Probable Redshift Research Articles

Z ≳ 7 GALAXIES WITH RED SPITZER/IRAC [3.6]–[4.5] COLORS IN THE FULL CANDELS DATA SET: THE BRIGHTEST-KNOWN GALAXIES AT z ∼ 7–9 AND A PROBABLE SPECTROSCOPIC CONFIRMATION AT z = 7.48

ABSTRACT We identify four unusually bright (H < 25.5) galaxies from Hubble Space Telescope (HST) and Spitzer CANDELS data with probable redshifts z ∼ 7–9. These identifications include the brightest-known galaxies to date at z ≳ 7.5. As Y-band observations are not available over the full CANDELS program to perform a standard Lyman-break selection of z > 7 galaxies, we employ an alternate strategy using deep Spitzer/IRAC data. We identify z ∼ 7.1–9.1 galaxies by selecting z ≳ 6 galaxies from the HST CANDELS data that show quite red IRAC [3.6]−[4.5] colors, indicating strong [O iii]+Hβ lines in the 4.5 μm band. This selection strategy was validated using a modest sample for which we have deep Y-band coverage, and subsequently used to select the brightest z ≥ 7 sources. Applying the IRAC criteria to all HST-selected optical dropout galaxies over the full ∼900 arcmin2 of the CANDELS survey revealed four unusually bright z ∼ 7.1, 7.6, 7.9, and 8.6 candidates. The median [3.6]−[4.5] color of our selected z ∼ 7.1–9.1 sample is consistent with rest-frame [O iii]+Hβ EWs of ∼1500 Å in the [4.5] band. Keck/MOSFIRE spectroscopy has been independently reported for two of our selected sources, showing Lyα at redshifts of 7.7302 ± 0.0006 and , respectively. We present similar Keck/MOSFIRE spectroscopy for a third selected galaxy with a probable 4.7σ Lyα line at z spec = 7.4770 ± 0.0008. All three have H160-band magnitudes of ∼25 mag and are ∼0.5 mag more luminous (M 1600 ∼ −22.0) than any previously discovered z ∼ 8 galaxy, with important implications for the UV luminosity function (LF). Our three brightest and highest redshift z > 7 galaxies all lie within the CANDELS-EGS field, providing a dramatic illustration of the potential impact of field-to-field variance.

Weighing the Giants – II. Improved calibration of photometry from stellar colours and accurate photometric redshifts

We present improved methods for using stars found in astronomical exposures to calibrate both star and galaxy colours as well as to adjust the instrument flat-field. By developing a spectroscopic model for the Sloan Digital Sky Survey (SDSS) stellar locus in colour–colour space, synthesizing an expected stellar locus, and simultaneously solving for all unknown zero-points when fitting to the instrumental locus, we increase the calibration accuracy of stellar locus matching. We also use a new combined technique to estimate improved flat-field models for the Subaru SuprimeCam camera, forming ‘star flats’ based on the magnitudes of stars observed in multiple positions or through comparison with available measurements in the SDSS catalogue. These techniques yield galaxy magnitudes with reliable colour calibration (≲0.01–0.02 mag accuracy) that enable us to estimate photometric redshift probability distributions without spectroscopic training samples. We test the accuracy of our photometric redshifts using spectroscopic redshifts zs for ∼5000 galaxies in 27cluster fields with at least five bands of photometry, as well as galaxies in the Cosmic Evolution Survey (COSMOS) field, finding σ((zp − zs)/(1 + zs)) ≈ 0.03 for the most probable redshift zp. We show that the full posterior probability distributions for the redshifts of galaxies with five-band photometry exhibit good agreement with redshifts estimated from thirty-band photometry in the COSMOS field. The growth of shear with increasing distance behind each galaxy cluster shows the expected redshift–distance relation for a flat Λ cold dark matter (Λ-CDM) cosmology. Photometric redshifts and calibrated colours are used in subsequent papers to measure the masses of 51 galaxy clusters from their weak gravitational shear and determine improved cosmological constraints. We make our python code for stellar locus matching publicly available at http://big-macs-calibrate.googlecode.com; the code requires only input catalogues and filter transmission functions.

CRITICAL STAR FORMATION RATES FOR REIONIZATION: FULL REIONIZATION OCCURS AT REDSHIFTz≈ 7

We assess the probable redshift (z{sub rei} Almost-Equal-To 7) for full reionization of the intergalactic medium (IGM) using a prescription for the comoving star formation rate (SFR) density ({rho}-dot{sub SFR}) required to maintain photoionization against recombination. Our newly developed online reionization simulator allows users to assess the required SFR and ionization histories, using a variety of assumptions for galactic and stellar populations, IGM clumping factor and temperature, and Lyman continuum (LyC) escape fraction. The decline in high-redshift galaxy candidates and Ly{alpha} emitters at z = 6-8 suggests a rising neutral fraction, with reionization at z {approx}> 7 increasingly difficult owing to increased recombination rates and constraints from the ionizing background and LyC mean free path. The required rate is {rho}-dot{sub SFR}{approx}(.018 M{sub sun}yr{sup -1}Mpc{sup -3})[(1+z)/8]{sup 3}(C{sub H}/3)(0.2/f{sub esc})T{sub 4}{sup -0.845} scaled to fiducial values of clumping factor C{sub H} = 3, escape fraction f{sub esc} = 0.2, electron temperature T{sub e} = 10{sup 4} K, and low-metallicity initial mass functions (IMFs) and stellar atmospheres. Our hydrodynamical + N-body simulations find a mean clumping factor C{sub H} Almost-Equal-To (2.9)[(1 + z)/6]{sup -1.1} in the photoionized, photoheated filaments at z = 5-9. The critical SFR could be reduced by increasing the minimummore » stellar mass, invoking a top-heavy IMF, or systematically increasing f{sub esc} at high z. The cosmic microwave background optical depth, {tau}{sub e} = 0.088 {+-} 0.015, could be explained by full reionization, producing {tau}{sub e} = 0.050 back to z{sub rei} Almost-Equal-To 7, augmented by {Delta}{tau}{sub e} Almost-Equal-To 0.01-0.04 in a partially ionized IGM at z > 7. In this scenario, the strongest 21 cm signal should occur at redshifted frequencies 124-167 MHz owing to IGM heating over an interval {Delta}z Almost-Equal-To 3 in the range z Almost-Equal-To 7.5-10.5.« less

New Imaging and Spectroscopy of the Locations of Several Short‐Hard Gamma‐Ray Bursts

The detection of the afterglow emission and host galaxies of short-hard gamma-ray bursts (SHBs) is one of the most exciting recent astronomical discoveries. Indications that SHB progenitors belong to old stellar populations, in contrast to those of the long-soft GRBs, provide a strong clue about their physical nature. Definitive conclusions however are limited by the small number of SHBs with known hosts. Here, we present our investigation of SHBs previously localized by the interplanetary network (IPN) using new and archival optical and X-ray observations. We show that we can likely identify the host galaxies/clusters for additional two bursts, significantly increasing the sample of SHBs with known hosts and/or distances. In particular, we determine that the bright SHB 790613 occurred within the rich galaxy cluster Abell 1892, making it probably the nearest SHB currently known. We show that the brightest galaxy within the error box of SHB 000607, at z=0.14, is most likely the host galaxy of this event. Additionally, we rule out the existence of galaxy overdensities (down to ~21mag) near the locations of two other SHBs, and set a lower limit on their probable redshift. We combine our SHB sample with events discovered recently by the Swift and HETE-2 missions, and investigate the properties of the extended sample. Comparison to SNe Ia shows that the progenitors of SHBs are typically older, implying a typical life time of several Gy. We also show that it is unlikely that there is a significant population of progenitors with life time shorter than 1Gy. This result disfavors the popular model of NS-NS mergers as the progenitors of SHBs.

Multi-Wavelength Analysis of 18$\mu $m-Selected Galaxies in the AKARI/Infrared-Camera monitor field towards the North Ecliptic Pole

Abstract We present an initial analysis of AKARI 18$\mu $m-selected galaxies using all 9 photometric bands at 2–24$\mu $m available in the Infrared Camera (IRC), in order to demonstrate new capabilities of AKARI cosmological surveys with this unprecedented wavelength coverage at mid-infrared (MIR) bands. We detected 72 sources at 18$\mu $m in an area of 50.2 arcmin$^2$ in the AKARI/IRC monitor field towards the North Ecliptic Pole (NEP). From this sample, 25 galaxies with probable redshifts of $z \gtrsim$ 0.5 were selected with a single colour cut (N2$-$N3$\gt$ 0.1) for a detailed spectral energy distribution (SED) analysis with ground-based $BVRi'z'JK$ data. Using an SED radiative transfer model of starbursts covering the wavelength range UV–submm, we derived photometric redshifts from the optical-MIR SEDs of 18$\mu $m-selected galaxies. From the best-fit SED models, we showed that the IRC all-band photometry is capable of tracing a steep rise in the flux at the blue side of the polycyclic aromatic hydrocarbon (PAH) 6.2$\mu $m emission feature. This indicates that the IRC all-band photometry is useful to constrain the redshift of infrared galaxies, specifically for dusty galaxies with a less prominent 4000Å break. Also, we found that the flux dip between the PAH 7.7 and 11.2$\mu $m emission feature is recognizable in the observed SEDs of galaxies at $z \sim 1$. This pilot study suggests the possibility of detecting many interesting galaxy properties in the NEP-Deep and Wide surveys, such as a systematic difference in SEDs between high–and low-$z$ Ultra-Luminous InfraRed Galaxies, and a large variation of the PAH inter-band strength ratio in galaxies at high redshifts.

Photometric Redshifts of Galaxies in COSMOS

We present photometric redshifts for the COSMOS survey derived from a new code, optimized to yield accurate and reliable redshifts and spectral types of galaxies down to faint magnitudes and redshifts out to z ~ 1.2. The technique uses χ^2 template fitting, combined with luminosity function priors and with the option to estimate the internal extinction [or E(B - V)]. The median most probable redshift, best-fit spectral type and reddening, absolute magnitude, and stellar mass are derived in addition to the full redshift probability distributions. Using simulations with sampling and noise similar to those in COSMOS, the accuracy and reliability is estimated for the photometric redshifts as a function of the magnitude limits of the sample, S/N ratios, and the number of bands used. We find from the simulations that the ratio of derived 95% confidence interval in the χ^2 probability distribution to the estimated photometric redshift (D_(95)) can be used to identify and exclude the catastrophic failures in the photometric redshift estimates. To evaluate the reliability of the photometric redshifts, we compare the derived redshifts with high-reliability spectroscopic redshifts for a sample of 868 normal galaxies with z 3σ(Δ(z)), where σ(Δ(z)) is the rms scatter in Δ(z)]. We also find good agreement [σ(Δ(z)) = 0.10] between photometric and spectroscopic redshifts for type II AGNs. We compare results from our photometric redshift procedure with three other independent codes and find them in excellent agreement. We show preliminary results, based on photometric redshifts for the entire COSMOS sample (to i < 25 mag).

GRB 060121: Implications of a Short-/Intermediate-Duration γ-Ray Burst at High Redshift

Since the discovery of the first short-population γ-ray burst (GRB) afterglows in 2005, the handful of observed events have been found to be embedded in nearby (z 102). A photometric redshift for this event places the progenitor at a most probable redshift of z = 4.6, with a less probable scenario of z = 1.7. In either case, GRB 060121 could be the farthermost short-population GRB detected to date and implies an isotropic-equivalent energy release in gamma rays comparable to that seen in long-population bursts. We discuss the implications of the released energy on the nature of the progenitor. These results suggest that GRB 060121 may belong to a family of energetic short-population events, lying at z > 1 and whose optical afterglows would outshine their host galaxies, unlike the first short GRBs observed in 2005. The possibility of GRB 060121 being an intermediate-duration burst is also discussed.

Statistical characteristics of large scale structure

We generalize and extend the statistical description of formation and evolution of Large Scale matter distribution in the Universe proposed in our previous papers. We investigate the impact of transverse motions – expansion and/or compression – on properties of the Large Scale Structure elements – walls, pancakes, filaments and clouds – and, generalizing the Press-Schechter formalism, derive their mass functions. Using the Zel'dovich theory of gravitational instability we show that these mass functions are approximately the same and the mass of each type of elements is found to be concentrated near the corresponding mean mass. At high redshifts, both the mass function and the mean mass of formed elements depend upon the small scale part of the initial power spectrum and, in particular, upon the mass of dominant fraction of dark matter (DM) particles. Using these results we obtain independent estimates of probable redshifts of the reionization and reheating periods of the Universe. We show that the transverse motions do not significantly change the redshift evolution of the observed mass function and the mean linear number density of low mass pancakes related to absorption lines in the spectra of the farthest quasars. Application of this approach to the observed Lyman–α forest allows one to directly estimate the shape of initial power spectrum on small scales.

Multi-band observations of gamma ray bursts

This talk focuses on the various aspects we learnt from multi- band observations of GRBs both, before and during the afterglow era. A statistical analysis to estimate the probable redshifts of host galaxies using the luminosity function of GRBs compatible with both the afterglow redshift data as well as the overall population of GRBs is discussed. We then address the question whether the observed fields of GRBs with precise localizations from third Inter-Planetary Network (IPN 3 ) contain suitable candidates for their host galaxies.

Error analysis of the photometric redshift technique

ABSTRA C T We present a calculation of the systematic component of the error budget in the photometric redshift technique. We make use of it to describe a simple technique that allows the assignment of confidence limits to redshift measurements obtained through photometric methods. We show that our technique, through the calculation of a redshift probability function, gives complete information on the probable redshift of an object and its associated confidence intervals. This information can and must be used in the calculation of any observable quantity that makes use of the redshift.

Infrared Observations of Three Extremely Red Objects

Deep infrared and optical surveys have recently revealed a large number of very red (R-K > 6) galaxies, labeled extremely red objects (EROs). Many have been identified with broadband photometry, but very few have been observed spectroscopically. From the limited spectra available, it appears that they may form a heterogeneous population. There are EROs at high redshifts with dusty, active star formation (studied by Dey and coworkers) as well as EROs with old stellar populations and little dust (studied by Soifer and coworkers). In order to further the study of these galaxies, we have taken near-infrared spectra with the Keck Telescope of three EROs found in the fields of high-redshift active galactic nuclei. The continuum is well detected in each, but no emission lines or spectral breaks are detected. We have found probable redshifts, extinctions, ages, and star formation histories for each of these EROs based on fitting their spectral energy distributions. For every age and star formation model, the fits are constrained in redshift and reddening to small regions. Due to the unknown nature of these objects, we cannot rule out values of Av as high as 15 at low redshifts. None of the EROs have spectra consistent with the redshifts of their nearby high-redshift objects.

The Infrared Einstein Ring in the Gravitational Lens MG J1131+0456 and the Death of the Dusty Lens Hypothesis

We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131+0456, which show that its lens galaxy is an H = 18.6 mag, transparent, early-type galaxy at a redshift of zl 0.84; it has a major axis effective radius Re = 07 ? 01, projected axis ratio b/a = 0.6 ? 0.1, and major axis P.A. = 55? ? 9?. The lens is the brightest member of a group of at least seven galaxies with similar R-I and I-H colors, and the two closest group members produce sufficient tidal perturbations to explain the shape of the ring. The host galaxy of the MG J1131+0456 source is a zs 2 extremely red object (ERO) that is lensed into optical and infrared rings of dramatically different morphologies. These differences imply a strongly wavelength-dependent source morphology that could be explained by embedding the host in a larger, dusty disk. At 1.6 ?m (H), the ring is spectacularly luminous, with a total observed flux of H = 17.4 mag and a demagnified flux of 19.3 mag, corresponding to a 1-2 L* galaxy at the probable source redshift of zs 2. Thus, it is primarily the stellar emission of the radio source host galaxy that produces the overall colors of two of the reddest radio lenses, MG J1131+0456 and JVAS B1938+666, aided by the suppression of optical active galactic nucleus emission by dust in the source galaxy. The dusty lens hypothesis ? that many massive early-type galaxies with 0 zl 1 have large, uniform dust opacities ? is ruled out.

ISOCAM 15 Micron Search for Distant Infrared Galaxies Lensed by Clusters

In a search for lensed infrared galaxies, ISOCAM images have been obtained toward the rich clusters Abell 2218 and Abell 2219 at 15 μm. Nine galaxies (four in Abell 2218 and five in Abell 2219) were detected with flux levels in the range 530–1100 μJy. Three of the galaxies detected in Abell 2218 have previously known redshifts; of these one is a foreground galaxy, and the other two are lensed background galaxies at z = 0.474 and z = 1.032. One of the objects detected in the field of Abell 2219 is a faint, optically red, extreme infrared-dominated galaxy with a probable redshift of 1.048.

Spectroscopic identification of a galaxy at a probable redshift of z = 6.68

The detection and identification of distant galaxies is an important goal of observational cosmology, as such galaxies are seen at a time when the Universe was very young. The development of new techniques and instrumentation permits the search for ever-fainter galaxies, and so aids attempts to determine when the first stars and galaxies formed. Here we report the identification of a galaxy at a probable redshift of 6.68, the most distant object yet detected. The galaxy's spectrum is characterized by an abrupt discontinuity at a wavelength λ≈ 9,300 A, which we interpret as arising from the absorption of light at shorter wavelengths by hydrogen gas along the line of sight (the Lyman-α decrement), and by an emission line at λ≈ 9,334 A, which we interpret as the Lyman-α line at a redshift of 6.68. The galaxy is relatively bright: the ultraviolet luminosity density contributed by this one galaxy is almost ten times the value measured at z = 3.

Deep Spectroscopy in the Field of 3C 212

We present the results of long-slit and multiaperture spectroscopy of faint galaxies in the field of the z = 1.049 quasar 3C 212. We show that an apparently aligned optical feature beyond the northwest radio lobe has a redshift z = 0.928, and a similarly aligned feature just beyond the southeast radio lobe has a redshift z = 1.053, quite close to that of the quasar. While the northwest optical component is extremely well aligned with the radio jet and has a morphology that is very similar to that of the radio lobe lying 3'' interior to it, the fact that we find three other field galaxies with closely similar redshifts indicates that it is most likely a member of an intervening group rather than an unusual example of true alignment with the radio structure. In addition, we have found two galaxies (besides the one near the southeast radio lobe) having redshifts close to that of 3C 212. We have firm or probable redshifts for 66 out of 82 galaxies we have observed in this field. Comparison with the redshift distribution of faint field galaxies indicates that a large fraction of the remaining 16 galaxies are likely to be at redshifts 1.4. There are at least two low-redshift dwarf starburst galaxies showing low metal abundance and high ionization in our sample; such galaxies are likely to be relatively common in very faint samples, and, under certain conditions, they could be confused with high-redshift objects.

The Blue Companion of 3C 65: A Star‐forming Galaxy with a Probable Redshift of 2.8

We present BVRIK images and photometry of the z = 1.175 radio galaxy 3C 65 and its extended blue companion, along with a 6 cm radio map. These data are used to test the hypotheses that the companion is scattering the continuum of a hidden active nucleus within the radio galaxy and/or is undergoing a starburst triggered by interaction with its radio plasma. However, we find that the object's spectral energy distribution (SED) is best fitted by a model of constant star formation with moderate dust extinction for a redshift of approximately 2.8, while no fit to the SED can be obtained for redshifts equal to or below that of 3C 65. The object thus appears to be part of the recently discovered population of star-forming galaxies at z ~ 3, which is also consistent with its morphology and size as revealed by Hubble Space Telescope WFPC2 images. The age of the object is not well-constrained by the model fits and could range from 0.2 to 3.5 Gyr. Our best-fitting model has an age of 1.4 Gyr, which at z ≅ 2.8 does not violate standard cosmologies.

Redshifts for flat-spectrum radio sources in the second Caltech-Jodrell Bank VLBI sample

We present optical spectra and redshifts for flat-spectrum radio sources taken from the second Caltech-Jodrell Bank VLBI sample. The sources were observed using the Faint Object Spectrograph on the Isaac Newton Telescope. We show optical spectra for 90 sources, out of a total of 101 observed; of the remaining 11 sources, nine were not detected, and two were mis-identified. Definite redshifts have been determined for 60 sources, and a further seven have probable redshifts determined. Five sources are shown to have featureless BL Lac type spectra, and 18 sources are too weak to give a reliable redshift.

Spectroscopy of the gravitational arcs in CL 2244 - 02, A370 (arclet A5), and CL 0024 + 1654

view Abstract Citations (64) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy of the Gravitational Arcs in CL 2244-02, A370 (Arclet A5), and CL 0024+1654 Mellier, Yannick ; Fort, Bernard ; Soucail, Genevieve ; Mathez, Guy ; Cailloux, Mireille Abstract We analyze new spectroscopic data on the blue giant arc in Cl 2244 - 02, on the arclet A5 in Abell 370, and on the split arc in Cl 0024+1654. A probable redshift z = 2.237 is derived for the source of the Cl 2244-02 arc, making this object one of the most distant "field" galaxies known today. A star formation rate is estimated from the Lyα intensity and compared to other distant field galaxies. For A5, no prominent emission line is found, but three absorption lines point to a tentative redshift z = 1.306. The spectra of the four parts of the Cl 0024+1654 arc look rather similar, but the absence of any spectral feature allows only the determination of a redshift range: 1 <z <2.1. The systematic search for such arcs and/or arclets, and the Toulouse spectroscopic survey of arcs which follows up, seems one of the promising methods of obtaining spectra of extremely distant field galaxies and of constraining their early evolution. Publication: The Astrophysical Journal Pub Date: October 1991 DOI: 10.1086/170592 Bibcode: 1991ApJ...380..334M Keywords: Astronomical Spectroscopy; Galactic Clusters; Galactic Evolution; Gravitational Effects; Absorption Spectra; Arcs; Emission Spectra; Lyman Alpha Radiation; Red Shift; Star Formation Rate; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: REDSHIFTS; GRAVITATIONAL LENSES full text sources ADS | data products SIMBAD (9) NED (6)

A Deep Spectral Survey on the 6-Meter Telescope

The observational program “Deep spectral survey of the selected sky areas” on the 6-meter telescope is described. Preliminary results for the central part of field SA57 are discussed. The spectrum of a QS0 with probable redshift z=3.87 is presented. The number of quasars per sq. degree is estimated to be 470–675 to B &lt; 23 mag., which gives the same slope in the increasing number of QSOs with magnitude as in brighter samples.

Optical and radio properties of X-ray selected BL Lacertae objects

view Abstract Citations (147) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical and radio properties of X-ray selected BL Lacertae objects. Stocke, J. T. ; Liebert, J. ; Schmidt, G. ; Gioia, I. M. ; Maccacaro, T. ; Schild, R. E. ; Maccagni, D. ; Arp, H. C. Abstract The eight BL Lac objects from the HEAO 1 A-2 all-sky survey and from the Einstein medium-sensitivity survey (MSS) form a flux-limited complete X-ray selected sample. The optical and radio properties of the MSS BL Lac objects are presented and compared with those of the HEAO 1 A-2 sample and with those of radio-selected BL Lac objects. The X-ray selected BL Lac objects possess smaller polarized fractions and less violent optical variability than radio-selected BL Lac objects. These properties are consistent with the substantial starlight fraction seen in the optical spectra of a majority of these objects. This starlight allows a determination of definite redshifts for two of four MSS BL Lac objects and a probable redshift for a third. These redshifts are 0.2, 0.3, and 0.6. Despite the differences in characteristics between the X-ray selected and radio-selected samples, it is concluded that these eight objects possess most of the basic qualities of BL Lac objects and should be considered members of that class. Moreover, as a class, these X-ray selected objects have the largest ratio of X-ray to optical flux of any active galactic nuclei yet discovered. Publication: The Astrophysical Journal Pub Date: November 1985 DOI: 10.1086/163646 Bibcode: 1985ApJ...298..619S Keywords: Bl Lacertae Objects; Galactic Nuclei; X Ray Sources; Active Galactic Nuclei; Astronomical Photometry; Galactic Clusters; Heao 1; Polarimetry; Radio Astronomy; Sky Surveys (Astronomy); Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (20) NED (8)