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Search Results: 1 - 10 of 24027 matches for " Linhua Jiang "
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A submillimeter observation and study of star-forming regions
Linhua Jiang,Yuefang Wu,M. Miller
Chinese Science Bulletin , 2002, DOI: 10.1360/02tb9003
Abstract: Using the 3-m radio telescope of KOSMA, we mapped 12CO (J = 3-2) lines for three molecular clouds, B35, S146 and TMC-2A. High-velocity molecular outflows are found in all these regions. The physical and dynamical parameters of the outflows are derived, and their shapes and driving sources are analyzed. Contour maps of center velocities show that the large scale systematic gradients exist in the three clouds. These observed motions are best explained by rotation after excluding the cause of outflows. Furthermore, in the core region of TMC-2A there is a velocity gradient in opposite direction from that of the large scale. It may be caused by magnetic braking. Finally, angular velocities of the clouds are calculated, and the effects of rotation against gravity and lowering the star-formation rate are also analyzed.
A submillimeter observation and study of star-forming regions
Linhua Jiang,Yuefang Wu,M. Miller
Chinese Science Bulletin , 2002, DOI: 10.1360/02tb9004
Abstract: Using the 3-m radio telescope of KOSMA, we mapped 12CO (J = 3-2) lines for three molecular clouds, B35, S146 and TMC-2A. High-velocity molecular outflows are found in all these regions. The physical and dynamical parameters of the outflows are derived, and their shapes and driving sources are analyzed. Contour maps of center velocities show that the large scale systematic gradients exist in the three clouds. These observed motions are best explained by rotation after excluding the cause of outflows. Furthermore, in the core region of TMC-2A there is a velocity gradient in opposite direction from that of the large scale. It may be caused by magnetic braking. Finally, angular velocities of the clouds are calculated, and the effects of rotation against gravity and lowering the star-formation rate are also analyzed.
A submillimeter observation and study of star-forming regions

JIANG Linhua,WU Yuefang,M Miller,

科学通报(英文版) , 2002,
Abstract: Using the 3-m radio telescope of KOSMA, we mapped 12CO (J = 3-2) lines for three molecular clouds, B35, S146 and TMC-2A. High-velocity molecular outflows are found in all these regions. The physical and dynamical parameters of the outflows are derived, and their shapes and driving sources are analyzed. Contour maps of center velocities show that the large scale systematic gradients exist in the three clouds. These observed motions are best explained by rotation after excluding the cause of outflows. Furthermore, in the core region of TMC-2A there is a velocity gradient in opposite direction from that of the large scale. It may be caused by magnetic braking. Finally, angular velocities of the clouds are calculated, and the effects of rotation against gravity and lowering the star-formation rate are also analyzed.
Multicolor photometry of 145 of the HII regions in M33
Linhua Jiang,Jun Ma,Xu Zhou,Jiansheng Chen,Hong Wu,Zhaoji Jiang,Suijian Xue,Jin Zhu
Physics , 2002, DOI: 10.1086/344681
Abstract: This paper is the first in a series presenting CCD multicolor photometry for 145 HII regions, selected from 369 candidate regions from Boulesteix et al. (1974), in the nearby spiral galaxy M33. The observations, which covered the whole area of M33, were carried out by the Beijing Astronomical Observatory 60/90 cm Schmidt Telescope, in 13 intermediate-band filters, covering a range of wavelength from 3800 to 10000 A. This provides a series of maps which can be converted to a multicolor map of M33, in pixels of 1.7''*1.7''. Using aperture photometry we obtain the spectral energy distributions (SEDs) for these HII regions. We also give their identification charts. Using the relationship between the BATC intermediate-band system used for the observations and the UBVRI broad-band system, the magnitudes in the B and V bands are then derived. Histograms of the magnitudes in V and in B-V are plotted, and the color-magnitude diagram is also given. The distribution of magnitudes in the V band shows that the apparent magnitude of almost all the regions is brighter than 18, corresponding to an absolute magnitude of -6.62 for an assumed distance modulus of 24.62, which corresponds to a single main sequence O5 star, while the distribution of color shows that the sample is blue, with a mode close to -0.05 as would be expected from a range of typical young clusters.
Spectral Energy Distributions and Age Estimates of 172 Globular Clusters in M31
Linhua Jiang,Jun Ma,Xu Zhou,Jiansheng Chen,Hong Wu,Zhaoji Jiang
Physics , 2002, DOI: 10.1086/345885
Abstract: In this paper we present CCD multicolor photometry for 172 globular clusters (GCs), taken from the Bologna catalog (Battistini et al. 1987), in the nearby spiral galaxy M31. The observations were carried out by using the National Astronomical Observatories 60/90 cm Schmidt Telescope in 13 intermediate-band filters, which covered a range of wavelength from 3800 to 10000A. This provides a multicolor map of M31 in pixels of 1.7"*1.7". By aperture photometry, we obtain the spectral energy distributions (SEDs) for these GCs. Using the relationship between the BATC intermediate-band system used for the observations and the UBVRI broad-band system, the magnitudes in the B and V bands are derived. The computed V and B-V are in agreement with the values given by Battistini et al. (1987) and Barmby et al. (2000). Finally, by comparing the photometry of each GC with theoretical stellar population synthesis models, we estimate ages of the sample GCs for different metallicities. The results show that nearly all our sample GCs have ages more than 10^{9} years, and most of them are around 10^{10} years old. Also, we find that GCs fitted by the metal-poor model are generally older than ones fitted by the metal-rich model.
Cosmic Evolution of Star Formation In SDSS Quasar Hosts Since z=1
Yong Shi,George H. Rieke,Patrick Ogle,Linhua Jiang,Aleksandar M. Diamond-Stanic
Physics , 2009, DOI: 10.1088/0004-637X/703/1/1107
Abstract: We present Spitzer IRS observations of a complete sample of 57 SDSS type-1 quasars at z~1. Aromatic features at 6.2 and/or 7.7 um are detected in about half of the sample and show profiles similar to those seen in normal galaxies at both low- and high-redshift, indicating a star-formation origin for the features. Based on the ratio of aromatic to star-formation IR (SFIR) luminosities for normal star-forming galaxies at z~1, we have constructed the SFIR luminosity function (LF) of z~1 quasars. As we found earlier for low-redshift PG quasars, these z~1 quasars show a flatter SFIR LF than do z~1 field galaxies, implying the quasar host galaxy population has on average a higher SFR than the field galaxies do. As measured from their SFIR LF, individual quasar hosts have on average LIRG-level SFRs, which mainly arise in the circumnuclear regions. By comparing with similar measurements of low-redshift PG quasars, we find that the comoving SFIR luminosity density in quasar hosts shows a much larger increase with redshift than that in field galaxies. The behavior is consistent with pure density evolution since the average SFR and the average SFR/BH-accretion-rate in quasar hosts show little evolution with redshift. For individual quasars, we have found a correlation between the aromatic-based SFR and the luminosity of the nuclear radiation, consistent with predictions of some theoretical models. We propose that type 1 quasars reside in a distinct galaxy population that shows elliptical morphology but that harbors a significant fraction of intermediate-age stars and is experiencing intense circumnuclear star formation.
Discovering the missing 2.2
Xue-Bing Wu,Ran Wang,Kasper B. Schmidt,Fuyan Bian,Linhua Jiang,Xiaohui Fan
Physics , 2011, DOI: 10.1088/0004-6256/142/3/78
Abstract: The identifications of quasars in the redshift range 2.2
Constraining Very High Mass Population III Stars through He II Emission in Galaxy BDF-521 at z = 7.01
Zheng Cai,Xiaohui Fan,Linhua Jiang,Romeel Dave,S. Peng Oh,Yujin Yang,Ann Zabludoff
Physics , 2014, DOI: 10.1088/2041-8205/799/2/L19
Abstract: Numerous theoretical models have long proposed that a strong He II 1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high redshift galaxies. The He II 1640 line strength can constrain the mass and IMF of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to look for strong He II lambda 1640 emission in the galaxy BDF-521 at z=7.01, one of the most distant spectroscopically-confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125W and F160W filters, we do not detect He II emission from this galaxy, but place a 2-sigma upper limit on the flux of 5.3x10^-19 ergs s^-1 cm^-2. This measurement corresponds to a 2-sigma upper limit on the Pop III star formation rate (SFR_PopIII) of ~ 0.2 M_solar yr^-1, assuming a Salpeter IMF with 50< M/M_solar < 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The spectral flux density is ~ 3.6x 10^-11 lambda^-2.32 ergs s^-1 cm^-2 A^-1, which corresponds to an overall unobscured SFR of ~ 5 M_solar yr^-1. Our upper limit on SFR_PopIII suggests that massive Pop III stars represent < 4% of the total star formation. Further, the HST high resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.
Dust properties in afterglow of GRB 071025 at z~5
Minsung Jang,Myungshin Im,Induk Lee,Yuji Urata,Lijin Huang,Hiroyuki Hirashita,Xiaohui Fan,Linhua Jiang
Physics , 2011, DOI: 10.1088/2041-8205/741/1/L20
Abstract: At high redshift, the universe was so young that core-collapse supernovae (SNe) are suspected to be the dominant source of dust production. However, some observations indicate that the dust production by SNe is an inefficient process, casting doubts on the existence of abundant SNe-dust in the early universe. Recently, Perley et al. (2010) reported that the afterglow of GRB 071025 - an unusually red GRB at z ~ 5 - shows evidence for the SNe-produced dust. Since this is perhaps the only high redshift GRB exhibiting compelling evidence for SNe-dust but the result could easily be affected by small systematics in photometry, we re-examined the extinction properties of GRB 071025 using our own optical/near-infrared data at a different epoch. In addition, we tested SNe-dust models with different progenitor masses and dust destruction efficiencies to constrain the dust formation mechanisms. By searching for the best-fit model of the afterglow spectral energy distribution, we confirm the previous claim that the dust in GRB 071025 is most likely to originate from SNe. We also find that the SNe-dust model of 13 or 25M_{\odot} without dust destruction fits the extinction property of GRB 071025 best, while pair-instability SNe (PISNe) models with a 170M_{\odot} progenitor poorly fit the data. Our results indicate that, at least in some systems at high redshift, SNe with intermediate masses within 10 - 30M_{\odot} were the main contributors for the dust enrichment, and the dust destruction effect due to reverse shock was negligible.
Reverberation Mapping with Intermediate-Band Photometry: Detection of Broad-Line Time Lags for a Sample of Quasars at $z>0.2$
Linhua Jiang,Yue Shen,Ian D. McGreer,Xiaohui Fan,Eric Morganson,Rogier A. Windhorst
Physics , 2015,
Abstract: We present the first attempt at a reverberation mapping (RM) experiment that combines broad and intermediate-band photometry, targeting a sample of 13 quasars at $0.20.2$.
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