The Cosmic Owl: Twin Active Collisional Ring Galaxies with Starburst Merging Front at $z=1.14$

Abstract

Galaxy mergers play a critical role in driving galaxy evolution, especially by transforming galaxy morphology, redistributing gas around galaxies, triggering active galactic nuclei (AGN), and stimulating star formation. We present the Cosmic Owl, a galaxy merger at $z=1.14$, identified in the COSMOS field. Deep imaging and spectroscopy from JWST, ALMA, and VLA reveal a complex system of twin collisional ring galaxies, exhibiting nearly identical morphologies. The grism spectra from the JWST COSMOS-3D program confirm that both galaxies host an AGN. A bipolar radio jet from one AGN extends to strike the merging front. In addition, we detect a starburst at the merging front, characterized by luminous extended nebular line emission and a massive cold gas reservoir. This starburst is likely triggered by interstellar shocks induced by galaxy collision and the AGN jet. The twin ring structure of the Cosmic Owl requires further numerical simulations to clarify the precise conditions that lead to the formation of this rare morphology. This system exemplifies how shock-induced star formation, driven by galaxy collision or AGN jet, can act as a crucial mechanism for triggering intense starbursts in the early Universe.

Figures (9)

• Figure 1: JWST NIRCam and MIRI wide band imaging of the Cosmic Owl. Upper: Pseudo-color image of the Cosmic Owl, with blue (F115W, F150W), green (F200W, F277W), and red (F356W, F444W) bands used. The right panel presents the composite image of all NIRCam wide bands (from F090W to F444W) after PSF matching. The three components, including NW eye, SE eye, and the beak, are annotated in the right panel. Lower: Imaging cutout stamps for the Cosmic Owl, including seven NIRCam bands (F090W, F115W, F150W, F200W, F277W, F356W, and F444W) and four MIRI bands (F770W, F1000W, F1800W, and F2100W). The rest-frame wavelength relative to $z=1.14$ is annotated at the bottom of each panel. The twelve NIRCam and MIRI images, including the F410M data now shown, are available as the data behind the Figure in the online Journal.
• Figure 2: Postage stamp images utilized for the SED analysis of the Cosmic Owl, complementing the JWST imaging presented in Fig. \ref{['fig:cover']}. From upper left to lower right, the panels display: CFHT u-band; Subaru HSC g, r, i, z, y bands; Spitzer/IRAC 3.6 $\mu$m, 4.5 $\mu$m, 5.8 $\mu$m, 8.0 $\mu$m; and Spitzer/MIPS 24 $\mu$m. The upper row panels are 10" in size, while the lower row panels are 40". The significant blending of the two nuclei and the central 'beak' region in these lower-resolution images, particularly in the GALEX and Spitzer images, necessitates treating the system as a single composite source for SED modeling across the wavelength range from UV to IR.
• Figure 3: The spectral energy distribution (SED) modeling for the whole Cosmic Owl system. The integrated model SED is shown by the black curve. Individual components, including stars, galaxy dust, and AGN, are shown by green, orange, and blue curves, respectively. The observed photometry and model photometry are included in red circles (with uncertainties) and blue squares, respectively. The photometric data include GALEX/NUV, CFHT/u, Subaru-HSC/grizy, Spitzer/IRAC, MIPS, JWST NIRCam, and MIRI.
• Figure 4: JWST NIRCam grism spectra for the Cosmic Owl from the COSMOS-3D program. The upper right panel shows the 2D spectrum with the extraction boxes overlaid as white dashed lines. The spatial axis has a pixel size of 00629. The 1D spectra of the SE eye, beak, and NW eye are shown in the lower three panels. The wavelength of emission lines at $z=1.14$ is annotated as vertical dashed lines. The Gaussian models for the Pa$\alpha$ line are overlaid as red curves with blue curves showing individual Gaussian components, and the dashed gray lines denote the continuum models. The F444W image of the Cosmic Owl is shown in the upper left panel, rotated to match the grism position angle, with each component labeled. The JWST NIRCam grism spectra for the Cosmic Owl are available as the data behind the Figure in the online Journal.
• Figure 5: JWST, VLA, and ALMA observations for the Cosmic Owl. (a) Pseudo-color image of the Cosmic Owl with F115W, F150W, and F200W band images. The three components, including NW eye, SE eye, and the beak, are annotated within. Note that the luminous H$\alpha$ emission line is in the F150W band, boosting the beak to be green. The two eyes are red due to the dust obscuration. (b) VLA 3GHz radio observation shown by cyan contours (3, 4, 5, 10, 30, 50, 70$\sigma$ with $1\sigma=2.4~\rm\mu Jy\,\mathrm{beam}^{-1}$), overlaid on the F200W image. The radio emission is spatially resolved into two hotspots, with a green diamond denoting the flux peak of hotspot E, coincident with the beak. The jet direction is indicated schematically by the cyan arrows. (c) ALMA observations of CO(4-3) (red lines) and [CI]($\rm^3P_1$-$\rm^3P_0$) (blue lines), overlaid on the F200W image. The 3, 5, 7, 9, 11$\sigma$ contours are shown with $\sigma_\mathrm{CO}=0.166~\rm Jy/beam\cdot km/s$ and $\sigma_\mathrm{[CI]}=0.143~\rm Jy/beam\cdot km/s$. The CO and [CI] emission line maps are not spatially resolved; however, the emission peak is located between the two eyes and slightly ($\sim0.3$ arcsec) north of the beak's location. (d) Pseudo-color image made from the F356W, F410M, and F444W band images. The Pa$\alpha$ emission line is in the F410M band, boosting the beak to be green. The Pa$\alpha$ emission line map around the beak is overlaid as green contours with surface brightness of $(4,8,12)\times10^{-16}~\rm erg~s^{-1}~cm^{-2}~arcsec^{-2}$. (e) Mean CO(4-3) velocity field relative to the systemic redshift of the CO(4-3) emission ($z = 1.1392$). Only pixels brighter than 5$\sigma$ are included. The F277W image is overlaid as black contours. (f) Spectrum of the CO(4-3) and [CI]($\rm^3P_1$-$\rm^3P_0$) lines from the Cosmic Owl. The velocity is relative to the systemic velocity of the CO(4-3) line. The dotted green line indicates the median 1$\sigma$ RMS uncertainty. Gaussian models fit to the data are shown in red dashed lines. The velocity range used to estimate the integrated line flux and mean velocity field is marked by the solid black bar.