A long-standing and profound problem in astronomy is the difficulty in obtaining deep near-infrared observations due to the extreme brightness and variability of the night sky at these wavelengths. A ...solution to this problem is crucial if we are to obtain the deepest possible observations of the early Universe, as redshifted starlight from distant galaxies appears at these wavelengths. The atmospheric emission between 1,000 and 1,800 nm arises almost entirely from a forest of extremely bright, very narrow hydroxyl emission lines that varies on timescales of minutes. The astronomical community has long envisaged the prospect of selectively removing these lines, while retaining high throughput between them. Here we demonstrate such a filter for the first time, presenting results from the first on-sky tests. Its use on current 8 m telescopes and future 30 m telescopes will open up many new research avenues in the years to come.
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 galaxies, cleared sightlines 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. Observations of the cosmic microwave background, and of galaxies and quasars at the highest redshifts, suggest that the Universe was reionized through a complex process that was completed about a billion years after the Big Bang, by redshift z 6. Detecting ionizing Lyman- photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionization. Here we report the detection of Ly photons emitted less than 600 million years after the Big Bang. UDFy-38135539 (ref. 5) is at a redshift of z = 8.5549 ± 0.0002, which is greater than those of the previously known most distant objects, at z = 8.2 (refs 6 and 7) and z = 6.96 (ref. 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.
Euclid preparation Barnett, R.; Warren, S. J.; Mortlock, D. J. ...
Astronomy and astrophysics (Berlin),
11/2019, Volume:
631
Journal Article
Peer reviewed
Open access
We provide predictions of the yield of 7 < z < 9 quasars from the Euclid wide survey, updating the calculation presented in the Euclid Red Book in several ways. We account for revisions to the Euclid ...near-infrared filter wavelengths; we adopt steeper rates of decline of the quasar luminosity function (QLF; Φ) with redshift, Φ ∝ 10 k ( z − 6) , k = −0.72, and a further steeper rate of decline, k = −0.92; we use better models of the contaminating populations (MLT dwarfs and compact early-type galaxies); and we make use of an improved Bayesian selection method, compared to the colour cuts used for the Red Book calculation, allowing the identification of fainter quasars, down to J AB ∼ 23. Quasars at z > 8 may be selected from Euclid O Y J H photometry alone, but selection over the redshift interval 7 < z < 8 is greatly improved by the addition of z -band data from, e.g., Pan-STARRS and LSST. We calculate predicted quasar yields for the assumed values of the rate of decline of the QLF beyond z = 6. If the decline of the QLF accelerates beyond z = 6, with k = −0.92, Euclid should nevertheless find over 100 quasars with 7.0 < z < 7.5, and ∼25 quasars beyond the current record of z = 7.5, including ∼8 beyond z = 8.0. The first Euclid quasars at z > 7.5 should be found in the DR1 data release, expected in 2024. It will be possible to determine the bright-end slope of the QLF, 7 < z < 8, M 1450 < −25, using 8 m class telescopes to confirm candidates, but follow-up with JWST or E-ELT will be required to measure the faint-end slope. Contamination of the candidate lists is predicted to be modest even at J AB ∼ 23. The precision with which k can be determined over 7 < z < 8 depends on the value of k , but assuming k = −0.72 it can be measured to a 1 σ uncertainty of 0.07.
Being observed only one billion years after the Big Bang, z ∼ 7 quasars are a unique opportunity for exploring the early Universe. However, only two z ∼ 7 quasars have been discovered in ...near-infrared surveys: the quasars ULAS J1120+0641 and ULAS J1342+0928 at z = 7.09 and z = 7.54, respectively. The rarity of these distant objects, combined with the difficulty of distinguishing them from the much more numerous population of Galactic low-mass stars, requires using efficient selection procedures. The Canada-France High-z Quasar Survey in the Near Infrared (CFHQSIR) has been carried out to search for z ∼ 7 quasars using near-infrared and optical imaging from the Canada-France Hawaii Telescope (CFHT). Our data consist of ∼130 deg2 of Wide-field Infrared Camera (WIRCam) Y-band images up to a 5σ limit of YAB ∼ 22.4 distributed over the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Wide fields. After follow-up observations in J band, a first photometric selection based on simple colour criteria led us to identify 36 sources with measured high-redshift quasar colours. However, we expect to detect only ∼2 quasars in the redshift range 6.8 < z < 7.5 down to a rest-frame absolute magnitude of M1450 = −24.6. With the motivation of ranking our high-redshift quasar candidates in the best possible way, we developed an advanced classification method based on Bayesian formalism in which we model the high-redshift quasars and low-mass star populations. The model includes the colour diversity of the two populations and the variation in space density of the low-mass stars with Galactic latitude, and it is combined with our observational data. For each candidate, we compute the probability of being a high-redshift quasar rather than a low-mass star. This results in a refined list of the most promising candidates. Our Bayesian selection procedure has proven to be a powerful technique for identifying the best candidates of any photometrically selected sample of objects, and it is easily extendable to other surveys.
Gamma-ray bursts (GRBs) have been proposed as a tool for studying star formation in the Universe, so it is crucial to investigate whether their host galaxies and immediate environments are in any way ...special compared with other star-forming galaxies. Here we present spatially resolved maps of dust emission of the host galaxyof the closest known GRB 980425 at z = 0.0085 using our new high-resolution observations from Herschel, Atacama Pathfinder Experiment (APEX), Atacama Large Millimeter Array (ALMA) and Australia Telescope Compact Array (ATCA). We modelled the spectral energy distributions of the host and of the star-forming region displaying the Wolf-Rayet signatures in the spectrum (WR region), located 800 pc from the GRB position. The host is characterised by low dust content and a high fraction of UV-visible star formation, similar to other dwarf galaxies. These galaxies are abundant in the local universe, so it is not surprising to find a GRB in one of them, assuming the correspondence between the GRB rate and star formation. The WR region contributes substantially to the host emission at the far-infrared, millimetre, and radio wavelengths and we propose that this is a consequence of its high gas density. If dense environments are also found close to the positions of other GRBs, then the ISM density should also be considered, along with metallicity, an important factor influencing whether a given stellar population can produce a GRB.
THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain ...astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1sr) with 0.5–1 arcmin localization, an energy band extending from several MeV down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift ∼10, signatures of Pop III stars, sources and physics of re-ionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late ’20s/early ’30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA).
Context. The Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) has been conducted over a 5-yr period at the CFHT with the MegaCam instrument, totaling 450 nights of observations. The Wide ...Synoptic Survey is one component of the CFHTLS, covering 155 square degrees in four patches of 23 to 65 square degrees through the whole MegaCam filter set (u*, g’, r’, i’, z’) down to i’AB = 24.5. Aims. With the motivation of searching for high-redshift quasars at redshifts above 6.5, we extend the multi-wavelength CFHTLS-Wide data in the Y -band down to magnitudes of ~22.5 for point sources (5σ). Methods. We observed the four CFHTLS-Wide fields (except one quarter of the W3 field) in the Y -band with the Wide-field InfraRed Camera (WIRCam) at the CFHT. Each field was visited twice, at least three weeks apart. Each visit consisted of two dithered exposures. The images are reduced with the Elixir software used for the CFHTLS and modified to account for the properties of near-InfraRed (IR) data. Two series of image stacks are subsequently produced: four-image stacks for each WIRCam pointing, and one-square-degree tiles matched to the format of the CFHTLS data release. Photometric calibration is performed on stars by fitting stellar spectra to their CFHTLS photometric data and extrapolating their Y -band magnitudes. Results. After corrections accounting for correlated noise, we measure a limiting magnitude of YAB ≃ 22.4 for point sources (5σ) in an aperture diameter of 0.′′93, over 130 square degrees. We produce a multi-wavelength catalogue combining the CFHTLS-Wide optical data with our CFHQSIR (Canada–France High-z quasar survey in the near-InfraRed) Y -band data. We derive the Y -band number counts and compare them to the Vista Deep Extragalactic Observations survey (VIDEO). We find that the addition of the CFHQSIR Y -band data to the CFHTLS optical data increases the accuracy of photometric redshifts and reduces the outlier rate from 13.8% to 8.8% in the redshift range 1.05 ≲ z ≲ 1.2.
Elucidating the processes that governed the assembly and evolution of galaxies over cosmic time is one of the main objectives of all of the proposed Extremely Large Telescopes (ELT). To make a leap ...forward in our understanding of these processes, an ELT will want to take advantage of Multi-Objects Adaptive Optics (MOAO) systems, which can substantially improve the natural seeing over a wide field of view. We have developed an end-to-end simulation to specify the science requirements of a MOAO-fed integral field spectrograph on either an 8-m or 42-m telescope. Our simulations rescale observations of local galaxies or results from numerical simulations of disc or interacting galaxies. The code is flexible in that it allows us to explore a wide range of instrumental parameters such as ensquared energy (EE), pixel size, spectral resolution, etc. For the current analysis, we limit ourselves to a local disc galaxy which exhibits simple rotation and a simulation of a merger. While the number of simulations is limited, we have attempted to generalize our results by introducing the simple concepts of ‘point spread function (PSF) contrast’ which is the amount of light polluting adjacent spectra which we find drives the smallest EE at a given spatial scale. The choice of the spatial sampling is driven by the ‘scale-coupling’. By scale-coupling we mean the relationship between the integral field unit (IFU) pixel scale and the size of the features that need to be recovered by 3D spectroscopy in order to understand the nature of the galaxy and its substructure. Because the dynamical nature of galaxies is mostly reflected in their large-scale motions, a relatively coarse spatial resolution is enough to distinguish between a rotating disc and a major merger. Although we used a limited number of morphokinematic cases, our simulations suggest that, on a 42-m telescope, the choice of an IFU pixel scale of 50–75 mas seems to be sufficient. Such a coarse sampling has the benefit of lowering the exposure time to reach a specific signal-to-noise ratio as well as relaxing the performance of the MOAO system. On the other hand, recovering the full 2D kinematics of z∼ 4 galaxies requires high signal-to-noise ratio and at least an EE of 34 per cent in 150 mas (2 pixels of 75 mas). Finally, we carried out a similar study for a hypothetical galaxy/merger at z= 1.6 with a MOAO-fed spectrograph for an 8 m, and find that at least an EE of 30 per cent at 0.25 arcsec spatial sampling is required to understand the nature of discs and mergers.
Aims. The Lyα luminosity function (LF) of high-redshift Lyα emitters (LAEs) is one of the few observables of the re-ionization epoch accessible with 8–10 m class telescopes. The evolution of the LAE ...LF with redshift is dependent upon the physical evolution of LAEs and the ionisation state of the Universe towards the end of the Dark Ages. Methods. We performed a narrow-band imaging program at 1.06 μm using CFHT/WIRCam. The observations target Lyα emitters at redshift z ~ 7.7 in the CFHT-LS D1 field. From these observations we derived a photometric sample of 7 LAE candidates at z ~ 7.7. Results. We derive luminosity functions for the full sample of seven objects and for subsamples of four objects. Assuming the brightest objects in our sample are real, we find that the resulting luminosity function is not consistent with previous work at lower redshifts. More definitive conclusions will require spectroscopic confirmation.
Euclid preparation Desprez, G.; Coupon, J.; Almosallam, I. ...
Astronomy and astrophysics (Berlin),
12/2020, Volume:
644
Journal Article
Peer reviewed
Open access
Forthcoming large photometric surveys for cosmology require precise and accurate photometric redshift (photo-
z
) measurements for the success of their main science objectives. However, to date, no ...method has been able to produce photo-
z
s at the required accuracy using only the broad-band photometry that those surveys will provide. An assessment of the strengths and weaknesses of current methods is a crucial step in the eventual development of an approach to meet this challenge. We report on the performance of 13 photometric redshift code single value redshift estimates and redshift probability distributions (PDZs) on a common set of data, focusing particularly on the 0.2 − 2.6 redshift range that the
Euclid
mission will probe. We designed a challenge using emulated
Euclid
data drawn from three photometric surveys of the COSMOS field. The data was divided into two samples: one calibration sample for which photometry and redshifts were provided to the participants; and the validation sample, containing only the photometry to ensure a blinded test of the methods. Participants were invited to provide a redshift single value estimate and a PDZ for each source in the validation sample, along with a rejection flag that indicates the sources they consider unfit for use in cosmological analyses. The performance of each method was assessed through a set of informative metrics, using cross-matched spectroscopic and highly-accurate photometric redshifts as the ground truth. We show that the rejection criteria set by participants are efficient in removing strong outliers, that is to say sources for which the photo-
z
deviates by more than 0.15(1 +
z
) from the spectroscopic-redshift (spec-
z
). We also show that, while all methods are able to provide reliable single value estimates, several machine-learning methods do not manage to produce useful PDZs. We find that no machine-learning method provides good results in the regions of galaxy color-space that are sparsely populated by spectroscopic-redshifts, for example
z
> 1. However they generally perform better than template-fitting methods at low redshift (
z
< 0.7), indicating that template-fitting methods do not use all of the information contained in the photometry. We introduce metrics that quantify both photo-
z
precision and completeness of the samples (post-rejection), since both contribute to the final figure of merit of the science goals of the survey (e.g., cosmic shear from
Euclid
). Template-fitting methods provide the best results in these metrics, but we show that a combination of template-fitting results and machine-learning results with rejection criteria can outperform any individual method. On this basis, we argue that further work in identifying how to best select between machine-learning and template-fitting approaches for each individual galaxy should be pursued as a priority.
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