arXiv subjects

Helene M Courtois

Publications and source records attributed to Helene M Courtois.

4 recordsLinked to original sources

arXiv2019

The orientation of planes of dwarf galaxies in the quasi-linear Universe

To date at least 10 highly flattened planes of dwarf galaxies are claimed to have been discovered in the Local Universe. The origin of these planes of galaxies remains unknown. One suggestion is that they are related to the large-scale structure of the cosmic web. A recent study found that the normal of a number of these dwarf galaxy planes are very closely aligned with the eigenvector of the shear tensor corresponding to the direction of greatest collapse obtained by reconstructing the full velocity field in the linear regime. Here we extend that work by both considering an additional 5 planes beyond the 5 examined previously and by examining the alignment with respect to the quasi-linear field, a more sophisticated reconstruction, which is a better approximation on smaller (quasi-linear) scales. Our analysis recovers the previous result while not finding a significantly tight alignment with the additional 5 planes. However, the additional 5 planes normals also do not appear to be randomly oriented. We conclude that this could either be due to the normals of the new planes being poorly defined and described; the quasi-linear field at those locations being poorly constrained; or different formation mechanisms for the orientation of planes of dwarf galaxies.

astro-ph.GA↗

arXiv2019

Cosmicflows-3: Cosmography of the Local Void

Cosmicflows-3 distances and inferred peculiar velocities of galaxies have permitted the reconstruction of the structure of over and under densities within the volume extending to 0.05c. This study focuses on the under dense regions, particularly the Local Void that lies largely in the zone of obscuration and consequently has received limited attention. Major over dense structures that bound the Local Void are the Perseus-Pisces and Norma-Pavo-Indus filaments separated by 8,500 km/s. The void network of the universe is interconnected and void passages are found from the Local Void to the adjacent very large Hercules and Sculptor voids. Minor filaments course through voids. A particularly interesting example connects the Virgo and Perseus clusters, with several substantial galaxies found along the chain in the depths of the Local Void. The Local Void has a substantial dynamical effect, causing a deviant motion of the Local Group of 200-250 km/s. The combined perturbations due to repulsion from the Local Void and attraction toward the Virgo Cluster account for about 50% of the motion of the Local Group in the rest frame given by the cosmic microwave background.

astro-ph.CO↗

arXiv2017

The Cosmic V-Web

The network of filaments with embedded clusters surrounding voids seen in maps derived from redshift surveys and reproduced in simulations has been referred to as the cosmic web. A complementary description is provided by considering the shear in the velocity field of galaxies. The eigenvalues of the shear provide information on whether a region is collapsing in three dimensions, the condition for a knot, expanding in three-dimensions, the condition for a void, or in the intermediate condition of a filament or sheet. The structures that are quantitatively defined by the eigenvalues can be approximated by iso-contours that provide a visual representation of the cosmic velocity (V) web. The current application is based on radial peculiar velocities from the Cosmicflows-2 collection of distances. The three-dimensional velocity field is constructed using the Wiener filter methodology in the linear approximation. Eigenvalues of the velocity shear are calculated at each point on a grid. Here, knots and filaments are visualized across a local domain of diameter ~0.1c.

astro-ph.CO↗

arXiv2009

The Extragalactic Distance Database: All Digital HI Profile Catalog

An important component of the Extragalactic Distance Database (EDD) at http://edd.ifa.hawaii.edu is a group of catalogs related to the measurement of HI line profile parameters. One of these is the All Digital HI catalog which contains an amalgam of information from new data and old. The new data results from observations with Arecibo and Parkes telescopes and with the Green Bank Telescope (GBT), including continuing input since the award of the NRAO Cosmic Flows Large Program. The old data has been collected from archives, wherever available, particularly the Cornell University Digital HI Archive, the Nancay Telescope extragalactic HI archive, and the Australia Telescope archive. The catalog currently contains information on ~15,000 profiles relating to ~13,000 galaxies. The channel - flux per channel files, from whatever source, are carried through a common pipeline. The derived parameter of greatest interest is W_m50, the profile width at 50% of the mean flux. After appropriate adjustment, the parameter W_mx is derived, the linewidth which statistically approximates the peak to peak maximum rotation velocity before correction for inclination, 2 V_max sin(i).

astro-ph.CO↗