研究者業績
基本情報
- 所属
- 千葉大学 先進科学センター 教授
- 学位
- 博士(理学)(2004年7月 東京大学)
- 研究者番号
- 60598572
- ORCID ID
https://orcid.org/0000-0003-3484-399X- J-GLOBAL ID
- 201801017753358631
- researchmap会員ID
- B000310867
- 外部リンク
経歴
6-
2022年2月 - 現在
-
2013年8月 - 2022年1月
-
2011年4月 - 2013年8月
-
2009年7月 - 2011年4月
-
2006年7月 - 2009年6月
学歴
3-
2000年4月 - 2004年7月
-
1998年4月 - 2000年3月
-
1996年4月 - 1998年3月
主要な委員歴
6-
2024年9月 - 現在
-
2023年6月 - 現在
-
2021年3月 - 現在
主要な受賞
8論文
345-
ASTROPHYSICAL JOURNAL LETTERS 872(1) 2019年2月 査読有りWe report the discovery of a quasar at z = 7.07, which was selected from the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. This quasar, HSC J124353.93 +010038.5, has an order of magnitude lower luminosity than do the other known quasars at z > 7. The rest-frame ultraviolet absolute magnitude is M-1450 = -24.13 +/- 0.08 mag and the bolometric luminosity is L-bol = (1.4 +/- 0.1) x 10(46) erg s(-1). Its spectrum in the optical to near-infrared shows strong emission lines, and shows evidence for a fast gas outflow, as the C IV line is blueshifted and there is indication of broad absorption lines. The Mg IT-based black hole mass is M-BH = (3.3 +/- 2.0) x 10(8) M-circle dot, thus indicating a moderate mass accretion rate with an Eddington ratio) lambda(Edd) = 0.34 0.20. It is the first z > 7 quasar with sub-Eddington accretion, besides being the third most distant quasar known to date. The luminosity and black hole mass are comparable to, or even lower than, those measured for the majority of low-z quasars discovered by the Sloan Digital Sky Survey, and thus this quasar likely represents a z > 7 counterpart to quasars commonly observed in the low-z universe.
-
Proceedings of Science 356 2019年Aim: As a measurement of distance modulus for type Ia supernovae becomes more stringent, it is important to study various systematics for the unbiased measurement of cosmological parameters. In this paper, the effects of gravitational lensing magnification on the measurement of supernovae distance modulus and estimation of cosmological parameters are presented. Method: We use Hyper Suprime-Cam survey data to estimate the interbening large-scale structure. Two distinct methods are applied; one based on weak lensing mass reconstruction and the other based on the galaxy distribution. Then those estimations are converted to predict the possible magnification of individual supernova. Results: We find a very weak correlation between the Hubble residuals and magnification and that the Ωm and dark energy parameter w alters best fit values by O(1)% level. Conclusion: The effect of magnification can be vanishingly small given the current SNLS supernovae sample; however, it becomes important in the era of LSST and WFIRST where the number of supernovae is dramatically increase.
-
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 481(4) 4445-4460 2018年12月We reinterpret the shear estimator developed by Zhang & Komatsu within the framework of shapelets and propose the Fourier Power Function Shapelets (FPFS) shear estimator. Four shapelet modes are calculated from the power function of every galaxy's Fourier transform after deconvolving the point-spread function (PSF) in Fourier space. We propose a novel normalization scheme to construct dimensionless ellipticity and its corresponding shear responsivity using these shapelet modes. Shear is measured in a conventional way by averaging the ellipticities and responsivities over a large ensemble of galaxies. With the introduction and tuning of a weighting parameter, noise bias is reduced below one per cent of the shear signal. We also provide an iterative method to reduce selection bias. The FPFS estimator is developed without any assumptions regarding galaxy morphology or any approximations for PSF correction. Moreover, our method does not rely on heavy image manipulations or complicated statistical procedures. We test the FPFS shear estimator using several Subaru Hyper Suprime-Cam (HSC)-like image simulations and the main results are as follows. (i) For simulations that only contain isolated galaxies, the amplitude of the multiplicative bias is below 1 x 10(-2). (ii) For more realistic simulations, which also contain blended galaxies, the blended galaxies are deblended by the first-generation HSC deblender before shear measurement. A multiplicative bias of (-5.71 +/- 0.31) x 10(-2) is found. The blending bias is calibrated by image simulations. Finally, we test the consistency and stability of this calibration.
-
ASTROPHYSICAL JOURNAL 869(2) 2018年12月 査読有りWe present new measurements of the quasar luminosity function (LF) at z similar to 6 over an unprecedentedly wide range of the rest-frame ultraviolet luminosity M-1450 from -30 to -22 mag. This is the fifth in a series of publications from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam Subaru Strategic Program survey. The LF was calculated with a complete sample of 110 quasars at 5.7 <= z <= 6.5, which includes 48 SHELLQs quasars discovered over 650 deg(2) and 63 brighter quasars discovered by the Sloan Digital Sky Survey and the Canada-France-Hawaii Quasar Survey (including one overlapping object). This is the largest sample of z similar to 6 quasars with a well-defined selection function constructed to date, which has allowed us to detect significant flattening of the LF at its faint end. A double power-law function fit to the sample yields a faint-end slope alpha = -1.23(-0.34)(+0.44), a bright-end slope beta = -2.73(-0.31)(+0.23), a break magnitude M*(1450) = -24.90(-0.90)(+0.75), and a characteristic space density Phi* = 10.9(-6.8)(+10.0) Gpc(-3) mag(-1). Integrating this best-fit model over the range -18 < M-1450 < -30 mag, quasars emit ionizing photons at the rate of <(n)over dot>(ion) = 10(48.8 +/- 0.1) s(-1) Mpc(-3) at z = 6.0. This is less than 10% of the critical rate necessary to keep the intergalactic medium ionized, which indicates that quasars are not a major contributor to cosmic reionization.
-
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 480(3) 3842-3855 2018年11月The detailed observation of the distribution of redshifts and chirp masses of binary black hole (BH) mergers is expected to provide a clue to their origin. In this paper, we develop a hybrid 3. model of the probability distribution function of gravitational lensing magnification taking account of both strong and weak gravitational lensing, and use it to study the effect of gravitational lensing magnification on the distribution of gravitational waves from distant binary BH mergers detected in ongoing and future gravitational wave observations. We find that the effect of gravitational lensing magnification is significant at high ends of observed chirp mass and redshift distributions. While a high-mass tail in the observed chirp mass distribution is produced by highly magnified gravitational lensing events, we find that highly demagnified images of strong lensing events produce a high-redshift (z(obs) greater than or similar to 15) tail in the observed redshift distribution, which can easily be observed in the third-generation gravitational wave observatories. Such a demagnified, apparently high-redshift event is expected to be accompanied by a magnified image that is observed typically 10-100 days before the demagnified image. For highly magnified events that produce apparently very high chirp masses, we expect pairs of events with similar magnifications with time delays typically less than a day. This work suggests the critical importance of gravitational lensing (de-)magnification on the interpretation of apparently very high mass or redshift gravitational wave events.
-
ASTROPHYSICAL JOURNAL 867(2) 2018年11月We investigate the local and line-of-sight (LOS) overdensities of strong gravitational lens galaxies using wide-area multiband imaging from the Hyper Suprime-Cam Subaru Strategic Program. We present 41. new definite or probable lens candidates discovered in Data Release 2 of the survey. Using a combined sample of 87. galaxy-scale lenses out to a lens redshift of z(L) similar to 0.8, we compare galaxy number counts in LOSs toward known and newly discovered lenses in the survey to those of a control sample consisting of random LOSs. We also compare the local overdensity of lens galaxies to a sample of "twin" galaxies that have similar redshift and velocity dispersion to test whether lenses lie in different environments from similar nonlens galaxies. We find that lens fields contain higher number counts of galaxies compared to the control fields, but this effect arises from the local environment of the lens. Once galaxies in the lens plane are removed, the lens LOSs are consistent with the control sample. The local environments of the lenses are overdense compared to the control sample, and are slightly overdense compared to those of the twin sample, although the significance is marginal. There is no significant evidence of the evolution of the local overdensity of lens environments with redshift.
-
ASTROPHYSICAL JOURNAL 866(1) 2018年10月RX J1347.5-1145 (z = 0.451) is one of the most luminous X-ray galaxy clusters; it hosts a prominent cool core and exhibits a signature of a major merger. We present the first direct observational evidence for the subsonic nature of the sloshing motion of the cool core. We find that a residual X-ray image from the Chandra X-ray Observatory after removing the global emission shows a clear dipolar pattern characteristic of gas sloshing, whereas we find no significant residual in the Sunyaev-Zel'dovich effect (SZE) image from the Atacama Large Millimeter/submillimeter Array (ALMA). We estimate the equation of state of perturbations in the gas from the X-ray and SZE residual images. The inferred velocity is 420(-420)(+310) km s(-1), which is much lower than the adiabatic sound speed of the intracluster medium in the core. We thus conclude that the perturbation is nearly isobaric, and the gas sloshing motion is consistent with being in pressure equilibrium. Next, we report evidence for gas stripping of an infalling subcluster, which likely shock-heats the gas to a temperature well in excess of 20 keV. Using the mass distribution inferred from strong lensing images of the Hubble Space Telescope (HST), we find that the mass peak is located away from the peak position of the stripped gas with a statistical significance of >5 sigma. Unlike for the gas sloshing, the velocity inferred from the equation of state of the excess hot gas is comparable to the adiabatic sound speed expected for the 20 keV intracluster medium. All of the results support that the southeast substructure is created by a merger. On the other hand, the positional offset between the mass and the gas limits the self-interaction cross section of dark matter to be less than 3.7 h(-1) cm(2) g(-1) (95% CL).
-
Astrophysical Journal Letters 864(1) 2018年9月1日The most distant galaxies known are at z ∼ 10-11, observed 400-500 Myr after the Big Bang. The few z ∼ 10-11 candidates discovered to date have been exceptionally small, barely resolved, if at all, by the Hubble Space Telescope. Here we present the discovery of SPT0615-JD1, a fortuitous z ∼ 10 (z phot = ) galaxy candidate stretched into an arc over ∼2.″5 by the effects of strong gravitational lensing. Discovered in the Reionization Lensing Cluster Survey (RELICS) Hubble Treasury program and companion S-RELICS Spitzer program, this candidate has a lensed H-band magnitude of 24.6 ± 0.1 AB mag. With a magnification of μ ∼ 4-7 estimated from our lens models, the delensed intrinsic magnitude is 26.7 ± 0.1 AB mag, and the half-light radius is r e < 0.8 kpc, both consistent with other z > 9 candidates. The inferred stellar mass () and star formation rate () indicate that this candidate is a typical star-forming galaxy on the z > 6 SFR-M ∗ relation. We note that three independent lens models predict two counter images, at least one of which should be of a similar magnitude to the arc, but these counter images are not yet detected. Counter images would not be expected if the arc were at lower redshift. The relatively large physical size could be due to a merger or accretion event, while the unprecedented lensed size of this z ∼ 10 candidate offers the potential for ALMA and the James Webb Space Telescope to study the geometric and kinematic properties of a galaxy observed 500 Myr after the Big Bang.
-
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 478(1) 1141-1160 2018年7月While various observations measured ellipticities of galaxy clusters and alignments between orientations of the brightest cluster galaxies and their host clusters, there are only a handful of numerical simulations that implement realistic baryon physics to allow direct comparisons with those observations. Here, we investigate ellipticities of galaxy clusters and alignments between various components of them and the central galaxies in the state-of-the-art cosmological hydrodynamical simulation Horizon-AGN, which contains dark matter, stellar, and gas components in a large simulation box of (100h(-1) Mpc)(3) with high spatial resolution (similar to 1 kpc). We estimate ellipticities of total matter, dark matter, stellar, gas surface mass density distributions, X-ray surface brightness, and the Compton y-parameter of the Sunyaev-Zel'dovich effect, as well as alignments between these components and the central galaxies for 120 projected images of galaxy clusters with masses M-200 > 5 x 10(13) M-circle dot. Our results indicate that the distributions of these components are well aligned with the major axes of the central galaxies, with the root-mean-square value of differences of their position angles of similar to 20 degrees, which vary little from inner to the outer regions. We also estimate alignments of these various components with total matter distributions, and find tighter alignments than those for central galaxies with the root-mean-square value of similar to 15 degrees. We compare our results with previous observations of ellipticities and position angle alignments and find reasonable agreements. The comprehensive analysis presented in this paper provides useful prior information for analysing stacked lensing signals as well as designing future observations to study ellipticities and alignments of galaxy clusters.
-
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 237(1) 2018年7月 査読有りWe report the discovery of 41 new high-z quasars and luminous galaxies that were spectroscopically identified at 5.7 <= z <= 6.9. This is the fourth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, based on the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the photometric candidates using a Bayesian probabilistic algorithm and then carried out follow-up spectroscopy with the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous papers, we have now spectroscopically identified 137 extremely red HSC sources over about 650 deg(2),which includes 64 high-z quasars, 24 high-z luminous galaxies, 6 [O III] emitters at z similar to 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown dwarfs). The new quasars span in luminosity range from M-1450 similar to -26 to -22 mag, and continue to populate luminosities a few magnitudes lower than have been probed by previous wide-field surveys. In a companion paper, we derive the quasar luminosity function at z similar to 6 over an unprecedentedly wide range of M-1450 similar to -28 to -21 mag, exploiting the SHELLQs and other survey outcomes.
-
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 477(2) 2128-2140 2018年6月We study the dependence of surface mass density profiles, which can be directly measured by weak gravitational lensing, on the orientation of haloes with respect to the line-of-sight direction, using a suite of N-body simulations. We find that, when major axes of haloes are aligned with the line-of-sight direction, surface mass density profiles have higher amplitudes than those averaged over all halo orientations, over all scales from 0.1 to 100 Mpc h(-1) we studied. While the orientation dependence at small scales is ascribed to the halo triaxiality, our results indicate even stronger orientation dependence in the so-called two-halo regime, up to 100 Mpc h(-1). The orientation dependence for the two-halo term is well approximated by a multiplicative shift of the amplitude and therefore a shift in the halo bias parameter value. The halo bias from the two-halo term can be overestimated or underestimated by up to similar to 30 per cent depending on the viewing angle, which translates into the bias in estimated halo masses by up to a factor of 2 from halo bias measurements. The orientation dependence at large scales originates from the anisotropic halo-matter correlation function, which has an elliptical shape with the axis ratio of similar to 0.55 up to 100 Mpc h(-1). We discuss potential impacts of halo orientation bias on other observables such as optically selected cluster samples and a clustering analysis of large-scale structure tracers such as quasars.
-
Publications of the Astronomical Society of Japan 70(3) S22.1‐S22.20 2018年6月
-
Nature Astronomy 2(4) 324-333 2018年4月A massive galaxy cluster can serve as a magnifying glass for distant stellar populations, as strong gravitational lensing magnifies background galaxies and exposes details that are otherwise undetectable. In time-domain astronomy, imaging programmes with a short cadence are able to detect rapidly evolving transients, previously unseen by surveys designed for slowly evolving supernovae. Here, we describe two unusual transient events discovered in a Hubble Space Telescope programme that combined these techniques with high-cadence imaging on a field with a strong-lensing galaxy cluster. These transients were faster and fainter than any supernovae, but substantially more luminous than a classical nova. We find that they can be explained as separate eruptions of a luminous blue variable star or a recurrent nova, or as an unrelated pair of stellar microlensing events. To distinguish between these hypotheses will require clarification of the cluster lens models, along with more high-cadence imaging of the field that could detect related transient episodes. This discovery suggests that the intersection of strong lensing with high-cadence transient surveys may be a fruitful path for future astrophysical transient studies.
-
ASTROPHYSICAL JOURNAL 857(1) 2018年4月A galaxy cluster acts as a cosmic telescope over background galaxies but also as a cosmic microscope magnifying the imperfections of the lens. The diverging magnification of lensing caustics enhances the microlensing effect of substructure present within the lensing mass. Fine-scale structure can be accessed as a moving background source brightens and disappears when crossing these caustics. The recent discovery of a distant lensed star near the Einstein radius of the galaxy cluster MACSJ1149.5+ 2223 allows a rare opportunity to reach subsolar-mass microlensing through a supercritical column of cluster matter. Here we compare these observations with high-resolution ray-tracing simulations that include stellar microlensing set by the observed intracluster starlight and also primordial black holes that may be responsible for the recently observed LIGO events. We explore different scenarios with microlenses from the intracluster medium and black holes, including primordial ones, and examine strategies to exploit these unique alignments. We find that the best constraints on the fraction of compact dark matter (DM) in the small-mass regime can be obtained in regions of the cluster where the intracluster medium plays a negligible role. This new lensing phenomenon should be widespread and can be detected within modest-redshift lensed galaxies so that the luminosity distance is not prohibitive for detecting individual magnified stars. High-cadence Hubble Space Telescope monitoring of several such optimal arcs will be rewarded by an unprecedented mass spectrum of compact objects that can contribute to uncovering the nature of DM.
-
NATURE ASTRONOMY 2(4) 334-342 2018年4月Galaxy-cluster gravitational lenses can magnify background galaxies by a total factor of up to similar to 50. Here we report an image of an individual star at redshift z = 1.49 (dubbed MACS J1149 Lensed Star 1) magnified by more than x 2,000. A separate image, detected briefly 0.26 '' from Lensed Star 1, is probably a counterimage of the first star demagnified for multiple years by an object of greater than or similar to 3 solar masses in the cluster. For reasonable assumptions about the lensing system, microlensing fluctuations in the stars' light curves can yield evidence about the mass function of intracluster stars and compact objects, including binary fractions and specific stellar evolution and supernova models. Dark-matter subhaloes or massive compact objects may help to account for the two images' long-term brightness ratio.
-
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 235(1) 2018年3月We present a catalog of 182 galaxy clusters detected through the Sunyaev-Zel'dovich (SZ) effect by the Atacama Cosmology Telescope in a contiguous 987.5 deg(2) field. The clusters were detected as SZ decrements by applying a matched filter to 148 GHz maps that combine the original ACT equatorial survey with data from the first two observing seasons using the ACTPol receiver. Optical/IR confirmation and redshift measurements come from a combination of large public surveys and our own follow-up observations. Where necessary, we measured photometric redshifts for clusters using a pipeline that achieves accuracy Delta z/(1 + z) = 0.015 when tested on Sloan Digital Sky Survey data. Under the assumption that clusters can be described by the so-called universal pressure profile (UPP) and its associated mass scaling law, the full signal-to-noise ratio > 4 sample spans the mass range 1.6 < M-500c(UPP)/10(14) M-circle dot < 9.1, with median M-500c(UPP) = 3.1 x 10(14) M-circle dot. The sample covers the redshift range 0.1 < z < 1.4 (median z = 0.49), and 28 clusters are new discoveries (median z = 0.80). We compare our catalog with other overlapping cluster samples selected using the SZ, optical, and X-ray wavelengths. We find that the ratio of the UPP-based SZ mass to richness-based weak-lensing mass is < M-500c(UPP)>/< M-500c(lambda WL)> = 0.68 +/- 0.11. After applying this calibration, the mass distribution for clusters with M-500c > 4 x 10(14) M-circle dot is consistent with the number of such clusters found in the South Pole Telescope SZ survey.
-
ASTROPHYSICAL JOURNAL 855(1) 2018年3月We construct z similar to 6-7, 8, and 9 faint Lyman break galaxy samples (334, 61, and 37 galaxies, respectively) with accurate size measurements with the software glafic from the complete Hubble Frontier Fields (HFF) cluster and parallel fields data. These are the largest samples hitherto and reach down to the faint ends of recently obtained deep luminosity functions. At faint magnitudes, however, these samples are highly incomplete for galaxies with large sizes, implying that derivation of the luminosity function sensitively depends on the intrinsic size-luminosity relation. We thus conduct simultaneous maximum-likelihood estimation of luminosity function and size-luminosity relation parameters from the observed distribution of galaxies on the size-luminosity plane with the help of a completeness map as a function of size and luminosity. At z similar to 6-7, we find that the intrinsic size-luminosity relation expressed as r(e) proportional to L-beta has a notably steeper slope of beta = 0.46(-0.09) (+0.08) than those at lower redshifts, which in turn implies that the luminosity function has a relatively shallow faint-end slope of alpha = -1.86(-0.18)(+0.17). This steep beta can be reproduced by a simple analytical model in which smaller galaxies have lower specific angular momenta. The beta and alpha values for the z similar to 8 and 9 samples are consistent with those for z similar to 6-7 but with larger errors. For all three samples, there is a large, positive covariance between beta and alpha, implying that the simultaneous determination of these two parameters is important. We also provide new strong lens mass models of Abell S1063 and Abell 370, as well as updated mass models of Abell 2744 and MACS J0416.1-2403.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(2) 2018年3月We present optimized source galaxy selection schemes for measuring cluster weak lensing (WL) mass profiles unaffected by clustermember dilution from the Subaru Hyper Suprime-Cam Strategic Survey Program (HSC-SSP). The ongoing HSC-SSP survey will uncover thousands of galaxy clusters to z less than or similar to 1.5. In deriving cluster masses viaWL, a critical source of systematics is contamination and dilution of the lensing signal by cluster members, and by foreground galaxies whose photometric redshifts are biased. Using the first-year CAMIRA catalog of similar to 900 clusters with richness larger than 20 found in similar to 140 deg(2) of HSC-SSP data, we devise and compare several source selection methods, including selection in color-color space (CC-cut), and selection of robust photometric redshifts by applying constraints on their cumulative probability distribution function (P-cut). We examine the dependence of the contamination on the chosen limits adopted for each method. Using the proper limits, these methods give mass profiles with minimal dilution in agreement with one another. We find that not adopting either the CC-cut or P-cut methods results in an underestimation of the total cluster mass (13% +/- 4%) and the concentration of the profile (24% +/- 11%). The level of cluster contamination can reach as high as similar to 10% at R approximate to 0.24 Mpc/ h for low-z clusters without cuts, while employing either the P-cut or CC-cut results in cluster contamination consistent with zero to within the 0.5% uncertainties. Our robust methods yield a similar to 60 sigma detection of the stacked CAMIRA surface mass density profile, with a mean mass of M-200c = [1.67 +/- 0.05(stat)] x 10(14) M-circle dot/h.
-
ASTROPHYSICAL JOURNAL 853(2) 2018年2月We present a morphological study of the 17 lensed Ly alpha emitter (LAE) galaxies of the Baryon Oscillation Spectroscopic Survey Emission-Line Lens Survey (BELLS) for the GALaxy-Ly alpha EmitteR sYstems (BELLS GALLERY) sample. This analysis combines the magnification effect of strong galaxy-galaxy lensing with the high resolution of the Hubble Space Telescope to achieve a physical resolution of similar to 80 pc for this 2 < z < 3 LAE sample, allowing a detailed characterization of the LAE rest-frame ultraviolet continuum surface brightness profiles and substructure. We use lens-model reconstructions of the LAEs to identify and model individual clumps, which we subsequently use to constrain the parameters of a generative statistical model of the LAE population. Since the BELLS GALLERY sample is selected primarily on the basis of Ly alpha emission, the LAEs that we study here are likely to be directly comparable to those selected in wide-field, narrowband LAE surveys, in contrast with the lensed LAEs identified in cluster-lensing fields. We find an LAE clumpiness fraction of approximately 88%, which is significantly higher than that found in previous (non-lensing) studies. We find a well-resolved characteristic clump half-light radii of similar to 350 pc, a scale comparable to the largest H II regions seen in the local universe. This statistical characterization of LAE surface-brightness profiles will be incorporated into future lensing analyses using the BELLS GALLERY sample to constrain the incidence of dark-matter substructure in the foreground lensing galaxies.
-
ASTROPHYSICAL JOURNAL 854(1) 2018年2月We present UV luminosity functions of dropout galaxies at z similar to 6-10 with the complete Hubble Frontier Fields data. We obtain a catalog of similar to 450 dropout-galaxy candidates (350, 66, and 40 at z similar to 6-7, 8, and 9, respectively), with UV absolute magnitudes that reach similar to-14 mag, similar to 2 mag deeper than the Hubble Ultra Deep Field detection limits. We carefully evaluate number densities of the dropout galaxies by Monte Carlo simulations, including all lensing effects such as magnification, distortion, and multiplication of images as well as detection completeness and contamination effects in a self-consistent manner. We find that UV luminosity functions at z similar to 6-8have steep faint-end slopes, alpha similar to -2, and likely steeper slopes, alpha less than or similar to -2 at z similar to 9-10. We also find that the evolution of UV luminosity densities shows a non-accelerated decline beyond z similar to 8 in the case of M-trunc = -15, but an accelerated one in the case of M-trunc = -17. We examine whether our results are consistent with the Thomson scattering optical depth from the Planck satellite and the ionized hydrogen fraction Q(H II) at z less than or similar to 7 based on the standard analytic reionization model. We find that reionization scenarios exist that consistently explain all of the observational measurements with the allowed parameters of f(esc) = 0.17(-0.03)(+0.07) and M-trunc > -14.0 for log xi(ion)/[erg(-1) Hz]= 25.34 , where f(esc) is the escape fraction, M-trunc is the faint limit of the UV luminosity function, and xi(ion) is the conversion factor of the UV luminosity to the ionizing photon emission rate. The length of the reionization period is estimated to be Delta z = 3.9(-1.6)(+ 2.0) (for 0.1 < Q(H) (II) < 0.99), consistent with the recent estimate from Planck.
-
ASTROPHYSICAL JOURNAL 854(1) 2018年2月We performed spectroscopic observations of the small-separation lensed quasar SDSS J1001+5027, whose images have an angular separation q = 2 ''.86, and placed constraints on the physical properties of gas clouds in the vicinity of the quasar (i.e., in the outflowing wind launched from the accretion disk). The two cylinders of sight to the two lensed images go through the same region of the outflowing wind and they become fully separated with no overlap at a very large distance from the source (similar to 330 pc). We discovered a clear difference in the profile of the C IV broad absorption line (BAL) detected in the two lensed images in two observing epochs. Because the kinematic components in the BAL profile do not vary in concert, the observed variations cannot be reproduced by a simple change of ionization state. If the variability is due to gas motion around the background source (i.e., the continuum source), the corresponding rotational velocity is v(rot) >= 18,000 km s(-1), and their distance from the source is r <= 0.06 pc assuming Keplerian motion. Among three Mg II and three C IV NAL systems that we detected in the spectra, only the Mg II system at z(abs) = 0.8716 shows a hint of variability in its Mg I profile on a rest-frame timescale of Delta t(rest) <= 191. days and an obvious velocity shear between the sightlines whose physical separation is similar to 7 kpc. We interpret this as the result of motion of a cosmologically intervening absorber, perhaps located in a foreground galaxy.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2-m Subaru telescope on the summit of Mauna Kea in Hawaii. A team of scientists from Japan, Taiwan, and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg(2) in five broad bands (grizy), with a 5 sigma point-source depth of r approximate to 26. The Deep layer covers a total of 26 deg(2) in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg(2)). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most important outstanding questions in astronomy today, including the nature of dark matter and dark energy. The survey has been awarded 300 nights of observing time at the Subaru Telescope, and it started in 2014 March. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 yr of observations (61.5 nights), and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i similar to 26.4, similar to 26.5, and similar to 27.0 mag, respectively (5 sigma for point sources). All the layers are observed in five broad bands (grizy), and the Deep and UltraDeep layers are observed in narrow bands as well. We achieve an impressive image quality of 0.'' 6 in the i band in the Wide layer. We show that we achieve 1%-2% point spread function (PSF) photometry (root mean square) both internally and externally (against Pan-STARRS1), and similar to 10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectro-scopic redshifts. Detailed descriptions of all the data can be found online. The data release website is https://hsc-release.mtk.nao.ac.jp.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We present the procedure to build and validate the bright-star masks for the Hyper-Suprime-Cam Strategic Subaru Proposal (HSC-SSP) survey. To identify and mask the saturated stars in the full HSC-SSP footprint, we rely on the Gaia and Tycho-2 star catalogues. We first assemble a pure star catalogue down to G(Gaia) < 18 after removing similar to 1.5% of sources that appear extended in the Sloan Digital Sky Survey (SDSS). We perform visual inspection on the early data from the S16A internal release of HSC-SSP, finding that our star catalogue is 99.2% pure down to GGaia < 18. Second, we build the mask regions in an automated way using stacked detected source measurements around bright stars binned per G(Gaia) magnitude. Finally, we validate those masks by visual inspection and comparison with the literature of galaxy number counts and angular two-point correlation functions. This version (Arcturus) supersedes the previous version (Sirius) used in the S16A internal and DR1 public releases. We publicly release the full masks and tools to flag objects in the entire footprint of the planned HSC-SSP observations at < ftp://obsftp.unige.ch/pub/coupon/brightStarMasks/HSC-SSP/>.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We utilize the Hyper Suprime-Cam (HSC) CAMIRA cluster catalog (Oguri et al. 2018 PASJ, 70, S20) and the photo-z galaxy catalog constructed in the HSC Wide field (S16A), covering similar to 174 deg(2), to study the star formation activity of galaxies in different environments over 0.2 < z < 1.1. We probe galaxies down to i similar to 26, corresponding to a stellarmass limit of log(10)(M-*/M-circle dot) similar to 8.2 and similar to 8.6 for star-forming and quiescent populations, respectively, at z similar to 0.2. The existence of the red sequence for low stellarmass galaxies in clusters suggests that the environmental quenching persists to halt the star formation in the low-mass regime. In addition, star-forming galaxies in groups or clusters are systematically biased toward lower values of specific star formation rate by 0.1-0.3 dex with respect to those in the field, and the offsets show no strong redshift evolution over our redshift range, implying a universal slow quenching mechanism acting in the dense environments since z similar to 1.1. Moreover, the environmental quenching dominates the mass quenching in low-mass galaxies, and the quenching dominance reverses in high-mass ones. The transition mass is greater in clusters than in groups, indicating that the environmental quenching is more effective for massive galaxies in clusters compared to groups.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月Using similar to 140 deg(2) Subaru Hyper Suprime-Cam (HSC) survey data, we stack the weak lensing (WL) signal around five Planck clusters found within the footprint. This yields a 15 sigma detection of the mean Planck cluster mass density profile. The five Planck clusters span a relatively wide mass range, M-WL,M-500c = (2-30) x 10(14) M-circle dot with a mean mass of M-WL,M-500c = (4.15 +/- 0.61) x 10(14) M-circle dot. The ratio of the stacked Planck Sunyaev-Zel'dovich (SZ) mass to the stacked WL mass is < M-SZ > / < M-WL > = 1 - b = 0.80 +/- 0.14. This mass bias is consistent with previous WL mass calibrations of Planck clusters within the errors. We discuss the implications of our findings for the calibration of SZ cluster counts and the much discussed tension between Planck SZ cluster counts and Planck Lambda CDM cosmology.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70 2018年1月We present a joint X-ray, optical, and weak-lensing analysis for X-ray luminous galaxy clusters selected from the MCXC (Meta-Catalog of X-Ray Detected Clusters of Galaxies) cluster catalog in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey field with S16A data. As a pilot study for a series of papers, we measure hydrostatic equilibrium (HE) masses using XMM-Newton data for four clusters in the current coverage area out of a sample of 22 MCXC clusters. We additionally analyze a non-MCXC cluster associated with one MCXC cluster. We show that HE masses for the MCXC clusters are correlated with cluster richness from the CAMIRA catalog, while that for the non-MCXC cluster deviates from the scaling relation. The mass normalization of the relationship between cluster richness and HE mass is compatible with one inferred by matching CAMIRA cluster abundance with a theoretical halo mass function. The mean gas mass fraction based on HE masses for the MCXC clusters is < f(gas)> = 0.125 +/- 0.012 at spherical overdensity Delta = 500, which is similar to 80%-90% of the cosmic mean baryon fraction, Omega(b)/Omega(m), measured by cosmic microwave background experiments. We find that the mean baryon fraction estimated from X-ray and HSC-SSP optical data is comparable to Omega(b)/Omega(m). A weak-lensing shear catalog of background galaxies, combined with photometric redshifts, is currently available only for three clusters in our sample. Hydrostatic equilibrium masses roughly agree with weak-lensingmasses, albeit with large uncertainty. This study demonstrates that further multiwavelength study for a large sample of clusters using X-ray, HSC-SSP optical, and weak-lensing data will enable us to understand cluster physics and utilize cluster-based cosmology.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月The Hyper Suprime-Cam (HSC) is an 870 megapixel prime focus optical imaging camera for the 8.2 m Subaru telescope. The wide-field corrector delivers sharp images of 0.'' 2 (FWHM) in the HSC-i band over the entire 1.degrees 5 diameter field of view. The collimation of the camera with respect to the optical axis of the primary mirror is done with hexapod actuators, the mechanical accuracy of which is a few microns. Analysis of the remaining wavefront error in off-focus stellar images reveals that the collimation of the optical components meets design specifications. While there is a flexure of mechanical components, it also is within the design specification. As a result, the camera achieves its seeing-limited imaging on Maunakea during most of the time; the median seeing over several years of observing is 0.'' 67 (FWHM) in the i band. The sensors use p-channel, fully depleted CCDs of 200 mu m thickness (2048 x 4176 15 mu m square pixels) and we employ 116 of them to pave the 50 cm diameter focal plane. The minimum interval between exposures is 34 s, including the time to read out arrays, to transfer data to the control computer, and to save them to the hard drive. HSC on Subaru uniquely features a combination of a large aperture, a wide field of view, sharp images and a high sensitivity especially at longer wavelengths, which makes the HSC one of the most powerful observing facilities in the world.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We present the result of searching for clusters of galaxies based on weak gravitational lensing analysis of the similar to 160 deg(2) area surveyed by Hyper Suprime-Cam (HSC) as a Subaru Strategic Program. HSC is a new prime focus optical imager with a 1.(omicron)5-diameter field of view on the 8.2 m Subaru telescope. The superb median seeing on the HSC i-band images of 0 ''.56 allows the reconstruction of high angular resolution mass maps via weak lensing, which is crucial for the weak lensing cluster search. We identify 65 mass map peaks with a signal-to-noise (S/N) ratio larger than 4.7, and carefully examine their properties by cross-matching the clusters with optical and X-ray cluster catalogs. We find that all the 39 peaks with S/N > 5.1 have counterparts in the optical cluster catalogs, and only 2 out of the 65 peaks are probably false positives. The upper limits of X-ray luminosities from the ROSAT All Sky Survey (RASS) imply the existence of an X-ray underluminous cluster population. We show that the X-rays from the shear-selected clusters can be statistically detected by stacking the RASS images. The inferred average X-ray luminosity is about half that of the X-ray-selected clusters of the same mass. The radial profile of the dark matter distribution derived from the stacking analysis is well modeled by the Navarro-Frenk-White profile with a small concentration parameter value of c(500) similar to 2.5, which suggests that the selection bias on the orientation or the internal structure for our shear-selected cluster sample is not strong.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We present a statistical study of the redshift evolution of the cluster galaxy population over a wide redshift range from 0.1 to 1.1, using similar to 1900 optically-selected CAMIRA clusters from similar to 232 deg(2) of the Hyper Suprime-Cam (HSC) Wide S16A data. Our stacking technique with a statistical background subtraction reveals color-magnitude diagrams of red-sequence and blue cluster galaxies down to faint magnitudes of m(z) similar to 24. We find that the linear relation of red-sequence galaxies in the color-magnitude diagram extends down to the faintest magnitudes we explore with a small intrinsic scatter sigma(int)(g - r) < 0.1. The scatter does not evolve significantly with redshift. The stacked color-magnitude diagrams are used to define red and blue galaxies in clusters in order to study their radial number density profiles without resorting to photometric redshifts of individual galaxies. We find that red galaxies are significantly more concentrated toward cluster centers and blue galaxies dominate the outskirts of clusters. We explore the fraction of red galaxies in clusters as a function of redshift, and find that the red fraction decreases with increasing distances from cluster centers. The red fraction exhibits a moderate decrease with increasing redshift. The radial number density profiles of cluster member galaxies are also used to infer the location of the steepest slope in the three-dimensional galaxy density profiles. For a fixed threshold in richness, we find little redshift evolution in this location.
-
PHYSICAL REVIEW D 97(2) 2018年1月The recent discovery of fast transient events near critical curves of massive galaxy clusters, which are interpreted as highly magnified individual stars in giant arcs due to caustic crossing, opens up the possibility of using such microlensing events to constrain a range of dark matter models such as primordial black holes and scalar field dark matter. Based on a simple analytic model, we study lensing properties of a point mass lens embedded in a high magnification region, and we derive the dependence of the peak brightness, microlensing time scales, and event rates on the mass of the point mass lens, as well as the radius of a source star that is magnified. We find that the lens mass and source radius of the first event MACS J1149 Lensed Star 1 (LS1) are constrained, with the lens mass range of 0.1 M-circle dot less than or similar to M less than or similar to 4 x 10(3) M-circle dot and the source radius range of 40R(circle dot) less than or similar to R 260R(circle dot). In the most plausible case with M approximate to 0.3 M-circle dot and R approximate to 180R(circle dot), the source star should have been magnified by a factor of approximate to 4300 at the peak. The derived lens properties are fully consistent with the interpretation that MACS J1149 LS1 is a microlensing event produced by a star that contributes to the intracluster light. We argue that compact dark matter models with high fractional mass densities for the mass range 10(-5) M-circle dot less than or similar to M less than or similar to 10(2) M-circle dot are inconsistent with the observation of MACS J1149 LS1 because such models predict too low magnifications. Our work demonstrates a potential use of caustic crossing events in giant arcs to constrain compact dark matter.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We present an optically-selected cluster catalog from the Hyper Suprime-Cam (HSC) Subaru Strategic Program. The HSC images are sufficiently deep to detect cluster member galaxies down to M-* similar to 10(10.2) M-circle dot even at z similar to 1, allowing a reliable cluster detection at such high redshifts. We apply the CAMIRA algorithm to the HSC Wide S16A dataset covering similar to 232 deg(2) to construct a catalog of 1921 clusters at redshift 0.1 < z < 1.1 and richness (N) over cap (mem) > 15 that roughly corresponds to M-200m greater than or similar to 10(14) h(-1) M-circle dot. We confirm good cluster photometric redshift performance, with the bias and the scatter in Delta z/(1 + z) being better than 0.005 and 0.01, respectively, over most of the redshift range. We compare our cluster catalog with large X-ray cluster catalogs from the XXL and XMM-LSS (the XMM Large Scale Structure) surveys and find good correlation between richness and X-ray properties. We also study the mis-centering effect from the distribution of offsets between optical and X-ray cluster centers. We confirm the high (> 0.9) completeness and purity for high-mass clusters by analyzing mock galaxy catalogs.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We study the UV luminosity functions (LFs) at z similar to 4, 5, 6, and 7 based on the deep large-area optical images taken by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). On the 100 deg(2) sky of the HSC SSP data available to date, we take enormous samples consisting of a total of 579565 dropout candidates at z similar to 4-7 by the standard color selection technique, 358 out of which are spectroscopically confirmed by our follow-up spectroscopy and other studies. We obtain UV LFs at z similar to 4-7 that span a very wide UV luminosity range of similar to 0.002-100 L*(UV) (-26 < M-UV < -14 mag) by combining LFs from our program and the ultra-deep Hubble Space Telescope legacy surveys. We derive three parameters of the best-fit Schechter function, phi*, M*(UV), and alpha, of the UV LFs in the magnitude range where the active galactic nucleus (AGN) contribution is negligible, and find that a and f* decrease from z similar to 4 to 7 with no significant evolution of M*(UV). Because our HSC SSP data bridge the LFs of galaxies and AGNs with great statistical accuracy, we carefully investigate the bright end of the galaxy UV LFs that are estimated by the subtraction of the AGN contribution either aided by spectroscopy or the best-fit AGN UV LFs. We find that the bright end of the galaxy UV LFs cannot be explained by the Schechter function fits at > 2 sigma significance, and require either double power-law functions or modified Schechter functions that consider a magnification bias due to gravitational lensing.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is an excellent survey for the search for strong lenses, thanks to its area, image quality, and depth. We use three different methods to look for lenses among 43000 luminous red galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) sample with photometry from the S16A internal data release of the HSC-SSP. The first method is a newly developed algorithm, named YATTALENS, which looks for arc-like features around massive galaxies and then estimates the likelihood of an object being a lens by performing a lens model fit. The second method, CHITAH, is a modeling-based algorithm originally developed to look for lensed quasars. The third method makes use of spectroscopic data to look for emission lines from objects at a different redshift from that of the main galaxy. We find 15 definite lenses, 36 highly probable lenses, and 282 possible lenses. Among the three methods, YATTALENS, which was developed specifically for this study, performs best in terms of both completeness and purity. Nevertheless, five highly probable lenses were missed by YATTALENS but found by the other two methods, indicating that the three methods are highly complementary. Based on these numbers, we expect to find similar to 300 definite or probable lenses by the end of the HSC-SSP.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We present wide-field (167 deg(2)) weak lensing mass maps from the Hyper Supreme-Cam Subaru Strategic Program (HSC-SSP). We compare these weak lensing based dark matter maps with maps of the distribution of the stellar mass associated with luminous red galaxies. We find a strong correlation between these two maps with a correlation coefficient of rho = 0.54 +/- 0.03 (for a smoothing size of 8'). This correlation is detected even with a smaller smoothing scale of 2' (rho = 0.34 +/- 0.01). This detection is made uniquely possible because of the high source density of the HSC-SSP weak lensing survey ((n) over bar similar to 25 arcmin(-2)). We also present a variety of tests to demonstrate that our maps are not significantly affected by systematic effects. By using the photometric redshift information associated with source galaxies, we reconstruct a three-dimensional mass map. This three-dimensional mass map is also found to correlate with the three-dimensional galaxy mass map. Cross-correlation tests presented in this paper demonstrate that the HSC-SSP weak lensing mass maps are ready for further science analyses.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月We present and characterize the catalog of galaxy shape measurements that will be used for cosmological weak lensing measurements in the Wide layer of the first year of the Hyper Suprime-Cam (HSC) survey. The catalog covers an area of 136.9 deg(2) split into six fields, with a mean i-band seeing of 0".58 and 5 sigma point-source depth of i similar to 26. Given conservative galaxy selection criteria for first-year science, the depth and excellent image quality results in unweighted and weighted source number densities of 24.6 and 21.8 arcmin(-2), respectively. We define the requirements for cosmological weak lensing science with this catalog, then focus on characterizing potential systematics in the catalog using a series of internal null tests for problems with point-spread function (PSF) modeling, shear estimation, and other aspects of the image processing. We find that the PSF models narrowly meet requirements for weak lensing science with this catalog, with fractional PSF model size residuals of approximately 0.003 (requirement: 0.004) and the PSF model shape correlation function rho(1) < 3 x 10(-7) (requirement: 4 x 10(-7)) at 0 degrees.5 scales. A variety of galaxy shape-related null tests are statistically consistent with zero, but star-galaxy shape correlations reveal additive systematics on > 1 degrees scales that are sufficiently large as to require mitigation in cosmic shear measurements. Finally, we discuss the dominant systematics and the planned algorithmic changes to reduce them in future data reductions.
-
Publications of the Astronomical Society of Japan 70(SP1) 2018年1月 査読有り
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) id.S31 2018年1月 査読有り` We investigate the galaxy overdensity around proto-cluster scale quasar pairs at high (z > 3) and low (z similar to 1) redshift based on the unprecedentedly wide and deep optical survey of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first-year survey data covering effectively similar to 121 deg(2) with the 5 sigma depth of i similar to 26.4 and the SDSS DR12Q catalog, we find two luminous pairs at z similar to 3.3 and 3.6 which reside in > 5s overdensity regions of g-dropout galaxies at i < 25. The projected separations of the two pairs are R-perpendicular to = 1.75 and 1.04 proper Mpc (pMpc), and their velocity offsets are Delta V = 692 and 1448 kms(-1), respectively. This result is in clear contrast to the average z similar to 4 quasar environments as discussed in Uchiyama et al. (2018, PASJ 70, S32) and implies that the quasar activities of the pair members are triggered via major mergers in proto-clusters, unlike the vast majority of isolated quasars in general fields that may turn on via non-merger events such as bar and disk instabilities. At z similar to 1, we find 37 pairs with R-perpendicular to < 2 pMpc and Delta V < 2300 kms(-1) in the current HSC-Wide coverage, including four from Hennawi et al. (2006, AJ, 131, 1). The distribution of the peak overdensity significance within two arcminutes around the pairs has a long tail toward high-density (>4 sigma) regions. Thanks to the large sample size, we find statistical evidence that this excess is unique to the pair environments when compared to single-quasar and randomly selected galaxy environments at the same redshift range. Moreover, there are nine small-scale (R-perpendicular to < 1 pMpc) pairs, two of which are found to reside in cluster fields. Our results demonstrate that <2 pMpc scale quasar pairs at both redshift ranges tend to occur in massive haloes, although perhaps not the most massive ones, and that they are useful in searching for rare density peaks.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(Special Issue 1) 2018年1月 査読有りWe present the Ly alpha luminosity functions (LFs) at z = 5.7 and 6.6 derived from a new large sample of 1266 Ly alpha emitters (LAEs) identified in total areas of 14 and 21 deg(2), respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam survey. Together with careful Monte Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Ly alpha LFs with unprecedentedly small statistical and systematic uncertainties in a wide Ly alpha luminosity range of 10(42.8-43.8) erg s(-1). We obtain best-fit Schechter parameters of L*(Ly alpha) = 1.6(-0.6)(+2.2) (1.7(-0.7)(+0.3)) x 10(43) erg s(-1), phi*(Ly alpha) = 0.85(-0.77)(+1.87) (0.47(-0.44)(+1.44)) x 10(-4) Mpc(-3), and alpha = -2.6(-0.4)(+0.6) (-2.5(-0.5)(+0.5)) at z = 5.7 (6.6). We confirm that our best-estimate Ly alpha LFs are consistent with the majority of the previous studies, but find that our Ly alpha LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.'s studies that may overcorrect the incompleteness and the flux systematics. Our Lya LFs at z = 5.7 and 6.6 show an indication that the faint-end slope is very steep (a similar or equal to -2.5), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Lya LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the intergalactic medium to be x(HI) = 0.3 +/- 0.2 at z = 6.6, which is consistent with the small Thomson scattering optical depth obtained by Planck 2016.
-
Publications of the Astronomical Society of Japan 70(SP1) S33.1‐S33.21 2018年1月
-
Publications of the Astronomical Society of Japan 70(SP1) S34.1‐S34.28 2018年1月
-
Monthly Notices of the Royal Astronomical Society 472(3) 3177-3216 2017年12月Gravitational lensing by clusters of galaxies offers a powerful probe of their structure and mass distribution. Several research groups have developed techniques independently to achieve this goal. While these methods have all provided remarkably high-precision mass maps, particularly with exquisite imaging data from the Hubble Space Telescope (HST), the reconstructions themselves have never been directly compared. In this paper, we present for the first time a detailed comparison of methodologies for fidelity, accuracy and precision. For this collaborative exercise, the lens modelling community was provided simulated cluster images that mimic the depth and resolution of the ongoing HST Frontier Fields. The results of the submitted reconstructions with the un-blinded true mass profile of these two clusters are presented here. Parametric, free-form and hybrid techniques have been deployed by the participating groups and we detail the strengths and trade-offs in accuracy and systematics that arise for each methodology. We note in conclusion that several properties of the lensing clusters are recovered equally well by most of the lensing techniques compared in this study. For example, the reconstruction of azimuthally averaged density and mass profiles by both parametric and freeform methods matches the input models at the level of ~10 per cent. Parametric techniques are generally better at recovering the 2D maps of the convergence and of the magnification. For the best-performing algorithms, the accuracy in the magnification estimate is ~10 per cent at μtrue = 3 and it degrades to ~30 per cent at μtrue ~ 10.
-
ASTROPHYSICAL JOURNAL 851(2) 2017年12月We study the internal structure of the circumgalactic medium (CGM), using 29 spectra of 13 gravitationally lensed quasars with image separation angles of a few arcseconds, which correspond to 100 pc to 10 kpc in physical distances. After separating metal absorption lines detected in the spectra into high ions with ionization parameter (IP) > 40 eV and low ions with IP < 20 eV, we find that (i) the fraction of absorption lines that are detected in only one of the lensed images is larger for low ions (similar to 16%) than high ions (similar to 2%), (ii) the fractional difference of equivalent widths (EWs) between the lensed images is almost the same (dEW similar to 0.2) for both groups although the low ions have a slightly larger variation, and (iii) weak low-ion absorbers tend to have larger dEW compared to weak high-ion absorbers. We construct simple models to reproduce these observed properties and investigate the distribution of physical quantities such as size and location of absorbers, using some free parameters. Our best models for absorbers with high ions and low ions suggest that (i) an overall size of the CGM is at least similar to 500 kpc, (ii) a size of spherical clumpy cloud is similar to 1 kpc or smaller, and (iii) only high-ion absorbers can have a diffusely distributed homogeneous component throughout the CGM. We infer that a high ionization absorber distributes almost homogeneously with a small-scale internal fluctuation, while a low ionization absorber consists of a large number of small-scale clouds in the diffusely distributed higher ionized region. This is the first result to investigate the internal small-scale structure of the CGM, based on the large number of gravitationally lensed quasar spectra.
-
ASTROPHYSICAL JOURNAL 851(2) 2017年12月 査読有りThe unprecedented depth and area surveyed by the Subaru Strategic Program with the Hyper Suprime-Cam (HSC-SSP) have enabled us to construct and publish the largest distant cluster sample out to z similar to 1 to date. In this exploratory study of cluster galaxy evolution from z = 1 to z = 0.3, we investigate the stellar mass assembly history of brightest cluster galaxies (BCGs), the evolution of stellar mass and luminosity distributions, the stellar mass surface density profile, as well as the population of radio galaxies. Our analysis is the first high-redshift application of the top N richest cluster selection, which is shown to allow us to trace the cluster galaxy evolution faithfully. Over the 230 deg(2) area of the current HSC-SSP footprint, selecting the top 100 clusters in each of the four redshift bins allows us to observe the buildup of galaxy population in descendants of clusters whose z approximate to 1 mass is about 2 x 10(14) M-circle dot. Our stellar mass is derived from a machine-learning algorithm, which is found to be unbiased and accurate with respect to the COSMOS data. We find very mild stellar mass growth in BCGs (about 35% between z = 1 and 0.3), and no evidence for evolution in both the total stellar mass-cluster mass correlation and the shape of the stellar mass surface density profile. We also present the first measurement of the radio luminosity distribution in clusters out to z similar to 1, and show hints of changes in the dominant accretion mode powering the cluster radio galaxies at z similar to 0.8.
-
\apj 851(2) 88 2017年11月22日 査読有りWe study the internal structure of the Circum-Galactic Medium (CGM), using 29 spectra of 13 gravitationally lensed quasars with image separation angles of a few arcseconds, which correspond to 100 pc to 10 kpc in physical distances. After separating metal absorption lines detected in the spectra into high-ions with ionization parameter (IP) $>$ 40 eV and low-ions with IP $<$ 20 eV, we find that i) the fraction of absorption lines that are detected in only one of the lensed images is larger for low-ions ($\sim$16%) than high-ions ($\sim$2%), ii) the fractional difference of equivalent widths ($EW$s) between the lensed images is almost same (${\rm d}EW$ $\sim$ 0.2) for both groups although the low-ions have a slightly larger variation, and iii) weak low-ion absorbers tend to have larger ${\rm d}EW$ compared to weak high-ion absorbers. We construct simple models to reproduce these observed properties and investigate the distribution of physical quantities such as size and location of absorbers, using some free parameters. Our best models for absorbers with high-ions and low-ions suggest that i) an overall size of the CGM is at least $\sim$ 500 kpc, ii) a size of spherical clumpy cloud is $\sim$ 1 kpc or smaller, and iii) only high-ion absorbers can have diffusely distributed homogeneous component throughout the CGM. We infer that a high ionization absorber distributes almost homogeneously with a small-scale internal fluctuation, while a low ionization absorber consists of a large number of small-scale clouds in the diffusely distributed higher ionized region. This is the first result to investigate the internal small-scale structure of the CGM, based on the large number of gravitationally lensed quasar spectra.
-
SPACE SCIENCE REVIEWS 212(3-4) 1743-1785 2017年11月Accurate astronomical distance determination is crucial for all fields in astrophysics, from Galactic to cosmological scales. Despite, or perhaps because of, significant efforts to determine accurate distances, using a wide range of methods, tracers, and techniques, an internally consistent astronomical distance framework has not yet been established. We review current efforts to homogenize the Local Group's distance framework, with particular emphasis on the potential of RR Lyrae stars as distance indicators, and attempt to extend this in an internally consistent manner to cosmological distances. Calibration based on Type Ia supernovae and distance determinations based on gravitational lensing represent particularly promising approaches. We provide a positive outlook to improvements to the status quo expected from future surveys, missions, and facilities. Astronomical distance determination has clearly reached maturity and near-consistency.
-
ASTROPHYSICAL JOURNAL 845(2) 2017年8月We present the results of a blind millimeter line emitter search using ALMA Band 6 data with a single-frequency tuning toward four gravitational lensing clusters (RXJ1347.5-1145, Abell S0592, MACS J0416.1-2403, and Abell 2744). We construct 3D signal-to-noise ratio (S/N) cubes with 60 and 100 MHz binning, and search for millimeter line emitters. We do not detect any line emitters with a peak S/N > 5, although we do find a line emitter candidate with a peak S/N similar or equal to 4.5. These results provide upper limits to the CO(3-2), CO(4-3), CO(5-4), and [C II] luminosity functions at z similar or equal to 0.3, 0.7, 1.2, and 6, respectively. Because of the magnification effect of gravitational lensing clusters, the new data provide the first constraints on the CO and [C II] luminosity functions at unprecedentedly low luminosity levels, i.e., down to less than or similar to 10(-3)-10(-1) Mpc(-3) dex(-1) at L'(CO) similar to 10(8)-10(10) Kkms(-1) pc(2) and less than or similar to 10(-3)-10(-2) Mpc(-3) dex(-1) at L[C II] similar to 10(8)-10(10) L-circle dot, respectively. Although the constraints to date are not yet stringent, we find that the evolution of the CO and [C II] luminosity functions are broadly consistent with the predictions of semi-analytical models. This study demonstrates that the wide observations with a single-frequency tuning toward gravitational lensing clusters are promising for constraining the CO and [C II] luminosity functions.
-
ASTROPHYSICAL JOURNAL LETTERS 843(2) 2017年7月We present long-baseline ALMA observations of the strong gravitational lens H-ATLAS J090740.0-004200 (SDP.9), which consists of an elliptical galaxy at z(L) = 0.6129 lensing a background submillimeter galaxy into two extended arcs. The data include Band 6 continuum observations, as well as CO J = 6 5 molecular line observations, from which we measure an updated source redshift of z(S) = 1.5747. The image morphology in the ALMA data is different from that of the Hubble Space Telescope (HST) data, indicating a spatial offset between the stellar, gas, and dust component of the source galaxy. We model the lens as an elliptical power law density profile with external shear using a combination of archival HST data and conjugate points identified in the ALMA data. Our best model has an Einstein radius of theta(E) = 0.66. +/- 0.01 and a slightly steeper than isothermal mass profile slope. We search for the central image of the lens, which can be used constrain the inner mass distribution of the lens galaxy including the central supermassive black hole, but do not detect it in the integrated CO image at a 3 sigma rms level of 0.0471 Jy km s(-1).
-
ASTROPHYSICAL JOURNAL LETTERS 835(2) 2017年2月We present predictions for time delays between multiple images of the gravitationally lensed supernova, iPTF16geu, which was recently discovered from the intermediate Palomar Transient Factory (iPTF). As the supernova is of Type Ia where the intrinsic luminosity is usually well known, accurately measured time delays of the multiple images could provide tight constraints on the Hubble constant. According to our lens mass models constrained by the Hubble Space Telescope F814W image, we expect the maximum relative time delay to be less than a day, which is consistent with the maximum of 100 hr reported by Goobar et al. but places a stringent upper limit. Furthermore, the fluxes of most of the supernova images depart from expected values suggesting that they are affected by microlensing. The microlensing timescales are small enough that they may pose significant problems to measure the time delays reliably. Our lensing rate calculation indicates that the occurrence of a lensed SN in iPTF is likely. However, the observed total magnification of iPTF16geu is larger than expected, given its redshift. This may be a further indication of ongoing microlensing in this system.
-
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 465(2) 2411-2419 2017年2月We report the serendipitous discovery of a quadruply lensed source at z(s) = 3.76, HSC J115252+004733, from the Hyper Suprime-Cam (HSC) Survey. The source is lensed by an early-type galaxy at z(1) = 0.466 and a satellite galaxy. Here, we investigate the properties of the source by studying its size and luminosity from the imaging and the luminosity and velocity width of the Ly-alpha line from the spectrum. Our analyses suggest that the source is most probably a low-luminosity active galactic nucleus (LLAGN) but the possibility of it being a compact bright galaxy (e.g. a Lyman-alpha emitter or lyman break galaxy) cannot be excluded. The brighter pair of lensed images appears point-like except in the HSC i band (with a seeing similar to 0.5 arcsec). The extended emission in the i-band image could be due to the host galaxy underneath the AGN, or alternatively, due to a highly compact lensed galaxy (without AGN) which appears point-like in all bands except in i band. We also find that the flux ratio of the brighter pair of images is different in the Ks band compared to optical wavelengths. Phenomena such as differential extinction and intrinsic variability cannot explain this chromatic variation. While microlensing from stars in the foreground galaxy is less likely to be the cause, it cannot be ruled out completely. If the galaxy hosts an AGN, then this represents the highest redshift quadruply imaged AGN known to date, enabling study of a distant LLAGN. Discovery of this unusually compact and faint source demonstrates the potential of the HSC survey.
主要なMISC
21-
天文月報 = The astronomical herald 118(2) 75-80 2025年2月
主要な担当経験のある科目(授業)
11主要な共同研究・競争的資金等の研究課題
16-
日本学術振興会 科学研究費助成事業 2025年4月 - 2030年3月
-
日本学術振興会 科学研究費助成事業 2022年12月 - 2029年3月
-
日本学術振興会 科学研究費助成事業 2025年4月 - 2028年3月
-
日本学術振興会 科学研究費助成事業 2024年4月 - 2027年3月
-
日本学術振興会 科学研究費助成事業 2019年10月 - 2025年3月