The near-infrared structure of the barred galaxy NGC 253 from VISTA^⋆,⋆⋆

¹ INAF – Astronomical Observatory of Capodimonte, via Moiariello 16, 80131 Naples, Italy
e-mail: iodice@na.astro.it
² ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
³ INAF-Astronomical Observatory of Turin, Strada Osservatorio 20, 10025 Turin, Italy
⁴ Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany
⁵ INAF Astronomical Observatory of Padua, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁶ ESO, Ave. Alonso de Cordova 3107, Casilla 19, 19001 Santiago, Chile
⁷ Institute of Astronomy, Madingley Road, Cambridge CB03 0HA, UK
⁸ Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK

Received: 20 January 2014
Accepted: 23 May 2014

Abstract

Context. The presence of a bar affects the distribution and dynamics of a stellar disk at all scales, from a fraction of a kpc in the inner central region to tens of kpc at the disk’s edge. The quantitative study of the disk response to a bar can be hampered by the presence of dust, which is common in late type spirals.

Aims. We want to quantify the structures in the stellar disk of the barred Sc galaxy NGC 253 located in the Sculptor group, at 3.47 Mpc distance.

Methods. We use J and Ks band images acquired with the VISTA telescope as part of the Science Verification. The wide field of view and the high angular resolution of this survey facility allow the mapping of the large and small scale structure of the stellar disk in NGC 253. We use unsharp masking and two dimensional modelling of the smooth light distribution in the disk to identify and measure the sub-structures induced by the bar in the stellar disk of NGC 253. We build azimuthally-averaged profiles in the J and Ks bands to measure the radial surface brightness profile of the central bulge, bar and disk.

Results. Moving outward from the galaxy center, we find a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring with 2.9 kpc radius, and spiral arms in the outer disk. From the Ks image we obtain a new measure of the de-projected length of the bar of 2.5 kpc. The bar’s strength, as derived from the curvature of the dust lanes in the J-Ks image, is typical of weak bars with Δα = 25 degree/kpc. From the de-projected length of the bar, we establish the co-rotation radius (R_CR = 3 kpc) and bar pattern speed (Ω_b = 61.3 km s^-1 kpc^-1), which provides the connection between the high frequency structures in the disk and the orbital resonances induced by the bar. The nuclear ring is located at the Inner Lindblad resonance. The second ring (at 2.9 kpc) does not have a resonant origin, but it could be a merger remnant or a transient structure formed during an intermediate stage of the bar formation. The inferred bar pattern speed places the Outer Lindblad resonance within the optical disk at 4.9 kpc, in the same radial range as the peak in the HI surface density. The disk of NGC 253 has a down-bending profile with a break at R ~ 9.3 kpc, which corresponds to about 3 times the scale length of the inner disk. We discuss the evidence for a threshold in star formation efficiency as a possible explanation for the steep gradient in the surface brightness profile at large radii.

Conclusions. The near-infrared photometry unveils the dynamical response of the NGC 253 stellar disk to its central bar. The formation of the bar may be related to the merger event that determined the truncation of stars and gas at large radii and the perturbation of the disk’s outer edge.