Brightest Cluster Galaxies （BCGs） are mostly elliptical galaxies and very rarely have prominent star formations. We found that five out of 8,812 BCGs are E＋A （i.e., post-starburst） galaxies, having an Hd absorpti...Brightest Cluster Galaxies （BCGs） are mostly elliptical galaxies and very rarely have prominent star formations. We found that five out of 8,812 BCGs are E＋A （i.e., post-starburst） galaxies, having an Hd absorption line with an equivalent width 〉2.5 A and no distinct emission lines in [O II] and Ha-. The E＋A features we identified from the BCGs for the first time are not as significant as those in general galaxies, indicating that historically the star formations were not very violent.展开更多
We present a systematic study to reveal the effect of host galaxy contamination to the identification of X-ray "unobscured" Seyfert 2 galaxies.We compiled a sample of 14 X-ray "unobscured" Seyfert ...We present a systematic study to reveal the effect of host galaxy contamination to the identification of X-ray "unobscured" Seyfert 2 galaxies.We compiled a sample of 14 X-ray "unobscured" Seyfert 2 galaxies and 29 X-ray obscured Seyfert 2s,with infrared [Ne II] and [O IV] emission line flux measurements.In this work we classify Seyfert 2s as "unobscured" or obscured in X-ray simply based on X-ray spectral fitting.We find that our X-ay "unobscured" Seyfert 2s have statistically higher [Ne II]/[O IV] line ratios,compared with obscured ones.Since the [Ne II]/[O IV] line ratio reflects the relative strength of star formation activity comparing with the SMBH accretion,the observed differences in [Ne II]/[O IV] line ratios clearly indicate relatively stronger X-ray contamination from star formation in the host galaxies in X-ray "unobscured" Seyfert 2s.Therefore we could attribute the X-ray "unobscured" appearance to host galaxy contamination for most(if not all) of our X-ray "unobscured" Seyfert 2s.Further analysis indicates that "unobscured" Seyfert 2s have intrinsically lower AGN luminosity but similar star formation rates,compared with obscured ones.This is also consistent with previous studies showing most X-ray "unobscured" Seyfert 2s are at lower luminosities,and relatively stronger contaminations from the host galaxies are thus expected.Finally we develop a screening criterion to distinguish potential pure Seyfert 2s from X-ray "unobscured" appearances which could be caused by strong host galaxy contamination.展开更多
We study the global star formation law, the relation between the gas and star formation rate （SFR） in a sample of 130 local galaxies with infrared （IR） luminosities spanning over three orders of magnitude （109-10...We study the global star formation law, the relation between the gas and star formation rate （SFR） in a sample of 130 local galaxies with infrared （IR） luminosities spanning over three orders of magnitude （109-1012 Lo）, which includes 91 normal spiral galaxies and 39 （ultra）luminous IR galaxies [（U）LIRGs]. We derive their total （atomic and molecular） gas and dense molecular gas masses using newly available HI, CO and HCN data from the literature. The SFR of galaxies is determined from total IR （8-1000 μm） and 1.4 GHz radio continuum （RC） luminosities. The galaxy disk sizes are defined by the de-convolved elliptical Gaussian FWHM of the RC maps. We derive the galaxy disk-averaged SFRs and various gas surface densities, and investigate their relationships. We find that the galaxy disk-averaged surface density of dense molecular gas mass has the tightest correlation with that of SFR （scatter -0.26 dex）, and is linear in log-log space （power-law slope of N=1.03±0.02） across the full galaxy sample. The correlation between the total gas and SFR surface densities for the full sample has a somewhat larger scatter （-0.48 dex）, and is best fit by a power-law with slope 1.45±0.02. However, the slope changes from -1 when only normal spirals are considered, to -1.5 when more and more （U）LIRGs are included in the fitting. When different CO-to-H2 conversion factors are used to infer molecular gas masses for normal galaxies and （U）LIRGs, the bi-modal relations claimed recently in CO observations of high-redshift galaxies appear to also exist in local populations of star-forming galaxies.展开更多
基金supported by the Liaoning Educational Foundation of China (Grant No.2009A646)the National Natural Science Foundation of China (Grant Nos.10773016,10821061 and 1083303)+1 种基金the National Key Basic Research Science Foundation of China (Grant No.2007CB815403)Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P.Sloan Foundation
文摘Brightest Cluster Galaxies （BCGs） are mostly elliptical galaxies and very rarely have prominent star formations. We found that five out of 8,812 BCGs are E＋A （i.e., post-starburst） galaxies, having an Hd absorption line with an equivalent width 〉2.5 A and no distinct emission lines in [O II] and Ha-. The E＋A features we identified from the BCGs for the first time are not as significant as those in general galaxies, indicating that historically the star formations were not very violent.
基金supported by the National Natural Sciences Foundation of China (Grant No. 10825321)
文摘We present a systematic study to reveal the effect of host galaxy contamination to the identification of X-ray "unobscured" Seyfert 2 galaxies.We compiled a sample of 14 X-ray "unobscured" Seyfert 2 galaxies and 29 X-ray obscured Seyfert 2s,with infrared [Ne II] and [O IV] emission line flux measurements.In this work we classify Seyfert 2s as "unobscured" or obscured in X-ray simply based on X-ray spectral fitting.We find that our X-ay "unobscured" Seyfert 2s have statistically higher [Ne II]/[O IV] line ratios,compared with obscured ones.Since the [Ne II]/[O IV] line ratio reflects the relative strength of star formation activity comparing with the SMBH accretion,the observed differences in [Ne II]/[O IV] line ratios clearly indicate relatively stronger X-ray contamination from star formation in the host galaxies in X-ray "unobscured" Seyfert 2s.Therefore we could attribute the X-ray "unobscured" appearance to host galaxy contamination for most(if not all) of our X-ray "unobscured" Seyfert 2s.Further analysis indicates that "unobscured" Seyfert 2s have intrinsically lower AGN luminosity but similar star formation rates,compared with obscured ones.This is also consistent with previous studies showing most X-ray "unobscured" Seyfert 2s are at lower luminosities,and relatively stronger contaminations from the host galaxies are thus expected.Finally we develop a screening criterion to distinguish potential pure Seyfert 2s from X-ray "unobscured" appearances which could be caused by strong host galaxy contamination.
基金supported by the National Natural Science Foundation of China (Grant Nos.10833006 and 10621303)the National Basic Research Program of China (Grant No.2007CB815406)
文摘We study the global star formation law, the relation between the gas and star formation rate （SFR） in a sample of 130 local galaxies with infrared （IR） luminosities spanning over three orders of magnitude （109-1012 Lo）, which includes 91 normal spiral galaxies and 39 （ultra）luminous IR galaxies [（U）LIRGs]. We derive their total （atomic and molecular） gas and dense molecular gas masses using newly available HI, CO and HCN data from the literature. The SFR of galaxies is determined from total IR （8-1000 μm） and 1.4 GHz radio continuum （RC） luminosities. The galaxy disk sizes are defined by the de-convolved elliptical Gaussian FWHM of the RC maps. We derive the galaxy disk-averaged SFRs and various gas surface densities, and investigate their relationships. We find that the galaxy disk-averaged surface density of dense molecular gas mass has the tightest correlation with that of SFR （scatter -0.26 dex）, and is linear in log-log space （power-law slope of N=1.03±0.02） across the full galaxy sample. The correlation between the total gas and SFR surface densities for the full sample has a somewhat larger scatter （-0.48 dex）, and is best fit by a power-law with slope 1.45±0.02. However, the slope changes from -1 when only normal spirals are considered, to -1.5 when more and more （U）LIRGs are included in the fitting. When different CO-to-H2 conversion factors are used to infer molecular gas masses for normal galaxies and （U）LIRGs, the bi-modal relations claimed recently in CO observations of high-redshift galaxies appear to also exist in local populations of star-forming galaxies.
