Characteristics of Spiral Arms in Late-Type Galaxies

Abstract

We have measured the positions of large numbers of H II regions in four nearly face-on, late-type, spiral galaxies: NGC 628 (M 74), NGC 1232, NGC 3184 and NGC 5194 (M 51). Fitting log-periodic spiral models to segments of each arm yields local estimates of spiral pitch angle and arm width. While pitch angles vary considerably along individual arms, among arms within a galaxy, and among galaxies, we find no systematic trend with galactocentric distance. We estimate the widths of the arm segments from the scatter in the distances of the H II regions from the spiral model. All major arms in these galaxies show spiral arm width increasing with distance from the galactic center, similar to the trend seen in the Milky Way. However, in the outer-most parts of the galaxies, where massive star formation declines, some arms reverse this trend and narrow. We find that spiral arms often appear to be composed of segments of ∼ 5 kpc length, which join to form kinks and abrupt changes in pitch angle and arm width; these characteristics are consistent with properties seen in the large N-body simulations of D'Onghia, Vogelsberger & Hernquist (2013) and others.

26Al kinematics: superbubbles following the spiral arms?

“…5), Honig & Reid (2015) map HII regions for two arms, A and B, and inside co-rotation, HI supershells are indeed found close to and overlapping with the HII regions, preferentially at their leading edges. Especially for arm B, which is located in an HI -rich part of the galaxy, the HI supershell locations relative to the HII regions change strikingly near the co-rotation radius: inside, three prominent HI supershells lie towards the leading edge of the HII arm, extending over about a quarter of a turn.…”

“…We investigated this for a few objects by combining HII regions from Honig & Reid (2015) with HI images with HI supershells using co-rotation radii from Tamburro et al (2008) and Scarano & Lépine (2013). For NGC 3184 and NGC 5194 we found evidence for HI supershells close to HII regions in the spiral arms.…”

“…Bagetakos et al (2011). Blue plus-signs denote the 650 H II regions identified by Honig & Reid (2015). Their spiral arm designations, A and B, are also indicated.…”

A guided map to the spiral arms in the galactic disk of the Milky Way

“…Elsewhere, in many nearby disk galaxies, the pitch angle appears roughly flat over 10 kpc, save for localized deviations with an amplitude near 20° [72].…”

Tracing the Spiral Structure of the Outer Milky Way with Dense Atomic Hydrogen Gas

“…On the other hand, observations of external galaxies indicate that the pitch angle can vary considerably along individual arms (Savchenko & Reshetnikov 2013;Davis & Hayes 2014;Honig & Reid 2015, and references therein). In the Milky Way, trigonometric parallax measurements of HMSFRs also found a considerable variation of pitch angles (7…”