Lyα Radiation from Collapsing Protogalaxies. I. Characteristics of the Emergent Spectrum

By M. Dijkstra, Zoltán Haiman, M. Spaans. 2005

252 citations recorded by the source corpus.

We present Monte Carlo calculations of Lyα radiative transfer through optically thick, spherically symmetric, collapsing gas clouds. These represent simplified models of protogalaxies in the process of their assembly. Such galaxies produce Lyα flux over an extended solid angle, either from a spatially extended Lyα emissivity, or from scattering effects, or both. We present a detailed study of the effect of the gas distribution and kinematics and of the Lyα emissivity profile on the emergent spectrum and surface brightness distribution. The emergent Lyα spectrum is typically double peaked and asymmetric. In practice, however, we find energy transfer from the infalling gas to the Lyα photons to significantly enhance the blue peak and to render the red peak, in most cases, undetectable. The resulting effective blueshift, combined with scattering in the intergalactic medium, renders extended Lyα emission from collapsing protogalaxies difficult to detect beyond redshift z ≳ 4. We find a strong wavelength dependence of the slope of the surface brightness distribution (with preferential flattening at the red side of the line) to be a robust indication that Lyα photons are being generated (rather than just scattered) in a spatially extended, collapsing region around the galaxy. For self-ionized clouds whose effective Lyα optical depth is ≲103, infall and outflow models can produce nearly identical spectra and surface brightness distributions and are practically indistinguishable. The presence of cosmic abundance of deuterium may produce a detectable dip in the spectra of systems with moderate hydrogen column densities, NH = 1018-1020 cm-2. Finally, we present a new analytic solution for the emerging Lyα spectrum in the limiting case of a static uniform sphere, extending previous solutions for slabs.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/217bdd84060ddb2bf6da0d5b89eaba778ff58f0b

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Citations in the corpus

Studying reionization with Lyα emitters (2007, methodology): “Both Dijkstra et al. (2006) and Stark et al. (2007) find that this simple parameterization is able to provide adequate fits to the z = 5.7 and z = 6.6 luminosity functions even when fixing Fc.”
THE HETDEX PILOT SURVEY. II. THE EVOLUTION OF THE Lyα ESCAPE FRACTION FROM THE ULTRAVIOLET SLOPE AND LUMINOSITY FUNCTION OF 1.9 (2010, background): “…the neutral gas inside a galaxy and in its immediate surround- ings also play an important role regarding the escape of Lyα photons (Verhamme et al. 2006; Dijkstra et al. 2006; Hansen & Oh 2006; Dijkstra et al. 2007; Verhamme et al. 2008; Adams et al. 2009; Laursen et al. 2010; Zheng et al. 2010).”
The impact of The IGM on high-redshift Lyα emission lines (2007, background): “The constraints on the IGM transmission can be further improved when Lyα luminosity functions are combined with the Lyα emitters’ rest-frame UV luminosity functions (as in Kashikawa et al. 2006, also see Dijkstra et al. 2006c).”
Lyα Emitting Galaxies as a Probe of Reionisation (2014, methodology): “Not unexpectedly, the same arguments outlined above can be applied to an inflowing medium: here we expect the blue peak to be enhanced and the red peak to be suppressed (e.g. Dijkstra et al. 2006; Barnes & Haehnelt 2010).”
UBIQUITOUS GIANT Lyα NEBULAE AROUND THE BRIGHTEST QUASARS AT z ∼ 3.5 REVEALED WITH MUSE (2016, background): “…al. 2014); ii) "continuumpumping" or Lyα scattering from the quasar broad-line region (see e.g. Cantalupo et al. 2014); iii) Lyα collisional excitation (so called Lyα "cooling radiation"; Haiman et al. 2000; Fardal et al. 2001; Dijkstra et al. 2006; Cantalupo et al. 2008,Rosdahl & Blaizot 2012 ).”
THE STRUCTURE AND KINEMATICS OF THE CIRCUMGALACTIC MEDIUM FROM FAR-ULTRAVIOLET SPECTRA OF z ≃ 2–3 GALAXIES (2010, background): “…treatments of Lyα radiative transfer in the context of galactic outflows (Verhamme et al. 2006, 2008; Schaerer & Verhamme 2008; Hansen & Oh 2006; Dijkstra et al. 2006b,a; Zheng & Miralda-Escudé 2002), and even in the highlyidealized geometric configurations considered in these papers, a given…”
Lyα COOLING EMISSION FROM GALAXY FORMATION (2010, methodology): “It differs by a factor of 2π from the expression in Dijkstra et al. (2006) because it is normalized to integrate to unity here.”
A Population of Faint Extended Line Emitters and the Host Galaxies of Optically Thick QSO Absorption Systems (2007, methodology): “Dijkstra et al. (2006) estimate the expected cooling radiation assuming that the gas in DM halos cools on a free-fall timescale and that the cooling is predominantly by Ly emission.”
Distant radio galaxies and their environments (2008, background): “Alternatively, they may be associated with cooling-flow-like phenomena (Haiman et al 2000; Dijkstra et al 2006,).”
Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum with ALMA (2018, background): “For example, based on radiative transfer calculations, theoretical studies (Dijkstra et al. 2006; Verhamme et al. 2006, 2015; Gronke et al. 2015) predict that the Lyα line is redshifted (blueshifted) with respect to the systemic redshift if a galaxy has an outflowing (inflowing) gas in the ISM.”
Lyα blobs as an observational signature of cold accretion streams into galaxies (2009, background): “In addition, we do not expect the systematic blueshift of the Lyα line that was predicted Dijkstra et al. (2006) for spherically symmetric models4.”