Local Sheet

Abstract: In this study, the local velocities of the liquid sheet formed by two low-speed impinging jets were directly measured using a LDV (laser Doppler velocimetry) instrument. The spatial distribution of the local sheet velocities at the forward part of the sheet and the effects of the impingement angle and jet velocity on the sheet velocities were examined. A parabolic velocity profile across the pre-impinging jet greatly affected the sheet velocity distribution, causing the sheet velocities to decrease while the azimuthal angle increased. This was attributed to the movement of a high velocity core, existing in the pre-impinging jets, to the region around the axis of the sheet. In the radial direction, the local sheet velocities were a little low around the impinging point, and remained constant, but then decreased near the edge of the sheet. The dependence of sheet velocities on the impingement angle was confirmed, and the tendency towards an even distribution of sheet velocities was found to increase as the impingement angle increased. With the exception of the lowest velocities measured near the edge of the sheet, the local sheet velocities at the forward part of the sheet were higher than the mean jet velocity.

Abstract: Archival HST data taken in F606W+F814W of two different fields in the outer regions of NGC 6946 is used to measure a tip of the red giant branch (TRGB) distance to the galaxy. We employ a Bayesian maximum-likelihood modeling method that incorporates the completeness of the photometry, and allows us to model the luminosity function of the RGB population. Our two fields provide us with distances of 7.74 $\pm$ 0.42 Mpc and 7.69 $\pm$ 0.50 Mpc, respectively. Our final distance of 7.72 $\pm$ 0.32 Mpc is higher than most values published previously in the literature. This has important implications for supernova measurements, as NGC 6946 is host to the most observed supernovae (10) of any galaxy to date. We find that the supernovae in NGC 6946 are on average $\sim$ 2.3 times more luminous than previous estimates. Our distance gives NGC 6946 a peculiar velocity of $v_{pec}$ = $-229$ $\pm$ $29$ km/s in the Local Sheet frame. This velocity is the projected component of a substantial negative SGZ motion, indicating a coherent motion along with the other members of the M101 wall toward the plane of the Local Sheet. The M101 wall, a spur off the Local Sheet into the Local Void, is experiencing the expansion of the Local Void.

Abstract: Distances and near-infrared luminosities of the brightest galaxies in the Local Volume have been re-evaluated in order to gain a fully homogeneous collection of data for elucidating the framework of the Local Sheet and its relevance to Local Group evolution. It is demonstrated that the Local Sheet is both geometrically and dynamically distinct from the Local Supercluster and that the evolution of the Sheet and Local Group were probably interconnected. The Sheet is inclined by 8° with respect to the Local Supercluster, and the dispersion of giant members about the mid-plane is only 230 kpc. A ‘Council of Giants’ with a radius of 3.75 Mpc encompasses the Local Group, demarcating a clear upper limit to the realm of influence of the Local Group. The only two giant elliptical galaxies in the Sheet sit on opposite sides of the Council, raising the possibility that they have somehow shepherded the evolution of the Local Group. The position vector of the Andromeda galaxy with respect to the Milky Way deviates only 11° from the Sheet plane and only 11° from the projected axis of the ellipticals. The Local Group appears to be moving away from a ridge in the potential surface of the Council on a path parallel to the elliptical axis. Spin directions of the giants in the Council are distributed over the sky in a pattern which is very different from that of giants beyond, possibly in reaction to the central mass asymmetry that developed into the Local Group. By matching matter densities of Group and Council giants, the edge of the volume of space most likely to have contributed to the development of the Local Group is shown to be very close to where gravitational forces from the Local Group and the Council balance. The boundary specification reveals that the Local Sheet formed out of a density perturbation of very low amplitude (∼10 per cent), but that normal matter was incorporated into galaxies with relatively high efficiency (∼40 per cent). It appears that the development of the giants of the Local Sheet was guided by a pre-existing flattened framework of matter.

Abstract: Archival HST data taken in F606W+F814W of two different fields in the outer regions of NGC 6946 is used to measure a tip of the red giant branch (TRGB) distance to the galaxy. We employ a Bayesian maximum-likelihood modeling method that incorporates the completeness of the photometry, and allows us to model the luminosity function of the RGB population. Our two fields provide us with distances of 7.74 $\pm$ 0.42 Mpc and 7.69 $\pm$ 0.50 Mpc, respectively. Our final distance of 7.72 $\pm$ 0.32 Mpc is higher than most values published previously in the literature. This has important implications for supernova measurements, as NGC 6946 is host to the most observed supernovae (10) of any galaxy to date. We find that the supernovae in NGC 6946 are on average $\sim$ 2.3 times more luminous than previous estimates. Our distance gives NGC 6946 a peculiar velocity of $v_{pec}$ = $-229$ $\pm$ $29$ km/s in the Local Sheet frame. This velocity is the projected component of a substantial negative SGZ motion, indicating a coherent motion along with the other members of the M101 wall toward the plane of the Local Sheet. The M101 wall, a spur off the Local Sheet into the Local Void, is experiencing the expansion of the Local Void.