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14 papers
First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
The Event Horizon Telescope Collaboration
We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A), the Galactic center source associated with a supermassive black hole. These observati…
The Greenland Telescope: Construction, Commissioning, and Operations in Pituffik
Ming-Tang Chen, Keiichi Asada, Satoki Matsushita +51
In 2018, the Greenland Telescope (GLT) started scientific observation in Greenland. Since then, we have completed several significant improvements and added new capabilities to the…
A ring-like accretion structure in M87 connecting its black hole and jet
Ru-Sen Lu, Keiichi Asada, Thomas P. Krichbaum +118
The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation^{1,2}. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3…
Behavior of Sulfur Abundances in Metal-Poor Giants and Dwarfs
M. Takada-Hidai, Y. Takeda, S. Sato +6
LTE and NLTE abundances of sulfur in 6 metal-poor giants and 61 dwarfs (62 dwarfs, including the Sun) were explored in the range of -3 \lsim [Fe/H] \lsim using high-resoluti…
The Deuterium Abundance at z=0.701 towards QSO 1718+4807
David Tytler, Scott Burles, Limin Lu +3
We present constraints on the deuterium to hydrogen ratio (D/H) in the metal-poor gas cloud at redshift towards QSO 1718+4807. We use new Keck spectra in addition to Hubb…
Highly Ionized High Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?
Kenneth R. Sembach, Blair D. Savage, Limin Lu +1
We have recently identified several high velocity (V < -100 km/s) clouds in the directions of Mrk 509 and PKS 2155-304 that have unusual ionization properties. The clouds exhibit s…
The HST Quasar Absorption Line Key Project. XIV. The Evolution of Ly-alpha Absorption Lines in the Redshift Interval 0 to 1.5
Ray J. Weymann, Buell T. Jannuzi, Limin Lu +10
We present an analysis of the evolution of the Ly alpha absorption lines in the redshift interval 0.0 to \sim 1.5 based upon a sample of 987 lines identified in the spectra of 63 Q…
The Relationship Between Galaxies and Low Redshift Weak Lyman alpha Absorbers in the Directions of H1821+643 and PG1116+215
Todd M. Tripp, Blair D. Savage, Limin Lu
To study the nature of low z Lya absorbers in the spectra of QSOs, we have obtained high signal-to-noise UV spectra of H 1821+643 (z = 0.297) and PG 1116+215 (z = 0.177) with the G…
The N/Si Abundance Ratio in Fifteen Damped Lyman-alpha Galaxies: Implications for the Origin of Nitrogen
Limin Lu, Wallace L. W. Sargent, Thomas A. Barlow
Galactic chemical evolution model calculations indicate that there should be considerable scatter in the observed N/O ratios at a fixed metallicity (O/H) for galaxies with very low…
The Metallicity and Dust Content of HVC 287.5+22.5+240: Evidence for a Magellanic Clouds Origin
Limin Lu, Blair D. Savage, Kenneth R. Sembach +3
We estimate the abundances of S and Fe in the high velocity cloud HVC 287.5+22.5+240, which has a velocity of +240 km/s with respect to the local standard of rest and is in the Gal…
Echelle Spectroscopy of QSO Absorption Line Systems with Metals in the Direction of HS 1700+6416
Todd M. Tripp, Limin Lu, Blair D. Savage
We present a high signal-to-noise high resolution spectrum of the radio-quiet QSO HS1700+6416 (z = 2.72). Analysis of the absorption line systems with metals yields the following r…
Evidence for Rotation in the Galaxy at z=3.15 Responsible for a Damped Lyman-alpha Absorption System in the Spectrum of Q2233+1310
Limin Lu, Wallace L. W. Sargent, Thomas A. Barlow
Proof of the existence of a significant population of normal disk galaxies at redshift z>2 would have profound implications for theories of structure formation and evolution. We pr…
Abundances at High Redshifts: the Chemical Enrichment History of Damped Lyman-alpha Galaxies
Limin Lu, Wallace L. W. Sargent, Thomas A. Barlow
Damped Lyman-alpha absorption systems found in the spectra of high redshift quasars are believed to trace the interstellar gas in high redshift galaxies. In this paper, we study th…
The Lyman-alpha Forest at z~4: Keck HIRES Observations of Q 0000-26
Limin Lu, Wallace L. W. Sargent, Donna S. Womble +1
This paper describes a study of the Lyman-alpha forest absorption clouds along the quasar sightline Q0000-26 (zem=4.1). The spectrum was obtained with the High Resolution Spectrome…