1,720,999 research outputs found
Flat Rotation Curves of z~1 Star Forming Galaxies
No full textThis dataset is useful for Dark matter studies at redshift one star-forming galaxies. Our catalog provides the effective radius, inclination, position angle, circular velocities at various radii etcetera
Dark matter fraction in z ~1 star-forming galaxies
No full textWe present a observational study of the dark matter fraction in 225 rotation supported star-forming galaxies at z≈0.9 having stellar mass range: 9.0≤log(M∗ M⊙)≤11.0 and star formation rate: 0.49≤log(SFR [M⊙ yr−1])≤1.77. This is a sub sample of KMOS redshift one spectroscopic survey (KROSS) previously studied by \citet{GS20}. The stellar masses (M∗) of these objects were previously estimated using mass-to-light ratios derived from fitting the spectral energy distribution of the galaxies. Star formation rates were derived from the Hα luminosities. The total gas masses (Mgas) are determined by scaling relations of molecular and atomic gas \citep[][respectively] {Tacconi2018, Lagos2011}. The dynamical masses (Mdyn) are directly derived from the rotation curves (RCs) at different scale lengths (effective radius: Re, ∼2 Re and ∼3 Re) and then the dark matter fractions (fDM=1−Mbar/Mdyn) at these radii are calculated. We report that at z∼1 only a small fraction (∼5%) of our sample has a low (72%) of SFGs in our sample have dark matter dominated outer disks (∼5−10 kpc) in agreement with local SFGs. Moreover, we find a large scatter in the fraction of dark matter at a given stellar mass (or circular velocity) with respect to local SFGs, suggesting that galaxies at z∼1, a) span a wide range of stages in the formation of stellar disks, b) have diverse DM halo properties coupled with baryon
Nature of Dark Matter from the Astrophysics of High Redshift Star-forming Galaxies
Full text linkIn the late 1970s, Vera Rubin showed that the flat rotation curves are ubiquitous in local spiral galaxies, and concluded that it is due the presence of invisible matter, the so-called `Dark Matter'. She remarked- “galaxies are surrounded by a dark matter halo that extends much further than their visible matter”. These observational results were later supported by theoretical models of structure formation. Thereafter dark matter became an essential building block of current cosmological models, which dominates the formation and evolution of all structures in the Universe. Recent observations of high redshift galaxy rotation curves show remarkable differences in dark matter profiles compared to the local Universe. Therefore, there is an urgent need to repeat the `classical' observational study of Rubin et al. at high redshift with a large dataset.
In search of dark matter and its astrophysical nature at high redshift, I study the shape of the rotation curves of z~1 star-forming disc-like galaxies. Thereby dark matter fraction, structural properties of dark matter halo, and fundamental scaling relations in the progenitors of local disc galaxies. For this purpose, I exploit star-forming galaxies of KMOS Redshift One Spectroscopic Survey (KROSS) from publicly available data. I first aimed to disentangle the prevailing observational and physical uncertainties of high redshift observations, namely beam smearing and pressure support. To this end, the kinematics of the KROSS sample is derived using 3D forward modelling with BAROLO, which accounts for beam smearing in 3D space and provide: kinematic maps, surface density, rotation, and dispersion curves. For the purpose of this work, I analysed and investigated 256 rotation dominated disc-like galaxies from the main sample, covering the redshift range . The main entity, i.e. rotation curves, are then corrected for pressure support using the pressure gradient correction. I have found that only a combination of the three techniques (3D-kinematic modelling + 3D-beam smearing correction + pressure gradient correction) yields the accurate rotation curves of high redshift galaxies. The rotation curves are then dynamically probed to determine the dark matter fraction. Then, in seek of the distribution of the dark matter profile, I dynamically mass modelled the rotation curves, employing Burkert and NFW halo profiles. The outcomes of the latter are cross-checked with previous studies, and state-of-the-art cosmological simulations: EAGLE and Illustris TNG. In this way, I was able to gain new insights into the structural properties of dark matter halos and current state of fundamental scaling relations of star-forming galaxies at z~1.
I confirm that the outer rotation curves of star-forming disc-like galaxies at are similar to the outer rotation curves of local star-forming disc galaxies. Statistically, the latter results indicate that the {em total mass} within the outer region ( to kpc) remains the same at and , while the {em stellar mass} distribution, defined by the stellar disc radii, varies as a function of the {em total mass} (or circular velocity). I show that star-forming galaxies at have outer discs dominated by dark matter ( to kpc). Only a small fraction () of star-forming galaxies at have a low dark matter fraction within the effective radius. The dynamical mass modelling of rotation curves and their various comparisons show that the Burkert halo profile fits our sample best. The results of the dark matter structural properties ( and ) show that the dark matter cores at are on average a factor of 0.3 smaller and more than an order of magnitude denser than those of local star-forming galaxies. As for the fundamental scaling relations, I find that star-forming disc-like systems at exhibit the same mass-size relations as local disc galaxies, as well as a similar scaling of the specific stellar angular momentum with stellar mass. On the other hand, I found a significant evolution in the slope of the stellar Tully-Fisher relation at , while its zero-point remains the same as that of the local disc galaxies.
To conclude, I have shown that dark matter is ubiquitous in star-forming disc-like galaxies at z~1. A preliminary study of dark matter halo structures indicates smaller and denser dark matter cores at z~1, which suggests that the predictions concerning the transformation of cusps into cores, which are observed in hydrodynamical simulations, indeed occur in nature. That is, the dark matter responds to the baryonic processes that dynamically heat-up the dark matter particles, leading to a disruption and displacement in its initial distribution. The latter can be interpreted as, transforming the original dense inner dark matter density (cusp) into a sparse distribution (core). Most importantly, with this study I attempted to provide the first empirical evidence of {em gravitational potential perturbations} in the inner region of galaxies, linking the dark and luminous matter properties, and constraining the dark matter halo structural properties. If my results are verified with high quality data, they will have implications for theories of galaxy formation and evolution, as well as for the nature of dark matter particle itself
Flat rotation curves of z ∼ 1 star-forming galaxies
Full text linkWe investigate the shape of the rotation curves (RCs) of z similar to 1 star-forming galaxies (SFGs) and compare them with local SFGs. For this purpose, we have used 344 galaxies from the K-band Multi-Object Spectrograph (KMOS) for Redshift One Spectroscopic Survey (KROSS). This sample covers the redshift range 0.57 <= z <= 1.04, the effective radii 0.69 <= R-e [kpc] <= 7.76, and the stellar masses 8.7 <= log (M-star[M-circle dot]) <= 11.32. Using (3D)BAROLO, we extract the H alpha kinematic maps and corresponding RCs. The main advantage of (3D)BAROLO is that it incorporates the beam smearing in the 3D observational space, which provide us with the intrinsic rotation velocity even in the low spatial resolution data. We have corrected the RCs for pressure support, which seems to be a more dominant effect than beam smearing in high-z galaxies. Only a combination of the three techniques (3D-kinematic modelling + 3D-beam smearing correction + pressure gradient correction) yields the intrinsic RC of an individual galaxy. Further, we present the co-added and binned RCs constructed out of 256 high-quality objects. We do not see any change in the shape of RCs with respect to the local SFGs. Moreover, we notice a significant evolution in the stellar-disc length (R-D) of the galaxies as a function of their circular velocity. Therefore, we conclude that the stellar disc of SFGs evolves over cosmic time (from z similar to 1) while the total mass stays constant (within similar to 20kpc)
Nervous About a Nuclear Neighbor: Japan's Policy on North Korea
No full textEvery chapter includes a review of each nation's diplomatic history and existing policy with Japan regarding North Korea as the foundation for policy recommendations provided at the beginning of each chapter. Additionally, the chapters on Japan-US, Japan-DPRK, and Japan-ROK include leadership analyses, which evaluate the North Korea policies of the relatively new administrations in the US and Japan as well as the two presidential candidates from South Korea. Our research demonstrates that a coordinated, multilateral policy approach is the only method to restart the stalled denuclearization efforts with the DPRK. As North Korea faces a contracting economy, natural disasters, and potential food and energy shortages in 2022, it is a prime opportunity for Japan and its allies to reform their coordinated policy approach and begin negotiating a denuclearization policy linked to a gradual normalization of relations with further incentives. The current international climate presents new opportunities for Japan to play a central role in the normalization of diplomatic relations and the denuclearization of North Korea
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
