National Autonomous University of Mexico

About: National Autonomous University of Mexico is a education organization based out in Mexico City, Distrito Federal, Mexico. It is known for research contribution in the topics: Population & Galaxy. The organization has 72868 authors who have published 127797 publications receiving 2285543 citations. The organization is also known as: UNAM & Universidad Nacional Autónoma de México.

Eigenvector 1: An Optimal Correlation Space for Active Galactic Nuclei.

Abstract: We identify a correlation space involving optical and UV emission-line parameters as well as the soft X-ray spectral index that provides optimal discrimination between all principal classes of active galactic nuclei (AGNs). Most of the sources in our three high-quality data samples show a strong intercorrelation with narrow-line Seyfert 1 (NLSy1) galaxies and steep-spectrum radio galaxies occupying opposite extrema in the space. NLSy1 sources show a clear continuity with broader line sources, indicating that they are not a disjoint class of AGN as is sometimes suggested. We interpret the principal intercorrelation in the parameter space as being driven by the AGN luminosity-to-black hole mass ratio (L/M is proportional to the Eddington ratio). Source orientation no doubt also plays an important role, but it is not yet clear whether FWHM Hβ or C IV λ1549 line shift is the better indicator. We tentatively identify two radio-quiet populations: an almost pure radio-quiet population A, with FWHM ≤ 4000, and population B, which occupies the same parameter domain as the flat-spectrum radio-loud sources. A possible interpretation sees population A/NLSy1 as lower mass/high accretion rate sources and population B/radio-loud sources as the opposite.

A repeating fast radio burst source localized to a nearby spiral galaxy

Abstract: Fast radio bursts (FRBs) are brief, bright, extragalactic radio flashes1,2. Their physical origin remains unknown, but dozens of possible models have been postulated3. Some FRB sources exhibit repeat bursts4–7. Although over a hundred FRB sources have been discovered8, only four have been localized and associated with a host galaxy9–12, and just one of these four is known to emit repeating FRBs9. The properties of the host galaxies, and the local environments of FRBs, could provide important clues about their physical origins. The first known repeating FRB, however, was localized to a low-metallicity, irregular dwarf galaxy, and the apparently non-repeating sources were localized to higher-metallicity, massive elliptical or star-forming galaxies, suggesting that perhaps the repeating and apparently non-repeating sources could have distinct physical origins. Here we report the precise localization of a second repeating FRB source6, FRB 180916.J0158+65, to a star-forming region in a nearby (redshift 0.0337 ± 0.0002) massive spiral galaxy, whose properties and proximity distinguish it from all known hosts. The lack of both a comparably luminous persistent radio counterpart and a high Faraday rotation measure6 further distinguish the local environment of FRB 180916.J0158+65 from that of the single previously localized repeating FRB source, FRB 121102. This suggests that repeating FRBs may have a wide range of luminosities, and originate from diverse host galaxies and local environments. Only one repeating fast radio burst has been localized, to an irregular dwarf galaxy; now another is found to come from a star-forming region of a nearby spiral galaxy.

Defining active sacroiliitis on MRI for classification of axial spondyloarthritis: update by the ASAS MRI working group

Abstract: Objectives To review and update the existing definition of a positive MRI for classification of axial spondyloarthritis (SpA). Methods The Assessment in SpondyloArthritis International Society (ASAS) MRI working group conducted a consensus exercise to review the definition of a positive MRI for inclusion in the ASAS classification criteria of axial SpA. Existing definitions and new data relevant to the MRI diagnosis and classification of sacroiliitis and spondylitis in axial SpA, published since the ASAS definition first appeared in print in 2009, were reviewed and discussed. The precise wording of the existing definition was examined in detail and the data and a draft proposal were presented to and voted on by the ASAS membership. Results The clear presence of bone marrow oedema on MRI in subchondral bone is still considered to be the defining observation that determines the presence of active sacroiliitis. Structural damage lesions seen on MRI may contribute to a decision by the observer that inflammatory lesions are genuinely due to SpA but are not required to meet the definition. The existing definition was clarified adding guidelines and images to assist in the application of the definition. Conclusion The definition of a positive MRI for classification of axial SpA should continue to primarily depend on the imaging features of ‘active sacroiliitis’ until more data are available regarding MRI features of structural damage in the sacroiliac joint and MRI features in the spine and their utility when used for classification purposes.

Imaging of the CO Snow Line in a Solar Nebula Analog

Abstract: Planets form in the disks around young stars Their formation efficiency and composition are intimately linked to the protoplanetary disk locations of “snow lines” of abundant volatiles We present chemical imaging of the CO snow line in the disk around TW Hya, an analog of the solar nebula, using high spatial and spectral resolution Atacama Large Millimeter/Submillimeter Array (ALMA) observations of N_2H^+, a reactive ion present in large abundance only where CO is frozen out The N_2H^+ emission is distributed in a large ring, with an inner radius that matches CO snow line model predictions The extracted CO snow line radius of ∼ 30 AU helps to assess models of the formation dynamics of the solar system, when combined with measurements of the bulk composition of planets and comets