Searches for Population III pair-instability supernovae: Predictions for ULTIMATE-Subaru and WFIRST
Takashi J. Moriya, Kenneth C. Wong, Yusei Koyama, Masaomi Tanaka, Masamune Oguri, Stefan Hilbert, Ken'ichi Nomoto
aa r X i v : . [ a s t r o - ph . H E ] M a r Publ. Astron. Soc. Japan (2019) 00(0), 1–10doi: 10.1093/pasj/xxx000 Searches for Population III pair-instabilitysupernovae: Predictions for ULTIMATE-Subaruand WFIRST
Takashi J. M
ORIYA , Kenneth C. W ONG , Yusei K
OYAMA , MasaomiT ANAKA , Masamune O GURI , Stefan H
ILBERT and Ken’ichi N
OMOTO Division of Theoretical Astronomy, National Astronomical Observatory of Japan, NationalInstitutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University ofTokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,Chiba 277-8583, Japan Subaru Telescope, National Astronomical Observatory of Japan, National Institutes ofNatural Sciences, 650 North A’ohoku Place, Hilo, HI 96720, USA Astronomical Institute, Tohoku University, 6-3 Aramaki Aza-Aoba, Aoba-ku, Sendai980-8578, Japan Research Center for the Early Universe, Graduate School of Science, The University ofTokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan Department of Physics, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo,Bunkyo, Tokyo 113-0033, Japan Exzellenzcluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany Ludwig-Maximilians-Universit ¨at, Universit ¨ats-Sternwarte, Scheinerstr. 1, D-81679 M ¨unchen,Germany ∗ E-mail: [email protected]
Received 18-Jan-2019; Accepted 02-Mar-2019
Abstract
ULTIMATE-Subaru (Ultra-wide Laser Tomographic Imager and MOS with AO for TranscendentExploration on Subaru) and WFIRST (Wide Field Infra-Red Survey Telescope) are the nextgeneration near-infrared instruments that have a large field-of-view. They allow us to conductdeep and wide transient surveys in near-infrared. Such a near-infrared transient survey en-ables us to find very distant supernovae that are redshifted to the near-infrared wavelengths.We have performed the mock transient surveys with ULTIMATE-Subaru and WFIRST to in-vestigate their ability to discover Population III pair-instability supernovae. We found that a5-year 1 deg K -band transient survey with the point-source limiting magnitude of 26.5 magwith ULTIMATE-Subaru may find about 2 Population III pair-instability supernovae beyond theredshift of 6. A 5-year 10 deg survey with WFIRST reaching 26.5 mag in the F band mayfind about 7 Population III pair-instability supernovae beyond the redshift of 6. We also find thatthe expected numbers of the Population III pair-instability supernova detections increase abouta factor of 2 if the near-infrared transient surveys are performed towards clusters of galaxies.Other supernovae such as Population II pair-instability supernovae would also be detected inthe same survey. This study demonstrates that the future wide-field near-infrared instrumentsallow us to investigate the explosions of the first generation supernovae by performing the deepand wide near-infrared transient surveys. c (cid:13) Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0
ULTIMATE-Subaru (Ultra-wide Laser Tomographic Imager and MOS with AO for TranscendentExploration on Subaru) and WFIRST (Wide Field Infra-Red Survey Telescope) are the nextgeneration near-infrared instruments that have a large field-of-view. They allow us to conductdeep and wide transient surveys in near-infrared. Such a near-infrared transient survey en-ables us to find very distant supernovae that are redshifted to the near-infrared wavelengths.We have performed the mock transient surveys with ULTIMATE-Subaru and WFIRST to in-vestigate their ability to discover Population III pair-instability supernovae. We found that a5-year 1 deg K -band transient survey with the point-source limiting magnitude of 26.5 magwith ULTIMATE-Subaru may find about 2 Population III pair-instability supernovae beyond theredshift of 6. A 5-year 10 deg survey with WFIRST reaching 26.5 mag in the F band mayfind about 7 Population III pair-instability supernovae beyond the redshift of 6. We also find thatthe expected numbers of the Population III pair-instability supernova detections increase abouta factor of 2 if the near-infrared transient surveys are performed towards clusters of galaxies.Other supernovae such as Population II pair-instability supernovae would also be detected inthe same survey. This study demonstrates that the future wide-field near-infrared instrumentsallow us to investigate the explosions of the first generation supernovae by performing the deepand wide near-infrared transient surveys. c (cid:13) Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0
Key words: supernovae: general — stars: massive — stars: Population III
The last decade encountered the great success of optical tran-sient surveys. Many optical transient surveys such as PTF (Lawet al. 2009), Pan-STARRS (Chambers et al. 2016), SkyMapper(Keller et al. 2007), KISS (Morokuma et al. 2014), and HSC(Tanaka et al. 2016, Moriya et al. 2019, Yasuda et al. sub-mitted) have shown that stellar deaths have much more vari-eties than expected before. One of the most fascinating dis-coveries from these optical transient surveys are the discoveryof very luminous supernovae (SNe) called superluminous su-pernovae (SLSNe, Quimby et al. 2011; see Moriya et al. 2018for a review). They are often more than 10 times brighter thancanonical SNe. Shortly after their discovery, it has been specu-lated that their huge luminosities could be due to massive pro-duction of radioactive Ni and, therefore, SLSNe might bepair-instability SNe (PISNe) (e.g., Smith et al. 2007; Gal-Yamet al. 2009). PISNe are theoretically predicted explosions ofvery massive stars (Rakavy & Shaviv 1967; Barkat et al. 1967).PISNe could lead to the production of more than 10 M ⊙ of Ni (Heger & Woosley 2002), which is generally required to explainthe huge luminosity of SLSNe.Although PISNe were originally suggested to be a probableorigin of SLSNe, it turned out that SLSNe generally show dif-ferent observational properties than those expected from PISNe(e.g., Kasen et al. 2011; Dessart et al. 2012; Whalen et al.2014; Jerkstrand et al. 2016; Tolstov et al. 2017 but see alsoKozyreva et al. 2016). PISNe are a natural consequence ofvery massive stars that have the helium core masses between ∼
70 M ⊙ and ∼
140 M ⊙ (Langer 2012), and we would ob-serve them if massive stars with such massive cores exist.Unfortunately, it is very hard to keep the cores massive enoughto explode as PISNe until their deaths in the solar metallicityenvironment (e.g., Yoshida et al. 2014, but see also Georgyet al. 2017) and PISNe are suggested to occur when the metal-licity is below one third of the solar metallicity (Langer et al.2007). The most promising stars to explode as PISNe are thefirst stars, or Population III (Pop III) stars. Pop III stars do notsuffer from wind mass loss and they can grow massive enoughcores to explode as PISNe when their zero-age main-sequence(ZAMS) masses are between ∼
140 M ⊙ and ∼
260 M ⊙ (Heger& Woosley 2002; Umeda & Nomoto 2002). Pop III stars arealso predicted to be dominated by massive stars including thosein the PISN mass range (e.g., Hirano et al. 2015). Therefore,many Pop III stars are likely to explode as PISNe.Pop III star formation could last until z ∼ (e.g., de Souzaet al. 2014) and, therefore, we need to reach at least z ∼ to look for Pop III PISNe. It is inevitable to perform transient surveys innear infrared (NIR) to search for transients at such high redshifts(e.g., Scannapieco et al. 2005; Tanaka et al. 2013; Whalen et al.2013b; de Souza et al. 2013; Hartwig et al. 2018). Only a hand-ful of NIR transient surveys are conducted in the last decade(e.g., Mattila et al. 2012; Kool et al. 2018; Kasliwal et al. 2017).However, many NIR wide field imaging instruments are cur-rently planned and NIR transient surveys would be the frontierof transient surveys in the coming decade (e.g., Inserra et al.2017; Hounsell et al. 2017). Among them, ULTIMATE-Subaru(Ultra-wide Laser Tomographic Imager and MOS with AO forTranscendent Exploration ) and WFIRST (Wide-Field InfraRedSurvey Telescope, Spergel et al. 2015) have a wide-field NIRimaging facility that is suitable to perform deep and wide NIRtransient surveys. In this paper, we perform mock NIR tran-sient surveys with ULTIMATE-Subaru and WFIRST to searchfor Pop III PISNe at z > ∼ and study optimal survey strategies todetect them. We also take the effect of the luminosity amplifica-tions due to gravitational lensing into account (cf. Whalen et al.2013a). In this paper, we focus on survey strategies and obser-vational methods to discover Pop III PISNe and we briefly showthe effect of the gravitational lensing in this paper. The detailson how gravitational lensing could affect the survey results, aswell as the details on how we estimate the gravitational lensingeffect, are discussed in an accompanying paper by Wong et al.(2019).The rest of this paper is organized as follows. We firstpresent our method of mock observations in Section 2. Wepresent our results of mock observations and discuss the opti-mal strategy to look for Pop III PISNe at z > ∼ in Section 3.We have general discussion of our results in Section 4 and con-clude this paper in Section 5. Throughout this paper, we adoptthe standard Λ CDM cosmology with H = 70 km s − Mpc − , Ω Λ = 0 . , and Ω M = 0 . . All the magnitudes presented in thispaper are in the AB magnitude system. We first introduce ULTIMATE-Subaru and WFIRST. The twoinstruments are complimentary to each other in terms of thewavelength coverage and the field-of-view (FoV). ublications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0 t r an s m i ss i on wavelength µ mF184(WFIRST) K(ULTIMATE-Subaru) Fig. 1.
Filters used in our SN survey simulations. The K -band filter as-sumed for ULTIMATE-Subaru is that currently used by Subaru/MOIRCS. The F filter is the reddest filter currently planned by WFIRST. ULTIMATE-Subaru is the next generation wide-field AO sys-tem with a wide-field NIR instrument. It is currently planned tohave the NIR imager with the FoV of ′ x ′ ( .
054 deg ). Itrequires 18.4 pointings to cover , for example.The details of the instrument are still under discussion. Thereddest band currently planned is the K band. We expectthat the instrument specification such as filters and exposuretime of ULTIMATE-Subaru will be similar to those of Multi-Object Infrared Camera and Spectrograph (MOIRCS) currentlyon Subaru (Suzuki et al. 2008; Ichikawa et al. 2006). We adoptthe K band filter of MOIRCS in this study (Fig. 1). Accordingto the exposure time calculator for MOIRCS , it takes 2.6 hoursto reach the limiting magnitude (signal-to-noise ratio of 5 for apoint source throughout this paper) of 26.0 mag in the K bandwith a standard condition ( . seeing with . aperture). Withthe best expected condition, it is possible to reach . seeing.Then, the limiting magnitude of 26.5 mag in the K band can bereached in 4.6 hours. WFIRST is the next generation space telescope with the wide-field imager that has the FoV of .
28 deg (Spergel et al. 2015).3.6 pointings are required to cover .The reddest filter for the imager currently planned is the F filter (Fig. 1) and we adopt it in this study. The deepest SNsurvey currently planned with WFIRST has the limiting magni-tude of about 26.5 mag. It takes 0.5 hours to reach 26.5 magin F . The limiting magnitude of 26.0 mag can be reachedin 0.2 hours. We also perform a simulation with the limitingmagnitude of 27.0 mag, which can be reached in 1.3 hours. We perform our mock observation simulations with several dif-ferent survey strategies. We fix our survey period to be 5 years.We only use one filter in our mock transient surveys, K forULTIMATE-Subaru and F for WFIRST.The survey field is assumed to be observed repeatedly withan interval of t int . We also set the minimum number of detec-tions N d for a transient to be regarded as a discovery. For ex-ample, if we assume N d = 3 , PISNe detected more than 3 timesare regarded as PISN discoveries. In this case, PISNe detectedonly two times are ignored.For the ULTIMATE-Subaru survey, we assume two differ-ent limiting magnitudes, 26.5 mag and 26.0 mag in the K band.It requires about 70 hours to cover with 26.5 mag forone epoch. Assuming t int = 180 days , the 5-year tran-sient survey with the 26.5 mag limit takes 860 hours in total.If we adopt 26.0 mag as the survey limiting magnitude, it takes48 hours to cover . With t int = 180 days for 5 years,480 hours and 960 hours are required to conduct the and surveys, respectively.WFIRST requires 2 hours and 0.75 hours to cover with the limiting magnitude of 26.5 mag and 26.0 mag, respec-tively. For instance, the transient survey with t int = 180 days covering
10 deg in 5 years takes 200 hours (26.5 mag limit)and 75 hours (26.0 mag limit). We adopt PISN light curves (LCs) predicted by Kasen et al.(2011) for our observation simulations. The LCs are numeri-cally obtained from the PISN progenitors of Heger & Woosley(2002). The peak luminosity of the R250 and He130 models(see the next paragraph for the description of the models) ex-ceeds K = 26 . at z = 6 (Fig. 2). The R225 and He120models are brighter than 26.5 mag in the K band at z = 6 (Fig. 2). Thus, the R225 and He120 explosions at z > ∼ canonly be observed when we conduct the transient surveys withthe limiting magnitude of 26.5 mag in the K band. If we use the F filter, only R250 and R225 are brighter than . atthe peak at z > ∼ (Fig. 2). For reference, the peak magnitude ofthe R250 model in the H band of WFIRST (Spergel et al. 2015)is around 27.1 mag and it is much more efficient to conduct asurvey in the F band. The F band magnitudes becomesignificantly faint in He130 and He120 models because the he-lium core models are redder than the red supergiant models. Forexample, the synthetic spectra of R250 at around the maximumluminosity peak at ∼ ˚A, while the helium core modelspeak at ∼ ˚A (Kasen et al. 2011). This difference likelyoriginates from the difference in Fe-group absorption. The redsupergiant models have the photosphere in their hydrogen-rich Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0
10 deg in 5 years takes 200 hours (26.5 mag limit)and 75 hours (26.0 mag limit). We adopt PISN light curves (LCs) predicted by Kasen et al.(2011) for our observation simulations. The LCs are numeri-cally obtained from the PISN progenitors of Heger & Woosley(2002). The peak luminosity of the R250 and He130 models(see the next paragraph for the description of the models) ex-ceeds K = 26 . at z = 6 (Fig. 2). The R225 and He120models are brighter than 26.5 mag in the K band at z = 6 (Fig. 2). Thus, the R225 and He120 explosions at z > ∼ canonly be observed when we conduct the transient surveys withthe limiting magnitude of 26.5 mag in the K band. If we use the F filter, only R250 and R225 are brighter than . atthe peak at z > ∼ (Fig. 2). For reference, the peak magnitude ofthe R250 model in the H band of WFIRST (Spergel et al. 2015)is around 27.1 mag and it is much more efficient to conduct asurvey in the F band. The F band magnitudes becomesignificantly faint in He130 and He120 models because the he-lium core models are redder than the red supergiant models. Forexample, the synthetic spectra of R250 at around the maximumluminosity peak at ∼ ˚A, while the helium core modelspeak at ∼ ˚A (Kasen et al. 2011). This difference likelyoriginates from the difference in Fe-group absorption. The redsupergiant models have the photosphere in their hydrogen-rich Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0
24 25 26 27 28 29 0 500 1000 1500 2000 2500 3000 AB m agn i t ude days after explosion in observer frameK (ULTIMATE-Subaru) He130He120R250R225z = 5.56.06.5 24 25 26 27 28 29 0 500 1000 1500 2000 2500 3000 AB m agn i t ude days after explosion in observer frameF184 (WFIRST) He130He120R250R225z = 5.56.06.5 Fig. 2.
Examples of PISN LCs adopted in our mock observation simulations. Left panel shows the K -band LCs expected for ULTIMATE-Subaru for whichwe assume the 26.0 mag and 26.5 mag limits (horizontal lines) in our survey simulations. Right panel shows the F -band LCs for WFIRST for which weassume the 26.5 mag limit (horizontal line) in the deepest survey simulations. envelope and it is far from the central region where Fe-group el-ements locate. However, the helium core models have the pho-tosphere at or close to where the Ni is synthesized and theyare more affected by absorption by the Fe-group elements.R250 and R225 are the red supergiant (RSG) PISN progeni-tors with the ZAMS mass of 250 M ⊙ and 225 M ⊙ , respectively.They have the initial metallicity of − Z ⊙ . The masses at thetime of the explosion are
236 M ⊙ (R250) and
200 M ⊙ (R225)because of slight mass loss. A similar amount of mass loss isfound even in the Pop III RSG PISN progenitors in Moriya &Langer (2015). Therefore, the RSG PISN LC properties are notlikely to be much different from those of the zero-matellicityprogenitors. He130 and He120 are the hydrogen-free PISNprogenitors with the initial helium core masses of 130 M ⊙ and120 M ⊙ , respectively. It is the zero-metallicity (Pop III) modelsand the initial masses are kept until the time of the explosionswithout mass loss. We adopt a PISN rate estimated by de Souza et al. (2014) in ourmock observations (Fig. 3). de Souza et al. (2014) estimatedthe Pop III PISN rate based on the cosmological simulation ofJohnson et al. (2013). We take the Pop III PISN rates estimatedfrom their high SFR estimates (SFR10 in de Souza et al. 2014).de Souza et al. (2014) estimated Pop III PISN rate above z = 6 .We also present the PISN discovery number estimates at Pop III PISN rate estimated by de Souza et al. (2014). (IMFs) to estimate the Pop III PISN rate. One is the SalpeterIMF and the other is the flat IMF. The cosmological simulationsof the first stars indicate that the IMF is close to the flat one inPop III stars (Hirano et al. 2015).The ZAMS mass range for Pop III PISNe is roughly between 140 M ⊙ and 260 M ⊙ (Heger & Woosley 2002). Only the R225(ZAMS mass of 225 M ⊙ ) and R250 (ZAMS mass of 250 M ⊙ )models in Pop III RSG PISN models of Kasen et al. (2011) be-come brighter than K = 26 . and F 184 = 26 . whenthey appear at z > ∼ . The R200 model (ZAMS mass of 200 M ⊙ )does not become bright enough. Kasen et al. (2011) does notprovide RSG PISN LCs between 200 M ⊙ and 225 M ⊙ and wecannot tell the exact minimum ZAMS mass to be brighter than26.5 mag. In this study, we assume that RSG Pop III PISNewhose ZAMS mass is above 215 M ⊙ become bright enough tobe observable at z ∼ with the K = 26 . limit.If we assume the K = 26 . limit, the R225 modelat z > ∼ cannot be observed and only R250 is observable.Similarly, Kasen et al. (2011) does not provide RSG PISN LCs ublications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0 between 225 M ⊙ and 250 M ⊙ and we cannot tell the exactminimum ZAMS mass to be bright enough to observe with thelimit. We assume that RSG Pop III PISNe whose ZAMS massis above 240 M ⊙ become bright enough to be observed at z ∼ with the K = 26 . limit. We assume that the R250 LC isthe representative LC of Pop III PISNe whose ZAMS massesare between 240 M ⊙ and 260 M ⊙ and the R225 LC is the rep-resentative LC of Pop III PISNe whose ZAMS masses are be-tween 215 M ⊙ and 240 M ⊙ .If we assume the flat IMF, the fraction of Pop III PISNe withthe ZAMS mass between 240 M ⊙ and 260 M ⊙ is 17%. In ourmock observations, we thus assume that the R250 PISNe ex-plode with the 17% rate of the total Pop III PISN rate obtainedby de Souza et al. (2014) in the case of the flat IMF. Similarly,21% of the Pop III PISN rate comes from between 215 M ⊙ and240 M ⊙ with the flat IMF and we assume that the R225 PISNeoccupies 21% of the Pop III IMF in case of the flat IMF. Onthe other hand, when we assume the Salpeter IMF, the PISNfraction in the ZAMS mass between 240 M ⊙ and 260 M ⊙ be-comes 8.7% and the PISN fraction in the ZAMS mass between 215 M ⊙ and 240 M ⊙ becomes 14%. Therefore, we assume thatthe R250 model and the R225 model explode with the 8.7% and14%, respectively, of the total PISN rate estimated by de Souzaet al. (2014) in the case of the Salpeter IMF.The bare helium core PISN models He120 and He130 areobservable at z > ∼ with our deep surveys (Fig. 2). However,it is not obvious from which ZAMS masses these massive barehelium core progenitors originate (see Section 4.1 for discus-sion). Therefore, we perform mock observations only consid-ering Pop III RSG PISN progenitors. We discuss the possibleeffect of helium core Pop III PISN progenitors in Section 4.The blue supergiant (BSG) Pop III PISNe are not observableat z > ∼ with the K = 26 . limit and a F 184 = 26 . limit. Many stellar evolution models predict that Pop III SLSNewith hydrogen explode as RSGs, not BSGs (e.g., Yoon et al.2012; Moriya & Langer 2015). Therefore, we ignore Pop IIIBSG PISNe in this study. We also study the effect of the brightness magnification due tothe gravitational lensing. Even if we observe a random fieldfor the survey, the SN brightness could be amplified becauseof the galaxies happened to exist at the line of sight. To studythe effect of the gravitational lensing towards the random field,we use the magnification probability distribution obtained byHilbert et al. (2007) based on ray tracing calculations throughthe Millennium simulation (Springel et al. 2005). The distri-butions are updated versions that include the effect of baryons(Hilbert et al. 2008). As presented in Wong et al. (2019), we findthe discrepancy between the magnification probability distribu- tions estimated by the HSC SSP survey data and those estimatedby using the simulation data. This discrepancy is likely fromthe incompleteness in the observational data and, therefore, weadopt the magnification probability distribution estimated basedon the simulation.The probability of the magnification amplification can besignificantly increased when the survey field is towards a mas-sive cluster of galaxies. We refer to Wong et al. (2019) for thedetails of the cluster magnification calculations, but provide abrief summary here. We calculate the magnification distribu-tion along lines of sight towards seven known massive ( M > M ⊙ ) clusters of galaxies to estimate this effect and extrap-olate it to our mock survey. These seven cluster models includethe model of the massive cluster J0850+3604 from Wong et al.(2017), as well as models of the six HST Frontier Fields (Lotzet al. 2017) clusters from Kawamata et al. (2016); Kawamataet al. (2018) constructed using Oguri (2010). Both methodsuse parameterized models that account for both the cluster darkmatter distribution and individual galaxies. We assume a ′ x ′ field-of-view. We calculate the source plane area as a func-tion of magnification for each of the seven clusters and take theaverage, extrapolated to the full area of our mock survey, tocalculate the expected number of detections. This is somewhatoptimistic, as these seven clusters are already among the mostmassive ones known, but there are potentially other clusters ofsimilar mass that are relatively unexplored (e.g., Wong et al.2013), and wide-area imaging surveys such as HSC, LSST, andEuclid could potentially find others. In regions of the sourceplane that are multiply-imaged, we take the magnification ofthe brightest image as the value at that particular location. We use our own code to conduct mock observations to estimatethe PISN detectability. The redshifts beyond 5 are binned with ∆ z = 0 . and PISNe are assumed to appear in each redshift binwith the PISN rates estimated in the previous section. Once aPISN appears at a redshift bin, the apparent magnitudes in theobserver frame at the time of the observation that is determinedby t int and the observational period are evaluated. For this pur-pose, we use redshifted PISN LCs that are calculated based onthe PISN spectral model of Kasen et al. (2011) in advance foreach redshifts. We check the expected observations and judge ifthe observations match our criteria, such as the limiting magni-tudes and N d , to regard them as a discovery. When we take thegravitational lensing effect into account, we randomly changePISN magnitudes based on the assumed magnification proba-bility distribution. Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0 Frontier Fields (Lotzet al. 2017) clusters from Kawamata et al. (2016); Kawamataet al. (2018) constructed using Oguri (2010). Both methodsuse parameterized models that account for both the cluster darkmatter distribution and individual galaxies. We assume a ′ x ′ field-of-view. We calculate the source plane area as a func-tion of magnification for each of the seven clusters and take theaverage, extrapolated to the full area of our mock survey, tocalculate the expected number of detections. This is somewhatoptimistic, as these seven clusters are already among the mostmassive ones known, but there are potentially other clusters ofsimilar mass that are relatively unexplored (e.g., Wong et al.2013), and wide-area imaging surveys such as HSC, LSST, andEuclid could potentially find others. In regions of the sourceplane that are multiply-imaged, we take the magnification ofthe brightest image as the value at that particular location. We use our own code to conduct mock observations to estimatethe PISN detectability. The redshifts beyond 5 are binned with ∆ z = 0 . and PISNe are assumed to appear in each redshift binwith the PISN rates estimated in the previous section. Once aPISN appears at a redshift bin, the apparent magnitudes in theobserver frame at the time of the observation that is determinedby t int and the observational period are evaluated. For this pur-pose, we use redshifted PISN LCs that are calculated based onthe PISN spectral model of Kasen et al. (2011) in advance foreach redshifts. We check the expected observations and judge ifthe observations match our criteria, such as the limiting magni-tudes and N d , to regard them as a discovery. When we take thegravitational lensing effect into account, we randomly changePISN magnitudes based on the assumed magnification proba-bility distribution. Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0 Table 1. Numbers of Pop III RSG PISN discoveries for the 5-year survey without the gravitational lensing effect. band FoV limit t int N d flat IMF Salpeter IMF deg mag days z > z > z > z > z > z > K a . ± . . ± . . ± . 03 0 . ± . . ± . 05 0 . ± . . ± . . ± . . ± . 004 0 . ± . 09 0 . ± . 04 0 . ± . . ± . . ± . 06 0 . ± . 02 0 . ± . . ± . . ± . . ± . 04 0 . ± . . ± . . ± . 06 0 . ± . 04 0 F b . ± . . ± . . ± . 08 0 . ± . 05 0 . ± . 03 0 . ± . 10 26.5 180 2 ± . ± . . ± . . ± . 10 26.0 180 2 . ± . . ± . a ULTIMATE-Subaru, b WFIRST nu m be r o f P op III P I S N e ( ∆ z - deg - ) redshift ∆ z = 0.1Flat IMF, RSG only26.5 mag, t int = 180 days, N d = 226.5 mag, t int = 180 days, N d = 326.0 mag, t int = 180 days, N d = 226.0 mag, t int = 180 days, N d = 326.0 mag, t int = 90 days, N d = 3 0.01 0.1 1 5 5.5 6 6.5 7 7.5 Fig. 4. Differences in Pop III PISN discoveries from the different survey pa-rameters with ULTIMATE-Subaru. AB m agn i t ude ( K band ) days in the observer frameR225 at z = 6.2R250 at z = 6.5R250 at z = 6.0 Fig. 5. Examples of Pop III PISN LCs observed by the t int = 180 days survey with a 26.5 mag limit in the K band with ULTIMATE-Subaru. Mock transient surveys with one condition are repeated 100times to check statistical errors. All the errors shown in thefollowing number estimates are the σ statistical errors. nu m be r o f P op III P I S N e ( ∆ z - deg - ) redshiftK = 26.5 mag limitFlat IMF, RSG onlyt int = 180 days, N d = 2, ∆ z = 0.1 no lensingrandom fieldclusters (average) 0.01 0.1 1 5 5.5 6 6.5 7 7.5 8 8.5 9 Fig. 6. Effect of the magnitude amplification due to gravitational lensing. Table 1 summarizes the numbers of Pop III RSG PISNe discov-ered in our mock transient surveys with several observationalstrategies. Fig. 4 shows the redshift distributions of the ob-served Pop III RSG PISNe in the case of the flat IMF. The ex-amples of the observed Pop III PISN LCs for the survey with t int = 180 days are presented in Fig. 5.We find that t int = 180 days works well to find Pop III PISNeat z > ∼ . If we set the survey FoV to be in the 26.5 magsurveys ( hours in total with t int = 180 days ) and inthe 26.0 mag surveys ( hours in total with t int = 180 days ),we predict to find a few Pop III PISNe at z > ∼ during the 5-year survey if the IMF is flat. If we assume the Salpeter IMF,the expected number of RSG Pop III PISN detections is as lowas ∼ . in the whole survey.The 26.5 mag limit surveys are predicted to find much morePop III RSG PISNe because the deeper surveys can find lessmassive Pop III PISN progenitors. Comparing the 26.0 mag survey that takes about 960 hours with the 26.5 mag survey that takes about 860 hours, having a deeper sur-vey with a smaller FoV is likely beneficial to find Pop III PISNethan having a shallower survey with a larger FoV (Table 1). ublications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0 Table 2. Numbers of RSG Pop III PISN discoveries forthe ULTIMATE-Subaru 5-year 1- deg t int = 180 daysN d = 2 survey with gravitational lensing. source z > z > z > K = 26 . mag limitno lensing . ± . . ± . . ± . random field . ± . . ± . . ± . cluster average . ± . . ± . . ± . K = 26 . mag limitno lensing . ± . . ± . 08 0 random field . ± . . ± . 09 0 . ± . cluster average . ± . . ± . . ± . The expected number of Pop III RSG PISN discoveries canbe enhanced if we perform the transient survey towards clus-ters of galaxies. Table 2 and Fig. 6 summarize the expectednumbers of Pop III RSG PISN discoveries obtained by adopt-ing the gravitational amplification probability distributions (seeSection 2.4 for details). We focus the K = 26 . survey with t int = 180 days and N d = 2 in this study to present the possi-bility to reach very high redshifts by the gravitational lensingby clusters of galaxies. We find that the cluster lensing roughlydoubles the expected number of Pop III RSG PISN detectionsat z > . We also find that the cluster lensing significantly in-creases the chance to observe PISNe at z > as seen in Fig. 6.The bumps in the detection numbers come from the bumps inthe Pop III PISN rates (Fig. 3). Table 1 presents the WFIRST Pop III RSG PISN discover-ies and Figure 7 shows their redshift distributions. AlthoughWFIRST does not reach as red as ULTIMATE-Subaru, it caneasily reach deeper limiting magnitudes thanks to being inspace. We find that the F -band survey with the limitingmagnitude of 26.5 mag with WFIRST can discover PISNe asdistant as the K -band survey with the limiting magnitude of26.0 mag with ULTIMATE-Subaru can do is. If we com-pare the same limiting magnitude survey with WFIRST andULTIMATE-Subaru, ULTIMATE-Subaru can reach higher red-shifts thanks to its redder band. However, WFIRST can reachdeeper limiting magnitudes rather easily and the WFIRST sur-vey with the limiting magnitude of 27.0 mag can go beyondthe ULTIMATE-Subaru survey with the limiting magnitude of26.5 mag. Pop III PISN discovery estimates in the previous section do nottake helium core PISN progenitors into account. One possible nu m be r o f P op III P I S N e ( ∆ z - deg - ) redshift ∆ z = 0.1Flat IMF, RSG onlyt int = 180 days, N d = 2WFIRST 27.0 mag limit (F184)26.5 mag limit (F184)26.0 mag limit (F184)ULTIMATE-Subaru 26.5 mag limit (K)26.0 mag limit (K) 0.01 0.1 1 5 5.5 6 6.5 7 7.5 8 Fig. 7. Results of the WFIRST Pop III RSG PISN mock surveys. The num-bers are per deg and the actual discovery numbers are proportional to thesurvey area. path for helium core Pop III PISNe to appear is by strippingthe envelope of massive RSG PISN progenitors through, e.g.,binary interaction. The helium core mass of the R250 model is124 M ⊙ (Kasen et al. 2011). Because helium core PISNe withthe helium core mass above ≃ 125 M ⊙ is able to observe in oursurveys (Section 2.3.2), Pop III massive stars with the ZAMSmasses of ∼ 250 M ⊙ , which are observable if they explode asRSGs, may not be observable if they explode as helium stars.Thus, the expected detection number could go down if somemassive RSG Pop III PISN progenitors explode as bare heliumcore Pop III PISNe.On the other hand, bare helium core Pop III PISN progeni-tors can originate from massive stars with relatively low ZAMSmass (e.g., Chatzopoulos & Wheeler 2012). For example, ifmassive stars rotate rapidly, the rapid rotations can enhancethe internal chemical mixing in massive stars and they couldevolve chemically homogeneously (Yoon & Langer 2005). Inthis case, the ZAMS mass of the He130 progenitor could beas low as ∼ 130 M ⊙ . Interestingly enough, a large fraction ofPop III massive stars might be rapidly rotating stars (Hirano &Bromm 2018). Close binary systems could also make massivestars to evolve through the chemically homogeneous channel(e.g., Marchant et al. 2016). It is also possible that rapidly ro-tating massive stars originate from mergers of two low massstars (e.g., van den Heuvel & Portegies Zwart 2013).In summary, it is currently very hard to quantify how the barehelium core PISN channel would affect the PISN detectability.We speculate that the expected RSG Pop III discovery numberwe discussed in the previous section could be lower limits be-cause of the many possible ways to make relatively low massmassive stars to be massive enough to explode as bare heliumcore PISN progenitors. However, we speculate that the K bandsurvey with ULTIMATE-Subaru is much better to detect the he-lium core PISNe because of their faintness in the F band Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0 130 M ⊙ . Interestingly enough, a large fraction ofPop III massive stars might be rapidly rotating stars (Hirano &Bromm 2018). Close binary systems could also make massivestars to evolve through the chemically homogeneous channel(e.g., Marchant et al. 2016). It is also possible that rapidly ro-tating massive stars originate from mergers of two low massstars (e.g., van den Heuvel & Portegies Zwart 2013).In summary, it is currently very hard to quantify how the barehelium core PISN channel would affect the PISN detectability.We speculate that the expected RSG Pop III discovery numberwe discussed in the previous section could be lower limits be-cause of the many possible ways to make relatively low massmassive stars to be massive enough to explode as bare heliumcore PISN progenitors. However, we speculate that the K bandsurvey with ULTIMATE-Subaru is much better to detect the he-lium core PISNe because of their faintness in the F band Publications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0, (2019), Vol. 00, No. 0 (Fig. 2). In this sense, ULTIMATE-Subaru has an advantage tofind different kinds of Pop III PISNe. We have focused on Pop III PISN discoveries in this study. At z ∼ , however, Pop II SFR is expected to be ∼ higherthan Pop III SFR (e.g., Wise et al. 2012). On the other hand,Pop II IMF might be closer to the Salpeter IMF than the flatIMF we mainly focused in our Pop III study. If Pop II IMF isapproximated as the Salpeter IMF and Pop II PISN propertiesare similar to Pop III PISN properties, we would roughly expectabout 100 times more PISNe than the Pop III PISN number esti-mates for the Salpeter IMF. This means that we typically expectto detect about or more Pop II PISNe at z ∼ in our deepestsurveys with ULTIMATE-Subaru and WFIRST if Pop II PISNefollows the Salpeter IMF (see Table 1). Thus, in addition to sev-eral Pop III PISNe, we might be able to find many Pop II PISNein the deep NIR transient surveys with ULTIMATE-Subaru andWFIRST. NIR transient surveys discussed in this paper not only have ca-pabilities to find Pop III PISNe but also high-redshift SLSNe.Detectability of high-redshift SLSNe with WFIRST was esti-mated in Tanaka et al. (2013). By scaling their results, we ex-pect to detect ∼ SLSNe at z > ∼ , including a few SLSNe at z > ∼ , with a and 26 mag limit survey in NIR. A simi-lar number is expected for a and 26.5 mag limit surveysurvey. We have shown that discovering Pop III PISNe is possibleby performing the proper transient surveys using ULTIMATE-Subaru and WFIRST. However, in order to confirm the Pop IIIPISN discovery, it is necessary to follow up the PISN candi-dates. In the era of ULTIMATE-Subaru and WFIRST opera-tions, we expect that James Webb Space Telescope (JWST) andseveral 30-m class telescopes such as Thirty Meter Telescope(TMT) are under operation and they will be essential tools forthe spectroscopic follow up.Even with these follow-up facilities, it is important to con-sider how to select the Pop III PISN candidates to follow. TheLCs obtained during the survey are already very important in-formation but having several other information is also impor-tant. Especially, we have assumed the NIR transient surveys in asingle filter here and we do not have color information to selectgood Pop III PISN candidates. Performing the NIR transientsurveys in a few filters are the best option, but it is also likelythat we can perform the transient survey only in a single filter because of the limited telescope time. In this respect, conduct-ing a coordinated simultaneous observational campaign withthe same field with ULTIMATE-Subaru and WFIRST is thebest option to have both the K band and F band informa-tion. It is also helpful to have simultaneous optical observationsin the same field for the efficient candidate selection, becausehigh-redshift SNe should be faint in optical. These photometricinformation can be processed by using SN photometric classifi-cation methods to search for genuine PISNe. Recently, SN pho-tometric classification schemes have been developing quicklyto prepare for the coming era of extensive time domain surveyswith, e.g., Large Synoptic Survey Telescope (e.g., Ishida et al.2019; Ishida & de Souza 2013; Charnock & Moss 2017; M¨oller& de Boissi`ere 2019). They will be essential to reject manycontaminants such as SNe Ia and core-collapse SNe at low red-shifts. They can also be trained by using the PISN LC modelsto directly identify the high-redshift PISN candidates. Havingmulti-band information including both optical and NIR is alsohelpful when we adopt photometric classification methods.Another important information is provided by the host galax-ies. If we perform a transient survey with legacy data frommany wavelengths such as the COSMOS field, we can use thepreexisting host galaxy information to estimate their photomet-ric redshifts, for example. The host galaxy photometric red-shifts are found to be useful in finding high-redshift SNe (e.g.,Moriya et al. 2019; Curtin et al. 2019). In order to identify z > ∼ galaxies photometrically, we can look for ”dropout” galaxies(e.g., Steidel et al. 1999; Ono et al. 2018). Galaxies at z ∼ are observed as ” i -dropout” galaxies and those at z ∼ − areobserved as ” z -dropout” or ” Y -dropout” galaxies. Deep NIRimages are required in advance for the identification of thesedropout galaxies. We have performed mock NIR transient surveys withULTIMATE-Subaru and WFIRST to estimate their expectednumbers of Pop III PISN detections at z > ∼ . We adopt Pop IIIPISN rates estimated based on the cosmological simulations byde Souza et al. (2014) and used the Pop III PISN LC modelsby Kasen et al. (2011). We found that a few Pop III PISNeat z > ∼ may be detected if we perform the K -bandULTIMATE-Subaru transient survey for 5 years with the limit-ing magnitude of 26.5 mag (860 hours in total), assuming theflat IMF for Pop III stars. If we assume the Salpeter IMF, theexpected number is decreased by a factor of 10. If we set thelimiting magnitude to be 26.0 mag, we expect about 1 Pop IIIPISN detection with the survey (960 hours in total). Wefound that the expected numbers of the Pop III discovery willbe doubled if the transient surveys are conducted towards clus- ublications of the Astronomical Society of Japan , (2019), Vol. 00, No. 0 ters of galaxies thanks to the magnification by the gravitationallensing.The reddest filter of WFIRST ( F ) is bluer than that ofULTIMATE-Subaru ( K ). However, WFIRST has the lager FoVthan ULTIMATE-Subaru and it allows to conduct wider tran-sient surveys. If we conduct the 5-year transient survey with the F filter with the limiting magnitude of 26.5 mag for 10 deg (200 hours), we expect to find about 7 Pop III PISNe with theflat IMF and about 0.3 Pop III PISNe with the Salpeter IMF.Our study has shown that the deep and wide NIR transientsurveys conducted by the planned wide-field NIR imagers willenable us to acquire valuable information on the first gener-ation stars in the Universe. They have a possibility to findPop III PISNe. Even if we do not discovery any Pop III PISNe,such NIR transient surveys will enable us to constrain the star-formation properties like IMF of the first stars. Acknowledgments TJM thanks horrible weather at Mauna Kea in Feb and Mar 2018 whichled to the cancellation of his Subaru observations that made this studydone. We thank Dan Kasen for sharing electric data of PISN LC mod-els. TJM thanks Chien-Hsiu Lee for discussion. TJM is supportedby the Grants-in-Aid for Scientific Research of the Japan Society forthe Promotion of Science (16H07413, 17H02864, 18K13585). KCW issupported in part by an EACOA Fellowship awarded by the East AsiaCore Observatories Association, which consists of the Academia SinicaInstitute of Astronomy and Astrophysics, the National AstronomicalObservatory of Japan, the National Astronomical Observatories of theChinese Academy of Sciences, and the Korea Astronomy and SpaceScience Institute. MO is supported in part by JSPS KAKENHI GrantNumber JP15H05892 and JP18K03693.This work was supported by World Premier International ResearchCenter Initiative (WPI Initiative), MEXT, Japan.The Hyper Suprime-Cam (HSC) collaboration includes the astro-nomical communities of Japan and Taiwan, and Princeton University.The HSC instrumentation and software were developed by the NationalAstronomical Observatory of Japan (NAOJ), the Kavli Institute for thePhysics and Mathematics of the Universe (Kavli IPMU), the Universityof Tokyo, the High Energy Accelerator Research Organization (KEK),the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan(ASIAA), and Princeton University. Funding was contributed by theFIRST program from Japanese Cabinet Office, the Ministry of Education,Culture, Sports, Science and Technology (MEXT), the Japan Society forthe Promotion of Science (JSPS), Japan Science and Technology Agency(JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA,and Princeton University.The Pan-STARRS1 Surveys (PS1) have been made possible throughcontributions of the Institute for Astronomy, the University of Hawaii,the Pan-STARRS Project Office, the Max-Planck Society and its partic-ipating institutes, the Max Planck Institute for Astronomy, Heidelbergand the Max Planck Institute for Extraterrestrial Physics, Garching,The Johns Hopkins University, Durham University, the Universityof Edinburgh, Queen’s University Belfast, the Harvard-SmithsonianCenter for Astrophysics, the Las Cumbres Observatory Global TelescopeNetwork Incorporated, the National Central University of Taiwan, theSpace Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through thePlanetary Science Division of the NASA Science Mission Directorate,the National Science Foundation under Grant No. AST-1238877, theUniversity of Maryland, and Eotvos Lorand University (ELTE).This paper makes use of software developed for the Large SynopticSurvey Telescope. 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