Engineering topics

Xinfa, Deng

Publications and source records attributed to Xinfa, Deng.

7 records

DOE OSTI2013

A COMPARISON OF THE CLUSTERING PROPERTIES BETWEEN GALAXIES AND GROUPS OF GALAXIES

In this study, I apply cluster analysis and perform comparative studies of clustering properties between galaxies and groups of galaxies. It is found that the number of objects N{sub max} of the richest system and the maximal length D{sub max} of the largest system for groups in all samples are apparently larger than ones for galaxies, and that galaxies preferentially form isolated, paired, and small systems, while groups preferentially form grouped and clustered systems. These results show that groups are more strongly clustered than galaxies, which is consistent with statistical results of the correlation function.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

CORRELATION BETWEEN GROUP LOCAL DENSITY AND GROUP LUMINOSITY

In this study, we investigate the correlation between group local number density and total luminosity of groups. In four volume-limited group catalogs, we can conclude that groups with high luminosity exist preferentially in high-density regions, while groups with low luminosity are located preferentially in low-density regions, and that in a volume-limited group sample with absolute magnitude limit M{sub r} = -18, the correlation between group local number density and total luminosity of groups is the weakest. These results basically are consistent with the environmental dependence of galaxy luminosity.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

SOME PROPERTIES OF ACTIVE GALACTIC NUCLEI IN THE VOLUME-LIMITED MAIN GALAXY SAMPLES OF SDSS DR8

Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 8 above and below the value of M*{sub r}, we have explored some properties of AGNs. In the luminous volume-limited sample, 9.5% is composite galaxies (C) and 5.0% AGNs, while in the faint volume-limited sample, these fractions are 7.2% and 2.9%, respectively. The C and AGN fractions increase with luminosity. We also note that the fraction of star-forming galaxies decreases with luminosity, but the fraction of low signal-to-noise star-forming galaxies slightly increases with luminosity. In two volume-limited samples, the fraction of star-forming galaxies decreases with density, while the AGN fraction is nearly insensitive to the local environment. If composite galaxies (C) are classified as AGNs, then the fraction of AGNs in the luminous volume-limited sample declines with increasing local density. When focusing on some properties of AGN host galaxies, we find that galaxies hosting AGNs are preferentially more massive and have high concentration indices. In the faint volume-limited sample, AGN host galaxies preferentially have low star formation rates (SFRs) and specific SFRs (SSFRs). However, in the luminous volume-limited sample, AGN host galaxies preferentially have moderate SFRs and SSFRs.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

ENVIRONMENTAL DEPENDENCE OF THE STAR FORMATION RATE, SPECIFIC STAR FORMATION RATE, AND THE PRESENCE OF ACTIVE GALACTIC NUCLEI FOR HIGH STELLAR MASS AND LOW STELLAR MASS GALAXIES

Using two volume-limited main galaxy samples of the Sloan Digital Sky Survey Data Release 8 (SDSS DR8), we explore the environmental dependence of the star formation rate (SFR), specific star formation rate (SSFR), and the presence of active galactic nuclei (AGNs) for high stellar mass (HSM) and low stellar mass (LSM) galaxies. It is found that the environmental dependence of the SFR and SSFR for luminous HSM galaxies and faint LSM ones remains very strong: galaxies in the lowest density regime preferentially have higher SFR and SSFR than galaxies in the densest regime, while the environmental dependence of the SFR and SSFR for luminous LSM galaxies is substantially reduced. Our result also shows that the fraction of AGNs in HSM galaxies decreases as a function of density, while the one in LSM galaxies depends very little on local density. In the faint LSM galaxy sample, the SFR and SSFR of galaxies strongly decrease with increasing density, but the fraction of AGNs depends very little on local density. Such a result can rule out that AGNs are fueled by the cold gas in the disk component of galaxies that is also driving the star formation of those galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

ENVIRONMENTAL DEPENDENCE OF ALL OF THE FIVE-BAND LUMINOSITIES FOR THE APPARENT-MAGNITUDE-LIMITED MAIN GALAXY SAMPLE OF THE SDSS DR7

In this study, I use the apparent-magnitude-limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 7 and investigate the environmental dependence of all of the five-band luminosities. To decrease the radial selection effect, I divide the whole sample into many subsamples with a redshift binning size of {Delta}z = 0.01 and analyze the environmental dependence of all of the five-band luminosities of subsamples in each redshift bin. It turns out that luminous galaxies in M{sub u} (the u-band absolute magnitude) exist preferentially in low-density regions of the universe, while faint galaxies in M{sub u} are located preferentially in high-density regions, especially in the redshift range 0.05 {<=} z {<=} 0.10.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

CORRELATION BETWEEN ENVIRONMENT AND GAS METALLICITY FOR STAR-FORMING GALAXIES IN THE MAIN GALAXY SAMPLE OF SDSS DR7

Using two volume-limited samples of the Main Galaxy sample of the Sloan Digital Sky Survey Data Release 7 with luminosities of -20.5 {<=} M{sub r} {<=} -18.5 and -22.5 {<=} M{sub r} {<=} -20.5, respectively, I explore the correlation between environment and gas metallicity for star-forming galaxies. Overall, results indicate that galaxies in the lowest density regime preferentially have lower gas metallicity than galaxies in the densest regimes, and that the correlation between environment and gas metallicity is fundamental.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

ENVIRONMENTAL DEPENDENCE OF THE STAR FORMATION RATE AND THE SPECIFIC STAR FORMATION RATE AT FIXED MORPHOLOGY

From the Main galaxy sample of the Sloan Digital Sky Survey Data Release 7, I construct two volume-limited samples with luminosities -20.5 {<=} M{sub r} {<=} -18.5 and -22.5{<=}M{sub r} {<=}-20.5, respectively, to explore the environmental dependence of the star formation rate (SFR) and the specific star formation rate (SSFR) at fixed morphology. It is found that in these two volume-limited samples, galaxies in the lowest density regime preferentially have higher SFR and SSFR than galaxies in the densest regime. I divide each volume-limited Main galaxy sample into two distinct populations, the early type and the late type, and observe that the environmental dependence of the SFR and SSFR of galaxies remains true at fixed morphology: the SFR and SSFR of galaxies in the densest regime is still preferentially lower than that of the ones in the lowest density regime with the same morphological type. I also note that the environmental dependence of the SFR and SSFR of late-type galaxies is stronger than that of early-type galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗