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

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 (∆V(Hα) = 203 ± 4 km s −1 ; ∆V(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 (∆V(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 H 2 1−0S(1) line suggests that further episodes of SF may take place again.

Neutral gas outflows in nearby [U]LIRGs via optical NaD feature

“…In three galaxies (F07027-6011 (S), F10409-4556, and F11506-3851), the rotation is detected in one kinematic component, but an additional outflowing component is also detected (Figs. A.13 and A.23, and Cazzoli et al 2014). However, while in case of an ideal rotating disk the velocity dispersion map should be centrally peaked, the observed neutral gas velocity dispersion maps are generally rather irregular.…”

“…We found some spectra that have strongly asymmetric profiles and their modeling requires two Gaussian pairs (i.e., a single component fitting is certainly an oversimplification). After visual inspecting all the spectra, we decided to apply a two-components line fitting for the spectra of four objects (F07027-6011 (S), F10409-4556, F11506-3851, and F12116-5615) similarly as in Cazzoli et al (2014). In a few other cases, there is evidence for the presence of multiple kinematic components in individual spectra (e.g., F04315-0840, F10257-4310, F13229-2934).…”

“…However, it is important to consider that the stellar contribution is computed in the integrated light. Therefore, in some cases even if the stellar absorption in the integrated spectrum is substantial, the 2D distribution may help to identify regions where the NaD absorption is dominated by neutral gas or the stellar component, as in F11056-3851 (Cazzoli et al 2014). Without the knowledge of the stellar properties and kinematics in these galaxies, we cannot investigate this further.…”

“…For a detailed analysis of the ionized gas kinematics, we refer to Bellocchi et al (2013). The LIRG IRAS 11506-3851 is discussed in detail by Cazzoli et al (2014) ionized disks and, therefore, they are likely to be thicker (i.e., larger h z ). This confirms that the ionized gas resides in regions of high density close to the innermost regions of the disk, while the neutral gas is located further out.…”

Galactic outflow and diffuse gas properties at z ≥ 1 using different baryonic feedback models

“…As a recent example at high redshift, Crighton et al (2014) observed absorbing gas clumps in a z = 2.5 galaxy CGM, produced by a wind with a mass outflow rate of ∼ 5M⊙/yr. At low redshift, Cazzoli et al (2014) detected kpc-scale neutral gas outflowing perpendicular to the disk of a z = 0.01 galaxy, at a rate ∼ 48M⊙/ yr, with a global mass loading factor η ≈ 1.4. Such values of mass outflow rate (a few to 10's M⊙/yr) and η lie within our simulation result range ( §4.3.2, §4.3.4).…”