PROBING GALAXY FORMATION MODELS IN COSMOLOGICAL SIMULATIONS WITH OBSERVATIONS OF GALAXY GROUPS

HABIB. G., KHOSROSHAHI,GOZALIASL, GHASSEM,FINOGUENOV, ALEXIS,RAOUF, MOJTABA,MIRAGHEE, HALIME The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We use multi-wavelength observations of galaxy groups to probe the formation models for galaxy formation in cosmological simulations, statistically. The observations include Chandra and XMM-Newton X-ray observations, optical photometry and radio observations at 1.4 GHz and 610 MHz. Using a large sample of galaxy groups observed by the XMM-Newton X-ray telescope as part of the XMM-Large Scale Survey, we carried out a statistical study of the redshift evolution of the luminosity gap for a well defined mass-selected group sample and show the relative success of some of the semi-analytic models in reproducing the observed properties of galaxy groups up to redshift z ~ 1.2. The observed trend argues in favour of a stronger evolution of the feedback from active galactic nuclei at z < 1 compared to the models. The slope of the relation between the magnitude of the brightest cluster galaxy and the value of the luminosity gap does not evolve with redshift and is well reproduced by the models. We find that the radio power of giant elliptic galaxies residing in galaxy groups with a large luminosity gap are lower compared to giant ellipticals of the same stellar masses but in typical galaxy groups.

COMPACT GROUPS OF GALAXIES WITH COMPLETE SPECTROSCOPIC REDSHIFTS IN THE LOCAL UNIVERSE

손주비,황호성,Margaret J. Geller,Antonaldo Diaferio,Kenneth J. Rines,이명균,이광호 한국천문학회 2015 Journal of The Korean Astronomical Society Vol.48 No.6

Dynamical analysis of compact groups provides important tests of models of compact group formation and evolution. By compiling 2066 redshifts from FLWO/FAST, from the literature, and from SDSS DR12 in the fields of compact groups in McConnachie et al. (2009), we construct the largest sample of compact groups with complete spectroscopic redshifts in the redshift range 0.01 < z < 0.22. This large redshift sample shows that the interloper fraction in the McConnachie et al. (2009) compact group candidates is 42%. A secure sample of 332 compact groups includes 192 groups with four or more member galaxies and 140 groups with three members. The fraction of early-type galaxies in these compact groups is 62%, higher than for the original Hickson compact groups. The velocity dispersions of early- and late-type galaxies in compact groups change little with groupcentric radius; the radii sampled are less than 100 h−1 kpc, smaller than the radii typically sampled by members of massive clusters of galaxies. The physical properties of our sample compact groups include size, number density, velocity dispersion, and local environment; these properties slightly differ from those derived for the original Hickson compact groups and for the DPOSS II compact groups. Differences result from subtle differences in the way the group candidates were originally selected. The abundance of the compact groups changes little with redshift over the range covered by this sample. The approximate constancy of the abundance for this sample is a potential constraint on the evolution of compact groups on a few Gigayear timescale.

GROUPS OF GALAXIES IN HISTORY: EVOLUTION IN THE MILLENNIUM SIMULATION

HASHEMIZADEH, ABDOLHOSEIN,KHOSROSHAHI, HABIB G.,RAOUF, MOJTABA,NEZHAD, ALIREZA MOLAEI The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We use the millennium simulation for studying the evolution of groups of galaxies over time. We find fossil and non-fossil groups as well as old and young groups at redshift z = 0 and follow them back in time to investigate the evolution of their parameters, such as mass assembly, luminosity gap and halo mass concentration. We find that fossils assemble a larger fraction of their mass at z = 0 than controls. The magnitude gaps between fossil and non-fossil groups are not the same because of major and minor mergers, in old and young groups as well. We also find that WMAP1 and WMAP7 cosmologies lead to the same evolutionary history for fossil and control groups.

INTERACTIONS BETWEEN GALAXIES IN A LOW-REDSHIFT GROUP: THE NGC 4065 GROUP

TASUYA, ORARIK,SAWANGWIT, UTANE,KRIWATTANAWONG, WICHEAN The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We presents a study of interactions between galaxies in the low-redshift group known as the NGC 4065 group. Imaging data were taken using the 2.4 meter telescope at the Thai National Observatory (TNO) for B, V and $R_c$ broadband filters and [$S\small{II}$] and Red-continuum narrowband filters. There are 21 galaxies in our sample. The results show that most early type galaxies (ETGs) with equivalent width EW($H{\alpha}$) < $10{\AA}$ are gas-deficient galaxies, while late type galaxies (LTGs) show more EW($H{\alpha}$) and are bluer than the ETGs. This means that star formation activity in the LTGs could be triggered by tidal interactions between galaxy members due to dense environmental effects in the compact group.

Galaxy-Galaxy Blending in SPHEREx Survey Data

김다찬,송현미,김이곤,김민진,심현진,김도형,김용정,이보미,이정환,정웅섭,양유진 한국천문학회 2024 Journal of The Korean Astronomical Society Vol.57 No.1

The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) will provide all-sky spectral survey data covering optical to mid-infrared wavelengths with a spatial resolution of 6.”2, which can be widely used to study galaxy formation and evolution. We investigate the galaxy-galaxy blending in SPHEREx datasets using the mock galaxy catalogs generated from cosmological simulations and observational data. Only ~0.7% of the galaxies will be blended with other galaxies in all-sky survey data with a limiting magnitude of 19 AB mag. However, the fraction of blended galaxies dramatically increases to ~7–9% in the deep survey area around the ecliptic poles, where the depth reaches ~22 AB mag. We examine the impact of the blending in the number count and luminosity function analyses using the SPHEREx data. We find that the number count can be overestimated by up to 10–20% in the deep regions due to the flux boosting, suggesting that the impact of galaxy-galaxy blending on the number count is moderate. However, galaxy-galaxy blending can marginally change the luminosity function by up to 50% over a wide range of redshifts. As we only employ the magnitude limit at K_s-band for the source detection, the blending fractions determined in this study should be regarded as lower limits.

IS THE PEGASUS DWARF GALAXY A MEMBER OF THE LOCAL GROUP?

Lee, Myung-Gyoon The Korean Astronomical Society 1995 Journal of The Korean Astronomical Society Vol.28 No.2

Deep V I CCD photometry of the Pegasus dwarf irregular galaxy shows that the tip of the red giant branch (RGB) is located at I = $21.15{\pm}0.10$ mag and (V - I) = $1.58{\pm}0.03$. Using the I magnitude of the tip of the RGB (TRGB), the distance modulus of the Pegasus galaxy is estimated to be $(m\;-\;M)_o\;=\;25.13{\pm}0.11$ mag (corresponding to a distance of d = $1060{\pm}50$ kpc). This result is in a good agreement with the recent distance estimate based on the TRGB method by Aparicio [1994, ApJ, 437, L27],$ (m\;-\;M)_o$ = 24.9 (d = 950 kpc). However, our distance estimate is much smaller than that based on the Cepheid variable candidates by Hoessel et al.[1990, AJ, 100, 1151], $(m\;-\;M)_o\;=\;26.22{\pm}0.20$ (d = $1750{\pm}160$ kpc) mag. The color-magnitude diagram illustrates that the Cepheid candidates used by Hoessel et al.are not located in the Cepheid instability strip, but in the upper part of the giant branch. This result shows that the Cepheid candidates studied by Hoessel et al.are probably not Cepheids, but other types of variable stars. Taking the average of our distance estimate and Aparicio's, the distance to the Pegasus galaxy is d= $1000{\pm}80$ kpc. Considering the distance and velocity of the Pegasus galaxy with respect to the center of the Local Group, we conclude that the Pegasus galaxy is probably a member of the Local Group.

STAR FORMATION ACTIVITY OF GALAXIES IN A NEARBY COMPACT GROUP: THE NGC 4095 GROUP

POOJON, PANOMPORN,SAWANGWIT, UTANE,KRIWATTANAWONG, WICHEAN The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

This work aims to study the evolution of galaxies, located in the dense environment of the NGC 4095 compact group, which have recession velocities 6,000 < v ($km\;s^{-1}$) < 8,000. Imaging observations for BV $R_c$ broad-band, and [$S\small{II}$] and red-continuum narrow-band were carried out with the 2.4 m Thai National Telescope (TNT) at Doi Inthanon, Chiang Mai, Thailand. The sample contains 13 galaxies, consisting of 8 spirals, 4 ellipticals and 1 irregular morphological type. Late type galaxies tend to be bluer than early type galaxies. The results show that most of the late type galaxies have ongoing star formation activity, which could be triggered by galaxy-galaxy or tidal interactions, and that young massive stars in these galaxies cause their colors to be bluer than the early type galaxies.

AGE DATING GALAXY GROUPS IN THE MILLENNIUM SIMULATION

RAOUF, MOJTABA,KHOSROSHAHI, HABIB G. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We study galaxies drawn from the semi-analytic models of Guo et al. (2011) based on the Millennium Simulation. We establish a set of four observationally measurable parameters which can be used in combination to identify a subset of galaxy groups which are old, with a very high probability. We therefore argue that a sample of fossil groups selected based on the luminosity gap will result in a contaminated sample of old galaxy groups. By adding constraints on the luminosity of the brightest galaxy, and its offset from the group luminosity centroid, we can considerably improve the age-dating.

The three-dimensional structural shape of the gravitational potential in the Local Group

Lee, Bomee,Lee, Jounghun Blackwell Publishing Ltd 2008 Monthly notices of the Royal Astronomical Society Vol.389 No.2

<P>ABSTRACT</P><P>The Local Group is a small galaxy cluster with a membership of 62 nearby galaxies including the Milky Way and M31. Although the Local Group has yet to be virialized, it interacts with the surrounding matter as one gravitationally bound system. To understand the formation and evolution of the Local Group as well as its member galaxies, it is important to reconstruct the gravitational potential field from the surrounding matter distribution in the local cosmic web. By measuring the anisotropy in the spatial distribution of the Local Group galaxies, which is assumed to be induced by the local gravitational tidal field, we resolve the three-dimensional structure of the gravitational potential in the vicinity of the Milky Way smoothed on the Local Group mass scale. Our results show that (i) the minor principal axis of the Local Group tidal field is in the equatorial direction of α<SUB>p</SUB>= 15<SUP>h</SUP>00<SUP>m</SUP> and δ<SUB>p</SUB>= 20°; (ii) it has a prolate shape with axial ratio of 0.5 ± 0.13; (iii) the global tides in the Local Group are quite strong, which may provide a partial explanation for the low abundance of dwarf galaxies in the Local Group.</P>

ORIGIN AND EVOLUTION OF STRUCTURE FOR GALAXIES IN THE LOCAL GROUP

LAN, NGUYEN QUYNH,MATHEWS, GRANT J.,VINH, NGUYEN ANH,LAM, DOAN DUC The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

The Milky Way did not form in isolation, but is the product of a complex evolution of generations of mergers, collapses, star formation, supernovae and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark-matter haloes, spiral density waves, and emerging dark energy. This paper summarizes a review of recent attempts to reconstruct this complex evolution. We compare simulated properties with various observed properties of the Local Group. Among the generic features of simulated systems is the tendency for galactic halos to form within the dark matter filaments that define a supergalactic plane. Gravitational interaction along this structure leads to a streaming flow toward the two dominant galaxies in the cluster. We analyze this alignment and streaming flow and compare with the observed properties of Local-Group galaxies. Our comparison with Local Group properties suggests that some dwarf galaxies in the Local Group are part of a local streaming flow. These simulations also suggest that a significant fraction of the Galactic halo formed at large distances and arrived later along these streaming flows.