Near-infrared and optical observations of galactic warps: a common, unexplained feature of most discs

Abstract

Context. Warps occurring in galactic discs have been studied extensively in HI and in the optical, but rarely in the near-infrared (NIR) bands that trace the older stellar populations. Aims. We provide NIR data of nearby edge-on galaxies, combined with optical observations, for direct comparison of the properties of galactic warps as a function of wavelength, and calculate warp curves for each galaxy and obtain the characteristic warp parameters. We discuss these properties as possible constraints to the different mechanisms that have been proposed for the development and persistence of galactic warps. Methods. We observed 20 galaxies that were selected from a statistically complete diameter-limited subsample of edge-on disc galaxies. We used the Cerro Tololo Infrared Imager (CIRIM) at the CTIO 1.5 m Ritchey-Chretien telescope to acquire the NIR data. We used the 1.54 m Danish and 0.92 m Dutch telescopes at the European Southern Observatory's La Silla site for our optical observations. Results. Our results show that 13 of our 20 sample galaxies are warped, with the warp more pronounced in the optical than at NIR wavelengths. In the remaining seven galaxies, no warp is apparent within the limitations of our automated detection method. The transition between the unperturbed inner disc and the outer, warped region is rather abrupt. S0 galaxies exhibit very small or no warps. The magnetic model remains one of a number of interesting formation scenarios.

The kinematic signature of the Galactic warp inGaiaDR1

“…The Galactic warp has since been seen in the dust and stars (Freudenreich et al 1994;Drimmel & Spergel 2001;López-Corredoira et al 2002;Momany et al 2006;Marshall et al 2006;Robin et al 2008;Reylé et al 2009). Our Galaxy is not peculiar with respect to other disk galaxies: more than 50 percent of spiral galaxies are warped (Sanchez-Saavedra et al 1990;Reshetnikov & Combes 1998;Guijarro et al 2010). The high occurrence of warps, even in isolated galaxies, implies that either these features are easily and continuously generated, or that they are stable over long periods of time.…”

A Search for Planetary Nebulae With the SDSS: the outer regions of M31

“…For instance, deep optical surveys of nearby face-on and edge-on dIrrs and disk galaxies have also found that their stellar distributions are much more extended than previously thought, e.g., NGC 6822 (de Blok & Walter 2006), Leo A (Vansevičius et al 2004), IC 1613 (Battinelli et al 2007), Pegasus (Kniazev et al 2009), the Magellanic Clouds (Casetti-Dinescu et al 2012, and references therein) and the works of Malin & Hadley (1999); Tikhonov (2005Tikhonov ( , 2006. Moreover, warps and flaring have been shown to be common features of galactic disks (e.g., Guijarro et al 2010; van der Kruit & Freeman 2011, and references therein). In addition, accretion features are now commonly detected (e.g., Martínez-Delgado et al 2008, 2009Mouhcine et al 2010;Miskolczi et al 2011;Ludwig et al 2012).…”

LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) — The survey's science plan

“…By utilizing radial velocities and proper motions from outside catalogs, one would be able to trace the structure and kinematics of the disk as a function of position in the Galaxy, especially in the following respects: (1) The depth of LAMOST will allow the 3-D structure of the northern Galactic warp (Guijarro et al 2010) in the Galaxy to be traced, using giants and red clump stars in distant clusters ; (2) Kinematic data of OCs will also allow us to systematically study the Galactocentric rotation velocity, which will provide definitive estimates of the mass of the Galaxy, and also the principal scale parameter − the distance of the Sun from the Galactic center, R ⊙ ; and (3) By combining chemical abundances and ages of OCs, one will be able to probe the correlations between age, velocity, and abundance as a function of position in the Galaxy (Yu et al 2012).…”