Search

This paper presents a new optical imaging survey of four deep drilling fields (DDFs), two Galactic and two extragalactic, with the Dark Energy Camera (DECam) on the 4 meter Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO). During the first year of observations in 2021, $>$4000 images covering 21 square degrees (7 DECam pointings), with $\sim$40 epochs (nights) per field and 5 to 6 images per night per filter in $g$, $r$, $i$, and/or $z$, have become publicly available (the proprietary period for this program is waived). We describe the real-time difference-image pipeline and how alerts are distributed to brokers via the same distribution system as the Zwicky Transient Facility (ZTF). In this paper, we focus on the two extragalactic deep fields (COSMOS and ELAIS-S1), characterizing the detected sources and demonstrating that the survey design is effective for probing the discovery space of faint and fast variable and transient sources. We describe and make publicly available 4413 calibrated light curves based on difference-image detection photometry of transients and variables in the extragalactic fields. We also present preliminary scientific analysis regarding Solar System small bodies, stellar flares and variables, Galactic anomaly detection, fast-rising transients and variables, supernovae, and active galactic nuclei., 22 pages, 17 figures, 2 tables. Accepted to MNRAS

We report on the galaxy density environment around a high-z radio galaxy (HzRG) at z=4.72, HSC J083913.17+011308.1 (HSC J0839+0113), probed using an r-dropout Lyman break galaxy (LBG) sample from the Hyper Suprime-Cam Subaru Strategic Program data. We find that HSC J0839+0113 resides in the outskirt of an overdense region identified by the r-dropout galaxies at a 4.7 sigma significance level. The projected distance between HSC J0839+0113 and the peak position of the overdense region is 0.4 physical Mpc which is shorter than the typical protocluster radius in this epoch. According to the extended Press Schechter and the light cone models, the HSC J0839+0113-hosted overdense region is expected to evolve into a halo > 10^14 Msun at z=0 with a high probability of >80 %. These findings suggest that HSC J0839+0113 is associated with a protocluster. The HSC J0839+0113 rich-system is the most overdense region of LBGs among the known protoclusters with LBGs in the same cosmic epoch., 7 pages, 3 figures, accepted in PASJ

We examine the redshift evolution of density environments around 2,163 radio galaxies with the stellar masses of $\sim10^{9}-10^{12} M_\odot$ between redshifts of $z=0.3-1.4$, based on the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and Faint Images of the Radio Sky at Twenty-cm (FIRST). We use the $k$-nearest neighbor method to measure the local galaxy number density around our radio galaxy sample. We find that the overdensities of the radio galaxies are weakly but significantly anti-correlated with redshift. This is consistent with the known result that the relative abundance of less-massive radio galaxies increases with redshift, because less-massive radio galaxies reside in relatively low density regions. Massive radio galaxies with stellar mass of $M_* >10^{11}M_\odot$ are found in high density environments compared with the control sample galaxies with radio-non-detection and matched-stellar-mass. Less-massive radio galaxies with $M_* 10^{11}M_\odot$ ($M_* 1.4$, while less-massive radio galaxies undergo active accretion just at this epoch, as they have avoided such merger events., 14 pages, 8 figures, ApJ accepted

The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology. Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($, Comment: 22 pages, 9 figures, accepted for publication in ApJ

Ongoing large-scale optical time-domain surveys, such as the Zwicky Transient Facility (ZTF), are producing alerts at unprecedented rates. Analysis of transient sources has so far followed two distinct paths: archival analysis of data on transient sources at a time when they are no longer observable and real-time analysis at the time when the sources are first detected. The latter is the realm of alert brokers such as the Arizona-NOIRLab Temporal Analysis and Response to Events System (ANTARES). In this paper, we synthesize the two analysis paths and present a first systematic study of archival alert-broker data, focusing on extragalactic transients with multipeaked light curves identified in the ANTARES archive of ZTF alerts. Our analysis yields a sample of 37 such sources, including core-collapse supernovae (with two analogs of iPTF14hls), thermonuclear supernovae interacting with their surrounding circumstellar medium, tidal disruption events, luminous blue variables, and as yet unclassified objects. A large fraction of the identified sources is currently active, warranting allocation of follow-up resources in the immediate future to further constrain their nature and the physical processes at work., Accepted for publication in ApJ Letters

We conduct a search for galaxy-scale strong gravitational lens systems in Data Release 4 of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP), consisting of data taken up to the S21A semester. We select 103191 luminous red galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) sample that have deep multiband imaging from the HSC SSP and use the YattaLens algorithm to automatically identify lens candidates with blue arc-like features. The candidates are visually inspected and graded based on their likelihood of being a lens. We find 8 definite lenses, 28 probable lenses, and 138 possible lenses. The new lens candidates generally have lens redshifts in the range $0.3 \lesssim z_{\mathrm{L}} \lesssim 0.9$, a key intermediate redshift range to study the evolution of galaxy structure. Follow-up spectroscopy will confirm these new lenses and measure source redshifts to enable detailed lens modeling., Comment: Accepted for publication in PASJ; 12 pages, 4 figures, 2 tables

We present the optical and infrared properties of 39 extremely radio-loud galaxies discovered by cross-matching the Subaru/Hyper Suprime-Cam (HSC) deep optical imaging survey and VLA/FIRST 1.4 GHz radio survey. The recent Subaru/HSC strategic survey revealed optically-faint radio galaxies (RG) down to $g_\mathrm{AB} \sim 26$, opening a new parameter space of extremely radio-loud galaxies (ERGs) with radio-loudness parameter of $\log \mathcal{R}_\mathrm{rest} = \log (f_{1.4 \mathrm{GHz,rest}}/f_{g,\mathrm{rest}}) >4$. Because of their optical faintness and small number density of $\sim1~$deg$^{-2}$, such ERGs were difficult to find in the previous wide but shallow, or deep but small area optical surveys. ERGs show intriguing properties that are different from the conventional RGs: (1) most ERGs reside above or on the star-forming main-sequence, and some of them might be low-mass galaxies with $\log (M_\star/M_\odot) < 10$. (2) ERGs exhibit a high specific black hole accretion rate, reaching the order of the Eddington limit. The intrinsic radio-loudness ($\mathcal{R}_\mathrm{int}$), defined by the ratio of jet power over bolometric radiation luminosity, is one order of magnitude higher than that of radio quasars. This suggests that ERGs harbor a unique type of active galactic nuclei (AGN) that show both powerful radiations and jets. Therefore, ERGs are prominent candidates of very rapidly growing black holes reaching Eddington-limited accretion just before the onset of intensive AGN feedback., 20 pages, 10 figures, accepted for publication in ApJ

We conduct intensity mapping to probe for extended diffuse Lyα emission around Lyα emitters (LAEs) at z ∼2−7, exploiting very deep (∼26 mag at 5σ) and large-area (∼4.5 deg2) Subaru/Hyper Suprime-Cam narrowband (NB) images and large LAE catalogs consisting of a total of 1540 LAEs at z = 2.2, 3.3, 5.7, and 6.6 obtained by the HSC-SSP and CHORUS projects. We calculate the spatial correlations of these LAEs with ∼1–2 billion pixel flux values of the NB images, deriving the average Lyα surface brightness (SBLyα ) radial profiles around the LAEs. By carefully estimating systematics such as fluctuations of sky background and point-spread functions, we detect Lyα emission at 100–1000 comoving kpc around z = 3.3 and 5.7 LAEs at the 3.2σ and 3.7σ levels, respectively, and tentatively (=2.0σ) at z = 6.6. The emission is as diffuse as ∼10−20–10−19 erg s−1 cm−2 arcsec−2 and extended beyond the virial radius of a dark matter halo with a mass of 1011 M ⊙. While the observed SBLyα profiles have similar amplitudes at z = 2.2–6.6 within the uncertainties, the intrinsic SBLyα profiles (corrected for the cosmological dimming effect) increase toward high redshifts. This trend may be explained by increasing hydrogen gas density due to the evolution of the cosmic volume. Comparisons with theoretical models suggest that extended Lyα emission around an LAE is powered by resonantly scattered Lyα photons in the CGM and IGM that originate from the inner part of the LAE and/or neighboring galaxies around the LAE.

Onoue, Masafusa, et al., We present deep Keck/MOSFIRE near-infrared spectroscopy of a strong Lyα emitting source at z = 6.1292, HSC J142331.71-001809.1, which was discovered by the SHELLQS program from imaging data of the Subaru Hyper Suprime-Cam (HSC) survey. This source is one of five objects that show narrow (FWHM < 500 km s-1) and prominent (LLyα > 1044 erg s-1) Lyα emission lines at absolute 1450 Å continuum magnitudes of M1450∼-22 mag. Its rest-frame Lyα equivalent width (EW) is 370 ± 30 Å. In the 2 hr Keck/MOSFIRE spectrum in Y band, the high-ionization C IV λλ1548,1550 doublet emission line was clearly detected with = - FWHM 120+20 20 km s-1 and a total rest-frame EW of - 37+5 6 Å. We also report the detection of weak continuum emission, and the tentative detection of O III]λλ1661,1666 in the 4 hr J-band spectrum. Judging from the UV magnitude, line widths, luminosities, and EWs of Lyα and C IV, we suggest that this source is a reionization-era analog of classical type-II AGNs, although there is a possibility that it represents a new population of AGN/galaxy composite objects in the early universe. We compare the properties of J1423-0018 to intermediate-redshift type-II AGNs and C IV emitters seen in z = 6-7 galaxy samples. Further observations of other metal emission lines in the rest-frame UV or optical, along with X-ray follow-up observations of the z = 6-7 narrow-line quasars, are needed for more robust diagnostics and to determine their nature., Funding was contributed by the FIRST program from Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. This work was supported by JSPS KAKENHI grant Nos. 17H04830 (YM), 20H01949 (TN), 18J01050 (YT). M.O. was supported by the ERC Advanced Grant 740246 Cosmic gas. Y. M. was supported by the Mitsubishi Foundation grant No. 30140. T.H. was supported by Leading Initiative for Excellent Young Researchers, MEXT, Japan (HJH02007).

Studies of white dwarfs have greatly benefited from time-domain surveys and subsequent follow-up observations. However, with the avalanche of alerts delivered by ZTF and LSST and the limited resources for follow-up, we will need brokers to select intriguing alerts that warrant follow-up in a timely manner. At the University of Arizona and NSF’s OIR Lab, we are developing the Arizona-NOAO Temporal Analysis and Response to Events System, to hunt for the rarest of the rare events in the time-domain. In this work, we provide an overview of the ANTARES system, how we use ZTF as a training set, and the way forwards to LSST.

We present ALMA [CII] line and far-infrared (FIR) continuum observations of seven z > 6 low-luminosity quasars (M1450 > −25 mag) discovered by our on-going Subaru Hyper Suprime-Cam survey. The [CII] line was detected in all targets with luminosities of ∼(2−10) × 108 L⊙, about one order of magnitude smaller than optically luminous quasars. Also found was a wide scatter of FIR continuum luminosity, ranging from LFIR < 1011L⊙ to ∼2 × 1012L⊙. With the [CII]-based dynamical mass, we suggest that a significant fraction of low-luminosity quasars are located on or even below the local Magorrian relation, particularly at the massive end of the galaxy mass distribution. This is a clear contrast to the previous finding that luminous quasars tend to have overmassive black holes relative to the relation. Our result is expected to show a less-biased nature of the early co-evolution of black holes and their host galaxies.

Recent progress in submillimetre surveys by single-dish telescopes allows us to further challenge the consistency between cosmological simulations and observations. In particular, we compare our simulations that include dust formation and destruction with the recent SCUBA-2 surveys (`STUDIES') by putting emphases on basic observational properties of dust emission such as dust temperature, size of infrared (IR)-emitting region, IR luminosity function and IRX--$\beta$ relation. After confirming that our models reproduce the local galaxy properties, we examine the STUDIES sample at $z\approx 1-4$, finding that the simulation reproduces the aforementioned quantities except for the $z\gtrsim 2$ IR luminosity function at the massive end ($\sim 10^{13}$ L$_{\odot}$). This means that the current simulation correctly reproduces the overall scaling between the size and luminosity (or star formation rate) of dusty region, but lacks extreme starburst phenomena at $z\gtrsim 2$. We also discuss extinction curves and possible AGN contribution., Comment: 13 pages, 10 figures, published in MNRAS

Izumi, T., et al., We present Atacama Large Millimeter/submillimeter Array [C ii] 158 μm line and far-infrared (FIR) continuum emission observations toward HSC J120505.09-000027.9 (J1205-0000) at z = 6.72 with a beam size of ∼0.″8 × 0.″5 (or 4.1 kpc × 2.6 kpc), the most distant red quasar known to date. Red quasars are modestly reddened by dust and are thought to be in rapid transition from an obscured starburst to an unobscured normal quasar, driven by powerful active galactic nucleus (AGN) feedback that blows out a cocoon of interstellar medium. The FIR continuum of J1205-0000 is bright, with an estimated luminosity of L FIR ∼ 3 × 1012 L o˙. The [C ii] line emission is extended on scales of r ∼ 5 kpc, greater than that of the FIR continuum. The line profiles at the extended regions are complex and broad (FWHM ∼ 630-780 km s-1). Although it is not practical to identify the nature of this extended structure, possible explanations include (i) companion/merging galaxies and (ii) massive AGN-driven outflows. For the case of (i), the companions are modestly star-forming (∼10 M o˙ yr-1) but are not detected by our Subaru optical observations (y AB,5σ = 24.4 mag). For the case of (ii), our lower limit to the cold neutral outflow rate is ∼100 M o˙ yr-1. The outflow kinetic energy and momentum are both much lower than predicted in energy-conserving wind models, suggesting that the AGN feedback in this quasar is not capable of completely suppressing its star formation., Funding was contributed by the FIRST program of the Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science, and Technology, the Japan Society for the Promotion of Science, the Japan Science and Technology Agency, the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. T.I. is supported by an ALMA Japan Research Grant of the NAOJ ALMA Project, NAOJ-ALMA-249.

Izumi, T., et al., We present Atacama Large Millimeter/submillimeter Array [C ii] 158 μm line and underlying far-infrared (FIR) continuum emission observations (0.″70 × 0.″56 resolution) toward HSC J124353.93+010038.5 (J1243+0100) at z = 7.07, the only low-luminosity (M 1450 > -25 mag) quasar currently known at z > 7. The FIR continuum is bright (1.52 mJy) and resolved with a total luminosity of L FIR = 3.5 × 1012 L o˙. The spatially extended component is responsible for ∼40% of the emission. The area-integrated [C ii] spectrum shows a broad wing (FWHM = 997 km s-1, L [C ii] = 1.2 × 109 L o˙), as well as a bright core (FWHM = 235 km s-1, L [C ii] = 1.9 × 109 L o˙). This wing is the first detection of a galactic-scale quasar-driven outflow (atomic outflow rate >447 M o˙ yr-1) at z > 7. The estimated large mass-loading factor of the total outflow (e.g., ⪆9 relative to the [C ii]-based star formation rate) suggests that this outflow will soon quench the star formation of the host. The core gas dynamics are governed by rotation, with a rotation curve suggestive of a compact bulge (∼3.3 × 1010 M o˙), although it is not yet spatially resolved. Finally, we found that J1243+0100 has a black hole mass-to-dynamical mass (and -to-bulge mass) ratio of ∼0.4% (∼1%), consistent with the local value within the uncertainties. Our results therefore suggest that the black hole-host coevolution relation is already in place at z ∼ 7 for this object., Funding was contributed by the FIRST program from the Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), the Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. T.H. was supported by th

Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome by-product of also removing the galaxy's large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and present the first HASHTAG images of Andromeda at 450 and 850um. We also have created a method to predict the CO(J=3-2) line flux across M31, which contaminates the 850um band. We find that while normally the contamination is below our sensitivity limit, the contamination can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed., Comment: 26 pages, 19 figures. Submitted to ApJS June 2021, Accepted September 2021

We present the spectroscopic discovery of 69 quasars at 5.8 < z < 7.0, drawn from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) imaging survey data. This is the 16th publication from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, and completes identification of all but the faintest candidates (i.e., i-band dropouts with zAB < 24 and y-band detections, and z-band dropouts with yAB < 24) with Bayesian quasar probability Pq > 0.1 in the HSC-SSP third public data release (PDR3). The sample reported here also includes three quasars with Pq < 0.1 at z ~ 6.6, which we selected in an effort to completely cover the reddest point sources with simple color cuts. The number of high-z quasars discovered in SHELLQs has now grown to 162, including 23 type-II quasar candidates. This paper also presents identification of seven galaxies at 5.6 < z < 6.7, an [O III] emitter at z = 0.954, and 31 Galactic cool stars and brown dwarfs. High-z quasars and galaxies comprise 75 % and 16 % respectively of all the spectroscopic SHELLQs objects that pass our latest selection algorithm with the PDR3 photometry. That is, a total of 91 % of the objects lie at z > 5.6. This demonstrates that the algorithm has very high efficiency, even though we are probing an unprecedentedly low-luminosity population down to M1450 ~ -21 mag., Accepted for publication in The Astrophysical Journal Supplement Series

We present the environmental properties around high-$z$ radio galaxies (HzRGs) at $z\sim4$, which have been poorly investigated because of their rarity. We use the largest samples of HzRGs and $g$-dropout galaxy overdense regions at $z\sim4$, which were constructed from Hyper Suprime-Cam Subaru Strategic Program, to characterize the HzRG environments statistically. We measure the $g$-dropout galaxy overdensities around 21 HzRGs whose rest-frame 1.4 GHz radio luminosities ($L_{1.4\mathrm{GHz}}$) are $10^{26-27}$ W Hz$^{-1}$. We find that the overdensities around the faint HzRGs with $L_{1.4\mathrm{GHz}}\sim10^{26.0-26.5}$ W Hz$^{-1}$ tend to be higher than that of the $g$-dropout galaxies. On the other hand, no significant difference of density environments is found between the luminous HzRGs with $ L_{1.4\mathrm{GHz}}\sim10^{26.5-27.0} $ W Hz$^{-1}$ and the $g$-dropout galaxies. The HzRGs are found to occupy more massive halos than $g$-dropout galaxies through a cross-correlation between the HzRGs and $g$-dropout galaxies. This trend is more pronounced in the faint HzRGs. These results are consistent with a scenario where HzRGs get older and more massive as the radio-luminosity decreases. The HzRGs are expected to trace the progenitors of local cluster halos from their calculated halo mass. In addition, we find that surrounding galaxies tend to distribute along the radio-jet major axis of the HzRGs at angular distances less than $\lesssim500$ physical kpc. Our findings imply the onset of the filamentary structures around the HzRGs at $z\sim4$., Comment: 22 pages, 8 figures, accepted in ApJ

We have developed an integral field unit (IFU) for the existing optical imaging spectrograph, Faint Object Camera And Spectrograph (FOCAS), on the Subaru telescope. FOCAS IFU finally saw a first light on March 2nd, 2018, and started the common use from 2019. In order to observe faint targets like distant galaxies, our IFU has a coarse sampling comparable to the best seeing size and high throughput. The field of view is 13.4 10.0 arcsec2 which is divided into 23 slices with the width of 0.435 arcsec. Our IFU has a slit separated by about 5.2 arcmin from an object field in order to simultaneously obtain a sky spectrum. We confirmed that the image quality is good enough for the 0.435-arcsec slice width and the best seeing size of 0.4 arcsec. Mean and median throughput of the IFU are respectively 85.0% and 87.3%. However some fields show lower throughput due to misalignment of the IFU optics and the worst throughput is 61.9% at one field corner. Flat fielding error is almost within ±3%, but worse errors are found at the low-throughput region. The worst error is 9% at the lowest throughput region.

With the avalanche of alerts to be delivered by Rubin Observatory's Legacy Survey of Space and Time and the limited resources for follow-up, we will need brokers to select intriguing alerts that warrant follow-up in a timely manner. At NSF's NOIRLab and University of Arizona, we are developing the Arizona-NOIRLab Temporal Analysis and Response to Events System (ANTARES, Saha et al. 2014, 2016, Narayan et al. 2018), to hunt for the rarest of the rare events in the time domain. In this work, we provide an overview of the ANTARES system, how we use real-time alerts from the ongoing Zwicky Transient Facility survey as a training set, and the way forwards to Rubin observatory.

Astrophysical phenomena occur on a range of timescales, and to properly characterize them, observations must be made at appropriate intervals on instrumentation determined by the scientific goals of the study. The traditional model of scheduling telescope time in blocks of consecutive nights and requiring the investigators to operate the instrument (either in person or remotely) is not optimal for this science. A queue-scheduled approach to time allocation can relieve the personal and financial burden of interactive observing runs. This is particularly powerful when requests for observations can be made through a programmatic interface, which provides not just a convenient tool for all astronomy programs, but also the opportunity to build fully automated observing programs. This will be an essential component of projects making follow-up observations for modern surveys that produce millions of alerts per night, as much of the science return will depend upon obtaining classification and characterization data rapidly and efficiently, as well as for coordination of observations across multiple facilities. The AEON Network is an initiative to build a programmatically accessible, queue-scheduled and user driven network of telescopes ideal for modern astronomical observing programs.

The spatial inhomogeneity is one of the important features for understanding the reionization process; however, it has not yet been fully quantified. To map this inhomogeneous distribution, we simultaneously detect Ly$\alpha$ emitters (LAEs) and Lyman break galaxies (LBGs) at $z \sim 6.6$ from the Subaru/Hyper Suprime-Cam (HSC) large-area ($\sim1.5\,\mathrm{ deg}^2 = 34000\,\mathrm{cMpc}^2$) deep survey. We estimate the neutral fraction, $x_\mathrm{HI}$, from the observed number density ratio of LAEs to LBGs, $n(\mathrm{LAE})/n(\mathrm{LBG})$ based on numerical radiative transfer simulation, in which model galaxies are selected to satisfy the observed selection function. While the average $x_\mathrm{HI}$ within the field of view is found to be $x_\mathrm{HI} < 0.4$, which is consistent with previous studies, the variation of $n(\mathrm{LAE})/n(\mathrm{LBG})$ within the field of view for each $140\,\mathrm{pMpc}^2$ is found to be as large as a factor of three. This may suggest a spatially inhomogeneous topology of reionization, but it also leaves open the possibility that the variation is based on the inherent large-scale structure of the galaxy distribution. Based on the simulations, it may be difficult to distinguish between the two from the current survey. We also find that LAEs in the high LAE density region are more populate high $\mathrm{EW}_0$, supporting that the observed $n(\mathrm{LAE})/n(\mathrm{LBG})$ is more or less driven by the neutral fraction, though the statistical significance is not high., Comment: 20 pages, 22 figures, accepted for publication in ApJ

Some supernovae such as pair-instability supernovae are predicted to have the duration of more than a year in the observer frame. To constrain the rates of supernovae lasting for more than a year, we conducted a long-term deep transient survey using Hyper Suprime-Cam (HSC) on the 8.2m Subaru telescope. HSC is a wide-field (a 1.75 deg2 field-of-view) camera and it can efficiently conduct transient surveys. We observed the same 1.75 deg2 field repeatedly using the g, r, i, and z band filters with the typical depth of 26 mag for 4 seasons (from late 2016 to early 2020). Using these data, we searched for transients lasting for more than a year. Two supernovae were detected in 2 continuous seasons, one supernova was detected in 3 continuous seasons, but no transients lasted for all 4 seasons searched. The discovery rate of supernovae lasting for more than a year with the typical limiting magnitudes of 26 mag is constrained to be 1.4^{+1.3}_{-0.7}(stat.)^{+0.2}_{-0.3}(sys.) events deg-2 yr-1. All the long-lasting supernovae we found are likely Type IIn supernovae and our results indicate that about 40% of Type IIn supernovae have long-lasting light curves. No plausible pair-instability supernova candidates lasting for more than a year are discovered. By comparing the survey results and survey simulations, we constrain the luminous pair-instability supernova rate up to z ~ 3 should be of the order of 100 Gpc-3 yr-1 at most, which is 0.01 - 0.1 per cent of the core-collapse supernova rate., 18 pages, 9 figures, 6 tables, accepted by The Astrophysical Journal

We describe the Arizona-NOIRLab Temporal Analysis and Response to Events System (ANTARES), a software instrument designed to process large-scale streams of astronomical time-domain alerts. With the advent of large-format CCDs on wide-field imaging telescopes, time-domain surveys now routinely discover tens of thousands of new events each night, more than can be evaluated by astronomers alone. The ANTARES event broker will process alerts, annotating them with catalog associations and filtering them to distinguish customizable subsets of events. We describe the data model of the system, the overall architecture, annotation, implementation of filters, system outputs, provenance tracking, system performance, and the user interface., 24 Pages, 8 figures, Accepted by AJ

Galaxies in dense environments, such as groups and clusters, experience various processes by which galaxies gain and lose gas. Using data from the SDSS-IV MaNGA survey, we previously reported the discovery of a giant (6 -- 8 kpc in diameter) H$\alpha$ blob, Totoro, about 8 kpc away from a pair of galaxies (Satsuki and Mei) residing in a galaxy group which is experiencing a group-group merger. Here, we combine interferometric $^{12}$CO(1--0) molecular gas data, new wide-field H$\alpha$, $u$-band data, and published X-ray data to determine the origin of the blob. Several scenarios are discussed to account for its multi-wavelength properties, including (1) H$\alpha$ gas being stripped from galaxy Satsuki by ram-pressure; (2) a separated low-surface-brightness galaxy; (3) gas being ejected or ionized by an active galactic nucleus (AGN); and (4) a cooling intra-group medium (IGM). Scenarios (1) and (2) are less favored by the present data. Scenario (3) is also less likely as there is no evidence for an active ongoing AGN in the host galaxy. We find that the CO (cold) and H$\alpha$ (warm) gas coexist with X-ray (hot) structures; moreover, the derived cooling time is within the regime where molecular and H$\alpha$ gas are expected. The coexistence of gas with different temperatures also agrees with that of cooling gas in other systems. Our multi-wavelength results strongly suggest that the CO and H$\alpha$ gas are the product of cooling from the IGM at its current location, i.e., cooling has occurred, and may be ongoing, well outside the host-galaxy core., Comment: 23 pages, 10 figures, Accepted for publication in ApJ

The ongoing Zwicky Transient Facility (ZTF) survey is generating a massive alert rate from a variety of optical transients and variable stars, which are being filtered down to subsets meeting user-specified criteria by broker systems such as ANTARES. In a beta implementation of the algorithm of Soraisam et al. (2020) on ANTARES, we flagged AT 2020iko from the ZTF real-time alert stream as an anomalous source. This source is located close to a red extended SDSS source. In the first few epochs of detection, it exhibited a V-shaped brightness profile, preceded by non-detections both in ZTF and in ASASSN extending to 2014. Its full light curve shows a precursor event, followed by a main superoutburst and at least two rebrightenings. A low-resolution spectrum of this source points to a dwarf nova (DN) nature. Although some of the features of AT 2020iko indicate an SU UMa-type DN, its large amplitude, presence of rebrightenings, and inferred supercycle period of > 6 yr are in favor of AT 2020iko being a new WZ Sge-type dwarf nova candidate, a subset of rare DNe consisting of extreme mass-ratio (< 0.1) binaries with orbital period around the period minimum. AT 2020iko's precursor event brightened by 6.5 mag, while its decay spanned 3-5 mag. We speculate this superoutburst is associated with a less expanded accretion disk than in typical superoutbursts in WZ Sge systems, with the large depth of the precursor decay implying an extremely small mass-ratio. To the best of our knowledge, such a precursor event has not been recorded for any DN. This result serves to demonstrate the efficacy of our real-time anomaly search algorithm., 11 pages, 4 figures; accepted to AJ

The Faint Object Camera and Spectrograph (FOCAS) is an optical imaging and spectroscopy instrument for the Subaru Telescope. It has been a workhorse instrument since the first-light phase of the telescope. We describe an integral field unit (IFU) that has recently been installed in FOCAS. The IFU utilizes an image slicer that divides a ${13{^{\prime \prime }_{.}}5}$ × ${10{^{\prime \prime }_{.}}0}$ field of view into 23 stripes, with a width of ${0{^{\prime \prime }_{.}}435}$. A sky spectrum separated from an object by approximately ${5{^{\prime }_{.}}2}$ can be obtained at the same time as an object spectrum. Test observations confirmed that the image quality of the IFU does not degrade the ${0{^{\prime \prime }_{.}}435}$ sampling, and that slice width and length are consistent with the design. Highly reflective multilayer dielectric coatings were coated on all the mirrors in the IFU, thereby offering a high mean IFU throughput of ∼85% over the field. However, the outer part of the field showed throughput degradation, which was mainly caused by vignetting as a result of misalignment. The flat-fielding accuracy was degraded by the vignetting, with the variation depending on the direction of the telescope.

We have conducted a comprehensive survey of emission-line galaxies at $z\lesssim1.6$ based on narrowband (NB) imaging data taken with Hyper Suprime-Cam (HSC) on the Subaru telescope. In this paper, we update the catalogs of H$\alpha$, [OIII], and [OII] emission-line galaxies using the data from the second Public Data Release (PDR2) of Subaru Strategic Program (SSP) of HSC and Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) survey along with the spectroscopic redshifts for 2,019 emission-line galaxies selected with the PDR1 data. The wider effective coverage of NB816 and NB921, 16.3 deg$^2$ and 16.9 deg$^2$ respectively, are available in the Deep and UltraDeep layers of HSC-SSP from the PDR2. The CHORUS survey provides us with data with additional three NBs (NB527, NB718, and NB973) in the COSMOS field in the UltraDeep layer (1.37 deg$^2$). The five NB datasets allow us to investigate the star-forming galaxies presenting emission-lines at 14 specific redshifts ranging from $z\sim1.6$ down to $z\sim0.05$. We revisit the distribution of large-scale structures and luminosity functions (LFs) for the emission-line galaxies with the large samples of 75,377 emission-line galaxies selected. The redshift revolution of LFs shows that the star formation rate densities (SFRDs) decreases monotonically from $z\sim1.6$, which is consistent with the cosmic SFRD ever known. Our samples of emission-line galaxies covering a sufficiently large survey volume are useful to investigate the evolution of star-forming galaxies since the cosmic noon in a wide range of environments including galaxy clusters, filaments, and voids., Comment: 32 pages, 23 figures, 6 tables, accepted for publication in PASJ. The catalog of emission-line galaxies from HSC-SSP PDR2 data will be available soon at https://hsc-release.mtk.nao.ac.jp/, and the catalog from CHORUS data will be available after the CHORUS data are publicly released

arXiv:2007.08685v2, We present the first discovery of dust-reddened quasars (red quasars) in the high-z universe (z > 5.6). This is a result from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which is based on the sensitive multi-band optical imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We identified four red quasar candidates from the 93 spectroscopically confirmed high-z quasars in the SHELLQs sample, based on detections in the Wide-field Infrared Survey Explorer (WISE) data at 3.4 and 4.6 μm (rest-frame ∼5000–6500 Å). The amount of dust reddening was estimated with spectral energy distribution (SED) fits over optical and mid-infrared wavelengths. Two of the four candidates were found to be red quasars with dust reddening of E(B − V) > 0.1. The remaining SHELLQs quasars without individual WISE detections are significantly fainter in the WISE bands and bluer than the red quasars, although we did detect them in the W1 band in a stacked image. We also conducted the same SED fits for high-z optically-luminous quasars, but no red quasar was found. This demonstrates the power of Subaru HSC to discover high-z red quasars, which are fainter than the limiting magnitudes of past surveys in the rest-frame ultraviolet, due to dust extinction., We are grateful to the referee for his/her useful comments to improve this paper. YM was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant No. JP17H04830 and the Mitsubishi Foundation grant No. 30140. TI acknowledges supports from the JSPS grant No. JP17K14247. The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of 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 the FIRST program from Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the 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 through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under Grant No. AST-1238877, the University of Maryland, and Eotvos Lorand University (ELTE). This paper makes use of software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code available as free software at 〈http://dm.lsst.org. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration.

We report a discovery of $z = 4.72$ radio galaxy, HSC J083913.17+011308.1, by using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for VLA FIRST radio sources. The number of known high-$z$ radio galaxies (HzRGs) at $z > 3$ is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected $r$-band dropouts with a radio detection, a follow-up optical spectroscopy with GMOS/Gemini has been performed. The obtained spectrum presents a clear Ly$\alpha$ emission line redshifted to $z=4.72$. The SED fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with $\log{M_*/M_{\odot}} = 11.4$. The small equivalent width of Ly$\alpha$ and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum: $\alpha^{325}_{1400}$ of $-1.1$ and $\alpha^{150}_{1400}$ of $-0.9$, demonstrating that the HSC-SSP survey compensates for a sub-population of HzRGs which are missed in surveys focusing on an ultra-steep spectral index., Comment: 10 pages, 5 figures, accepted for publication in AJ

We report the largest sample of candidate strong gravitational lenses belonging to the Survey of Gravitationally-lensed Objects in HSC Imaging for group-to-cluster scale (SuGOHI-c) systems. These candidates are compiled from the S18A data release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) Survey. We visually inspect $\sim39,500$ galaxy clusters, selected from several catalogs, overlapping with the Wide, Deep, and UltraDeep fields, spanning the cluster redshift range $0.05, Comment: Accepted for publication in MNRAS, 19 pages, 11 figures

We present a CO(3-2) survey of selected regions in the M31 disc as part of the JCMT large programme, HARP and SCUBA-2 High-Resolution Terahertz Andromeda Galaxy Survey (HASHTAG). The 12 CO(3-2) fields in this survey cover a total area of 60 square arcminutes, spanning a deprojected radial range of 2 - 14 kpc across the M31 disc. Combining these observations with existing IRAM 30m CO(1-0) observations and JCMT CO(3-2) maps of the nuclear region of M31, as well as dust temperature and star formation rate surface density maps, we are able to explore the radial distribution of the CO(3-2)/CO(1-0) integrated intensity ratio (R31) and its relationship with dust temperature and star formation. We find that the value of R31 between 2 - 9 kpc galactocentric radius is 0.14, significantly lower than what is seen in the nuclear ring at ~1 kpc (R31 ~ 0.8), only to rise again to 0.27 for the fields centred on the 10 kpc star forming ring. We also found that R31 is positively correlated with dust temperature, with Spearman's rank correlation coefficient $\rho$ = 0.55. The correlation between star formation rate surface density and CO(3--2) intensity is much stronger than with CO(1-0), with $\rho$ = 0.54 compared to -0.05, suggesting that the CO(3-2) line traces warmer and denser star forming gas better. We also find that R31 correlates well with star formation rate surface density, with $\rho$ = 0.69., Comment: 21 pages, 10 figures, accepted by MNRAS for publication

We report the serendipitous discovery of HSC J0904$-$0102, a quadruply-lensed Lyman break galaxy (LBG) in the Survey of Gravitationally-lensed Objects in Hyper Suprime-Cam Imaging (SuGOHI). Owing to its point-like appearance, the source was thought to be a lensed active galactic nucleus. We obtained follow-up spectroscopic data with the Gemini Multi-Object Spectrographs on the Gemini South Telescope, which confirmed this to be a lens system. The deflecting foreground galaxy is a typical early-type galaxy at a high redshift of $z_{\ell} = 0.957$ with stellar velocity dispersion $\sigma_v=259\pm56$ km~s$^{-1}$. The lensed source is identified as an LBG at $z_{\rm s} = 3.403$, based on the sharp drop bluewards of Ly$\alpha$ and other absorption features. A simple lens mass model for the system, assuming a singular isothermal ellipsoid, yields an Einstein radius of $\theta_{\rm Ein} = 1. 23^{\prime\prime}$ and a total mass within the Einstein radius of $M_{\rm Ein} = (5.55\pm 0.24) \times 10^{11}M_{\odot}$ corresponding to a velocity dispersion of $\sigma_{\rm SIE}= 283\pm 3$ km~s$^{-1}$, which is in good agreement with the value derived spectroscopically. The most isolated lensed LBG image has a magnification of $\sim 6.5$. In comparison with other lensed LBGs and typical $z\sim4$ LBG populations, HSC J0904$-$0102 is unusually compact, an outlier at $>2\sigma$ confidence. Together with a previously discovered SuGOHI lens, HSC J1152$+$0047, that is similarly compact, we believe that the HSC Survey is extending LBG studies down to smaller galaxy sizes., Comment: Accepted for publication on MNRAS, 10 pages, 6 figures