1,721,123 research outputs found
Deficiency of Broad-Line AGNs in Compact Groups of Galaxies
No full textBased on a new survey of AGN activity in compact groups of galaxies, we report a remarkable deficiency of broad-line AGNs as compared to narrow-line AGNs. The cause of such deficiency could be related to the average low luminosity of AGNs in CGs: 1039 ergs s-1. This result may imply lower accretion rates in CG AGNs, making broad-line regions (BLRs) undetectable, or may indicate a genuine absence of BLRs. Both phenomena are consistent with gas stripping through tidal interaction and dry mergers
Spectral Classification and Analysis of Nuclear Activity in the UZC-Compact Group Sample
No full textCompact Groups are ideal systems to study galaxy-galaxy interactions and eventually the activity-environment-morphology relationship
Nuclear Activity in UZC Compact Groups Galaxies
No full textCompact Groups are ideal places to investigate the role of environment on galaxy formation and evolution. Their high galaxy density coupled with their low velocity dispersion makes them the most suitable systems to study galaxy-galaxy interaction and the AGN-environment relation. UZC Compact Groups sample (UZC-CG, Focardi & Kelm 2002) contains 986 galaxies belonging to 291 groups. We have taken 642 low resolution UZC spectra from the Z-Machine Archive and 221 medium resolution spectra from the Sloan Data Archive (Release Four). As 131 are in common with the first ones, we have a total of 732 spectra. The main goal of this study is to measure and classify the nuclear activity found in galaxies belonging to compact groups, with this aim we have measured the equivalent width of emission lines (Hβ, [OIII], Hα, [NII], [SII]...) and their ratio. Diagnostic diagrams, like log([OIII]/Hβ) vs log([NII]/Hα) and log ([OIII]/Hβ) vs log([SII](6717+6731Å)/Hα) have been used to do the spectral classification. As a whole, from the 732 galaxies with available spectra, 65% show emission lines. We present a detailed analysis of the 159 UZC-CGs with spectra for all member. We show that 65 % of these galaxies have nuclear activity (HII nuclear regions, LINERs or Syefert2). Finally we will show how galaxy and CG properties relate to the presence and kind of nuclear activity
The influence of local environment on the emergence of AGN activity in galaxies
No full textWe have carried out a spectroscopic study to determine the frequency and nature of the nuclear activity found in compact groups. With this aim we chose two samples, one selected from the Hickson Compact Groups Catalogue and another one from the Updated Zwicky Catalogue of Compact Groups. With the analysis of 1056 galaxies we found that more than 71% present some kind of emission, most of them, being low luminosity AGN (L_{Hα}=10^{39} erg s^{-1}). From these we only detect broad components in 16 which means a remarkable deficiency of broad line AGNs as compared to narrow line AGNs, despite the high frequency of active galaxies encountered ingeneral in these groups
Optical spectral properties of radio loud quasars along the main sequence
No full textWe analyze the optical properties of Radio-Loud quasars along the Main Sequence (MS) of quasars. A sample of 355 quasars selected on the basis of radio detection was obtained by cross-matching the FIRST survey at 20cm and the SDSS DR12 spectroscopic survey. We consider the nature of powerful emission at the high-Fe ii end of the MS. At variance with the classical radio-loud sources which are located in the Population B domain of the MS optical plane, we found evidence indicating a thermal origin of the radio emission of the highly accreting quasars of Population A
Neuroinflammation, Alzheimer's disease and periodontal disease: is there an association between the two processes?
No full textAlzheimers disease (AD) is a very common cause of dementia in developed countries and increases its prevalence progressively with age. AD etiopathogenesis is not yet understood. However, it is recognized that neuroinflammation plays a key role in its pathogenesis with the activation of microglia and the secretion of proinflammatory cytokines triggering irreversible neurodegenerative deterioration. This paper is a short review of the relationship between AD and periodontal disease (PD). Both processes may have common causes: both are inflammatory diseases and the prevalence and progression increases with ageing. However, we must consider that AD begins to develop many years before its clinical diagnosis. It is thought that in this prodromal period a connection could be established between both processes, both sustained by low intensity inflammation. There are several studies that relate both processes such as the possible systemic exposure to certain periodontopathogenic bacteria or the proinflammatory cytokines and other elements. It is argued that there are no modifiable factors such as age, or genetic factors, but that there are other factors that could be avoided, modified or controlled such as periodontal peripheral inflammation
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
Nuclear activity in UZC Compact Groups.
No full textIt is well known that environment has an important influence on galaxy formation and evolution including mass assembly, star formation, morphological evolution and the presence of nuclear activity. In order to study the influence of the environment in galaxy properties while testing for the presence of nuclear (AGN or star formation) activity, we look for systems with high galaxy density and low velocity dispersion to maximize the number of galaxy encounters. Compact Groups of Galaxies satisfy these two conditions as well as to be located in low density environments, this means that galaxy influences come only from the interactions with galaxies of the group.
To carry out this study we have selected a sample of compact groups from the UZC catalogue (UZC-CGs) with all spectra available
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