Sebastiano Cantalupo

Fluorescent Lyα Emission from the High-Redshift Intergalactic Medium

We combine a high-resolution hydro simulation of the ΛCDM cosmology with two radiative transfer schemes (for continuum and line radiation) to predict the properties, spectra, and spatial distribution of fluorescent Lyα emission at z ~ 3. We focus on line radiation produced by recombinations in the dense intergalactic medium ionized by UV photons. In particular, we consider both a uniform background and the case in which gas clouds are illuminated by a nearby quasar. We find that the emission from optically thick regions is substantially less than predicted from the widely used static, plane-parallel model. The effects induced by a realistic velocity field and by the complex geometric structure of the emitting regions are discussed in detail. We make predictions for the expected brightness and size distributions of the fluorescent sources. Our results account for recent null detections and can be used to plan new observational campaigns both in the field (to measure the intensity of the diffuse UV background) and in the proximity of bright quasars (to understand the origin of high column density absorbers).

The MUSE 3D view of the Hubble Deep Field South

We observed Hubble Deep Field South with the new panoramic integral-field spectrograph MUSE that we built and have just commissioned at the VLT. The data cube resulting from 27 h of integration covers one arcmin(2) field of view at an unprecedented depth with a 1 sigma emission-line surface brightness limit of 1 x 10(-19) erg s(-1) cm(-2) arcsec(-2), and contains similar to 90 000 spectra. We present the combined and calibrated data cube, and we performed a first-pass analysis of the sources detected in the Hubble Deep Field South imaging. We measured the redshifts of 189 sources up to a magnitude I-814 = 29.5, increasing the number of known spectroscopic redshifts in this field by more than an order of magnitude. We also discovered 26 Ly alpha emitting galaxies that are not detected in the HST WFPC2 deep broad-band images. The intermediate spectral resolution of 2.3 angstrom allows us to separate resolved asymmetric Ly alpha emitters, [O II] 3727 emitters, and C III] 1908 emitters, and the broad instantaneous wavelength range of 4500 angstrom helps to identify single emission lines, such as [O III] 5007, H beta, and H alpha, over a very wide redshift range. We also show how the three-dimensional information of MUSE helps to resolve sources that are confused at ground-based image quality. Overall, secure identifications are provided for 83% of the 227 emission line sources detected in the MUSE data cube and for 32% of the 586 sources identified in the HST catalogue. The overall redshift distribution is fairly flat to z = 6.3, with a reduction between z = 1.5 to 2.9, in the well-known redshift desert. The field of view of MUSE also allowed us to detect 17 groups within the field. We checked that the number counts of [O II] 3727 and Ly alpha emitters are roughly consistent with predictions from the literature. Using two examples, we demonstrate that MUSE is able to provide exquisite spatially resolved spectroscopic information on the intermediate-redshift galaxies present in the field. This unique data set can be used for a wide range of follow-up studies. We release the data cube, the associated products, and the source catalogue with redshifts, spectra, and emission-line fluxes.

Mapping Neutral Hydrogen during Reionization with the Lyα Emission from Quasar Ionization Fronts

We present a new method to directly map the neutral-hydrogen distribution during the reionization epoch and constrain the emission properties of the highest redshift quasars (QSOs). As a tracer of H I, we propose to use the Lyα radiation produced by quasar ionization fronts (I-fronts) that expand in the partially ionized intergalactic medium (IGM) before reionization is complete. These Lyα photons are mainly generated by H I collisional excitations. Combining two radiative transfer models (one for the QSO ionizing radiation and one for the Lyα photons), we estimate the expected Lyα spectral shape and surface brightness (SBLyα) for a large number of configurations where we varied both the properties of the ionizing QSO and of the surrounding medium. We find that the expected signal is observable as a single (broad) emission line with a characteristic width of 100-200 km s−1. The expected SBLyα produced at redshift z 6.5 within a fully neutral region (at mean density) by a typical QSO I-front lies in the range 10−21 to 10−20 ergs s−1 cm−2 arcsec−2 and decreases proportionally to (1 + z)2 for a given QSO age. QSOs with harder spectra may produce a significantly brighter emission at early phases. The signal may cover up to a few hundred square arcminutes on the sky and should be already detectable with current facilities by means of moderate- to high-resolution spectroscopy. The detection of this Lyα emission can shed new light on the reionization history, the age and the emission properties of the highest redshift QSOs.

Plausible Fluorescent Lyα Emitters around the z = 3.1 QSO 0420–388*

We report the results of a survey for fluorescent Ly? emission carried out in the field surrounding the z = 3.1 quasar QSO 0420-388 using the Focal Reducer/Low Dispersion Spectrograph 2 (FORS2) instrument on the Very Large Telescope (VLT). We first review the properties expected for fluorescent Ly? emitters, compared with those of other nonfluorescent Ly? emitters. Our observational search detected 13 Ly? sources sparsely sampling a volume of ~14,000 comoving Mpc3 around the quasar. The properties of these in terms of (1) the line equivalent width, (2) the line profile, and (3) the value of the surface brightness related to the distance from the quasar all suggest that several of these may be plausibly fluorescent. Moreover, their number is in good agreement with the expectation from theoretical models. One of the best candidates for fluorescence is sufficiently far behind QSO 0420-388 that it would imply that the quasar has been active for (at least) ~60 Myr. Further studies on such objects will give information about protogalactic clouds and on the radiative history (and beaming) of the high-redshift quasars.

A young star-forming galaxy at z = 3.5 with an extended Lyman α halo seen with MUSE

Spatially resolved studies of high-redshift galaxies, an essential insight into galaxy formation processes, have been mostly limited to stacking or unusually bright objects. We present here the study of a typical (L * , M = 6 × 10 9 M) young lensed galaxy at z = 3.5, observed with Multi Unit Spectroscopic Explorer (MUSE), for which we obtain 2D resolved spatial information of Lyα and, for the first time, of C III] emission. The exceptional signal-to-noise ratio of the data reveals UV emission and absorption lines rarely seen at these redshifts, allowing us to derive important physical properties (T e ∼ 15600 K, n e ∼ 300 cm −3 , covering fraction f c ∼ ˜ 0.4) using multiple diagnostics. Inferred stellar and gas-phase metallicities point towards a low-metallicity object (Zstellar = ˜0.07 Z⊙ and ZISM < 0.16 Z⊙). The Lyα emission extends over ˜10 kpc across the galaxy and presents a very uniform spectral profile, showing only a small velocity shift which is unrelated to the intrinsic kinematics of the nebular emission. The Lyα extension is approximately four times larger than the continuum emission, and makes this object comparable to low-mass LAEs at low redshift, and more compact than the Lyman-break galaxies and Lyα emitters usually studied at high redshift. We model the Lyα line and surface brightness profile using a radiative transfer code in an expanding gas shell, finding that this model provides a good description of both observables.

The Stacked Lyman-Alpha Emission Profile from the Circum-Galactic Medium of z~2 Quasars

In the context of the FLASHLIGHT survey, we obtained deep narrow band images of 15

MUSE searches for galaxies near very metal-poor gas clouds at z~3 : new constraints for cold accretion models.

z\sim2

Discovery of an Enormous Lyα Nebula in a Massive Galaxy Overdensity at z = 2.3

quasars with GMOS on Gemini-South in an effort to measure Ly

The MUSE Hubble Ultra Deep Field Survey. I. Survey description, data reduction, and source detection

\alpha

MUSE deep-fields: the Ly α luminosity function in the Hubble Deep Field-South at 2.91 < z < 6.64

emission from circum- and inter-galactic gas on scales of hundreds of kpc from the central quasar. We do not detect bright giant Ly