The Norma spiral arm: large-scale pitch angle

Monthly Notices of the Royal Astronomical Society

2020

This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the 'Outer Norma' arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literaturesee column 8 in Table 1 here, having been obtained via the existing networks ( US VLBA , the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm, and those congregating within an 'interarm island' located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus we delineate an interarm island (6x2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small 'Local Orion arm' (4x2 kpc) found earlier between the Perseus and Sagittarius arms, and of the old 'Loop' (2x0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, HII regions, HI gas, young stars, CO 1-0 gas).

Section: Resultsmentioning

confidence: 99%

Section: Arm Model As Fitted To the Broad Co 1-0 Molecules Seen At Tmentioning

confidence: 92%

Section: The Segmented Reid Et Al Arm Model Constructed Piecewises Bmentioning

confidence: 94%

Section: Trigonometric Masers and A New 4-arm Modelmentioning

confidence: 99%

Section: Three Trigonometric Masers Inmentioning

confidence: 99%

See 3 more Smart Citations

Interarm islands in the Milky Way – the one near the Cygnus spiral arm

Monthly Notices of the Royal Astronomical Society

2020

Meta-analysis from different tracers of the small Local Arm around the Sun—extent, shape, pitch, origin

2018

Astrophys Space Sci

Self Cite

The Sun in not located in a major spiral arm, and sits in a small 'Local Arm' (variously called arm, armlet, blob, branch, bridge, feather, finger, segment, spur, sub-arm, swath, etc). The diversity of names for the 'Local Arm' near the Sun indicates an uncertainty about its shape or pitch or its extent from the Sun in each galactic quadrant, as well as an uncertainty about its origin.Here we extract data about the small 'Local Arm' near the Sun, from the recent observational literature, over many arm tracers, and we use statistics in order to find the local arm's mean extent from the Sun, its possible shape and pitch angle from the direction of galactic longitude 90 o . Employing all tracers, the Local Arm is about 4 kpc long by 2 kpc large. The Sun is within 1 kpc of the center of the local arm. Proposed 'bridges' and 'fingers' are assessed. These bridges to nearby spiral arms and fingers across spiral arms may not reach the nearest spiral arms, owing to kinematic and photometric distance effects.We then compare these statistical results with some predictions from recent models proposed to explain the local arm (perturbations, resonances, density wave, halo supercloud, debris trail from a dwarf galaxy).The least controversial models involve importing materials from elsewhere (halo supercloud, debris trail) as a first step, and to be later deformed in a second step (by the Galaxy's differential rotation into become roughly parallel to spiral arms) and then subjected to ongoing forces (global density waves, local perturbations).

Spatial offsets between interstellar bone-like filaments, radio masers, and cold diffuse CO gas, in the Scutum spiral arm

2019

Astrophys Space Sci

Self Cite

The advent of more precise measurements of distance estimates for some objects (bayesian estimates for filaments, trigonometric estimates for masers) permits a better comparison of their relative locations, and a comparison with a most recent spiral arm model fitted to the diffuse CO 1-0 gas. Our results support the idea that some 'bone-like' filaments, greater than 10 pc (labeled elsewhere as 'bones', 'mst', 'herschel') and smaller than 100 pc, are observed near the potential minimum of the Scutum spiral arm (bone-like filaments are offset outward from masers by about 200 pc).