Zhengyi Shao

Inclination-dependent Luminosity Function of Spiral Galaxies in the Sloan Digital Sky Survey: Implications for Dust Extinction

Using a samples of 61506 spiral galaxies selected from the SDSS DR2, we examine the luminosity function (LF) of spiral galaxies with different inclination angles. We find that the characteristic luminosity of the LF, L � , decreases with increasing inclination, while the faint-end slope, α, depends only weakly on it. The inclination-dependence of the LF is consistent with that expected from a simple model where the optical depth is proportional to the cosine of the inclination angle, and we use a likelihood method to recover both the coefficient in front ofthe cosine, γ, and the LF for galaxies viewed face-on. The value of γ is quite independent of galaxy luminosity in a given band, and the values of γ obtained in this way for the 5 SDSS bands give an extinction curve which is a power law of wavelength (τ ∝ λ n ), with a power index n = 0.96 ± 0.04. Using the dust extinction for galaxies obtained by Kauffmann et al. (2003), we derive an ‘extinction-corrected’ luminosity function

THE NEAREST HIGH-VELOCITY STARS REVEALED BY LAMOST DATA RELEASE 1

We report the discovery of 28 candidate high-velocity stars (HVSs) at heliocentric distances of less than 3 kpc, based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 1. Our sample of HVS candidates covers a much broader color range than the equivalent ranges discussed in previous studies and comprises the first and largest sample of HVSs in the immediate solar neighborhood, at heliocentric distances less than 1-3 kpc. The observed as well as the derived parameters for all candidates are sufficiently accurate to allow us to ascertain their nature as genuine HVSs, of which a subset of 12 objects represents the most promising candidates. Our results also highlight the great potential of discovering statistically large numbers of HVSs of different spectral types in LAMOST survey data. This will ultimately enable us to achieve a better understanding of the nature of Galactic HVSs and their ejection mechanisms, and to constrain the structure of the Galaxy.

THE ORIENTATION OF THE NUCLEAR OBSCURER OF THE ACTIVE GALACTIC NUCLEI

We examine the distribution of axis ratios of a large sample of disk galaxies hosting type 2 active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey and compare it with a well-defined control sample of non-active galaxies. We find them significantly different, where the type 2 AGNs show both an excess of edge-on objects and deficit of round objects. This systematical bias cannot be explained by a nuclear obscurer oriented randomly with respect to the stellar disk. However, a nuclear obscurer coplanar with the stellar disk also does not fit the data very well. By assuming that the nuclear obscurer having an opening angle of similar to 60 degrees, we find that the observed axis ratio distribution can be nicely reproduced by a mean tilt angle of similar to 30 degrees between the nuclear obscurer and the stellar disk.

Colour–magnitude relations of late-type galaxies

We use a large sample of galaxies drawn from the Sloan Digital Sky Survey (SDSS) and Two-Micron All-Sky Survey (2MASS) to present colour-magnitude relations (CMRs) for late-type galaxies in both optical and optical-infrared (optical-IR) bands. A sample from SDSS Data Release 4 (DR4) is selected to investigate the optical properties. Optical-IR colours are estimated from a position matched sample of DR4 and the 2MASS, in which the photometric aperture mismatch between these two surveys is carefully corrected. It is shown that, after correcting the dust attenuation, the optical colours for faint galaxies (i.e.M-r > -21) have a very weak correlation with the luminosity, whereas the optical colours for bright galaxies (i.e. M-r < -21) are redder than those for more-luminous galaxies. All (optical, optical-IR and IR) colours show similar but stronger correlations with stellar mass than with absolute magnitude. The optical colours correlate more strongly with stellar mass surface density than with stellar mass, whereas optical-IR and IR colours show stronger correlations with stellar mass. By comparing the observed colours of our sample galaxies with the colours predicted by stellar population synthesis model, we find that massive late-type galaxies have older and higher-metallicity stellar population than that of less-massive galaxies. This suggests that CMRs for late-type galaxies are trends defined by the combination of stellar mean age and metallicity. Moreover, our results suggest that the stellar mean metallicity of late-type galaxy is mainly determined by its stellar mass, whereas the star formation history is mainly regulated by the stellar mass surface density.

New Estimates of the Inclination, Position Angle, Pitch Angle, and Scale Height of the Whirlpool Galaxy

The inclination (i) and position angle (PA) of the Whirlpool galaxy (M51) are critical to modeling and interpreting observations. Here we make improved estimates of these parameters by fitting logarithmic spirals to the main arms. From separate fits to each major arm, we obtain i = 203 ± 28 and PA = 120 ± 25. We then use Poissons equation for the logarithmic perturbation of the density to estimate the mean vertical scale height (H) of M51 to be 95-178 pc.

Selecting M Giants with Infrared Photometry: Distances, Metallicities, and the Sagittarius Stream

Using a spectroscopically confirmed sample of M giants, M dwarfs, and quasars from the LAMOST survey, we assess how well Wide-field Infrared Survey Explorer (WISE) and Two Micron All Sky Survey color cuts can be used to select M giant stars. The WISE bands are very efficient at separating M giants from M dwarfs, and we present a simple classification that can produce a clean and relatively complete sample of M giants. We derive a new photometric relation to estimate the metallicity for M giants, calibrated using data from the APOGEE survey. We find a strong correlation between the (W1-W2) color and [{{M}}/{{H}}], where almost all of the scatter is due to photometric uncertainties. We show that previous photometric distance relations, which are mostly based on stellar models, may be biased and devise a new empirical distance relation, investigating trends with metallicity and star formation history. Given these relations, we investigate the properties of M giants in the Sagittarius stream. The offset in the orbital plane between the leading and trailing tails is reproduced, and by identifying distant M giants in the direction of the Galactic anticenter, we confirm that the previously detected debris in the outer halo is the apocenter of the trailing tail. We also find tentative evidence supporting an existing overdensity near the leading tail in the northern Galactic hemisphere, possibly an extension to the trailing tail (so-called Branch C). We have measured the metallicity distribution along the stream, finding a clear metallicity offset between the leading and trailing tails, in agreement with models for the stream formation. We include an online table of M giants to facilitate further studies.

AN APPARENT REDSHIFT DEPENDENCE OF QUASAR CONTINUUM: IMPLICATION FOR COSMIC DUST EXTINCTION?

We investigate the luminosity and redshift dependence of the quasar continuum by means of composite spectrum using a large non-BAL radio-quiet quasar sample drawn from the Sloan Digital Sky Survey. Quasar continuum slopes in the UV-Opt band are measured at two different wavelength ranges, i.e.,

THE MORPHOLOGICAL-DEPENDENT TULLY-FISHER RELATION OF SPIRAL GALAXIES

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THE LUMINOSITY DEPENDENCE OF QUASAR UV CONTINUUM SLOPE: DUST EXTINCTION SCENARIO

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Candidate members of star clusters from LAMOST DR2

1000\sim 2000 \rm\AA