arXiv subjects

Changbom Park

Publications and source records attributed to Changbom Park.

At least 199 records · Page 11Linked to original sources

arXiv2007

The Connection between Star-Forming Galaxies, AGN Host Galaxies and Early-Type Galaxies in the SDSS

We present a study of the connection between star-forming galaxies, AGN host galaxies, and normal early-type galaxies in the Sloan Digital Sky Survey (SDSS). Using the SDSS DR5 and DR4plus data, we select our early-type galaxy sample in the color versus color-gradient space, and we classify the spectral types of the selected early-type galaxies into normal, star-forming, Seyfert, and LINER classes, using several spectral line flux ratios. We investigate the slope in the fundamental space for each class of early-type galaxies and find that there are obvious differences in the slopes of the fundamental planes (FPs) among the different classes of early-type galaxies, in the sense that the slopes for Seyferts and star-forming galaxies are flatter than those for normal galaxies and LINERs. This may be the first identification of the systematic variation of the FP slope among the subclasses of early-type galaxies. The difference in the FP slope might be caused by the difference in the degree of nonhomology among different classes or by the difference of gas contents in their merging progenitors. One possible scenario is that the AGN host galaxies and star-forming galaxies are formed by gas-rich merging and that they may evolve into normal early-type galaxies after finishing their star formation or AGN activities.

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arXiv2007

Environmental Dependence of Properties of Galaxies in the Sloan Digital Sky Survey

We investigate the dependence of physical properties of galaxies brighter than M_r=-18.0 in the SDSS on environment, as measured by local density using an adaptive smoothing kernel. We find that variations of galaxy properties with environment are almost entirely due to the dependence of morphology and luminosity on environment. Because galaxy properties depend not only on luminosity but also on morphology, it is clear that galaxy properties cannot be determined solely by dark halo mass. When morphology and luminosity are fixed, other physical properties, such as color, color-gradient, concentration, size, velocity dispersion, and star formation rate, are nearly independent of local density. The only feature is the sharp decrease of late type fraction above the critical luminosity of about M_r=-21.3 in the morphology versus luminosity relation. Weak residual dependences on environment include that of the color of late-types (bluer at lower density) and of the L-sigma relation of early-types (larger dispersion at higher density for bright galaxies). The early-type fraction is a monotonically increasing function of local density and luminosity. The morphology-density- luminosity relation should be a key constraint on galaxy formation models. We demonstrate that the dependence on environment of the morphology of galaxie originates from variations in density on effective Gaussian smoothing scales much smaller than 12 h^{-1}Mpc. We find that galaxy morphology varies both with density measured on an effective Gaussian smoothing scale of 4.7 h^{-1} Mpc and on distance to the nearest bright galaxy (particularly, for about 0.2 h^{-1}Mpc). We propose a mechanism that the morphology of galaxies in galaxy systems is transformed by the tidal force.

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arXiv2007

Internal and Collective Properties of Galaxies in the Sloan Digital Sky Survey

We examine volume-limited samples from the SDSS galaxies to look for relations among internal and collective physical parameters of galaxies as faint as M_r=- 17.5, which include morphology, luminosity, color, color gradient, concentration, size, velocity dispersion, equivalent width (EW) of H_alpha line,axis ratio, the luminosity and velocity dispersion functions. At fixed morphology and luminosity, we find that bright (M_r<-20) early-types show very small dispersions in color, color gradient, concentration, size, and velocity dispersion. These dispersions increase at fainter magnitudes, where the fraction of blue early-types increases. Late-types show wider dispersions in all physical parameters compared to early types at the same luminosity. Concentration indices of early-types are well-correlated with velocity dispersion, but are insensitive to luminosity and color for bright galaxies. The slope of the Faber-Jackson relation continuously changes from 4.6 +- 0.4 to 2.7+- 0.2 when luminosity changes from M_r = -22 to -20. The size of early- types is well-correlated with stellar velocity dispersion (for >100 km/s). We find that passive spirals are well-separated from star-forming late-types at EW (H_alpha) of about 4. An interesting finding is that many physical parameters of galaxies manifest different behaviors across the absolute magnitude of about M_* +- 1. The morphology fraction as a function of luminosity depends less sensitively on large scale structure than the luminosity function (LF) does, and thus seems to be more universal. The effects of internal extinction in late-types on the completeness of volume limited samples and on the LF and morphology fraction are found to be very important. (abridged)

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arXiv2006

Empirical distributions of galactic $λ$ spin parameters from the SDSS

Using simple dimensional arguments for both spiral and elliptical galaxies, we present formulas to derive an estimate of the halo spin parameter $λ$ for any real galaxy, in terms of common observational parameters. This allows a rough estimate of $λ$, which we apply to a large volume limited sample of galaxies taken from the SDSS data base. The large numbers involved (11,597) allow the derivation of reliable $λ$ distributions, as signal adds up significantly in spite of the errors in the inferences for particular galaxies. We find that if the observed distribution of $λ$ is modeled with a log-normal function, as often done for this distribution in dark matter halos that appear in cosmological simulations, we obtain parameters $λ_{0}=0.04 \pm 0.005$ and $σ_λ=0.51 \pm 0.05$, interestingly consistent with values derived from simulations. For spirals, we find a good correlation between empirical values of $λ$ and visually assigned Hubble types, highlighting the potential of this physical parameter as an objective classification tool.

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arXiv2006

Topology of structure in the Sloan Digital Sky Survey: model testing

We measure the three-dimensional topology of large-scale structure in the Sloan Digital Sky Survey (SDSS). This allows the genus statistic to be measured with unprecedented statistical accuracy. The sample size is now sufficiently large to allow the topology to be an important tool for testing galaxy formation models. For comparison, we make mock SDSS samples using several state-of-the-art N-body simulations: the Millennium run of Springel et al. (2005)(10 billion particles), Kim & Park (2006) CDM models (1.1 billion particles), and Cen & Ostriker (2006) hydrodynamic code models (8.6 billion cell hydro mesh). Each of these simulations uses a different method for modeling galaxy formation. The SDSS data show a genus curve that is broadly characteristic of that produced by Gaussian random phase initial conditions. Thus the data strongly support the standard model of inflation where Gaussian random phase initial conditions are produced by random quantum fluctuations in the early universe. But on top of this general shape there are measurable differences produced by non-linear gravitational effects (cf. Matsubara 1994), and biasing connected with galaxy formation. The N-body simulations have been tuned to reproduce the power spectrum and multiplicity function but not topology, so topology is an acid test for these models. The data show a ``meatball'' shift (only partly due to the Sloan Great Wall of Galaxies; this shift also appears in a sub-sample not containing the Wall) which differs at the 2.5σlevel from the results of the Millennium run and the Kim & Park dark halo models, even including the effects of cosmic variance.

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arXiv2006

Genus Topology of the Cosmic Microwave Background from the WMAP 3-Year Data

We have independently measured the genus topology of the temperature fluctuations in the cosmic microwave background seen in the Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data. A genus analysis of the WMAP data indicates consistency with Gaussian random-phase initial conditions, as predicted by standard inflation. We set 95% confidence limits on non-linearities of -101 < f_{nl} < 107. We also find that the observed low l (l <= 8) modes show a slight anti-correlation with the Galactic foreground, but not exceeding 95% confidence, and that the topology defined by these modes is consistent with that of a Gaussian random-phase distribution (within 95% confidence).

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arXiv2006

Cleaned Three-Year WMAP CMB Map: Magnitude of the Quadrupole and Alignment of Large Scale Modes

[Abridged] We have produced a cleaned map of the Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data using an improved foreground subtraction technique. We perform an internal linear combination (ILC) to subtract the Galactic foreground emission from the temperature fluctuations observed by the WMAP. We divide the whole sky into hundreds of pixel groups with similar foreground spectral indices over a range of WMAP frequencies, apply the ILC for each group, and obtain a CMB map with foreground emission effectively reduced. With the resulting foreground-reduced ILC map, we have investigated the known anomalies in CMB maps at large scales. The quadrupole and the octopole powers measured from our ILC map are δT_2^2 = 276_{-126}^{+94} uK^2 and δT_3^2 = 952_{-83}^{+64} uK^2, respectively. The measured quadrupole power is lower than the value expected in the concordance LCDM model (1250 uK^2), in which the probability of finding a quadrupole power lower than the measured value is 5.7%. We have confirmed that the quadrupole and the octopole are strongly aligned with angle θ_{23} = 11.8_{-8.0}^{+6.4} degree, and are planar with high planarity parameters t=0.98_{-0.02}^{+0.02} for l=2 and t=0.91_{-0.03}^{+0.02} for l=3. The observed angular separation θ_{23} is marginally statistically significant because the probability of finding the angular separation as low as the observed value is 4.3%. However, the observed planarity is not statistically significant. The probability of observing such a planarity as high as the measured t values is over 18%. The ILC simulations show that the residual foreground emission in the ILC map does not affect the estimated values significantly.

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arXiv2005

Morphology Segregation of Galaxies in the Color-Color Gradient Space

We have found the u -r color versus g -i color gradient space can be used for highly successful morphology classification of galaxies in the Sloan Digital Sky Survey. In this space galaxies form early and late type branches well-separated from each other. The location of galaxies along the branches reflects the degree and locality of star formation activity, and monotonically corresponds to the sequence of morphological subclasses. When the concentration index is used together, the completeness and reliability of classification reaches about 91% for a training set of SDSS galaxies brighter than r~15.9. At faintest magnitudes (r~17.5) of the SDSS spectroscopic sample, the performance still remains at about 88%. The new classification scheme will help us find accurate relations of galaxy morphology with spatial and temporal environments, and help one understand the origin of morphology of galaxies.

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arXiv2005

Power Spectrum of Cosmic Momentum Field Measured from the SFI Galaxy Sample

We have measured the cosmic momentum power spectrum from the peculiar velocities of galaxies in the SFI sample. The SFI catalog contains field spiral galaxies with radial peculiar velocities derived from the I-band Tully-Fisher relation. As a natural measure of the large-scale peculiar velocity field, we use the cosmic momentum field that is defined as the peculiar velocity field weighted by local number of galaxies. We have shown that the momentum power spectrum can be derived from the density power spectrum for the constant linear biasing of galaxy formation, which makes it possible to estimate β_S = Ω_m^{0.6} / b_S parameter precisely where Ω_m is the matter density parameter and b_S is the bias factor for optical spiral galaxies. At each wavenumber k we estimate β_S(k) as the ratio of the measured to the derived momentum power over a wide range of scales (0.026 h^{-1}Mpc <~ k <~ 0.157 h^{-1}Mpc) that spans the linear to the quasi-linear regimes. The estimated β_S(k)'s have stable values around 0.5, which demonstrates the constancy of β_S parameter at scales down to 40 h^{-1}Mpc. We have obtained β_S=0.49_{-0.05}^{+0.08} or Ω_m = 0.30_{-0.05}^{+0.09} b_S^{5/3}, and the amplitude of mass fluctuation as σ_8Ω_m^{0.6}=0.56_{-0.21}^{+0.27}. The 68% confidence limits include the cosmic variance. We have also estimated the mass density power spectrum. For example, at k=0.1047 h Mpc^{-1} (λ=60 h^{-1}Mpc) we measure Ω_m^{1.2} P_δ(k)=(2.51_{-0.94}^{+0.91})\times 10^3 (h^{-1}Mpc)^3, which is lower compared to the high-amplitude power spectra found from the previous maximum likelihood analyses of peculiar velocity samples like Mark III, SFI, and ENEAR.

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arXiv2005

Fourier Phase Analysis of SDSS Galaxies

We present a first analysis of the clustering of SDSS galaxies using the distribution function of the sum of Fourier phases. This statistic was recently proposed by one of authors as a new method to probe phase correlations of cosmological density fields. Since the Fourier phases are statistically independent of Fourier amplitudes, the phase statistic plays a complementary role to the conventional two-point statistics of galaxy clustering. In particular, we focus on the distribution functions of phase sum over three closed wavevectors as a function of the configurations of triangle wavevectors. We find that the observed distribution functions of phase sum are in good agreement with the lowest-order approximation from perturbation theory. For direct comparison with observations, we construct mock catalogs from N-body simulations taking account of several observational effects such as the survey geometry, the redshift distortion, and the discreteness due to the limited number of data. Indeed the observed phase correlations for the galaxies in the range of absolute magnitude -22<Mr<-18 agree well with those for Lambda CDM predictions with sigma8=0.9 evolved from Gaussian initial condition. This agreement implies that the galaxy biasing is approximately linear in redshift space. Instead, assuming that the galaxy biasing is described by a quadratic deterministic function at scale larger than 30Mpc/h, we can constrain the ratio of the quadratic biasing parameter b2 to the linear biasing parameter b1. We find that resulting b2/b1 is mainly dependent on sigma8 and that it is well fitted by b2/b1=0.54(+-0.06)-0.62(+-0.08)sigma8 in CDM models. Indeed, b2/b1 is nearly zero when sigma8=0.9.

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arXiv2005

Topology Analysis of the Sloan Digital Sky Survey: I. Scale and Luminosity Dependences

We measure the topology of volume-limited galaxy samples selected from a parent sample of 314,050 galaxies in the Sloan Digital Sky Survey(SDSS), which is now complete enough to describe the fully three-dimensional topology and its dependence on galaxy properties. We compare the observed genus statistic Gν_f) to predictions for a Gaussian random field and to the genus measured for mock surveys constructed from new large-volume simulations of the LambdaCDM cosmology. In this analysis we carefully examine the dependence of the observed genus statistic on the Gaussian smoothing scale R_G from 3.5 to 11 h^-1Mpc and on the luminosity of galaxies over the range -22.50<M_r<-18.5. The void multiplicity A_V is less than unity at all smoothing scales. Because A_V cannot become less than 1 through gravitational evolution, this result provides strong evidence for biased galaxy formation in low density environments. We also find clear evidence of luminosity bias of topology within the volume-limited sub-samples. The shift parameter Delta nu indicates that the genus of brighter galaxies shows a negative shift toward a ``meatball'' (i.e. cluster-dominated) topology, while faint galaxies show a positive shift toward a ``bubble'' (i.e. void-dominated) topology. The transition from negative to positive shift occurs approximately at the characteristic absolute magnitude M_{r*}=-20.4. Even in this analysis of the largest galaxy sample to date, we detect the influence of individual large-scale structures, as the shift parameter Delta nu and cluster multiplicity A_C reflect (at ~3 sigma) the presence of the Sloan Great Wall and a X-shaped structure which runs for several hundred Mpc across the survey volume.

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arXiv2005

Effects of Gravitational Evolution, Biasing, and Redshift Space Distortion on Topology

We have studied the dependence of topology of large scale structure on tracer, gravitational evolution, redshift space distortion, and cosmology. A series of large N-body simulations of the $Λ$CDM and SCDM models that have evolved 1.1 or 8.6 billion particles, are used in the study. Evolution of the genus statistic, used as a topology measure, from redshift 8 to 0 is accurately calculated over a wide range of smoothing scales using the simulations. The tracers of large scale structure considered are the CDM matter, biased peaks in the initial density field, dark halos, and `galaxies' populating the dark halos in accordance with a Halo Occupation Distribution (HOD) model. We have found that the effects of biasing, gravitational evolution, and initial conditions on topology of large scale structure are all comparable. The redshift space distortion effects are relatively small down to about 5 $h^{-1}$Mpc for all tracers except for the high threshold part of the genus curve. The gravitational effects are found to be well-modeled by the analytic perturbation theory when the CDM matter distribution is considered. But the direction of gravitational evolution of topology can be even reversed for different tracers. For example, the shift parameter of the genus curve evolves in opposite directions for matter and HOD `galaxies' at large scales. At small scales there are interesting deviations of the genus curve of dark halos and `galaxies' from that of matter in our initially Gaussian simulations. The deviations should be understood as due to combined effects of gravitational evolution and biasing.

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arXiv2005

Korean Nova Records in A.D. 1073 and A.D. 1074: R Aquarii

R Aqr is known to be a symbiotic binary system with an associated extended emission nebula, possibly produced by a historic outburst. To find the associated historic records, we searched for and compiled all 'Guest Star' and 'Peculiar Star' records in three Korean 'official' history books that cover almost two thousand years, Samguksagi, Goryeosa, Joseonwangjosillok. In addition to the record of A.D. 1073, previously noted by Li (1985), we have found in Goryeosa another candidate record of A.D. 1074, which has the same positional description as that of A.D. 1073 with an additional brightness description. We examined various aspects of the two records and conclude that they both are likely to be the records of outburst of R Aqr. This means that there were two successive outbursts in A.D. 1073 and in A.D. 1074, separated by approximately one year. Based on these records, we estimate the distance to R Aqr to be 273 pc if the expansion of the nebula has been at a constant rate. The brightness record of A.D. 1074 corresponds to the absolute magnitude at outburst of M_(outburst) = -6.2 mag. ~ -5.2 mag. at this distance. The two Korean records associated with R Aqr may provide astronomically meaningful constraints to the outburst model of R Aqr and the formative process of its nebulosity.

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arXiv2005

Analysis of historical meteor and meteor shower records: Korea, China, and Japan

We have compiled and analyzed historical Korean meteor and meteor shower records in three Korean official history books, Samguksagi which covers the three Kingdoms period (57 B.C -- A.D. 935), Goryeosa of Goryeo dynasty (A.D. 918 -- 1392), and Joseonwangjosillok of Joseon dynasty (A.D. 1392 -- 1910). We have found 3861 meteor and 31 meteor shower records. We have confirmed the peaks of Perseids and an excess due to the mixture of Orionids, north-Taurids, or Leonids through the Monte-Carlo test. The peaks persist from the period of Goryeo dynasty to that of Joseon dynasty, for almost one thousand years. Korean records show a decrease of Perseids activity and an increase of Orionids/north-Taurids/Leonids activity. We have also analyzed seasonal variation of sporadic meteors from Korean records. We confirm the seasonal variation of sporadic meteors from the records of Joseon dynasty with the maximum number of events being roughly 1.7 times the minimum. The Korean records are compared with Chinese and Japanese records for the same periods. Major features in Chinese meteor shower records are quite consistent with those of Korean records, particularly for the last millennium. Japanese records also show Perseids feature and Orionids/north-Taurids/Leonids feature, although they are less prominent compared to those of Korean or Chinese records.

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arXiv2004

A New Halo Finding Method for N-Body Simulations

We have developed a new halo finding method, Physically Self-Bound (PSB) group finding algorithm, which can efficiently identify halos located even at crowded regions. This method combines two physical criteria such as the tidal radius of a halo and the total energy of each particle to find member particles. Two hierarchical meshes are used to increase the speed and the power of halo identification in the parallel computing environments. First, a coarse mesh with cell size equal to the mean particle separation $l_{\rm mean}$ is used to obtain the density field over the whole simulation box. Mesh cells having density contrast higher than a local cutoff threshold $δ_{\rm LOC}$ are extracted and linked together for those adjacent to each other. This produces local-cell groups. Second, a finer mesh is used to obtain density field within each local-cell group and to identify halos. If a density shell contains only one density peak, its particles are assigned to the density peak. But in the case of a density shell surrounding at least two density peaks, we use both the tidal radii of halo candidates enclosed by the shell and the total energy criterion to find physically bound particles with respect to each halo. Similar to DENMAX and HOP, the \hfind method can efficiently identify small halos embedded in a large halo, while the FoF and the SO do not resolve such small halos. We apply our new halo finding method to a 1-Giga particle simulation of the $Λ$CDM model and compare the resulting mass function with those of previous studies. The abundance of physically self-bound halos is larger at the low mass scale and smaller at the high mass scale than proposed by the Jenkins et al. (2001) who used the FoF and SO methods. (abridged)

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arXiv2003

GOTPM: A Parallel Hybrid Particle-Mesh Treecode

We describe a parallel, cosmological N-body code based on a hybrid scheme using the particle-mesh (PM) and Barnes-Hut (BH) oct-tree algorithm. We call the algorithm GOTPM for Grid-of-Oct-Trees-Particle-Mesh. The code is parallelized using the Message Passing Interface (MPI) library and is optimized to run on Beowulf clusters as well as symmetric multi-processors. The gravitational potential is determined on a mesh using a standard PM method with particle forces determined through interpolation. The softened PM force is corrected for short range interactions using a grid of localized BH trees throughout the entire simulation volume in a completely analogous way to P$^3$M methods. This method makes no assumptions about the local density for short range force corrections and so is consistent with the results of the P$^3$M method in the limit that the treecode opening angle parameter, $θ\to 0$. (abridged)

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arXiv2003

Observational Strategies of CMB Temperature and Polarization Interferometry Experiments

We have simulated the interferometric observation of the Cosmic Microwave Background (CMB) temperature and polarization fluctuations. We have constructed data pipelines from the time-ordered raw visibility samples to the CMB power spectra which utilize the methods of data compression, maximum likelihood analysis, and optimal subspace filtering. They are customized for three observational strategies, such as the single pointing, the mosaicking, and the drift-scanning. For each strategy, derived are the optimal strategy parameters that yield band power estimates with minimum uncertainty. The results are general and can be applied to any close-packed array on a single platform such as the CBI and the forthcoming AMiBA experiments. We have also studied the effect of rotation of the array platform on the band power correlation by simulating the CBI single pointing observation. It is found that the band power anti-correlations can be reduced by rotating the platform and thus densely sampling the visibility plane. This enables us to increase the resolution of the power spectrum in the l-space down to the limit of the sampling theorem (Delta l = 226 = pi / theta), which is narrower by a factor of about sqrt{2} than the resolution limit (Delta l = 300) used in the recent CBI single pointing observation. The validity of this idea is demonstrated for a two-element interferometer that samples visibilities uniformly in the uv-annulus. From the fact that the visibilities are the Fourier modes of the CMB field convolved with the beam, a fast unbiased estimator (FUE) of the CMB power spectra is developed and tested. It is shown that the FUE gives results very close to those from the quadratic estimator method without requiring large computer resources even though uncertainties in the results increase.

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arXiv2002

Correlation Functions of the Abell, APM, and X-ray Clusters of Galaxies

We have measured the correlation functions of the optically selected clusters of galaxies in the Abell and the APM catalogs, and of the X-ray clusters in the X-ray-Brightest Abell-type Clusters of galaxies (XBACs) catalog and the Brightest Clusters Sample (BCS). The same analysis method and the same method of characterizing the resulting correlation functions are applied to all observational samples. We have found that the amplitude of the correlation function of the APM clusters is much higher than what has been previously claimed, in particular for richer subsamples. The correlation length of the APM clusters with the richness R >= 70 (as defined by the APM team) is found to be r_0 = 25.4(+3.1,-3.0) h^(-1)Mpc. The amplitude of correlation function is about 2.4 times higher than that of Croft et al. (1997). The correlation lengths of the Abell clusters with the richness class RC >= 0 and 1 are measured to be r_0 = 17.4(+1.2,-1.1) and 21.0(+2.8,-2.8) h^(-1)Mpc, respectively, which is consistent with our results for the APM sample at the similar level of richness. The richness dependence of cluster correlations is found to be r_0 = 0.40*d_c + 3.2 where d_c is the mean intercluster separation. This is identical in slope with the Bahcall & West (1992)'s estimate, but is inconsistent with the weak dependence of Croft et al. (1997). The X-ray bright Abell clusters in the XBACs catalog and the X-ray selected clusters in the BCS catalog show strong clustering. The correlation length of the XBACs clusters with L_x >= 0.65*10^44 h^(-2)erg/s is 30.3(+8.2,-6.5) h^(-1)Mpc, and that of the BCS clusters with L_x >= 0.70*10^44 h^(-2)erg/s is 30.2(+9.8,-8.9) h^(-1)Mpc. The clustering strength of the X-ray clusters is much weaker than what is expected from the optical clusters.

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