Monthly Notices of the Royal Astronomical Society, 2015
We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour ... more We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour photometric observations from the Dark Energy Survey (DES). Here we report the discovery and spectroscopic confirmation of the z AB , Y AB = 20.2, 20.2 (M 1450 = -26.5) quasar DES J0454-4448 with a redshift of z = 6.09±0.02 based on the onset of the Ly α forest and an H I near zone size of 4.1 +1.1 -1.2 proper Mpc. The quasar was selected as an i-band drop out with i-z = 2.46 and z AB < 21.5 from an area of ∼300 deg 2 . It is the brightest of our 43 candidates and was identified for spectroscopic follow-up solely based on the DES i-z and z-Y colours. The quasar is detected by WISE and has W1 AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and z AB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ∼ 6. DES when completed will have imaged ∼5000 deg 2 to Y AB = 23.0 (5σ point source) and we expect to discover 50-100 new quasars with z > 6 including 3-10 with z > 7 dramatically increasing the numbers of quasars currently known that are suitable for detailed studies.
TotalDat.fits.gz: A FITS table storing information for each of the quasars used in the sample. Th... more TotalDat.fits.gz: A FITS table storing information for each of the quasars used in the sample. The names, formats, and contents of each of the columns in this table are described in Table 1. All time-series data (MJD_x, MAG_x, MAG_ERR_x), structure function data (DT_REST_x, SF_x, SF_ERR_x), and PSD data (REST_FREQ_x, CARMA_PSD_x, CARMA_PSD_ERR_L_x, CARMA_PSD_ERR_U_x) are stored as arrays. EnsDat.fits.gz: A FITS table storing information for the ensemble analysis conducted on different subsets of the total sample. The names, formats, and contents of each of the columns in this table are described in Table 2. Similar to the previous file, time-series, structure function, and PSD data are stored as arrays. It should be noted that for each quasar/ensemble, each array will be the same length to conform to the FITS file standards. Therefore, to force each array to be the same shape, arrays shorter than the largest array will be filled with either NaNs or empty strings until they reach thi...
, has carried out imaging and spectroscopy over roughly 1/3 of the Celestial Sphere. The SDSS use... more , has carried out imaging and spectroscopy over roughly 1/3 of the Celestial Sphere. The SDSS uses a dedicated 2.5-meter wide-field telescope (Gunn et al. 2006), instrumented with a sequence of sophisticated imagers and spectrographs. The SDSS has gone through a series of stages. SDSS-I (York et al. 2000), which was in operation through 2005, focused on a "Legacy" survey of five-band imaging (using what was at the time the largest camera ever used in optical astronomy; Gunn et al. 1998) and spectroscopy of well-defined samples of galaxies (Strauss et al. 2002; Eisenstein et al. 2001) and quasars (Richards et al. 2002), using a 640fiber pair of spectrographs (Smee et al. 2013). SDSS-II
Monthly Notices of the Royal Astronomical Society, 2018
We present a structural and morphological catalogue for 45 million objects selected from the firs... more We present a structural and morphological catalogue for 45 million objects selected from the first year data of the Dark Energy Survey (DES). Single Sérsic fits and non-parametric measurements are produced for g, r, and i filters. The parameters from the best-fitting Sérsic model (total magnitude, half-light radius, Sérsic index, axis ratio, and position angle) are measured with GALFIT; the non-parametric coefficients (concentration, asymmetry, clumpiness, Gini, M20) are provided using the Zurich Estimator of Structural Types (ZEST+). To study the statistical uncertainties, we consider a sample of state-of-the-art image simulations with a realistic distribution in the input parameter space and then process and analyse them as we do with real data: this enables us to quantify the observational biases due to PSF blurring and magnitude effects and correct the measurements as a function of magnitude, galaxy size, Sérsic index (concentration for the analysis of the non-parametric measurements) and ellipticity. We present the largest structural catalogue to date: we find that accurate and complete measurements for all the structural parameters are typically obtained for galaxies with SEXTRACTOR MAG AUTO I ≤ 21. Indeed, the parameters in the filters i and r can be overall well recovered up to MAG AUTO ≤ 21.5, corresponding to a fitting completeness of ∼90 per cent below this threshold, for a total of 25 million galaxies. The combination of parametric and non-parametric structural measurements makes this catalogue an important instrument to explore and understand how galaxies form and evolve. The catalogue described in this paper will be publicly released alongside the DES collaboration Y1 cosmology data products at the following URL: https://des.ncsa.illinois.edu/releases .
The collapse of a stellar core is expected to produce gravitational waves (GWs), neutrinos, and i... more The collapse of a stellar core is expected to produce gravitational waves (GWs), neutrinos, and in most cases a luminous supernova. Sometimes, however, the optical event could be significantly less luminous than a supernova and a direct collapse to a black hole, where the star just disappears, is possible. The GW event GW150914 was detected by the LIGO Virgo Collaboration via a burst analysis that gave localization contours enclosing the Large Magellanic Cloud (LMC). Shortly thereafter, we used DECam to observe 102 deg 2 of the localization area, including 38 deg 2 on the LMC for a missing supergiant search. We construct a complete catalog of LMC luminous red supergiants, the best candidates to undergo invisible core collapse, and collected catalogs of other candidates: less luminous red supergiants, yellow supergiants, blue supergiants, luminous blue variable stars, and Wolf-Rayet stars. Of the objects in the imaging region, all are recovered in the images. The timescale for stellar disappearance is set by the free-fall time, which is a function of the stellar radius. Our observations at 4 and 13 days after the event result in a search sensitive to objects of up to about 200 solar radii. We conclude that it is unlikely that GW150914 was caused by the core collapse of a relatively compact supergiant in the LMC, consistent with the LIGO Collaboration analyses of the gravitational waveform as best interpreted as a high mass binary black hole merger. We discuss how to generalize this search for future very nearby core-collapse candidates.
Monthly Notices of the Royal Astronomical Society, 2017
We report the discovery of a stellar overdensity 8 • north of the centre of the Small Magellanic ... more We report the discovery of a stellar overdensity 8 • north of the centre of the Small Magellanic Cloud (SMC; Small Magellanic Cloud Northern Over-Density; SMCNOD), using data from the first 2 yr of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarily composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of ∼ 6 • × 2 •. It has an absolute magnitude of M V ∼ = −7.7, r h = 2.1 kpc, and μ V (r < r h) = 31.2 mag arcsec −2. We estimate a stellar mass of ∼10 5 M , following a Kroupa mass function. The SMCNOD was probably removed from the SMC disc by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent Large Magellanic Cloud-SMC encounters. This scenario is supported by the lack of significant H I gas. Other potential scenarios for the SMCNOD origin are a transient overdensity within the SMC tidal radius or a primordial SMC satellite in advanced stage of disruption.
Monthly Notices of the Royal Astronomical Society, 2017
We present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a p... more We present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad Fe II (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explained by the emergence of a young quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. The age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario.
Monthly Notices of the Royal Astronomical Society, 2017
We present the results of the first observations of the emission line galaxies (ELG) of the exten... more We present the results of the first observations of the emission line galaxies (ELG) of the extended Baryon Oscillation Spectroscopic Survey. From the total 9000 targets, 4600 have been selected from the Dark Energy Survey (DES). In this subsample, the total success rate for redshifts between 0.6 and 1.2 is 71 and 68 per cent for a bright and a faint samples, respectively, including redshifts measured from a single strong emission line. The mean redshift is 0.80 for the bright and 0.87 for the faint sample, while the percentage of unknown redshifts is 15 and 13 per cent, respectively. In both cases, the star contamination is lower than 2 per cent. We evaluate how well the ELG redshifts are measured using the target selection photometry and validating with the spectroscopic redshifts measured by eBOSS. We explore different techniques to reduce the photometric redshift outliers fraction with a comparison between the template fitting, the neural networks and the random forest methods. Finally, we study the clustering properties of the DES SVA1 ELG samples. We select only the most secure spectroscopic redshift in the redshift range 0.6 < z < 1.2, leading to a mean redshift for the bright and faint sample of 0.85 and 0.90, respectively. We measure the projected angular correlation function and obtain a galaxy bias averaging on scales from 1 to 10 Mpc h −1 of 1.58 ± 0.10 for the bright sample and 1.65 ± 0.12 for the faint sample. These values are representative of a galaxy population with M B − log(h) < −20.5, in agreement with what we measure by fitting galaxy templates to the photometric data.
We present photometric redshift estimates for galaxies used in the weak lensing analysis of the D... more We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model-or machine learning-based photometric redshift methods-annz2, bpz calibrated against BCC-Ufig simulations, skynet, and tpz-are analysed. For training, calibration, and testing of these methods, we construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evaluated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 ± 0.01 over the range 0.3 < z < 1.3, we construct three tomographic bins with means of z = {0.45, 0.67, 1.00}. These bins each have systematic uncertainties δz 0.05 in the mean of the fiducial skynet photo-z n(z). We propagate the errors in the redshift distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of σ 8 of approx. 3%. This shift is within the one sigma statistical errors on σ 8 for the DES SV shear catalog. We further study the potential impact of systematic differences on the critical surface density, Σ crit , finding levels of bias safely less than the statistical power of DES SV data. We recommend a final Gaussian prior for the photo-z bias in the mean of n(z) of width 0.05 for each of the three tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.
We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite EridanusII... more We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite EridanusII (Eri II). We identify 28 member stars in EriII, from which we measure a systemic radial velocity of
We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifi... more We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to 150 deg 2 of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited, and contains 786 clusters with richness λ > 20 (roughly equivalent to M 500c 10 14 h −1 70 M) and 0.2 < z < 0.9. The DR8 catalog consists of 26311 clusters with 0.08 < z < 0.6, with a sharply increasing richness threshold as a function of redshift for z 0.35. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the σ z /(1 + z) ∼ 0.01 level for z 0.7, rising to ∼ 0.02 at z ∼ 0.9 in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev-Zeldovich data to show that the centering performance and massrichness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.
The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents t... more The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents the tenth public data release (DR10) from its current incarnation, SDSS-III. This data release includes the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The APOGEE instrument is a near-infrared R ∼ 22,500 300-fiber spectrograph covering 1.514-1.696 µm. The APOGEE survey is studying the chemical abundances and radial velocities of roughly 100,000 red giant star candidates in the bulge, bar, disk, and halo of the Milky Way. DR10 includes 178,397 spectra of 57,454 stars, each typically observed three or more times, from APOGEE. Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included.
We report the discovery of a stellar stream in the Dark Energy Survey (DES) Year 1 (Y1A1) data. T... more We report the discovery of a stellar stream in the Dark Energy Survey (DES) Year 1 (Y1A1) data. The discovery was made through simple color-magnitude filters and visual inspection of the Y1A1 data. We refer to this new object as the Phoenix stream, after its resident constellation. After subtraction of the background stellar population we detect a clear signal of a simple stellar population. By fitting the ridge line of the stream in color-magnitude space, we find that a stellar population with age τ = 11.5 ± 0.5 Gyr and [F e/H] < 1.6 located 17.5±0.9 kpc from the Sun gives an adequate description of the stream stellar population. The stream is detected over an extension of 8. • 1 (2.5 kpc) and has a width of ∼54 pc assuming a Gaussian profile, indicating that a globular cluster is a probable progenitor. There is no known globular cluster within 5 kpc compatible with being the progenitor of the stream, assuming that the stream traces its orbit. We examined overdensities along the stream, however no obvious counterpart bound stellar system is visible in the coadded images. We also find overdensities along the stream that appear to be symmetrically distributed-consistent with the epicyclic overdensity scenario for the formation of cold streams-as well as a misalignment between the Northern and Southern part of stream. Despite the close proximity we find no evidence that this stream and the halo cluster NGC 1261 have a common accretion origin linked to the recently found EriPhe overdensity (Li et al. 2015).
We report the discovery of eight new Milky Way companions in ∼ 1,800 deg 2 of optical imaging dat... more We report the discovery of eight new Milky Way companions in ∼ 1,800 deg 2 of optical imaging data collected during the first year of the Dark Energy Survey (DES). Each system is identified as a statistically significant over-density of individual stars consistent with the expected isochrone and luminosity function of an old and metalpoor stellar population. The objects span a wide range of absolute magnitudes (M V from −2.2 mag to −7.4 mag), physical sizes (10 pc to 170 pc), and heliocentric distances (30 kpc to 330 kpc). Based on the low surface brightnesses, large physical sizes, and/or large Galactocentric distances of these objects, several are likely to be new ultra-faint satellite galaxies of the Milky Way and/or Magellanic Clouds. We introduce a likelihoodbased algorithm to search for and characterize stellar over-densities, as well as identify stars with high satellite membership probabilities. We also present completeness estimates for detecting ultra-faint galaxies of varying luminosities, sizes, and heliocentric distances in the first-year DES data. 1. Introduction Milky Way satellite galaxies provide a unique opportunity to study the low-luminosity threshold of galaxy formation and to better connect the baryonic component of galaxies with the dark
We study a phenomenological class of models where dark matter converts to dark radiation in the l... more We study a phenomenological class of models where dark matter converts to dark radiation in the low redshift epoch. This class of models, dubbed DMDR, characterizes the evolution of comoving dark matter density with two extra parameters, and may be able to help alleviate the observed discrepancies between early- and late-time probes of the universe. We investigate how the conversion affects key cosmological observables such as the CMB temperature and matter power spectra. Combining 3x2pt data from Year 1 of the Dark Energy Survey, Planck-2018 CMB temperature and polarization data, supernovae (SN) Type Ia data from Pantheon, and baryon acoustic oscillation (BAO) data from BOSS DR12, MGS and 6dFGS, we place new constraints on the amount of dark matter that has converted to dark radiation and the rate of this conversion. The fraction of the dark matter that has converted since the beginning of the universe in units of the current amount of dark matter, ζ, is constrained at 68% confiden...
We present the statistical methods that have been developed to analyse the OzDES reverberation ma... more We present the statistical methods that have been developed to analyse the OzDES reverberation mapping sample. To perform this statistical analysis we have created a suite of customisable simulations that mimic the characteristics of each individual source in the OzDES sample.These characteristics include: the variability in the photometric and spectroscopic lightcurves,the measurement uncertainties and the observational cadence. By simulating six real sources that contain the CIV emission line, we developed a set of quality criteria that ranks the reliability of a recovered time lag depending on the agreement between different recovery methods, the magnitude of the uncertainties, and the rate at which false positives were found in the simulations. Of these six sources, two were given a quality rating of 1, corresponding to our 'gold standard'. Lags were recovered at 223±56 and 378±104 days with redshifts of 1.93 and 2.74 respectively. Future work will apply these methods to...
We present a novel approach for creating science-ready catalogs through a software infrastructure... more We present a novel approach for creating science-ready catalogs through a software infrastructure developed for the Dark Energy Survey (DES). We integrate the data products released by the DES Data Management and additional products created by the DES collaboration in an environment known as DES Science Portal. Each step involved in the creation of a science-ready catalog is recorded in a relational database and can be recovered at any time. We describe how the DES Science Portal automates the creation and characterization of lightweight catalogs for DES Year 1 Annual Release, and show its flexibility in creating multiple catalogs with different inputs and configurations. Finally, we discuss the advantages of this infrastructure for large surveys such as DES and the Large Synoptic Survey Telescope. The capability of creating science-ready catalogs efficiently and with full control of the inputs and configurations used is an important asset for supporting science analysis using data ...
Monthly Notices of the Royal Astronomical Society, 2015
We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour ... more We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour photometric observations from the Dark Energy Survey (DES). Here we report the discovery and spectroscopic confirmation of the z AB , Y AB = 20.2, 20.2 (M 1450 = -26.5) quasar DES J0454-4448 with a redshift of z = 6.09±0.02 based on the onset of the Ly α forest and an H I near zone size of 4.1 +1.1 -1.2 proper Mpc. The quasar was selected as an i-band drop out with i-z = 2.46 and z AB < 21.5 from an area of ∼300 deg 2 . It is the brightest of our 43 candidates and was identified for spectroscopic follow-up solely based on the DES i-z and z-Y colours. The quasar is detected by WISE and has W1 AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and z AB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ∼ 6. DES when completed will have imaged ∼5000 deg 2 to Y AB = 23.0 (5σ point source) and we expect to discover 50-100 new quasars with z > 6 including 3-10 with z > 7 dramatically increasing the numbers of quasars currently known that are suitable for detailed studies.
TotalDat.fits.gz: A FITS table storing information for each of the quasars used in the sample. Th... more TotalDat.fits.gz: A FITS table storing information for each of the quasars used in the sample. The names, formats, and contents of each of the columns in this table are described in Table 1. All time-series data (MJD_x, MAG_x, MAG_ERR_x), structure function data (DT_REST_x, SF_x, SF_ERR_x), and PSD data (REST_FREQ_x, CARMA_PSD_x, CARMA_PSD_ERR_L_x, CARMA_PSD_ERR_U_x) are stored as arrays. EnsDat.fits.gz: A FITS table storing information for the ensemble analysis conducted on different subsets of the total sample. The names, formats, and contents of each of the columns in this table are described in Table 2. Similar to the previous file, time-series, structure function, and PSD data are stored as arrays. It should be noted that for each quasar/ensemble, each array will be the same length to conform to the FITS file standards. Therefore, to force each array to be the same shape, arrays shorter than the largest array will be filled with either NaNs or empty strings until they reach thi...
, has carried out imaging and spectroscopy over roughly 1/3 of the Celestial Sphere. The SDSS use... more , has carried out imaging and spectroscopy over roughly 1/3 of the Celestial Sphere. The SDSS uses a dedicated 2.5-meter wide-field telescope (Gunn et al. 2006), instrumented with a sequence of sophisticated imagers and spectrographs. The SDSS has gone through a series of stages. SDSS-I (York et al. 2000), which was in operation through 2005, focused on a "Legacy" survey of five-band imaging (using what was at the time the largest camera ever used in optical astronomy; Gunn et al. 1998) and spectroscopy of well-defined samples of galaxies (Strauss et al. 2002; Eisenstein et al. 2001) and quasars (Richards et al. 2002), using a 640fiber pair of spectrographs (Smee et al. 2013). SDSS-II
Monthly Notices of the Royal Astronomical Society, 2018
We present a structural and morphological catalogue for 45 million objects selected from the firs... more We present a structural and morphological catalogue for 45 million objects selected from the first year data of the Dark Energy Survey (DES). Single Sérsic fits and non-parametric measurements are produced for g, r, and i filters. The parameters from the best-fitting Sérsic model (total magnitude, half-light radius, Sérsic index, axis ratio, and position angle) are measured with GALFIT; the non-parametric coefficients (concentration, asymmetry, clumpiness, Gini, M20) are provided using the Zurich Estimator of Structural Types (ZEST+). To study the statistical uncertainties, we consider a sample of state-of-the-art image simulations with a realistic distribution in the input parameter space and then process and analyse them as we do with real data: this enables us to quantify the observational biases due to PSF blurring and magnitude effects and correct the measurements as a function of magnitude, galaxy size, Sérsic index (concentration for the analysis of the non-parametric measurements) and ellipticity. We present the largest structural catalogue to date: we find that accurate and complete measurements for all the structural parameters are typically obtained for galaxies with SEXTRACTOR MAG AUTO I ≤ 21. Indeed, the parameters in the filters i and r can be overall well recovered up to MAG AUTO ≤ 21.5, corresponding to a fitting completeness of ∼90 per cent below this threshold, for a total of 25 million galaxies. The combination of parametric and non-parametric structural measurements makes this catalogue an important instrument to explore and understand how galaxies form and evolve. The catalogue described in this paper will be publicly released alongside the DES collaboration Y1 cosmology data products at the following URL: https://des.ncsa.illinois.edu/releases .
The collapse of a stellar core is expected to produce gravitational waves (GWs), neutrinos, and i... more The collapse of a stellar core is expected to produce gravitational waves (GWs), neutrinos, and in most cases a luminous supernova. Sometimes, however, the optical event could be significantly less luminous than a supernova and a direct collapse to a black hole, where the star just disappears, is possible. The GW event GW150914 was detected by the LIGO Virgo Collaboration via a burst analysis that gave localization contours enclosing the Large Magellanic Cloud (LMC). Shortly thereafter, we used DECam to observe 102 deg 2 of the localization area, including 38 deg 2 on the LMC for a missing supergiant search. We construct a complete catalog of LMC luminous red supergiants, the best candidates to undergo invisible core collapse, and collected catalogs of other candidates: less luminous red supergiants, yellow supergiants, blue supergiants, luminous blue variable stars, and Wolf-Rayet stars. Of the objects in the imaging region, all are recovered in the images. The timescale for stellar disappearance is set by the free-fall time, which is a function of the stellar radius. Our observations at 4 and 13 days after the event result in a search sensitive to objects of up to about 200 solar radii. We conclude that it is unlikely that GW150914 was caused by the core collapse of a relatively compact supergiant in the LMC, consistent with the LIGO Collaboration analyses of the gravitational waveform as best interpreted as a high mass binary black hole merger. We discuss how to generalize this search for future very nearby core-collapse candidates.
Monthly Notices of the Royal Astronomical Society, 2017
We report the discovery of a stellar overdensity 8 • north of the centre of the Small Magellanic ... more We report the discovery of a stellar overdensity 8 • north of the centre of the Small Magellanic Cloud (SMC; Small Magellanic Cloud Northern Over-Density; SMCNOD), using data from the first 2 yr of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarily composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of ∼ 6 • × 2 •. It has an absolute magnitude of M V ∼ = −7.7, r h = 2.1 kpc, and μ V (r < r h) = 31.2 mag arcsec −2. We estimate a stellar mass of ∼10 5 M , following a Kroupa mass function. The SMCNOD was probably removed from the SMC disc by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent Large Magellanic Cloud-SMC encounters. This scenario is supported by the lack of significant H I gas. Other potential scenarios for the SMCNOD origin are a transient overdensity within the SMC tidal radius or a primordial SMC satellite in advanced stage of disruption.
Monthly Notices of the Royal Astronomical Society, 2017
We present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a p... more We present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad Fe II (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explained by the emergence of a young quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. The age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario.
Monthly Notices of the Royal Astronomical Society, 2017
We present the results of the first observations of the emission line galaxies (ELG) of the exten... more We present the results of the first observations of the emission line galaxies (ELG) of the extended Baryon Oscillation Spectroscopic Survey. From the total 9000 targets, 4600 have been selected from the Dark Energy Survey (DES). In this subsample, the total success rate for redshifts between 0.6 and 1.2 is 71 and 68 per cent for a bright and a faint samples, respectively, including redshifts measured from a single strong emission line. The mean redshift is 0.80 for the bright and 0.87 for the faint sample, while the percentage of unknown redshifts is 15 and 13 per cent, respectively. In both cases, the star contamination is lower than 2 per cent. We evaluate how well the ELG redshifts are measured using the target selection photometry and validating with the spectroscopic redshifts measured by eBOSS. We explore different techniques to reduce the photometric redshift outliers fraction with a comparison between the template fitting, the neural networks and the random forest methods. Finally, we study the clustering properties of the DES SVA1 ELG samples. We select only the most secure spectroscopic redshift in the redshift range 0.6 < z < 1.2, leading to a mean redshift for the bright and faint sample of 0.85 and 0.90, respectively. We measure the projected angular correlation function and obtain a galaxy bias averaging on scales from 1 to 10 Mpc h −1 of 1.58 ± 0.10 for the bright sample and 1.65 ± 0.12 for the faint sample. These values are representative of a galaxy population with M B − log(h) < −20.5, in agreement with what we measure by fitting galaxy templates to the photometric data.
We present photometric redshift estimates for galaxies used in the weak lensing analysis of the D... more We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model-or machine learning-based photometric redshift methods-annz2, bpz calibrated against BCC-Ufig simulations, skynet, and tpz-are analysed. For training, calibration, and testing of these methods, we construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evaluated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 ± 0.01 over the range 0.3 < z < 1.3, we construct three tomographic bins with means of z = {0.45, 0.67, 1.00}. These bins each have systematic uncertainties δz 0.05 in the mean of the fiducial skynet photo-z n(z). We propagate the errors in the redshift distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of σ 8 of approx. 3%. This shift is within the one sigma statistical errors on σ 8 for the DES SV shear catalog. We further study the potential impact of systematic differences on the critical surface density, Σ crit , finding levels of bias safely less than the statistical power of DES SV data. We recommend a final Gaussian prior for the photo-z bias in the mean of n(z) of width 0.05 for each of the three tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.
We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite EridanusII... more We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite EridanusII (Eri II). We identify 28 member stars in EriII, from which we measure a systemic radial velocity of
We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifi... more We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to 150 deg 2 of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited, and contains 786 clusters with richness λ > 20 (roughly equivalent to M 500c 10 14 h −1 70 M) and 0.2 < z < 0.9. The DR8 catalog consists of 26311 clusters with 0.08 < z < 0.6, with a sharply increasing richness threshold as a function of redshift for z 0.35. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the σ z /(1 + z) ∼ 0.01 level for z 0.7, rising to ∼ 0.02 at z ∼ 0.9 in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev-Zeldovich data to show that the centering performance and massrichness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.
The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents t... more The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents the tenth public data release (DR10) from its current incarnation, SDSS-III. This data release includes the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The APOGEE instrument is a near-infrared R ∼ 22,500 300-fiber spectrograph covering 1.514-1.696 µm. The APOGEE survey is studying the chemical abundances and radial velocities of roughly 100,000 red giant star candidates in the bulge, bar, disk, and halo of the Milky Way. DR10 includes 178,397 spectra of 57,454 stars, each typically observed three or more times, from APOGEE. Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included.
We report the discovery of a stellar stream in the Dark Energy Survey (DES) Year 1 (Y1A1) data. T... more We report the discovery of a stellar stream in the Dark Energy Survey (DES) Year 1 (Y1A1) data. The discovery was made through simple color-magnitude filters and visual inspection of the Y1A1 data. We refer to this new object as the Phoenix stream, after its resident constellation. After subtraction of the background stellar population we detect a clear signal of a simple stellar population. By fitting the ridge line of the stream in color-magnitude space, we find that a stellar population with age τ = 11.5 ± 0.5 Gyr and [F e/H] < 1.6 located 17.5±0.9 kpc from the Sun gives an adequate description of the stream stellar population. The stream is detected over an extension of 8. • 1 (2.5 kpc) and has a width of ∼54 pc assuming a Gaussian profile, indicating that a globular cluster is a probable progenitor. There is no known globular cluster within 5 kpc compatible with being the progenitor of the stream, assuming that the stream traces its orbit. We examined overdensities along the stream, however no obvious counterpart bound stellar system is visible in the coadded images. We also find overdensities along the stream that appear to be symmetrically distributed-consistent with the epicyclic overdensity scenario for the formation of cold streams-as well as a misalignment between the Northern and Southern part of stream. Despite the close proximity we find no evidence that this stream and the halo cluster NGC 1261 have a common accretion origin linked to the recently found EriPhe overdensity (Li et al. 2015).
We report the discovery of eight new Milky Way companions in ∼ 1,800 deg 2 of optical imaging dat... more We report the discovery of eight new Milky Way companions in ∼ 1,800 deg 2 of optical imaging data collected during the first year of the Dark Energy Survey (DES). Each system is identified as a statistically significant over-density of individual stars consistent with the expected isochrone and luminosity function of an old and metalpoor stellar population. The objects span a wide range of absolute magnitudes (M V from −2.2 mag to −7.4 mag), physical sizes (10 pc to 170 pc), and heliocentric distances (30 kpc to 330 kpc). Based on the low surface brightnesses, large physical sizes, and/or large Galactocentric distances of these objects, several are likely to be new ultra-faint satellite galaxies of the Milky Way and/or Magellanic Clouds. We introduce a likelihoodbased algorithm to search for and characterize stellar over-densities, as well as identify stars with high satellite membership probabilities. We also present completeness estimates for detecting ultra-faint galaxies of varying luminosities, sizes, and heliocentric distances in the first-year DES data. 1. Introduction Milky Way satellite galaxies provide a unique opportunity to study the low-luminosity threshold of galaxy formation and to better connect the baryonic component of galaxies with the dark
We study a phenomenological class of models where dark matter converts to dark radiation in the l... more We study a phenomenological class of models where dark matter converts to dark radiation in the low redshift epoch. This class of models, dubbed DMDR, characterizes the evolution of comoving dark matter density with two extra parameters, and may be able to help alleviate the observed discrepancies between early- and late-time probes of the universe. We investigate how the conversion affects key cosmological observables such as the CMB temperature and matter power spectra. Combining 3x2pt data from Year 1 of the Dark Energy Survey, Planck-2018 CMB temperature and polarization data, supernovae (SN) Type Ia data from Pantheon, and baryon acoustic oscillation (BAO) data from BOSS DR12, MGS and 6dFGS, we place new constraints on the amount of dark matter that has converted to dark radiation and the rate of this conversion. The fraction of the dark matter that has converted since the beginning of the universe in units of the current amount of dark matter, ζ, is constrained at 68% confiden...
We present the statistical methods that have been developed to analyse the OzDES reverberation ma... more We present the statistical methods that have been developed to analyse the OzDES reverberation mapping sample. To perform this statistical analysis we have created a suite of customisable simulations that mimic the characteristics of each individual source in the OzDES sample.These characteristics include: the variability in the photometric and spectroscopic lightcurves,the measurement uncertainties and the observational cadence. By simulating six real sources that contain the CIV emission line, we developed a set of quality criteria that ranks the reliability of a recovered time lag depending on the agreement between different recovery methods, the magnitude of the uncertainties, and the rate at which false positives were found in the simulations. Of these six sources, two were given a quality rating of 1, corresponding to our 'gold standard'. Lags were recovered at 223±56 and 378±104 days with redshifts of 1.93 and 2.74 respectively. Future work will apply these methods to...
We present a novel approach for creating science-ready catalogs through a software infrastructure... more We present a novel approach for creating science-ready catalogs through a software infrastructure developed for the Dark Energy Survey (DES). We integrate the data products released by the DES Data Management and additional products created by the DES collaboration in an environment known as DES Science Portal. Each step involved in the creation of a science-ready catalog is recorded in a relational database and can be recovered at any time. We describe how the DES Science Portal automates the creation and characterization of lightweight catalogs for DES Year 1 Annual Release, and show its flexibility in creating multiple catalogs with different inputs and configurations. Finally, we discuss the advantages of this infrastructure for large surveys such as DES and the Large Synoptic Survey Telescope. The capability of creating science-ready catalogs efficiently and with full control of the inputs and configurations used is an important asset for supporting science analysis using data ...
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Papers by Aurelio Carnero Rosell