Talks

 Kenneth Ganga(APC)

"Planck and the CMB"

Planck, launched on May 14, 2009, is now imaging the anisotropies in the Cosmic Microwave Background (CMB), over the entire sky, in both polarization and total intensity, with an unprecedented combination of sensitivity and angular resolution. I will present the Planck mission, its recent public results, show some of our future plans, and try to put these in the context of other CMB measurements, past, present and future.

 Istvan Szapudi(Hawaii)

"Hot and Cold Spots on the CMB"

The late time Integrated Sachs-Wolfe (ISW) is expected to leave an imprint of superstructures on the cosmic microwave background (CMB). Previously, we found that the largest superclusters and supervoids selected from the SDSS LRG sample indeed correspond to cold and spots on the CMB at better than 4 sigma significance. The size of the effect, approximately 10muK, is higher than naive expectation. To judge the plausibility that these measurements are indeed due to the ISW effect, I will present further measurements, in particular, a photo-z galaxy survey towards the Cold Spot region, as well as theoretical estimates of the ISW effect based on the statistics of rare structures observed in the SDSS.

 Graziano Rossi(KIAS)

 "Non-Gaussianities in the CMB"

I will describe how to use the statistics of regions above or below a temperature threshold (excursion sets) to study the cosmic microwave background (CMB) anisotropy in models with primordial non-Gaussianity of the local type. In particular, I will show that by computing the full-sky spatial distribution and clustering of pixels above/below threshold from a large set of simulated maps with different levels of non-Gaussianity, a positive value of the dimensionless non-linearity parameter f_NL enhances the number density of the cold CMB excursion sets along with their clustering strength, and reduces that of the hot ones. This peculiar feature can be used to discriminate between the simpler Gaussian hypothesis and non-Gaussian scenarios, arising either from non-standard inflation or alternative early-universe models.

 Hellwing Wojtek(Warsaw))

"Persistent Alpha-Shape Topology of the LCDM Universe"

We investigate the topological structure of the dark matter density field and the spatial distribution of dark haloes in the LCDM cosmology scenarios. To this end, we assess the homology of the manifolds defined by the cosmic matter distribution and introduce betti numbers to quantify their topology in terms of disconnected components, tunnels and voids. Working within the context of computational topology and geometry, level set manifolds are triangulated by means of their alphashape. This allow us to compute the 3 Betti numbers characterising the manifolds topology at a given alpha scale. It defines a 3-D parameter space, in which we characterize the topology of a cosmological scenario by its parameterized track. We demonstrate the sensitivity and high potential of this topological characterization for discriminating between cosmological models and the exploitation of the weblike geometry of the cosmic mass and galaxy distribution for cosmological purposes.

 Arman Shafieloo(Oxford)

 "The Crossing Statistic: Dealing with Unknown Errors in the Dispersion of Type Ia Supernovae"

We propose a new statistic that has been designed to be used in situations where the intrinsic dispersion of a data set is not well known: `The Crossing Statistic. This statistic is in general less sensitive than `chi^2 to the intrinsic dispersion of the data, and hence allows us to make progress in distinguishing between different models using goodness of fit to the data even when the errors involved are poorly understood. The proposed statistic makes use of the shape and trends of a model"s predictions in a quantifiable manner. It is applicable to a variety of circumstances, although we consider it to be especially well suited to the task of distinguishing between different cosmological models using type Ia supernovae. We show that this statistic can easily distinguish between different models in cases where the `chi^2 statistic fails. We also show that the last mode of Crossing Statistic is identical to `chi^2, so that one can consider it as a generalization of `chi^2.

 Jaichan Hwang(KNU)

 "Cosmological Nonlinear Perturbations"

In this talk I will report second-order density power spectrum in a zero-pressure cosmology in Einstein gravity, and second-order curvature power spectrum generated during slow-roll inflation supported by a minimally coupled scalar field.

 Masahiro Takada(IPMU)

 "Subaru Weak Lensing Studies of X-ray Luminous Clusters"

We use Subaru data to conduct a detailed weak-lensing study of the dark matter distribution in a sample of 30 X-ray luminous galaxy clusters in the redshift range 0.15<z<0.3. We in detail explore the best-available accuracy of estimating cluster masses from weak lensing information, for each cluster basis and for stacked cluster signals.  We have also developed the new 2D shear fitting method where the two-dimensional weak lensing signals are fully used. Some highlights of our findings are (1) cluster mass enclosed by the spherical over-density 500 can be constrained at 10-20% accuracy for individual clusters and (2) the mass-halo concentration scaling relation is found at a 2-sigma level, and (3) a significant detection of the elliptical shape of dark matter halos at 7-sigma level. I will talk about these results, and will briefly mention about our future Subaru survey, Hyper Suprime-Cam Survey, if time allows.

 Yong-Seon Song(KIAS)

 "Measuring Coherent Motions in the Universe"

We present new measurements of the coherent motion of galaxies based on observations of the large-scale redshift--space distortions seen in the two--dimensional two--point correlation function of Luminous Red Galaxies in Data Release Seven of the Sloan Digital Sky Survey. We have developed a new methodology for estimating these coherent motions, which is less dependent on the details of galaxy bias and of the cosmological model to explain the late--time acceleration of the expansion of the Universe. We measure a one--dimensional velocity dispersion of galaxies on large--scales of sigma_v=3.01^{+0.45}_{-0.46} Mpc/h and sigma_v=3.69^{+0.47}_{-0.47} Mpc/h at a mean redshift of z=0.25 and 0.38 respectively. These values are fully consistent with predictions for a WMAP7--normalised LCDM Universe and inconsistent (at >5 sigma) with a Dvali-Gabadadze-Porrati (DGP) model for the Universe. We can convert the units of these sigma_v measurements to 270^{+40}_{-41} km/s and 320^{+41}_{-41} km/s respectively (assuming a LCDM universe), which are much lower than that expected based on recent low redshift (z<0.2) measurements of the peculiar velocity field (or ``bulk flows"), i.e., we would have predicted motions of ~ 600 km/s over our redshift range (0.16<z<0.47) to be consistent with these local measurements. One possible explanation for such a large discrepancy is that our Galaxy is located in unusually over, or under, dense region of the Universe.

 Ilian Iliev(Sussex)

 "Character and Observable Signatures of the Early Cosmic Structures"

I will present some of our recent results, based on extremely large N-body and radiative transfer simulations, on the formation and radiative feedback of early cosmic structures. I will discuss some of the resulting observable signatures of Cosmic Reionization at redshifted 21-cm line and at other wavelengths.

 Hyung Mok Lee(SNU)

 "Cosmic Near-Infrared Background Radiation and the First Galaxies"

Direct detection of the first galaxies is very difficult with current observational facilities because they are too faint. At the moment, the best way to infer the light from first the galaxies is to detect and analyze the near infrared diffuse radiation.  We used the recent data at 2.4, 3.2 and 4.1 mm from AKARI space telescope to detect the infrared background radiation. The absolute brightness of background radiation due to distant galaxies is difficult to obtain because the diffuse component of near infrared light is dominated by the zodiacal emission. In order to avoid such difficulties, we looked for the fluctuating component since the zodiacal emission is likely to be very smooth. The power spectrum analysis shows that there is a significant residual fluctuation at angular scales larger than 100 arcseconds. The fluctuating component cannot be explained by zodiacal light, diffuse galactic light, shot noise of faint galaxies or clustering of low redshift galaxies. Thus we conclude that the detected fluctuation could be attributed to the very early generation of stars in the universe. Observed fluctuating component at angular scales of ~100 arcseconds has a blue spectrum. The obtained spatial structure and power spectrum are consistent with the theoretical prediction, biased star formation of the population III stars which follows density distribution of the dark matter. We also outline the ongoing and planned projects for the cosmic near infrared background studies.

 Atsushi Taruya(Tokyo)

 "Baryon Acoustic Oscillations in 2D: Theoretical Issues and Obsetvational Prospects"

Baryon acoustic oscillations (BAOs) imprinted in the galaxy power spectrum can be used as standard ruler to determine the angular diameter distance and Hubble parameter at high redshift galaxies. Combining redshift distortion effect which apparently distorts the galaxy clustering pattern, we can also constrain the growth rate of large-scale structure formation. In this talk, we address several theoretical issues on accurately modeling BAOs in 2D, taking proper account of both non-linear gravitational evolution and redshift distortion. We also discuss how well we can tightly constrain cosmic expansion and growth history from the 2D BAOs.

 Luigi Guzzo(INAF, BRERA)

 "Cosmology and Dark Energy with Current and Future Redshift Surveys"

 Myungshin Im(SNU)

 "Observational Constraints on the Growth of Supermassive Black Holes  at the Edge of the Universe"

 (i) SMBHs at z ~ 6 are rapdily growing, (ii) there is a lack of 10^10 solar mass

 Hoseong Hwang(CEA Saclay)

"Evolution of Star Formation Activity of Galaxies as seen by Herschel"

Understanding how star formation activity of galaxies evolves through cosmic time has been a challenge for modern astrophysics. The all-sky surveys at far-infrared (FIR) wavelengths with IRAS and AKARI enabled us to understand the nature of the bolometric luminosities of local star-forming galaxies. On the other hand, a great deal of effort has been put into understanding the spectral energy distributions (SEDs) of high-redshift galaxies with infrared satellites (ISO, Spitzer and BLAST) and ground-based submillimeter telescopes, but the limited wavelength coverages, the small sky coverages, and the large beam sizes have prevented us from having a fair comparison with local siblings. Thanks to the advent of the Herschel Space Observatory with very wide FIR windows (70-500 micron), we started having a complete view of SEDs for a large number of high-redshift galaxies at z~1-3.  In this talk, I summarize the scientific results from the deepest extragalactic survey with Herschel in the fields of the Great Observatories Origins Deep Survey (GOODS). In combination with multiwavelength data from HST, Spitzer, Chandra and ground-based telescopes, we study the FIR properties (infrared luminosity and dust temperature) of several galaxy populations (normal star-forming galaxies and submillimeter galaxies) at z~1-3. As a reference sample, we also study the FIR properties of local galaxies at z<0.1 using data from IRAS, AKARI, and SDSS. Comparison of two samples helps us to understand the evolution of star formation activity of galaxies through cosmic time.

 Changbom Park(KIAS)

 "Simulation of the SDSS Survey Region of the Universe"

 Xuelei Chen(NAOC)

"Topics in 21cm Cosmology"

I will present several recent researches I have done on 21cm cosmology. This include model on the 21cm signal from minihalos and IGM, the 21cm forest as a probe of reionization, IGM temperature, and first galaxies, and finally a proposal to conduct low redshift 21cm experiment in China.

 Michael Vogeley(Drexel)

 "Structure and Contents of Cosmic Voids"

Using the Sloan Digital Sky Survey (SDSS) we find that voids fill over 60% of the Universe and are dominated by voids with radius ~20Mpc/h. The shapes, sizes, and internal structures of voids can be used as cosmological tests. The detailed properties of objects in voids are a strong test of structure formation models. The 10% of galaxies that live in voids tend to be fainter, bluer, and have higher rates of star formation than similar galaxies in denser environments. While all types of galaxies respect the same voids, we find that Lyman-alpha absorbers do not match the underlying galaxy distribution; roughly 60% of Ly-alpha absorbers live in large (R>10 Mpc/h) cosmic voids.

 Rien van de Weygaert (Kapteyn)

 "The Void Galaxy Survey"

The void galaxy survey consists of a multiwavelength - optical, infrared, ultraviolet and radio-observational study of void galaxies. The galaxies are located in the deepest troughs of voids that were identified from the SDSS DR7 survey sample. The identication is uniquely based on a pure (tessellation-based) geometric procedure, guaranteeing an objective census of the void galaxy population in the nearby Universe. The aim of the project is to compare the physical intrinsic properties of void galaxies and to assess in how far they differ from the regular field population in terms of morphology, brightness, colour, star formation activity and (HI) gas content and morphology. With these galaxies living in the most pristine regions in the local Universe, the survey will yield essential insights on the first stages of galaxy formation and on environmental influences on the galaxy formation process. In this presentation, we will present the first results of our program. This will involve a discussion of the finished pilot program of 15 galaxies, along with some of the unique constellations we have encountered. Amongst others, special attention will be devoted to the polar ring galaxy we have found in a tenuous wall between voids and on the elongated group of three void galaxies. Also, we report on the recent finding of a constellation of three void galaxies within the deep interior of a void, one surrounded by stellar streams, embedded within a common highly elongated mantle of neutral hydrogen.

 Carlos Frenk(Durham)

 "Cosmology in Our Backyard"

The standard model of cosmology -- the "Lambda cold dark matter'' model -- is based on the idea that the dark matter is a collisionless elementary, probably a supersymmetric, particle. This model has been famously verified by observations of the cosmic microwave background radiation and the large-scale distribution of galaxies. Yet, the reality is that we have no direct evidence to support the key assumption of the model - that the dark matter is indeed a cold, very weakly interacting particle. I will review our current understanding of the distribution of dark matter on galactic scales, which derives largely from large cosmological N-body simulations, and address the perceived ``cusp'' and ``satellite galaxy'' problems, often viewed as evidence against the standard model. I will then discuss the prospects for detecting dark matter, perhaps indirectly through gamma-ray annihilation radiation.

 Sukyoung Yi(Yonsei)

 "SFH of Galaxies from GALEX-SDSS"

I present the latest update on this ongoing project. I will show that 20% or more of super-L* ellipticals are still forming stars and present a thorough demographics on ellipticals in terms of UV properties and AGN diagnostics. Semi-analytic models based on the hierarchical paradigm are used to reproduce this and other SF-related properties but fail miserably especially on satellite galaxies in cluster environments. I show how the use of realistic diffuse gas stripping prescriptions in addition to AGN feedback prescriptions help us reconcile some of these shortcomings of models.

 Joseph Silk(Oxford)

 "Feedback in Galaxy Formation"

Specific issues that I address include the galaxy luminosity function, feedback by supernovae and by AGN, and downsizing. I argue that current evidence favours two distinct modes of star formation in the early universe, in order to account for the origin of disk and massive spheroidal galaxies. A multi-phase treatment of supernova feedback leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. These considerations are extended to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central AGN. During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced feedback and outflows. Black hole growth in the gas-rich accretion phase eventually saturates on the universal relation between black hole mass and spheroid velocity dispersion. Downsizing of both SMBH and spheroids may be a consequence of AGN-driven positive feedback.

 Yipeng Jing(SAO)

"Theoretical challenges for high-precision measurement of dark energy"

I will present results on shapes, growth and environments of dark matter halos.

 Myung Gyoon Lee(SNU)

"Wandering Globular Clusters in Galaxy Clusters and the First Stellar Systems in the Universe "

 Recently we discovered a large scale structure of globular clusters in the Virgo cluster, including wandering globular clusters as well as galaxy globular clusters. It is expected most galaxy clusters and groups possess wandering globular clusters. We discuss the implication of this finding, including the relation between wandering globular clusters and the first stellar systems in the universe.

 Sung Eun Kim(Sejong)

"Submillimeter Properties of Galaxies Behind the Large Magellanic Cloud"

Posters

Hyunmi Song(SNU)

"Merging Rates of the First Objects and the Formation of First Mini-Filaments in Models with Massive Neutrinos"

We study the effect massive neutrinos on the evolution of the early mini-halos(M~10^6 solar mass/h at z~20) where the first stars may have formed. In the framework of the extended Press-Schechter formalism, we evalutate analytically the rate of merging of the mini-halos into zero-dimensional larger halos and one dimensional minai-filaments. It is shown that the halo-to-filament merging rate increases sharly with the neutrino mass fraction f_\nu while the halo-to-halo merging rate decreases with f_nu. For f_nu <= 0.04, the halo-to-filament merging rate is negligibly low at all filament mass scales while for f_nu >= 0.07 the halo-to-filament merging rate exceeds the halo-to-halo merging rate at the characteristic filament mass scale of 10^9 -10^10 solar mass/h. The distribution of the epochs of the longest-axis collapse of these first filaments is also derived and found to reach a sharp maximum at z~8-9. Once the first mini-filaments form,they would provide bridges along which the matter and gas more rapidly accrete onto the constituent halos, causing the early formation of the first galaxies and rapid growth of their central blackholes. Furthermore, the longest axis collapse of these first mini-filaments would spur the supermassive blackholes to power the ultraluminous high-z quasars. In this scenario, the mass estimate ~3x10^9 solar mass/h by Willot et al. in 2003 corresponds to an upper limit of the neutrino mass, m_nu <= 0.22eV.

Frederico Arroja(Ewha)

"A Note on the Equivalence of a Barotropic Perfect Fluid with a K-Essence Scalar Field"

We obtain the necessary and sufficient condition for a class of non-canonical single scalar field models to be exactly equivalent to barotropic perfect fluids, under the assumption of an irrotational fluid flow. An immediate consequence of this result is that the non-adiabatic pressure perturbation in this class of scalar field systems vanishes exactly at all orders in perturbation theory and on all scales. The Lagrangian for this general class of scalar field models depends on both the kinetic term and the value of the field. However, after a field redefinition, it can be effectively cast in the form of a purely kinetic K-essence model.

Beygu Burcu(Kapteyn)

"The Void Galaxy Survey "

The Void Galaxy Survey consists of a multi-wavelength observational study of void galaxies. The galaxies are located in the deepest troughs of voids that were identified from the SDSS DR7 survey sample. The aim of the project is to compare the physical intrinsic properties of void galaxies and to assess in how far they differ from the regular field population in terms of morphology, brightness, color, star formation activity and (HI) gas content. In this poster we present the first results of our program.

 "A Study of Edge-on Galaxy Discs using S4G Imaging"

The ongoing S4G (the Spitzer Survey of Stellar Structure in Galaxies) aims to obtain space-based deep 3.6 and 4.5 micrometer imaging of 2331 galaxies located at a distance smaller than 40 Mpc. The PI of the survey is Dr. Kartik Sheth. As the mid-infrared traces well stellar mass distribution and is not much affected by dust, the S4G can be used to study the structure of galaxy discs in edge-on galaxies. Most disc galaxies are thought to have a thin (classical) disc and a thick disc. Thick discs are in many models thought to be a necessary consequence of the disc formation and/or evolution. I will present a detailed study on the edge-on galaxy NGC4244 which, until now was thought not to have a thick disc and thus to be a challenge to disc formation and evolution models. I will also present the results of an ongoing study of the thick disc properties in a large sample of edge-on galaxies.

Bernardo Cervantes Sodi(KASI)

"Quantifying Galactic Morphological Transformations in the Cluster Environment"

We study the effects of the cluster environment on galactic morphology by defining a dimensionless angular momentum parameter lambda_{d}, to obtain a quantitative and objective measure of galaxy type. The use of this physical parameter allows us to take the study of morphological transformations in clusters beyond the measurements of merely qualitative parameters, e.g. S/E ratios, to a more physical footing. To this end, we employ an extensive Sloan Digital Sky Survey sample, with galaxies associated with Abell galaxy clusters. The sample contains 93 relaxed Abell clusters and over 34,000 individual galaxies, which guarantees a thorough statistical coverage over a wide range of physical parameters. We find that the median lambda_{d} value tends to decrease as we approach the cluster center, with different dependences according to the mass of the galaxies and the hosting cluster; low and intermediate mass galaxies showing a strong dependence, while massive galaxies seems to show, at all radii, low lambda_{d} values. By analysing trends in lambda_{d} as functions of the nearest galactic neighbour environment, clustercentric radius and velocity dispersion of clusters, we can identify clearly the leading physical processes at work. We find that in massive clusters, the interaction with the cluster central region dominates, whilst in smaller clusters galaxy-galaxy interactions are chiefly responsible for driving galactic morphological transformations.

Hector Aceves(IA-UNAM)

"Phase-Space Density Distribution in Major Merger Remnants"

We calculate the coarse-grained phase-space density distribution, f, and its volume density v(f), in remnants of N-body mergers of spiral-like galaxies. In particular, we study the preservation of the power-law dependence of v(f) ~ f^a (a=constant) in major mergers.

Marius Cautun(Kapteyn)

"Topology of the Haloes in the MMF Web"

We use the Multiscale Morphology Filter to dissect in a scale-free way the structure of the Cosmic web into its elements: clusters, filaments and walls. We analyze and characterize the topological structure of the resulting distinct filament, wall and cluster halo populations in terms of Betti numbers, following the instruments of alphashapes and persistence.

Sungwook Hong(KAIST)

A novel method to characterize the topology of the early-universe intergalactic medium during the epoch of cosmic reionization is presented. The 21-cm radiation background from high redshift is analyzed through calculation of the 2-dimensional (2D) genus. The radiative transfer of hydrogen-ionizing photons and ionization-rate equations are calculated in a suite of numerical simulations under various input parameters. The 2D genus is calculated from the mock 21-cm images of high-redshift universe. We construct the 2D genus curve by varying the threshold differential brightness temperature, and compare this to the 2D genus curve of the underlying density field. We find that (1) the 2D genus curve reflects the evolutionary track of cosmic reionization and (2) the 2D genus curve can discriminate between certain reionization scenarios and thus indirectly probe the properties of radiation-sources. Choosing the right beam shape of a radio antenna is found crucial for this analysis. Square Kilometer Array (SKA) is found to be a suitable apparatus for this analysis in terms of sensitivity, even though some deterioration of the data for this purpose is unavoidable under the planned size of the antenna core.

 Hongbae Ann(PNU)

 "Morphology and Physical Properties of Nearby Dwarf Elliptical Galaxies"

Dwarf elliptical galaxies are most dominant population of the local universe. They are known to have simple morphology like their giant cousin, classical elliptical galaxy. However, there seem to be a variety of morphologies that need classification of subtypes. We will present the results of a detailed analysis of the morphology and physical properties of dwarf elliptical galaxies observed in the SDSS DR7.

 Hyeong-Chan Kim(Chungju)

 "Cosmological Perturbations from the Anisotropic Universe"

We discuss the spectra of the curvature and gravitational wave perturbations, produced during the anisotropic epoch before the onset of inflation, as the continuation of the previous work \cite{km},discussing the behaviors of a quantized, massless and minimally coupled scalar field. As the background model, we consider the Einstein gravity coupled to a massive scalar field, i.e., inflaton. We assume that initially the inflaton field has a zero velocity and then slowly rolls on the potential until reaching the origin. The effect of the scalar field to the geometry is too small, and the regular branch of the Kasner-de Sitter solution with a planar symmetryis the good approximation as the background geometry. The quantization of the perturbation variables is done in the similar way to the massless scalar case\cite{km}, since the tensor-scalar coupling is absent in the initial time and the adiabatic approximation becomes valid. We quantize the perturbations in the initial adiabatic vacuum. If $k_1\lesssim k$, where $k$ is the total comoving momentum and $k_1$ is the comoving momentum along the special direction, the WKB approximation is valid in the whole stage of the isotropization. Thus, the effects of the tensor-scalar mixing is suppressed by the slow-roll parameter. Then, the leading order corrections to the power spectra have the universal oscillatory form. In contrast, for the planar modes, $k_1\ll k$, the WKB approximation is temporalily violated during the isotropization and the tensor-scalar mixing becomes important. The final spectra of the scalar mode and two tensor polarizations do not share the same spectra, which may be the characterstic signals to distinguish the anisotropic universe from the future observations.

 Encieh Erfani(Bonn)

"Running-Mass Inflation Model and Primordial Black Holes"

We revisit the running mass-inflation model after WMAP seven year data for Primordial Black Hole (PBH) formation that could be a candidate for Dark Matter (DM). We show that with rescent CMB data and considering the correlation between spectral index and its running, even with introducing positive running of running of spectral index, it is not possible anymore to get DM PBHs.

Johannes Hidding(Kapteyn)

We study the formation of the Cosmic Web in the context of the geometric adhesion model. Using singularities in the mapping between Eulerian and Lagrangian space we identify clusters, filaments, pancakes and voids in a well defined way. On this poster we illustrate the geometric formalism and present several statistics (mass functions and tidal field characteristics) on the evolution of the Cosmic Web. We find we can reproduce many established results using this elegant model.

Mira Seo(PNU)

"Morphology and Physical Properties of Nearby Dwarf Elliptical Galaxies"

Dwarf elliptical galaxies are most dominant population of the local universe. They are known to have simple morphology like their giant cousin, classical elliptical galaxy. However, there seem to be a variety of morphologies that need classification of subtypes. We will present the results of a detailed analysis of the morphology and physical properties of dwarf elliptical galaxies observed in the SDSS DR7.

Seong-Kook Lee(KIAS)

"SED-fitting Analysis of High-redshift Star-forming Galaxies: Effects of Assumed Star-Formation Histories"

Estimating physical parameters of galaxies, including star-formation rate and stellar mass, from observational data is indispensible procedure in the study of galaxy formation and cosmology. Our investigation on the systematic bias in SED-fitting analysis of high-redshift star-forming galaxies reveals that (i) assumed forms of star-formation histories affect the derived results from SED-fitting, especially significantly for star-formation rates and ages, and (ii) increasing (or delayed) star-formation histories are more appropriate forms (than exponentially declining star-formation histories) in the SED-fitting analysis of high-redshift star-forming galaxies. This newly proposed forms of star-formation histories provide not only the improved estimation of star-formation rates and stellar population ages of high-redshift galaxies but also better understanding of galaxy evolution at high redshifts.

Jeong-Sun Hwang(KIAS)

"Models of Arp 285: The Formation of "Beads on a String" in the Accretion Tail"

We present hydrodynamical simulations of the interaction in the peculiar galaxy pair Arp 285 (NGC 2856/2854). This system contains a striking example of "beads on a string": a series of star-formation complexes ~1 kpc apart. These "beads" are observed in a tail-like feature that is perpendicular to the disk of NGC 2856. We tested several conceptual ideas of the formation of the tail-like feature in our simulations. In our model, gas from a connecting bridge falling into the potential of the companion overshoots the companion, piling up in an accretion tail on the far side of the companion. Star formation occurs in this region. Our model suggests that the "beads on the string" may be the result of stochastic processes, albeit in a density enhanced pileup zone.  

We study the small scale cross-correlation of CMB temperature and galaxy overdensities (CMB-Galaxy for short) to search for the signature of the abnormally large bulk motions of galaxies and clusters extending to several hundred Mpc, which is claimed by two independent measurements recently. The presence of the large bulk flow will introduce a CMB-Galaxy cross-correlation on pretty small scales due to the kinetic Sunyaev–Zel'dovich effect (KSZ for short) and the fluctuation of galaxy density on the bulk flow. For full sky survey this bluk flow induced KSZ (BF-KSZ for short) is zero if averaged over the survey, so it does not contribute to the ISW-like measurements using CMB-Galaxy cross-correlation. We apply a weighting scheme to nullify the statically isotropic terms in CMB-Galaxy cross-correlation, while maximize the BF-KSZ. The data we used are KIAS-VAGC catalog for galaxies and WMAP-7year temperature map for CMB. The results indicate that we do see the signature of large bulk flow at about two-sigma level. We also check the systematic effects for CMB fluctuations and galaxy shotnoise. Since the weighted galaxy-CMB cross-correlation depends on the direction of the bulk flow, it is possible to detect the direction of the bulk flow which should make the BF-KSZ maximum.