The physical properties of galaxies with unusually high gas-phase metallicity

We use 1221 galaxies with unusually high gas-phase metallicity to study their physical properties.The scope of redshift is 0.02 < z < 0.25 for these galaxies with unusually high gas-phase metallicity.Our goal is to understand the physical origins of the high gas-phase metallicity.To address this study,we select a control sample matching similar redshift and stellar mass.Our main results are as follows.(i) Compared with the control sample,the high-metallicity sample shows lower ionization parameter,higher electron density and more dust content.(ii) We also find that the high-metallicity sample has older stellar age and higher [Mgb/] ratio,which indicates that the high-metallicity sample has shorter timescale of star formation.(iii) According to the plane of Hδ_A vs.D_n4000,we can see that the control sample has higher HδAand lower D_n4000 than the high-metallicity sample,which may imply that the control sample experiences recent star formation.(iv) There is a significant difference in gas distribution between the highmetallicity and control samples.The high-metallicity sample has lower gas fraction than control sample,which indicates that galaxies have high gas-phase metallicity probably due to their low HI gas fraction.(v) There is no significant difference between the high-metallicity and control samples in environment,which may suggest that the environment has no effect on gas-phase metallicity.

The morphology, kinematics and metallicity of blue-core galaxies

We select 107 blue-core galaxies from the MaNGA survey, studying their morphology, kinematics as well as the gas-phase metallicity. Our results are as follows:(i) In our sample, 26% of blue-core galaxies have decoupled gas-star kinematics, indicating external gas accretion;15% have bar-like structure and 8% show post-merger features, such as tidal tails and irregular gas/star velocity field. All these processes/features, such as accreting external misaligned gas, interaction and bar, can trigger gas inflow. Thus the central star-forming activities lead to bluer colors in their centers(blue-core galaxies).(ii) By comparing with the SDSS DR7 star-forming galaxy sample, we find that the blue-core galaxies have higher central gas-phase metallicity than what is predicted by the local mass-metallicity relation. We explore the origin of the higher metallicity, finding that not only the blue-core galaxies, but also the flat-gradient and red-core galaxies all have higher metallicity. This can be explained by the combined effect of redshift and galaxy color.

Variation of physical properties across the green valley for local galaxies

We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is limited to a narrow range in the color-stellar mass diagram. After splitting green valley galaxies into two parts—a bluer green valley(green 1) and a redder one(green 2) and three stellar mass bins,we investigate the variation of physical properties across the green valley region. Our main results are as follows:(i) The percentages of pure bulge and bulge-dominated/elliptical galaxies increase gradually from blue cloud to red sequence while the percentages of pure disk and disk-dominated/spiral galaxies decrease gradually in all stellar mass bins and different environments.(ii) With the analysis of morphological and structural parameters(e.g., concentration(C) and the stellar mass surface density within the central 1 kpc(Σ1)), red galaxies show more luminous and compact cores than both green valley and blue galaxies, while blue galaxies show the opposite behavior in all stellar mass bins.(iii) A strong negative(positive) relationship between bulge-to-total light ratio(B/T) and specific star formation rate(sSFR)(D_(4000)) is found from blue to red galaxies. Our results indicate that the growth in bulge plays an important role when the galaxies change from the blue cloud, to the green valley and to the red sequence.

The Variability of the Narrow-line Seyfert 1 Galaxies from the Pan-STARRS's View

By means of the data sets from the Pan-STARRS1 survey, we have systematically examined the relationship between the variability characteristics and the physical parameters of the largest NLS1 galaxy sample up to now.The results are summarized as follows:(1). We find significant anti-correlations between variability amplitude and absolute magnitude in g, r, i, z and y bands, which are consistent with the results in previous works.(2) The correlations between the variability amplitude in optical band and many physical parameters(e.g., λL(5100 A),black hole mass, Eddington ratio, R;and R;) are investigated. The results show the variability amplitude is significantly anti-correlated with L(5100 A), MBH, Eddington ratio and R_(4570), but positively correlated with R;.The relation could be explained by the simple standard accretion disk model.(3) We further investigate the relationship between optical variability and radio luminosity/radio-loudness. The results present weak positive correlation in g and r bands, but insignificant correlation in i, z and y bands. The large error of the approximate fraction of the host galaxy in i, z and y bands may lead to insignificant correlations.

The beaming effect and γ-ray emission for Fermi blazars

We study the γ-ray luminosity and beaming effect for Fermi blazars.Our results are as follows.（i） There are significant correlations between γ-ray luminosity and radio core luminosity,and between γ-ray luminosity and R_v,which suggests that the γ-ray emissions have a strong beaming effect,（ⅱ） Using the L_（ext）/M_（abs） as an indicator of environment effects,we find that there is no significant correlation betweenγ-ray luminosity and L_（ext）/M_（abs） for all sources when we remove the effect of redshift.Flat spectrum radio quasars considered alone also do not show a significant correlation,but BL Lacertae objects（BL Lacs） still show a significant correlation when we remove the effect of redshift.These results suggest that the γ-ray emission may be affected by the environment on a kiloparsec scale for BL Lacs.