Spatially resolved kinematics, galactic wind, and quenching of star formation in the luminous infrared galaxy IRAS F11506-3851

¹ CSIC – Departamento de Astrofisica-Centro de Astrobiologia (CSIC-INTA), Torrejon de Ardoz, Madrid, Spain
e-mail: scazzoli@cab.inta-csic.es
² Cavendish Laboratory, University of Cambridge 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK
³ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Received: 20 December 2013
Accepted: 11 May 2014

Abstract

We present a multi-wavelength integral field spectroscopic (IFS) study of the low-z luminous infrared galaxy IRAS F11506-3851 (ESO 320-G030) on the basis of the moderate spectral resolution observations (R ~ 3400−4000) taken with the VIMOS and SINFONI instruments at the ESO VLT. The morphology and the 2D kinematics of the gaseous (neutral and ionized) and stellar components have been mapped in the central regions (<3 kpc) using the NaDλλ5890, 5896 Å absorption doublet, the Hαλ6563 Å line, and the near-IR CO(2–0)λ2.293 μm and CO(3–1)λ2.322 μm bands. The kinematics of the ionized gas and the stars are dominated by rotation, with large observed velocity amplitudes (ΔV(Hα) = 203 ± 4 km s^-1; ΔV(CO) = 188 ± 11 km s^-1, respectively) and centrally peaked velocity dispersion maps (σ_c(Hα) = 95 ± 4 km s^-1 and σ_c(CO) = 136 ± 20 km s^-1). The stars lag behind the warm gas and represent a dynamically hotter system, as indicated by the observed V/σ ratios (4.5 and 2.4 for the gas and the stars, respectively). Thanks to these IFS data we have disentangled the contribution of the stars and the interstellar medium to the NaD feature, finding that it is dominated by absorption of neutral gas clouds in the interstellar medium (~2/3 of total EW). The 2D kinematics of the neutral gas shows a complex structure dominated by two main components. On the one hand, the thick slowly rotating disk (ΔV(NaD) = 81 ± 12 km s^-1) lags significantly compared to the ionized gas and the stars, and it has an irregular and off-center velocity dispersion map (with values of up to ~150 km s^-1 at ~1 kpc from the nucleus). On the other hand, a kpc-scale neutral gas outflow perpendicular to the disk, as is revealed by the large blueshifted velocities (in the range 30−154 km s^-1) observed along the galaxy’s semi-minor axis (within the inner 1.4 kpc). On the basis of a simple free wind scenario, we derive an outflowing mass rate (Ṁ_w) in neutral gas of about 48 M_⊙ yr^-1. Although this implies a global mass loading factor (i.e., η = Ṁ_w/SFR) of ~1.4, the 2D distribution of the ongoing SF as traced by the Hα emission map suggests a much larger value of η associated with the inner regions (R< 200 pc), where the current observed star formation (SF) represents only ~3 percent of the total. However, the relatively strong emission by supernovae in the central regions, as traced by the [FeII] emission, indicates recent strong episodes of SF. Therefore, our data show clear evidence of the presence of a strong outflow with large loading factors associated with the nuclear regions, where recent starburst activity took place about 7 Myr ago, although it currently shows relatively modest SF levels. All together these results strongly suggest that we are witnessing (nuclear) quenching due to SF feedback in IRAS F11506-3851. However, the relatively large mass of molecular gas detected in the nuclear region via the H₂ 1−0S(1) line suggests that further episodes of SF may take place again.