Hu Zou

Estimating the H I gas fractions of galaxies in the local universe

We use a sample of 800 galaxies with H I mass measurements from the HyperLeda catalogue and optical photometry from the fourth data release of the Sloan Digital Sky Survey (SDSS) to calibrate a new photometric estimator of the H i-to-stellar-mass ratio for nearby galaxies. Our estimator, which is motivated by the Kennicutt-Schmidt star formation law, is log 10 (G H1 /S) = - 1.73238(g - r) + 0.215 182μ i - 4.08451, where μ i is the i-band surface brightness and g - r is the optical colour estimated from the g- and r-band Petrosian apparent magnitudes. This estimator has a scatter of σ = 0.31 dex in log (G HI /S), compared to σ ∼ 0.4 dex for previous estimators that were based on colour alone. We investigate whether the residuals in our estimate of log (G HI /S) depend in a systematic way on a variety of different galaxy properties. We find no effect as a function of stellar mass or 4000 A break strength, but there is a systematic effect as a function of the concentration index of the light. We then apply our estimator to a sample of 10 5 emission-line galaxies in the SDSS Data Release 4 (DR4) and derive an estimate of the H I mass function, which is in excellent agreement with recent results from H I blind surveys. Finally, we re-examine the well-known relation between gas-phase metallicity and stellar mass, and ask whether there is a dependence on H I-to-stellar-mass ratio, as predicted by chemical evolution models. We do find that gas-poor galaxies are more metal rich at fixed stellar mass. We compare our results with the semi-analytic models of De Lucia & Blaizot, which include supernova feedback, as well as the cosmological infall of gas.

TYPE IIn SUPERNOVA SN 2010jl: OPTICAL OBSERVATIONS FOR OVER 500 DAYS AFTER EXPLOSION

We present extensive optical observations of a Type IIn supernova (SN IIn) 2010jl for the first 1.5 years after its discovery. The UBVRI light curves demonstrated an interesting two-stage evolution during the nebular phase, which almost flatten out after about 90 days from the optical maximum. SN 2010jl has one of the highest intrinsic Ha luminosities ever recorded for an SN IIn, especially at late phase, suggesting a strong interaction of SN ejecta with the dense circumstellar material (CSM) ejected by the progenitor. This is also indicated by the remarkably strong Balmer lines persisting in the optical spectra. One interesting spectral evolution about SN 2010jl is the appearance of asymmetry of the Balmer lines. These lines can be well decomposed into a narrow component and an intermediate-width component. The intermediate-width component showed a steady increase in both strength and blueshift with time until t similar to 400 days after maximum, but it became less blueshifted at t similar to 500 days, when the line profile appeared relatively symmetric again. Owing to the fact that a pure reddening effect will lead to a sudden decline of the light curves and a progressive blueshift of the spectral lines, we therefore propose that the asymmetric profiles of H lines seen in SN 2010jl are unlikely due to the extinction by newly formed dust inside the ejecta, contrary to the explanation by some early studies. Based on a simple CSM-interaction model, we speculate that the progenitor of SN 2010jl may suffer a gigantic mass loss (similar to 30-50 M-circle dot) a few decades before explosion. Considering a slow-moving stellar wind (e. g., similar to 28 km s(-1)) inferred for the preexisting, dense CSM shell and the extremely high mass-loss rate (1-2 M-circle dot yr(-1)), we suggest that the progenitor of SN 2010jl might have experienced a red supergiant stage and may explode finally as a post-red supergiant star with an initial mass above 30-40 M-circle dot.

The extended Baryon Oscillation Spectroscopic Survey: a cosmological forecast

We present a science forecast for the extended Baryon Oscillation Spectroscopic Survey (eBOSS) survey. Focusing on discrete tracers, we forecast the expected accuracy of the baryonic acoustic oscillation (BAO), the redshift-space distortion (RSD) measurements, the fNL parameter quantifying the primordial non-Gaussianity, the dark energy and modified gravity parameters. We also use the line-of-sight clustering in the Lyman a forest to constrain the total neutrino mass. We find that eBOSS luminous red galaxies, emission line galaxies and clustering quasars can achieve a precision of 1, 2.2 and 1.6 per cent, respectively, for spherically averaged BAO distance measurements. Using the same samples, the constraint on fob is expected to be 2.5, 3.3 and 2.8 per cent, respectively. For primordial non-Gaussianity, eBOSS alone can reach an accuracy of a (f(NL)) similar to 10-15. eBOSS can at most improve the dark energy figure of merit by a factor of 3 for the Chevallier-Polarski-Linder parametrization, and can well constrain three eigenmodes for the general equation-of-state parameter. eBOSS can also significantly improve constraints on modified gravity parameters by providing the RSD information, which is highly complementary to constraints obtained from weak lensing measurements. A principal component analysis shows that eBOSS can measure the eigenmodes of the effective Newtons constant to 2 per cent precision; this is a factor of 10 improvement over that achievable without eBOSS. Finally, we derive the eBOSS constraint (combined with Planck, Dark Energy Survey and BOSS) on the total neutrino mass, sigma (Em(upsilon)) = 0.03 eV (68 per cent CL), which in principle makes it possible to distinguish between the two scenarios of neutrino mass hierarchies.

The 0.1 <z < 1.65 evolution of the bright end of the [O ii] luminosity function

We present the [Oii] (λλ3729,3726) luminosity function measured in the redshift range 0.1 <z< 1.65 with unprecedented depth and accuracy. Our measurements are based on medium resolution flux-calibrated spectra of emission line galaxies with the visual and near UV FOcal Reducer and low dispersion Spectrograph (FORS2) for the Very Large Telescope (VLT) of the European Southern Observatory (ESO) and with the SDSS-III/BOSS spectrograph. The FORS2 spectra and the corresponding catalog containing redshifts and line fluxes are released along with this paper. In this work we use a novel method to combine these surveys with GAMA, zCOSMOS, and VVDS, which have different target selection, producing a consistent weighting scheme to derive the [Oii] luminosity function. The[Oii] luminosity function is in good agreement with previous independent estimates. The comparison with two state-of-the-art semi-analytical models is good, which is encouraging for the production of mock catalogs of [Oii] flux limited surveys. We observe the bright end evolution over 8.5 Gyr: we measure the decrease of log L∗ from 42.4 erg/s at redshift 1.44 to 41.2 at redshift 0.165 and we find that the faint end slope flattens when redshift decreases. This measurement confirms the feasibility of the target selection of future baryonic acoustic oscillation surveys aiming at observing [Oii] flux limited samples.

Sky Brightness and Transparency in the i-band at Dome A, Antarctica

The i-band observing conditions at Dome A on the Antarctic plateau have been investigated using data acquired during 2008 with the Chinese Small Telescope Array. The sky brightness, variations in atmospheric transparency, cloud cover, and the presence of aurorae are obtained from these images. The median sky brightness of moonless clear nights is 20.5 mag arcsec(-2) in the SDSS i band at the south celestial pole (which includes a contribution of about 0.06 mag from diffuse Galactic light). The median over all Moon phases in the Antarctic winter is about 19.8 mag arcsec(-2). There were no thick clouds in 2008. We model contributions of the Sun and the Moon to the sky background to obtain the relationship between the sky brightness and transparency. Aurorae are identified by comparing the observed sky brightness to the sky brightness expected from this model. About 2% of the images are affected by relatively strong aurorae.

A study on the orientation relationship between the scallop-type Cu6Sn5 grains and (011) Cu substrate using electron backscattered diffraction

The wetting reaction between molten Sn and (011) Cu single crystal was investigated. Based on the electron backscattered diffraction technique, the preferential orientation relationships between the scallop-type Cu6Sn5 grains and (011) Cu single crystals were detected. The strong texture of Cu6Sn5 grains was formed on the normal direction although the Sn/(011) Cu couple was aged at 170 °C for 40 days. This indicates that the Cu6Sn5 grains do not desultorily form on the (011) Cu substrate for these scallop-type Cu6Sn5 grains.

SDSS-IV eBOSS emission-line galaxy pilot survey

The Sloan Digital Sky Survey IV extended Baryonic Oscillation Spectroscopic Survey (SDSS-IV/eBOSS) will observe 195 000 emission-line galaxies (ELGs) to measure the baryonic acoustic oscillation (BAO) standard ruler at redshift 0.9. To test different ELG selection algorithms, 9000 spectra were observed with the SDSS spectrograph as a pilot survey based on data from several imaging surveys. First, using visual inspection and redshift quality flags, we show that the automated spectroscopic redshifts assigned by the pipeline meet the quality requirements for a reliable BAO measurement. We also show the correlations between sky emission, signal-to-noise ratio in the emission lines, and redshift error. Then we provide a detailed description of each target selection algorithm we tested and compare them with the requirements of the eBOSS experiment. As a result, we provide reliable redshift distributions for the different target selection schemes we tested. Finally, we determine an target selection algorithms that is best suited to be applied on DECam photometry because they fulfill the eBOSS survey efficiency requirements.

The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: selecting emission line galaxies using the Fisher discriminant

We present a new selection technique to produce spectroscopic target catalogues for massive spectroscopic surveys for cosmology. This work was conducted in the context of the extended Baryon Oscillation Spectroscopic Survey (eBOSS), which will use∼200,000 emission line galaxies (ELGs) at 0.6 ≤ zspec ≤ 1.0 to obtain a precise Baryonic Acoustic Oscillation measurement. Our proposed selection technique is based on optical and near-infrared broad-band filter photometry. We use a training sample to defin e a quantity, the Fisher discriminant (linear combination of colours), which correlates best with the desired properties of the targ et: redshift and [Oii] flux. The proposed selections are simply done by applying a c ut on magnitudes and this Fisher discriminant. We used public data and dedicated SDSS spectroscopy to quantify the redshift distribution and [Oii] flux of our ELG target selections. We demonstrate that two of our selections fulfill the initial eBOSS /ELG redshift requirements: for a target density of 180 deg −2 ,∼70% of the selected objects have 0.6 ≤ zspec ≤ 1.0 and only∼1% of those galaxies in the range 0.6 ≤ zspec ≤ 1.0 are expected to have a catastrophic zspec estimate. Additionnaly, the stacked spectra and stacked deep images for those two selections show characteristic features of star-forming galaxies. The proposed approach using Fisher discriminant could however be used to effi ciently select other galaxy populations, based on multi-band photometry, providing that spectroscopic information is available. This technique could thus be useful for other future massive spectroscopic surveys such as PFS, DESI, and 4MOST.

Estimation of absolute magnitude-dependent Galactic model parameters in intermediate latitude with SDSS and SCUSS

Based on the Sloan Digital Sky Survey and South Galactic Cap of u-band Sky Survey (SCUSS) early data, we use a star count method to estimate the Galactic structure parameters in an intermediate latitude with 10 180 main-sequence (MS) stars in an absolute magnitude interval of 4 <= M-r <= 13. We divide the absolute magnitude into five intervals, 4 <= M-r < 5, 5 <= M-r < 6, 6 <= M-r < 8, 8 <= M-r < 10 and 10 <= M-r <= 13, and estimate the Galactic structure parameters in each absolute magnitude interval to explore their possible variation with the absolute magnitude. Our study shows that the parameters depend on absolute magnitude. For the thin disc, the intrinsic faint MS stars have large local space density and they tend to stay close to the Galactic plane. A plausible explanation is that faint MS stars with long lifetime experience and long gravitational interaction time result in a short scaleheight. However, for the thick disc, the parameters show a complex trend with absolute magnitude, which may imply the complicated original of the thick disc. For the halo, the intrinsic faint MS stars have large local density and small axial ratio, which indicate a flattened inner halo and a more spherical outer halo.

SOUTH GALACTIC CAP u-BAND SKY SURVEY (SCUSS): DATA REDUCTION

The South Galactic Cap u-band Sky Survey (SCUSS) is a deep u-band imaging survey in the Southern Galactic Cap, using the 90Prime wide-field imager on the 2.3 Bok telescope at Kitt Peak. The survey observations started in 2010 and ended in 2013. The final survey area is about 5000 deg(2) with a median 5s point source limiting magnitude of similar to 23.2. This paper describes the survey data reduction process, which includes basic imaging processing, astrometric and photometric calibrations, image stacking, and photometric measurements. Survey photometry is performed on objects detected both on SCUSS u-band images and in the SDSS database. Automatic, aperture, point-spread function (PSF), and model magnitudes are measured on stacked images. Co-added aperture, PSF, and model magnitudes are derived from measurements on single-epoch images. We also present comparisons of the SCUSS photometric catalog with those of the SDSS and Canada-France-Hawaii Telescope Legacy surveys.