Alberto Fernandez-Soto

A New Catalog of Photometric Redshifts in the Hubble Deep Field

Using the newly available infrared images of the Hubble Deep Field in the J, H, and K bands and an optimal photometric method, we have refined a technique to estimate the redshifts of 1067 galaxies. A detailed comparison of our results with the spectroscopic redshifts in those cases where the latter are available shows that this technique gives very good results for bright enough objects [AB(8140)<26.0]. From a study of the distribution of residuals [Δzrms/(1+z)≈0.1 at all redshifts], we conclude that the observed errors are mainly due to cosmic variance. This very important result allows for the assessment of errors in quantities to be directly or indirectly measured from the catalog. We present some of the statistical properties of the ensemble of galaxies in the catalog, and we finish by presenting a list of bright high-redshift (z≈5) candidates extracted from our catalog together with recent spectroscopic redshift determinations confirming that two of them are at z=5.34 and z=5.60.

GRB 090423 at a redshift of z ≈ 8.1

Gamma-ray bursts (GRBs) are produced by rare types of massive stellar explosion. Their rapidly fading afterglows are often bright enough at optical wavelengths that they are detectable at cosmological distances. Hitherto, the highest known redshift for a GRB was z = 6.7 (ref. 1), for GRB 080913, and for a galaxy was z = 6.96 (ref. 2). Here we report observations of GRB 090423 and the near-infrared spectroscopic measurement of its redshift, z = . This burst happened when the Universe was only about 4 per cent of its current age. Its properties are similar to those of GRBs observed at low/intermediate redshifts, suggesting that the mechanisms and progenitors that gave rise to this burst about 600,000,000 years after the Big Bang are not markedly different from those producing GRBs about 10,000,000,000 years later.

Star-forming galaxies at very high redshifts

Analysis of the deepest available images of the sky, obtained by the Hubble Space Telescope, reveals a large number of candidate high-redshift galaxies. A catalogue of 1,683 objects is presented, with estimated redshifts ranging from z = 0 to z > 6. The high-redshift objects are interpreted as regions of star formation associated with the progenitors of present-day normal galaxies, at epochs that may reach back 95% of the time to the Big Bang.

The Star Formation Rate Intensity Distribution Function: Implications for the Cosmic Star Formation Rate History of the Universe

We address the effects of cosmological surface brightness dimming on observations of faint galaxies by examining the distribution of unobscured star formation rate intensities versus redshift. We use the star formation rate intensity distribution function to assess the ultraviolet luminosity density versus redshift, based on our photometry and photometric redshift measurements of faint galaxies in the Hubble Deep Field (HDF) and the Hubble Deep Field-South (HDF-S) Wide Field Planetary Camera 2 and Near-Infrared Camera and Multi-Object Spectrometer fields. We find that (1) previous measurements have missed a dominant fraction of the ultraviolet luminosity density of the universe at high redshifts by neglecting cosmological surface brightness dimming effects, which are important at redshifts larger than z ≈ 2; (2) the incidence of the highest intensity star-forming regions increases monotonically with redshift; and (3) the ultraviolet luminosity density plausibly increases monotonically with redshift through the highest redshifts observed. By measuring the spectrum of the luminosity density versus redshift, we also find that (4) previous measurements of the ultraviolet luminosity density at redshifts z < 2 must be reduced by a factor of ≈2 to allow for the spectrum of the luminosity density between rest-frame wavelengths 1500 and 2800 A. And, by comparing with observations of high-redshift damped Lyα absorption systems detected toward background quasi-stellar objects, we further find that (5) the distribution of star formation rate intensities matches the distribution of neutral hydrogen column densities at redshifts z ≈ 2-5, which establishes a quantitative connection between high-redshift galaxies and high column density gas and suggests that high-redshift damped Lyα absorption systems trace lower star formation rate intensity regions of the same galaxies detected in starlight in the HDF and HDF-S. Because our measurements neglect the effects of obscuration by dust, they represent lower limits to the total star formation rate density.

MEASURING BARYON ACOUSTIC OSCILLATIONS ALONG THE LINE OF SIGHT WITH PHOTOMETRIC REDSHIFTS: THE PAU SURVEY

Baryon Acoustic Oscillations (BAOs) provide a standard ruler of known physical length, making it one of the most promising probes of the nature of dark energy (DE). The detection of BAOs as an excess of power in the galaxy distribution at a certain scale requires measuring galaxy positions and redshifts. Transversal (or angular) BAOs measure the angular size of this scale projected in the sky and provide information about the angular distance. Line-of-sight (or radial) BAOs require very precise redshifts, but provide a direct measurement of the Hubble parameter at different redshifts, a more sensitive probe of DE. The main goal of this paper is to show that it is possible to obtain photometric redshifts with enough precision (? z ) to measure BAOs along the line of sight. There is a fundamental limitation as to how much one can improve the BAO measurement by reducing ? z . We show that ? z ~ 0.003(1 + z) is sufficient: a much better precision will produce an oversampling of the BAO peak without a significant improvement on its detection, while a much worse precision will result in the effective loss of the radial information. This precision in redshift can be achieved for bright, red galaxies, featuring a prominent 4000 ? break, by using a filter system comprising about 40 filters, each with a width close to 100 ?, covering the wavelength range from ~4000 to ~8000 ?, supplemented by two broad-band filters similar to the Sloan Digital Sky Survey u and z bands. We describe the practical implementation of this idea, a new galaxy survey project, PAU16Physics of the Accelerating Universe (PAU): http://www.ice.cat/pau., to be carried out with a telescope/camera combination with an etendue about 20 m2 deg2, equivalent to a 2 m telescope equipped with a 6 deg2 field of view camera, and covering 8000 deg2 in the sky in four years. We expect to measure positions and redshifts for over 14 million red, early-type galaxies with L > L and iAB 22.5 in the redshift interval 0.1 < z < 0.9, with a precision ? z < 0.003(1 + z). This population has a number density n 10?3 Mpc?3 h 3 galaxies within the 9 Gpc3 h ?3 volume to be sampled by our survey, ensuring that the error in the determination of the BAO scale is not limited by shot noise. By itself, such a survey will deliver precisions of order 5% in the dark-energy equation of state parameter w, if assumed constant, and can determine its time derivative when combined with future cosmic microwave background measurements. In addition, PAU will yield high-quality redshift and low-resolution spectroscopy for hundreds of millions of other galaxies, including a very significant high-redshift population. The data set produced by this survey will have a unique legacy value, allowing a wide range of astrophysical studies.

GRB 050904 at redshift 6.3: observations of the oldest cosmic explosion after the Big Bang ⋆

We present optical and near-infrared observations of the afterglow of the gamma-ray burst GRB 050904. We derive a photometric redshift z = 6.3, estimated from the presence of the Lyman break falling between the I and J filters. This is by far the most distant GRB known to date. Its isotropic-equivalent energy is 3.4 × 10 53 erg in the rest-frame 110−1100 keV energy band. Despite the high redshift, both the prompt and the afterglow emission are not peculiar with respect to other GRBs. We find a break in the J-band light curve at tb = 2.6 ± 1.0 d (observer frame). If we assume this is the jet break, we derive a beaming-corrected energy Eγ ∼ (4 ÷ 12) × 10 51 erg. This limit shows that GRB 050904 is consistent with the Amati and Ghirlanda relations. This detection is consistent with the expected number of GRBs at z > 6 and shows that GRBs are a powerful tool to study the star formation history up to very high redshift.

A Blind Test of Photometric Redshift Prediction

Results of a blind test of photometric redshift predictions against spectroscopic galaxy redshifts obtained in the Hubble Deep Field with the Keck Telescope are presented. The best photometric redshift schemes predict spectroscopic redshifts with a redshift accuracy of Δz < 0.1 for more than 68% of sources and with Δz < 0.3 for 100%, when single-feature spectroscopic redshifts are removed from consideration. This test shows that photometric redshift schemes work well, at least when the photometric data are of high quality and when the sources are at moderate redshifts.

The ALHAMBRA Survey: A Large Area Multimedium-Band Optical and Near-Infrared Photometric Survey

Here we describe the first results of the Advanced Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey, which provides cosmic tomography of the evolution of the contents of the universe over most of cosmic history. Our novel approach employs 20 contiguous, equal-width, medium-band filters covering from 3500 A to 9700 A, plus the standard JHKs near-infrared (NIR) bands, to observe a total area of 4 deg2 on the sky. The optical photometric system has been designed to maximize the number of objects with accurate classification by spectral energy distribution type and redshift, and to be sensitive to relatively faint emission features in the spectrum. The observations are being carried out with the Calar Alto 3.5 m telescope using the wide-field cameras in the optical, Large Area Imager for Calar Alto, and in the NIR, Omega-2000. The first data confirm that we are reaching the expected magnitude limits (for a total of 100 ks integration time per pointing) of AB ≤ 25 mag (for an unresolved object, signal-to-noise ratio = 5) in the optical filters from the blue to 8300 A, and from AB = 24.7 to 23.4 for the redder ones. The limit in the NIR, for a total of 15 ks exposure time per pointing, is (in the Vega system) Ks ≈ 20 mag, H≈ 21 mag, J≈ 22 mag. Some preliminary results are presented here to illustrate the capabilities of the ongoing survey. We expect to obtain accurate redshift values, Δz/(1 + z) ≤ 0.03 for about five ×105 galaxies with I ≤ 25 (60% completeness level), and z med = 0.74. This accuracy, together with the homogeneity of the selection function, will allow for the study of the redshift evolution of the large-scale structure, the galaxy population and its evolution with redshift, the identification of clusters of galaxies, and many other studies, without the need for any further follow-up. It will also provide targets for detailed studies with 10 m class telescopes. Given its area, spectral coverage, and its depth, apart from those main goals, the ALHAMBRA survey will also produce valuable data for galactic studies.

A tale of two GRB-SNe at a common redshift of z=0.54

We present ground-based and Hubble Space Telescope optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z= 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broad-band spectral energy distributions (SEDs) of the OT resemble those of local Type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB supernova, and SN1994I, a typical Type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly available Swift-XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t-to > 0.5 d. We then compare the rest-frame, peak V-band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local Type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe. --------------------------------------------------------------------------------

A tale of two GRB-SNe at a common redshift of z = 0.54

We present ground-based and Hubble Space Telescope optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z= 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broad-band spectral energy distributions (SEDs) of the OT resemble those of local Type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB supernova, and SN1994I, a typical Type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly available Swift-XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t-to > 0.5 d. We then compare the rest-frame, peak V-band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local Type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe. --------------------------------------------------------------------------------