On THE CONTRIBUTION OF FLUORESCENCE TO LYα HALOS AROUND STAR-FORMING GALAXIES

Abstract

We quantify the contribution of Lyα fluorescence to observed spatially extended Lyα halos around Lyα emitters (LAE) at redshift z = 3.1. The key physical quantities that describe the fluorescent signal include (i) the distribution of cold gas in the circum-galactic medium (CGM); we explore simple analytic models and fitting functions to recent hydrodynamical simulations; (ii) local variations in the ionizing background due to ionizing sources that cluster around the central galaxy. We account for clustering by boosting the observationally inferred volumetric production rate of ionizing photons, LyC , by a factor 1 + ξ LyC (r), in which ξ LyC (r) quantifies the clustering of ionizing sources around the central galaxy. We compute ξ LyC (r) by assigning an "effective" bias parameter to the ionizing sources. This novel approach allows us to quantify our ignorance of the population of ionizing sources in a simple parametrized form. We find a maximum enhancement in the local ionizing background in the range 50 − 200 at r ∼ 10 physical kpc. For spatially uncorrelated ionizing sources and fluorescing clouds we find that fluorescence can contribute up to ∼ 50 − 60% of the observed spatially extended Lyα emission. We briefly discuss how future observations can shed light on the nature of Lyα halos around star forming galaxies.

Lyα emitters with very large Lyα equivalent widths, EW0(Lyα) ≃ 200–400 Å, atz∼ 2

“…First, we have presumed the Case B recombination. As pointed out by Raiter et al (2010) and Dijkstra (2014), significant departures from Case B are expected at the low metallicity range of Z 0.03 Z⊙ (see also Mas-Ribas et al 2016). The departures can contribute to strong Lyα emission up to EW0(Lyα) ∼ 4000Å because of (i) the increased importance of collisional excitation at the high gas temperature (ii) and the hard ionizing spectra emitted by metal poor stars (Dijkstra 2014).…”

Modeling 237 Lyman-αspectra of the MUSE-Wide survey

“…The distribution is furthermore faster declining towards smaller values of σ i which makes the canonical value of σ i ∼ 13 km s −1 -corresponding to thermal motion of a gas with T ∼ 10 4 K -unlikely. However, both turbulent motion of the emitting gas (in the case of, e.g., Lyα production through fluorescence Hogan & Weymann 1987;Mas-Ribas & Dijkstra 2016) and of cold gas relatively nearby the emitting source will lead to a broadening of the Lyα line prior to additional radiative transfer effects, and these larger σ i values are relatively easy to justify. Interestingly, although even broader intrinsic lines of σ i 400 km s −1 are allowed by the fitting pipeline (up to σ i ≤ 800 km s −1 ), they are not favored by the data.…”

The MUSEHubbleUltra Deep Field Survey

“…Nevertheless, at fixed IMF, Forero-Romero & Dijkstra (2013) hinted that the stochastic sampling of the IMF can induce fluctuations in the predicted EW 0 values for a given star formation event, hence broadening the EW 0 distributions (see also Mas-Ribas et al 2016). Alternatively, bursty star formation may also help reconcile models and observations.…”