Hakim Atek

3D Lyα radiation transfer III. Constraints on gas and stellar properties of z ∼ 3 Lyman break galaxies (LBG) and implications for high-z LBGs and Lyα emitters

Aims. The aim of our study is to understand the variety of observed Lyα line profiles and strengths in Lyman Break Galaxies (LBGs) and Lyα emitters (LAEs), the physical parameters governing them, and hence derive constraints on the gas and dust content and stellar populations of these objects. Methods. Using our 3D Lyα radiation transfer code including gas and dust, MCLya, we fit 11 LBGs from the FORS Deep Field with redshifts between 2.8 and 5. A simple geometry of a spherically expanding shell of H i is adopted. Results. The variety of observed Lyα profiles is successfully reproduced. Most objects show outflow velocities of Vexp ∼ 150−200 km s −1 ; two objects are most likely quasi-static. The radial H i column density ranges from NHI ∼ 2 × 10 19 to 7 × 10 20 cm −2 . Our Lyα profile fits yield values of E(B − V) ∼ 0.05−0.2 for the gas extinction. We find indications for a dust-to-gas ratio higher than the Galactic value, and for a substantial scatter. The escape fraction of Lyα photons is found to be determined primarily by the extinction, and a simple fit formula is proposed. In this case a measurement of EW(Lyα)obs can yield E(B − V), if the intrinsic Lyα equivalent width is known (or assumed). Intrinsic EW(Lyα)int ∼ 50−100 A are found for 8/11 objects, as expected for stellar populations forming constantly over long periods (>10−100 Myr). In three cases we found indications of younger populations. Our model results also allow us to understand observed correlations between EW(Lyα)obs and other observables such as FWHM(Lyα), E(B − V), SFR(UV) etc. We suggest that most observed trends of Lyα, both in LBGs and LAEs, are driven by variations of NHI and the accompanying variation of the dust content. Ultimately, the main parameter responsible for these variations may be the galaxy mass. We also show that there is a clear overlap between LBGs and LAEs: at z ∼ 3 approximately 20−25% of the LBGs of Shapley et al. (2003, ApJ, 588, 65) overlap with ∼23% of the LAEs of Gronwal et al. (2007, ApJ, 667, 79). Radiation transfer and dust effects explain the increase of the LAE/LBG ratio, and a higher percentage of LBGs with strong Lyα emission with increasing redshift.

On the Redshift Evolution of the Lyα Escape Fraction and the Dust Content of Galaxies

The Lyα emission line has been proven to be a powerful tool for studying evolving galaxies at the highest redshift. However, in order to use Lyα as a physical probe of galaxies, it becomes vital to know the Lyα escape fraction (f^(Lyα)_(esc)). Unfortunately, due to the resonant nature of Lyα, f^(Lyα)_(esc) may vary unpredictably and requires empirical measurement. Here, we compile Lyα luminosity functions (LFs) between redshifts z = 0 and 8 and, combined with Hα and ultraviolet data, assess how f^(Lyα)_(esc) evolves with redshift. We find a strong upward evolution in f^(Lyα)_(esc) over the range z = 0.3-6, which is well fit by the power law f^(Lyα)_(esc)α(1 + z)^ξwith ξ = (2.57^(+0.19)_(–0.12)). This predicts that f^(Lyα)_(esc) should reach unity at z = 11.1. By comparing f^(Lyα)_(esc) and E_(B–V) in individual galaxies we derive an empirical relationship between f^(Lyα)_(esc) and E_(B–V) , which includes resonance scattering and can explain the redshift evolution of f^(Lyα)_(esc) between z = 0 and 6 purely as a function of the evolution in the dust content of galaxies. Beyond z ≈ 6.5, f^(Lyα)_(esc) drops more substantially, an effect attributed to either ionizing photon leakage, or an increase in the neutral gas fraction of the intergalactic medium. While distinguishing between these two scenarios may be extremely challenging, by framing the problem this way we remove the uncertainty of the halo mass from Lyα-based tests of reionization. We finally derive a new method by which to estimate the dust content of galaxies, based purely upon the observed Lyα and UV LFs. These data are characterized by an exponential with an e-folding scale of z_(EBV) ≈ 3.4.

VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES* , **

The WFC3 Infrared Spectroscopic Parallel Survey uses the Hubble Space Telescope (HST) infrared grism capabilities to obtain slitless spectra of thousands of galaxies over a wide redshift range including the peak of star formation history of the universe. We select a population of very strong emission-line galaxies with rest-frame equivalent widths (EWs) higher than 200 A. A total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the 180 arcmin^2 area that we have analyzed so far. This population consists of young and low-mass starbursts with high specific star formation rates (sSFR). After spectroscopic follow-up of one of these galaxies with Keck/Low Resolution Imaging Spectrometer, we report the detection at z = 0.7 of an extremely metal-poor galaxy with 12 + log(O/H) =7.47 ± 0.11. After estimating the active galactic nucleus fraction in the sample, we show that the high-EW galaxies have higher sSFR than normal star-forming galaxies at any redshift. We find that the nebular emission lines can substantially affect the total broadband flux density with a median brightening of 0.3 mag, with some examples of line contamination producing brightening of up to 1 mag. We show that the presence of strong emission lines in low-z galaxies can mimic the color-selection criteria used in the z ~ 8 dropout surveys. In order to effectively remove low-redshift interlopers, deep optical imaging is needed, at least 1 mag deeper than the bands in which the objects are detected. Without deep optical data, most of the interlopers cannot be ruled out in the wide shallow HST imaging surveys. Finally, we empirically demonstrate that strong nebular lines can lead to an overestimation of the mass and the age of galaxies derived from fitting of their spectral energy distribution (SED). Without removing emission lines, the age and the stellar mass estimates are overestimated by a factor of 2 on average and up to a factor of 10 for the high-EW galaxies. Therefore, the contribution of emission lines should be systematically taken into account in SED fitting of star-forming galaxies at all redshifts.

Escape of about five per cent of Lyman-alpha photons from high-redshift star-forming galaxies.

The Lyman-α (Lyα) emission line is the primary observational signature of star-forming galaxies at the highest redshifts, and has enabled the compilation of large samples of galaxies with which to study cosmic evolution. The resonant nature of the line, however, means that Lyα photons scatter in the neutral interstellar medium of their host galaxies, and their sensitivity to absorption by interstellar dust may therefore be greatly enhanced. This implies that the Lyα luminosity may be significantly reduced, or even completely suppressed. Hitherto, no unbiased empirical test of the escaping fraction (fesc) of Lyα photons has been performed at high redshifts. Here we report that the average fesc from star-forming galaxies at redshift z = 2.2 is just 5 per cent by performing a blind narrowband survey in Lyα and Hα. This implies that numerous conclusions based on Lyα-selected samples will require upwards revision by an order of magnitude and we provide a benchmark for this revision. We demonstrate that almost 90 per cent of star-forming galaxies emit insufficient Lyα to be detected by standard selection criteria. Both samples show an anti-correlation of fesc with dust content, and we show that Lyα- and Hα-selection recovers populations that differ substantially in dust content and fesc.

DUST EXTINCTION FROM BALMER DECREMENTS OF STAR-FORMING GALAXIES AT 0.75 z 1.5 WITH HUBBLE SPACE TELESCOPE/WIDE-FIELD-CAMERA 3 SPECTROSCOPY FROM THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY

Spectroscopic observations of H and H emission lines of 128 star-forming galaxies in the redshift range 0:75 z 1:5 are presented. These data were taken with slitless spectroscopy using the G102 and G141 grisms of the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of the WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust extinction is measured from stacked spectra that cover the Balmer decrement (H /H ). We present dust extinction as a function of H luminosity (down to 3 10 41 erg s 1 ), galaxy stellar mass (reaching 4 10 8 M ), and rest-frame H equivalent width. The faintest galaxies are two times fainter in H luminosity than galaxies previously studied at z 1:5. An evolution is observed where galaxies of the same H luminosity have lower extinction at higher redshifts, whereas no evolution is found within our error bars with stellar mass. The lower H luminosity galaxies in our sample are found to be consistent with no dust extinction. We

Physical properties of emission-line galaxies at z ∼ 2 from near-infrared spectroscopy with magellan fire

We present results from near-infrared spectroscopy of 26 emission-line galaxies at z ~ 2.2 and z ~ 1.5 obtained with the Folded-port InfraRed Echellette (FIRE) spectrometer on the 6.5 m Magellan Baade telescope. The sample was selected from the WFC3 Infrared Spectroscopic Parallels survey, which uses the near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 (WFC3) to detect emission-line galaxies over 0.3 ≾z ≾2.3. Our FIRE follow-up spectroscopy (R ~ 5000) over 1.0-2.5 μm permits detailed measurements of the physical properties of the z ~ 2 emission-line galaxies. Dust-corrected star formation rates for the sample range from ~5-100 M☉ yr^(–1) with a mean of 29 M☉ yr^(–1). We derive a median metallicity for the sample of 12 + log(O/H) = 8.34 or ~0.45 Z☉. The estimated stellar masses range from ~10^(8.5)-10^(9.5) M☉, and a clear positive correlation between metallicity and stellar mass is observed. The average ionization parameter measured for the sample, log U ≈–2.5, is significantly higher than what is found for most star-forming galaxies in the local universe, but similar to the values found for other star-forming galaxies at high redshift. We derive composite spectra from the FIRE sample, from which we measure typical nebular electron densities of ~100-400 cm^(–3). Based on the location of the galaxies and composite spectra on diagnostic diagrams, we do not find evidence for significant active galactic nucleus activity in the sample. Most of the galaxies, as well as the composites, are offset diagram toward higher [O III]/Hβ at a given [N II]/Hα, in agreement with other observations of z ≳1 star-forming galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local star-forming sequence on the [O III]/Hβ versus [S II]/Hα diagram. We infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local star-forming sequence in the [O III]/Hβ versus [N II]/Hα diagram. We speculate that the elevated nitrogen abundance could result from substantial numbers of Wolf-Rayet stars in starbursting galaxies at z ~ 2.

THE LYMAN ALPHA MORPHOLOGY OF LOCAL STARBURST GALAXIES: RELEASE OF CALIBRATED IMAGES

We present reduced and calibrated high resolution Lyman-alpha (Lyα) images for a sample of six local star-forming galaxies. Targets were selected to represent a range in luminosity and metallicity ...

NEW CONSTRAINTS ON THE FAINT-END OF THE UV LUMINOSITY FUNCTION AT Z 7 8 USING THE GRAVITATIONAL LENSING OF THE HUBBLE FRONTIER FIELDS CLUSTER A2744 †

Exploiting the power of gravitational lensing, the Hubble Frontier Fields (HFF) program aims at observing six massive galaxy clusters to explore the distant Universe far beyond the depth limits of blank field surveys. Using the complete Hubble Space Telescope observations of the first HFF cluster Abell 2744, we report the detection of 50 galaxy candidates at

THE WFC3 INFRARED SPECTROSCOPIC PARALLEL (WISP) SURVEY

z \sim 7

On the detectability of Ly

and eight candidates at