MUSE Analysis of Gas around Galaxies (MAGG) - VII. Emission line galaxies near strong blended Ly$α$ absorption systems at $z\gtrsim3$

TL;DR

This study tests whether strong blended Lyα absorption systems (SBLAs) trace the circumgalactic medium (CGM) of high-redshift galaxies by cross-correlating SBLA pixels with a comprehensive MAGG LAE sample at $z\gtrsim3$. Using SBLA selection defined by $-0.05<F<0.25$ over $\approx138\ \rm km\,s^{-1}$ bins in X-Shooter spectra and a large LAE catalog from MUSE, the authors quantify SBLA–LAE associations, and compute 2D cross-correlations and LAE luminosity functions near SBLAs. They find significant LAE clustering around SBLAs for $F<0.25$, especially at small impact parameters ($R\lesssim150$ kpc) and with larger spectral windows ($\Delta v_{\rm spec}$ up to $276\ \rm km\,s^{-1}$), while regions with $F>0.25$ show no clustering. Approximately 40% of SBLAs are linked to CGM gas around LAEs, and the SBLA signal depends strongly on selection parameters, underscoring the need to calibrate SBLA definitions across redshift and binning. Overall, SBLAs emerge as probes of the CGM–IGM interface and of halos with typical masses around $M_h\sim10^{11} M_\odot$ at $z\gtrsim3$, with future work needed to refine the SBLA framework as a halo tracer.

Abstract

We investigate the connection between strong, blended Ly$α$ absorption systems (SBLAs) and $\approx1000$ Ly$α$ emitting galaxies (LAEs) at $z\gtrsim3$ in 28 quasar fields from the MUSE Analysis of Gas around Galaxies (MAGG) survey. Selecting SBLAs as spectral regions with transmitted flux $-0.05<F<0.25$ over $\approx138\text{ km s}^{-1}$ bins, we find a strong correlation with LAEs within a projected distance of $R\le300\rm\,kpc$ and line-of-sight velocity separation of $|Δv|\le300 \text{ km s}^{-1}$. The association rate increases significantly with decreasing flux, a trend that persists also at smaller separations ($R<100$ kpc). A two-dimensional cross-correlation analysis confirms significant clustering of LAEs around SBLAs, while no such clustering is seen for spectral regions with $F>0.25$. The correlation appears to also depend on the width of the spectral window used to identify SBLAs, with a larger window yielding a stronger signal. Our analysis confirms that SBLAs serve as probes of the CGM at the interface between the Ly$α$ forest and the optically-thick Lyman limit systems. The significant dependence of the LAE-SBLA cross-correlation on the spectral binning used to select these absorbers motivates future tests of the current SBLA framework as a tracer of halos.

Figures (6)

• Figure 1: Average transmitted flux in the rest-frame region $1041~\AA~<\lambda_{\rm RF,QSO}<1185$ Å of the quasar spectra, as a function of the Ly$\alpha$ redshift, compared to the average cosmic value measured by Becker2013. Shown are the mean (purple) and median (violet) stacked spectra in three Ly$\alpha$ redshift intervals within $2.5\lesssim z\lesssim4.5$. The uncertainties reproduce the standard deviation in each bin. In the background, there is the average transmission of individual spectra (in grey).
• Figure 2: Results of the search for SBLAs in the X-Shooter spectrum of the quasar J200324.14-325144.8. The spectrum has been continuum-normalized, convolved with a Gaussian filter to match the resolution of BOSS, and re-sampled into a wavelength grid with a constant bin size of $138~\rm km\,s^{-1}$. The pixels selected as SBLAs (orange) in the region $1041~\AA<\lambda_{\rm RF,QSO}<1185$ Å (that is, excluding the gray shaded regions) have a transmitted flux within the range $-0.05<F<0.25$ (blue shaded region). Known LLS are shown as green diamonds. We also show LAEs that are matched (filled purple stars) and not matched (empty purple stars) to at least one SBLA within $R<300\rm\,kpc$ and $\lvert\Delta\varv\rvert\le300\rm\,km\,s^{-1}$ in Section \ref{['sec:correlation']}.
• Figure 3: Fraction of $138~\rm km\,s^{-1}$ wavelength bins, as a function of their transmitted fluxes, that are associated with at least one LAE within a projected distance $R\le300\rm\,kpc$ and line-of-sight separation $\left | \Delta\varv \right |\le300\rm km\,s^{-1}$. The pink histograms show the results for all the absorption systems, while the green ones show the contribution to each flux interval of the wavelength bins that are also identified as LLSs. The gray shaded area highlights the wavelength bins with fluxes $-0.05<F<0.25$ that are identified as SBLAs. In the three panels, we show associations with the full sample of MAGG LAEs (left panel), and those above the $50$ percent (middle panel) and $80$ percent (right panel) completeness limit. Fractions computed with the respective completeness corrections are also shown (purple histogram).
• Figure 4: Same as the left panel in Fig. \ref{['fig:correlation']}, but for LAEs detected within 100 kpc of the quasar line of sight.
• Figure 5: Two-dimensional LAE-absorber cross-correlation functions, $\xi$. Upper panels: Cross-correlation functions for systems with $-0.05<F<0.25$. The linking velocity window, $\Delta\varv_{\rm th}$, and projected separation, $\Delta R_{\rm th}$, vary along the vertical and horizontal axis, respectively. Each of the three panels shows the results for SBLAs identified in quasar spectra with a pixel size of $\Delta v_{\rm spec}=69\rm\,km\,s^{-1}$ (left panel), $138\rm\,km\,s^{-1}$ (middle panel), and $276\rm\,km\,s^{-1}$ (right panel). Line of sight separations $\Delta\varv_{\rm th}<\Delta v_{\rm spec}$ are masked. Lower panels: Cross-correlation functions between LAEs and systems with $F>0.25$. Note the different limits on the $\xi$ color scale.