H. Spinrad

University of California, Berkeley, Berkeley, California, United States

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Publications (349)1258.93 Total impact

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    ABSTRACT: We present the evidence that strong Hα emitters (HAEs) comprise more than 70% of galaxies with spectroscopic redshifts of 3.8 < z < 5.0, from the clear flux excess observed in the Spitzer/IRAC 3.6-μm band. HAEs are strongly star-forming galaxies with star formation rate of 20–500 M⊙yr–1, with unusually large Hα equivalent widths (EW) of > 350 Å. The rest-frame UV to optical morphologies for half of the HAEs do not show any signs of mergers or tidal interactions. The large Hα EW of HAEs despite their relatively old stellar population age suggests that HAEs are producing stars continuously at a constant rate, rather than through multiple bursts invoked by major mergers. The observed number density of HAEs is consistent with the predicted number of halos which have gas infall rate comparable to the observed star formation rate. Therefore, HAEs provide indirect evidence supporting that star formation mechanism other than mergers, such as cold gas accretion, is the dominant driver of star formation at z ˜ 4.
    10/2013;
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    ABSTRACT: We present observations of a luminous galaxy at redshift z=6.573 --- the end of the reioinization epoch --- which has been spectroscopically confirmed twice. The first spectroscopic confirmation comes from slitless HST ACS grism spectra from the PEARS survey (Probing Evolution And Reionization Spectroscopically), which show a dramatic continuum break in the spectrum at restframe 1216 A wavelength. The second confirmation is done with Keck + DEIMOS. The continuum is not clearly detected with ground-based spectra, but high wavelength resolution enables the Lyman alpha emission line profile to be determined. We compare the line profile to composite line profiles at redshift z=4.5. The Lyman alpha line profile shows no signature of a damping wing attenuation, confirming that the intergalactic gas is ionized at redshift z=6.57. Spectra of Lyman breaks at yet higher redshifts will be possible using comparably deep observations with IR-sensitive grisms, even at redshifts where Lyman alpha is too attenuated by the neutral IGM to be detectable using traditional spectroscopy from the ground.
    The Astrophysical Journal 02/2013; 773(1). · 6.73 Impact Factor
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    ABSTRACT: The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850 micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF 850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDF 850.1, from a millimetre-wave molecular line scan. This places HDF 850.1 in a galaxy overdensity at z ≈ 5.2, corresponding to a cosmic age of only 1.1 billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3 × 10(11) solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive.
    Nature 06/2012; 486(7402):233-6. · 38.60 Impact Factor
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    ABSTRACT: This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at z 1.5-8, and to study Type Ia supernovae at z > 1.5. Five premier multi-wavelength sky regions are selected, each with extensive multi-wavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 infrared channel (WFC3/IR) and the WFC3 ultraviolet/optical channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers ~125 arcmin2 within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of ~800 arcmin2 across GOODS and three additional fields (Extended Groth Strip, COSMOS, and Ultra-Deep Survey). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up-to-date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including charge transfer efficiency degradation for ACS, removal of electronic bias-striping present in ACS data after Servicing Mission 4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.
    The Astrophysical Journal Supplement Series 12/2011; 197(2):36. · 16.24 Impact Factor
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    ABSTRACT: We present evidence for strong Hα emission in galaxies with spectroscopic redshifts in the range of 3.8 < z < 5.0 over the Great Observatories Origins Deep Survey fields. Among 74 galaxies detected in the Spitzer IRAC 3.6 and 4.5 μm bands, more than 70% of the galaxies show clear excess at 3.6 μm compared to the expected flux density from stellar continuum only. We provide evidence that this 3.6 μm excess is due to Hα emission redshifted into the 3.6 μm band, and classify these 3.6 μm excess galaxies to be Hα emitter (HAE) candidates. The selection of HAE candidates using an excess in broadband filters is sensitive to objects whose rest-frame Hα equivalent width (EW) is larger than 350 Å. The Hα inferred star formation rates (SFRs) of the HAEs range between 20 and 500 M ☉ yr–1 and are a factor of ~6 larger than SFRs inferred from the UV continuum. The ratio between the Hα luminosity and UV luminosity of HAEs is also on average larger than that of local starbursts. Possible reasons for such strong Hα emission in these galaxies include different dust extinction properties, young stellar population ages, extended star formation histories, low metallicity, and a top-heavy stellar initial mass function. Although the correlation between UV slope β and L Hα/L UV raises the possibility that HAEs prefer a dust extinction curve which is steeper in the UV, the most dominant factor that results in strong Hα emission appears to be star formation history. The Hα EWs of HAEs are large despite their relatively old stellar population ages constrained by spectral energy distribution fitting, suggesting that at least 60% of HAEs produce stars at a constant rate. Under the assumption that the gas supply is sustained, HAEs are able to produce 50% of the stellar mass density that is encompassed in massive (M * > 1011 M ☉) galaxies at z ~ 3. This "strong Hα phase" of star formation plays a dominant role in galaxy growth at z ~ 4, and they are likely progenitors of massive red galaxies at lower redshifts.
    The Astrophysical Journal 08/2011; 738(1):69. · 6.73 Impact Factor
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    ABSTRACT: We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the SDF and GOODS-N. For 3 out of 11 objects, we detect an emission line at ~ 1um with a signal-to-noise ratio of ~ 10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Lya, yielding redshifts of z=7.213, 6.965, and 6.844. Specifically, we confirm the z=7.213 object in two independent DEIMOS runs with different spectroscopic configurations. The z=6.965 object is a known Lya emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Lya fluxes of 3 x 10^-17 erg s^-1 cm^-2 and rest-frame equivalent widths EW_0^Lya = 33-43A. Based on the largest spectroscopic sample of 43 z-dropouts that is the combination of our and previous data, we find that the fraction of Lya-emitting galaxies (EW_0^Lya > 25A) is low at z ~ 7; 17 +- 10% and 24 +- 12% for bright (Muv ~= -21) and faint (Muv ~= -19.5) galaxies, respectively. The fractions of Lya-emitting galaxies drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the IGM increases from z ~ 6 to 7, and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model.
    07/2011;
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    ABSTRACT: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, over the approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies using three separate cameras on the Hubble Space Telescope, from the mid-ultraviolet to the near-infrared, and will find and measure Type Ia supernovae at z>1.5 to test their accuracy as standardizable candles for cosmology. Five premier multi-wavelength sky regions are selected, each with extensive ancillary data. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to a stellar mass of 10^9 M_\odot to z \approx 2, reaching the knee of the ultraviolet luminosity function (UVLF) of galaxies to z \approx 8. The survey covers approximately 800 arcmin^2 and is divided into two parts. The CANDELS/Deep survey (5\sigma\ point-source limit H=27.7 mag) covers \sim 125 arcmin^2 within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and three additional fields (EGS, COSMOS, and UDS) and covers the full area to a 5\sigma\ point-source limit of H \gtrsim 27.0 mag. Together with the Hubble Ultra Deep Fields, the strategy creates a three-tiered "wedding cake" approach that has proven efficient for extragalactic surveys. Data from the survey are nonproprietary and are useful for a wide variety of science investigations. In this paper, we describe the basic motivations for the survey, the CANDELS team science goals and the resulting observational requirements, the field selection and geometry, and the observing design. The Hubble data processing and products are described in a companion paper.
    The Astrophysical Journal Supplement Series 05/2011; · 16.24 Impact Factor
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    ABSTRACT: This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at $z\sim1.5-8$, and to study Type Ia SNe beyond $z>1.5$. Five premier multi-wavelength sky regions are selected, each with extensive multiwavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and UVIS channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of \sim800 square arcminutes across GOODS and three additional fields (EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up to date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including CTE degradation for ACS, removal of electronic bias-striping present in ACS data after SM4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.
    Astrophysical Journal Supplement Series - ASTROPHYS J SUPPL SER. 05/2011; 197.
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    ABSTRACT: We present evidence for unusually strong Halpha emission in galaxies with spectroscopic redshifts in the range of 3.8<z<5.0, over the Great Observatories Origins Deep Survey (GOODS) fields. Among 74 galaxies detected in the Spitzer IRAC 3.6 and 4.5um bands, more than 70% of the galaxies show clear excess at 3.6um compared to the expected flux density from stellar continuum only. We provide evidence that this 3.6um excess is due to Halpha emission redshifted into the 3.6um band, and classify these 3.6um excess galaxies to be Halpha emitter (HAE) candidates. The selection of HAE candidates using an excess in broad-band filters is sensitive to objects whose rest-frame H$\alpha$ equivalent width is larger than 350A, star formation rates of 20-500 Msun/yr. The Halpha-to-UV luminosity ratio of HAEs is on average larger than that of local starbursts. Possible reasons for such strong Halpha emission in these galaxies include different dust extinction properties, young stellar population age, continuous star formation history, low metallicity, and top-heavy stellar initial mass function. Although the correlation between UV slope beta and L(Ha)/L(UV) raises the possibility that HAEs prefer a dust extinction curve which is steeper in the UV, the most dominant factor that results in strong Halpha emission appears to be star formation history. The Halpha equivalent widths of HAEs are large despite their relatively old stellar population ages constrained by SED fitting, suggesting that at least 60% of HAEs produce stars at a constant rate. Under the assumption that the cold gas supply is sustained, HAEs are able to produce ~50% of the observed stellar mass density at z~3 that is caught in massive (M*>10^11 Msun) galaxies. This 'strong Halpha phase' of star formation plays a dominant role in early galaxy growth, being a feasible progenitors of massive red galaxies at lower redshifts.
    03/2011;
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    ABSTRACT: We present Spitzer 16 μm imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We survey 150 arcmin2 in each of the two GOODS fields (North and South), to an average 3σ depth of 40 and 65 μJy, respectively. We detect ~1300 sources in both fields combined. We validate the photometry using the 3-24 μm spectral energy distribution of stars in the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM and AKARI observations in the same fields shows reasonable agreement, though the uncertainties are large. We provide a catalog of photometry, with sources cross-correlated with available Spitzer, Chandra, and Hubble Space Telescope data. Galaxy number counts show good agreement with previous results from ISOCAM and AKARI with improved uncertainties. We examine the 16-24 μm flux ratio and find that for most sources it lies within the expected locus for starbursts and infrared luminous galaxies. A color cut of S 16/S 24>1.4 selects mostly sources which lie at 1.1 < z < 1.6, where the 24 μm passband contains both the redshifted 9.7 μm silicate absorption and the minimum between polycyclic aromatic hydrocarbon emission peaks. We measure the integrated galaxy light of 16 μm sources and find a lower limit on the galaxy contribution to the extragalactic background light at this wavelength to be 2.2 ± 0.2 nW m–2 sr–1.
    The Astronomical Journal 12/2010; 141(1):1. · 4.97 Impact Factor
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    ABSTRACT: We present Spitzer 16 micron imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We survey 150 square arcminutes in each of the two GOODS fields (North and South), to an average 3 sigma depth of 40 and 65 micro-Jy respectively. We detect about 1300 sources in both fields combined. We validate the photometry using the 3-24 micron spectral energy distribution of stars in the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM and AKARI observations in the same fields show reasonable agreement, though the uncertainties are large. We provide a catalog of photometry, with sources cross correlated with available Spitzer, Chandra, and HST data. Galaxy number counts show good agreement with previous results from ISOCAM and AKARI, with improved uncertainties. We examine the 16 to 24 micron flux ratio and find that for most sources it lies within the expected locus for starbursts and infrared luminous galaxies. A color cut of S_{16}/S_{24}>1.4 selects mostly sources which lie at 1.1<z<1.6, where the 24 micron passband contains both the redshifted 9.7 micron silicate absorption and the minimum between PAH emission peaks. We measure the integrated galaxy light of 16 micron sources, and find a lower limit on the galaxy contribution to the extragalactic background light at this wavelength to be 2.2\pm 0.2$ nW m^{-2} sr^{-1}. Comment: Accepted for Publication in the AJ. 53 preprint pages, including 15 figures and 8 tables. Table 1-4 are truncated in the ms.tex but are included in full in the tar file (and will be available in the online version of the AJ)
    10/2010;
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    ABSTRACT: We use ultra-deep ultraviolet VLT/VIMOS intermediate-band and VLT/FORS1 narrow-band imaging in the GOODS Southern field to derive limits on the distribution of the escape fraction (f_esc) of ionizing radiation for L >~ L*(z=3) Lyman Break Galaxies (LBGs) at redshift 3.4--4.5. Only one LBG, at redshift z=3.795, is detected in its Lyman continuum (LyC; S/N~5.5), the highest redshift galaxy currently known with a direct detection. Its ultraviolet morphology is quite compact (R_eff=0.8, kpc physical). Three out of seven AGN are also detected in their LyC, including one at redshift z=3.951 and z850 = 26.1. From stacked data (LBGs) we set an upper limit to the average f_esc in the range 5%--20%, depending on the how the data are selected (e.g., by magnitude and/or redshift). We undertake extensive Monte Carlo simulations that take into account intergalactic attenuation, stellar population synthesis models, dust extinction and photometric noise in order to explore the moments of the distribution of the escaping radiation. Various distributions (exponential, log-normal and Gaussian) are explored. We find that the median f_esc is lower than ~6% with an 84% percentile limit not larger than 20%. If this result remains valid for fainter LBGs down to current observational limits, then the LBG population might be not sufficient to account for the entire photoionization budget at the redshifts considered here, with the exact details dependent upon the assumed ionizing background and QSO contribution thereto. It is possible that f_esc depends on the UV luminosity of the galaxies, with fainter galaxies having higher f_esc, and estimates of f_esc from a sample of faint LBG from the HUDF (i775<28.5) are in broad quantitative agreement with such a scenario. Comment: 58 pages, 23 figures; submitted to ApJ, revised version in response to referee's comments
    The Astrophysical Journal 09/2010; · 6.73 Impact Factor
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    ABSTRACT: We report on the identification of the highest redshift submillimetre-selected source currently known LESS J033229.4−275619. This source was detected in the Large Apex Bolometer Camera (LABOCA) Extended Chandra Deep Field-South (ECDF-S) Submillimetre Survey (LESS), a sensitive 870-μm survey (σ870 μm∼ 1.2 mJy) of the full 30 × 30 arcmin2 ECDF-S with the LABOCA on the Atacama Pathfinder Experiment telescope. The submillimetre emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z= 4.76. We show that the bolometric emission is dominated by a starburst with a star formation rate of ∼1000 M⊙ yr−1, although we also identify a moderate luminosity active galactic nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z∼ 2 submillimetre galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) quasi-stellar objects at z∼ 5, but was also occurring in less extreme galaxies at a time when the Universe was less than 10 per cent of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z∼ 3 and that the current estimate of the space density of z > 4 SMGs is only sufficient to produce ≳10 per cent of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z∼ 3 go through an ultraluminous starburst at z≳ 4 then the required volume density of z > 4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude.
    Monthly Notices of the Royal Astronomical Society 05/2009; 395(4):1905 - 1914. · 5.52 Impact Factor
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    ABSTRACT: We report on the identification of the highest redshift submm-selected source currently known: LESSJ033229.4-275619. This source was detected in the Large Apex BOlometer CAmera (LABOCA) Extended Chandra Deep Field South (ECDFS) Submillimetre Survey (LESS), a sensitive 870-um survey (~1.2-mJy rms) of the full 30'x30' ECDFS with the LABOCA camera on the Atacama Pathfinder EXperiment (APEX) telescope. The submm emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z=4.76. We show that the bolometric emission is dominated by a starburst with a star formation rate of ~1000 Msun/yr, although we also identify a moderate luminosity Active Galactic Nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z~2 submm galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) QSOs at z~5, but was also occurring in less extreme galaxies at a time when the Universe was less than 10% of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z~3 and that the current estimate of the space density of z>4 SMGs is only sufficient to produce ~10% of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z~3 go through an ultraluminous starburst at z>4 then the required volume density of z>4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude. Comment: 10 pages, 4 figures, 1 table, Accepted for publication in MNRAS Feb 23
    02/2009;
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    ABSTRACT: The weak radio source LBDS 53W091 is associated with a very faint (R ≈ 24.5) red (R - K ≈ 5.8) galaxy. Long spectroscopic integrations with the W. M. Keck telescope have provided an absorption-line redshift, z = 1.552 ± 0.002. The galaxy has a rest frame ultraviolet spectrum very similar to that of an F6 V star, and a single-burst old stellar population that matches the IR colors, the optical energy distribution and the spectral discontinuities has a minimum age of 3.5 Gyr. We present detailed population synthesis analyses of the observed spectrum in order to estimate the time since the last major epoch of star formation. We discuss the discrepancies in these estimates resulting from using different models, subjecting the UV spectrum of M32 to the same tests as a measure of robustness of these techniques. The models most consistent with the data tend to yield ages at z = 1.55 of 3.5 Gyr, similar to that inferred for the intermediate-age population in M32. Depending upon the assumed Hubble constant and the value of Ω0, only certain cosmological expansion times are consistent with the age of LBDS 53W091; in particular, for Ω0 = 1, only models with H0 45 km s-1 Mpc-1 are permitted. For H0 = 50 km s-1 Mpc-1 and Ω0 = 0.2, we derive a formation redshift, zf ≥ 5.
    The Astrophysical Journal 01/2009; 484(2):581. · 6.73 Impact Factor
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    ABSTRACT: We present deep near-infrared images of high-redshift radio galaxies (HzRGs) obtained with the near-infrared camera (NIRC) on the Keck I telescope. In most cases, the near-IR data sample rest wavelengths that are free of contamination from strong emission lines and at λrest > 4000 Å, where older stellar populations, if present, might dominate the observed flux. At z > 3, the rest-frame optical morphologies generally have faint, large-scale (~50 kpc) emission surrounding multiple, ~10 kpc components. The brightest of these components are often aligned with the radio structures. These morphologies change dramatically at 2 < z < 3, where the K-band images show single, compact structures without bright, radio-aligned features. The linear sizes (~10 kpc) and luminosities [M(Brest) ~ -20 to -22] of the individual components in the z > 3 HzRGs are similar to the total sizes and luminosities of normal radio-quiet star forming galaxies at z = 3-4. For objects where such data are available, our observations show that the line-free, near-IR colors of the z > 3 galaxies are very blue, consistent with models in which recent star formation dominates the observed light. Direct spectroscopic evidence for massive star formation in one of the z > 3 HzRGs exists (4C 41.17). Our results suggest that the z > 3 HzRGs evolve into much more massive systems than the radio-quiet galaxies and that they are qualitatively consistent with models in which massive galaxies form in hierarchical fashion through the merging of smaller star-forming systems. The presence of relatively luminous subcomponents along the radio axes of the z > 3 galaxies suggests a causal connection with the AGN. We compare the radio and near-IR sizes as a function of redshift and suggest that this parameter may be a measure of the degree to which the radio sources have induced star formation in the parent objects. We also discuss the Hubble diagram of radio galaxies, the possibility of a radio power dependence in the K-z relation, and its implications for radio galaxy formation. Finally, we present for the first time in published format basic radio and optical information on 3C 257 (z = 2.474), the highest redshift galaxy in the 3C sample and among the most powerful radio sources known.
    The Astrophysical Journal 01/2009; 502(2):614. · 6.73 Impact Factor
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    ABSTRACT: We present and discuss optical continuum images made with the Hubble Space Telescope of the radio galaxy 1138-262 at z = 2.2. This object possesses one of the clumpiest optical morphologies of all known high-redshift radio galaxies, consisting of a bright nucleus aligned along the radio axis and a number of smaller components distributed over a region as large as the radio source (130 kpc). The clumps have sizes ranging from 3 to 13 kpc and absolute visual magnitudes between MV = -21.8 and MV = -19.4. On the basis of HST and previous observations, we claim that these clumps are star-forming galaxies that will be accreted by the host galaxy of 1138-262. We compare this radio galaxy with other high-redshift objects and with the predictions of current scenarios of galaxy formation.
    The Astrophysical Journal 01/2009; 504(1):139. · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of Lyα emission from a galaxy at z=5.34, the first object at z>5 with a spectroscopically confirmed redshift. The faint continuum emission [mAB(8000 Å) ≈ 27], the relatively small rest-frame equivalent width of the emission line (WrestLyα ≈ 95 Å), and the limits on the N V/Lyα ratio suggest that this is a star-forming galaxy and not an active galactic nucleus. The star formation rates implied by the UV continuum emission and the Lyα emission are (in the absence of dust extinction) fairly modest (~6 h−250 M☉ yr-1 for q0=0.5). The continuum luminosity is similar to that of sub-L*1500 star-forming galaxies at z~3, and the width of the Lyα line yields an upper limit to the mass of less than 2.6×1010 M☉. The strong emission line detected in this low-luminosity galaxy provides hope for the discovery of higher luminosity primeval galaxies at redshifts z>5.
    The Astrophysical Journal 01/2009; 498(2):L93. · 6.73 Impact Factor
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    ABSTRACT: We present Keck Low Resolution Imaging Spectrometer spectroscopy along with Near-Infrared Camera and Multiobject Spectrometer (NICMOS) F110W (~J) and F160W (~H) images of the galaxy HDF 4-473.0 in the Hubble Deep Field (HDF), with a detection of an emission line consistent with Lyα at a redshift of z=5.60. Attention to this object as a high-redshift galaxy was first drawn by Lanzetta, Yahil, & Fernandez-Soto and appeared in their initial list of galaxies with redshifts estimated from the Wide Field Planetary Camera 2 (WFPC2) HDF photometry. It was selected by us for spectroscopic observation, along with others in the HDF, on the basis of the NICMOS F110W and F160W and WFPC2 photometry. For H0=65 km s-1 Mpc-1 and q0=0.125, the use of simple evolutionary models along with the F814W (~I), F110W, and F160W magnitudes allow us to estimate the star formation rate (~13 M☉ yr-1). The colors suggest a reddening of E(B-V)~0.06. The measured flux in the Lyα line is approximately 1.0×10−17 ergs cm-2 s-1, and the rest-frame equivalent width, correcting for the absorption caused by intervening H I, is ~90 Å. The galaxy is compact and regular, but resolved, with an observed FWHM of ~044. Simple evolutionary models can accurately reproduce the colors, and these models predict the Lyα flux to within a factor of 2. Using this object as a template shifted to higher redshifts, we calculate the magnitudes through the F814W and two NICMOS passbands for galaxies at redshifts 6<z<10.
    The Astrophysical Journal 01/2009; 505(2):L95. · 6.73 Impact Factor
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    ABSTRACT: We report on a new survey for z ≈ 4.5 Lyα sources, the Large-Area Lyman Alpha (LALA) survey. Our survey achieves an unprecedented combination of volume and sensitivity by using narrowband filters on the new 81922 pixel CCD Mosaic camera at the 4 m Mayall telescope of Kitt Peak National Observatory. Well-detected sources with flux and equivalent width matching previously known high-redshift Lyα galaxies (i.e., observed equivalent width EW > 80 Å; 2.6 × 10-17 ergs cm-2 s-1 < line + continuum flux < 5.2 × 10-17 ergs cm-2 s-1, and a small uncertainty on the equivalent width, δEW < EW/4) have an observed surface density corresponding to 11,000 ± 700 deg-2 per unit redshift at z = 4.5. Variations in this surface density are apparent on comparison between counts in 6561 ± 40 and 6730 ± 40 Å filters. Early spectroscopic followup results from the Keck telescope included three sources meeting our criteria for good Lyα candidates. Of these, one is confirmed as a z = 4.52 source, another remains consistent with either z = 4.55 or z = 0.81, and the third is an [O III] λ5007 emitter at z = 0.34. These pilot spectroscopic results suggest that approximately one-third of our good candidates are bona fide Lyα emitters, implying a net density of ~4000 Lyα emitters per square degree per unit redshift.
    The Astrophysical Journal 12/2008; 545(2):L85. · 6.73 Impact Factor

Publication Stats

5k Citations
1,258.93 Total Impact Points

Institutions

  • 1971–2013
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, California, United States
    • University of Texas at Dallas
      Richardson, Texas, United States
  • 2012
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2011
    • University of California, Irvine
      • Department of Physics and Astronomy
      Irvine, California, United States
  • 2008
    • University of Florence
      Florens, Tuscany, Italy
  • 1993–2003
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 1989–2002
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 1988
    • Arizona State University
      Phoenix, Arizona, United States
  • 1985
    • University of Houston – Victoria
      Houston, Texas, United States
  • 1978–1984
    • CSU Mentor
      Long Beach, California, United States
  • 1980
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, California, United States
  • 1979
    • University of Sydney
      Sydney, New South Wales, Australia
  • 1978–1979
    • University of California, Santa Cruz
      Santa Cruz, California, United States