Effect of local environment on Ly$α$ line profile in DESI/ODIN LAEs

Abstract

Lyman-Alpha Emitters (LAEs) are star-forming galaxies with significant Ly$α$ emission and are often used as tracers of large-scale structure at high redshift. We explore the relationship between the Ly$α$ line profile and environmental density with spectroscopy from the Dark Energy Spectroscopic Instrument (DESI) of LAEs selected with narrow-band photometry through the One-hundred-deg$^2$ DECam Imaging in Narrowbands (ODIN) survey. We use LAE surface density maps in the N419 (z $\sim$ 2.45) and N501 (z $\sim$ 3.12) narrow bands to probe the relationship between local environmental density and the Ly$α$ line profile. In both narrow bands, we stack the LAE spectra in bins of environmental density and inside and outside of protocluster regions. The N501 data shows $\sim$15% higher Ly$α$ line luminosity for galaxies in protoclusters, suggesting increased star formation in these regions. However, the line luminosity is not appreciably greater in protocluster galaxies in the N419 band, suggesting a potential redshift evolution of this effect. The shape of the line profile itself does not vary with environmental density, suggesting that line shape changes are caused by local effects independent of a galaxy's environment. These data indicate a potential relationship between LAE local environmental density, ionized gas distribution, and Ly$α$ line luminosity.

Figures (16)

• Figure 1: Transmission curves for narrow- and broad-band filters used in this analysis. Curves are normalized to a maximum transmission of 1.
• Figure 2: Inverse-variance-weighted mean stacks of the Ly$\alpha$ line profile for DESI/ODIN LAEs in the N501 band, binned in linear bins (left) and percentile bins (right) of $\delta_{\rm LAE}$. Lighter colors indicate denser environments. The legend denotes the range of $\delta_{\rm LAE}$ values represented in each bin. The dashed line represents 1215.67 Å, the rest-frame Ly$\alpha$ wavelength. Bins containing only one galaxy are excluded.
• Figure 3: Velocity offset of the Ly$\alpha$ redshift from the systemic redshift (determined from He II emission), as a function of LAE overdensity $\delta_{\rm LAE}$. Offsets were determined from the tenth percentile-binned stacks seen in Figure \ref{['fig:501_stacks']}. Horizontal error bars denote the range of $\delta_{\rm LAE}$ values in each stack, while vertical error bars denote 1$\sigma$. Dashed lines denote linear (orange) and logistic (green) fits.
• Figure 4: Inverse-variance-weighted mean stacks (left) and median spectra (right) of the Ly$\alpha{}$ line profile for DESI/ODIN LAEs in the N501 band, inside (blue) and outside (orange) of protocluster regions in the COSMOS field. The dashed line represents 1215.67 Å, the rest-frame Ly$\alpha$ wavelength. Shaded regions denote 1$\sigma$ bootstrapped errors.
• Figure 5: Inverse-variance-weighted mean stacks (left) and median spectra (right) of the Ly$\alpha{}$ line profile for DESI/ODIN LAEs in the N419 band, inside (blue) and outside (orange) of protocluster regions combined over the COSMOS and XMM-LSS fields. The dashed line represents 1215.67 Å, the rest-frame Ly$\alpha$ wavelength. Shaded regions denote 1$\sigma$ bootstrapped errors.