SPIRAL ARM MORPHOLOGY IN CLUSTER ENVIRONMENT

Choi, Isaac Yeoun-Gyu,Ann, Hong-Bae The Korean Astronomical Society 2011 Journal of The Korean Astronomical Society Vol.44 No.5

We examine the dependence of the morphology of spiral galaxies on the environment using the KIAS Value Added Galaxy Catalog (VAGC) which is derived from the Sloan Digital Sky Survey (SDSS) DR7. Our goal is to understand whether the local environment or global conditions dominate in determining the morphology of spiral galaxies. For the analysis, we conduct a morphological classification of galaxies in 20 X-ray selected Abell clusters up to z~0.06, using SDSS color images and the X-ray data from the Northern ROSAT All-Sky (NORAS) catalog. We analyze the distribution of arm classes along the clustercentric radius as well as that of Hubble types. To segregate the effect of local environment from the global environment, we compare the morphological distribution of galaxies in two X-lay luminosity groups, the low-$L_x$ clusters ($L_x$ < $0.15{\times}10^{44}$erg/s) and high-$L_x$ clusters ($L_x$ > $1.8{\times}10^{44}$erg/s). We find that the morphology-clustercentric relation prevails in the cluster environment although there is a brake near the cluster virial radius. The grand design arms comprise about 40% of the cluster spiral galaxies with a weak morphology-clustercentric radius relation for the arm classes, in the sense that flocculent galaxies tend to increase outward, regardless of the X-ray luminosity. From the cumulative radial distribution of cluster galaxies, we found that the low-$L_x$ clusters are fully virialized while the high-$L_x$ clusters are not.

STAR FORMING ACTIVITY OF CLUSTER GALAXIES AT z~1

KIM, JAE-WOO,IM, MYUNGSHIN,LEE, SEONG-KOOK,HYUN, MINHEE The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

The galaxy cluster is an important object for investigating the large scale structure and evolution of galaxies. Recent wide and deep near-IR surveys provide an opportunity to search for galaxy clusters in the high redshift universe. We have identified candidate clusters of 0.8< z <1.2 from the $25deg^2$ SA22 field using an optical-near-IR dataset from merged UKIDSS DXS, IMS and CFHTLS catalogs. Using these candidates, we investigate the star forming activity of member galaxies. Consequently, at z ~1, the star forming activity of cluster galaxies is not distinguishable from those of field galaxies, which is different from members in local clusters. This means the environmental effect becomes more important for $M_{\ast}>10^{10}M_{\odot}$ galaxies at z <1.

Quantifying galactic morphological transformations in the cluster environment

Cervantes‐,Sodi, B.,Park, Changbom,Hernandez, X.,Hwang, Ho Seong Blackwell Publishing Ltd 2011 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.414 No.1

<P><B>ABSTRACT</B></P><P>We study the effects of the cluster environment on galactic morphology by defining a dimensionless angular momentum parameter, λ<SUB>d</SUB>, 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. spiral/elliptical (S/E) ratios, to a more physical footing. To this end, we employ an extensive Sloan Digital Sky Survey sample (Data Release 7) with galaxies associated with Abell galaxy clusters. The sample contains 121 relaxed Abell clusters and over 51 000 individual galaxies, which guarantees a thorough statistical coverage over a wide range of physical parameters. We find that the median λ<SUB>d</SUB> value tends to decrease as we approach the cluster centre, with different dependences according to the mass of the galaxies and the hosting cluster; low‐ and intermediate‐mass galaxies show a strong dependence, while massive galaxies seem to show, at all radii, low λ<SUB>d</SUB> values. By analysing trends in λ<SUB>d</SUB> as functions of the nearest 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 (σ > 700 km s<SUP>−1</SUP>), the interaction with the cluster central region dominates, whilst in smaller clusters galaxy–galaxy interactions are chiefly responsible for driving galactic morphological transformations.</P>

ON THE FORMATION OF GIANT ELLIPTICAL GALAXIES AND GLOBULAR CLUSTERS

LEE MYUNG GYOON The Korean Astronomical Society 2003 Journal of The Korean Astronomical Society Vol.36 No.3

I review the current status of understanding when, how long, and how giant elliptical galaxies formed, focusing on the globular clusters. Several observational evidences show that massive elliptical galaxies formed at z > 2 (> 10 Gyr ago). Giant elliptical galaxies show mostly a bimodal color distribution of globular clusters, indicating a factor of $\approx$ 20 metallicity difference between the two peaks. The red globular clusters (RGCs) are closely related with the stellar halo in color and spatial distribution, while the blue globular clusters (BGCs) are not. The ratio of the number of the RGCs and that of the BGCs varies depending on galaxies. It is concluded that the BGCs might have formed 12-13 Gyr ago, while the RGCs and giant elliptical galaxies might have formed similarly 10-11 Gyr ago. It remains now to explain the existence of a gap between the RGC formation epoch and the BGC formation epoch, and the rapid metallicity increase during the gap (${\Delta}t{\approx}$ 2 Gyr). If hierarchical merging can form a significant number of giant elliptical galaxies > 10 Gyr ago, several observational constraints from stars and globular clusters in elliptical galaxies can be explained.

STAR FORMATION ACTIVITY OF GALAXIES UNDERGOING RAM PRESSURE STRIPPING IN THE VIRGO CLUSTER

문재연,황호성,Myung Gyoon Lee,정애리,Hyein Yoon,Jong Chul Lee 한국천문학회 2021 Journal of The Korean Astronomical Society Vol.54 No.1

We study galaxies undergoing ram pressure stripping in the Virgo cluster to examine whether we can identify any discernible trend in their star formation activity. We first use 48 galaxies undergoing different stages of stripping based on HⅠ morphology, HⅠ deficiency, and relative extent to the stellar disk, from the VIVA survey. We then employ a new scheme for galaxy classification which combines HⅠ mass fractions and locations in projected phase space, resulting in a new sample of 365 galaxies. We utilize a variety of star formation tracers, which include g - r, WISE [3.4]-[12] colors, and starburstiness that are defined by stellar mass and star formation rates to compare the star formation activity of galaxies at different stripping stages. We find no clear evidence for enhancement in the integrated star formation activity of galaxies undergoing early to active stripping. We are instead able to capture the overall quenching of star formation activity with increasing degree of ram pressure stripping, in agreement with previous studies. Our results suggest that if there is any ram pressure stripping induced enhancement, it is at best locally modest, and galaxies undergoing enhancement make up a small fraction of the total sample. Our results also indicate that it is possible to trace galaxies at different stages of stripping with the combination of HⅠ gas content and location in projected phase space, which can be extended to other galaxy clusters that lack high-resolution HⅠ imaging.

The <i>UV</i>–optical colour dependence of galaxy clustering in the local universe

Loh, Yeong-Shang,Rich, R. Michael,Heinis, Sé,bastien,Scranton, Ryan,Mallery, Ryan P.,Salim, Samir,Martin, D. Christopher,Wyder, Ted,Arnouts, Sté,phane,Barlow, Tom A.,Forster, Karl,Friedman Blackwell Publishing Ltd 2010 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.407 No.1

<P>ABSTRACT</P><P>We measure the UV-optical colour dependence of galaxy clustering in the local Universe. Using the clean separation of the red and blue sequences made possible by the <I>NUV</I>−<I>r</I> colour–magnitude diagram, we segregate the galaxies into red, blue and intermediate ‘green’ classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that ξ(<I>r</I><SUB>p</SUB>, π) for both red and green galaxies shows strong redshift-space distortion on small scales – the ‘finger-of-God’ effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, ξ(<I>r</I><SUB>p</SUB>, π) for all three samples show the effect of large-scale streaming from coherent infall. On scales of 1 <I>h</I><SUP>−1</SUP> Mpc < <I>r</I><SUB>p</SUB> < 10 <I>h</I><SUP>−1</SUP> Mpc, the projected auto-correlation function <I>w</I><SUB>p</SUB>(<I>r</I><SUB>p</SUB>) for red and green galaxies fits a power law with slope γ∼ 1.93 and amplitude <I>r</I><SUB>0</SUB>∼ 7.5 and 5.3, compared with γ∼ 1.75 and <I>r</I><SUB>0</SUB>∼ 3.9 <I>h</I><SUP>−1</SUP> Mpc for blue sequence galaxies. Compared to the clustering of a fiducial <I>L</I>* galaxy, the red, green and blue have a relative bias of 1.5, 1.1 and 0.9, respectively. The <I>w</I><SUB>p</SUB>(<I>r</I><SUB>p</SUB>) for blue galaxies display an increase in convexity at ∼ 1 <I>h</I><SUP>−1</SUP> Mpc, with an excess of large-scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive haloes, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and colour.</P>

CORRELATION FUNCTIONS OF THE ABELL, APM, AND X-RAY CLUSTERS OF GALAXIES

LEE SUNGHO,PARK CHANGBOM The Korean Astronomical Society 2002 Journal of The Korean Astronomical Society Vol.35 No.3

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 $\ge$ 70 (as defined by the APM team) is found to be $r_0 = 25.4_{-3.0}^{+3.1}\;h^{-1}$ 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 $\ge$ 0 and 1 are measured to be $r_0 = 17.4_{-1.1}^{+1.2}$ 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 $r_0= 0.40d_c + 3.2$ 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 $L_x {\ge}0.65{\times} 10^{44}\;h^{-2}erg\;s^{-1}$ is $30.3_{-6.5}^{+8.2}\;h^{-1}$ Mpc, and that of the BCS clusters with $L_x {\ge}0.70{\times} 10^{44}\;h^{-2}erg\;s^{-1}$ is $30.2_{-8.9}^{+9.8}\;h^{-1}$ Mpc. The clustering strength of the X-ray clusters is much weaker than what is expected from the optical clusters.

PANORAMIC VIEWS OF GALAXY CLUSTER EVOLUTION: GALAXY ECOLOGY

Kodama, Tadayuki,Koyama, Yusei,Hayashi, Masao,Ken-ichi, Tadaki The Korean Astronomical Society 2010 天文學論叢 Vol.25 No.3

Taking the great advantage of Subaru's wide field coverage both in the optical and in the near infrared, we have been providing panoramic views of distant clusters and their surrounding environments over the wide redshift range of 0:4 < z < 3. From our unique data sets, a consistent picture has been emerging that the star forming activity is once enhanced and then truncated in galaxy groups in the outskirts of clusters during the course of cluster assembly at z < 1. Such activity is shifted into cluster cores as we go further back in time to z ~ 1.5. At z = 2 - 2.5, we begin to enter the epoch when massive galaxies are actually forming in the cluster core. And by z ~ 3, we eventually go beyond the major epoch of massive galaxy formation. It is likely that the environmental dependence of star forming activity is at least partly due to the external environmental effects such as galaxy-galaxy interaction in medium density regions at z < 1, while the intrinsic effect of galaxy formation bias overtakes the external effect at higher redshifts, resulting in a large star formation activity in the cluster center.

A WFC3 study of globular clusters in NGC 4150: an early‐type minor merger

Kaviraj, Sugata,Crockett, R. Mark,Whitmore, Bradley C.,Silk, Joseph,O’Connell, Robert W.,Windhorst, Rogier A.,Mutchler, Max,Rejkuba, Marina,Yi, Sukyoung,Frogel, Jay A.,Calzetti, Daniela Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society. Vol.422 No.1

<P><B>ABSTRACT</B></P><P>We combine near‐ultraviolet (NUV; 2250 Å) and optical (<I>U</I>, <I>B</I>, <I>V</I>, <I>I</I>) imaging from the Wide Field Camera 3 (WFC3), on‐board the <I>Hubble Space Telescope</I> (<I>HST</I>), to study the globular cluster (GC) population in NGC 4150, a sub‐L* (<I>M</I><SUB><I>B</I></SUB>∼−18.48 mag) early‐type minor‐merger remnant in the Coma I cloud. We use broad‐band NUV–optical photometry from the WFC3 to estimate individual ages, metallicities, masses and line‐of‐sight extinctions [<I>E</I>(<I>B</I>−<I>V</I>)] for 63 bright (<I>M</I><SUB><I>V</I></SUB> < −5 mag) GCs in this galaxy. In addition to a small GC population with ages greater than 10 Gyr, we find a dominant population of clusters with ages centred around 6 Gyr, consistent with the expected peak of stellar mass assembly in faint early types residing in low‐density environments. The old and intermediate‐age GCs in NGC 4150 are metal poor, with metallicities less than 0.1 Z<SUB>⊙</SUB>, and reside in regions of low extinction [<I>E</I>(<I>B</I>−<I>V</I>) < 0.05 mag]. We also find a population of young, metal‐rich (<I>Z</I> > 0.3 Z<SUB>⊙</SUB>) clusters that have formed within the last Gyr and reside in relatively dusty [<I>E</I>(<I>B</I>−<I>V</I>) > 0.3 mag] regions that are coincident with the part of the galaxy core that hosts significant recent star formation. Cluster disruption models (in which ∼80–90 per cent of objects younger than a few ×10<SUP>8</SUP> yr dissolve every dex in time) suggest that the bulk of these young clusters are a transient population.</P>

Unveiling the 3D temperature structure of galaxy clusters by means of the thermal Sunyaev–Zel’dovich effect

Prokhorov, D. A.,Dubois, Y.,Nagataki, S.,Akahori, T.,Yoshikawa, K. Blackwell Publishing Ltd 2011 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.415 No.3

<P><B>ABSTRACT</B></P><P>The Sunyaev–Zel’dovich (hereinafter SZ) effect is a promising tool to derive the gas temperature of galaxy clusters. Approximation of a spherically symmetric gas distribution is usually used to determine the temperature structure of galaxy clusters, but this approximation cannot properly describe merging galaxy clusters. The methods used so far, which do not assume the spherically symmetric distribution, permit us to derive 2D temperature maps of merging galaxy clusters. In this paper, we propose a method to derive the standard temperature deviation and temperature variance along the line of sight, which permits us to analyse the 3D temperature structure of galaxy clusters by means of the thermal SZ effect. We also propose a method to reveal merger shock waves in galaxy clusters by analysing the presence of temperature inhomogeneities along the line of sight.</P>