Scrutiny of a very young, metal-poor star-forming Lyα-emitter at z ~ 3.7

Abstract

The origin of the Lyman-$\alpha$ (Ly$\alpha$) emission in galaxies is a long-standing issue: despite several processes known to originate this line (e.g. AGN, star formation, cold accretion, shock heating), it is difficult to discriminate among these phenomena based on observations. Recent studies have suggested that the comparison of the ultraviolet (UV) and optical properties of these sources could solve the riddle. For this reason, we investigate the rest-frame UV and optical properties of A2895b, a strongly lensed Ly$\alpha$-emitter at redshift z ~ 3.7. From this study, we find that our target is a compact (r ~ 1.2 pkpc) star-forming (star formation rate ~ 11 M${}_{\odot }$/yr) galaxy having a young stellar population. Interestingly, we measure a high ratio of the H$\beta$ and the UV continuum monochromatic luminosities (L(H$\beta$)/L(UV) ~ 100). Based on tracks of theoretical stellar models (Starburst99, BPASS), we can only partially explain this result by assuming a recent (< 10 Myr), bursty episode of star-formation and considering models characterised by binary stars, a top-heavy initial-mass function (IMF) and sub-solar metallicities (Z < 0.01 Z${}_{\odot }$). These assumptions also explain the observed low (C/O) abundance of our target (~ 0.23(C/O)${}_{\odot }$). By comparing the UV and optical datasets, we find that the Ly$\alpha$ and UV continuum are more extended (x2) than the Balmer lines, and that the peak of the Ly$\alpha$ is offset (~ 0.6 pkpc). The multi-wavelength results of our analysis suggest that the observed Ly$\alpha$ emission originates from a recent star-formation burst, likely taking place in an off-centre clump.

18 pages (including Appendix), 5 figures. Paper accepted for publication on MNRAS. Accepted 2022 November 2. Received 2022 October 22; in original form 2022 August 3

References in corpus (41)

• Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope I. Overview of the instrument and its capabilities
• PyNeb: a new tool for analyzing emission lines. I. Code description and validation of results
• 3D Lyman-alpha radiation transfer. I. Understanding Lyman-alpha line profile morphologies
• The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction and source detection
• Modelling the nebular emission from primeval to present-day star-forming galaxies
• Lyman Alpha Emitting Galaxies as a Probe of Reionization
• New insights into the stellar content and physical conditions of star-forming galaxies at z = 2-3 from spectral modelling
• Ultraviolet Emission Lines in Young Low Mass Galaxies at z~2: Physical Properties and Implications for Studies at z>7
• Observations of the Lyman-$\alpha$ Universe
• Resolved spectroscopy of gravitationally lensed galaxies: global dynamics and star-forming clumps on ~100pc scales
• The Chemical Evolution of Carbon, Nitrogen, and Oxygen in Metal-Poor Dwarf Galaxies
• A spectroscopic search for AGN activity in the reionization era
• Lyman alpha Resonant Scattering in Young Galaxies - Predictions from Cosmological Simulations
• The Rest-Frame Optical Spectroscopic Properties of Ly$\alpha$-Emitters at $z\sim 2.5$: The Physical Origins of Strong Ly$\alpha$ Emission
• Deep spectroscopy of the FUV-optical emission lines from a sample of radio galaxies at z~2.5: metallicity and ionization
• MUSE integral-field spectroscopy towards the Frontier Fields Cluster Abell S1063: I. Data products and redshift identifications
• Resolved Spectroscopy of a Gravitationally Lensed L* Lyman-break Galaxy at z~5
• The MUSE Hubble Ultra Deep Field Survey XIII. Spatially resolved spectral properties of Lyman alpha haloes around star-forming galaxies at z > 3
• The Star Formation Burstiness and Ionizing Efficiency of Low-mass Galaxies
• The X-SHOOTER Lyman-$\alpha$ survey at z=2 (XLS-z2) I: What makes a galaxy a Lyman-$\alpha$ emitter?
• The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyman Alpha Emission of High-Redshift Galaxies
• An extremely young massive clump forming by gravitational collapse in a primordial galaxy
• Directional Lya equivalent boosting I. Spherically symmetric distributions of clumps
• Exploring HeII$\lambda$1640 emission line properties at $z\sim 2-4$
• Spectral Energy Distribution Fitting of HETDEX Pilot Survey Lyman-alpha Emitters in COSMOS and GOODS-N
• On the Diffuse Lyman-alpha Halo Around Lyman-alpha Emitting Galaxies
• Sizes of Lensed Lower-luminosity z=4-8 Galaxies from the Hubble Frontier Field Program
• Reconstruction of the ground-layer adaptive-optics point spread function for MUSE Wide Field Mode observations
• Constraining Lyman-alpha spatial offsets at $3<z<5.5$ from VANDELS slit spectroscopy
• A gravitationally-boosted MUSE survey for emission-line galaxies at z>~5 behind the massive cluster RCS 0224
• On the AGN nature of two UV bright sources at z_spec~5.5 in the CANDELS fields: an update of the AGN space density at M1450~-22.5
• Using photo-ionisation models to derive carbon and oxygen gas-phase abundances in the rest UV
• A comparison of UV and optical metallicities in star-forming galaxies
• Lyman-Alpha Escape from Low-Mass, Compact, High-Redshift Galaxies
• The HETDEX Survey: The Ly$\alpha$ Escape Fraction from 3D-HST Emission Line Galaxies at $z\sim 2$
• Stellar feedback in a clumpy galaxy at $z\sim$ 3.4
• OV] $\lambda \lambda$1213.8,1218.3 emission from extended nebulae around quasars: contamination of Ly$\alpha$ and a new diagnostic for AGN activity in Ly$\alpha$-emitters
• Resolved galactic superwinds reconstructed around their host galaxies at z>3
• A Peculiar Type~II QSO Identified via Broad-band Detection of Extreme Nebular Line Emission
• Carbon-loud SDSS BOSS QSO2s at z > 2: High density gas or secondary production of Carbon?

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