Alina Streblyanska

A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34

Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts—that is, increased rates of star formation—in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ∼5 (refs 2–4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A ‘maximum starburst’ converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang.

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: measuring growth rate and geometry with anisotropic clustering

We use the observed anisotropic clustering of galaxies in the Baryon Oscillation Spectroscopic Survey Data Release 11 CMASS sample to measure the linear growth rate of structure, the Hubble expansion rate and the comoving distance scale. Our sample covers 8498 deg2 and encloses an effective volume of 6 Gpc3 at an effective redshift of z¯=0.57. We find fσ8 = 0.441 ± 0.044, H = 93.1 ± 3.0 km s−1 Mpc−1 and DA = 1380 ± 23 Mpc when fitting the growth and expansion rate simultaneously. When we fix the background expansion to the one predicted by spatially flat Λ cold dark matter (ΛCDM) model in agreement with recent Planck results, we find fσ8 = 0.447 ± 0.028 (6 per cent accuracy). While our measurements are generally consistent with the predictions of ΛCDM and general relativity, they mildly favour models in which the strength of gravitational interactions is weaker than what is predicted by general relativity. Combining our measurements with recent cosmic microwave background data results in tight constraints on basic cosmological parameters and deviations from the standard cosmological model. Separately varying these parameters, we find w = −0.983 ± 0.075 (8 per cent accuracy) and γ = 0.69 ± 0.11 (16 per cent accuracy) for the effective equation of state of dark energy and the growth rate index, respectively. Both constraints are in good agreement with the standard model values of w = −1 and γ = 0.554.

Gravitational Lens Models Based on Submillimeter Array Imaging of Herschel-selected Strongly Lensed Sub-millimeter Galaxies at z > 1.5

Strong gravitational lenses are now being routinely discovered in wide-field surveys at (sub-)millimeter wavelengths. We present Submillimeter Array (SMA) high-spatial resolution imaging and Gemini-South and Multiple Mirror Telescope optical spectroscopy of strong lens candidates discovered in the two widest extragalactic surveys conducted by the Herschel Space Observatory: the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). From a sample of 30 Herschel sources with S 500 > 100 mJy, 21 are strongly lensed (i.e., multiply imaged), 4 are moderately lensed (i.e., singly imaged), and the remainder require additional data to determine their lensing status. We apply a visibility-plane lens modeling technique to the SMA data to recover information about the masses of the lenses as well as the intrinsic (i.e., unlensed) sizes (r half) and far-infrared luminosities (L FIR) of the lensed submillimeter galaxies (SMGs). The sample of lenses comprises primarily isolated massive galaxies, but includes some groups and clusters as well. Several of the lenses are located at z lens > 0.7, a redshift regime that is inaccessible to lens searches based on Sloan Digital Sky Survey spectroscopy. The lensed SMGs are amplified by factors that are significantly below statistical model predictions given the 500 μm flux densities of our sample. We speculate that this may reflect a deficiency in our understanding of the intrinsic sizes and luminosities of the brightest SMGs. The lensed SMGs span nearly one decade in L FIR (median L FIR = 7.9 × 1012 L ☉) and two decades in FIR luminosity surface density (median ΣFIR = 6.0 × 1011 L ☉ kpc–2). The strong lenses in this sample and others identified via (sub-)mm surveys will provide a wealth of information regarding the astrophysics of galaxy formation and evolution over a wide range in redshift.

The Sloan Digital Sky Survey Quasar Catalog: Twelfth data release

We present the Data Release 12 Quasar catalog (DR12Q) from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. This catalog includes all SDSS-III/BOSS objects that were spectroscopically targeted as quasar candidates during the full survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities M i [ z = 2] H 0 = 70 km s -1 Mpc -1 , Ω M = 0.3, and Ω Λ = 0.7), and either display at least one emission line with a full width at half maximum (FWHM) larger than 500 km s -1 or, if not, have interesting/complex absorption features. The catalog also includes previously known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. The catalog contains 297 301 quasars (272 026 are new discoveries since the beginning of SDSS-III) detected over 9376 deg 2 with robust identification and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (184 101, of which 167 742 are new discoveries) is about an order of magnitude greater than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii], Mg ii). The catalog identifies 29 580 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band ( u , g , r , i , z ) CCD-based photometry with typical accuracy of 0.03 mag together with some information on the optical morphology and the selection criteria. When available, the catalog also provides information on the optical variability of quasars using SDSS and Palomar Transient Factory multi-epoch photometry. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3600–10 500 A at a spectral resolution in the range 1300 R < 2500, can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 4841 quasars that have been identified serendipitously outside of the superset defined to derive the main quasar catalog.

XMM-Newton observations of the Lockman Hole IV: spectra of the brightest AGN ,

This paper presents the results of a detailed X-ray spectral analysis of a sample of 123 X-ray sources detected with XMM-Newton in the Lockman Hole field. This is the deepest observation carried out with XMM-Newton with more that 600 ks of good EPIC-pn data. We have spectra with good signal to noise (>500 source counts) for all objects down to 0.2−12 keV fluxes of ∼5 × 10 −15 erg cm −2 s −1 (flux limit of ∼6 × 10 −16 erg cm −2 s −1 in the 0.5− 2a nd 2−10 keV bands). At the time of the analysis, we had optical spectroscopic identifications for 60% of the sources, 46 being optical type-1 AGN and 28 optical type-2 AGN. Using a single power law model our sources’ average spectral slope hardens at faint 0.5−2 keV fluxes but not at faint 2−10 keV fluxes. We have been able to explain this effect in terms of an increase in X-ray absorption at faint fluxes. We did not find in our data any evidence for the existence of a population of faint intrinsically harder sources. The average spectral slope of our sources is ∼1.9, with an intrinsic dispersion of ∼0.28. We detected X-ray absorption (F-test significance ≥95%) in 37% of the sources, ∼10% in type-1 AGN (rest-frame NH ∼ 1.6 × 10 21 −1.2 × 10 22 cm −2 )a nd∼77% (rest-frame NH ∼ 1.5 × 10 21 −4 × 10 23 cm −2 ) in type-2 AGN. Using X-ray fluxes corrected for absorption, the fraction of absorbed objects and the absorbing column density distribution did not vary with X-ray flux. Our type-1 and type-2 AGN do not appear to have different continuum shapes, but the distribution of intrinsic (rest-frame) absorbing column densities is different among both classes. A significant fraction of our type-2 AGN (5 out of 28) were found to display no substantial absorption (NH < 10 21 cm −2 ). We discuss possible interpretations to this in terms of Compton-thick AGN and intrinsic Broad Line Region properties. An emission line compatible with Fe Kα was detected in 8 sources (1 type-1 AGN, 5 type-2 AGN and 2 unidentified) with rest frame equivalent widths 120−1000 eV. However weak broad components can be easily missed in other sources by the relatively noisy data. The AGN continuum or intrinsic absorption did not depend on X-ray luminosity and/or redshift. Soft excess emission was detected in 18 objects, but only in 9 (including 4 type-1 AGN and 4 type-2 AGN) could we fit this spectral component with a black body model. The measured 0.5− 2k eV luminosities of the fitted black body were not significantly different in type-1 and type-2 AGN, although the temperatures of the black body were slightly higher in type-2 AGN (� kT� = 0.26 ± 0.08) than in type-1 AGN (� kT� = 0.09 ± 0.01). For 9 sources (including 1 type-1 AGN and 3 type-2 AGN) a scattering model provided a better fit of the soft excess emission. We found that the integrated contribution from our sources to the X-ray background in the 2−7 keV band is softer ( Γ= 1.5−1.6) than the background itself, implying that fainter sources need to be more absorbed.

CROSS-CORRELATION OF SDSS DR7 QUASARS AND DR10 BOSS GALAXIES: THE WEAK LUMINOSITY DEPENDENCE OF QUASAR CLUSTERING AT z ∼ 0.5

We present the measurement of the two-point cross-correlation function (CCF) of 8198 Sloan Digital Sky Survey Data Release 7 quasars and 349,608 Data Release 10 CMASS galaxies from the Baryonic Oscillation Spectroscopic Survey at 0.3 Mi (z = 2) > –25.5, implying a weak luminosity dependence of clustering for luminous quasars at . We compare our measurements with theoretical predictions, halo occupation distribution (HOD) models, and mock catalogs. These comparisons suggest that quasars reside in a broad range of host halos. The host halo mass distributions significantly overlap with each other for quasars at different luminosities, implying a poor correlation between halo mass and instantaneous quasar luminosity. We also find that the quasar HOD parameterization is largely degenerate such that different HODs can reproduce the CCF equally well, but with different satellite fractions and host halo mass distributions. These results highlight the limitations and ambiguities in modeling the distribution of quasars with the standard HOD approach.

HerMES: CANDIDATE HIGH-REDSHIFT GALAXIES DISCOVERED WITH HERSCHEL/SPIRE*, **

We present a method for selecting z > 4 dusty, star-forming galaxies (DSFGs) using Herschel/Spectral and Photometric Imaging Receiver 250/350/500 μm flux densities to search for red sources. We apply this method to 21 deg2 of data from the HerMES survey to produce a catalog of 38 high-z candidates. Follow-up of the first five of these sources confirms that this method is efficient at selecting high-z DSFGs, with 4/5 at z = 4.3-6.3 (and the remaining source at z = 3.4), and that they are some of the most luminous dusty sources known. Comparison with previous DSFG samples, mostly selected at longer wavelengths (e.g., 850 μm) and in single-band surveys, shows that our method is much more efficient at selecting high-z DSFGs, in the sense that a much larger fraction are at z > 3. Correcting for the selection completeness and purity, we find that the number of bright (S 500 μm ≥ 30 mJy), red Herschel sources is 3.3 ± 0.8 deg–2. This is much higher than the number predicted by current models, suggesting that the DSFG population extends to higher redshifts than previously believed. If the shape of the luminosity function for high-z DSFGs is similar to that at z ~ 2, rest-frame UV based studies may be missing a significant component of the star formation density at z = 4-6, even after correction for extinction.

Clustering of intermediate redshift quasars using the final SDSS III-BOSS sample

Author(s): Eftekharzadeh, S; Myers, AD; White, M; Weinberg, DH; Schneider, DP; Shen, Y; Font-Ribera, A; Ross, NP; Paris, I; Streblyanska, A | Abstract:

The first Frontier Fields cluster: 4.5 μm excess in a z ~ 8 galaxy candidate in Abell 2744

Aims: We present in this letter the first analysis of a z ~ 8 galaxy candidate found in the Hubble and Spitzer imaging data of Abell 2744 as part of the Hubble Frontier Fields legacy program. Methods: We applied the most commonly used methods to select exceptionally high-redshift galaxies by combining non-detection and color criteria using seven HST bands. We used GALFIT on IRAC images to fit and subtract contamination of bright nearby sources.The physical properties were inferred from spectral energy distribution-fitting using templates with and without nebular emission. Results: This letter is focused on the brightest candidate we found (mF160W = 26.2) over the 4.9 arcmin2 field of view covered by the WFC3. It is not detected in the ACS bands and at 3.6 μm, while it is clearly detected at 4.5 μm with rather similar depths. This break in the IRAC data might be explained by strong [OIII]+Hβ lines at z ~ 8 that contribute to the 4.5 μm photometry. The best photo-z is found at z ~ 8.0+0.2-0.5, although solutions at low-redshift (z ~ 1.9) cannot be completely excluded , but they are strongly disfavored by the SED-fitting. The amplification factor is relatively small at μ = 1.49 ± 0.02. The star formation rate in this object ranges from 8 to 60 M⊙ yr-1, the stellar mass is on the order of M⋆ = (2.5-10) × 109 M⊙, and the size is r ≈ 0.35 ± 0.15 kpc. Conclusions: This object is one of the first z ~ 8 Lyman break galaxy candidates showing a clear break between 3.6 μm and 4.5 μm, which is consistent with the IRAC properties of the first spectroscopically confirmed galaxy at a similar redshift. Due to its brightness, the redshift of this object could potentially be confirmed by near-infrared spectroscopy with current 8-10 m telescopes. The nature of this candidate will be revealed in the coming months with the arrival of new ACS and Spitzer data, increasing the depth at optical and near-infrared wavelengths.

The clustering of galaxies in the SDSS-III DR10 baryon oscillation spectroscopic survey: No detectable colour dependence of distance scale or growth rate measurements

We study the clustering of galaxies, as a function of their colour, from Data Release Ten (DR10) of the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillation Spectroscopic Survey. DR10 contains 540 505 galaxies with 0.43 < z < 0.7; from these we select 122 967 for a ‘Blue’ sample and 131 969 for a ‘Red’ sample based on k + e corrected (to z =0.55) r − i colours and i-band magnitudes. The samples are chosen such that both contain more than 100 000 galaxies, have similar redshift distributions and maximize the difference in clustering amplitude. The Red sample has a 40 per cent larger bias than the Blue (bRed/bBlue = 1.39 ± 0.04), implying that the Red galaxies occupy dark matter haloes with an average mass that is 0.5 log10 M⊙ greater. Spherically averaged measurements of the correlation function, ξ0, and the power spectrum are used to locate the position of the baryon acoustic oscillation (BAO) feature of both samples. Using ξ0, we obtain distance scales, relative to the distance of our reference Λ cold dark matter cosmology, of 1.010 ± 0.027 for the Red sample and 1.005 ± 0.031 for the Blue. After applying reconstruction, these measurements improve to 1.013 ± 0.020 for the Red sample and 1.008 ± 0.026 for the Blue. For each sample, measurements of ξ0 and the second multipole moment, ξ2, of the anisotropic correlation function are used to determine the rate of structure growth, parametrized by fσ8. We find fσ8,Red = 0.511 ± 0.083, fσ8, Blue = 0.509 ± 0.085 and fσ8, Cross = 0.423 ± 0.061 (from the cross-correlation between the Red and Blue samples). We use the covariance between the bias and growth measurements obtained from each sample and their cross-correlation to produce an optimally combined measurement of fσ8, comb = 0.443 ± 0.055. This result compares favourably to that of the full 0.43 < z < 0.7 sample (fσ8, full = 0.422 ± 0.051) despite the fact that, in total, we use less than half of the number of galaxies analysed in the full sample measurement. In no instance do we detect significant differences in distance scale or structure growth measurements obtained from the Blue and Red samples. Our results are consistent with theoretical predictions and our tests on mock samples, which predict that any colour-dependent systematic uncertainty on the measured BAO position is less than 0.5 per cent.