The link between galaxy merger, radio jet expansion and molecular outflow in the ULIRG IRAS 00183-7111

TL;DR

The paper investigates IRAS 00183-7111, a z=0.328 ULIRG hosting a compact radio jet, to elucidate how a recent major merger triggers AGN activity and drives a kpc-scale molecular outflow. By combining high-resolution ALMA CO(1-0) and CO(3-2) data with deep VST i-band imaging, the authors map the gas distribution, excitation, and kinematics, finding a high-excitation, jet-ISM–impacted environment around the radio cores and a prominent molecular outflow with v$_{out} \,\approx\;439$ km s$^{-1}$ and $\dot{M}_{out}\;\approx\;609$ M$_\odot$ yr$^{-1}$. The gas mass is $M_{mol} \approx 1.0\times10^{10}$ M$_\odot$, and the CO line ratio R$_{31}$ indicates $T_{ex} \gg 50$ K near the jets, consistent with jet-driven heating. Energetic considerations show that SN feedback and current AGN radiation pressure are unlikely to power the outflow alone, while jet kinetic power and age derived from jet-ISM modeling are compatible with driving the observed molecular outflow. Overall, the work reinforces the role of radio jets as a significant mode of AGN feedback in ULIRGs and links merger-driven gas inflows, AGN ignition, jet evolution, and multi-phase outflows in a single system.

Abstract

The ultraluminous infrared galaxy (ULIRG) IRAS 00183-7111 ($z=0.328$) is one of the three ULIRGs that are currently known to host an active galactic nucleus (AGN) with small-scale radio jets. We present a detailed study of the link between galaxy merger, AGN ignition, radio jet expansion and kpc-scale molecular outflow in IRAS 00183-7111, using high-resolution Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the $^{12}$CO(1-0) and $^{12}$CO(3-2) lines and very deep $i$-band VLT Survey Telescope (VST) imaging. The latter allows us to put constraints on the assembly history of the system, suggesting that it formed through a major merger between two gas-rich spirals, likely characterised by a prograde encounter and no older than $\approx2$~Gyr. The recent merger channelled about $(1.5\pm0.3)\times10^{10}$~M\textsubscript{$\odot$} of molecular gas in the central regions of the remnant, as traced by the CO detections. The spatial correlation between the CO distribution and the radio core suggests that this gas likely contributed to the ignition of the AGN and thus to the launch of the radio jets. Furthermore, by comparing the relative strength of the two CO transitions, we find extreme gas excitation (i.e.\,$T_{\rm ex}\gg50$~K) around the radio lobes, supporting the case for a jet-ISM interaction. A qualitative study of the CO kinematics also demonstrates that, despite the overall disturbed dynamical state with no clear signs of regular rotation, at least one non-rotational kinematic component can be identified and likely associated to an outflow with $v_{\rm out}\approx439$~km~s$^{-1}$ and $\dot{M_{\rm out}}\approx 609$~M$_{\odot}$~yr$^{-1}$.

Figures (11)

• Figure 1: Continuum maps of I00183 in ALMA Band 3 (panel a) and 6 (panel b). The reference frequency of each map is indicated in its top-right corner. The bar to the right of each panel shows the colour scale in mJy beam$^{-1}$. The synthesised beam and a scale bar are shown in the bottom-left and bottom-right corners, respectively. In both panels, the image centre is set to the preferred sky coordinates of the optical galaxy centre, which are reported in Table \ref{['tab:I00183_properties']}; East is to the left and North to the top. The black star indicates the position of the radio core, as inferred from the very-long baseline interferometry (VLBI) observations of I00183 presented in Norris12. The properties of the continuum maps are summarised in Section \ref{['sec:ALMA_imaging']} and discussed in Section \ref{['sec:cont_discuss']}
• Figure 2: Left panel: VST i-band ($770$ nm) sky-subtracted image of the $25\arcsec \times 25\arcsec$ ($\approx120\times120$ kpc$^{2}$) around I00183. The image resolution (i.e. seeing FWHM) is $\approx0.85\arcsec$, and the reached surface brightness depth is $\mu_{i} \sim$ 29.5 mag arcsec$^{-2}$. The white star indicates the preferred position assumed so far for the optical galaxy centre (corresponding to the coordinates reported in Table \ref{['tab:I00183_properties']}), while the light-blue star indicates the position of the radio core as inferred from the very-long baseline interferometry (VLBI) observations presented in Norris12 (see also Section \ref{['sec:ratios_results']}). Right panel, top: Zoom-in of the VST $i$-band map in the central $8\arcsec \times 8\arcsec$ ($\approx38\times38$ kpc$^{2}$) with overlaid in white CO(1-0) integrated intensity contours from the Cycle 7 ALMA observations presented in this paper. Right panel, bottom: As above, but with overlaid CO(3-2) integrated intensity contours from the Cycle 2 ALMA observations presented in this paper. A scale bar is shown in the bottom-right corner of each panel, the CO synthesised beam sizes are shown in the bottom-left corners of the right panels. For each CO transition, we show 10 contours, which are equally spaced between the minimum and the maximum significant values of the integrated intensity map (as illustrated by the colour scale in the left-hand panels of Figure \ref{['fig:CO_moments']}).
• Figure 3: I00183 moment 0 (integrated intensity; left panels), moment 1 (intensity-weighted mean line-of-sight velocity; middle panels) and moment 2 (intensity weighted line-of-sight velocity dispersion; right panels) maps of the CO(1-0) and CO(3-2) transitions (top and bottom row, respectively). The maps were created using data cubes with a channel width of 20 km s$^{-1}$ (see Table \ref{['tab:line images']}). The synthesised beam and a scale bar are shown in the bottom-left and bottom-right corner, respectively, of each moment 0 map. The bar to the right of each map shows the colour scales (in mJy beam$^{-1}$ km s$^{-1}$ and km s$^{-1}$ for moment 0 and moment 1/2 maps, respectively). The phase centre of each map is set to the sky coordinates reported in Table \ref{['tab:I00183_properties']}, corresponding to the optical peak of the system (see also Section \ref{['sec:VST_obs']} for details); East is to the left and North to the top. In each panel, this is also marked with a grey star, while the black star indicates the position of the radio core, as inferred with high precision from the VLBI observations of I00183 presented in Norris12. Velocities are measured in the source frame, so that the systemic velocity of each CO line corresponds to the redshifted central frequency of the line ($\nu_{\rm sky}$, reported in Table \ref{['tab:ALMA observations summary']}; see also Section \ref{['sec:ALMA_imaging']}). The black dashed lines in the middle panel of the top row illustrate the direction of the ionised gas outflow, as inferred from the [OIII] data presented in Iwasawa17.
• Figure 4: Position-velocity diagrams (PVDs) of the CO(1-0) transition extracted within rectangular areas whose long axes are orientated according to the position angles indicated in the bottom left corners of each panel, and illustrated by the mean velocity map in the bottom-left panel. The PA is measured counterclockwise from North through East. A scale bar is shown in the bottom-right corner of each PVD. Velocities are measured in the source frame, so that the systemic velocity (i.e. the point along the y-axis where $v=0$) corresponds to the redshifted central frequency of the CO line ($\nu_{\rm sky}$, reported in Table \ref{['tab:ALMA observations summary']}; see also Section \ref{['sec:ALMA_imaging']}). As detailed in Section \ref{['sec:line_profiles']}, however, the observed centroids of both lines are clearly shifted with respect to those expected from $\nu_{\rm sky}$, thus explaining the slight shift observed in the PVDs between the estimated $v_{\rm sys}$ and the observed centroid of the emission. Coordinates are with respect to the image phase centre, which is set to the preferred sky coordinates of the optical galaxy centre reported in Table \ref{['tab:I00183_properties']} (see also Section \ref{['sec:VST_obs']}); East is to the left and North to the top.
• Figure 5: As in Figure \ref{['fig:CO10_PVDs']}, but for the CO(3-2) transition.