Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization (original) (raw)
Related papers
The Astrophysical Journal, 2011
We present the final results from our ultra-deep spectroscopic campaign with FORS2 at the ESO Very Large Telescope (VLT) for the confirmation of z 7 "z-band dropout" candidates selected from our VLT/Hawk-I imaging survey over three independent fields. In particular, we report on two newly discovered galaxies at redshift ∼6.7 in the New Technology Telescope Deep Field. Both galaxies show an Lyα emission line with rest-frame equivalent widths (EWs) of the order of 15-20 Å and luminosities of (2-4) × 10 42 erg s −1 . We also present the results of ultra-deep observations of a sample of i-dropout galaxies, from which we set a solid upper limit on the fraction of interlopers. Out of the 20 z-dropouts observed we confirm 5 galaxies at 6.6 < z < 7.1. This is systematically below the expectations drawn on the basis of lower redshift observations: in particular, there is a significant lack of objects with intermediate Lyα EWs (between 20 and 55 Å). We conclude that the observed trend for the rising fraction of Lyα emission in Lyman break galaxies from z ∼ 3 to z ∼ 6 is most probably reversed from z ∼ 6 to z ∼ 7. Explaining the observed rapid change in the Lyα emitter fraction among the dropout population with reionization requires a fast evolution of the neutral fraction of hydrogen in the universe. Assuming that the universe is completely ionized at z = 6 and adopting a set of semi-analytical models, we find that our data require a change of the neutral hydrogen fraction of the order of Δχ H i ∼ 0.6 in a time Δz ∼ 1, provided that the escape fraction does not increase dramatically over the same redshift interval.
A galaxy as the source of a C iv absorption system close to the epoch of reionization★
Monthly Notices of the Royal Astronomical Society, 2011
A galaxy as the source of a C iv absorption system close to the epoch of reionization ⋆ ABSTRACT We find a bright (L UV = 2.5 L ⋆ z=6 ) Lyman alpha emitter (LAE) at redshift z = 5.719 at a projected distance of 79 physical kpc from a strong triply ionized carbon (C iv) absorption system at redshift z = 5.7238 previously reported in the spectrum of the z em = 6.309 QSO SDSS J1030+0524. This is the highest redshift galaxy-absorber pair detected to-date, supporting the idea that galaxy-wide outflows were already in place at the end of the epoch of reionization. The proximity of this object makes it the most likely source of metals, consistent with models of outflows at lower redshift where significant observational evidence relates metal absorption systems with galaxies hosting outflows. Moreover, we estimate that the probability of a closer, fainter galaxy being responsible for the absorption system is only ∼ 10 −3 .
Spectroscopic confirmation of z~ 7 LBGs: probing the earliest galaxies and the epoch of reionization
We present the final results from our ultra-deep spectroscopic campaign with FORS2 at the ESO/VLT for the confirmation of z ≃ 7 "z-band dropout" candidates selected from our VLT/Hawk-I imaging survey over three independent fields. In particular we report on two newly discovered galaxies at redshift ∼ 6.7 in the NTT deep field: both galaxies show a Lyα emission line with rest-frame EWs of the order 15-20Å and luminosities of 2-4×10 42 ergs −1 . We also present the results of ultra-deep observations of a sample of i-dropout galaxies, from which we set a solid upper limit on the fraction of interlopers.
Luminous Lyman Break Galaxies at z > 5 and the Source of Reionization
The Astrophysical Journal, 2003
We have discovered six galaxies with spectroscopically confirmed redshifts of 4.8 < z < 5.8 in a single 44 square arcminute field imaged deeply in R, I and z−bands. All the spectra show an emission-line in the region around 7000-8400Å with a spectroscopically-detected faint continuum break across the line. These six were drawn from 13 sources with I AB < 26.2 and R AB − I AB > 1.5 in the field, this photometric cut designed to select galaxies at z > 4.8. The line fluxes range between 0.2 to 2.5×10 −17 ergs cm −2 s −1 indicating luminosities of around 10 42−43 ergs s −1 for Lyα and their high emission line equivalent widths suggest very young ages (10 8 yrs). A further line-emitting object with no detectable continuum was serendipitously detected by spectroscopy. If this line is Lyα then it is from a source at z = 6.6, making this the most distant galaxy known. However, the redshift cannot be considered secure as it is based on a single line. No broad emission line objects (quasars) were detected. The 13 sources at I AB < 26.2 are less than that expected if the luminosity function of dropout galaxies remained unchanged between z = 3 and z = 6, although the deficit is not highly significant given possible cosmic variance. The UV luminosity density from galaxies brighter than our flux limit is considerably less than that necessary to keep the volume probed by our field at < z >∼ 5.3 ionized. These galaxies are observed within several hundred Myr of the end of the epoch of reionization (z = 6 − 7), with little time for the luminosity function to evolve. This, and the lack of detected quasars, imply that the bulk of the UV flux that reionized the universe came from faint galaxies with M AB (1700Å) > −21.
Monthly Notices of the Royal Astronomical Society, 2015
Deep spectroscopic observations of z ∼ > 6.5 galaxies have revealed a marked decline with increasing redshift in the detectability of Lyα emission. While this may offer valuable insight into the end of the reionisation process, it presents a fundamental challenge to the detailed spectroscopic study of the many hundreds of photometrically-selected distant sources now being found via deep HST imaging, and particularly those bright sources viewed through foreground lensing clusters. In this paper we demonstrate the validity of a new way forward via the convincing detection of an alternative diagnostic line, CIII]λ1909Å , seen in spectroscopic exposures of two star forming galaxies at z Lyα = 6.029 and 7.213. The former detection is based on a 3.5 hour X-shooter spectrum of a bright (J 125 = 25.2) gravitationally-lensed galaxy behind the cluster Abell 383. The latter detection is based on a 4.2 hour MOSFIRE spectra of one of the most distant spectroscopically confirmed galaxies, GN-108036, with J 140 = 25.2. Both targets were chosen for their continuum brightness and previously-known redshift (based on Lyα), ensuring that any CIII] emission would be located in a favorable portion of the near-infrared sky spectrum. We compare our CIII] and Lyα equivalent widths in the context of those found at z 2 from earlier work and discuss the motivation for using lines other than Lyα to study galaxies in the reionisation era.
The Astrophysical Journal, 2014
We report the LBT/MODS1 spectroscopic confirmation of two images of faint Lyman alpha emitters at z = 6.4 behind the Frontier Fields galaxy cluster MACSJ0717.5+3745. A wide range of lens models suggests that the two images are highly magnified, with a strong lower limit of µ > 5. These are the faintest z > 6 candidates spectroscopically confirmed to date. These may be also multiple images of the same z = 6.4 source as supported by their similar intrinsic properties, but the lens models are inconclusive regarding this interpretation. To be cautious, we derive the physical properties of each image individually. Thanks to the high magnification, the observed near-infrared (restframe ultraviolet) part of the spectral energy distributions and Lyα lines are well detected with S/N (m 1500) 10 and S/N (Lyα) ≃ 10 − 15. Adopting µ > 5, the absolute magnitudes, M 1500 , and Lyα fluxes, are fainter than −18.7 and 2.8 × 10 −18 ergs −1 cm −2 , respectively. We find a very steep ultraviolet spectral slope β = −3.0 ± 0.5 (F λ = λ β), implying that these are very young, dust-free and low metallicity objects, made of standard stellar populations or even extremely metal poor stars (age 30Myr, E(B-V)=0 and metallicity 0.0 − 0.2Z/Z ⊙). The objects are compact (< 1kpc 2), and with a stellar mass M ⋆ < 10 8 M ⊙. The very steep β, the presence of the Lyα line and the intrinsic FWHM (< 300 kms −1) of these newborn objects do not exclude a possible leakage of ionizing radiation. We discuss the possibility that such faint galaxies may resemble those responsible for cosmic reionization.
The Astrophysical Journal, 2012
We use the spatially-resolved, multi-band photometry in the GOODS South field acquired by the CANDELS project to constrain the nature of candidate Lyman continuum (LyC) emitters at redshift z ∼ 3.7 identified using ultra-deep imaging below the Lyman limit (1-sigma limit of ≈30 AB in a 2 ′′ diameter aperture). In 18 candidates, out of a sample of 19 with flux detected at >3-sigma level, the light centroid of the candidate LyC emission is offset from that of the LBG by up to 1.5 ′′ . We fit the SED of the LyC candidates to spectral population synthesis models to measure photometric redshifts and the stellar population parameters. We also discuss the differences in the UV colors between the LBG and the LyC candidates, and how to estimate the escape fraction of ionizing radiation (f esc ) in cases, like in most of our galaxies, where the LyC emission is spatially offset from the host galaxy. In all but one case we conclude that the candidate LyC emission is most likely due to lower redshift interlopers. Based on these findings, we argue that the majority of similar measurements reported in the literature need further investigation before it can be firmly concluded that LyC emission is detected. Our only surviving LyC candidate is a LBG at z = 3.795, which shows the bluest (B − V ) color among LBGs at similar redshift, a stellar mass of M ∼ 2 × 10 9 M ⊙ , weak interstellar absorption lines and a flat UV spectral slope with no Lyα in emission. We estimate its f esc to be in the range 25%-100%, depending on the dust and intergalactic attenuation.
Spectroscopic confirmation of a galaxy at redshift z = 8.6
Nature, 2010
Galaxies had their most significant impact on the Universe when they assembled their first generations of stars. Energetic photons emitted by young, massive stars in primeval galaxies ionized the intergalactic medium surrounding their host 1 arXiv:1010.4312v1 [astro-ph.CO] 20 Oct 2010 galaxies, cleared sight-lines along which the light of the young galaxies could escape, and fundamentally altered the physical state of the intergalactic gas in the Universe continuously until the present day 1,2. Observations of the Cosmic Microwave Background 3 , and of galaxies and quasars at the highest redshifts 4 , suggest that the Universe was reionised through a complex process that was completed about a billion years after the Big Bang, by redshift z≈6. Detecting ionizing Ly-alpha photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionisation. Here we report the detection of Lyα photons emitted less than 600 million years after the Big Bang. UDFy-38135539 5 is at a redshift z=8.5549±0.0002, which is greater than those of the previously known most distant objects, at z=8.2 6,7 and z=6.96 8. We find that this single source is unlikely to provide enough photons to ionize the volume necessary for the emission line to escape, requiring a significant contribution from other, probably fainter galaxies nearby 9. UDFy-38135539 was selected as a candidate z≈8.6 galaxy from deep Wide Field Camera 3 observations of the Hubble Ultra Deep field 5. Its red Y 105-J 125 colour is one of the reddest in the parent sample of z=8-9 candidates, and, together with the sensitive upper limits in the optical through the Y 105 band, make it the most plausible z≈8.6 galaxy 5,10. To search for its Lyα emission, we obtained sensitive near-infrared integral-field spectroscopic observations of UDFy-38135539 using the SINFONI spectrograph at the ESO Very Large Telescope, with an integration time on the source of 14.8 h in the near-infrared J-band (1.1-1.4µm).
On the relative contribution of high-redshift galaxies and active galactic nuclei to reionization
Monthly Notices of the Royal Astronomical Society, 2012
In this paper we discuss the contribution of different astrophysical sources to the ionization of neutral hydrogen at different redshifts. We critically revise the arguments in favour/against a substantial contribution of Active Galactic Nuclei (AGNs) and/or Lyman Break Galaxies (LBGs) to the reionization of the Universe at z > 5. We consider extrapolations of the high-z QSO and LBG luminosity functions and their redshift evolution as well as indirect constraints on the space density of lower luminosity Active Galactic Nuclei based on the galaxy stellar mass function. Since the hypothesis of a reionization due to LBGs alone requires a significant contribution of faint dwarf galaxies and a LyC photon escape fraction (f esc) of the order of ∼ 20%, in tension with present observational constraints, we examine under which hypothesis AGNs and LBGs may provide a combined relevant contribution to the reionization. We show that a relatively steep faint-end of the AGN luminosity function, consistent with present constraints, provides a relevant (although subdominant) contribution, thus allowing us to recover the required ionizing photon rates with f esc ∼ 5% up to z ∼ 7. At higher redshifts, we test the case for a luminosity-dependent f esc scenario and we conclude that, if the observed LBGs are indeed characterized by very low f esc , values of the order of f esc ∼ 70% are needed for objects below our detection threshold, for this galaxy population to provide a substantial contribution to reionization. Clearly, the study of the properties of faint sources (both AGNs and LBGs) is crucial.
A Lyman-α Galaxy at Redshift z = 6.944 in the COSMOS Field1
2016
Lyman-α emitting galaxies can be used to study cosmological reionization, because a neutral intergalactic medium scatters Lyman-α photons into diffuse halos whose surface brightness falls below typical survey detection limits. Here we present the Lyman-α emitting galaxy LAE J095950.99+021219.1, identified at redshift z = 6.944 in the COSMOS field using narrowband imaging and followup spectroscopy with the IMACS instrument on the Magellan I Baade telescope. With a single object spectroscopically confirmed so far, our survey remains con-sistent with a wide range of IGM neutral fraction at z ≈ 7, but further obser-vations are planned and will help clarify the situation. Meantime, the object we present here is only the third Lyman-α-selected galaxy to be spectroscopically confirmed at z & 7, and is ∼ 2–3 times fainter than the previously confirmed z ≈ 7 Lyman-α galaxies. Subject headings: galaxies: high-redshift — dark ages, reionization, first stars 1.