Publications (7)6.02 Total impact
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Article: The growth of the disk galaxy UGC8802
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ABSTRACT: The disk galaxy UGC8802 has high neutral gas content and a flat profile of star formation rate compared to other disk galaxies with similar stellar mass. It also shows a steep metallicity gradient. We construct a chemical evolution model to explore its growth history by assuming its disk grows gradually from continuous gas infall, which is shaped by a free parameter -- the infall-peak time. By adopting the recently observed molecular surface density related star formation law, we show that a late infall-peak time can naturally explain the observed high neutral gas content, while an inside-out disk formation scenario can fairly reproduce the steep oxygen abundance gradient. Our results show that most of the observed features of UGC8802 can be well reproduced by simply `turning the knob' on gas inflow with one single parameter, which implies that the observed properties of gas-rich galaxies could also be modelled in a similar way.06/2012; -
Article: Milky Way vs Andromeda: a tale of two disks
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ABSTRACT: We study the chemical evolution of the disks of the Milky Way (MW) and of Andromeda (M31), in order to reveal common points and differences between the two major galaxies of the Local group. We use a large set of observational data for M31, including recent observations of the Star Formation Rate (SFR) and gas profiles, as well as stellar metallicity distributions along its disk. We show that, when expressed in terms of the corresponding disk scale lengths, the observed radial profiles of MW and M31 exhibit interesting similarities, suggesting the possibility of a description within a common framework. We find that the profiles of stars, gas fraction and metallicity of the two galaxies, as well as most of their global properties, are well described by our model, provided the star formation efficiency in M31 disk is twice as large as in the MW. We show that the star formation rate profile of M31 cannot be fitted with any form of the Kennicutt-Schmidt law (KS Law) for star formation. We attribute those discrepancies to the fact that M31 has undergone a more active star formation history, even in the recent past, as suggested by observations of a "head-on" collision with the neighboring M32 galaxy about 200 Myr ago. The MW has most probably undergone a quiescent secular evolution, making possible a fairly successful description with a simple model. If M31 is more typical of spiral galaxies, as recently suggested by Hammer et al. (2007), more complex models, involving galaxy interactions, will be required for the description of spirals. Comment: 13 Pages, 7 figures, 2 tables, accepted for publication in Astronomy and Astrophysics06/2009; -
Article: The color gradients of spiral disks in the Sloan Digital Sky Survey
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ABSTRACT: We investigate the radial color gradients of galactic disks using a sample of about 20,000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentration, size and luminosity to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R_{50}<3 kpc), almost all galaxies show negative disk color gradients with mean g-r gradient G_{gr}=-0.006 mag kpc^{-1} and r-z gradient G_{rz}=-0.018 mag kpc^{-1}. The disk color gradients are independent of the morphological types of galaxies and strongly dependent on the disk surface brightness \mu_{d}, with lower surface brightness galactic disks having steeper color gradients. We quantify the intrinsic correlation between color gradients and surface brightness as G_{gr}=-0.011\mu_{d}+0.233 and G_{rz}=-0.015\mu_{d}+0.324. These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies. Comment: 20 pages, 5 figures, Accepted for publication in RAA (Research in Astronomy and Astrophysics)05/2009; -
Article: Metallicity and H I Column Density Properties of Damped Lyα Systems
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ABSTRACT: On the basis of the disk galaxy formation theory within the framework of the standard ΛCDM hierarchical picture (Mo, Mao, & White), we selected modeled damped Lyα systems (DLAs), according to their observational criterion N 1020.3 cm-2 by Monte Carlo simulation using random inclinations to examine their observed properties. By best-fitting the predicted metallicity distribution to the observed ones, we get an effective yield of about 0.25 Z☉ for DLAs, which is comparable to those for the SMC and LMC. And the predicted distribution is the same as that of the observations at a significance level of higher than 60%. The predicted column density distribution of modeled DLAs is compared with the observed ones with the corresponding number density, with a discussion of the gas content. We found that the predicted number density n(z) at redshift 3 agrees well with the observed value, but the gas content ΩDLA is about 3 times larger than that observed, since our model predicts more DLAs with higher column density. It should be noted that the predicted star formation rate density contributed by DLAs is consistent with the most recent observations if the star formation timescale in DLAs is assumed to be 1-3 Gyr. Meanwhile, the connection between DLAs and Lyman break galaxies (LBGs) is discussed by comparing their UV luminosity functions, which shows that the DLAs' host galaxies are much fainter than LBGs. We also predict that only a few percent of DLAs can host LBGs, which is also consistent with current observations. However, there is a discrepancy between model prediction and observation in the correlation between metallicity and H I column density for DLAs. We suggest that this could result from either the inadequacy of a Schmidt-type star formation law at high redshift, the diversities of DLA populations, or the model limitations. Although our current simple model cannot fully reproduce the observed DLA velocity distribution, we argue that this kind of model can still provide valuable information about the nature of DLAs.The Astrophysical Journal 12/2008; 624(2):561. · 6.02 Impact Factor -
Article: Star Formation and Chemical Evolution of DLAs with Semi-Analytical Model
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ABSTRACT: We have examined some basic properties of damped Ly$\alpha$ systems(DLAs) by semi-analytic model. We assume that DLA hosts are disk galaxies whose mass function is generated by Press-Schechter formulism at redshift 3. Star formation and chemical evolution undergo in the disc. We select modelled DLAs according to their observational criterion by Monte Carlo simulation using random line of sights and disk inclinations. The DLA ages are set to be 1 to 3 Gyr. By best-fitting the predicted metallicity distribution to the observed ones, we get the effective yield for DLAs about $0.25Z_{\odot}$. On the basis of this constrain, we further compared our model predictions with observations at redshift 3 in the following items: number density; gas content; HI frequency distribution; star formation rate density; relationship between metallicity and HI column density. We found that the predicted number density at redshift 3 agree well with the observed value, but the gas content $\Omega_{DLA}$ is about 3 times larger than observed since our model predicts more DLA systems with higher column density. The frequency distribution at higher HI column density is quite consistent with observation while some difference exists at lower HI end. The predicted star formation rate density contributed by DLAs is consistent with the most recent observations. Meanwhile, the connection between DLAs and Lyman Break galaxies(LBGs) is discussed by comparing their UV luminosity functions which shows that the DLAs host galaxies are much fainter than LBGs. However, there is a discrepancy between model prediction and observation in the correlation between metallicity and HI column density for DLAs. Further investigations are needed for the star formation mode at high redshift environments.06/2005; -
Article: Metallicity and HI Column Density Properties of Damped Lyman-$\alpha$ Systems
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ABSTRACT: Based on the disk galaxy formation theory within the framework of standard LCDM hierarchical picture, we selected modelled DLAs, according to their observational criterion, by Monte Carlo simulation with the random inclinations being considered, to examine their observed properties. By best-fitting the predicted metallicity distribution to the observed ones, we get the effective yield for DLAs about 0.25Z_sun, which is comparable to those for SMC and LMC. And the predicted distribution is the same as that of observation at the significant level higher than 60%. The predicted column density distribution of modelled DLAs is compared with the observed ones with the corresponding number density, gas content being discussed. We found that the predicted number density n(z) at redshift 3 agree well with the observed value, but the gas content \Omega_DLA is about 3 times larger than observed since our model predicts more DLA systems with higher column density. It should be noted that the predicted star formation rate density contributed by DLAs is consistent with the most recent observations if the star formation timescale in DLAs is assumed to be 1 to 3 Gyr. Meanwhile, the connection between DLAs and LBGs is discussed by comparing their UV luminosity functions which shows that the DLAs host galaxies are much fainter than LBGs. We also predict that only few percent of DLAs can host LBGs which is also consistent with current observations. However, there is a discrepancy between model prediction and observation in the correlation between metallicity and HI column density for DLAs. We suggest that this could result from either the inadequacy of Schmidt-type star formation law at high redshift, the diversities of DLA populations, or the model limitations.02/2005; -
Article: The fundamental plane of spiral galaxies: theoretical expectations
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ABSTRACT: Current theory of disc galaxy formation is used to study fundamental-plane (FP) type of relations for disc galaxies. We examine how the changes in model parameters affect these relations and explore the possibility of using such relations to constrain theoretical models. The distribution of galaxy discs in the space of their fundamental properties are predicted to be concentrated in a plane, with the Tully-Fisher (TF) relation (a relation between luminosity L and maximum rotation velocity V-m) being an almost edge-on view. Using rotation velocities at larger radii generally leads to larger TF scatter. In searching for a third parameter, we find that both the disc scalelength R-d (or surface brightness) and the rotation-curve shape are correlated with the TF scatter. The FP relation in the (log L, log V-m, log R-d)-space obtained from the theory is L proportional to R-d(alpha') V-m(beta'), with alpha' similar to 0.50 and beta' similar to 2.60, consistent with the preliminary result we obtain from observational data. Using the isophotal radius instead of R-d leads to higher alpha', lower beta' and smaller scatter. Among the model parameters we probe, variation in any of them can generate significant scatter in the TF relation, but the effects of the spin parameter and halo concentration can be reduced significantly by introducing R-d While the scatter caused by varying m(d) (the ratio between disc mass and halo mass) is most effectively reduced by introducing the parameters which describe the rotation-curve shape. The TF and FP relations combined should therefore provide useful constraints on models of galaxy formation.Monthly Notices of the Royal Astronomical Society, v.331, 259-272 (2002).
