiescent galaxy fraction of galaxy clusters and the significance of LSSs around them is found in the simulation, we verify that the quiescent galaxy fractions of infallers such as groups ($M_{200} \geq 10^{12}$ \SI{}{M_{\odot}}) and galaxies ($M_{200} < 10^{12}$ \SI{}{M_{\odot}}) is smaller than the quiescent fraction of cluster members and that infallers can lower the quiescent fraction of clusters. These results imply that cluster-to-cluster variations of quiescent galaxy fraction at $z \leq 1$ can at least partially be explained by feeding materials through cosmic webs to clusters.

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arXiv2024

Exploring Unobscured QSOs in the Southern Hemisphere with KS4

We present a catalog of unobscured QSO candidates in the southern hemisphere from the early interim data of the KMTNet Synoptic Survey of Southern Sky (KS4). The KS4 data covers $\sim2500\,{\rm deg}^{2}$ sky area, reaching 5$σ$ detection limits of $\sim$22.1-22.7 AB mag in the $BVRI$ bands. Combining this with available infrared photometric data from the surveys covering the southern sky, we select the unobscured QSO candidates based on their colors and spectral energy distributions (SEDs) fitting results. The final catalog contains 72,964 unobscured QSO candidates, of which only 0.4% are previously identified as QSOs based on spectroscopic observations. Our selection method achieves an 87% recovery rate for spectroscopically confirmed bright QSOs at $z<2$ within the KS4 survey area. In addition, the number count of our candidates is comparable to that of spectroscopically confirmed QSOs from the Sloan Digital Sky Survey in the northern sky. These demonstrate that our approach is effective in searching for unobscured QSOs in the southern sky. Future spectro-photometric surveys covering the southern sky will enable us to discern their true nature and enhance our understanding of QSO populations in the southern hemisphere.

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arXiv2024

Red Type-1 Quasars after Cosmic Noon and Impact on $L_{\rm UV}$-related Quasar Statistics

Over the past decades, nearly a million quasars have been explored to shed light on the evolution of supermassive black holes and galaxies. The ultraviolet-to-optical spectra of type-1 quasars particularly offer insights into their black hole activities. Recent findings, however, raise questions about the prevalence of red type-1 quasars of which colors might be due to dust-obscuration and their potential influence on luminosity-related properties of quasars. We examine the fraction of red type-1 quasars within the redshift range of $0.68\leq z < 2.20$, applying spectral energy distribution (SED) fitting using optical-to-MIR photometric data of Sloan Digital Sky Survey Data Release 14 quasars. Approximately 10\,\% of the type-1 quasars exhibit red colors suggestive of dust obscuration. There is an association between the brightness of the MIR luminosity and a higher fraction of red type-1 quasars, albeit with negligible redshift evolution. By employing $E(B-V)$ values from the SED fitting, we obtained dereddened luminosity of the red type-1 quasars and reassess the quasar luminosity function (QLF) and black hole mass ($M_{\rm BH}$) estimates. Result shows a modest increase in the number density of bright quasars, linking to more flatten bright-end slope of QLFs, while $M_{\rm BH}$ adjustments are minimal. Current SDSS selections in optical could miss a significant population of heavily dust-obscured quasars. As future MIR surveys like SPHEREx expand, they may reveal enough obscured quasars to prompt a more profound revision of fundamental quasar properties.

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arXiv2024

Eddington Ratios of Dust-obscured Quasars at $z \lesssim 1$: Evidence Supporting Dust-obscured Quasars as Young Quasars

Dust-obscured quasars have been suspected as the intermediate stage galaxies between merger-driven star-forming galaxies and unobscured quasars. This merger-driven galaxy evolution scenario suggests that dust-obscured quasars exhibit higher Eddington ratios ($λ_{\rm Edd}$) than those of unobscured quasars. However, their high dust obscuration poses challenges to accurately measuring their $λ_{\rm Edd}$ using commonly employed bolometric luminosity ($L_{\rm bol}$) and black hole (BH) mass ($M_{\rm BH}$) estimators based on the ultraviolet (UV) or optical luminosity. Recently, Kim et al. (2023) established new estimators for $L_{\rm bol}$ and $M_{\rm BH}$ based on mid-infrared (MIR) continuum luminosity ($L_{\rm MIR}$), which are less affected by dust obscuration. These estimators enable the study of a large number of dust-obscured quasars across a wide redshift range. In this study, we measure the $λ_{\rm Edd}$ values of 30 dust-obscured quasars at $z \lesssim 1$, the largest sample size to date, using the $L_{\rm MIR}$-based $L_{\rm bol}$ and $M_{\rm BH}$ estimators. Our findings reveal that dust-obscured quasars exhibit significantly higher $λ_{\rm Edd}$ values compared to unobscured quasars. Moreover, we confirm that the enhanced $λ_{\rm Edd}$ values of dust-obscured quasars maintain consistency across the redshift span of 0 to 1. Our results strongly support the picture that dust-obscured quasars are in the earlier stage than unobscured quasars in the merger-driven galaxy evolutionary track.

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arXiv2024

Host Galaxy Properties of Gamma-ray Bursts Involving Neutron Star Binary Mergers and Its Impact on Kilonovae Rates

In the upcoming gravitational wave (GW) observing runs, identifying host galaxies is crucial as it provides essential redshift information and enables the use of GW events as standard sirens. However, pinpointing host galaxies remains challenging due to the large localization uncertainties and the rapidly fading nature of their optical counterparts. Analyzing the host galaxies of short gamma-ray bursts (sGRBs) offers an alternative approach to deepen our understanding of the environments where binary neutron stars (BNS) primarily merge. This study compiles archival photometric data for the host galaxies of 76 sGRBs and 4 hybrid GRBs that are long GRBs accompanied by kilonova-like signals. We use this data to evaluate their physical properties through spectral energy distribution (SED) fitting. To assess the characteristics of the host galaxies, we utilized a volume-limited sample ($z<0.5$) from the COSMOS field as a control group. Contrary to expectations that the BNS merger rate is proportional to host stellar mass, the short and hybrid GRB population appears less massive than the mass-weighted distribution of the control sample. Instead, we propose a formulation for the expected BNS merger rate from a galaxy as $\log(n_{\mathrm{BNS}}/\mathrm{Gyr}) = 0.86 \times \log(M_*/M_{\odot}) + 0.44 \times \log(\mathrm{sSFR}/\mathrm{yr}) + 0.857$, which optimally explains the deviation between the stellar mass distributions of the GRB host galaxies and the control sample. These insights provide a strategic framework for targeted GW follow-ups and enhance our ability to identify potential host galaxies for future GW events.

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arXiv2024

TCSpy: Multi-telescope Array Control Software for 7-Dimensional Telescope (7DT)

We introduce a novel software called TCSpy which is designed to efficiently control a multi-telescope array through network-based protocols. The primary objectives of TCSpy include centralized control of the array, support for diverse observation modes, and swift responses to the follow-up observations of astronomical transients. To achieve these objectives, TCSpy utilizes the ASCOM Alpaca protocol in conjunction with Alpyca, establishing robust communication among multiple telescope units. For the practical application of TCSpy, we implement TCSpy within the 7-Dimensional Telescope (7DT). 7DT is a telescope array consisting of 20, 0.5-m telescopes, equipped with 40 different medium-band filters. The main scientific goals of 7DT include detecting the optical counterparts of gravitational-wave sources, identifying kilonovae, and the spectral mapping of the southern sky. Through the integration of TCSpy, 7DT can achieve these scientific objectives with its unique observation modes and rapid follow-up capabilities.

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arXiv2024

Multi-Object Spectroscopy of Galaxy Clusters at $z \sim 0.95$ in Ultra Deep Survey Field with Different Star-formation Properties and Large-scale Environments

While galaxy clusters are dominated by quiescent galaxies at local, they show a wide range in quiescent galaxy fraction (QF) at higher redshifts. Here, we present the discovery of two galaxy clusters at $z \sim 0.95$ with contrasting QFs despite having similar masses (log ($M_{200}/M_{\odot}$)$ \sim 14$) and spectra and redshifts of 29 galaxies in these clusters and 76 galaxies in the surrounding area. The clusters are found in the Ultra Deep Survey (UDS) field and confirmed through multi-object spectroscopic (MOS) observation using the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope. The two clusters exhibit QFs of $0.094^{+0.11}_{-0.032}$ and $0.38^{+0.14}_{-0.11}$, respectively. Analysis of large-scale structures (LSSs) surrounding these clusters finds that properties of these clusters are consistent with the anti-correlation trend between the QF and the extent of surrounding LSS, found in Lee et al. (2019), which can be interpreted as a result from the replenishment of young, star-forming galaxies keeps the QF low when galaxy clusters are accompanied by rich surrounding environments.

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arXiv2024

Introduction to the 7-Dimensional Telescope: Commissioning Procedures and Data Characteristics

The 7-Dimensional Telescope (7DT) is a multi-telescope system designed to identify electromagnetic (EM) counterparts of gravitational-wave (GW) sources. Consisting of 20 50-cm telescopes along with 40 medium-band filters of 25 nm width, 7DT can obtain spectral mapping images for a large field of view (~1.25 square degrees). Along with flexible operation, real-time data reduction, and analysis, the 7DT's spectral mapping capability enables 7DT to follow up GW events quickly and discover EM counterparts. Among 20 planned telescopes, 12 units are deployed at the El Sauce Observatory located at Rio Hurtado Valley in Chile. Since we obtained the first light of 7DT in October 2023, we started its commissioning procedures including examination of bias levels, master flat production, and spectrophotometric standardization. In this talk, we present 7DT instruments and their set-up, commissioning procedures, and data characteristics of 7DT along with our three-layered surveys which are assumed to be initiated in early 2024.

astro-ph.IM↗

arXiv2024

Project Management for Ground-based Telescope Array Development

Center for the Gravitational-Wave Universe at Seoul National University has been operating its main observational facility, the 7-Dimensional Telescope (7DT) since October 2023. Located at El Sauce Observatory in Chilean Rio Hurtado Valley, 7DT consists of 20 50-cm telescopes equipped with 40 medium-band filters of 25 nm full width at half maximum along with a CMOS camera of 61 megapixels. 7DT produces about 1 TB per night of spectral mapping image data including calibration, and the byproduct of the data reduction pipeline once our planned three layered surveys (Reference Imaging Survey, Wide Field Survey, and Intensive Monitoring Survey) start in 2024. We are expecting to generate 1 PB per year by combining raw data, reduced data, and data products (e.g. calibrated stacked images, spectral cubes, and object catalogs). To incorporate this huge amount of data, we now have a data storage for 1 PB which we will increment by 1 PB per year. We also have a high-performance computation facility that is equipped with 2 NVIDIA A100 GPU cards since we plan to carry out real-time data reduction and analysis for follow-up observation data of gravitational wave events. To incorporate this, we established a 400 Mbps network connection between the facilities in Korea and Chile. Taking advantage of the high-performance network, we have been carrying out fully remote operations since October 2023. In this talk, we present details of designing, planning, and executing the ground-based telescope facility project, especially within low-budget academic environments. While we cover as much ground as possible, we will emphasize human resource management, project risk management, and financial contingency management.

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arXiv2024

The Robotic MAAO 0.7m Telescope System: Performance and Standard Photometric System

We introduce a 0.7m telescope system at the Miryang Arirang Astronomical Observatory (MAAO), a public observatory in Miryang, Korea. System integration and a scheduling program enable the 0.7m telescope system to operate completely robotically during nighttime, eliminating the need for human intervention. Using the 0.7m telescope system, we obtain atmospheric extinction coefficients and the zero-point magnitudes by observing standard stars. As a result, we find that atmospheric extinctions are moderate but they can sometimes increase depending on the weather conditions. The measured 5-sigma limiting magnitudes reach down to BVRI=19.4-19.6 AB mag for a point source with a total integrated time of 10 minutes under clear weather conditions, demonstrating comparable performance with other observational facilities operating under similar specifications and sky conditions. We expect that the newly established MAAO 0.7m telescope system will contribute significantly to the observational studies of astronomy. Particularly, with its capability for robotic observations, this system, although its primary duty is for public viewing, can be extensively used for the time-series observation of transients.

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arXiv2023

Gravitational-wave Electromagnetic Counterpart Korean Observatory (GECKO): GECKO Follow-up Observation of GW190425

One of the keys to the success of multimessenger astronomy is the rapid identification of the electromagnetic wave counterpart, kilonova (KN), of the gravitational-wave (GW) event. Despite its importance, it is hard to find a KN associated with a GW event, due to a poorly constrained GW localization map and numerous signals that could be confused as a KN. Here, we present the Gravitational-wave Electromagnetic wave Counterpart Korean Observatory (GECKO) project, the GECKO observation of GW190425, and prospects of GECKO in the fourth observing run (O4) of the GW detectors. We outline our follow-up observation strategies during O3. In particular, we describe our galaxy-targeted observation criteria that prioritize based on galaxy properties. Armed with this strategy, we performed an optical and/or near-infrared follow-up observation of GW190425, the first binary neutron star merger event during the O3 run. Despite a vast localization area of 7460 deg^2, we observed 621 host galaxy candidates, corresponding to 29.5% of the scores we assigned, with most of them observed within the first 3 days of the GW event. Ten transients were discovered during this search, including a new transient with a host galaxy. No plausible KN was found, but we were still able to constrain the properties of potential KNe using upper limits. The GECKO observation demonstrates that GECKO can possibly uncover a GW170817-like KN at a distance less than 200 Mpc if the localization area is of the order of hundreds of square degrees, providing a bright prospect for the identification of GW electromagnetic wave counterparts during the O4 run.

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arXiv2023

Estimators of Bolometric Luminosity and Black Hole Mass with Mid-infrared Continuum Luminosities for Dust-obscured Quasars: Prevalence of Dust-obscured SDSS Quasars

We present bolometric luminosity ($L_{\rm bol}$) and black hole (BH) mass ($M_{\rm BH}$) estimators based on mid-infrared (MIR) continuum luminosity (hereafter, $L_{\rm MIR}$) that are measured from infrared (IR) photometric data. The $L_{\rm MIR}$-based estimators are relatively immune from dust extinction effects, hence they can be used for dust-obscured quasars. To derive the $L_{\rm bol}$ and $M_{\rm BH}$ estimators, we use unobscured quasars selected from the Sloan Digital Sky Survey (SDSS) quasar catalog, which have wide ranges of $L_{\rm bol}$ ($10^{44.62}$--$10^{46.16}$\,$\rm erg\,s^{-1}$) and $M_{\rm BH}$ ($10^{7.14}$--$10^{9.69}$\,$M_{\odot}$). We find empirical relations between (i) continuum luminosity at 5100\,$\rm{Å}$ (hereafter, L5100) and $L_{\rm MIR}$; (ii) $L_{\rm bol}$ and $L_{\rm MIR}$. Using these relations, we derive the $L_{\rm MIR}$-based $L_{\rm bol}$ and $M_{\rm BH}$ estimators. We find that our estimators allow the determination of $L_{\rm bol}$ and $M_{\rm BH}$ at an accuracy of $\sim$0.2\,dex against the fiducial estimates based on the optical properties of the unobscured quasars. We apply the $L_{\rm MIR}$-based estimators to SDSS quasars at $z \lesssim 0.5$ including obscured ones. The ratios of $L_{\rm bol}$ from the $L_{\rm MIR}$-based estimators to those from the optical luminosity-based estimators become larger with the amount of the dust extinction, and a non-negligible fraction ($\sim$15\,\%) of the SDSS quasars exhibits ratios greater than 1.5. This result suggests that dust extinction can significantly affect physical parameter derivations even for SDSS quasars, and that dust extinction needs to be carefully taken into account when deriving quasar properties.

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arXiv2023

PEARLS: Near Infrared Photometry in the JWST North Ecliptic Pole Time Domain Field

We present Near-Infrared (NIR) ground-based Y, J, H, and K imaging obtained in the James Webb Space Telescope North Ecliptic Pole Time Domain Field (TDF) using the MMT-Magellan Infrared Imager and Spectrometer (MMIRS) on the MMT.These new observations cover a field of approximately 230 arcmin^2 in Y, H, and K and 313 arcmin^2 in J. Using Monte Carlo simulations we estimate a 1 sigma depth relative to the background sky of (Y, J, H, K}) = (23.80, 23.53, 23.13, 23.28) in AB magnitudes for point sources at a 95% completeness level. These observations are part of the ground-based effort to characterize this region of the sky, supplementing space-based data obtained with Chandra, NuSTAR, XMM, AstroSat, HST, and JWST. This paper describes the observations and reduction of the NIR imaging and combines these NIR data with archival imaging in the visible, obtained with the Subaru Hyper-Suprime-Cam, to produce a merged catalog of 57,501 sources. The new observations reported here, plus the corresponding multi-wavelength catalog, will provide a baseline for time-domain studies of bright sources in the TDF.

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arXiv2023

The Early Light Curve of a Type Ia Supernova 2021hpr in NGC 3147: Progenitor Constraints with the Companion Interaction Model

The progenitor system of Type Ia supernovae (SNe Ia) is expected to be a close binary system of a carbon/oxygen white dwarf (WD) and a non-degenerate star or another WD. Here, we present results from a high-cadence monitoring observation of SN 2021hpr in a spiral galaxy, NGC 3147, and constraints on the progenitor system based on its early multi-color light curve data. First, we classify SN 2021hpr as a normal SN Ia from its long-term photometric and spectroscopic data. More interestingly, we found a significant "early excess" in the light curve over a simple power-law $\sim t^{2}$ evolution. The early light curve evolves from blue to red and blue during the first week. To explain this, we fitted the early part of $BVRI$-band light curves with a two-component model of the ejecta-companion interaction and a simple power-law model. The early excess and its color can be explained by shock cooling emission due to a companion star having a radius of $8.84\pm0.58$$R_{\odot}$. We also examined HST pre-explosion images with no detection of a progenitor candidate, consistent with the above result. However, we could not detect signs of a significant amount of the stripped mass from a non-degenerate companion star ($\lesssim0.003\,M_{\odot}$ for H$α$ emission). The early excess light in the multi-band light curve supports a non-degenerate companion in the progenitor system of SN 2021hpr. At the same time, the non-detection of emission lines opens a door for other methods to explain this event.

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arXiv2023

Unusual Hard X-ray Flares Caught in NICER Monitoring of the Binary Supermassive Black Hole Candidate AT2019cuk/Tick Tock/SDSS J1430+2303

The nuclear transient AT2019cuk/Tick Tock/SDSS J1430+2303 has been suggested to harbor a supermassive black hole (SMBH) binary near coalescence. We report results from high-cadence NICER X-ray monitoring with multiple visits per day from January-August 2022, as well as continued optical monitoring during the same time period. We find no evidence of periodic/quasi-periodic modulation in the X-ray, UV, or optical bands, however we do observe exotic hard X-ray variability that is unusual for a typical AGN. The most striking feature of the NICER light curve is repetitive hard (2-4 keV) X-ray flares that result in distinctly harder X-ray spectra compared to the non-flaring data. In its non-flaring state, AT2019cuk looks like a relatively standard AGN, but it presents the first case of day-long, hard X-ray flares in a changing-look AGN. We consider a few different models for the driving mechanism of these hard X-ray flares, including: (1) corona/jet variability driven by increased magnetic activity, (2) variable obscuration, and (3) self-lensing from the potential secondary SMBH. We prefer the variable corona model, as the obscuration model requires rather contrived timescales and the self-lensing model is difficult to reconcile with a lack of clear periodicity in the flares. These findings illustrate how important high-cadence X-ray monitoring is to our understanding of the rapid variability of the X-ray corona and necessitate further high-cadence, multi-wavelength monitoring of changing-look AGN like AT2019cuk to probe the corona-jet connection.

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arXiv2023

The JCMT SCUBA-2 Survey of the James Webb Space Telescope North Ecliptic Pole Time-Domain Field

The James Webb Space Telescope Time-Domain Field (JWST-TDF) is an $\sim$14$'$ diameter field near the North Ecliptic Pole that will be targeted by one of the JWST Guaranteed Time Observations programs. Here, we describe our James Clerk Maxwell Telescope SCUBA-2 850 $μ$m imaging of the JWST-TDF and present the submillimeter source catalog and properties. We also present a catalog of radio sources from Karl J. Jansky Very Large Array 3 GHz observations of the field. These observations were obtained to aid JWST's study of the dust-obscured galaxies that contribute significantly to the cosmic star formation at high redshifts. Our deep 850 $μ$m map covers the JWST TDF at a noise level of $σ_{850}$ = 1.0 mJy beam$^{-1}$, detecting 83/31 sources in the main/supplementary signal-to-noise ratio (S/N $>$ 4 / S/N = 3.5 - 4) sample respectively. The 3 GHz observations cover a 24$'$ diameter field with a 1 $σ$ noise of 1$μ$Jy beam$^{-1}$ at a 0$.\!\!^{\prime\prime}$7 FWHM. We identified eighty-five 3 GHz counterparts to sixty-six 850 $μ$m sources and then matched these with multiwavelength data from the optical to the mid-infrared wave bands. We performed spectral energy distribution fitting for 61 submillimeter galaxies (SMGs) matched with optical/near-infrared data, and found that SMGs at S/N $>$ 4 have a median value of $z_{phot} = $2.22 $\pm$ 0.12, star formation rates of 300 $\pm$ 40 M$_{\odot}\,{\rm yr^{-1}}$ (Chabrier initial mass function), and typical cold dust masses of 5.9 $\pm$ 0.7 $ \times$ 10$^{8} $M$_{\odot}$, in line with bright SMGs from other surveys. The large cold dust masses indicate correspondingly large cool gas masses, which we suggest are a key factor necessary to drive the high star formation rates seen in this population

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