Auswahl der wissenschaftlichen Literatur zum Thema „Z-cluster“

ABSTRACT We study brightest cluster galaxies (BCGs) in ∼5000 galaxy clusters from the Hyper Suprime-Cam (HSC) Subaru Strategic Program. The sample is selected over an area of 830 deg2 and is uniformly distributed in redshift over the range of z = 0.3−1.0. The clusters have stellar masses in the range of 1011.8−1012.9M⊙. We compare the stellar mass of the BCGs in each cluster to what we would expect if their masses were drawn from the mass distribution of the other member galaxies of the clusters. The BCGs are found to be ‘special’, in the sense that they are not consistent with being a statistical extreme of the mass distribution of other cluster galaxies. This result is robust over the full range of cluster stellar masses and redshifts in the sample, indicating that BCGs are special up to a redshift of z = 1.0. However, BCGs with a large separation from the centre of the cluster are found to be consistent with being statistical extremes of the cluster member mass distribution. We discuss the implications of these findings for BCG formation scenarios.

Abstract The current consensus on the formation and evolution of the brightest cluster galaxies is that their stellar mass forms early ($z$ ≳ 4) in separate galaxies that then eventually assemble the main structure at late times ($z$ ≲ 1). However, advances in observational techniques have led to the discovery of protoclusters out to $z$ ∼ 7. If these protoclusters assemble rapidly in the early Universe, they should form the brightest cluster galaxies much earlier than suspected by the late-assembly picture. Using a combination of observationally constrained hydrodynamical and dark-matter-only simulations, we show that the stellar assembly time of a sub-set of brightest cluster galaxies occurs at high redshifts ( $z$ > 3) rather than at low redshifts ($z$ < 1), as is commonly thought. We find, using isolated non-cosmological hydrodynamical simulations, that highly overdense protoclusters assemble their stellar mass into brightest cluster galaxies within ∼1 Gyr of evolution – producing massive blue elliptical galaxies at high redshifts ($z$ ≳ 1.5). We argue that there is a downsizing effect on the cluster scale wherein some of the brightest cluster galaxies in the cores of the most-massive clusters assemble earlier than those in lower mass clusters. In those clusters with $z$ = 0 virial mass ≥ 5 × 1014 M⊙, we find that $9.8{{\ \rm per\ cent}}$ have their cores assembly early, and a higher fraction of $16.4{{\ \rm per\ cent}}$ in those clusters above 1015 M⊙. The James Webb Space Telescope will be able to detect and confirm our prediction in the near future, and we discuss the implications to constraining the value of σ8.

ABSTRACT We first present a catalogue of photometric redshifts for 14.68 million galaxies derived from the 7-band photometric data of Hyper Suprime-Cam Subaru Strategic Program and the Wide-field Infrared Survey Explorer using the nearest-neighbour algorithm. The redshift uncertainty is about 0.024 for galaxies of z ≤ 0.7, and steadily increases with redshift to about 0.11 at z ∼ 2. From such a large data set, we identify 21 661 clusters of galaxies, among which 5537 clusters have redshifts z > 1 and 642 clusters have z > 1.5, significantly enlarging the high redshift sample of galaxy clusters. Cluster richness and mass are estimated, and these clusters have an equivalent mass of M500 ≥ 0.7 × 1014 M⊙. We find that the stellar mass of the brightest cluster galaxies (BCGs) in each richness bin does not significantly evolve with redshift. The fraction of star-forming BCGs increases with redshift, but does not depend on cluster mass.

ABSTRACT Contradictory results have been reported on the time evolution of the alignment between clusters and their brightest cluster galaxy (BCG). We study this topic by analysing cosmological hydrosimulations of 24 massive clusters with $M_{200}|_{z=0} \gtrsim 10^{15}\, \rm {\, M_{\odot }}$, plus 5 less massive with $1 \times 10^{14} \lesssim M_{200}|_{z=0} \lesssim 7 \times 10^{14}\, \rm {\, M_{\odot }}$, which have already proven to produce realistic BCG masses. We compute the BCG alignment with both the distribution of cluster galaxies and the dark matter (DM) halo. At redshift z = 0, the major axes of the simulated BCGs and their host cluster galaxy distributions are aligned on average within 20°. The BCG alignment with the DM halo is even tighter. The alignment persists up to z ≲ 2 with no evident evolution. This result continues, although with a weaker signal, when considering the projected alignment. The cluster alignment with the surrounding distribution of matter (3R200) is already in place at z ∼ 4 with a typical angle of 35°, before the BCG–cluster alignment develops. The BCG turns out to be also aligned with the same matter distribution, albeit always to a lesser extent. These results taken together might imply that the BCG–cluster alignment occurs in an outside–in fashion. Depending on their frequency and geometry, mergers can promote, destroy or weaken the alignments. Clusters that do not experience recent major mergers are typically more relaxed and aligned with their BCG. In turn, accretions closer to the cluster elongation axis tend to improve the alignment as opposed to accretions closer to the cluster minor axis.

Abstract We estimate the mass accretion rate (MAR) of 321 clusters of galaxies in the HectoMAP Cluster Survey. The clusters span the redshift range 0.17–0.42 and the M 200 mass range ≈ (0.5–3.5) × 1014 M ⊙. The MAR estimate is based on the caustic technique along with a spherical infall model. Our analysis extends the measurement of MARs for 129 clusters at z < 0.3 from the Cluster Infall Regions in the Sloan Digital Sky Survey and the Hectospec Cluster Survey to redshift z ∼ 0.42. Averaging over redshift, low-mass clusters with masses near 0.7 × 1014 M ⊙ roughly accrete 3 × 104 M ⊙ yr−1; more massive clusters with masses near 2.8 × 1014 M ⊙ roughly accrete 1 × 105 M ⊙ yr−1. Low- and high-mass clusters increase their MAR by approximately 46% and 84%, respectively, as the redshift increases from z in the range 0.17–0.29 to z in the range 0.34–0.42. The MARs at fixed redshift increase with mass and MARs at fixed mass increase with redshift in agreement with the ΛCDM cosmological model for hierarchical structure formation. We consider the extension of MAR measurements to z ∼ 1.

Abstract To understand structure formation in the universe and impose stronger constraints on the cluster mass function and cosmological models, it is important to have large galaxy cluster catalogs. The Swift AGN and Cluster Survey is a serendipitous X-ray survey aimed at building a large statistically selected X-ray cluster catalog with 442 cluster candidates in its first release. Our initial SDSS follow-up study confirmed 50% of clusters in the Sloan Digital Sky Survey footprint as z < 0.5 clusters. Here we present further optical follow-up analysis of 248 (out of 442) cluster candidates from the Swift cluster catalog using multiband imaging from the MDM 2.4 m telescope and the Pan-STARRS survey. We report the optical confirmation of 55 clusters with >3σ galaxy overdensities and detectable red sequences in the color–magnitude space. The majority of these confirmed clusters have redshifts z < 0.6. The remaining candidates are potentially higher-redshift clusters that are excellent targets for infrared observations. We report the X-ray luminosity and the optical richness for these confirmed clusters. We also discuss the distinction between X-ray and optical observables for the detected and nondetected cluster candidates.

Context. In the currently debated context of using clusters of galaxies as cosmological probes, the need for well-defined cluster samples is critical. Aims. The XXL Survey has been specifically designed to provide a well characterised sample of some 500 X-ray detected clusters suitable for cosmological studies. The main goal of present article is to make public and describe the properties of the cluster catalogue in its present state, as well as of associated catalogues of more specific objects such as super-clusters and fossil groups. Methods. Following from the publication of the hundred brightest XXL clusters, we now release a sample containing 365 clusters in total, down to a flux of a few 10−15 erg s−1 cm−2 in the [0.5–2] keV band and in a 1′ aperture. This release contains the complete subset of clusters for which the selection function is well determined plus all X-ray clusters which are, to date, spectroscopically confirmed. In this paper, we give the details of the follow-up observations and explain the procedure adopted to validate the cluster spectroscopic redshifts. Considering the whole XXL cluster sample, we have provided two types of selection, both complete in a particular sense: one based on flux-morphology criteria, and an alternative based on the [0.5–2] keV flux within 1 arcmin of the cluster centre. We have also provided X-ray temperature measurements for 80% of the clusters having a flux larger than 9 × 10−15 erg s−1 cm−2. Results. Our cluster sample extends from z ~ 0 to z ~ 1.2, with one cluster at z ~ 2. Clusters were identified through a mean number of six spectroscopically confirmed cluster members. The largest number of confirmed spectroscopic members in a cluster is 41. Our updated luminosity function and luminosity–temperature relation are compatible with our previous determinations based on the 100 brightest clusters, but show smaller uncertainties. We also present an enlarged list of super-clusters and a sample of 18 possible fossil groups. Conclusions. This intermediate publication is the last before the final release of the complete XXL cluster catalogue when the ongoing C2 cluster spectroscopic follow-up is complete. It provides a unique inventory of medium-mass clusters over a 50 deg2 area out to z ~ 1.

SummaryWe present the results of several surveys for supernovae (SNe) in galaxy clusters. SNe discovered in deep, archival HST images were used to measure the cluster SN Ia rate to z = 1. A search for SNe in nearby (0.06 ≤ z ≤ 0.2) Abell galaxy clusters yielded 15 SNe, 12 of which were spectroscopically confirmed. Of these, 7 are cluster SNe Ia, which we will use to measure the SN Ia rate in nearby clusters. This search has also discovered the first convincing examples of intergalactic SNe. We conclude with a brief description of ongoing and future cluster SN surveys.

Abstract We apply a friends-of-friends (FoF) algorithm to identify galaxy clusters and we use the catalog to explore the evolutionary synergy between brightest cluster galaxies (BCGs) and their host clusters. We base the cluster catalog on the dense HectoMAP redshift survey (2000 redshifts deg−2). The HectoMAP FoF catalog includes 346 clusters with 10 or more spectroscopic members within the range 0.05 < z < 0.55 and with a median z = 0.29. We list these clusters and their members. We also include central velocity dispersions (σ *,BCG) for the FoF cluster BCGs, a distinctive feature of the HectoMAP FoF catalog. HectoMAP clusters with higher galaxy number density (80 systems) are all genuine clusters with a strong concentration and a prominent BCG in Subaru/Hyper Suprime-Cam images. The phase-space diagrams show the expected elongation along the line of sight. Lower-density systems include some low reliability systems. We establish a connection between BCGs and their host clusters by demonstrating that σ *,BCG /σ cl decreases as a function of cluster velocity dispersion (σ cl), in contrast, numerical simulations predict a constant σ *,BCG/σ cl. Sets of clusters at two different redshifts show that BCG evolution in massive systems is slow over the redshift range z < 0.4. The data strongly suggest that minor mergers may play an important role in BCG evolution in clusters with σ cl ≳ 300 km s−1. For lower mass systems (σ cl < 300 km s−1), major mergers may play a significant role. The coordinated evolution of BCGs and their host clusters provides an interesting test of simulations in high-density regions of the universe.

We present the first results from a galaxy population study in the highest redshift galaxy clusters identified in the 2500 deg2 South Pole Telescope Sunyaev Zel’dovich effect (SPT-SZ) survey, which is sensitive to M500 ≳ 3 × 1014 M⊙ clusters from z ∼ 0.2 out to the highest redshifts where such massive structures exist. The cluster selection is to first order independent of galaxy properties, making the SPT-SZ sample particularly well suited for cluster galaxy population studies. We carried out a four-band imaging campaign with the Hubble and Spitzer Space Telescopes of the five z ≳ 1.4, S/NSZE > 5 clusters, that are among the rarest most massive clusters known at this redshift. All five clusters show clear overdensities of red galaxies whose colors agree with the initial cluster redshift estimates, although one (SPT-CLJ0607–4448) shows a galaxy concentration much less prominent than the others. The highest redshift cluster in this sample, SPT-CLJ0459–4947 at z ∼ 1.72, is the most distant M500 > 1014 M⊙ cluster discovered thus far through its intracluster medium, and is one of only three known clusters in this mass range at z ≳ 1.7, regardless of selection. Based on UVJ-like photometric classification of quiescent and star-forming galaxies, we find that the quiescent fraction in the cluster central regions (r/r500 < 0.7) is higher than in the field at the same redshift, with corresponding environmental quenching efficiencies typically in the range ∼0.5 − 0.8 for stellar masses log(M/M⊙) > 10.85. We have explored the impact of emission from star formation on the selection of this sample, concluding that all five clusters studied here would still have been detected with S/NSZE> 5, even if they had the same quiescent fraction as measured in the field. Our results thus point towards an efficient suppression of star formation in the central regions of the most massive clusters, occurring already earlier than z ∼ 1.5.

We present a detailed study of the colours of late-type galaxy discs for ten of the EDisCS galaxy clusters with 0.5 less than or similar to z less than or similar to 0.8. Our cluster sample contains 172 spiral galaxies, and our control sample is composed of 96 field disc galaxies. We deconvolved their ground-based V and I images obtained with FORS2 at the VLT with initial spatial resolutions between 0.4 and 0.8 arcsec to achieve a final resolution of 0.1 arcsec with 0.05 arcsec pixels, which is close to the resolution of the ACS at the HST. After removing the central region of each galaxy to avoid pollution by the bulges, we measured the V - I colours of the discs. We find that 50% of cluster spiral galaxies have disc V - I colours redder by more than 1 sigma of the mean colours of their field counterparts. This is well above the 16% expected for a normal distribution centred on the field disc properties. The prominence of galaxies with red discs depends neither on the mass of their parent cluster nor on the distance of the galaxies to the cluster cores. Passive spiral galaxies constitute 20% of our sample. These systems are not abnormally dusty. They are are made of old stars and are located on the cluster red sequences. Another 24% of our sample is composed of galaxies that are still active and star forming, but less so than galaxies with similar morphologies in the field. These galaxies are naturally located in the blue sequence of their parent cluster colour-magnitude diagrams. The reddest of the discs in clusters must have stopped forming stars more than similar to 5 Gyr ago. Some of them are found among infalling galaxies, suggesting preprocessing. Our results confirm that galaxies are able to continue forming stars for some significant period of time after being accreted into clusters, and suggest that star formation can decline on seemingly long (1 to 5 Gyr) timescales.

We present an investigation into the environments of quasars with respect to galaxy clus- ters, and environment evolution with redshift and luminosity. The positions of quasars with respect to clusters have been studied using cluster and quasar catalogues available, covering the redshift range 0.2 < z < 1.2. The 2D projected separations and the 3D separations have been found and the orientation of the quasar with respect to the major axis of the closest cluster calculated, introducing new information to previous work. The positions of quasars with respect to clusters of galaxies will give an indication of the large scale environment of quasars and potentially clues as to which formation mechanisms are likely to dominate at various redshifts. For example, galaxy mergers are most likely to occur in galaxy group environments and will create luminous quasars. Galaxy harassment is more likely to occur on the outskirts of galaxy clusters and create lower luminosity AGN. Secular processes such as bar instability can also create AGN and are likely to be the cause of nuclear activity in isolated galaxies. The aim of this work is to study the large scale environment over a large redshift range and study the evolution as well as any change in environment with quasar luminosity and redshift. Another aim of this work is to study the orientation of a quasar with respect to a galaxy cluster. If galaxy clusters lie orientated along filaments, the position of a quasar with respect to a cluster will give an indication as to where quasars lie with respect to the filament and therefore the large scale structure. There is a deficit of quasars lying close to cluster centres for 0.4 < z < 0.8, indicating a preference for less dense environments, in agreement with previous work. Studying the separations as a function of cluster richness, there was a change in quasars lying closer to poorer clusters for z < 0.2 (Lietzen et al. 2009) to lying closer to richer clusters for 0.2 < z < 0.4, though more clusters at low redshifts will be needed to confirm this. There is no obvious relation between the orientation angle between a quasar and the major axis of the closest galaxy cluster and 2D projected separations. Using faint (Mr > −23.0 mag) and bright (Mr < −23.0 mag) quasars, there is no difference between the two magnitude samples for the 2D separations or the cluster richness, in contrast to Strand et al. (2008) who found brighter quasars lying in denser environments than dimmer quasars. These is no change with redshift (over 0 < z < 1.2) in the positions of the quasars with respect to the cluster or the cluster richness as a function of absolute quasar magnitude. There is also no preferred orientation between the quasar and the cluster major axis for bright or faint quasars. Spectra of a selection of 680 star forming galaxies, red galaxies, and AGN were taken by Luis Campusano and Ilona S¨ochting and 515 redshifts calculated. Though few of these galaxies turned out to be cluster members as was originally intended, it was possible to use these galaxies to study the environments of quasars with respect to star-forming galaxies and galaxy clusters. The objects were classified (33 classed as AGN), and star formation rates calculated and compared. Three AGN and 10 star forming galaxies lie at the same redshift (z = 0.29) as three galaxy clusters. The three galaxy clusters have the same orientation angle and may be part of a filament along with the star forming galaxies and AGN. Further study will investigate the relation between AGN positions and filaments of structure. A sample of quasar spectra taken by Lutz Haberzettl using Hectospec on the MMT were taken to increase the number of quasars used in this study. However, when studying the spectra, a number of high redshift quasars showed evidence of ultra-strong UV Feii emission in their spectra. The redshifts of these quasars were too high to be included in the main body of the study. However, a significantly large number of ultra-strong UV Feii emitting quasars have been found in the direction of three LQGs in the redshift range 1.1 < z < 1.6, including the Clowes-Campusano Large Quasar Group (CCLQG). Ly� fluorescence can increase the UV Feii emission. However, Ly� emission from other quasars was found to be negligible compared to emission from the quasar’s central source. Though there has been no previous indication that the LQG environment is unique, the high level of iron emission may indicate a difference in environment. Plans for future work based on these results are outlined.

2002/2003
Il lavoro di questa tesi è basato sull'analisi dell'ammasso di galassie ABCG 209, a zrv 0.2, che e' caratterizzato da una forte evoluzione dinamica. Lo studio si basa su dati ottici nuovi (EMMI-NTT: immagini nelle bande B, V e R, e spettri MOS) acquisiti in ottobre 2001 all'osservatorio europeo del sud (ESO) in Cile. Sono stati analizzati, inoltre, dati ottici di archivio (immagini a grande campo nelle bande B ed R del CFHR12k), dati X-ray (Chandra) e osservazioni (VLA). Lo scopo principale di questa analisi è lo studio della relazione tra la dinamica degli ammassi e la storia di formazione stellare delle galassie, al fine di capire i complessi meccanisn1i della formazione e dell'evoluzione degli ammassi. Sulla base di 112 spettri di galassie di ammasso è stata studiata la dinamica interna di ABCG 209. Questa analisi ha mostrato che l'ammasso è caratterizzato da un valore particolarmente alto della dispersione di velocità lungo la linea di vista: av = 1250-1400 km s- 1 , che implica un valore della massa viriale pari a M = 1.6-2.2 x 1015 h- 1 M0 all'interno di un raggio viriale, Rvir· Inoltre, l'ammasso presenta un'elongazione lungo la direzione SE-NW, come mostrato da: a) la presenza di un gradiente di velocità; b) l'elongaziòne della distribuzione spaziale delle galassie di ammasso selezionate in base alla sequenza della colore-magnitudine; c) l'elongazione dei contorni dell'emissione X; d) l'allungamento della galassia centrale dominante (cD). La presenza di sottostrutture è indicata sia dalla non-gaussianità della distribuzione delle velocità, che presenta due sottogruppi spazialmente segregati a z = 0.199 e z = 0.215, sia dal test di Dressler & Schectrnan in 3 dimensioni, che utilizza contemporaneamente l'informazione in ascensione retta e declinazione, e quella in velocità. Infine le galassie selezionate in base alla colore-magnitudine presentano una segregazione in luminosità, ovvero le galassie brillanti R < 19.5 sono concentrate intorno alla galassia cD, mentre quelle deboli R > 19.5 mostrano dei sottogruppi, dei quali quello più ad est coincide con il picco secondario dell'emissione X. Lo studio della funzione di luminosità (LF) nelle bande B, V ed R, ha mostrato che l'ammasso presenta caratteristiche intermedie tra un ammasso ricco rilassato ed un ammasso irregolare, dinamic; unente giovane. Questi risultati suggeriscono che ABCG 209 è un ammasso che si sta ancora evolvendo dinamicamente, in cui vi è stato un merging di due o più sottogruppi lungo la direzione SE-NW, in un piano non parallelo a quello del cielo. Il merging potrebbe essere in uno stadio avanzato in cui le galassie luminose tracciano la struttura del sottogruppo che ospitava la galassie centrale dominante prima del rnerging. L'elongazione e l'asimmetria della distribuzione di galassie e dell'emissione X, e la forma della funzione di luminosità indicano, infine, che l'ammasso non è ancora rilassato. L'effetto dell'ambiente (valutato in termini di densità superficiale locale delle galassie con magnitudini R < 23.0) sulle proprietà globali dell'ammasso è stato esaminato mediante l'analisi delle funzioni di luminosità, delle relazioni colore-magnitudine, e dei colori medi dell'ammasso, usando immagini a grande campo (30'x42') nelle bande B ed R. La funzione di luminosità dipende fortemente dall'ambiente, in particolare la slope diventa sempre più ripida andando dalle regioni ad alta densità a quelle a bassa densità (livelli di confidenza maggiori di 3o-). Inoltre la sequenza della relazione colore-magnitudine è 0.022 ± 0.014 mag più rossa nelle regioni a densità alta rispetto a quelle a densità intermedia, e la frazione di galassie blu decresce monotonicamente con la densità, in accordo con altri studi. Tutti questi risultati sono comprensibili sulla base della relazione densità-morfologia, per la quale la frazione di galassie early-type, caratterizzate da colori rossi e funzioni di luminosità piatte, decresce lentamente e monotonicamente dalle regioni ad alta densità a quelle a bassa densità; mentre la frazione di galassie late-type, che sono blu ed hanno funzioni di luminosità ripide, cresce. L'analisi dei colori medi delle galassie luminose (R < 21) in funzione della loro posizione spaziale mostra chiaramente i complessi effetti dell'ambiente e dell'evoluzione dinamica dell'ammasso sulle galassie che lo costituiscono. Le galassie più rosse sono concentrate attorno alla cD e in una regione a 5 arcmin dal centro, coincidente con la sottostruttura prevista dal weak lensing. L'effetto di una direzione preferenziale SE-NW per ABCG 209 è evidente nella presenza di galassie blu brillanti vicino alla cD lungo perpendicolarmente alla direzione di allungamento, e quindi non affette dal merging, e nell'estensione delle galassie rosse a SE che potrebbe indicare un gruppo di galassie che sta cadendo sull'amn1asso lungo il filamento. L'allungamento dell'ammasso lungo la direzione SE-NW sen1bra anche legato alla struttura a larga scala in cui ABCG 209 è vicino a due ammassi ricchi ABCG 222 az= 0.211 e ABCG 223 a z = 0.2070, che si trovano a 1.5° (15 Mpc) a NW lungo questo asse preferenziale. La dinamica degli ammassi e la struttura a larga scala hanno una forte influenza sull'evoluzione delle galassie. Per questo motivo è stato fatto uno studio dettagliato delle proprietà spettroscopiche di 102 galassie membro dell'ammasso. Sono state individuati cinque differenti tipi di galassie: i) galassie che evolvono passivamente (E), che hanno colori rossi e non presentano nel loro spettro righe di emissione, ii) galassie con righe di emissione (ELG), che sono blu, iii-iv) galassie con profonde righe di assorbimento H5, che possono essere divise in due gruppi: blu (HDSblue) e rosse (HDSred), in base al loro colore B-R ed al break a 4000 A v) e infine galassie a spirale anemiche (Ab-spirals), che hanno proprietà spettrali uguali a quelle della galassie passive, ma sono sistemi a disco. Queste differenti classi spettrali sono fortemente segregate nello spazio delle fasi, in accordo con il test di Kolmogorov & Smirnov in 2 dimensioni. Le galassie che evolvono passivamente rappresentano il 74% delle galassie di ammasso esaminate. Questa popolazione si è formata molto presto, durante il collasso iniziale dell'ammasso. Queste galassie si trovano principalmente nella regione ad alta densità ed hanno una dispersione di velocità consistente con quella totale dell'ammasso. Questo risultato è comprensibile sulla base del modello cos1nologico di formazione della struttura a larga scala, secondo il quale le galassie early-type si formano nelle regioni di più alta densità, corrispondenti alle zone centrali degli ammassi. Le galassie HDSred sono distribuite lungo l'allungamento dell'ammasso, principalmente in regioni a densità intermedia ed hanno una bassa dispersione di velocità, che suggerisce che questa popolazione sia il nucleo di un gruppo che è caduto sull'ammasso. Sulla base dei modelli di evoluzione delle galassie, la presenza di forti righe di assorbimento H 6 nei loro spettri, indica che queste galassie hanno sperimentato un piccolo burst di formazione stellare pochi Gyrs fa. In particolare sulla base di un modello di starburst l'aver osservato [H6] > 3.0 A implica che il burst deve essere avvenuto non più di 2 Gyrs fa. Le galassie HDSblue si trovano in regioni a densità intermedia, 1na lungo una direzione perpendicolare a quella di allungamento dell'ammasso, vicine al picco secondario dell'emissione X, ed in una regione in cui l'intracluster medium è particolarmente denso. Queste galassie sono caratterizzate da un'alta dispersione di velocità. Le galassie con righe di emissione si trovano principalmente nelle regioni a bassa densità e hanno alta dispersione di velocità. Sia la posizione spaziale, che la dispersione di velocità di queste ultime due classi di galassie indicano che queste potrebbero essere due popolazioni recentemente cadute nell'ammasso dal campo. Tutti questi risultati indicano uno scenario evolutivo in cui ABCG 209 è caratterizzato principalmente dalla sovrapposizione di due componenti: una popolazione di galassie vecchie che si sono forrr1ate molto presto (zJ ;G 3), ed una popolazione più giovane di galassie che sono state accresciute dal campo. Inoltre, l'ammasso potrebbe aver sperimentato un merging con un gruppo l o 2 Gyrs fa, come indicato anche precedentemente dall'analisi dinamica. Questo studio dettagliato ha mostrato chiaramente l'importanza di avere dati multi-banda e di un approccio multi-direzionale nello studio di questi sistemi così complessi. E', a questo punto, fondamentale estendere questo tipo di analisi ad altri ammassi a redshifts maggiori, e con differenti proprietà dinamiche. Per rispondere definitivamente alla domanda se gli ammassi sono generalmente giovani o vecchi è necessario avere informazioni sulle proprietà di un gran numero di ammassi e contemporaneamente studiare in dettaglio le componenti appartenenti a diverse strutture ed ambienti in un singolo ammasso.
The thesis work is focused on the analysis of the galaxy clusters ABCG 209, at zrv 0.2, which is characterized by a strong dynamical evolution. The data sample used is based mainly on new optical data (EMMI-NTT: B, V and R band images and MOS spectra), acquired in October 2001 at the European Southern Observatory in Chile. Archive optical data ( CFHR12k: B and R images), and X-ray (Chandra) and radio (VLA) observations are also analysed. The n1ain goal of this analysis is the investigation of the connection between internal cluster clynamics and star formation history, aimed at understanding the complex mechanisms of cluster formation and evolution. The internal dynamics of the cluster was studied through a spectroscopic survey of 112 cluster Inembers. The dynamical analysis has pointed out that ABCG 209 is characterized by a very high value of the line of sight velocity dispersion: av = 1250-1400 km s- 1that results in a virial mass of M = 1.6-2.2 x 1015 h-1 M0 within Rvir· A preferential SE-NW direction is indicated by: a) the presence of a velocity gradient in the velocity field; b) the elongation in the spatial distribution of colour-selected cluster members; c) the elongation of the X-ray contour levels in the Chandra image; d) the elongation of the cD galaxy. T h ere is evidence of substructure, as shown by i) significant cleviation of the velocity distribution from a Gaussian, with evidence for two secondary clumps at z = 0.199 and z = 0.215, which appear spatially segregated from the main cluster, ii) the Dressler & Schectman test and iii) the two-dimensional distribution of the colour-selected members shows a strong luminosity segregation: bright galaxies R < 19.5 are centered around the cD galaxy, while faint galaxies R > 19.5 show some clumps. The main one, Eastern with respect to the cD galaxy, is well coincident with the secondary X -ray peak. ' The study of the galaxy luminosity function (LF) in B, V and R bands has pointed out that ABCG 209 is a cluster with intermediate characteristic between a dynamically-evolved, rich clusters and clusters with central dominant galaxies having bright characteristic luminosities and shallow faint-end slopes and less evolved clusters, characterized by steep faint-end slopes, thus reconciling the asynnnetric properties of X-ray emission with the non flat-LF shape of irregular systen1s. This observational scenario suggests that ABCG 209 is undergoing a strong dynan1ical evolution with the Inerging of two or more subclumps along the SE-NW direction in a plane which is not parallel to the plane of sky. The merging might be in a more advanced status, where luminous galaxies trace the remnant of the core-halo structure of a pre-merging clump hosting the cD galaxy. The elongation and asymmetry of the galaxy distribution (of the X-ray emission) and the shape of the LFs show that ABCG 209 is not yet a fully relaxed system. The effect of cluster environment (as measured in terms of the local surface density of R < 23.0 galaxies) o n the global properties of the cluster galaxies is examined through the analysis of the L Fs, colour-magnitude relations, and average colours by using wide field (30'x42') B- and R-band images. The faint-end slope of the LF, a, shows a strong dependence on environment, becoming steeper at > 3a significance level from high- to low-density environments. The red sequence is found to be 0.022 ± 0.014 mag redder in the high-density region than for the intermediate-density region by fixing the slope. In contrast no correlation between the slope of the red sequence and environment was observed. Studying the effect of the cluster environment on galaxy star-formation, we find that the blue galaxy fraction decreases monotonically with density, in agreement with other studies. The observed trends of steepening of the faint-end slope, faintening of the characteristic luminosity, and increasing blue galaxy fraction, from high- to low-density environments, are manifestations of the morphology-density relation, where the fraction of early-type galaxies decreases smoothly and monotonically from the cluster core to the periphery, while the fraction of late-type galaxies increases in the same manner. The observed trends in the composite LF reflect this morphology-density relation: the galaxy population in the cluster core is dominateci by early-type galaxies and so the cornposite LF resembles that of this type of galaxy, with a shallow faint-end slope and a bright characteristic lun1inosity; whereas in lower density regions the fraction ~f late-type galaxies increases, and so the composite LF increasingly resembles that of the late-type, with a steep faint-end slope and a fainter characteristic magnitude. The analysis of the mean colour of luminous (R < 21) cluster galaxies as a function of their spatial position shows clearly the complex effects of the cluster environment and dynamics on their constituent galaxies. The reddest galaxies are concentrateci around the cD galaxy (main cluster) and a more diffuse region 5 arcmin to the north is coincident with the structure predicted from weak lensing analysis. The effect of the preferential SE-NW direction for ABCG 209 is apparent in the presence of bright blue galaxies near the cD galaxy perpendicular to the axis and hence unaffected by the cluster merger, and an extension of red galaxies to the SE which may indicate the irifall of galaxies into the cluster along a filament. This preferential SE-NW direction appears also related to the large-scale structure in which ABCG 209 is embedded, with two rich (Abell class R=3) clusters ABCG 222 at z = 0.211 and ABCG 223 at z = 0.2070 are located 1.5° (15M pc) to the NW along this preferential axis. Cluster dynamics and large-scale structure clearly have a strong influence on galaxy evolution, so we have performed a detailed study of spectroscopic properties of 102 luminous member galaxies. W e find five different galaxy types: i) passive evolving galaxies (E), which exhibit red colours and no emission lines, ii) emission line galaxies (ELG), which are blue and have prominent emission lines, iiiiv) strong Hc5 galaxies, that are characterized by the presence of strong Hc5 equivalent width and can be divided into blue (HDSblue) and red (HDSred), according to the break at 4000 A and the B-R colours, v) and finally anemie spirals (Ab-spirals), that have spectral properties equal to passive evolving galaxies, but are disk-dominateci systems. These different spectral classes are strongly segregated in the phase-space, as indicated by the two dimensionai Kolmogorov-Smirnov test. Passive evolving galaxies represent the I"V 74% of the cluster members. This population formed very early, during the initial collapse of the cluster. They lie mainly in high density regions and ha ve a velocity dispersion fully consistent with those of the whole cluster. This result is understandable in terms of cosmological models of structure formation, in which early-type galaxies form in the highestdensity regions corresponding to the cores of rich clusters. HDSred galaxies are distributed along the elongation of the cluster mainly in intermediate density regions and have a significant low velocity dispersion, suggesting that this population could be the remnant of an infalling group. According to the evolution models, the presence of a strong Hc5 absorption line in their spectra indicates that these galaxies have experimented a short starburst of star formation in the past few Gyrs. In the starburst nwdel [Hc5] and Dn(4000) declines on a timescale of I"V 2Gyr after the burst has ceased, irregardless of their SFR before the burst. Thus the fact that we see these galaxies, detecting [Hc5] > 3.0 A implies that the burst has occurred no more than 2 Gyr ago. HDSblue galaxies are found in intermediate density regions in a direction perpendicular to the cluster elongation, dose to the secondary peak of the X-ray flux andina region where the intracluster Inedium (ICM) is dense. Moreover galaxies belonging to this class seem to be aligned Thus the burst in the star formation seen in these galaxies could be due to the interaction with the hot dense ICM. They have high velocity dispersion. ELGs lie in low density regions and have high line-of-sight velocity dispersion. Both the spatial position and the velocity dispersion suggest that these two populations of galaxies have recently fallen into the cluster from the field. All these results support an evolutionary scenario in which ABCG 209 is characterized by a sum of two components: an old galaxy population, formed very earlier (zJ ;:G 3), and a younger population of infalling galaxies. Moreover this cluster may have experimented l or 2 Gyrs ago a merging with an infalling galaxy group, as indicated also by the previous dynamical analysis. This detailed study has showed clearly the importance to have multi-band data and to perform a n1ulti-directional analysis, in order to precisely characterize the different cluster components. It is now fundamental to extend this kind of analysis to other clusters at higher redshift and with different dynamical properties. To address the issue if clusters are generally young or old one needs to have measurements of subclustering properties of a large sample of clusters and at the same time it is fundamental to precisely characterize cluster components belonging to different structures and environments inside a single cluster.
XVI Ciclo
1976
Versione digitalizzata della tesi di dottorato cartacea.

A fundamental pursuit of astronomy is to understand how galaxies form and evolve. What drives the decline in the cosmic star formation rate density? Why are high redshift galaxies clumpy and turbulent? How can we explain the emergence of the Hubble sequence? To answer these questions we must unravel a complex interplay of different processes, including gas accretion, star formation, feedback, and environmental effects. Studying the gas kinematics of galaxies can provide valuable insight. In this thesis we use integral field spectroscopy to probe the evolution of star-forming field and cluster galaxies over the past 8 billion years. We first present a multi-wavelength analysis of 27 dusty starburst galaxies in a massive cluster at z~0.4. It is thought that starbursts represent an intermediate phase in the transition from spirals to S0s in dense environments. We combine H-alpha kinematics with far-infrared imaging and millimetre spectroscopy, and find that most galaxies are rotationally supported, with high angular momentum and large cold gas reservoirs. It appears that the starbursts have only recently been accreted to the cluster. To complete the transition to S0s, they must undergo a dynamical heating of the disk, increase in concentration, and reduce their angular momentum by ~40%. We conclude that the most likely way to achieve this is via multiple tidal interactions with other cluster members. We next study the velocity dispersion properties of 472 galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). Most galaxies at this epoch are rotationally supported, but dynamically hot and highly turbulent. In order to make robust kinematic measurements, we model the effects of beam smearing using a series of mock KMOS data cubes. We then combine KROSS with data from the SAMI survey (z~0.05) and an intermediate redshift MUSE sample (z~0.5), and find that while there is a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase in velocity dispersion with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. We also test the predictions of two analytic models which suggest that turbulence in the ISM is driven by gravitational instabilities or stellar feedback. However we find that further observations are required to rule-out either model. Finally, to understand the role of galaxy kinematics in “crystallising” the Hubble sequence, we study the HST images of 231 KROSS galaxies. We quantify differences in morphology using the asymmetry parameter. This metric correlates very well with our visual interpretation of “clumpiness”, however there are no strong trends as a function of galaxy kinematics. On average, the velocity dispersion of clumps is consistent with the underlying disk, and there is no evidence to suggest that these star-forming regions are preferentially located towards the outskirts of the galaxy. We propose that adaptive optics assisted IFU observations would provide further insight, allowing us to test clump evolution theories and to study the radial distribution of angular momentum.

This thesis describes searching for high-risk clusters of portals in the Ingress game by using data mining techniques. The work contains background for descibed problematics and methods and experiments used to search for theese information.

This thesis describes searching for high-risk clusters of portals in the Ingress game by using data mining techniques. The work contains background for descibed problematics and methods and experiments used to search for theese information.

We present an extremely deep CO(1-0) observation of a confirmed z = 1.62 galaxy cluster. We detect two spectroscopically confirmed cluster members in CO(1-0) with signal-to-noise ratio >5. Both galaxies have log (M-star/M-circle dot) > 11 and are gas rich, with M-mol/(M-star + M-mol) similar to 0.17-0.45. One of these galaxies lies on the star formation rate (SFR)-M-star sequence, while the other lies an order of magnitude below. We compare the cluster galaxies to other SFR-selected galaxies with CO measurements and find that they have CO luminosities consistent with expectations given their infrared luminosities. We also find that they have gas fractions and star formation efficiencies (SFE) comparable to what is expected from published field galaxy scaling relations. The galaxies are compact in their stellar light distribution, at the extreme end for all high-redshift star-forming galaxies. However, their SFE is consistent with other field galaxies at comparable compactness. This is similar to two other sources selected in a blind CO survey of the HDF-N. Despite living in a highly quenched protocluster core, the molecular gas properties of these two galaxies, one of which may be in the process of quenching, appear entirely consistent with field scaling relations between the molecular gas content, stellar mass, star formation rate, and redshift. We speculate that these cluster galaxies cannot have any further substantive gas accretion if they are to become members of the dominant passive population in z < 1 clusters.

AbstractIn recent years, fungi have attracted avid interest from the research community. This interest stems from several motives, including their network creation capabilities and fundamental role in the ecosystem. Controlled laboratory experiments of fungal behaviors are crucial to further understanding their role and functionalities.In this paper, we propose a method for automating the quantification and observation of fungal spores. Our approach consists of four steps: 1) a Z-stack image acquisition of the sample is performed, 2) a detection algorithm is applied to all Z-planes, 3) clustering of spores detected in different Z-planes, 4) determination of the optimal Z-plane for each cluster through an ad-hoc focus measure. We compared the spore count obtained through the automated tool to a manual count and the count obtained by applying the detection algorithm to a single plane. The result is a highly automated, non-invasive tool to determine spore count, estimate each spore depth, and retrieve an all-in-focus image to analyze further.

Abstract To better understand the flow features of pebble cluster in pebble bed, discharging of the pebble cluster were simulated by DEM. The pebble entangled cluster was composed of eight particles connected by rigid bonds and the simulated cluster models are divided into two types: axisymmetric u-particle and distorted z-particle. The simulation starts with the closed discharge outlet and the bonded clusters with different ID are randomly added from the entrance section. The pebbles fall freely and accumulate freely in the pebble bed. The discharge hole opens after all the pebbles being stationary for a period. Then the pebbles are discharged from the pebble bed under gravity. The discharging process is time-dependent bulk-movement behavior. There is not much mixing between layers on the boundary. The vertical end makes the packing loose, but also intensifies the interaction between particles due to entanglement. Consequently, the discharge features of pebble clusters of different included angles were quantified. The results show that the pebble discharging speeds depend on entanglement angle (α of u-particle and η of z-particle) and discharging outlet diameter. A large included angle may play the role of retarding or inhibiting the discharging flowrate. Therefore, the entanglement of particles component also always plays the key role of retarding the discharge.

This paper analyses the financial health of firms that are members of selected cluster organizations operating in the Czech and Slovak Republics. The research includes two research samples, which are member firms of cluster organizations IT Cluster and Košice IT Valley. Both of the above-mentioned cluster organizations were established as a result of a cluster initiative and associated entities from the ITC sector. The firms that form the cores of the above-mentioned cluster organizations are mostly active in the sectors with the following statistical classification: NACE 620100, 620200, and 620900. The main objective of the present research is to analyze selected financial health indicators of member firms of both cluster organizations and to determine whether or not there are significant differences in the development of selected financial indicators between individual firms. To achieve the objective, the profitability ratios and Altman's Z´´score model were used. The research results are discussed in the conclusion of the paper.

Aim/Purpose. This study examined the self-perception of adolescents and young people aged 17-21 – how they perceived their personal characteristics, self-image, vitality, belonging to a local and global (glocal) society, happiness index and activity, media usage habits in general and smartphones in particular – in other words, it sought to produce a sketch of their character. Background. Different age groups are influenced by various factors that shape them, including living environment, technological developments, experiences, common issues, events of glocal significance, and more. People belonging to Gen Z were born at the end of the previous century and the beginning of the 21st century (up to 2010). This generation was born into the digital technological age and is the first one born into the environment defined by smartphones, and social media. Its members are referred to as “digital natives” because they were born after the widespread adoption of digital technology in the Western world. They entered an environment characterized by the widespread daily use of smartphones, the Internet, and technology in general. Methodology. This was a quantitative study based on a sample of 418 Israeli adolescents and young people aged 17-21. The following questionnaires were administered anonymously and disseminated online to an audience of youths aged 17-21 across Israel: A demographic questionnaire; Self-esteem; Vitality; Belonging vs. alienation; Social-emotional aspects; Usage habits in digital environments; Usage habits of learning on a smartphone; Open questions. Contribution. The current study tried to define clusters to characterize adolescents and youth aged 17-21. Findings Results show that study participants had high self-esteem and vitality, felt belonging, happy, and satisfied with their life, and perceived themselves as active and enterprising at an average level or above. The study identified two clusters. Participants in Cluster 1 were characterized by higher parameter averages than those in Cluster 2 on the self-image, vitality, belonging, happiness, and activism scales. Participants in Cluster 1 felt that using a smartphone made life easier, helped them solve everyday problems, made everyday conduct easier, and allowed them to express themselves, keep up to date with what is happening with their friends, disseminate information conveniently, be involved in social life, and establish relationships with those around them. They thought that it was easy to collaborate with others and to plan activities and events. Recommendations for Practitioners. When examining cluster correlations with data in relation to other variables, it is apparent that participants in Cluster 1 had more options to reach out for help, report more weekly hours spent talking and meeting with friends and feel that using a smartphone makes everyday life easier and facilitates their day-to-day conduct than did participants in Cluster 2. The smartphone allows them to express themselves, keep updated regarding what is happening with their friends and disseminate information easily, helps them be involved in social life and establish connections with those around them. They find it easy to communicate and cooperate with others and to plan activities and events. By contrast, participants in Cluster 2 felt that the smartphone complicates things for them and creates problems in their daily lives. They feel that the use of social networks burdens them and that the smartphone prevents them from being more involved in their social life, and from establishing relationships with those around them. They felt that communication by smartphone creates more problems in understanding messages. Recommendations for Researchers. One of the challenges of this generation is forming an independent identity and self-regulation in a digital, global, across-the-border era that offers a variety of possibilities and communities. They must examine the connection between the digital and personal spaces, to be able to enjoy virtual communities and a sense of togetherness, and at the same time maintain privacy, autonomy, and individuality. Many studies point to the blurring of boundaries between the private-personal and the public, at numerous problems in social networks, including social problems, shaming, and exclusion from various groups and activities. The fear of shaming and the desire to keep up with everything that is happening create a state of mental stress, and adolescents often feel that they urgently need to check their smartphones. Sharing with others can help them deal with negative content and experiences and avoid the dangers lurking in their web surfing. Yet sharing, especially with friends, often causes intimate content to become public and leads to shaming and invasion of privacy. Impact on Society. Gen Z was born into an environment where smartphones, the Internet, and technology in general, are widely used in everyday routine, and they make extensive use of technological means in all areas of life. One of the characteristics of this generation is “globalization.” The present study showed that about 84% of participants felt to a moderate degree or higher that they were citizens of the world. Future Research. The findings of this study revealed a significant difference in self-image between males and females. An attempt was made to explain the findings in light of previous studies, but the need arose for studies on the self-image of young people of Gen Z that would shed light on the subject.