Distance and properties of NGC 4993 as the host galaxy of a gravitational wave source, GW170817

Recently, the optical counterpart of a gravitational wave source GW170817 has been identified in NGC 4993 galaxy. Together with evidence from observations in electromagnetic waves, the event has been suggested as a result of a merger of two neutron stars. We analyze the multi-wavelength data to characterize the host galaxy property and its distance to examine if the properties of NGC 4993 are consistent with this picture. Our analysis shows that NGC 4993 is a bulge-dominated galaxy with reff ~ 2-3 kpc and the Sersic index of n = 3-4 for the bulge component. The spectral energy distribution from 0.15 to 24 micron indicates that this galaxy has no significant ongoing star formation, the mean stellar mass of (0.3 - 1.2) times 10^11 Msun,the mean stellar age greater than ~3 Gyr, and the metallicity of about 20% to 100% of solar abundance. Optical images reveal dust lanes and extended features that suggest a past merging activity. Overall, NGC 4993 has characteristics of normal, but slightly disturbed elliptical galaxies. Furthermore, we derive the distance to NGC 4993 with the fundamental plane relation using 17 parameter sets of 7 different filters and the central stellar velocity dispersion from literature, finding an angular diameter distance of 37.7 +- 8.7 Mpc. NGC 4993 is similar to some host galaxies of short gamma-ray bursts but much different from those of long gamma-ray bursts, supporting the picture of GW170817 as a result of a merger of two NSs.

Seoul National University Camera II (SNUCAM-II): The New SED Camera for the Lee Sang Gak Telescope (LSGT)

We present the characteristics and the performance of the new CCD camera system, SNUCAM-II (Seoul National University CAMera system II) that was installed on the Lee Sang Gak Telescope (LSGT) at the Siding Spring Observatory in 2016. SNUCAM-II consists of a deep depletion chip covering a wide wavelength from 0.3 {mu}m to 1.1 {mu}m with high sensitivity (QE at > 80% over 0.4 to 0.9 {mu}m). It is equipped with the SDSS ugriz filters and 13 medium band width (50 nm) filters, enabling us to study spectral energy distributions (SEDs) of diverse objects from extragalactic sources to solar system objects. On LSGT, SNUCAM-II offers 15.7 {times} 15.7 arcmin field-of-view (FOV) at a pixel scale of 0.92 arcsec and a limiting magnitude of g = 19.91 AB mag and z=18.20 AB mag at 5{sigma} with 180 sec exposure time for point source detection.

The Infrared Medium-Deep Survey. V. A New Selection Strategy for Quasars at z > 5 based on Medium-Band Observation with SQUEAN

Multiple color selection techniques have been successful in identifying quasars from wide-field broad-band imaging survey data. Among the quasars that have been discovered so far, however, there is a redshift gap at $5 lesssim {rm z} lesssim 5.7$ due to the limitations of filter sets in previous studies. In this work, we present a new selection technique of high redshift quasars using a sequence of medium-band filters: nine filters with central wavelengths from 625 to 1025 nm and bandwidths of 50 nm. Photometry with these medium-bands traces the spectral energy distribution (SED) of a source, similar to spectroscopy with resolution R $sim$ 15. By conducting medium-band observations of high redshift quasars at 4.7 $leq$ z $leq$ 6.0 and brown dwarfs (the main contaminants in high redshift quasar selection) using the SED camera for QUasars in EArly uNiverse (SQUEAN) on the 2.1-m telescope at the McDonald Observatory, we show that these medium-band filters are superior to multi-color broad-band color section in separating high redshift quasars from brown dwarfs. In addition, we show that redshifts of high redshift quasars can be determined to an accuracy of $Delta{rm z}/(1+{rm z}) = 0.002$ -- $0.026$. The selection technique can be extended to z $sim$ 7, suggesting that the medium-band observation can be powerful in identifying quasars even at the re-ionization epoch.

Linking galaxies to dark matter haloes at $zsim1$ : dependence of galaxy clustering on stellar mass and specific star formation rate

We study the dependence of angular two-point correlation functions on stellar mass ($M_{*}$) and specific star formation rate (sSFR) of $M_{*}>10^{10}M_{odot}$ galaxies at $zsim1$. The data from UKIDSS DXS and CFHTLS covering 8.2 deg$^{2}$ sample scales larger than 100 $h^{-1}$Mpc at $zsim1$, 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 $M_{*}/M_{rm halo}$ ratio. The ratio for central galaxies shows a peak at $M_{rm halo}sim10^{12}h^{-1}M_{odot}$, and satellites predominantly contribute to the total stellar mass in cluster environments with $M_{*}/M_{rm halo}$ values of 0.01--0.02. Using star-forming galaxies split by sSFR, we find that main sequence galaxies ($rm log,sSFR/yr^{-1}sim-9$) are mainly central galaxies in $sim10^{12.5} h^{-1}M_{odot}$ haloes 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 $M_{rm halo}$ samples in each $M_{*}$ bin, massive central galaxies reside in more massive haloes 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 ($rm log,sSFR/yr^{-1}>-8.5$) are in more massive haloes 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.

J and H-band Imaging of AKARI North Ecliptic Pole Survey Field

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 (FLAMINGOS) on the Kitt Peak National Observatory 2.1m telescope covering a 5.1 deg2 area down to a 5 sigma depth of ~21.6 mag and ~21.3 mag (AB) for J and H-band with an astrometric accuracy of 0.14 and 0.17 for 1 sigma in R.A. and Decl. directions, respectively. We detected 208,020 sources for J-band and 203,832 sources for H-band. This NIR data is being used for studies including analysis of the physical properties of infrared sources such as stellar mass and photometric redshifts, and will be a valuable dataset for various future missions.

Swifts GRB GRB071010B : outlier of the $rm E^{src}_{peak} - E_{gamma}$ and ${rm E_{iso}-E^{src}_{peak}-t^{src}_{jet}}$ correlations

We present multi-band results for GRB071010B based on Swift, Suzaku, and ground-based optical observations. This burst is an ideal target to evaluate the robustness of the ${rm E^{src}_{peak}-E_{iso}}$ and ${rm E^{src}_{peak}-E_{gamma}}$ relations, whose studies have been in stagnation due to the lack of the combined estimation of $rm E^{src}_{peak}$ and long term optical monitoring. The joint prompt spectral fitting using Swift/Burst Alert Telescope and Suzaku/Wide-band All sky Monitor data yielded the spectral peak energy as E$^{src}_{peak}$ of $86.5^{+6.4}_{-6.3}$ keV and E$_{iso}$ of $2.25^{+0.19}_{-0.16}times10^{52}$ erg with $z=0.947$. The optical afterglow light curve is well fitted by a simple power law with temporal index $alpha=-0.60pm0.02$. The lower limit of temporal break in the optical light curve is 9.8 days. Our multi-wavelength analysis reveals that GRB071010B follows ${rm E^{src}_{peak}-E_{iso}}$ but violates the ${rm E^{src}_{peak}-E_{gamma}}$ and ${rm E_{iso}-E^{src}_{peak}-t^{src}_{jet}}$ at more than the 3$sigma$ level.

Optical-Near Infrared Color Gradients of Elliptical Galaxies and Their Environmental Dependence

We have studied the environmental effect on optical-NIR color gradients of 273 nearby elliptical galaxies. Color gradient is a good tool to study the evolutionary history of elliptical galaxies, since the steepness of the color gradient reflects merging history of early types. When an elliptical galaxy goes through many merging events, the color gradient can be get less steep or reversed due to mixing of stars. One simple way to measure color gradient is to compare half-light radii in different bands. We have compared the optical and near infrared half-light radii of 273 early-type galaxies from Pahre(1999). Not surprisingly, we find that r$_{e}$(V)s (half-light radii measured in V-band) are in general larger than r$_{e}$(K)s (half-light radii measured in K-band). However, when divided into different environments, we find that elliptical galaxies in the denser environment have gentler color gradients than those in the less dense environment. Our finding suggests that elliptical galaxies in the dense environment have undergone many merging events and the mixing of stars through the merging have created the gentle color gradients.

A Measurement of the Cosmological Constant Using Elliptical Galaxies as Strong Gravitational Lenses

We have identified seven (field) elliptical galaxies acting as strong gravitational lenses and have used them to measure cosmological parameters. To find the most likely value for Omega_m (= Omega_matter) and Lambda, we have used the combined probabilities of these lens systems having the observed critical radii (or image deflection) for the measured or estimated values of lens redshifts, source redshifts, and lens magnitudes. Our measurement gives Lambda=0.64 (+0.15 -0.26) if Omega_m + Lambda = 1, and the Omega_m = 1 model is excluded at the 97 % confidence level. We also find, at the 68 % (Omega = 0) -- 82 % (Omega = 0.3) confidence level, that an open universe is less likely than a flat universe with non-zero Lambda. Except for the possibility of strong perturbations due to cluster potentials and the systematic overestimate of the lens magnitudes, other possible systematic errors do not seem to influence our results strongly: correction of possible systematic errors seems to increase the significance of the result in favor of a non-zero Lambda model.