We present results from a deep 2′ × 3′ (comoving scale of 3.7 Mpc × 5.5 Mpc at z = 3) survey at 1.1 mm, taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in the SSA22 field. We ...observe the core region of a z = 3.09 protocluster, achieving a typical rms sensitivity of 60 Jy beam−1 at a spatial resolution of 0 7. We detect 18 robust ALMA sources at a signal-to-noise ratio (S/N) > 5. Comparison between the ALMA map and a 1.1 mm map, taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE), indicates that three submillimeter sources discovered by the AzTEC/ASTE survey are resolved into eight individual submillimeter galaxies (SMGs) by ALMA. At least 10 of our 18 ALMA SMGs have spectroscopic redshifts of z 3.09, placing them in the protocluster. This shows that a number of dusty starburst galaxies are forming simultaneously in the core of the protocluster. The nine brightest ALMA SMGs with S/N > 10 have a median intrinsic angular size of ( physical kpc at z = 3.09), which is consistent with previous size measurements of SMGs in other fields. As expected, the source counts show a possible excess compared to the counts in the general fields at S1.1mm ≥ 1.0 mJy, due to the protocluster. Our contiguous mm mapping highlights the importance of large-scale structures on the formation of dusty starburst galaxies.
We present the results of a spectroscopic survey with LRIS-B on Keck of more than 280 star-forming galaxies and AGNs at redshifts 1.4 z 3.0 in the GOODS-N field. Candidates are selected by their U ...sub(n)GR colors using the "BM/BX" criteria to target redshift 1.4 z 2.5 galaxies and the LBG criteria to target redshift z 6 3 galaxies; combined these samples account for 625%-30% of the R and K sub(s) band counts to R = 25.5 and K sub(s)(AB) = 24.4, respectively. The 212 BM/BX galaxies and 74 LBGs constitute the largest spectroscopic sample of galaxies at z > 1.4 in GOODS-N. Extensive multiwavelength data allow us to investigate the stellar populations, stellar masses, bolometric luminosities (L sub(bol)), and extinction of z 6 2 galaxies. Deep Chandra and Spitzer data indicate that the sample includes galaxies with a wide range in L sub(bol) ( 10 super(10) to >10 super(12) L sub( )) and 4 orders of magnitude in dust obscuration (L sub(bol)/L sub(UV)). The sample includes galaxies with a large dynamic range in evolutionary state, from very young galaxies (ages 650 Myr) with small stellar masses (M* 10 super(9) M sub( )) to evolved galaxies with stellar masses comparable to the most massive galaxies at these redshifts (M* > 10 super(11) M sub( )). Spitzer data indicate that the optical sample includes some fraction of the obscured AGN population at high redshifts: at least 3 of 11 AGNs in the z > 1.4 sample are undetected in the deep X-ray data but exhibit power-law SEDs longward of 62 km (rest frame) indicative of obscured AGNs. The results of our survey indicate that rest-frame UV selection and spectroscopy presently constitute the most timewise efficient method of culling large samples of high-redshift galaxies with a wide range in intrinsic properties, and the data presented here will add significantly to the multiwavelength legacy of GOODS.
ABSTRACT We present U336V606J125H160 follow-up Hubble Space Telescope (HST) observations of 16 z ∼ 3 candidate Lyman continuum (LyC) emitters in the HS1549+1919 field. With these data, we obtain high ...spatial-resolution photometric redshifts of all sub-arcsecond components of the LyC candidates in order to eliminate foreground contamination and identify robust candidates for leaking LyC emission. Of the 16 candidates, we find one object with a robust LyC detection that is not due to foreground contamination. This object (MD5) resolves into two components; we refer to the LyC-emitting component as MD5b. MD5b has an observed 1500 to 900 flux-density ratio of , compatible with predictions from stellar population synthesis models. Assuming minimal IGM absorption, this ratio corresponds to a relative (absolute) escape fraction of = 75%-100% ( = 14%-19%). The stellar population fit to MD5b indicates an age of 50 Myr, which is in the youngest 10% of the HST sample and the youngest third of typical z ∼ 3 Lyman break galaxies, and may be a contributing factor to its LyC detection. We obtain a revised, contamination-free estimate for the comoving specific ionizing emissivity at z = 2.85, indicating (with large uncertainties) that star-forming galaxies provide roughly the same contribution as QSOs to the ionizing background at this redshift. Our results show that foreground contamination prevents ground-based LyC studies from obtaining a full understanding of LyC emission from z ∼ 3 star-forming galaxies. Future progress in direct LyC searches is contingent upon the elimination of foreground contaminants through high spatial-resolution observations, and upon acquisition of sufficiently deep LyC imaging to probe ionizing radiation in high-redshift galaxies.
The chemical composition of high-redshift galaxies is an important property that gives clues to their past history and future evolution and yet is difficult to measure with current techniques. In ...this paper we investigate new metallicity indicators based on the strengths of stellar photospheric features at rest-frame ultraviolet wavelengths. By combining the evolutionary spectral synthesis code Starburst99 with the output from the non-LTE model atmosphere code WM-basic, we have developed a code that can model the integrated ultraviolet stellar spectra of star-forming regions at metallicities between 1/20 and twice solar. We use our models to explore a number of spectral regions that are sensitive to metallicity and clean of other spectral features. The most promising metallicity indicator is an absorption feature between 1935 and 2020 AA, which arises from the blending of numerous Fe III transitions. We compare our model spectra with observations of two well-studied high-redshift star-forming galaxies, MS 1512-cB58 (a Lyman break galaxy at z sub(em) = 2.7276) and Q1307-BM1163 (a UV-bright galaxy at z sub(em) = 1.411). The profiles of the photospheric absorption features observed in these galaxies are well reproduced by the models. In addition, the metallicities inferred from their equivalent widths are in good agreement with previous determinations based on interstellar absorption and nebular emission lines. Our new technique appears to be a promising alternative, or complement, to established methods, which have only a limited applicability at high redshifts.
We use a sample of rest-frame UV-selected and spectroscopically observed galaxies at redshifts 1.9 less than or equal to z < 3.4, combined with ground-based spectroscopic Ha and Spitzer MIPS 24 mu m ...data, to derive the most robust measurements of the rest-frame UV, H alpha , and infrared (IR) luminosity functions (LFs) at these redshifts. Our sample is by far the largest of its kind, with over 2000 spectroscopic redshifts in the range 1.9 less than or equal to z < 3.4 and similar to 15,000 photometric candidates in 29 independent fields covering a total area of almost a square degree. Our method for computing the LFs takes into account a number of systematic effects, including photometric scatter, Ly alpha line perturbations to the observed optical colors of galaxies, and contaminants. Taking into account the latter, we find no evidence for an excess of UV-bright galaxies over what was inferred in early z similar to 3 LBG studies. The UV LF appears to undergo little evolution between z similar to 4 and z similar to 2. Corrected for extinction, the UV luminosity density (LD) at z similar to 2 is at least as large as the value at z similar to 3 and a factor of similar to 9 larger than the value at z similar to 6, primarily reflecting an increase in the number density of bright galaxies between z similar to 6 and z similar to 2. Our analysis yields the first constraints anchored by extensive spectroscopy on the infrared and bolometric LFs for faint and moderately luminous (L sub(bol) unk 10 super(12) L unk) galaxies. Adding the IR to the emergent UV luminosity, incorporating independent measurements of the LD from ULIRGs, and assuming realistic dust attenuation values for UV-faint galaxies, indicates that galaxies with L sub(bol) < 10 super(12) L unk account for approximately 80% of the bolometric LD and SFRD at z similar to 2 3. This suggests that previous estimates of the faint end of the L sub(bol) LF may have underestimated the steepness of the faint-end slope at L sub(bol) < 10 super(12) L unk. Our multiwavelength constraints on the global SFRD indicate that approximately one-third of the present-day stellar mass density was formed in subultraluminous galaxies between redshifts z = 1.9 3.4.
We present a high spectral resolution survey of the most metal-poor damped Lyα absorption systems (DLAs) aimed at probing the nature and nucleosynthesis of the earliest generations of stars. Our ...survey comprises 22 systems with iron abundance less than 1/100 solar; observations of seven of these are reported here for the first time. Together with recent measures of the abundances of C and O in Galactic metal-poor stars, we reinvestigate the trend of C/O in the very metal-poor (VMP) regime and we compare, for the first time, the O/Fe ratios in the most metal-poor DLAs and in halo stars. We confirm the near-solar values of C/O in DLAs at the lowest metallicities probed, and find that their distribution is in agreement with that seen in Galactic halo stars. We find that the O/Fe ratio in VMP DLAs is essentially constant, and shows very little dispersion, with a mean 〈O/Fe〉=+0.39 ± 0.12, in good agreement with the values measured in Galactic halo stars when the oxygen abundance is measured from the O i λ6300 line. We speculate that such good agreement in the observed abundance trends points to a universal origin for these metals. In view of this agreement, we construct the abundance pattern for a typical VMP DLA and compare it to model calculations of Population II and Population III nucleosynthesis to determine the origin of the metals in VMP DLAs. Our results suggest that the most metal-poor DLAs may have been enriched by a generation of metal-free stars; however, given that abundance measurements are currently available for only a few elements, we cannot yet rule out an additional contribution from Population II stars.
We have discovered 16 Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to provide the first conclusive evidence for cosmic deceleration that preceded the current ...epoch of cosmic acceleration. These objects, discovered during the course of the GOODS ACS Treasury program, include 6 of the 7 highest redshift SNe Ia known, all at z > 1.25, and populate the Hubble diagram in unexplored territory. The luminosity distances to these objects and to 170 previously reported SNe Ia have been determined using empirical relations between light-curve shape and luminosity. A purely kinematic interpretation of the SN Ia sample provides evidence at the greater than 99% confidence level for a transition from deceleration to acceleration or, similarly, strong evidence for a cosmic jerk. Using a simple model of the expansion history, the transition between the two epochs is constrained to be at z = 0.46 plus or minus 0.13. The data are consistent with the cosmic concordance model of Omega sub(M) ~ 0.3, Omega sub( lambda ) ~ 0.7 ( Chi image = 1.06) and are inconsistent with a simple model of evolution or dust as an alternative to dark energy. For a flat universe with a cosmological constant, we measure Omega sub(M) = 0.29 plus or minus image (equivalently, Omega sub( lambda ) = 0.71). When combined with external flat-universe constraints, including the cosmic microwave background and large-scale structure, we find w =-1.02 plus or minus image (and w <-0.76 at the 95% confidence level) for an assumed static equation of state of dark energy, P = wrhoc super(2). Joint constraints on both the recent equation of state of dark energy, w sub(0), and its time evolution, dw/dz, are a factor of approx8 more precise than the first estimates and twice as precise as those without the SNe Ia discovered with HST. Our constraints are consistent with the static nature of and value of w expected for a cosmological constant (i.e. w sub(0) =-1.0, dw/dz = 0) and are inconsistent with very rapid evolution of dark energy. We address consequences of evolving dark energy for the fate of the universe.
We present observations of a population of Ly alpha emitters (LAEs) exhibiting fluorescent emission via the reprocessing of ionizing radiation from nearby hyperluminous QSOs. These LAEs are part of a ...survey at redshifts 2.5 < z < 2.9 combining narrow-band photometric selection and spectroscopic follow-up to characterize the emission mechanisms, physical properties, and three-dimensional locations of the emitters with respect to their nearby hyperluminous QSOs. These data allow us to probe the radiation field, and thus the radiative history, of the QSOs, and we determine that most of the eight QSOs in our sample have been active and of comparable luminosity for a time 1 Myr < ~ t sub(Q) < ~ 20 Myr. Furthermore, we find that the ionizing QSO emission must have an opening angle straighttheta ~ 30degrees or larger relative to the line of sight.
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