ARE GALACTIC WARPS INDUCED BY INTERGALACTIC FLOWS?

SANCHEZ-SALCEDO F. J. The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.4

The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanism of the generation of galactic warps. Here we discuss conditions under which intergalactic flows can be relevant for warping field galaxies. Constraints include the heating of the outer disk, the level of asymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, the symmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and the speed of the intergalactic flow whether subsonic or supersonic. These constraints are discussed in this paper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequence of accretion flows onto the disk.

HIGH REDSHIFT QUASAR SURVEY WITH IMS

JEON, YISEUL,IM, MYUNGSHIN The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We describe a survey of quasars in the early universe, beyond z ~ 5, which is one of the main science goals of the Infrared Medium-deep Survey (IMS) conducted by the Center for the Exploration of the Origin of the Universe (CEOU). We use multi-wavelength archival data from SDSS, CFHTLS, UKIDSS, WISE, and SWIRE, which provide deep images over wide areas suitable for searching for high redshift quasars. In addition, we carried out a J-band imaging survey at the United Kingdom InfraRed Telescope with a depth of ~23 AB mag and survey area of ${\sim}120deg^2$, which makes IMS a suitable survey for finding faint, high redshift quasars at z ~ 7. In addition, for the quasar candidates at z ~ 5.5, we are conducting observations with the Camera for QUasars in EArly uNiverse (CQUEAN) on the 2.1m telescope at McDonald Observatory, which has a custom-designed filter set installed to enhance the efficiency of selecting robust quasar candidate samples in this redshift range. We used various color-color diagrams suitable for the specific redshift ranges, which can reduce contaminating sources such as M/L/T dwarfs, low redshift galaxies, and instrumental defects. The high redshift quasars we are confirming can provide us with clues to the growth of supermassive black holes since z ~ 7. By expanding the quasar sample at 5 < z < 7, the final stage of the hydrogen reionization in the intergalactic medium (IGM) can also be fully understood. Moreover, we can make useful constraints on the quasar luminosity function to study the contribution of quasars to the IGM reionization.

THE VELOCITY INHOMOGENEITY IN THE COMA CLUSTER OF GALAXIES

KIM KWANG TAE The Korean Astronomical Society 1995 Journal of The Korean Astronomical Society Vol.28 No.1

A velocity inhomogeneity, which is defined as a regional preponderence of either radial or tangential orbits, is searched with a new technique for the Coma cluster of galaxies. It is found within $\~2h^{-1}$ Mpc from the cluster center that the Coma shows conspicuous inhomogeneities in velocity and that the inhomogeneities are real at a $99\%$ level of confidence. Even in the central region (7' - 30' from the center), zones that are dominated by radial and tangential orbits are distinguishable. Defining the cluster's 'equator' as the direction defined by the Coma-A1367 supercluster, tangential orbits dominate the 'polar' zones in the central region. Galaxies that are located in 30'-100' also inhomogeneous in velocity in that the 'polar' zones are mostly radial while the rest is nearly homogeneous. These results indicate that the Coma galaxies are exceedingly more radial in orbit, implying that merging or infalls are either still going on or an earlier virialization is likely to have occurred preferentially near the 'equator'. Incorporating the velocity inhomogeneity into mass estimators, the most appropriate mass is turned out to be $0.4\times10^{15}h^{-1}M_\bigodot(R\;\leq\;0.6h^{-1} Mpc),\;and\;1.0\times10^{15}h^{-1} M_\bigodot(R\;\leq\;2.1h^{-1}Mpc)$. The corresponding mass to blue light ratio on the average is $\~$300h. These estimates are consistent with Merritt (1987) and Hughes (1989) and the MILE is seemed to favour the mass-follows-light models than the uniform spread of dark matter throughout the cluster.

ACTIVE GALACTIC NUCLEUS INTERACTION WITH THE HOT GAS ENVIRONMENT: UNDERSTANDING FROM THE RADIO AND X-RAY DATA

LAL, DHARAM V. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

Recognition of the role of radio galaxies in the universe has been increasing in recent years. Their colossal energy output over huge volumes is now widely believed to play a key role not only in the formation of galaxies and their supermassive black holes, but also in the evolution of clusters of galaxies and, possibly, the cosmic web itself. In this regard, we need to understand the inflation of radio bubbles in the hot gas atmospheres of clusters and the importance of the role that radio galaxies play in the overall energy budget of the intracluster medium. Here, we present results from X-ray and radio band observations of the hot gas atmospheres of powerful, nearby radio galaxies in poor clusters.

ARE GALACTIC WARPS INDUCED BY INTERGALACTIC FLOWS?

F. J. SÁNCHEZ-SALCEDO 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanismof the generation of galactic warps. Here we discuss conditions under which intergalactic ows canbe relevant for warping eld galaxies. Constraints include the heating of the outer disk, the level ofasymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, thesymmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and thespeed of the intergalactic ow whether subsonic or supersonic. These constraints are discussed in thispaper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequenceof accretion ows onto the disk.

Models of Stephan’s Quintet: hydrodynamic constraints on the group’s evolution

Hwang, Jeong‐,Sun,Struck, Curtis,Renaud, Florent,Appleton, Philip N. Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society Vol.419 No.2

<P><B>ABSTRACT</B></P><P>We present smoothed particle hydrodynamic models of the interactions in the compact galaxy group, Stephan’s Quintet. This work is extension of the earlier collisionless <I>N</I>‐body simulations of Renaud et al. in which the large‐scale stellar morphology of the group was modelled with a series of galaxy–galaxy interactions in the simulations. Including thermohydrodynamic effects in this work, we further investigate the dynamical interaction history and evolution of the intergalactic gas of Stephan’s Quintet. The major features of the group, such as the extended tidal features and the group‐wide shock, enabled us to constrain the models reasonably well, while trying to reproduce multiple features of the system. We found that reconstructing the two long tails extending from NGC 7319 towards NGC 7320c one after the other in two separate encounters is very difficult and unlikely, because the second encounter usually destroys or distorts the already‐generated tidal structure. Our models suggest that the two long tails may be formed simultaneously from a single encounter between NGC 7319 and NGC 7320c, resulting in a thinner and denser inner tail than the outer one. The tails then also run parallel to each other as observed. The model results support the idea that the group‐wide shock detected in multiwavelength observations between NGC 7319 and NGC 7318b and also the starburst region north of NGC 7318b are triggered by the high‐speed collision between NGC 7318b and the intergalactic gas. Our models show that a gas bridge is formed by the high‐speed collision and clouds in the bridge continue to interact for some tens of millions of years after the impact. This produces many small shocks in that region, resulting in a much longer cooling time than that of a single impact shock.</P>

The Kramers-Heisenberg Formula and the Gunn-Peterson Trough

박기훈,이희원 한국천문학회 2014 Journal of The Korean Astronomical Society Vol.47 No.5

Recent cosmological observations indicate that the reionized universe may have started at around z=6, where a significant suppression around Lyα has been observed from the neutral intergalactic medium. The associated neutral hydrogen column density is expected to exceed 1021 cm-2, where it is very important to use the accurate scattering cross section known as the Kramers-Heisenberg formula that is obtained from the fully quantum mechanical time-dependent second order perturbation theory. We present the Kramers-Heisenberg formula and compare it with the formula introduced in a heuristic way by Peebles (1993) considering the hydrogen atom as a two-level atom, from which we find a deviation by a factor of two in the red wing region far from the line center. Adopting a representative set of cosmological parameters, we compute the Gunn-Peterson optical depths and absorption profiles. Our results are quantitatively compared with previous work by Madau & Rees (2000), who adopted the Peebles approximation in their radiative transfer problems. We find deviations up to 5 per cent in the Gunn-Peterson transmission coefficient for an accelerated expanding universe in the red off-resonance wing part with the rest wavelength Δλsim 10Α.

COSMIC RAYS AND GAMMA-RAYS IN LARGE-SCALE STRUCTURE

INOUE SUSUMU,NAGASHIMA MASAHIRO,SUZUKI TAKERU K.,AOKI WAKO The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5

During the hierarchical formation of large scale structure in the universe, the progressive collapse and merging of dark matter should inevitably drive shocks into the gas, with nonthermal particle acceleration as a natural consequence. Two topics in this regard are discussed, emphasizing what important things nonthermal phenomena may tell us about the structure formation (SF) process itself. 1. Inverse Compton gamma-rays from large scale SF shocks and non-gravitational effects, and the implications for probing the warm-hot intergalactic medium. We utilize a semi-analytic approach based on Monte Carlo merger trees that treats both merger and accretion shocks self-consistently. 2. Production of $^6Li$ by cosmic rays from SF shocks in the early Galaxy, and the implications for probing Galaxy formation and uncertain physics on sub-Galactic scales. Our new observations of metal-poor halo stars with the Subaru High Dispersion Spectrograph are highlighted.

X-RAY STUDIES OF THE INTRACLUSTER MEDIUM IN CLUSTERS OF GALAXIES - CHARACTERIZING GALAXY CLUSTERS AS GIANT LABORATORIES

BOHRINGER HANS The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5

Galaxy clusters as the densest and most prominent regions within the large-scale structure can be used as well characterizable laboratories to study astrophysical processes on the largest scales. X-ray observations provide currently the best way to determine the physical properties of galaxy clusters and the environmental parameters that describe them as laboratories. We illustrate this use of galaxy clusters and the precision of our understanding of them as laboratory environments with several examples. Their application to determine the matter composition of the Universe shows good agreement with results from other methods and is therefore a good test of our understanding. We test the reliability of mass measurements and illustrate the use of X-ray diagnostics to study the dynamical state of clusters. We discuss further studies on turbulence in the cluster ICM, the interaction of central AGN with the radiatively cooling plasma in cluster cooling cores and the lessons learned from the ICM enrichment by heavy elements.

IMAGING THE RADIO HALO IN THE ABELL 2256 CLUSTER OF GALAXIES

KIM K.-T. The Korean Astronomical Society 1999 Journal of The Korean Astronomical Society Vol.32 No.2

Diffuse radio emission in Abell 2256 was detected above 3 $\sigma$ with DRAO observations at 1420 MHz. The halo size is $\~13' {\times}10' (\~1h^{-1}_{50}\;Mpc$) in full extent and is elongated along a position angle of about $112^{\circ}$. The total flux density contained in the halo is 30$\pm$10 mJy at 1420 MHz and its spectral index is -2.04$\pm$0.04, showing no evidence for steepening up to 1420 MHz. Using the size estimate, yields a more reliable equipartition magnetic field strength which is $0.34(1 + k)^{2/7}{\mu}G$. In addition, five new radio sources are identified.