The nuclear source of the galactic wind in NGC 253

Abstract

We present Brγ emission line kinematics of the nuclear region of NGC 253, recently known to host a strong galactic wind that limits the global star formation of the galaxy. We obtained high-resolution long-slit spectroscopic data with PHOENIX at Gemini South, positioning the slit on the nucleus infrared core (IRC), close to the nuclear disk major axis. The spatial resolution was 0.″35 (∼6 pc) and the slit length was 14″ (∼240 pc). The spectral resolution was ∼74,000, unprecedentedly high for galactic nuclei observations at ∼2.1 μm. The line profiles appear highly complex, with blue asymmetry up to 3.″5 away of the IRC, and red asymmetries further away to northeast. Several Gaussian components are necessary to fit the profile, nevertheless a narrow and a wide one predominate. The IRC presents kinematic widths above 700 km s-1 (FWZI), and broad component FWHM ∼ 400 km s-1, the highest detected in a nearby galaxy. At the IRC, the blueshifted broad component displays a 90 km s-1 bump in radial velocity distribution, a feature we previously detected in molecular gas kinematics. The narrow component velocity dispersion (∼32 km s-1) is within the expected for normal galaxies and luminous infrared galaxies (LIRGs). Intermediate components (FWHM ∼ 150 km s-1, redshifted to the northeast, blueshifted to the southwest) appear at some positions, as well as weaker blue (-215 km s-1) and red line wings (+300 km s-1). The IRC depicts a large broad-versus-narrow line flux ratio (F(B)/F(N) ∼ 1.35), and the broad component seems only comparable with those observed at very high star-forming rate galaxies. The results indicate that the IRC would be the main source of the galactic winds originated in the central region of NGC 253.