# The metal content of the circumgalactic medium around star-forming galaxies at z $\sim$ 2.6 as revealed by the VIMOS Ultra-Deep Survey

**Authors:** H. Méndez-Hernández, P. Cassata, E. Ibar, R Amorín, M. Aravena, S. Bardelli, O. Cucciati, B. Garilli, M. Giavalisco, L. Guaita, N. Hathi, A. Koekemoer, V. Le Brun, B. C. Lemaux, D. Maccagni, B. Ribeiro, L. Tasca, N. Tejos, R. Thomas, L. Tresse  
**arXiv:** [2206.08923](https://arxiv.org/abs/2206.08923)  
**Date:** 2022-06-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2206.08923v1/

## Key points

- The circumgalactic medium (CGM) is important for galactic outflows and gas accretion onto galaxies.
- Understanding the spatial distribution of metals in different ionization states within the CGM can provide insights into galaxy formation and evolution.
- The study analyzed 238 close pairs of star-forming galaxies from the VIMOS Ultra Deep Survey (VUDS).
- Composite spectra were generated by co-adding spectra of background galaxies to examine the spatial distribution of gas around these galaxies.
- Metal absorption lines, including C II, Si II, Si IV, and C IV, were detected up to separations of approximately 172 kpc.
- Radial profiles suggest a potential redshift evolution for the CGM gas content responsible for these absorptions.
- Correlations were found between equivalent widths (W0) of C II and C IV with star formation rate, stellar mass, effective radius, and azimuthal angle.
- Galaxies with high star formation rates exhibit stronger C IV absorptions compared to those with low star formation rates and low stellar masses.
- Possible explanations include stronger outflows in high-star-formation-rate galaxies or softer radiation fields that cannot ionize high-ionization state lines.
- The galactic fountain scenario suggests metal-rich gas ejected from previous star formation episodes falls back onto the galaxy.
- The study is based on data from the VUDS survey which obtained spectra of 5590 galaxies in the redshift range 1.5 < z < 4.5 using the VIMOS spectrograph on the ESO Very Large Telescope.
- The study provides new insights into the spatial distribution of the circumgalactic medium around star-forming galaxies and contributes to understanding galaxy formation and evolution processes.

## Summary

The circumgalactic medium (CGM) plays a crucial role in the interplay between galactic outflows and gas accretion onto galaxies. Understanding the spatial distribution of metals in different ionization states within the CGM and their relation to galaxy properties can provide valuable insights into models of galaxy formation and evolution. In this study, the authors analyze a sample of 238 close pairs of star-forming galaxies at redshifts between 1.5 and 4.5 from the VIMOS Ultra Deep Survey (VUDS). They generate composite spectra by co-adding spectra of background galaxies that provide different sight-lines across the CGM, allowing them to examine the spatial distribution of gas around these galaxies. The authors detect several metal absorption lines, including C II, Si II, Si IV, and C IV, up to separations of approximately 172 kpc. The radial profiles of these metal lines suggest a potential redshift evolution for the CGM gas content responsible for these absorptions. Furthermore, they find correlations between the equivalent widths (W0) of C II and C IV with star formation rate, stellar mass, effective radius, and azimuthal angle. Specifically, galaxies with high star formation rates exhibit stronger C IV absorptions compared to those with low star formation rates and low stellar masses. These results could be explained by stronger outflows in high-star-formation-rate galaxies or by softer radiation fields that are unable to ionize high-ionization state lines. Another possible explanation is the galactic fountain scenario, where metal-rich gas ejected from previous star-formation episodes falls back onto the galaxy. The study is based on data from the VUDS survey which obtained spectra of 5590 galaxies in the redshift range 1.5 < z < 4.5. The spectroscopic targets were selected based on their photometric redshifts and observed optical flux. The VUDS observations were conducted using the VIMOS spectrograph on the ESO Very Large Telescope, with a spectral resolution of approximately 230 and a signal-to-noise ratio of 5 on the continuum at 8500 Å. In conclusion, this study provides new insights into the spatial distribution of the circumgalactic medium around star-forming galaxies. The observed correlations between metal absorption features and galaxy properties contribute to our understanding of galaxy formation and evolution processes.