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1
Fan, Yi-Liu. « Theoretical Analysis of Moving Galaxies in the Large Scale Structure of SpaceTime ». Space Science Journal 1, no 2 (10 juin 2024) : 01–08. http://dx.doi.org/10.33140/ssj.01.02.05.
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In this paper we will make further theoretical analysis for the validity of the accelerating universe based on General Relativity and three new problems of the standard model of the universe are presented from different perspectives. The first part, analyzed the explosion mechanism of the cosmic initial singularity and put forward a different view from the rest. It’s virtually impossible to start with a giant explosion, the big bang by now cosmologists had refined the idea. The second part devised a new model of the twin paradox. It’s one in which people have been consider to include both special and general relativity in the calculations to expose the counterintuitive weirdness of relativity theory. It seems to has a curious coincidence with the cat-a feline in a locked box that is both dead and alive until the box is opened-was a thought experiment devised by physicist Schr ö dinger. In part three the author makes determination on the cosmological deceleration parameter q0 by using mathematical derivation, and based on which to construct a thought experiment on cosmological redshift. It is needed to make a static model of the universe that both conforms to the Copernican principle and satisfies Hubble’s law and it’s possible to make us a fresh perspective and thought process.
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Masters, Karen L. « Galaxy Zoo 3D : Identifying Bars, Spirals and Foreground Stars in MaNGA Galaxy Data ». Proceedings of the International Astronomical Union 17, S373 (août 2021) : 39–41. http://dx.doi.org/10.1017/s1743921322004306.
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AbstractGalaxies, particularly disc galaxies, show a wide variety of internal structures (e.g. spirals, bars, and bulges). Mapping Nearby Galaxies at Apache Point Observatory (MaNGA, part of the fourth incarnation of the Sloan Digital Sky Surveys), obtained spatially resolved spectral maps for 10,010 nearby galaxies. Many results from MaNGA have collapsed this structure into azimuthally averaged radial gradients, or symmetric 2D shapes, but there is significantly more information about the effect internal structures have on the evolution of galaxies available if we can identify different internal structures. One of the simplest ways to identify irregular internal structures in galaxies is by visual inspection. By employing a citizen science technique to ask this question of N independent volunteers we have obtained quantitatively robust masks (and errors) for spirals and bars in MaNGA target galaxies. In addition to internal features the interface asked users to identify foreground stars and foreground/background galaxies.
3
Ge, Xue, Yi-Zhou Gu, Cheng-Long Lei et Xing-Han Zhang. « The connections among morphology, environment, and star formation with Galaxy Zoo Hubble ». Monthly Notices of the Royal Astronomical Society 536, no 1 (4 décembre 2024) : 905–12. https://doi.org/10.1093/mnras/stae2569.
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ABSTRACT Morphology is an important implication for studying the formation and evolution of galaxies. Previous studies have investigated the effects of spiral arms on star formation activities, but it is not clear how clumpy structure affects this process. In this work, we combine Galaxy Zoo Hubble project and 3D-HST/Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey programs to study the influence of morphological structure on star formation processes and the relationship between morphology and the environment at $0 \lt z \lt 1.0$. We find that galaxies with spiral arms and clumpy structures have higher star formation rates than smooth galaxies, and as the redshift decreases, this result remains unchanged. Analysis based on the subsamples, We find that stellar mass is related to the number of arms but not to the number of clumps. In addition, we do not find that an increase in the numbers of arms and/or clumps stimulates greater star formation. We also find that less-clump galaxies preferentially inhabit high-density environments, while more-clump galaxies preferentially inhabit low-density environments. This phenomenon is not significant in spiral galaxies. Our results show that environmental effects may have a greater influence on clumpy structures compared to spiral arm structures, which in turn affects the star formation activities of galaxies.
4
Shaver, PA. « Radio Surveys and Large Scale Structure ». Australian Journal of Physics 44, no 6 (1991) : 759. http://dx.doi.org/10.1071/ph910759.
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An analysis of the Molonglo Reference Catalogue indicates that significant departures from isotropy are present in the sky distribution of strong extragalactic radio sources. This has been shown to be due to local large scale structure, specifically a concentration to the supergalactic plane, which also influences the slope of the source counts. A study of the three-dimensional distribution of local radio galaxies shows that they are more strongly concentrated to the supergalactic plane than are optically�selected galaxies, and that the supergalactic concentration is more extensive than hitherto believed. It appears that radio galaxies (and clusters of galaxies) trace the 'skeleton' of large scale structure, about which normal galaxies are more loosely distributed. Thus, while large scale structure evidently complicates the interpretation of radio source counts, it appears that radiO surveys can be of value in exploring structures on the largest scales.
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Nasution, Budiman, Ruben Cornelius Siagian, Winsyahputra Ritonga, Lulut Alfaris, Aldi Cahya Muhammad et Arip Nurahman. « A Monte Carlo Density Distribution Model Study to Analyze Galaxy Structure, Mass Distribution, and Dark Matter Phenomena ». Indonesian Review of Physics 6, no 1 (30 juin 2023) : 24–44. http://dx.doi.org/10.12928/irip.v6i1.8240.
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This research uses the Monte Carlo density distribution model to study the structure and mass distribution of galaxies and the dark matter phenomenon. Through computer simulations, the research developed a mathematical model with parameters such as rho0, rc, beta, and others, to describe the structure and mass distribution of galaxies. The results show that the model can reproduce various galaxy structures, including groups, clusters and filaments, and influence the behavior and characteristics of individual galaxies. This research provides a deeper understanding of dark matter and its impact on the evolution of the universe. It has implications for improving our understanding of dark matter and the use of Monte Carlo density distribution models to study galaxies. This study provides new insights into the evolution of galaxies and their relationship with dark matter in cosmology. Using both physics and mathematical concepts, this research helps to understand the phenomenon of dark matter and the structure of galaxies, and provides a basis for further research on dark matter and galaxy evolution.
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Erwin, Peter. « The coexistence of classical bulges and disky pseudobulges in early-type disk galaxies ». Proceedings of the International Astronomical Union 3, S245 (juillet 2007) : 113–16. http://dx.doi.org/10.1017/s1743921308017419.
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AbstractClose examination of “pseudobulges” in several early-type disk galaxies indicates that they are actually composite structures consisting of both a flattened, kinematically cool disklike structure (“disky pseudobulge”) and a rounder, kinematically hot spheroidal structure (“classical bulge”). This indicates that pseudobulges, thought to form from internal secular evolution, and classical bulges, thought to form from rapid mergers, are not exclusive phenomena: some galaxies can have both.
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Yee, H. K. C., M. J. Sawicki, R. G. Carlberg, H. Lin, S. L. Morris, D. R. Patton, G. D. Wirth et al. « The CNOC2 Field Galaxy Redshipt Survey ». Highlights of Astronomy 11, no 1 (1998) : 460–63. http://dx.doi.org/10.1017/s153929960002178x.
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Fundamental to our understanding of the universe is the evolution of structures, from galaxies to clusters of galaxies to large-scale sheets and filaments of galaxies and voids. The investigation of the evolution of large-scale structure not only provides us with the key test of theories of structure formation, but also allows us to measure fundamental cosmological parameters. The CNOC2 (Canadian Network for Observational Cosmology) Field Galaxy Redshift Survey is the first large redshift survey of faint galaxies carried out with the explicit goal of investigating the evolution of large scale structure. This survey also provides the largest redshift and photometric data set currently available for the study of galaxy population and evolution at the moderate redshift range between 0.1 and 0.6. In this paper we describe the scope and technique of the survey, its status, and some preliminary results.
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Gao, Tiao. « State-of-art Simulations and Observations for Star Formation ». Highlights in Science, Engineering and Technology 72 (15 décembre 2023) : 66–70. http://dx.doi.org/10.54097/fmnb7351.
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In recent year, the formation and formation of galaxies is a hot spot in astrophysics which has been widely investigated and discussed. On the basis of the theory of formation and formation of large-scale structures in modern cosmology, this study intends to systematically investigate and analyze the physical characteristics of galaxies in different stages, such as morphological structure, star family structure, gas accretion, stellar formation, black hole growth, chemical elements, stellar and gas movements, and their physical relationships with large-scale structures. According to the analysis and evaluations, it aims to reveal the physical origin and formation of galaxies in different stages, as well as their physical relationships with large-scale structures, and then summarize the universal physical laws affecting galaxy formation. Moreover, the current limitations of the state-of-art results will be demonstrated and prospects will be given accordingly. Overall, these results shed light on guiding further exploration of investigation of star formation.
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Fraser-McKelvie, A., L. Cortese, J. van de Sande, J. J. Bryant, B. Catinella, M. Colless, S. M. Croom et al. « A SAMI and MaNGA view on the stellar kinematics of galaxies on the star-forming main sequence ». Monthly Notices of the Royal Astronomical Society 503, no 4 (1 mars 2021) : 4992–5005. http://dx.doi.org/10.1093/mnras/stab573.
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ABSTRACT Galaxy internal structure growth has long been accused of inhibiting star formation in disc galaxies. We investigate the potential physical connection between the growth of dispersion-supported stellar structures (e.g. classical bulges) and the position of galaxies on the star-forming main sequence at z ∼ 0. Combining the might of the SAMI and MaNGA galaxy surveys, we measure the λRe spin parameter for 3289 galaxies over $9.5 \lt \log M_{\star } [\rm {M}_{\odot }] \lt 12$. At all stellar masses, galaxies at the locus of the main sequence possess λRe values indicative of intrinsically flattened discs. However, above $\log M_{\star }[\rm {M}_{\odot }]\sim 10.5$ where the main sequence starts bending, we find tantalizing evidence for an increase in the number of galaxies with dispersion-supported structures, perhaps suggesting a connection between bulges and the bending of the main sequence. Moving above the main sequence, we see no evidence of any change in the typical spin parameter in galaxies once gravitationally interacting systems are excluded from the sample. Similarly, up to 1 dex below the main sequence, λRe remains roughly constant and only at very high stellar masses ($\log M_{\star }[\rm {M}_{\odot }]\gt 11$), do we see a rapid decrease in λRe once galaxies decline in star formation activity. If this trend is confirmed, it would be indicative of different quenching mechanisms acting on high- and low-mass galaxies. The results suggest that whilst a population of galaxies possessing some dispersion-supported structure is already present on the star-forming main sequence, further growth would be required after the galaxy has quenched to match the kinematic properties observed in passive galaxies at z ∼ 0.
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HAQUE-COPILAH, S., et A. ACHONG. « THE FILAMENTARY NATURE OF PISCES-PERSEUS ». International Journal of Modern Physics D 12, no 03 (mars 2003) : 527–39. http://dx.doi.org/10.1142/s0218271803003141.
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Minimal Spanning Tree (MST) statistics and associated reducing procedures have been used to establish the level of filamentary structure, if any in Pisces-Perseus, a sample containing 4501 galaxies. The procedure has been applied to subsets of galaxies with 247 galaxies that we call the Most Conspicuous sample which contain the larger intrinsic linear diameters and the brighter galaxies, and to the Least Conspicuous samples with 253 galaxies containing the smaller intrinsic linear diameter and the fainter members as well as the entire sample. The results show that there are longer filaments in the Most Conspicuous samples with less coiling as opposed to the Least Conspicuous sample. Pruning and separating also highlight the key structures in this region and not only the filamentary ones. Voids are highlighted, also indicating that MST's can be used to identify voids in the large scale structure of the Universe.
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Giraud, E., J. Melnick, Q. S. Gu, H. Quintana, F. Selman, I. Toledo et P. Zelaya. « Galaxy Evolution in a Pilot Survey up toz=1and CDM Halos ». Advances in Astronomy 2011 (2011) : 1–13. http://dx.doi.org/10.1155/2011/508381.
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We study spectral evolution of galaxies in a magnitude limited sample of 550 galaxies fromz=1down toz=0.3on a pencil beam of≈10′×10′. We concentrate on the large apparent cosmological structures along the line of sight, and we bin our individual galaxy spectra to obtain representative high S/N spectra based upon these structures. We divide the resulting average spectra in three groups to facilitate the analysis:galaxies with pure absorption line spectra, galaxies with emission lines and blue continua, and galaxies with emission lines and red continua. We revisit the question of downsizing in emission-line galaxies betweenz=0.9andz=0.45in our pencil-beam and find the following results: strong star formation in emission line galaxies, aging in emission line galaxies, and aging in absorption systems, are shifting from bright to faint systems as cosmological time increases. Each redshift bin is repopulated in new starbursts. Therefore at redshiftsz⩽1galaxy formation is downsizing both in luminosity and number density. Our observations indicate that atz⩽1star formation and hierarchical structure formation of CDM halos are not in phase.
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Hulst, J. M. Van Der. « The Interstellar Medium in Nearby Galaxies ». Highlights of Astronomy 9 (1992) : 101–7. http://dx.doi.org/10.1017/s1539299600008790.
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AbstractRecent observations of the several phases of the interstellar medium in galaxies reveal a wide range of structures and physical properties. The HI structure in nearby galaxies is very filamentary with a large number of shells and filaments suggestive of a close interaction between the star formation in the disk and the surrounding interstellar medium.
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Mazzolini, Margaret, et Rachel Webster. « Preliminary Radio Continuum Maps of Three Spiral Galaxies ». Publications of the Astronomical Society of Australia 13, no 2 (mai 1996) : 107–20. http://dx.doi.org/10.1017/s1323358000020646.
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AbstractThe Australia Telescope Compact Array has been used in two 6 km configurations to make 12 hour observations of the radio continuum structure of three spiral galaxies at 1380 MHz and 2378 MHz. Radio maps of NGC 1792, 6300 and 1097 are presented here, as part of a survey to find examples of anomalous radio structures in spiral galaxies.
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Guo, Beibei, Xufen Wu et Guangwen Chen. « Collisions of Young Disk Galaxies in the Early Universe ». Astrophysical Journal 926, no 2 (1 février 2022) : 224. http://dx.doi.org/10.3847/1538-4357/ac48f2.
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Abstract In the local universe, disk galaxies are generally well evolved and Toomre stable. Their collisions with satellite galaxies naturally produce ring structures, which have been observed and extensively studied. By contrast, at high redshifts, disk galaxies are still developing and clumpy. These young galaxies interact with each other more frequently. However, the products of their collisions remain elusive. Here, we systematically study the minor collisions between a clumpy galaxy and a satellite on orbits with different initial conditions, and find a new structure that is different from the local collisional ring galaxies. The clumpiness of the target galaxy is fine-tuned by the values of Toomre parameter, Q. Interestingly, a thick and knotty ring structure is formed without any sign of a central nucleus in the target galaxy. Our results provide a promising explanation of the empty ring galaxy recently observed in R5519 at redshift z = 2.19. Moreover, we show that the clumpy state of the collided galaxy exists for a much longer timescale compared to isolated self-evolved clumpy galaxies that have been widely investigated.
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Kruuse, M., E. Tempel, R. Kipper et R. S. Stoica. « Photometric redshift galaxies as tracers of the filamentary network ». Astronomy & ; Astrophysics 625 (mai 2019) : A130. http://dx.doi.org/10.1051/0004-6361/201935096.
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Context. Galaxy filaments are the dominant feature in the overall structure of the cosmic web. The study of the filamentary web is an important aspect in understanding galaxy evolution and the evolution of matter in the Universe. A map of the filamentary structure is an adequate probe of the web. Aims. We propose that photometric redshift galaxies are significantly positively associated with the filamentary structure detected from the spatial distribution of spectroscopic redshift galaxies. The long-term aim is to use the photometric galaxies in addition to spectroscopic galaxies to create a more detailed and far-reaching map of the filamentary structure. Methods. The catalogues of spectroscopic and photometric galaxies are seen as point-process realisations in a sphere, and the catalogue of filamentary spines is proposed to be a realisation of a random set in a sphere. The positive association between these sets was studied using a bivariate J-function, which is a summary statistics studying clustering. A quotient D was built to estimate the distance distribution of the filamentary spine to galaxies in comparison to the distance distribution of the filamentary spine to random points in 3-dimensional Euclidean space. This measure also gives a physical distance scale to the distances between filamentary spines and the studied sets of galaxies. In the 3-dimensional case, galaxies and random points are described as line of sights following through their positions on the sphere. Results. The bivariate J-function shows a statistically significant clustering effect in between filamentary spines and photometric redshift galaxies. The quotient D confirms the previous result that smaller distances exist with higher probability between the photometric galaxies and filaments. The trend of smaller distances between the objects grows stronger at higher redshift. Additionally, the quotient D for photometric galaxies gives a rough estimate for the filamentary spine width of about 1 Mpc. Conclusions. Photometric redshift galaxies are positively associated with filamentary spines detected from the spatial distribution of spectroscopic galaxies. In addition to the spatial distribution of spectroscopic galaxies, the information embedded in the photometric galaxies could contribute greatly to the detection of cosmic web structures.
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Rampazzo, R., A. Omizzolo, M. Uslenghi, J. Román, P. Mazzei, L. Verdes-Montenegro, A. Marino et M. G. Jones. « Morphology and surface photometry of a sample of isolated early-type galaxies from deep imaging ». Astronomy & ; Astrophysics 640 (août 2020) : A38. http://dx.doi.org/10.1051/0004-6361/202038156.
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Context. Isolated early-type galaxies are evolving in unusually poor environments for this morphological family, which is typical of cluster inhabitants. We investigate the mechanisms driving the evolution of these galaxies. Aims. Several studies indicate that interactions, accretions, and merging episodes leave their signature on the galaxy structure, from the nucleus down to the faint outskirts. We focus on revealing such signatures, if any, in a sample of isolated early-type galaxies, and we quantitatively revise their galaxy classification. Methods. We observed 20 (out of 104) isolated early-type galaxies, selected from the AMIGA catalog, with the 4KCCD camera at the Vatican Advanced Technology Telescope in the Sloan Digital Sky Survey g and r bands. These are the deepest observations of a sample of isolated early-type galaxies so far: on average, the light profiles reach μg ≈ 28.11 ± 0.70 mag arcsec−2 and μr ≈ 27.36 ± 0.68 mag arcsec−2. The analysis was performed using the AIDA package, providing point spread function-corrected 2D surface photometry up to the galaxy outskirts. The package provides a model of the 2D galaxy light distribution, which after model subtraction enhances the fine and peculiar structures in the residual image of the galaxies. Results. Our re-classification suggests that the sample is composed of bona fide early-type galaxies spanning from ellipticals to late-S0s galaxies. Most of the surface brightness profiles are best fitted with a bulge plus disc model, suggesting the presence of an underlying disc structure. The residuals obtained after the model subtraction show the nearly ubiquitous presence of fine structures, such as shells, stellar fans, rings, and tails. Shell systems are revealed in about 60% of these galaxies. Conclusions. Because interaction, accretion, and merging events are widely interpreted as the origin of the fans, ripples, shells and tails in galaxies, we suggest that most of these isolated early-type galaxies have experienced such events. Because they are isolated (after 2–3 Gyr), these galaxies are the cleanest environment in which to study phenomena connected with events like these.
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Mosenkov, Aleksandr V., Anton A. Smirnov, Olga K. Sil’chenko, R. Michael Rich, Vladimir P. Reshetnikov et John Kormendy. « Tilted outer and inner structures in edge-on galaxies ? » Monthly Notices of the Royal Astronomical Society 497, no 2 (3 juillet 2020) : 2039–56. http://dx.doi.org/10.1093/mnras/staa1885.
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ABSTRACT Tilted and warped discs inside tilted dark matter haloes are predicted from numerical and semi-analytical studies. In this paper, we use deep imaging to demonstrate the likely existence of tilted outer structures in real galaxies. We consider two SB0 edge-on galaxies, NGC 4469 and NGC 4452, which exhibit apparent tilted outer discs with respect to the inner structure. In NGC 4469, this structure has a boxy shape, inclined by ΔPA ≈ 3° with respect to the inner disc, whereas NGC 4452 harbours a discy outer structure with ΔPA ≈ 6°. In spite of the different shapes, both structures have surface brightness profiles close to exponential and make a large contribution (∼30 per cent) to the total galaxy luminosity. In the case of NGC 4452, we propose that its tilted disc likely originates from a former fast tidal encounter (probably with IC 3381). For NGC 4469, a plausible explanation may also be galaxy harassment, which resulted in a tilted or even a tumbling dark matter halo. A less likely possibility is accretion of gas-rich satellites several Gyr ago. New deep observations may potentially reveal more such galaxies with tilted outer structures, especially in clusters. We also consider galaxies, mentioned in the literature, where a central component (a bar or a bulge) is tilted with respect to the stellar disc. According to our numerical simulations, one of the plausible explanations of such observed ‘tilts’ of the bulge/bar is a projection effect due to a not exactly edge-on orientation of the galaxy coupled with a skew angle of the triaxial bulge/bar.
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Menéndez-Delmestre, Karín, Yasmin Coelho, Marco Grossi et Kartik Sheth. « Mass Distribution in Stellar Structures of Local Dwarfs ». Proceedings of the International Astronomical Union 14, S344 (août 2018) : 340–44. http://dx.doi.org/10.1017/s1743921318008098.
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AbstractWe study the distribution of mid-infrared light in stellar structures in a large sample (∽ 400) of low-mass (Mstellar <109 MSun) galaxies. Our sample is selected from the Spitzer Survey of Stellar Structures in Galaxies (S4G), which entails deep imaging of nearby galaxies with the IRAC instrument at 3.6/4.5 μ m. Based on the 2D decomposition of the 3.6μ m images, we find that the majority (∽65%) of galaxies in our sample is well-fit by a single disk profile. The rest of the sample is more adequately fit by a disk and an additional component (e.g., bar, nucleus, bulge, second disk component). Bars are present in ∽11% of the sample, marking a sharp drop in the bar fraction compared to that found for more massive galaxies. The typical contribution of bars to the 3.6 μ m light in dwarfs is ∽1-2%, lower than that found in more massive galaxies. These results bring a number of issues into question: why do low-mass galaxies have such low bar fraction? does the bar instability act differently in low-mass galaxies such that a smaller proportion of stellar mass is typically involved in the bar structure? Is the fact that dwarfs are more dark matter dominated playing a role?
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Chudakova, Ekaterina. « 3D-structure of galactic disks ». Proceedings of the International Astronomical Union 10, S309 (juillet 2014) : 306. http://dx.doi.org/10.1017/s1743921314010023.
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AbstractWe suggest a new photometric method to estimate thicknesses of galactic disks which is working for the galaxies seen under arbitrary inclination. We have applied our method to 45 galaxies from the open SDSS archive and to 57 galaxies from the Spitzer Survey S4G).
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Ferrarese, Laura, et Patrick Côté. « The inner workings of early-type galaxies : cores, nuclei and supermassive black holes ». Proceedings of the International Astronomical Union 2, S238 (août 2006) : 261–68. http://dx.doi.org/10.1017/s1743921307005108.
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AbstractRecent years have seen dramatic progress in the study of the core and nuclear properties of galaxies. The structure of the cores has been shown to vary methodically with global and nuclear properties, as cores respond to the mechanisms by which galaxies form/evolve. The dynamical centers of galaxies have been found capable of hosting two seemingly disparate objects: supermassive black holes (SBHs) and compact stellar nuclei. In a drastic departure from previous beliefs, it has been discovered that both structures are common: galaxies lacking SBHs and/or stellar nuclei are the exception, rather than the norm. This review explores the connection between cores, SBHs and stellar nuclei in early-type galaxies, as revealed by the ACS Virgo Cluster Survey.
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Mosenkov, A. V. « Deep photometry of spiral galaxies ». Publications of the Pulkovo Observatory 227 (décembre 2022) : 1–13. http://dx.doi.org/10.31725/0367-7966-2022-227-10.
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In this study, we consider the potential of using deep photometry for exploring the structure of spiral galaxies. As a source of deep photometry, the modern DESI Legacy Imaging Surveys is chosen, with a wide coverage of the Northern hemisphere. Several examples of spiral galaxies with various structural features of low surface brightnesses are presented which are not seen in images with an ordinary depth. In particular, we consider faint spirals beyond the optical radius, tidal structures (disk warps, stellar streams, and loops), as well as faint polar structures, which are arranged perpendicularly to the disk plane. Therefore, the use of deep photometry reveals new opportunities for studying the structural properties of galaxies and allows one to make more reliable conclusions about their evolution.
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Ogiya, Go. « Learning from interactions between the Milky Way and satellite galaxies ». Proceedings of the International Astronomical Union 13, S334 (juillet 2017) : 349–50. http://dx.doi.org/10.1017/s1743921317006512.
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AbstractThe Milky Way (MW) is interacting with its satellite galaxies and the tidal remnants of satellite galaxies have been observed especially in the MW halo. Understanding the spatial and velocity distributions of stars stripped from satellite galaxies will be of particular importance when interpreting the data from upcoming observations, such as Gaia, Subaru-HSC and PFS. We study tidal stripping events of satellite galaxies with various internal structures using high resolution N-body simulations. The dynamics of satellite galaxies is dominated by dark matter halos, but their density structure is still uncertain. The simulations reveal satellite galaxies with more tightly bound dark matter halos are more robust against the tidal force of the MW and have longer lifetimes than loosely bound ones (Ogiya et al., in prep.). Density scratches on the MW caused by the gravitational force of satellite galaxies and the observability are also discussed (Ogiya & Burkert 2016).
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Ito, Kei, Masayuki Tanaka, Francesco Valentino, Sune Toft, Gabriel Brammer, Katriona M. L. Gould, Olivier Ilbert et al. « COSMOS2020 : Discovery of a Protocluster of Massive Quiescent Galaxies at z = 2.77 ». Astrophysical Journal Letters 945, no 1 (1 mars 2023) : L9. http://dx.doi.org/10.3847/2041-8213/acb49b.
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Abstract Protoclusters of galaxies have been found in the last quarter-century. However, most of them have been found through the overdensity of star-forming galaxies, and there have been no known structures identified by more than two spectroscopically confirmed quiescent galaxies at z > 2.5. In this letter, we report the discovery of an overdense structure of massive quiescent galaxies with the spectroscopic redshift z = 2.77 in the COSMOS field, QO-1000. We first photometrically identify this structure as a 4.2σ overdensity with 14 quiescent galaxies in 7 × 4 pMpc2 from the COSMOS2020 catalog. We then securely confirm the spectroscopic redshifts of four quiescent galaxies by detecting multiple Balmer absorption lines with Keck/MOSFIRE. All the spectroscopically confirmed members are massive ( log ( M ⋆ / M ⊙ ) > 11.0 ) and located in a narrow redshift range (2.76 < z < 2.79). Moreover, three of them are in the 1 × 1 pMpc2 in the transverse direction at the same redshift (z = 2.760–2.763). Such a concentration of four spectroscopically confirmed quiescent galaxies implies that QO-1000 is >68 times denser than the general field. In addition, we confirm that they form a red sequence in the J − K s color. This structure’s halo mass is estimated as log ( M halo / M ⊙ ) > 13.2 from its stellar mass. Similar structures found in the IllustrisTNG simulation are expected to evolve into massive galaxy clusters with log ( M halo / M ⊙ ) ≥ 14.8 at z = 0. These results suggest that QO-1000 is a more mature protocluster than the other known protoclusters. It is likely in a transition phase between star-forming protoclusters and quenched galaxy clusters.
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Smirnov, Anton A., et Sergey S. Savchenko. « New X-shaped bulge photometric model as a tool for measuring B/PS bulges and their X-structures in photometric studies ». Monthly Notices of the Royal Astronomical Society 499, no 1 (2 octobre 2020) : 462–81. http://dx.doi.org/10.1093/mnras/staa2892.
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ABSTRACT Recent orbital studies of 3D bar structure in various numerical and analytical models show that X-structures that reside in boxy/peanut-shaped (B/PS) bulges are not delineated by some specific type of orbits, but are natural parts of them and formed by the same orbits that constitute such bulges. This implies that to accurately account for B/PS bulges and their X-structures in photometric studies, one needs the photometric model of B/PS bulge that includes an X-structure as its natural part. To find such a model, we considered a self-consistent numerical galaxy model where a typical B/PS bulge arises. Using spectral characteristics of particle-‘stars’, we decomposed the galaxy model on to the bar and non-bar components. We used the extracted 3D bar component to find an appropriate B/PS bulge photometric model, which can account for X-structures residing in such bulges. The resulted B/PS bulge photometric model has a truncated 2D Sersic profile with truncations introduced above (in the upper half-plane) and below (in the bottom half-plane) the rays of X-structures. We applied this model to represent B/PS bulges of various numerical models and some real galaxies. The comparison with previous works revealed that there are systematic shifts between the X-structure parameters of the same galaxies measured within the different approaches. We found that the geometric parameters of X-structures of real and modelled galaxies are consistent with each other if we measure them using our new model.
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Krishan, V., et C. Sivaram. « Formation of Large Sacle Structures in the Universe by Inverse Cascade : Cosmosynergetics ». International Astronomical Union Colloquium 132 (1993) : 193–98. http://dx.doi.org/10.1017/s0252921100066069.
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AbstractIt is suggested that inverse cascade that may occur in the turbulent cosmic medium can result in the formation of very large scale structures in the universe, upto the largest scales like the Great Wall. Again clustering of galaxies on all scales is interpreted to be due to these self-organisation processes occurring in a turbulent medium, the largest structures being anisotropic and nearly two dimensional, the smaller structures remaining isotropic. The observed fractal distribution of galaxies is also interpreted on this basis. The direct proportionality between the flow velocity and the linear dimension of the structure may show a way out of the dilemma of missing matter.
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GODŁOWSKI, WŁODZIMIERZ. « GLOBAL AND LOCAL EFFECTS OF ROTATION : OBSERVATIONAL ASPECTS ». International Journal of Modern Physics D 20, no 09 (31 août 2011) : 1643–73. http://dx.doi.org/10.1142/s0218271811019475.
Texte intégralRésumé :
In this paper we discussed the observational aspects of rotation in the Universe on different scales. We show dependence between the angular momentum of the structures and their size. The presented observational situation is that the galaxies, their pairs and compact groups have a non-vanishing angular momentum. In the structures of mass corresponding to groups of galaxies, this feature has not been found, while in the clusters and superclusters, alignment of galaxy orientation has been actually found. Also we know that galaxies have net angular momentum due to the fact that we actually measure the rotation curves of galaxies. These facts lead to the conclusion that theories which connect galaxy angular momentum with its surrounding structure are at some extend favored by data. We show that in the light of scenarios of galaxy formations this result could be interpreted as an effect of tidal force's mechanism, but it is also consistent with Li's model, in which galaxies form in the rotating universe. The theoretical and observational aspects of possible global rotation of the Universe were discussed as well.
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Faure, Baptiste, Frédéric Bournaud, Jérémy Fensch, Emanuele Daddi, Manuel Behrendt, Andreas Burkert et Johan Richard. « Hierarchical fragmentation in high redshift galaxies revealed by hydrodynamical simulations ». Monthly Notices of the Royal Astronomical Society 502, no 3 (3 février 2021) : 4641–57. http://dx.doi.org/10.1093/mnras/stab272.
Texte intégralRésumé :
ABSTRACT High-redshift star-forming galaxies have very different morphologies compared to nearby ones. Indeed, they are often dominated by bright star-forming structures of masses up to 108–9 M⊙ dubbed ‘giant clumps’. However, recent observations questioned this result by showing only low-mass structures or no structure at all. We use Adaptative Mesh Refinement hydrodynamical simulations of galaxies with parsec-scale resolution to study the formation of structures inside clumpy high-redshift galaxies. We show that in very gas-rich galaxies star formation occurs in small gas clusters with masses below 107–8 M⊙ that are themselves located inside giant complexes with masses up to 108 and sometimes 109 M⊙. Those massive structures are similar in mass and size to the giant clumps observed in imaging surveys, in particular with the Hubble Space Telescope. Using mock observations of simulated galaxies, we show that at very high resolution with instruments like the Atacama Large Millimeter Array or through gravitational lensing, only low-mass structures are likely to be detected, and their gathering into giant complexes might be missed. This leads to the non-detection of the giant clumps and therefore introduces a bias in the detection of these structures. We show that the simulated giant clumps can be gravitationally bound even when undetected in mocks representative for ALMA observations and HST observations of lensed galaxies. We then compare the top-down fragmentation of an initially warm disc and the bottom-up fragmentation of an initially cold disc to show that the process of formation of the clumps does not impact their physical properties.
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Hutchings, J. B., et S. G. Neff. « Radio Source Structure and Unified Models ». Symposium - International Astronomical Union 159 (1994) : 427. http://dx.doi.org/10.1017/s0074180900176120.
Texte intégralRésumé :
The results are presented of a program to study the radio structure of radio galaxies, and to compare them with quasars. The samples are matched in redshift and luminosity in the redshift range 0.2 to 1.0, and mapped with the same VLA configuration. The quasar results have been published in earlier papers and the radio galaxy results are in press. We compare 100 quasars with 80 radio galaxies. The comparison shows the following radio galaxies differ from quasars in the following ways: 1)The overall sizes are larger for radio galaxies by 2 to 3 times.2)There are few large bend angles in radio galaxies.3)The lobe length ratio distribution differs.4)The radio galaxies have no population of one-sided sources.5)The lobe flux ratio has less range in the radio galaxies.6)Radio galaxies have few core-dominated sources and many with no detectable core: few with comparable core and lobe flux.7)The most luminous sources are lobe-dominated and more powerful than the quasars. The most luminous quasars are unresolved cores.Points 1,2,3 can be fit with a single ‘unified’ model which has a distribution of sizes and bend angles up to 25°, with small expansion velocities. The quasars are viewed within a cone angle of 50° and the radio galaxies outside the cone. However, the model does incorporate a source growth scenario and points 4 through 7 imply that there are instrinsic differences between the source types as well as orientation. We also discuss the limitations on beaming and bulk motions implied by the results.
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Schilizzi, RT. « Compact Structure in Continuum Radio Sources ». Australian Journal of Physics 44, no 6 (1991) : 771. http://dx.doi.org/10.1071/ph910771.
Texte intégralRésumé :
Present-day VLBI networks make observations of compact structure in a wide variety of radio sources. Examples are shown of milli-arcsecond scale structures in radio galaxies, quasars, stars and supernova remnants.
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DEMARCO, RICARDO, HOLLAND C. FORD et PIERO ROSATI. « PANCHROMATIC STUDIES OF DISTANT CLUSTERS OF GALAXIES ». Modern Physics Letters A 20, no 19 (21 juin 2005) : 1409–22. http://dx.doi.org/10.1142/s0217732305017615.
Texte intégralRésumé :
High redshift (z≳1) clusters are ideal probes to study the formation and evolution of large scale structures and galaxies in the universe. A 10-m class ground based telescope, X-ray observatories (Chandra, XMM-Newton) and HST/ACS are allowing us to perform an unprecedented study of distant massive clusters of galaxies in the redshift range 0.84<z<1.3, selected from X-rays surveys. In this paper we summarize our results on the structure and dynamics of two of these clusters derived from imaging and spectroscopic data as well as our results on the evolution of early-type galaxies.
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Tikhonov, N. A. « Stellar structure of irregular galaxies : Edge-on galaxies ». Astronomy Reports 50, no 7 (juillet 2006) : 517–25. http://dx.doi.org/10.1134/s1063772906070018.
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Makarova, L., D. Makarov, A. Klypin et S. Gottlöber. « 3D structure of nearby groups of galaxies ». Proceedings of the International Astronomical Union 11, S308 (juin 2014) : 207–8. http://dx.doi.org/10.1017/s1743921316009868.
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AbstractUsing high accuracy distance estimates, we study the three-dimensional distribution of galaxies in five galaxy groups at a distance less than 5 Mpc from the Milky Way. Due to proximity of these groups our sample of galaxies is nearly complete down to extremely small dwarf galaxies with absolute magnitudes MB = -12. We find that the average number-density profile of the groups shows a steep power-law decline dn/dV ∼ R-3 at distances R=(100–500) kpc consistent with predictions of the standard cosmological model. We also find that there is no indication of a truncation or a cutoff in the density at the expected virial radius: the density profile extends at least to 1.5 Mpc. Vast majority of galaxies within 1.5 Mpc radius around group centres are gas-rich star-forming galaxies. Early-type galaxies are found only in the central ∼ 300 kpc region. Lack of dwarf spheroidal and dwarf elliptical galaxies in the field and in the outskirts of large groups is a clear indication that these galaxies experienced morphological transformation when they came close to the central region of forming galaxy group.
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Tahmasebzadeh, Behzad, Ling Zhu, Juntai Shen, Ortwin Gerhard et Glenn van de Ven. « Orbit-superposition Dynamical Modeling of Barred Galaxies ». Astrophysical Journal 941, no 2 (1 décembre 2022) : 109. http://dx.doi.org/10.3847/1538-4357/ac9df6.
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Abstract Barred structures are important in understanding galaxy evolution, but they were not included explicitly in most dynamical models for nearby galaxies due to their complicated morphological and kinematic properties. We modify the triaxial orbit-superposition Schwarzschild implementation by van den Bosch et al. to include barred structures explicitly. The gravitational potential is a combination of a spherical dark matter halo and stellar mass; with the 3D stellar density distribution deprojected from the observed 2D image using a two-component deprojection method, including an axisymmetric disk and a triaxial barred bulge. We consider figure rotation of the galaxy with the bar pattern speed as a free parameter. We validate the method by applying it to a mock galaxy with integral field unit (IFU) data created from an N-body simulation with a boxy/peanut or X-shaped bar. Our model fits the observed 2D surface density and all kinematic features well. The bar pattern speed is recovered well with a relative uncertainty smaller than 10%. Based on the internal stellar orbit distribution of the model, we decompose the galaxy into an X-shaped bar, a boxy bulge, a vertically extended structure and a disk, and demonstrate that our model recovers these structures generally well, similar to the true structures in the N-body simulation. Our method provides a realistic way of modeling the bar structure explicitly for nearby barred galaxies with IFU observations.
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Chincarini, G., et G. Vettolani. « The Distribution of Bright Galaxies ». Symposium - International Astronomical Union 124 (1987) : 275–300. http://dx.doi.org/10.1017/s0074180900159236.
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Following a brief review of the early developments in the field, we discuss a few new advances in the distribution of bright galaxies which occured after the extensive review paper by Oort (1983) We show that the large scale structure, shells, filaments and/or sheets, may bias the determination of the velocity dispersion in clusters of galaxies and that the boundaries of the voids may often be biassed by the clusters and groups velocity dispersion.Of interest are the very large structures selected on catalogs of clusters of galaxies. The “Local Structure” claimed by Tully seems to be somewhat flattened and about parallel to the plane of the Local Supercluster. If the structure is real the alignement is relevant in relation to the physical mechanisms at work at the time of formation. Noticeable progress has been done in the measurement of the large scale velocity field. Large scale motions may somewhat bias the study of the topology of the Universe.Relevant work has be done on the shape of the boundaries of the voids and observational work is progressing to detect faint galaxies in voids and determine their charactestics. This is important also in relation to the theory of biassed galaxy formation. To better focus the observational problem and eventually related biasses, we give some statistics on dwarf galaxies in the Virgo cluster.
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Heinämäki, Pekka. « Giant radio galaxies and cosmic web ». Proceedings of the International Astronomical Union 11, S308 (juin 2014) : 484–85. http://dx.doi.org/10.1017/s1743921316010462.
Texte intégralRésumé :
AbstractGiant radio galaxies create the well distinguishable class of sources. These sources are characterized with edge-brightened radio lobes with highly collimated radio jets and large linear sizes which make them the largest individual structures in the Universe. They are also known to be hosted by elliptical/disturbed host galaxies and avoid clusters and high galaxy density regions. Because of GRG, large linear sizes lobes extend well beyond the interstellar media and host galaxy halo the evolution of the radio lobes may depend on interaction with this environment. Using our method to extract filamentary structure of the galaxies in our local universe we study whether radio lobe properties in some giant radio galaxies are determined on an interaction of this filament ambient.
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Lin, C. C., et G. Bertin. « Formation and maintenance of spiral structure in galaxies ». Symposium - International Astronomical Union 106 (1985) : 513–32. http://dx.doi.org/10.1017/s0074180900243052.
Texte intégralRésumé :
The formation and maintenance of spiral structure in galaxies is discussed in terms of spiral modes with a general perception consistent with the hypothesis of quasi-stationary spiral structure. The latter is explained in some detail to give it the original proper perspective and to contrast it with recent studies of non-stationary spiral structures. We again emphasize the possible coexistence of fast-evolving spiral features and slow-evolving spiral grand designs. Spiral modes are described in terms of three categories of propagating waves. The reason is given why isolated non-barred galaxies with spiral grand design are found to be mostly two-armed. Some suggestions are made for future research.
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Smith, Beverly J., Matthew Watson, Mark L. Giroux et Curtis Struck. « Grand Design versus Multiarmed Spiral Galaxies : Dependence on Galaxy Structure ». Astronomical Journal 168, no 1 (11 juin 2024) : 12. http://dx.doi.org/10.3847/1538-3881/ad46fb.
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Abstract We developed an algorithm to use Galaxy Zoo 3D spiral arm masks produced by citizen scientist volunteers to semiautomatically classify spiral galaxies as either multiarmed or grand design spirals. Our final sample consists of 299 multiarmed and 245 grand design galaxies. On average, the grand design galaxies have smaller stellar masses than the multiarmed galaxies. For a given stellar mass, the grand design galaxies have larger concentrations, earlier Hubble types, smaller half-light radii, and larger central surface mass densities than the multiarmed galaxies. Lower-mass galaxies of both arm classes have later Hubble types and lower concentrations than higher-mass galaxies. In our sample, a higher fraction of grand design galaxies have classical bulges rather than pseudo-bulges, compared to multiarmed galaxies. These results are consistent with theoretical models and simulations, which suggest that dense classical bulges support the development and/or longevity of two-armed spiral patterns. Similar specific star formation rates (sSFRs) are found in multiarmed and grand design galaxies with similar stellar masses and concentrations. This implies that the sSFRs in spiral galaxies are a function of concentration and stellar mass, but independent of the number of spiral arms. Our classifications are consistent with arm counts from the Galaxy Zoo 2 project and published m = 3 Fourier amplitudes.
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Einasto, J. « Regularity of the Large-Scale Structure of the Universe ». Symposium - International Astronomical Union 183 (1999) : 169–77. http://dx.doi.org/10.1017/s0074180900132498.
Texte intégralRésumé :
The observed structure of the Universe is hierarchical. Galaxies and clusters of galaxies are concentrated within elongated filamentary chains of various richness. High-density regions of the Universe form superclusters consisting of one or several clusters of galaxies and chains of galaxies surrounding and joining clusters. The space between filaments is void of galaxies. Superclusters and voids form a continuous network of alternating high- and low-density regions in the Universe.
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van der Marel, Roeland P. « The Central Kiloparsec-Scale Structure of Galaxies ». Symposium - International Astronomical Union 205 (2001) : 154–61. http://dx.doi.org/10.1017/s0074180900220822.
Texte intégralRésumé :
This review summarizes some aspects of the central kiloparsec scale structure of galaxies, and in particular spiral galaxies, elliptical galaxies and merger remnants. The focus is on results from optical and near-IR imaging and spectroscopy, with emphasis on recent work with the Hubble Space Telescope.
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Fernandez, Julia, Sol Alonso, Valeria Mesa, Fernanda Duplancic et Georgina Coldwell. « Properties of galaxies with ring structures ». Astronomy & ; Astrophysics 653 (septembre 2021) : A71. http://dx.doi.org/10.1051/0004-6361/202141208.
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Aims. We present a statistical analysis of different characteristics of ringed spiral galaxies with the aim of assessing the effects of rings on disk galaxy properties. Methods. We built a catalog of ringed galaxies from the Sloan Digital Sky Survey Data Release 14 (SDSS-DR14). Via visual inspection of SDSS images, we classified the face-on spiral galaxies brighter than g < 16.0 mag into galaxies with: an inner ring, an outer ring, a nuclear ring, both an inner and an outer ring, and a pseudo-ring. In addition to rings, we recorded morphological types and the existence of bars, lenses, and galaxy pair companions with or without interaction. With the goal of providing an appropriate quantification of the influence of rings on galaxy properties, we also constructed a suitable control sample of non-ringed galaxies with similar redshift, magnitude, morphology, and local density environment distributions to those of ringed ones. Results. We found 1868 ringed galaxies, accounting for 22% of the full sample of spiral galaxies. In addition, within galaxies with ringed structures, 46% have an inner ring, 10% an outer ring, 20% both an inner and an outer ring, 6% a nuclear ring, and 18% a partial ring. Moreover, 64% of the ringed galaxies present bars. We also found that ringed galaxies have both a lower efficiency of star formation activity and older stellar populations (as derived with the Dn(4000) spectral index) with respect to non-ringed disk objects from the control sample. Moreover, there is a significant excess of ringed galaxies with red colors. These effects are more important for ringed galaxies that have inner rings and bars with respect to their counterparts that have some other types of rings and are non-barred. The color-magnitude and color-color diagrams show that ringed galaxies are mostly concentrated in the red region, while non-ringed spiral objects are more extended to the blue zone. Galaxies with ringed structures present an excess of high metallicity values compared to non-ringed ones, which show a 12 + Log(O/H) distribution toward lower values. These findings seem to indicate that rings are peculiar structures that produce an accelerating galactic evolution, strongly altering the physical properties of their host galaxies.
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Comoretto, G., L. Feretti et G. Giovannini. « VLBI Cores in a Sample of Radio Galaxies ». Symposium - International Astronomical Union 129 (1988) : 75–76. http://dx.doi.org/10.1017/s0074180900133996.
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We present the first results of a statistical study of the milliarcsec structure in a complete sample of radio galaxies. We have selected from the B2 and 3CR samples of galaxies the sources which present, at the VLA or WSRT angular resolution, an unresolved core with a flux density at 5 GHz Sc ≥ 100 mJy. The total sample consists of 30 radio galaxies, 17 from the B2 and 13 from the 3CR catalog. This complete sample covers a range of total radio power at 408 MHz log P = 23.5 – 26.5 W/Hz (low-intermediate luminosity). The radio structure of these sources on the arcsec-arcmin scale is well known, thanks to good dynamic range VLA and/or WSRT maps; a large variety of structures is present in the sample, from classical doubles to head-tail sources; flat, inverted and steep spectrum cores are also present.
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Drinkwater, M. J., D. Proust, Q. A. Parker, H. Quintana et E. Slezak. « New Structure in the Shapley Supercluster ». Publications of the Astronomical Society of Australia 16, no 2 (1999) : 113–23. http://dx.doi.org/10.1071/as99113.
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AbstractWe present new radial velocities for 306 bright (R < 16) galaxies in a 77 deg2 region of the Shapley supercluster, measured with the FLAIR-II spectrograph on the UK Schmidt Telescope. The galaxies we measured were uniformly distributed over the survey area, in contrast to previous samples which were concentrated in several rich Abell clusters. Most of the galaxies (230) were members of the Shapley supercluster: they trace out two previously unknown sheets of galaxies linking the Abell clusters of the supercluster. In a 44 deg2 area of the supercluster excluding the Abell clusters, these sheets alone represent an overdensity of a factor of 2·0 ± 0·2 compared to a uniform galaxy distribution. The supercluster is not flattened in the Declination direction as has been suggested in previous papers. Within our survey area the new galaxies contribute an additional 50% to the known contents of the Shapley supercluster, with a corresponding increase in its contribution to the motion of the Local Group.
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Boogaard, Leindert A., Steven Gillman, Jens Melinder, Fabian Walter, Luis Colina, Göran Östlin, Karina I. Caputi et al. « MIDIS : JWST/MIRI Reveals the Stellar Structure of ALMA-selected Galaxies in the Hubble Ultra Deep Field at Cosmic Noon ». Astrophysical Journal 969, no 1 (26 juin 2024) : 27. http://dx.doi.org/10.3847/1538-4357/ad43e5.
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Abstract We present deep James Webb Space Telescope (JWST)/Mid-Infrared Instrument (MIRI) F560W observations of a flux-limited, Atacama Large Millimeter/submillimeter Array (ALMA)-selected sample of 28 galaxies at z = 0.5–3.7 in the Hubble Ultra Deep Field (HUDF). The data from the MIRI Deep Imaging Survey (MIDIS) reveal the stellar structure of the HUDF galaxies at rest-frame wavelengths of λ > 1 μm for the first time. We revise the stellar mass estimates using new JWST photometry and find good agreement with pre-JWST analyses; the few discrepancies can be explained by blending issues in the earlier lower-resolution Spitzer data. At z ∼ 2.5, the resolved rest-frame near-infrared (1.6 μm) structure of the galaxies is significantly more smooth and centrally concentrated than seen by the Hubble Space Telescope at rest-frame 450 nm (F160W), with effective radii of R e (F560W) = 1–5 kpc and Sérsic indices mostly close to an exponential (disk-like) profile (n ≈ 1), up to n ≈ 5 (excluding active galactic nuclei). We find an average size ratio of R e (F560W)/R e (F160W) ≈ 0.7 that decreases with stellar mass. The stellar structure of the ALMA-selected galaxies is indistinguishable from a HUDF reference sample of all galaxies with a MIRI flux density greater than 1 μJy. We supplement our analysis with custom-made, position-dependent, empirical point-spread function models for the F560W observations. The results imply that a smoother stellar structure is in place in massive gas-rich, star-forming galaxies at “Cosmic Noon,” despite a more clumpy rest-frame optical appearance, placing additional constraints on galaxy formation simulations. As a next step, matched-resolution, resolved ALMA observations will be crucial to further link the mass- and light-weighted galaxy structures to the dusty interstellar medium.
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Davies, J. I., S. Sabatini et S. Roberts. « Low Luminosity Galaxies ». Publications of the Astronomical Society of Australia 21, no 4 (2004) : 360–65. http://dx.doi.org/10.1071/as04046.
Texte intégralRésumé :
AbstractLow luminosity (dwarf) galaxies play a crucial role in our current theories of galaxy and large scale structure formation. In the hierarchical picture they are the building blocks from which other structures form. These theories in their basic form overpredict the numbers of small dark matter halos (dwarf galaxies?) unless some form of star formation supression is invoked. In this paper we describe observations of dwarf galaxies in a range of different environments. We find that there are far too few dwarf galaxies in low density environments to be compatible with the theories. These observations are not consistent with an environment-independent mechanism suppressing dwarf galaxy formation. It is also not clear how these mechanisms can supress star formation if dwarf galaxies have large mass-to-light ratios (≈100). Either the whole idea of hierarchical galaxy formation has to be rejected or other environmentally dependent physical processes have to be invoked. We suggest that small, gas-rich dI galaxies have their evolution rapidly advanced as they move into the dense cluster environment.
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VAN DE WEYGAERT, RIEN, et ERWIN PLATEN. « COSMIC VOIDS : STRUCTURE, DYNAMICS AND GALAXIES ». International Journal of Modern Physics : Conference Series 01 (janvier 2011) : 41–66. http://dx.doi.org/10.1142/s2010194511000092.
Texte intégralRésumé :
In this contribution we review and discuss several aspects of Cosmic Voids. Voids are a major component of the large scale distribution of matter and galaxies in the Universe. Their instrumental importance for understanding the emergence of the Cosmic Web is clear. Their relatively simple shape and structure makes them into useful tools for extracting the value of a variety cosmic parameters, possibly including even that of the influence of dark energy. Perhaps most promising and challenging is the issue of the galaxies found within their realm. Not only does the pristine environment of voids provide a promising testing ground for assessing the role of environment on the formation and evolution of galaxies, the dearth of dwarf galaxies may even represent a serious challenge to the standard view of cosmic structure formation.
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Epinat, B., T. Contini, H. Finley, L. A. Boogaard, A. Guérou, J. Brinchmann, D. Carton et al. « Ionised gas structure of 100 kpc in an over-dense region of the galaxy group COSMOS-Gr30 at z ~ 0.7 ». Astronomy & ; Astrophysics 609 (janvier 2018) : A40. http://dx.doi.org/10.1051/0004-6361/201731877.
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We report the discovery of a 104 kpc2 gaseous structure detected in [O ii]λλ3727, 3729 in an over-dense region of the COSMOS-Gr30 galaxy group at z ~ 0.725 with deep MUSE Guaranteed Time Observations. We estimate the total amount of diffuse ionised gas to be of the order of (~5 ± 3) × 1010 M⊙ and explore its physical properties to understand its origin and the source(s) of the ionisation. The MUSE data allow the identification of a dozen group members that are embedded in this structure through emission and absorption lines. We extracted spectra from small apertures defined for both the diffuse ionised gas and the galaxies. We investigated the kinematics and ionisation properties of the various galaxies and extended gas regions through line diagnostics (R23, O32, and [O iii]/Hβ) that are available within the MUSE wavelength range. We compared these diagnostics to photo-ionisation models and shock models. The structure is divided into two kinematically distinct sub-structures. The most extended sub-structure of ionised gas is likely rotating around a massive galaxy and displays filamentary patterns that link some galaxies. The second sub-structure links another massive galaxy that hosts an active galactic nucleus (AGN) to a low-mass galaxy, but it also extends orthogonally to the AGN host disc over ~ 35 kpc. This extent is likely ionised by the AGN itself. The location of small diffuse regions in the R23 vs. O32 diagram is compatible with photo-ionisation. However, the location of three of these regions in this diagram (low O32, high R23) can also be explained by shocks, which is supported by their high velocity dispersions. One edge-on galaxy shares the same properties and may be a source of shocks. Regardless of the hypothesis, the extended gas seems to be non-primordial. We favour a scenario where the gas has been extracted from galaxies by tidal forces and AGN triggered by interactions between at least the two sub-structures.
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Wan, Zhen, William H. Oliver, Geraint F. Lewis, Justin I. Read et Michelle L. M. Collins. « On the origin of the asymmetric dwarf galaxy distribution around andromeda ». Monthly Notices of the Royal Astronomical Society 492, no 1 (12 décembre 2019) : 456–67. http://dx.doi.org/10.1093/mnras/stz3477.
Texte intégralRésumé :
ABSTRACT The dwarf galaxy distribution surrounding M31 is significantly anisotropic in nature. Of the 30 dwarf galaxies in this distribution, 15 form a disc-like structure and 23 are contained within the hemisphere facing the Milky Way. Using a realistic local potential, we analyse the conditions required to produce and maintain these asymmetries. We find that some dwarf galaxies are required to have highly eccentric orbits in order to preserve the presence of the hemispherical asymmetry with an appropriately large radial dispersion. Under the assumption that the dwarf galaxies originate from a single association or accretion event, we find that the initial size and specific energy of that association must both be relatively large in order to produce the observed hemispherical asymmetry. However if the association was large in physical size, the very high-energy required would enable several dwarf galaxies to escape from the M31 and be captured by the Milky Way. Furthermore, we find that associations that result in this structure have total specific energies concentrated around $E = V_{\rm esc}^{2} - V_{\rm init}^{2} \sim 200^2$ – $300^2\ \rm {km^2\ s^{-2}}$, implying that the initial velocity and initial position needed to produce the structure are strongly correlated. The overlap of initial conditions required to produce the radial dispersion, angular dispersion, and the planar structure is small and suggests that either they did not originate from a single accretion event, or that these asymmetric structures are short-lived.
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Tikhonov, N. A. « The stellar structure of irregular galaxies. Face-on galaxies ». Astronomy Reports 49, no 7 (juillet 2005) : 501–9. http://dx.doi.org/10.1134/1.1985947.
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Psychogyios, A., M. Vika, V. Charmandaris, S. Bamford, G. Fasano, B. Häußler, A. Moretti, B. Poggianti et B. Vulcani. « Multi-wavelength structure analysis of local cluster galaxies ». Astronomy & ; Astrophysics 633 (janvier 2020) : A104. http://dx.doi.org/10.1051/0004-6361/201833522.
Texte intégralRésumé :
We present a multi-wavelength analysis of the galaxies in nine clusters selected from the WINGS dataset, examining how galaxy structure varies as a function of wavelength and environment using the state of the art software GALAPAGOS-2. We simultaneously fit single-Sérsic functions on three optical (u, B and V) and two near-infrared (J and K) bands thus creating a wavelength-dependent model of each galaxy. We measure the magnitudes, effective radius (Re), the Sérsic index (n), axis ratio, and position angle in each band. The sample contains 790 cluster members (located close to the cluster centre < 0.64 × R200) and 254 non-member galaxies that we further separate based on their morphology into ellipticals, lenticulars, and spirals. We find that the Sérsic index of all galaxies inside clusters remains nearly constant with wavelength while Re decreases as wavelength increases for all morphological types. We do not observe a significant variation on n and Re as a function of projected local density and distance from the clusters centre. Comparing the n and Re of bright cluster galaxies with a subsample of non-member galaxies we find that bright cluster galaxies are more concentrated (display high n values) and are more compact (low Re). Moreover, the light profile (𝒩) and size (ℛ) of bright cluster galaxies does not change as a function of wavelength in the same manner as non-member galaxies.
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Di Nella, H., et G. Paturel. « Possible Connection between Large-scale Structures ». Publications of the Astronomical Society of Australia 12, no 1 (avril 1995) : 26–30. http://dx.doi.org/10.1017/s1323358000020002.
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AbstractFrom the Lyon-Meudon Extragalactic Database (LEDA) we constructed a sample of 27000 galaxies with radial velocities smaller than 15 000 kms−1. From this first sample we selected the 5683 largest galaxies, which constitute a sample complete up to the diameter limit D25 = 1·6′. This sub-sample has been used to search for the most populated plane. The result is that the plane defined by the pole (l = 52°; b= 16°) contains twice as many galaxies as would be found for randomly distributed galaxies. This plane is not far from the supergalactic plane. The distribution of galaxies in this plane has been studied by using the radial velocity as an estimate of the distance. An excess of galaxies appears at a distance of about 70 Mpc. We discuss the reality of this density enhancement which could result from selection effects.