1,721,180 research outputs found
Stellar Mass Profiles of Galaxies in the Hubble Frontier Fields: Evidence for Mass Dependency in Environmental Quenching
Full text linkQuiescent galaxies have more diverse morphologies than star-forming galaxies, which might result from being either mass/environmentally quenched. At some point in their lifetimes, galaxies will stop forming new stars and become quiescent, in a process called quenching, which can be driven by internal (mass-dependent) or environmental processes. In the local universe, those two processes are considered independent of each other, but at higher redshift, they might not be separable. We explore the effect environment has on the morphology of quiescent galaxies by analyzing the stellar mass profiles of cluster and field galaxies from the Hubble Frontier Fields at a redshift range of 0.25 < z < 0.6. SED-fitting was used on the photometry to create resolved stellar mass maps, which were parameterized with a Sersic profile to quantify their morphology. The quiescent cluster galaxies were separated into disk-like and bulge-like depending the similarity of their Sersic parameters to star-forming galaxies. The fraction of disk-like quiescent galaxies have an inverse relation to stellar mass and are most abundant at the lowest masses. Since disk-like quiescents arise from environmental-quenching, cluster galaxies with M_ < 10^{9.5}M_ are predominantly environmentally-quenched, and predominantly mass-quenched above that mass limit. This shows that quenching processes that galaxy morphology in clusters are highly mass dependent
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
Resolving the Stellar Populations of Clumpy Star-Forming Galaxies Using Finite Resolution Deconvolution
Full text linkUnderstanding the physical details of when and where stars form within galaxies remains as one of the key goals in extragalactic astronomy. Kiloparsec-scale, star-forming structures found in distant, irregular galaxies are often suggested to have a crucial role in the stellar mass build-up of galaxies. These structures are generally dubbed as star-forming clumps and the host galaxies as clumpy galaxies. The origin and evolution of clumpy galaxies have not been well-constrained, as the study of clumpy galaxies requires high resolution and multi-wavelength observations to resolve these compact structures and to infer their physical properties. Current efforts are directed toward space-based slitless spectroscopy and ground-based adaptive optics, but such studies are generally limited to smaller samples owing to the need for long integration times. We present an affordable alternative, in which we apply an image deconvolution algorithm (finite resolution deconvolution) on ground-based images of the Cosmic Evolution Survey field to provide resolved colour and stellar population maps for ~20000 distant galaxies. We track the evolution of the fraction of galaxies that exhibit clumpy morphologies as a function of redshift. Such measurements are essential in order to provide further constraints on the origin of star-forming clumps and their role in galaxy evolution
The Morphology-Density Relation of Galaxies at z~1.6
No full textThe relationship between galaxy morphology and environment has been well-studied in the local universe and at low redshift, showing that galaxies in dense clusters tend to be elliptical and bulge-like while galaxies in low-density fields tend to be spiral and disk-like. However, this relationship is less understood at higher redshifts, and the few studies at high-z rely on samples with incomplete redshift measurements and poorly constrained stellar masses. We explore the morphology-density relation at z~1.6, the tail end of cosmic noon, using a sample of 3 SpARCS clusters and 2 fields from 3D-HST/CANDELS. Using Sersic index as a proxy for galaxy morphology, we find that the morphology-density relation is already in place in clusters at this epoch. Additionally, we find a significant difference in the relationship between galaxy morphology and stellar mass in clusters compared to field environments. This suggests that the morphology-density relation may be driven by mass-dependent environmental processes
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
Extreme Emission Line Galaxies Observed with the James Webb Space Telescope's Medium-Band Filters
No full textSince the beginning of the James Webb Space Telescope's science operations, there have been many observations dedicated to characterizing galaxies during the Epoch of Reionization (EoR). This thesis uses medium-band photometry from the JWST to search for Extreme Emission Line Galaxies (EELGs) in the EoR and analogues at lower redshifts. We present a sample of EELGs over 1.7 < z < 6.7 selected on their strong Halpha and [OIII] + Hbeta emission lines. We measure the equivalent widths (EWs) and physical properties of the galaxies in our sample, finding high EWs (median EW(Halpha) = 893 Angstroms, EW([OIII] + Hbeta) = 1255 Angstroms) and properties typical of EELGs: mostly compact with low stellar mass, low metallicity, little dust, and high specific star formation rates. Follow-up NIRSpec spectroscopy of 15 of the EELGs in our sample confirm the nature and EWs of the EELGs measured from medium-band photometry, demonstrating the accuracy of our colour selections.
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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