Eugene Kang

Seoul National University Bright Quasar Survey in Optical (SNUQSO). I. First Phase Observations and Results

We present results from the first phase of the Seoul National University Bright Quasar Survey in Optical (SNUQSO) as well as its basic observational setup. Previous and current large-area surveys have been successful in identifying many quasars, but they could have missed bright quasars due to their survey design. In order to help complete the census of bright quasars, we have performed spectroscopic observations of new bright quasar candidates selected from various methods based on optical colors, near-infrared colors, radio, and X-ray data. In 2005/2006, we observed 55 bright quasar candidates using the Bohyunsan Optical Echelle Spectrograph (BOES) on the 1.8 m telescope at the Bohyunsan Optical Astronomy Observatory in Korea. We identify 14 quasars/Seyferts from our observation, including an optically bright quasar with i = 14.98 mag at z = 0.092 (SDSS J003236.59–091026.2). Non-quasar/Seyfert objects are found to be mostly stars, among which there are five M-type stars and one cataclysmic variable. Our result shows that there still exist bright quasars to be discovered. However, at the same time, we conclude that finding new bright quasars in high Galactic latitude regions is very challenging and that the existing compilation of optically bright quasars is nearly complete in the northern hemisphere.

OVERDENSITIES OF GALAXIES AT z ∼ 3.7 IN CHANDRA DEEP FIELD-SOUTH

We report the discovery of possible overdensities of galaxies at z ~ 3.7 in Chandra Deep Field-South (CDF-S). These overdensities are identified from a photometric redshift-selected sample and a BVz-selected sample. One overdensity is identified in the proximity of two active galactic nuclei and Lyman break galaxies at z = 3.66 and z = 3.70 at 7σ significance level. The other overdensity is less significant. It is identified around six z spec 3.6 galaxies at 3σ significance level. The line-of-sight velocity dispersions of these overdensities are found to be σ v 500-800 km s–1, comparable to the velocity dispersions of clusters of galaxies today. Through spectral energy distribution fitting, we find ~15 massive galaxies with M 1011 M ☉ around the z 3.7 overdensity. The mass of the z 3.7 overdensity is found to be a few ×1014 M ☉. Our result suggests that high-redshift overdense regions can be found in a supposedly blank field, and that the emergence of massive structures can be traced back to redshifts as high as z ~ 3.7.We report the discovery of possible overdensities of galaxies at z ~ 3.7 in the Chandra Deep Field South (CDF-S). These overdensities are identified from the photometric redshift selected sample, and the BVz-selected sample. One over-density is identified in the proximity of 2 AGNs and LBGs at z=3.66 and z=3.70 at 7-sigma significance level. The other over-density is less significant. It is identified around six z_{spec} ~ 3.6 galaxies at 3-sigma significance level. The line of sight velocity dispersions of these overdensities are found to be sigma_{v} ~ 500-800 km/sec, comparable to the velocity dispersions of clusters of galaxies today. Through the spectral energy distribution (SED) fitting, we find ~15 massive galaxies with M > 10^{11}M_sun around the z ~ 3.7 overdensity. The mass of the z ~ 3.7 overdensity is found to be a few times 10^{14}M_sun. Our result suggests that high redshift over-dense regions can be found in a supposedly blank field, and that the emergence of massive structures can be traced back to redshift as high as z ~ 3.7.

MASSIVE STRUCTURES OF GALAXIES AT HIGH REDSHIFTS IN THE GREAT OBSERVATORIES ORIGINS DEEP SURVEY FIELDS

If the Universe is dominated by cold dark matter and dark energy as in the currently popular ΛCDM cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass M ? 10 14 M ⊙ appearing at around 6 Gyrs after the Big Bang (z ∼ 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few times 10 13 M ⊙ at redshifts between z = 0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited samples of galaxies using a combination of spectroscopic and photometric redshifts. We analyze the Millennium simulation data in a similar way to the analysis of the observational data in order to test the _CDM cosmology. We find that there are too many massive structures (M > 7×1013M ⊙ ) observed at z > 2 in comparison with the simulation predictions by a factor of a few, giving a probability of < 1/2500 of the observed data being consistent with the simulation. Our result suggests that massive structures have emerged early, but the reason for the discrepancy with the simulation is unclear. It could be due to the limitation of the simulation such as the lack of key, unrecognized ingredients (strong non-Gaussianity or other baryonic physics), or simply a difficulty in the halo mass estimation from observation, or a fundamental problem of the ΛCDM cosmology. On the other hand, the over-abundance of massive structures at high redshifts does not favor heavy neutrino mass of ∼ 0.3 eV or larger, as heavy neutrinos make the discrepancy between the observation and the simulation more pronounced by a factor of 3 or more.

OVERDENSITIES OF GALAXIES ATz∼ 3.7 INCHANDRADEEP FIELD-SOUTH

We report the discovery of possible overdensities of galaxies at z ~ 3.7 in Chandra Deep Field-South (CDF-S). These overdensities are identified from a photometric redshift-selected sample and a BVz-selected sample. One overdensity is identified in the proximity of two active galactic nuclei and Lyman break galaxies at z = 3.66 and z = 3.70 at 7σ significance level. The other overdensity is less significant. It is identified around six z spec 3.6 galaxies at 3σ significance level. The line-of-sight velocity dispersions of these overdensities are found to be σ v 500-800 km s–1, comparable to the velocity dispersions of clusters of galaxies today. Through spectral energy distribution fitting, we find ~15 massive galaxies with M 1011 M ☉ around the z 3.7 overdensity. The mass of the z 3.7 overdensity is found to be a few ×1014 M ☉. Our result suggests that high-redshift overdense regions can be found in a supposedly blank field, and that the emergence of massive structures can be traced back to redshifts as high as z ~ 3.7.We report the discovery of possible overdensities of galaxies at z ~ 3.7 in the Chandra Deep Field South (CDF-S). These overdensities are identified from the photometric redshift selected sample, and the BVz-selected sample. One over-density is identified in the proximity of 2 AGNs and LBGs at z=3.66 and z=3.70 at 7-sigma significance level. The other over-density is less significant. It is identified around six z_{spec} ~ 3.6 galaxies at 3-sigma significance level. The line of sight velocity dispersions of these overdensities are found to be sigma_{v} ~ 500-800 km/sec, comparable to the velocity dispersions of clusters of galaxies today. Through the spectral energy distribution (SED) fitting, we find ~15 massive galaxies with M > 10^{11}M_sun around the z ~ 3.7 overdensity. The mass of the z ~ 3.7 overdensity is found to be a few times 10^{14}M_sun. Our result suggests that high redshift over-dense regions can be found in a supposedly blank field, and that the emergence of massive structures can be traced back to redshift as high as z ~ 3.7.

Overdensities of galaxies at z ~ 3.7 in CDF-S

We report the discovery of possible overdensities of galaxies at z ~ 3.7 in Chandra Deep Field-South (CDF-S). These overdensities are identified from a photometric redshift-selected sample and a BVz-selected sample. One overdensity is identified in the proximity of two active galactic nuclei and Lyman break galaxies at z = 3.66 and z = 3.70 at 7σ significance level. The other overdensity is less significant. It is identified around six z spec 3.6 galaxies at 3σ significance level. The line-of-sight velocity dispersions of these overdensities are found to be σ v 500-800 km s–1, comparable to the velocity dispersions of clusters of galaxies today. Through spectral energy distribution fitting, we find ~15 massive galaxies with M 1011 M ☉ around the z 3.7 overdensity. The mass of the z 3.7 overdensity is found to be a few ×1014 M ☉. Our result suggests that high-redshift overdense regions can be found in a supposedly blank field, and that the emergence of massive structures can be traced back to redshifts as high as z ~ 3.7.We report the discovery of possible overdensities of galaxies at z ~ 3.7 in the Chandra Deep Field South (CDF-S). These overdensities are identified from the photometric redshift selected sample, and the BVz-selected sample. One over-density is identified in the proximity of 2 AGNs and LBGs at z=3.66 and z=3.70 at 7-sigma significance level. The other over-density is less significant. It is identified around six z_{spec} ~ 3.6 galaxies at 3-sigma significance level. The line of sight velocity dispersions of these overdensities are found to be sigma_{v} ~ 500-800 km/sec, comparable to the velocity dispersions of clusters of galaxies today. Through the spectral energy distribution (SED) fitting, we find ~15 massive galaxies with M > 10^{11}M_sun around the z ~ 3.7 overdensity. The mass of the z ~ 3.7 overdensity is found to be a few times 10^{14}M_sun. Our result suggests that high redshift over-dense regions can be found in a supposedly blank field, and that the emergence of massive structures can be traced back to redshift as high as z ~ 3.7.