Mapping the Extended Lyman-Alpha Emission within the Circumgalactic Medium of Quasars Hosted by Dusty Starbursts with CubeCarve

TL;DR

This work tackles the challenge of mapping faint Ly$\alpha$ emission in the CGM around four SMG-QSO composites, systems that may represent a transitional phase in quasar evolution. It introduces CubeCarve, a dual-channel deconvolution method that explicitly separates unresolved quasar light from extended CGM emission in IFU datasets, enabling artifact-free recovery of Ly$\alpha$ morphology and kinematics. Applying CubeCarve to KCWI and resampled MUSE data, the authors derive Ly$\alpha$ surface-brightness profiles and moment maps, finding that these SMG-QSOs have fainter and shallower halos on average than the broader QSO population, with nebular luminosities $L_{\rm Ly\alpha} \approx (0.6$--$2.5)\times10^{43}$ erg s$^{-1}$ and notable diversity in morphology and velocity structure. They also identify an inverse relation between Ly$\alpha$ output and host far-IR flux $S_{870}$, suggesting the dust and cold-gas content of the host influences CGM illumination, potentially reflecting an evolutionary stage from dusty starbursts to luminous quasars. Overall, CubeCarve advances CGM studies by enabling reliable inner-region measurements and can be widely applied to future large IFU datasets to better understand quasar-driven CGM conditions during peak galaxy formation.

Abstract

We present a study of extended Ly$α$ emission around four quasars hosted by dusty starbursts, which are composite systems thought to represent a transitional stage in quasar evolution. To extract faint CGM emission in the presence of bright point sources, we introduce {\it CubeCarve}, a dual-channel deconvolution algorithm that separates unresolved quasar emission from spatially extended structure. This approach enables reliable recovery of \Lya\ emission projected onto the quasar position without introducing subtraction artifacts. Using {\it CubeCarve}, we find that the \Lya\ surface brightness profiles of these systems are, on average, fainter and shallower than those of quasars of similar bolometric luminosities. We also find that the total integrated \Lya\ luminosities of the nebulae are lower in systems whose host galaxies exhibit brighter far-infrared emission. These results suggest that the CGM conditions in composite systems differ from those in the broader quasar population. Our study highlights both the physical diversity of quasar CGM environments and the effectiveness of {\it CubeCarve} for recovering diffuse emission in modern IFU datasets.

Figures (8)

• Figure 1: The finder chart for each SMG-QSO composite system. Middle Panel: The KiDS gri tri-color image of the field centered at the position of the Herschel $250$$$m source. The red-dashed circle corresponds to its positional uncertainty ($12\hbox{$.\!\!^{\prime\prime}$}5$). Top Panel: We provide the ALMA $870$$$m continuum maps of each Herschel-detected source. Each panel is $4\hbox{$.\!\!^{\prime\prime}$} \times 4\hbox{$.\!\!^{\prime\prime}$}$, and we indicate its location relative to the KiDS image as a white box. Additionally, the ellipse in the lower-right corner represents the shape of the CLEAN beam. Bottom Panel: We present the pseudo-$g$-band images of the field as seen through KCWI and MUSE.
• Figure 2: A visual demonstration of the MUSE resampling procedure to generate "KCWI-like" datacubes. Each panel is an integrated surface brightness map across a $v = \pm 1000$ km s$^{-1}$. Left: Original MUSE pixel sampling. Right: Resampled MUSE datacube.
• Figure 3: A visual demonstration of CubeCarve deployed on a simulated 3D datacube. Top-Left: The "observed" image taken from a single wavelength slice. Top-Right: 1D spectra of different spatial locations within the datacube. Bottom: From left to right, the resolved emission model, PSF subtraction using the inferred flux from the unresolved emission model, and the residual between the observed image and the final model.
• Figure 4: Top Row: Ly$$ SB map for a single wavelength layer containing the nebula. Bottom Row: Integrated spectrum extracted from the red aperture shown in the top panels. The vertical red line marks the chosen wavelength layer used in the top row.
• Figure 5: The normalized flux density for both the QSO and the Ly$$ nebula as a function of velocity. For all panels, we plot the spectrum of the QSO and Ly$$ nebula for each SMG-QSO composite system as blue and black lines respectively and overlay the best-fit 1D Gaussian in red with its mean value shown as a vertical magenta line. The green dashed-line corresponds to the Ly$$ line at the redshift of each galaxy.