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Featured researches published by L. G. Hou.


Astronomy and Astrophysics | 2014

The observed spiral structure of the Milky Way

L. G. Hou; J. L. Han

Context. The spiral structure of the Milky Way is not yet well determined. The keys to understanding this structure are to increase the number of reliable spiral tracers and to determine their distances as accurately as possible. HII regions, giant mol ecular clouds (GMCs), and 6.7-GHz methanol masers are closely related to high mass star formation, and hence they are excellent spiral tracers. The distances for many of them have been determined in literature with trigonometric, photometric and/or kinematic methods. Aims. We update the catalogs of Galactic HII regions, GMCs, and 6.7-GHz methanol masers, and then outline the spiral structure of the Milky Way. Methods. We collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7-GHz methanol masers. If the photometric or trigonometric distance was not yet available, we determined the kinematic distance using a Galaxy rotation curve with the current IAU standard, R0 = 8.5 kpc and �0 = 220 km s −1 , and the most recent updated values of R0 = 8.3 kpc and �0 = 239 km s −1 , after we modified the velocities of tracers with the adopted s olar motions. With the weight factors based on the excitation parameters of HII regions or the masses of GMCs, we get the distributions of these spiral tracers. Results. The distribution of tracers shows at least four segments of arms in the first Galactic quadrant, and three segments in the f ourth quadrant. The Perseus Arm and the Local Arm are also delineated by many bright HII regions. The arm segments traced by massive star forming regions and GMCs are able to match the HI arms in the outer Galaxy. We found that the models of three-arm and fourarm logarithmic spirals are able to connect most spiral tracers. The four-arm model provides a better match to the observed tangential directions of spiral arms, and is consistent with the two-fo ld symmetry of the Galaxy structure. A model of polynomial-logarithmic spirals not only delineates the tracer distribution but als o matches the observed tangential directions.


The Astrophysical Journal | 2010

DO ULTRAHIGH ENERGY COSMIC RAYS COME FROM ACTIVE GALACTIC NUCLEI AND FERMI gamma-RAY SOURCES?

Yun-Ying Jiang; L. G. Hou; Jiaxin Han; Xiao-Na Sun; Wei Wang

We study possible correlations between ultrahigh energy cosmic rays (UHECRs), observed by Auger, AGASA, and Yakutsk, and nearby active galactic nuclei (AGNs) and Fermi sources. We consider the deflection effects by a Galactic magnetic field (GMF) model constrained by the most updated measurements. We found that the average deflection angles of UHECRs by the Galactic magnetic fields are less than 4?. A correlation between the Auger cosmic-ray events and nearby AGNs with a significance level of ~4? was found for the Auger UHECR data sets with or without deflection correction. No correlation was found between the AGASA/Yakutsk events with nearby AGNs. Marginal correlations between the Auger events and the Fermi sources, and between AGASA events and Fermi AGNs were found when the deflections calculated by the GMF model were considered. However, no correlation was found between the Yakutsk data and Fermi sources. Some Fermi sources are close to the arrival directions of UHECR events detected by Auger, AGASA, and Yakutsk, most of which are probably chance coincidences rather than objects producing UHECRs in the nearby universe. Four Fermi sources, NGC 4945, ESO 323-G77, NGC 6951, and Cen A, within 100?Mpc have UHECR events within 31 from their positions, which could potentially be cosmic-ray accelerators. However, the association can only be confirmed if more UHECRs are preferably detected in these directions.


The Astrophysical Journal | 2009

ULTRA-LUMINOUS INFRARED GALAXIES IN SLOAN DIGITAL SKY SURVEY DATA RELEASE 6

L. G. Hou; Xue-Bing Wu; J. L. Han

Ultra-luminous infrared galaxies (ULIRGs) are interesting objects with dramatic properties. Many efforts have been made to understand the physics of their luminous infrared emission and evolutionary stages. However, a large ULIRG sample is still needed to study the properties of their central black holes (BHs), the BH–host galaxy relation, and their evolution. We identified 308 ULIRGs from the Sloan Digital Sky Survey Data Release 6, and classified them into the NL ULIRGs (with only narrow emission lines) and the Type I ULIRGs (with broad emission lines). About 56% of ULIRGs in our total sample show interaction features, and this percentage is 79% for redshift z < 0.2. Optical identifications of these ULIRGs show that the active galactic nucleus percentage is at least 49%, and the percentage increases with the infrared luminosity. We found 62 Type I ULIRGs, and estimated their BH masses and velocity dispersions from their optical spectra. Together with known Type I ULIRGs in the literature, a sample of 90 Type I ULIRGs enables us to make a statistical study. We found that the BH masses of Type I ULIRGs are typically smaller than those of Palomar–Green QSOs, and most Type I ULIRGs follow the MBH–σ relation. However, some ULIRGs with a larger Eddington ratio deviate from this relation, even though the line width of the [Oiii] narrow-line (NL) core or the [Sii] line was used as the surrogate of velocity dispersion. This implies that at least some ULIRGs are probably still in the early evolution stage toward QSOs. The anti-correlation between the mass deviation from the MBH–σ relation and the Eddington ratio supports that the evolution of Type I ULIRGs is probably followed by the building up of the MBH–σ relation and the evolution to the QSO phase.


Monthly Notices of the Royal Astronomical Society | 2015

Offset between stellar spiral arms and gas arms of the Milky Way

L. G. Hou; Jiaxin Han

Spiral arms shown by different components may not be spatially coincident, which can constrain formation mechanisms of spiral structure in a galaxy. We reassess the spiral arm tangency directions in the Milky Way through identifying the bump features in the longitude plots of survey data for infrared stars, radio recombination lines (RRLs), star formation sites, CO, high density regions in clouds, and HI. The bump peaks are taken as indications for arm tangencies, which are close to the real density peaks near the spiral arm tangency point but often have


The Astrophysical Journal | 2011

STELLAR POPULATIONS OF ULTRALUMINOUS INFRARED GALAXIES

L. G. Hou; J. L. Han; M. Z. Kong; Xue-Bing Wu

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Monthly Notices of the Royal Astronomical Society | 2013

A statistical study of gaseous environment of Spitzer interstellar bubbles

L. G. Hou; Xu-Dong Gao

1


Astronomy and Astrophysics | 2012

Influence of major mergers on the radio emission of elliptical galaxies

Y. H. Wen; Z. L. Wen; J. L. Han; L. G. Hou

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arXiv: Astrophysics of Galaxies | 2012

The spiral structure of our Milky Way

L. G. Hou; J. L. Han

offset to the interior of spiral arms. The arm tangencies identified from the longitudes plots for RRLs, HII regions, methanol masers, CO, high density gas regions, and HI gas appear nearly the same Galactic longitude, and therefore there is no obvious offset for spiral arms traced by different gas components. However, we find obvious displacements of 1.3


Monthly Notices of the Royal Astronomical Society | 2015

Spectrum of Lin–Shu-type density waves in the Galaxy: a number of discrete spiral modes of collective oscillations?

Evgeny Griv; N. V. Kharchenko; A. E. Piskunov; L. G. Hou; Ing-Guey Jiang

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Monthly Notices of the Royal Astronomical Society | 2017

The nearby spiral density-wave structure of the Galaxy: line-of-sight and longitudinal velocities of 223 Cepheids

Evgeny Griv; L. G. Hou; Ing-Guey Jiang; Chow-Choong Ngeow

5.8

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Evgeny Griv

Ben-Gurion University of the Negev

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Ing-Guey Jiang

National Tsing Hua University

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J. L. Han

Chinese Academy of Sciences

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Jiaxin Han

Chinese Academy of Sciences

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Chow-Choong Ngeow

National Central University

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M. Z. Kong

Hebei Normal University

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Wei Wang

Chinese Academy of Sciences

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Xu-Dong Gao

Chinese Academy of Sciences

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