arXiv subjects

L. C. Deng

Publications and source records attributed to L. C. Deng.

22 records · Page 2Linked to original sources

arXiv2006

The oxygen abundance calibrations and N/O abundance ratios of ~40,000 SDSS star-forming galaxies

Using a large sample of 38,478 star-forming galaxies selected from the Second Data Release of the Sloan Digital Sky Survey database (SDSS-DR2), we derive analytical calibrations for oxygen abundances from several metallicity-sensitive emission-line ratios: [N II]/H_alpha, [O III]/[N II], [N II]/[O II], [N II]/[S II], [S II]/H_alpha, and [O III]/H_beta. This consistent set of strong-line oxygen abundance calibrations will be useful for future abundance studies. Among these calibrations, [N II]/[O II] is the best for metal-rich galaxies due to its independence on ionization parameter and low scatter. Dust extinction must be considered properly at first. These calibrations are more suitable for metal-rich galaxies (8.4<12+log(O/H)<9.3), and for the nuclear regions of galaxies. The observed relations are consistent with those expected from the photoionization models of Kewley & Dopita (2002). However, most of the observational data spread in a range of ionization parameter q from 1*10^7 to 8*10^7 cm s^{-1}, corresponding to logU= -3.5 to -2.5, narrower than that suggested by the models. We also estimate the (N/O) abundance ratios of this large sample of galaxies, and these are consistent with the combination of a "primary" and a dominant "secondary" components of nitrogen.

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arXiv2006

The asymmetric structure of the Galactic halo

Using the stellar photometry catalogue based on the latest data release (DR4) of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using star counts is carried out for selected areas of the sky. The sample areas are selected along a circle at a Galactic latitude of +60$^\circ$, and 10 strips of high Galactic latitude along different longitudes. Direct statistics of the data show that the surface densities of $\ell$ from $180^{\circ}$ to $360^{\circ}$ are systematically higher than those of $\ell$ from $0^{\circ}$ to $180^{\circ}$, defining a region of overdensity (in the direction of Virgo) and another one of underdensity (in the direction of Ursa Major) with respect to an axisymmetric model. It is shown by comparing the results from star counts in the $(g-r)$ colour that the density deviations are due to an asymmetry of the stellar density in the halo. Theoretical models for the surface density profile are built and star counts are performed using a triaxial halo of which the parameters are constrained by observational data. Two possible reasons for the asymmetric structure are discussed.

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arXiv2005

Multiwavelength Observations of one Galaxy in Marano Field

We report the multiwavelength observations of one intermediate redshift (z=0.3884) galaxy in the Marano Field. These data include ISOCAM middle infrared, VLT/FORS2 spectroscopic and photometric data, associated with the ATCA 1.4 GHz radio and ROSAT PSPC X-ray observations from literature. The Spectral Energy Distribution obtained by VLT spectroscopy exhibits its early-type galaxy property, while, in the same time, it has obvious [OIII]5007 emission line. The diagnostic diagram from the optical emission line ratios shows its Seyfert galaxy property. Its infrared-radio relation follows the correlation of sources detected at 15 μand radio. It has a high X-ray luminosity of 1.26*10^{43} ergs/s, which is much higher than the general elliptical galaxies s with the similar B band luminosity, and is about 2 orders of magnitude higher than the derived value from the star forming tracer, the FIR luminosity. This means that the X-ray sources of this galaxy are not stellar components, but the AGN is the dominant component.

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arXiv2001

Metallicity distribution of halo stars and minor merger processes of the Galaxy

A possible relation between the high dispersion in metallicity of metal-poor halo stars and the minor merger processes in the history of the Galaxy is presented. The foreign populations of stars in the satellites through minor merger processes, make considerable contributions to the Galactic halo, therefore alter the intrinsic distribution of metallicities of the halo stars. Our model reproduces the observed trends in the metallicity distribution of the extremely metal-poor halo field stars in the Galaxy. Taken all the parameters for our model, a density of $1.9\times 10^{-3}kpc^{-3}$ of extremely metal-poor halo stars in $-5<[Fe/H]<-4$ is predicted, which explains why no such stars have been observed so far.

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