The impact of The IGM on high-redshift Lyα emission lines

By M. Dijkstra, A. Lidz, S. Wyithe. 2007

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We calculate the impact of the intergalactic medium (IGM) on the observed Lyα lines emitted by galaxies in an ionized IGM at z 4. Our model accounts for gas clumping in the IGM and for the fact that high-redshift galaxies reside in overdense regions, which causes the velocity field of the IGM to depart from the Hubble flow. The observed shape of the Lyα line varies widely, with dependence on the intrinsic width and systemic velocity of the line, a galaxies star formation rate and the local extragalactic UV background. For large star formation rates and levels of the UV background, absorption in the IGM does not result in a Lyα line that is asymmetric as is common among known high-redshift Lyα emitters (LAEs). For models in which the lines do show the observed strong asymmetry, the IGM typically transmits only 10‐30 per cent of the Lyα flux. The increase in the ionizing background that accompanied the completion of reionization barely increased the IGM transmission, which suggests that LAEs of comparable luminosity should not appear to be significantly dimmer prior to overlap. In this light, we briefly discuss the potential of LAEs as a probe into the epoch of reionization.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/452124a6f8fdddc3fc0bf8d3210f4c2bb58afef4

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Citations in the corpus

Identification of the brightest Lyα emitters at z = 6.6 : Implications for the evolution of the luminosity function in the reionization era (2015, background): “The observed clustering of LAEs increases since the observability is favoured when sources are in overlapping ionised spheres (McQuinn et al. 2007), while the line-profile becomes more asymmetric due to absorption and re-scattering of Lyα photons in a more neutral medium (Dijkstra et al. 2007).”
The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, background): “As any photons emitted bluer than the halo circular velocity will be resonantly absorbed by intervening neutral hydrogen (Gunn & Peterson 1965; Dijkstra et al. 2007; Zheng et al. 2010; Laursen et al. 2011; Schroeder et al. 2013), Jα is described as: Jα(∆v,Mh, v) ∝ 1√2πσα e− (v−∆v)2 2σ2α if v ≥…”
STATISTICS OF 207 Lyα EMITTERS AT A REDSHIFT NEAR 7: CONSTRAINTS ON REIONIZATION AND GALAXY FORMATION MODELS (2010, methodology): “We use models of Lyα lines made by Dijkstra et al. (2007a), and evaluate the Lyα line broadening.”
Studying reionization with Lyα emitters (2007, background): “Several studies have attempted to understand the impact that reionization has on the profile of Lyα lines using simple analytic models (Miralda-Escude 1998; Santos 2004; Haiman & Cen 2005; Furlanetto et al. 2004c; Dijkstra et al. 2007).”
Lyα COOLING EMISSION FROM GALAXY FORMATION (2010, background): “…and systematic infall around massive halos (e.g., Faucher-Giguère et al. 2008c) can amplify and shift the absorption, whereas galactic winds act to “let through” more radiation by redshifting it away from the Lyα line center (e.g., Santos 2004; Dijkstra et al. 2007; Dijkstra & Wyithe 2010).”
Reionization and Galaxy Evolution Probed by z = 7 Lyα Emitters (2007, methodology): “This procedure is not straightforward because this translation is generally model dependent (e.g., Santos 2004; Dijkstra et al. 2007).”
Lyα blobs as an observational signature of cold accretion streams into galaxies (2009, background): “Since the massive halos of interest reside in dense parts of the Universe, we expect the local to be more opaque than average (e.g. Dijkstra et al. 2007; Dijkstra 2009), which motivates our choice Tα = 0.5 at z 6 3.”
Keck spectroscopy of faint 3 < z < 7 Lyman break galaxies – I. New constraints on cosmic reionization from the luminosity and redshift-dependent fraction of Lyman α emission (2010, result): “…erase a fraction of the Lyα line redwards of rest frame 1216 Å; the combination of these effects can cause the redshift evolution in the transmission of Lyα photons through a reionized IGM to be considerably different than implied by our model given above (e.g. Santos 2004; Dijkstra et al. 2007b).”
Lyα Emitting Galaxies as a Probe of Reionisation (2014, background): “This is related to the fact that the mean density of the Universe at z = 6.5 was ∼ 50% higher than at z = 5.7, which translates to an increase in the Gunn-Peterson optical depth by a factor of ∼ 1.7 (Dijkstra et al. 2007).”
COMPLETING THE CENSUS OF Lyα EMITTERS AT THE REIONIZATION EPOCH (2011, background): “LYα PROFILE OF THE COMPOSITE SPECTRUM The Lyα emission-line profile is also a useful reionization signature, in principle, because the neutral IGM imposes a damping absorption feature on it (Dayal et al. 2008, Dijkstra et al. 2007a).”
SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES (2011, background): “…Haiman & Spaans 1999; Malhotra & Rhoads 2004; Santos et al. 2004; Mesinger et al. 2004; Stern et al. 2005; Haiman & Cen 2005; Furlanetto et al. 2006; McQuinn et al. 2007; Dijkstra et al. 2007; Kobayashi et al. 2007; Mesinger & Furlanetto 2008; Iliev et al. 2008; Dayal et al. 2008, 2009, 2011).”
SILVERRUSH. IV. Lyα luminosity functions at z = 5.7 and 6.6 studied with ∼1300 Lyα emitters on the 14–21 deg2 sky (2017, background): “A comparison of our Lyα transmission fraction result with these two models (Figure 6 of Dijkstra et al. 2007b and the top panel of Figure 1 of Furlanetto et al. 2006) yields xHI ∼ 0.1− 0.3.”
THE HETDEX PILOT SURVEY. II. THE EVOLUTION OF THE Lyα ESCAPE FRACTION FROM THE ULTRAVIOLET SLOPE AND LUMINOSITY FUNCTION OF 1.9 (2010, background): “As discussed in §1, the effects of the ISM and IGM kinematics in and around galaxies makes this correction very difficult (Dijkstra et al. 2007; Verhamme et al. 2008).”