We present the results of a new study investigating the relationship between observed Ly alpha equivalent width (W-lambda(Ly alpha)) and the metallicity of the ionizing stellar population (Z(star)) for a sample of 768 star-forming galaxies at 3 <= z <= 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame W-lambda(Ly alpha) across the range-58 angstrom less than or similar to W-lambda(Ly alpha) less than or similar to 110 angstrom, we determine Z(star) from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between W-lambda(Ly alpha) and Z(star). Our results indicate that Z(star) decreases by a factor greater than or similar to 3 between the lowest W-lambda(Ly alpha) quartile (< W-lambda(Ly alpha)> = -18 angstrom) and the highest W-lambda(Ly alpha) quartile (< W-lambda(Ly alpha)> = 24 angstrom). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; W-lambda(Ly a) > 20 A) are, on average, metal poor with respect to the non-LAE galaxy population (W-lambda(Ly alpha) <= 20 angstrom) with Z(star non-LAE) greater than or similar to 2 x Z(star LAE). Finally, based on the best-fitting stellarmodels, we estimate that the increasing strength of the stellar ionizing spectrum towards lower Z(star) is responsible for similar or equal to 15-25 per cent of the observed variation in W-lambda(Ly alpha) across our sample, with the remaining contribution (similar or equal to 75-85 per cent) being due to a decrease in the HI/dust covering fractions in low-Z(star) galaxies.
Cullen, F., McLure, R.J., Dunlop, J.S., Carnall, A.C., McLeod, D.J., Shapley, A.E., et al. (2020). The VANDELS survey: a strong correlation between Ly α equivalent width and stellar metallicity at 3 ≤ z ≤ 5. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 495(1), 1501-1510 [10.1093/mnras/staa1260].
The VANDELS survey: a strong correlation between Ly α equivalent width and stellar metallicity at 3 ≤ z ≤ 5
Bolzonella, M;Cimatti, AMembro del Collaboration Group
;Cucciati, O;Pozzetti, L;Talia, MMembro del Collaboration Group
;Cresci, G;
2020
Abstract
We present the results of a new study investigating the relationship between observed Ly alpha equivalent width (W-lambda(Ly alpha)) and the metallicity of the ionizing stellar population (Z(star)) for a sample of 768 star-forming galaxies at 3 <= z <= 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame W-lambda(Ly alpha) across the range-58 angstrom less than or similar to W-lambda(Ly alpha) less than or similar to 110 angstrom, we determine Z(star) from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between W-lambda(Ly alpha) and Z(star). Our results indicate that Z(star) decreases by a factor greater than or similar to 3 between the lowest W-lambda(Ly alpha) quartile (< W-lambda(Ly alpha)> = -18 angstrom) and the highest W-lambda(Ly alpha) quartile (< W-lambda(Ly alpha)> = 24 angstrom). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; W-lambda(Ly a) > 20 A) are, on average, metal poor with respect to the non-LAE galaxy population (W-lambda(Ly alpha) <= 20 angstrom) with Z(star non-LAE) greater than or similar to 2 x Z(star LAE). Finally, based on the best-fitting stellarmodels, we estimate that the increasing strength of the stellar ionizing spectrum towards lower Z(star) is responsible for similar or equal to 15-25 per cent of the observed variation in W-lambda(Ly alpha) across our sample, with the remaining contribution (similar or equal to 75-85 per cent) being due to a decrease in the HI/dust covering fractions in low-Z(star) galaxies.| File | Dimensione | Formato | |
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