Detailed lens modeling and kinematics of the submillimeter galaxy G09v1.97. An analysis of CO, H2O, H2O+, and dust continuum emission

Abstract

The formation mechanisms of intensely starbursting galaxies at high redshift remain unknown. One possible mechanism for triggering these starbursts is mergers and interactions, but detecting these at high redshift remains a challenge. Observations of high-redshift gravitationally lensed galaxies enable studies of the interstellar medium and environment of these extreme starbursts in detail. We used high angular resolution observations of dust continuum, CO(6-5), H2O(211-202), and H2O+(202-111) emission to constrain the ongoing processes in the z = 3.63 gravitationally lensed submillimeter galaxy H-ATLAS J083051.0+013224 (G09v1.97). We used PyAutoLens to create a de-magnified source plane CO(6-5) emission line cube and performed kinematic modeling using 3DBarolo. Additionally, we investigated the properties of the continuum and molecular line emission in the source plane. We find that the regions of CO(6-5) and H2O(211-202) emission match closely in the source plane but that the dust continuum emission is more compact. We find that our lens modeling results do not require more than one source, contrary to what has been found in previous studies. Instead, we find that G09v1.97 resembles a rotating disk with Vmax/sigma = 2.8 +/- 0.4 with evidence for residual emission indicative of non-circular motions such as outflows, tidal tails, or an additional background galaxy. We suggest that the origin of the non-circular motions may be associated with a bi-conical outflow, a tidal tail from an interaction, or indicate the possible presence of an additional galaxy. We calculate the dynamical mass, gas mass, star-formation rate, and depletion time for G09v1.97 and find a high star-formation rate and low gas depletion time. In combination, this suggests that G09v1.97 has recently undergone an interaction, triggering intense star formation, and is in the process of settling into a disk.

Figures (19)

• Figure 1: Continuum image of G09v1.97, imaged using a natural weighting scheme. The contours are shown at $-3, -2, 3, 4, 5, 6, 7, 8, 9, 10\sigma$ levels ($\sigma$=0.02 mJy/beam). The black region shows the region from which the continuum emission was extracted. The synthesized beam is shown in the bottom left of the image and corresponds to $0.11" \times 0.084"$.
• Figure 2: Spectra of the detected molecular line species in G09v1.97; top left: CO(6--5) spectrum, top right: H_2O spectrum, bottom: H_2O $^+$ spectrum. Note that the H_2O $^+$ emission was not detected in the high-resolution data, and thus, the spectrum was taken from the combined data (as described in Sections \ref{['sec:observation_details']} and \ref{['subsec:lineemission_results']}), resulting in a different spectral resolution than for the CO(6--5) and H_2O emission. The spectrum for each molecule was extracted from a region corresponding to the region shown in Fig. \ref{['fig:continuum']}. For each molecule, the spectrum is shown in the top panel, and the residuals from the Gaussian fits are shown in the lower panel. Single Gaussian profiles are shown in red, and double Gaussian profiles are shown in blue; similarly, in the lower panel, the residuals from fitting using a single Gaussian profile are shown in red and in blue for fits using two Gaussian profiles. It is clear that double Gaussian profiles fit the spectra better for all detected molecular line species. The dashed gray line in the top panel and the gray region in the lower panel represent the per-channel RMS. The top axis in the top panel for each spectrum shows the corresponding redshift. Note that the red residuals in the bottom panel are shown as slightly narrower (i.e., appear to have a smaller channel width) than the blue, purely for clarity purposes.
• Figure 3: Moment-0 and moment-1 maps of the molecular line emission detected towards G09v1.97, top: CO(6--5), middle: H$_2$O, bottom: H_2O$^+$. The contours are shown at $-3, -2, 3, 4, 5, 6, 7, 8, 9, 10\sigma$ levels for the CO(6--5) and H_2O emission and at $-3, -2, 3, 4, 5\sigma$ levels for the H_2O $^+$ emission. The synthesized beam is shown in the bottom left of every image, beam sizes can be found in Table \ref{['tab:obs_details']} for each line. Note that the angular resolution is significantly lower for the H_2O $^+$ emission as it was imaged from the combined dataset as described in Section \ref{['sec:observation_details']}. A clear velocity gradient is visible in the moment-1 map of the CO(6--5) emission.
• Figure 4: Comparison of the normalized CO(6--5), H_2O, and H_2O $^+$ emission. Note that the noise appears significantly higher in the H_2O $^+$ emission due to the line's relatively lower SNR ratio. The line profiles of all three emission lines are very similar.
• Figure 5: Parametric lens and source modeling results for the detected emission towards G09v1.97, first row: dust continuum, second row: CO(6--5), third row: H$_2$O, fourth row: H_2O $^+$ emission. The first column shows the dirty image as produced by PyAutoLens with contours shown at $3, 4, 5, 6, 7, 8, 9, 10\sigma$ levels where $1\sigma$ is the rms of a blank region of the image, note that this is not a cleaned image and structures may look slightly different than those shown in cleaned images. The second column shows the dirty model image as produced by PyAutoLens with contours shown at $3, 4, 5, 6, 7, 8, 9, 10\sigma$ levels. The third column shows the dirty residual image produced by PyAutoLens with contours shown at $-3, -2, 2, 3, 4, 5\sigma$ levels. The fourth column shows the image plane emission parametric model of the data produced by PyAutoLens. The white line represents the critical line. The fifth column shows the source plane emission parametric model of the data produced by PyAutoLens. The white line shows the caustic line. All images are centered around the ALMA phase center for each image. Note that the H_2O $^+$ emission is of significantly lower angular resolution as the lensing model was created using the combined data, as described in Section \ref{['sec:observation_details']}.