Lyman-<i>α</i>emitters as tracers of the transitioning Universe

Nilsson, K.; Møller, P.

doi:10.1051/0004-6361/201016313

Cited by 14 publications

(16 citation statements)

References 44 publications

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“…those with UV slopes β≳−0.5; Bouwens et al 2009), since the drop‐out galaxy luminosity functions used in this paper have been corrected for this bias (see Bouwens et al 2009). Secondly, narrow‐band surveys can pick up galaxies such as ULIRGs which do not make it into drop‐out surveys (Nilsson & Møller 2011). However, the ULIRG fraction among LAEs drops dramatically to ≲10 per cent at z > 2.5 (Nilsson & Møller 2011), and this is unlikely to be a significant effect.…”

Section: Discussionmentioning

confidence: 99%

An empirical study of the relationship between Lyα and UV-selected galaxies: do theorists and observers ‘select’ the same objects?

Dijkstra

Wyithe

2011

Monthly Notices of the Royal Astronomical Society

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Lyman α emitters (LAEs) are galaxies that have been selected on the basis of a strong Lyα emission line in their spectra. Observational campaigns over the last decade have dramatically increased the sample of known LAEs, which now extends out to z= 7. These discoveries have motivated numerous theoretical studies on the subject, which usually define LAEs in their models based on sharp Lyα luminosity and equivalent width (EW) cuts. While broadly representative, this procedure does not mimic the selection from observational programmes in detail, which instead use cuts in various colour spaces. In this paper, we investigate what implications this disjoint may have for theoretical studies that aim to model the observed population of LAEs. We construct an empirical model for the number density of star‐forming galaxies as a function of their ultraviolet (UV) and Lyα luminosity, utilizing measured constraints on the luminosity functions of drop‐out galaxies, and their luminosity‐dependent probability distribution function of Lyα EW. In particular, we investigate whether the LAE luminosity functions can be reproduced by defining LAEs using a (z‐dependent) Lyα luminosity and EW threshold. While we are able to reproduce the observed distribution of Lyα EW among LAEs out to rest‐frame EW (REW) ∼ 200Å, we find that our formalism overpredicts both the UV and Lyα luminosity functions of LAEs by a factor of 2–3, and is inconsistent with observations at the ∼95 per cent level. This tension is partially resolved if we assume the Lyα EW distribution of drop‐out galaxies to be truncated at REW ≳ 150 Å. However, the overprediction indicates that modelling LAEs with simple REW and luminosity cuts does not accurately mimic observed selection criteria, and can therefore lead to uncertainties in the predicted number density of LAEs. On the other hand, the predicted redshift evolution is not affected. We apply our formalism to drop‐out galaxies at z > 6 and predict the luminosity functions of LAEs at z= 7 ‐9.

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Section: Discussionmentioning

confidence: 99%

An empirical study of the relationship between Lyα and UV-selected galaxies: do theorists and observers ‘select’ the same objects?

Dijkstra

Wyithe

2011

Monthly Notices of the Royal Astronomical Society

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“…Even though these fractions are lower than in Nilsson et al (2009a), they are still ∼2.5 times that what was reported at z = 3 in Ouchi et al (2008). For a longer discussion on AGN fractions, see Nilsson & Møller (2011). The LAE AGN have total X-ray fluxes between log L 0.5−10 keV = 43.3−45.5 erg s −1 , if at z = 2.25.…”

Section: Updated Photometrymentioning

confidence: 99%

The nature ofz ~ 2.3 Lyman-αemitters

Nilsson

Östlin

Møller

et al. 2011

A&A

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116

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We study the multi-wavelength properties of a set of 171 Lyα emitting candidates at redshift z = 2.25 found in the COSMOS field, with the aim of understanding the underlying stellar populations in the galaxies. We especially seek to understand what the dust contents, ages and stellar masses of the galaxies are, and how they relate to similar properties of Lyα emitters at other redshifts. The candidates here are shown to have different properties from those of Lyα emitters found at higher redshift, by fitting the spectral energy distributions (SEDs) using a Monte-Carlo Markov-Chain technique and including nebular emission in the spectra. The stellar masses, and possibly the dust contents, are higher, with stellar masses in the range log M * = 8.5−11.0 M and A V = 0.0−2.5 mag. Young population ages are well constrained, but the ages of older populations are typically unconstrained. In 15% of the galaxies only a single, young population of stars is observed. We show that the Lyα fluxes of the best fit galaxies are correlated with their dust properties, with higher dust extinction in Lyα faint galaxies. Testing for whether results derived from a light-weighted stack of objects correlate to those found when fitting individual objects we see that stellar masses are robust to stacking, but ages and especially dust extinctions are derived incorrectly from stacks. We conclude that the stellar properties of Lyα emitters at z = 2.25 are different from those at higher redshift and that they are diverse. Lyα selection appears to be tracing systematically different galaxies at different redshifts.

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“…Six of the 241 sample galaxies are found to be X-ray sources (ID=29,101,257,440,473,720 in the Chandra catalog) and are all classified as AGNs with L 0.5−8 keV ≥ 3 × 10 42 erg s −1 . However, previous works have revealed that the sample of Lyα emitters contains a comparable fraction of AGNs at this redshift (Nilsson & Møller 2011). We cannot determine whether these six sources are LAEs at z = 2.24 or C IVλλ1548,1550Å at z = 1.54.…”

Section: Selection Of Emitter Candidatesmentioning

confidence: 73%

“…For the LAHAEs in the COSMOS field, 4 of 11 are identified as AGNs (Nilsson & Møller 2011). The fraction of AGNs in LAHAEs is roughly one-thrid for the ECDFS and COSMOS samples.…”

Section: Extinction Correctionmentioning

confidence: 97%

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Extinction Correction Significantly Influences the Estimate of the Lyα Escape Fraction

Zheng

Hao

et al. 2017

ApJ

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The Lyα escape fraction is a key measure to constrain the neutral state of the intergalactic medium and then to understand how the universe was fully reionized. We combine deep narrowband imaging data from the custom-made filter NB393 and the H 2 S1 filter centered at 2.14 µm to examine the Lyα emitters and Hα emitters at the same redshift z = 2.24. The combination of these two populations allows us to determine the Lyα escape fraction at z = 2.24. Over an area of 383 arcmin 2 in the Extended Chandra Deep Field South (ECDFS), 124 Lyα emitters are detected down to NB393 = 26.4 mag at the 5σ level, and 56 Hα emitters come from An et al. Of these, four have both Lyα and Hα emissions (LAHAEs). We also collect the Lyα emitters and Hα emitters at z = 2.24 in the COSMOS field from the literature, and increase the number of LAHAEs to 15 in total. About onethird of them are AGNs. We measure the individual/volumetric Lyα escape fraction by comparing the observed Lyα luminosity/luminosity density to the extinction-corrected Hα luminosity/luminosity density. We revisit the extinction correction for Hα emitters using the Galactic extinction law with the color excess for nebular emission. We also adopt the Calzetti extinction law together with an identical color excess for stellar and nebular regions to explore how the uncertainties in extinction correction affect the estimate of individual and global Lyα escape fractions. In both cases, an anti-correlation between the Lyα escape fraction and dust attenuation is found among the LAHAEs, suggesting that dust absorption is responsible for the suppression of the escaping Lyα photons. However, the estimated Lyα escape fraction of individual LAHAEs varies by up to ∼ 3 percentage points between the two methods of extinction correction. We find the global Lyα escape fraction at z = 2.24 to be (3.7 ± 1.4)% in the ECDFS. The variation in the color excess of the extinction causes a discrepancy of ∼ 1 percentage point in the global Lyα escape fraction.

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Lyman-αemitters as tracers of the transitioning Universe

Cited by 14 publications

References 44 publications

An empirical study of the relationship between Lyα and UV-selected galaxies: do theorists and observers ‘select’ the same objects?

An empirical study of the relationship between Lyα and UV-selected galaxies: do theorists and observers ‘select’ the same objects?

The nature ofz ~ 2.3 Lyman-αemitters

Extinction Correction Significantly Influences the Estimate of the Lyα Escape Fraction

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