Search Publications
A Large Population of Obscured AGN in Disguise as Low-luminosity AGN in Chandra Deep Field South
Heckman, Timothy; Vito, Fabio; Chiaberge, Marco +3 more
Population synthesis models of actively accreting supermassive black holes (or active galactic nuclei (AGN)) predict a large fraction that must grow behind dense, obscuring screens of gas and dust. Deep X-ray surveys are thought to have provided the most complete and unbiased samples of AGN, but there is strong observational evidence that a portio…
Elemental Abundances in M31: A Comparative Analysis of Alpha and Iron Element Abundances in the the Outer Disk, Giant Stellar Stream, and Inner Halo of M31
Gilbert, Karoline M.; Wojno, Jennifer; Guhathakurta, Puragra +3 more
We measured [Fe/H] and [α/Fe] using spectral synthesis of low-resolution stellar spectroscopy for 70 individual red-giant-branch stars across four fields spanning the outer disk, Giant Stellar Stream (GSS), and inner halo of M31. Fields at M31-centric projected distances of 23 kpc in the halo, 12 kpc in the halo, 22 kpc in the GSS, and 26 kpc in t…
Exploring the Perturbed Milky Way Disk and the Substructures of the Outer Disk
Xu, Y.; Liu, C.; Tian, H. +7 more
The recent discovery of a spiral feature in the Z - VZ phase plane in the solar neighborhood implies that the galactic disk has been remarkably affected by a dwarf galaxy passing through it some hundreds of millions of years ago. Using 429,500 Large Sky Area Multi-Object Fibre Spectroscopic Telescope K giants stars, we show that the spi…
A Comparison of the Stellar, CO, and Dust-continuum Emission from Three Star-forming HUDF Galaxies at z ∼ 2
Inami, Hanae; Smail, Ian; Neeleman, Marcel +17 more
We compare the extent of the dust, molecular gas, and stars in three star-forming galaxies, at z = 1.4, 1.6, and 2.7, selected from the Hubble Ultra Deep Field based on their bright carbon monoxide (CO) and dust-continuum emission as well as their large rest-frame optical sizes. The galaxies have high stellar masses, ${M}_{* }\gt {10}^{11}{M}_{\od…
Asteroseismic Modeling of Gravity Modes in Slowly Rotating A/F Stars with Radiative Levitation
Dotter, Aaron; Aerts, Conny; Van Reeth, Timothy +3 more
It has been known for several decades that transport of chemical elements is induced by the process of microscopic atomic diffusion. Yet the effect of atomic diffusion, including radiative levitation, has hardly been studied in the context of gravity-mode pulsations of core hydrogen burning stars. In this paper we study the difference in the prope…
Mapping the Galactic Disk with the LAMOST and Gaia Red Clump Sample. V. On the Origin of the "Young" [α/Fe]-enhanced Stars
Wang, H. -F.; Huang, Y.; Chen, B. -Q. +8 more
Using a sample of nearly 140,000 primary red-clump stars selected from the LAMOST and Gaia surveys, we have identified a large sample of "young" [α/Fe]-enhanced stars with stellar ages younger than 6.0 Gyr and [α/Fe] ratios greater than 0.15 dex. The stellar ages and [α/Fe] ratios are measured from LAMOST spectra, using a machine-learning method t…
Detection of the Strongest Magnetic Field in a Sunspot Light Bridge
Lagg, Andreas; Solanki, Sami K.; Castellanos Durán, J. S. +1 more
Traditionally, the strongest magnetic fields on the Sun have been measured in sunspot umbrae. More recently, however, much stronger fields have been measured at the ends of penumbral filaments carrying the Evershed and counter-Evershed flows. Superstrong fields have also been reported within a light bridge separating two umbrae of opposite polarit…
On the AGN Nature of Two UV-bright Sources at zspec ∼ 5.5 in the CANDELS Fields: An Update on the AGN Space Density at M1450 ∼ -22.5
Dickinson, M.; Fiore, F.; Grazian, A. +8 more
It is widespread opinion that hydrogen reionization is mainly driven by primeval star-forming galaxies, with high-z active galactic nuclei (AGNs) having a minor role. Recent observations, however, challenge this notion, indicating a number of issues related to a galaxy-driven reionization scenario. We provide here an updated assessment of the spac…
Delay Time Distributions of Type Ia Supernovae from Galaxy and Cosmic Star Formation Histories
Pacifici, Camilla; Graur, Or; Strolger, Louis-Gregory +2 more
We present analytical reconstructions of SN Ia delay time distributions (DTDs) by way of two independent methods: by a Markov Chain Monte Carlo best-fit technique comparing the volumetric SN Ia rate history to today's compendium cosmic star formation history, and second through a maximum likelihood analysis of the star formation rate histories of …
A Systematic Study of the Dust of Galactic Supernova Remnants. I. The Distance and the Extinction
Jiang, Biwei; Chen, Bingqiu; Zhao, He +3 more
By combining the photometric, spectroscopic, and astrometric information of the stars in the sightline of supernova remnants (SNRs), the distances to and the extinctions of 32 Galactic SNRs are investigated. The stellar atmospheric parameters are from the Sloan Digital Sky Survey-DR14/Apache Point Observatory Galaxy Evolution Experiment and Large …