Kinematics of Arp 270: gas flows, nuclear activity and two regimes of star formation

Abstract

We have observed the Arp 270 system (NGC 3395 & NGC 3396) in Hα emission using the GHαFaS Fabry-Perot spectrometer on the 4.2m William Herschel Telescope (La Palma). In NGC 3396, which is edge-on to us, we detect gas inflow towards the centre, and also axially confined opposed outflows, characteristic of galactic superwinds, and we go on to examine the possibility that there is a shrouded AGN in the nucleus. The combination of surface brightness, velocity and velocity dispersion information enabled us to measure the radii, FWHM, and the masses of 108 HII regions in both galaxies. We find two distinct modes of physical behaviour, for high and lower luminosity regions. We note that the most luminous regions show especially high values for their velocity dispersions and hypothesize that these occur because the higher luminosity regions form from higher mass, gravitationally bound clouds while those at lower luminosity HII regions form within molecular clouds of lower mass, which are pressure confined.

Outer regions of the merging system Arp 270★

“…The lowvelocity stellar component hardly may be ascribed to the second galaxy, because its adjacent side is the receding one, having a lager line-of-sight velocity. Gas velocity field of both galaxies reveals a strong non-circular motion, although a rotational pattern of the velocity field of NGC 3395 is evident (Zaragoza-Cardiel et al 2013). Measured velocities of emission gas (Zaragoza-Cardiel et al 2013) and Hi (Clemens et al 1999) in this area are several tens km s −1 above the velocity of galaxy centre due to the disc rotation, whereas our measurements give the velocities of stars which are several tens km s −1 lower than that of gas.…”

“…Gas velocity field of both galaxies reveals a strong non-circular motion, although a rotational pattern of the velocity field of NGC 3395 is evident (Zaragoza-Cardiel et al 2013). Measured velocities of emission gas (Zaragoza-Cardiel et al 2013) and Hi (Clemens et al 1999) in this area are several tens km s −1 above the velocity of galaxy centre due to the disc rotation, whereas our measurements give the velocities of stars which are several tens km s −1 lower than that of gas. The most natural explanation of the discrepancy is that the gas and stars are spatially separated there because of strong disc tidal distortion, so that the stellar disc is more face-on oriented than the gas layer in the region crossed by the slit, and, as a result, its rotational velocity component is small.…”

“…We compared the velocity range estimated in this paper with that of the velocity field of Zaragoza-Cardiel et al (2013). For the Slit №1, we got the velocity variance of ∆v ≈ 1565 − 1655 km s −1 for ionized gas ( 1535 − 1655 km s −1 for stars).…”

“…Later, the two-dimensional velocity field in the line Hα, was obtained in the framework of the project GHASP (Garrido et al 2002;Epinat, Amram & Marcelin 2008), which confirmed the rotation of both galaxies, as well as the presence of significant non-circular velocity in the system reaching a few tens km s −1 . Zaragoza-Cardiel et al (2013) also constructed two-dimensional map of gas velocities in this system which demonstrates the existence of radial gas motion in the central region of NGC 3396. Based on the measurements of the velocity dispersion of emission gas the authors concluded that in both galaxies star formation is associated mostly with high luminous Hii regions, which apparently are connected with gravitationally bound clouds.…”

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

“…It is a visiting instrument on the William Herschel Telescope (WHT) in La Palma. 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.…”