[en] We present the J- and H-band source catalog covering the AKARI North Ecliptic Pole field. Filling the gap between the optical data from other follow-up observations and mid-infrared (MIR) data from AKARI, our near-infrared (NIR) data provides contiguous wavelength coverage from optical to MIR. For the J- and H-band imaging, we used the FLoridA Multi-object Imaging Near-ir Grism Observational Spectrometer on the Kitt Peak National Observatory 2.1m telescope covering a 5.1 deg² area down to a 5σ depth of ∼21.6 mag and ∼21.3 mag (AB) for the J and H bands with an astrometric accuracy of 0.''14 and 0.''17 for 1σ in R.A. and decl. directions, respectively. We detected 208,020 sources for the J band and 203,832 sources for the H band. This NIR data is being used for studies including the analysis of the physical properties of infrared sources such as stellar mass and photometric redshifts, and will be a valuable data set for various future missions

[en] We present the detection of day-timescale periodic variability in the r-band lightcurve of newly outbursting FU Orionis-type object HBC 722, taken from >42 nights of observation with the CQUEAN instrument on the McDonald Observatory 2.1 m telescope. The optical/near-IR lightcurve of HBC 722 shows a complex array of periodic variability, clustering around 5.8-day (0.044 mag amplitude) and 1.28-day (0.016 mag amplitude) periods, after removal of overall baseline variation. We attribute the unusual number of comparable strength signals to a phenomenon related to the temporary increase in accretion rate associated with FUors. We consider semi-random 'flickering', magnetic braking/field compression and rotational asymmetries in the disk instability region as potential sources of variability. Assuming that the 5.8-day period is due to stellar rotation and the 1.28-day period is indicative of Keplerian rotation at the inner radius of the accretion disk (at 2 R _*), we derive a B-field strength of 2.2-2.7 kG, slightly larger than typical T Tauri stars. If instead the 5.8-day signal is from a disk asymmetry, the instability region has an outer radius of 5.4 R _*, consistent with models of FUor disks. Further exploration of the time domain in this complicated source and related objects will be key to understanding accretion processes.

[en] We present the source catalog and the properties of the B-, R-, and I-band images obtained to support the AKARI North Ecliptic Pole Wide (NEP-Wide) survey. The NEP-Wide is an AKARI infrared imaging survey of the north ecliptic pole covering a 5.8 deg² area over 2.5-6 μm wavelengths. The optical imaging data were obtained at the Maidanak Observatory in Uzbekistan using the Seoul National University 4k x 4k Camera on the 1.5 m telescope. These images cover 4.9 deg² where no deep optical imaging data are available. Our B-, R-, and I-band data reach the depths of ∼23.4, ∼23.1, and ∼22.3 mag (AB) at 5σ, respectively. The source catalog contains 96,460 objects in the R band, and the astrometric accuracy is about 0.''15 at 1σ in each R.A. and decl. direction. These photometric data will be useful for many studies including identification of optical counterparts of the infrared sources detected by AKARI, analysis of their spectral energy distributions from optical through infrared, and the selection of interesting objects to understand the obscured galaxy evolution.

[en] We study the dependence of angular two-point correlation functions on stellar mass (M_*) and specific star formation rate (sSFR) of $M_{\ast <!--\; ???\; -->}><!--\; >\; -->{10}^{10}{M}_{\odot <!--\; ???\; -->}$ galaxies at $z\sim <!--\; ???\; -->1$. The data from the UK Infrared Telescope Infrared Deep Sky Survey Deep eXtragalactic Survey and Canada–France–Hawaii Telescope Legacy Survey cover 8.2 deg² sample scales larger than 100 $h^{-<!--\; ???\; -->1}\mathrm{M}\mathrm{p}\mathrm{c}$ at $z\sim <!--\; ???\; -->1$, allowing us to investigate the correlation between clustering, M_*, and star formation through halo modeling. Based on halo occupation distributions (HODs) of M_* threshold samples, we derive HODs for M_* binned galaxies, and then calculate the $M_{\ast <!--\; ???\; -->}/M_{\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}}$ ratio. The ratio for central galaxies shows a peak at $M_{\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}}\sim <!--\; ???\; -->{10}^{12}{h}^{-<!--\; ???\; -->1}{M}_{\odot <!--\; ???\; -->}$, and satellites predominantly contribute to the total stellar mass in cluster environments with $M_{\ast <!--\; ???\; -->}/M_{\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}}$ values of 0.01–0.02. Using star-forming galaxies split by sSFR, we find that main sequence galaxies ($\mathrm{l}\mathrm{o}\mathrm{g}\mathrm{s}\mathrm{S}\mathrm{F}\mathrm{R}/{\mathrm{y}\mathrm{r}}^{-<!--\; ???\; -->1}\sim <!--\; ???\; -->-<!--\; ???\; -->9$) are mainly central galaxies in $\sim <!--\; ???\; -->{10}^{12.5}{h}^{-<!--\; ???\; -->1}{M}_{\odot <!--\; ???\; -->}$ halos with the lowest clustering amplitude, while lower sSFR galaxies consist of a mixture of both central and satellite galaxies where those with the lowest M_* are predominantly satellites influenced by their environment. Considering the lowest $M_{\mathrm{h}\mathrm{a}\mathrm{l}\mathrm{o}}$ samples in each M_* bin, massive central galaxies reside in more massive halos with lower sSFRs than low mass ones, indicating star-forming central galaxies evolve from a low M_*–high sSFR to a high M_*–low sSFR regime. We also find that the most rapidly star-forming galaxies ($\mathrm{l}\mathrm{o}\mathrm{g}\mathrm{s}\mathrm{S}\mathrm{F}\mathrm{R}/{\mathrm{y}\mathrm{r}}^{-<!--\; ???\; -->1}><!--\; >\; -->-<!--\; ???\; -->8.5$) are in more massive halos than main sequence ones, possibly implying galaxy mergers in dense environments are driving the active star formation. These results support the conclusion that the majority of star-forming galaxies follow secular evolution through the sustained but decreasing formation of stars.

[en] We carried out photometric observations for HBC 722 in the Sloan Digital Sky Survey r, i, and z bands from 2011 April to 2013 May with the Camera for QUasars in EArly uNiverse attached to the 2.1 m Otto Struve telescope at McDonald Observatory. The post-outburst phenomena were classified into five phases according to not only brightness but also color variations, which might be caused by physical changes in the emitting regions of optical and near-infrared bands. A series of spectral energy distributions (SEDs) is presented to support color variations and track the time evolution of the SED in optical/near-infrared bands after the outburst. Given two years of data, possible periodicities of r, i, and z bands were checked. We found three families of signals around ∼6, ∼10, and ∼1 days in three bands, which is broadly consistent with Green et al. We also examined short-term variability (intra-day and day scales) to search for evidences of flickering by using the micro-variability method. We found clear signs of day scale variability and weak indications of intra-day scale fluctuations, which implies that the flickering event occurs in HBC 722 after outburst.

[en] We present the variability and time-lag measurements of PG 0934+013 based on a photometric and spectroscopic monitoring campaign over a two year period. We obtained 46 epochs of data from the spectroscopic campaign, which was carried out using the Southern African Large Telescope with ∼1 week cadence over two sets of four month-long observing period, while we obtained 80 epochs of B-band imaging data using a few 1 m class telescopes. Due to the seven month gap between the two observing periods, we separately measured the time lags of broad emission lines, including Hβ, by comparing the emission line light curve with the B-band continuum light curve using the cross-correlation function techniques. We determined the Hβ lag, ${\mathrm{\tau <!--\; ??\; -->}}_{\mathrm{c}\mathrm{e}\mathrm{n}\mathrm{t}}={8.46}_{-<!--\; ???\; -->2.14}^{+2.08}$ days in the observed frame based on Year 2 data, while the time lag from Year 1 data was not reliably determined. Using the rms spectrum of Year 2 data, we measured the Hβ line dispersion ${\mathrm{\sigma <!--\; ??\; -->}}_{\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}$ = 668 ± 44 km s⁻¹ after correcting for the spectral resolution. Adopting a virial factor f = 4.47 from Woo et al. (2015), we determined the black hole mass M _BH $={3.13}_{-<!--\; ???\; -->0.93}^{+0.91}\times <!--\; ??\; -->{10}^6$ M _⊙, based on the Hβ time lag and velocity.

[en] Activity at the centers of galaxies, during which the central supermassive black hole is accreting material, is nowadays accepted to be rather ubiquitous and most probably a phase of every galaxy's evolution. It has been suggested that galactic mergers and interactions may be the culprits behind the triggering of nuclear activity. We use near-infrared data from the new Infrared Medium-Deep Survey and the Deep eXtragalactic Survey of the VIMOS-SA22 field and radio data at 1.4 GHz from the FIRST survey and a deep Very Large Array survey to study the environments of radio active galactic nuclei (AGNs) over an area of ∼25 deg² and down to a radio flux limit of 0.1 mJy and a J-band magnitude of 23 mag AB. Radio AGNs are predominantly found in environments similar to those of control galaxies at similar redshift, J-band magnitude, and (M_u – M_r ) rest-frame color. However, a subpopulation of radio AGNs is found in environments up to 100 times denser than their control sources. We thus preclude merging as the dominant triggering mechanism of radio AGNs. By fitting the broadband spectral energy distribution of radio AGNs in the least and most dense environments, we find that those in the least dense environments show higher radio-loudness, higher star formation efficiencies, and higher accretion rates, typical of the so-called high-excitation radio AGNs. These differences tend to disappear at z > 1. We interpret our results in terms of a different triggering mechanism for these sources that is driven by mass loss through winds of young stars created during the observed ongoing star formation.

[en] We present spectra of 1796 sources selected in the AKARI North Ecliptic Pole Wide Survey field, obtained with MMT/Hectospec and WIYN/Hydra, for which we measure 1645 redshifts. We complemented the generic flux-limited spectroscopic surveys at 11 μm and 15 μm, with additional sources selected based on the MIR and optical colors. In MMT/Hectospec observations, the redshift identification rates are ∼80% for objects with R < 21.5 mag. On the other hand, in WIYN/Hydra observations, the redshift identification rates are ∼80% at R magnitudes brighter than 19 mag. The observed spectra were classified through the visual inspection or from the line diagnostics. We identified 1128 star-forming or absorption-line-dominated galaxies, 198 Type-1 active galactic nuclei (AGNs), 8 Type-2 AGNs, 121 Galactic stars, and 190 spectra in unknown category due to low signal-to-noise ratio. The spectra were flux-calibrated but to an accuracy of 0.1-0.18 dex for most of the targets and worse for the remainder. We derive star formation rates (SFRs) from the mid-infrared fluxes or from the optical emission lines, showing that our sample spans an SFR range of 0.1 to a few hundred M_☉ yr^–1. We find that the extinction inferred from the difference between the IR and optical SFR increases as the IR luminosity increases but with a large scatter

[en] The ΛCDM cosmological model successfully reproduces many aspects of the galaxy and structure formation of the universe. However, the growth of large-scale structures (LSSs) in the early universe is not well tested yet with observational data. Here, we have utilized wide and deep optical–near-infrared data in order to search for distant galaxy clusters and superclusters (0.8 < z < 1.2). From the spectroscopic observation with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope, three massive clusters at z ∼ 0.91 are confirmed in the SSA22 field. Interestingly, all of them have similar redshifts within Δ z ∼ 0.01 with velocity dispersions ranging from 470 to 1300 km s"−"1. Moreover, as the maximum separation is ∼15 Mpc, they compose a supercluster at z ∼ 0.91, meaning that this is one of the most massive superclusters at this redshift to date. The galaxy density map implies that the confirmed clusters are embedded in a larger structure stretching over ∼100 Mpc. ΛCDM models predict about one supercluster like this in our surveyed volume, consistent with our finding so far. However, there are more supercluster candidates in this field, suggesting that additional studies are required to determine if the ΛCDM cosmological model can successfully reproduce the LSSs at high redshift

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