Interlocking Resonance Patterns in Galaxy Disks

Abstract

We have developed a method for finding dynamical resonances in disk galaxies using the change in sense of the radial component of the in-plane velocity at a resonance radius. Using simulations we show that we would expect to find these changes at corotation radii, with a weaker effect at the ILR and a small effect at the OLR. The method works well with observations at high spectral and angular resolutions, and is suited to the analysis of 2D velocity fields in H! from Fabry-Perot spectroscopy, (though it is also applicable to fields in 21cm emission from HI, or to CO emission lines). The observations are mainly from the GHASP spectrometer data base, taken on the 1.93m telescope at Haute Provence, plus some data from the GH!FaS spectrometer on the 4.2m WHT at La Palma. We find clear indications of resonance effects in the disk velocity fields of virtually all of the 104 galaxies. The number of resonance radii detected ranges from one to seven, with a median of four. We have derived the resonance curves: ", "±#/2, "±#/4 against radius for all the galaxies, and used them to derive the ILR, the OLR, and the two 4:1 resonances for each corotation in each galaxy. This led us to discover a pattern in over 70% of the sample: given two pattern speeds, say " 1 and " 2 , the OLR of " 1 coincides with the corotation of " 2 , and the inner 4:1 resonance of " 2 coincides with the corotation of " 1 . Although the second coincidence has been predicted, a prediction of this double coincidence is not found in the literature. This pattern is found once in 42 of the galaxies, twice in a further 26, three times in five, and even four times in one galaxy. We also compute the ratio of corotation radius to bar length where we have good enough image quality, finding a mean value of 1.3, and a shallow increase towards later type galaxies.

Kinematic Clues to Bar Evolution for Galaxies in the Local Universe: Why the Fastest Rotating Bars are Rotating Most Slowly

“…A detailed description of the sample selection criteria is given in Font et al (2014a). From that sample we have selected those galaxies that are classified as barred, or show a bar-like central structure, and also have a spiral arm structure.…”

“…In this article we determine the bar corotation radius (and hence its pattern speed) with the Font-Beckman method (Font et al 2011(Font et al , 2014a, which uses phase-reversals of the streaming motions. In essence, from the line-of-sight velocity field in Hα we extract the rotation curve, which is used to construct a 2D model of the circular velocity, which is then subtracted from the original velocity field in order to produce the residual velocity map.…”

“…They are (i) the well-known Tremaine-Winberg method (Tremaine & Weinberg 1984); its later modification to include multiple density wave patterns (Meidt et al 2008a(Meidt et al , 2008b combines photometric data with velocities derived from long-slit spectra placed parallel to the galaxy major axis (Kent 1987;Merrifield & Kruijken 1995;Gerssen et al 1999;Debattista et al 2002;Aguerri et al 2003;Corsini et al 2003;Debattista & Williams 2004;Rand & Wallin 2004;Zimmer et al 2004;Hernandez et al 2005;Fathi et al 2009;Corsini 2011, and references therein, Aguerri et al 2015). (ii) the gravitational potential distribution to reproduce the velocity map (Sanders & Tubbs 1980;England et al 1990;Garcia-Burillo et al 1993;Piñol-Ferrer et al 2014); (iii) the morphologies of the non-circular velocity map of the gas in the galaxy can be used (Canzian 1993;Rand 1995;Sempere et al 1995;Canzian & Allen 1997;Font et al 2011Font et al , 2014aFont et al , 2014b; (iv) finally, numerical simulations of barred galaxies are another method (Lindblad et al 1996;Laine & Heller 1999;Aguerri et al 2001;Weiner et al 2001;Pérez et al 2004;Rautiainen et al 2005Rautiainen et al , 2008Treuthardt et al 2008).…”

“…A quantitative step forward in terms of the number of galaxies measured was made by Font & Beckman (Font et al 2011, 2014a, 2014b, who took full advantage of the high spectral and spatial resolution made possible with scanning Fabry-Pérot spectroscopic technology to analyze the twodimensional velocity fields of over 100 galaxies observed in Hα. Instead of trying to determine the pattern speeds of the structures in these galaxies, the authors directed their attention directly to measuring the corotation radius (to be precise, the corotation radii, as they found radii associated with more than one structural component of the disk in virtually all cases).…”

Hα kinematics of S4G spiral galaxies – II. Data description and non-circular motions

“…The GHαFaS instrument has been operative since 2007 , and has been used to study pattern speeds of bars and spiral arms (Fathi et al 2009), to analyse the kinematics of planetary nebulae (Santander-García et al 2010), and the gas flows (Font et al 2011b), star formation and the kinematics of interacting galaxies (Zaragoza-Cardiel et al 2013 and starburst galaxies (Blasco-Herrera et al 2013). It has also been used to study the resonance radii and interlocking resonance patterns in galaxy discs (Font et al 2011a(Font et al , 2014a.…”