Yi-Nan Zhu

Effects of Metallicity and AGN Activity on the Mid-Infrared Dust Emission of Galaxies

Using a sample of the Spitzer SWIRE-field galaxies whose optical spectra are taken from Data Release 4 of the Sloan Digital Sky Survey, we study possible correlations between the mid-infrared (MIR) dust emission from these galaxies and both their metallicities and AGN activities. We find that both metallicity and AGN activity are well correlated with the following ratios: PAH-to-star, VSG-to-star, and PAH-to-VSG, which can be characterized by νLν[8 μm(dust)]/νLν[3.6 μm], νLν[24 μm]/νLν[3.6 μm], and νLν[8 μm(dust)]/νLν[24 μm], respectively. We argue that our MIR-metallicity correlation could be explained by either the amount of dust (ongoing dust formation) or dust destruction (PAHs and VSGs could be destroyed by hard and intense radiation fields), and that the MIR-AGN correlation could arise due to either PAH destruction or an enhanced VSG continuum by the central AGN.

Morphological Dependence of Mid-Infrared Properties of SDSS Galaxies in the Spitzer SWIRE Survey

We explore the correlation between morphological types and mid-infrared (MIR) properties of an optically flux-limited sample of 154 galaxies from the Fourth Data Release (DR4) of the Sloan Digital Sky Survey (SDSS), cross-correlated with Spitzer SWIRE fields of ELAIS-N1, ELAIS-N2, and the Lockman Hole. Aperture photometry is performed on the SDSS and Spitzer images to obtain optical and MIR properties. The morphological classifications are given based on both visual inspection and bulge-disk decomposition in SDSS g- and r-band images. The average bulge-to-total ratio (B/T) is a smooth function over different morphological types. Both the 8 μm (dust) and 24 μm (dust) luminosities and their relative luminosity ratios to 3.6 μm (MIR dust-to-star ratios) present obvious correlations with both the Hubble T-type and B/T. The early-type galaxies notably differ from the late types in the MIR properties, especially in the MIR dust-to-star ratios. It is suggested that the MIR dust-to-star ratio of either νLν[8 μm (dust)]/νLν[3.6 μm] or νLν[24 μm (dust)]/νLν[3.6 μm] is an effective way to separate the early-type galaxies from the late-type ones. Based on the tight correlation between the stellar mass and the 3.6 μm luminosity, we have derived a formula to calculate the stellar mass from the latter. We have also investigated the MIR properties of both edge-on galaxies and barred galaxies in our sample. Since they present similar MIR properties to the other sample galaxies, they do not influence the MIR properties obtained for the entire sample.

Stellar Mass Estimation Based on IRAC Photometry for Spitzer SWIRE-field Galaxies

We analyze the feasibility of estimating the stellar mass of galaxies by mid-infrared luminosities based on a large sample of galaxies cross-identified from Spitzer SWIRE fields and the SDSS spectrographic survey. We derived the formulae to calculate the stellar mass by using IRAC 3.6 μm and 4.5 μm luminosities. The mass-to-luminosity ratios of IRAC 3.6 μm and 4.5 μm luminosities are more sensitive to the star formation history of galaxies than to other factors, such as the intrinsic extinction, metallicity and star formation rate. To remove the effect of star formation history, we used g - r color to recalibrate the formulae and obtain a better result. Researchers must be more careful when estimating the stellar mass of low metallicity galaxies using our formulae. Due to the emission from dust heated by the hottest young stars, luminous infrared galaxies present higher IRAC 4.5 μm luminosities compared to IRAC 3.6 μm luminosities. For most of type-II AGNs, the nuclear activity cannot enhance 3.6 μm and 4.5 μm luminosities compared with normal galaxies. Star formation in our AGNhosting galaxies is also very weak, almost all of which are early-type galaxies.

The star formation reference survey - I. Survey description and basic data

ABSTRACT.Star formation is arguably the most important physical process in the cosmos. It is a fundamental driver of galaxy evolution and the ultimate source of most of the energy emitted by galaxies in the local universe. A correct interpretation of star formation rate (SFR) measures is therefore essential to our understanding of galaxy formation and evolution. Unfortunately, however, no single SFR estimator is universally available or even applicable in all circumstances: the numerous galaxies found in deep surveys are often too faint (or too distant) to yield significant detections with most standard SFR measures, and until now there have been no global multiband observations of nearby galaxies that span all the conditions under which star formation is taking place. To address this need in a systematic way, we have undertaken a multiband survey of all types of star-forming galaxies in the local universe. This project, the Star Formation Reference Survey (SFRS), is based on a statistically valid sample ...

Far-Infrared and submillimeter properties of SDSS galaxies in the Herschel ATLAS science demonstration phase field ∗

Using the Herschel ATLAS science demonstration phase data crossidentified with SDSS DR7 spectra, we select 297 galaxies with F 250μm > 5σ. The sample galaxies are classified into five morphological types, and more than 40% of the galaxies are peculiar/compact galaxies. The peculiar galaxies show higher far-infrared/submillimeter luminosity-to-mass ratios than the other types. We perform and analyze the correlations of far-infrared/submillimeter and Hα luminosities for different morphological types and different spectral types. The Spearman rank coefficient decreases and the scatter increases with the wavelength increasing from 100 μm to 500 μm. We conclude that a single Herschel SPIRE band is not good for tracing star formation activities in galaxies. AGNs contribute less to the far-infrared/submillimeter luminosities and do not show a difference from star-forming galaxies. However, the earlier type galaxies present significant deviations from the best fit of star-forming galaxies.

The Xinglong 2.16-m Telescope: Current Instruments and Scientific Projects

The Xinglong 2.16-m reflector is the first 2-meter class astronomical telescope in China. It was jointly designed and built by the Nanjing Astronomical Instruments Factory (NAIF), Beijing Astronomical Observatory (now National Astronomical Observatories, Chinese Academy of Sciences, NAOC) and Institute of Automation, Chinese Academy of Sciences in 1989. It is Ritchey-Chretien (R-C) reflector on an English equatorial mount and the effective aperture is 2.16 meters. It had been the largest optical telescope in China for

Long-slit Spectroscopy of Edge-on Low Surface Brightness Galaxies

\sim18

Molecular Gas and Star-formation in Low Surface Brightness Galaxies

years until the Guoshoujing Telescope (also called Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST) and the Lijiang 2.4-m telescope were built. At present, there are three main instruments on the Cassegrain focus available: the Beijing Faint Object Spectrograph and Camera (BFOSC) for direct imaging and low resolution (

The discovery of 64 luminous infrared galaxies in the LAMOST Complete Spectroscopic Survey of Pointing Area at the Southern Galactic Cap

R\sim500-2000

The H i-dominated low-surface-brightness galaxy KKR 17

) spectroscopy, the spectrograph made by Optomechanics Research Inc. (OMR) for low resolution spectroscopy (the spectral resolutions are similar to those of BFOSC) and the fiber-fed High Resolution Spectrograph (HRS,