arXiv subjects

Qiu-Sheng Gu

Publications and source records attributed to Qiu-Sheng Gu.

22 records · Page 2Linked to original sources

arXiv2010

IRAS F13308+5946: A Possible Transition Phase From Type I ULIRG To Optical Quasar

We present a stellar population synthesis study of a type I luminous infrared galaxy (LIRG): IRAS F13308+5946. It is a quasar with absolute magnitude Mi = -22.56 and has a spectral feature of a Seyfert 1.5 galaxy. Optical images show characteristics of later stages of a merger. With the help of the stellar synthesis code STARLIGHT (Cid Fernandes et al. 2005) and both Calzetti et al. (2000) and Leitherer et al.'s (2002) extinction curves, we estimate the past infrared (IR) luminosities of the host galaxy and find it may have experienced an ultraluminous infrared galaxy (ULIRG) phase for nearly 300 Myr, so this galaxy has probably experienced a type I ULIRG phase. Both nuclear starburst and active galactic nuclei (AGN) contribute to the present IR luminosity budget, and starburst contributes ~70%. The mass of supermassive black-hole (SMBH) is M_BH = 1.8*10^8 M_sun and the Eddington ratio L_bol/L_Edd is 0.12, which both approximate to typical values of PG QSOs. These results indicate that IRAS F13308+5946 is probably at the transitional phase from a type I ULIRG to a classical QSO.

astro-ph.CO↗

arXiv2009

Recent Star-Forming Activity in Local Elliptical Galaxies

The formation and evolution of elliptical galaxies (EGs) is still an open question. In particular, recent observations suggest that elliptical galaxies are not only simple spheroidal systems of old stars. In this paper we analyze a sample of elliptical galaxies selected from the Sloan Digital Sky Survey in order to study the star-forming activity in local elliptical galaxies. Among these 487 ellipticals we find that 13 EGs show unambiguous evidence of recent star-formation activity betrayed by conspicuous nebular emission lines. Using the evolutionary stellar population synthesis models and Lick absorption line indices we derive stellar ages, metallicities, and $α$-element abundances, and thus reconstruct the star formation and chemical evolution history of the star-forming elliptical galaxies (SFEGs) in our sample. We find that SFEGs have relative younger stellar population age, higher metallicity, and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, $α$ element abundance, and stellar mass for local elliptical galaxies.

astro-ph.GA↗

arXiv2008

A note on black hole masses estimated by the second moment in Narrow Line Seyfert 1 Galaxies

The second moment of the H$β$ emission line is calculated for 329 narrow line Seyfert 1 galaxies (NLS1s) selected from the Sloan Digital Sky Survey (SDSS), which is used to calculate the central supermassive black hole (SMBHs) mass of each. We find that the second moment depends strongly on the broader component of the H$β$ line profile. We find that for the NLS1s requiring two Gaussians to fit the H$β$ line the mean value of the SMBH mass from the H$β$ second moment is larger by about 0.50 dex than that from the full width at half maximum (FWHM). Using the gas velocity dispersion of the core/narrow component of \oiii $λ$ 5007 to estimate the stellar velocity dispersion, $σ_{*}$, the new mass makes NLS1s fall very close to the $\mbh - σ_{*}$ relation for normal AGNs. By using $σ_{*}$ measured directly from SDSS spectra with a simple stellar population synthesis method, we find that for NLS1s with mass lower than $10^7 \msun$, they fall only marginally below the $\mbh - σ_{*}$ relation considering the large scatter in the mass calculation.

astro-ph↗

arXiv2005

Elliptical Galaxies with Emission Lines from the Sloan Digital Sky Survey

We present the results of 11 elliptical galaxies with strong nebular emission lines during our study of star formation history along the Hubble sequence. After removing the dilution from the underlying old stellar populations by use of stellar population synthesis model, we derive the accurate fluxes of all emission lines for these objects, which are later classified with emission line ratios into one Seyfert 2, six LINERs and four HII galaxies. We also identify one HII galaxy (A1216+04) as a hitherto unknown Wolf-Rayet galaxy from the presence of the Wolf-Rayet broad bump at 4650 Å. We propose that the star-forming activities in elliptical galaxies are triggered by either galaxy-galaxy interaction or the merging of a small satellite/a massive star cluster, as already suggested by recent numerical simulations.

astro-ph↗