Strong C IV emission from star-forming galaxies: a case for high Lyman continuum photon escape

Abstract

Finding reliable indicators of Lyman continuum (LyC) photon leakage from galaxies is essential in order to infer their escape fraction in the epoch of reionisation, where direct measurements of LyC flux are impossible. To this end, here we investigate whether strong C IV $\lambda \lambda 1548,1550$ emission in the rest-frame UV spectra of galaxies traces conditions ripe for ample production and escape of LyC photons. We compile a sample of 19 star-forming galaxies in the redshift range $z=3.1-4.6$ from the VANDELS survey that exhibit strong C IV emission, producing a stacked spectrum where all major rest-UV emission lines are clearly detected. Best-fitting spectral energy distribution models containing both stellar and nebular emission suggest the need for low stellar metallicities ($Z=0.1-0.2Z_{\odot }$), young stellar ages ($\log (age/yr)=6.1-6.5$), a high ionisation parameter ($\log U=-2$) and little to no dust attenuation ($E(B-V)=0.00-0.01$). However, these models are unable to fully reproduce the observed C IV and He II line strengths. We find that the Ly$\alpha$ line in the stacked spectrum is strong and peaks close to the systemic velocity, features that are indicative of significant LyC photon leakage along the line-of-sight. The covering fractions of low-ionisation interstellar absorption lines are also low implying LyC escape fraction in the range $\approx 0.05-0.30$, with signatures of outflowing gas. Finally, C IV/C III] ratios of >0.75 for a subset of individual galaxies with reliable detections of both lines are also consistent with physical conditions that enable significant LyC leakage. Overall, we report that multiple spectroscopic indicators of LyC leakage are present in the stacked spectrum of strong C IV emitting galaxies, potentially making C IV an important tracer of LyC photon escape at $z>6$.

15 pages, 10 figures, published in MNRAS

References in corpus (40)

• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• The Chandra Deep Field-South Survey: 7 Ms Source Catalogs
• Modelling the nebular emission from primeval to present-day star-forming galaxies
• The Direct Detection of Lyman-Continuum Emission from Star-forming Galaxies at z~3
• Using Lyman-alpha to detect galaxies that leak Lyman continuum
• Lyman Alpha Emitting Galaxies as a Probe of Reionization
• Lyman-alpha spectral properties of five newly discovered Lyman continuum emitters
• Ultraviolet spectra of extreme nearby star-forming regions --- approaching a local reference sample for JWST
• The Ly-alpha Properties of Faint Galaxies at z2-3 with Systemic Redshifts and Velocity Dispersions from Keck-MOSFIRE
• The Low-Redshift Lyman Continuum Survey I: New, Diverse Local Lyman-Continuum Emitters
• The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics
• Lyman continuum leakage from low-mass galaxies with Mstar < 1.E8 Msun
• X-ray binaries as the origin of nebular HeII emission in low-metallicity star-forming galaxies
• Evidence for a Hard Ionizing Spectrum from a z=6.11 Stellar Population
• The VANDELS survey: the stellar metallicities of star-forming galaxies at 2.5 < z < 5.0
• The COS Legacy Archive Spectroscopy SurveY (CLASSY) Treasury Atlas
• The origin of the escape of Lyman alpha and ionizing photons in Lyman Continuum Emitters
• The Low-Redshift Lyman Continuum Survey. Unveiling the ISM properties of low-$z$ Lyman continuum emitters
• The VANDELS ESO public spectroscopic survey: final Data Release of 2087 spectra and spectroscopic measurements
• Intense CIV and HeII Emission in z~0 Galaxies: Probing High-Energy Ionizing Photons
• Do galaxies that leak ionizing photons have extreme outflows?
• Probing Cosmic Dawn : Ages and Star Formation Histories of Candidate $z\ge$9 Galaxies
• The MUSE Deep Lensed Field on the Hubble Frontier Field MACS~J0416
• The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyman Alpha Emission of High-Redshift Galaxies
• Strong Lyman continuum emitting galaxies show intense CIV 1550 emission
• Exploring HeII$\lambda$1640 emission line properties at $z\sim 2-4$
• The VANDELS survey: the relation between UV continuum slope and stellar metallicity in star-forming galaxies at z~3
• No strong dependence of Lyman continuum leakage on physical properties of star-forming galaxies at $3.1\lesssim \mathbf{z}\lesssim 3.5$
• UV absorption lines and their potential for tracing the Lyman continuum escape fraction
• Hoki: Making BPASS accessible through Python
• New Methods for Identifying Lyman Continuum Leakers and Reionization-Epoch Analogues
• A systematic study of the escape of LyC and Ly$\alpha$ photons from star-forming, magnetized turbulent clouds
• Assessing the sources of reionisation: a spectroscopic case study of a 30$\times$ lensed galaxy at $z\sim 5$ with Lyα, CIV, MgII, and [NeIII]
• Can nebular HeII emission be explained by ultra-luminous X-ray sources?
• The MUSE Hubble Ultra Deep Field Survey. XV. The mean rest-UV spectra of Ly-alpha emitters at z>3
• EMPRESS. VII. Ionizing Spectrum Shapes of Extremely Metal-Poor Galaxies: Uncovering the Origins of Strong HeII and the Impact on Cosmic Reionization
• Stellar populations and star formation histories of the most extreme [OIII] emitters at $z=1.3-3.7$
• No correlation of the Lyman continuum escape fraction with spectral hardness
• Upper limits on the escape fraction of ionizing radiation from galaxies at $2\lesssim z<6$
• Deciphering stellar metallicities in the early Universe: Case study of a young galaxy at z = 4.77 in the MUSE eXtremely Deep Field

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