The Shock-Induced Star Formation Sequence Resulting From a Constant Spiral Pattern Speed

Abstract

We utilize a suite of multiwavelength data of nine nearby spirals to analyze the shock-induced star formation sequence that may result from a constant spiral pattern speed. The sequence involves tracers as the H i, CO 24 μm, and FUV, where the spiral arms were analyzed with Fourier techniques in order to obtain their azimuthal phases as a function of radius. It was found that only two of the objects, NGC 628 and NGC 5194, present coherent phases resembling the theoretical expectations, as indicated by the phase shifts of CO-24 μm. The evidence is more clear for NGC 5194 and moderate for NGC 628. It was also found that the phase shifts are different for the two spiral arms. With the exception on NGC 3627, a two-dimensional Fourier analysis showed that the rest of the objects do not exhibit bi-symmetric spiral structures of stellar mass, i.e., grand-design spirals. A phase order inversion indicates a corotation radius of ∼89 for NGC 628 and ∼202 for NGC 5194. For these two objects, the CO-Hα phase shifts corroborate the CO-24 μm azimuthal offsets. Also for NGC 5194, the CO-70 μm, CO-140 μm, and CO-250 μm phase shifts indicate a corotation region.

Characterizing bars in low surface brightness disc galaxies

“…This method has been used to determine the corotation radii for HSBs, and has found consistent results with both direct measurements of the pattern speed and numerical simulations of real galaxies (Aguerri et al 1998;Vera-Villamizar et al 2001;Sierra et al 2015). In addition, Martínez-García & Puerari (2014) expanded the use of this method to HI, CO, 24 µm, and FUV with success.…”

Statistics on 24 spiral galaxies having different observed arm locations using different arm tracers

“…14 andsection 4.3 in Foyle et al 2011). Later on, the results of Foyle et al (2011) were questioned by Martinez-Garcia & Puerari (2014), who employed a Fourier transform method ('y') to analyze the signal intensity over a 360 o azimuthal range ('x'), at an angular resolution of 13"; they found an offset between CO and 24µm tracers for NGC 628 and NGC 5194. The HI tracer used in Foyle et al (2011) does not take account of the large-scale dissociation of molecular gas by newly formed stars in galaxies (Allen 1986).…”

The Behavior of the Pitch Angle of Spiral Arms Depending on Optical Wavelength

“…Under the proposed scenario, the "blue spiral" will intersect the "red spiral" near the corotation radius (R CR ). This would indicate that the angular speed of the spiral pattern (Ω p ) can be assumed to be constant for all radii (Martínez-García & Puerari 2014), at least in the object's current stage of evolution.…”