Search Publications
Rapid Changes of Photospheric Magnetic Fields around Flaring Magnetic Neutral Lines
Wang, Haimin
In this paper we study the short-term evolution of magnetic fields associated with five flares in δ-sunspots. We concentrate on the analysis of the magnetic gradient along the flaring neutral lines (NLs). Obvious changes of the magnetic gradient occurred immediately and rapidly following the onset of each flare. A rapid gradient increase was found…
Measuring the Average Evolution of Luminous Galaxies at z < 3: The Rest-Frame Optical Luminosity Density, Spectral Energy Distribution, and Stellar Mass Density
van Dokkum, Pieter G.; Franx, Marijn; Labbé, Ivo +11 more
We present the evolution of the volume-averaged properties of the rest-frame optically luminous (LV>3×1010 h-270 Lsolar) galaxy population to z~3, determined from four disjoint deep fields. We characterize their rest-frame UV through optical properties via the mean SED. To measure evolution…
Searching for Low Surface Brightness Galaxies in the Hubble Ultra Deep Field: Implications for the Star Formation Efficiency in Neutral Gas at z~3
Chen, Hsiao-Wen; Wolfe, Arthur M.
Applying the Kennicutt-Schmidt law to damped Lyα absorption systems (DLAs), we predict that 3% of the sky should be covered with extended objects brighter than µV~28.4 mag arcsec-2, if DLAs at redshift z=[2.5, 3.5] undergo in situ star formation. We test this hypothesis by searching the Hubble Ultra Deep Field (UDF) F60…
LINER-like Extended Nebulae in ULIRGs: Shocks Generated by Merger-Induced Flows
Colina, L.; Monreal-Ibero, A.; Arribas, S.
In this work we studied the two-dimensional ionization structure of the circumnuclear and extranuclear regions in a sample of six low-z ultraluminous infrared galaxies using integral field spectroscopy. The ionization conditions in the extranuclear regions of these galaxies (~5-15 kpc) are typical of LINERs as obtained from the Veilleux-Osterbrock…
The Homogeneity of Interstellar Elemental Abundances in the Galactic Disk
Sofia, Ulysses J.; Meyer, David M.; Cartledge, Stefan I. B. +1 more
We present interstellar elemental abundance measurements derived from Space Telescope Imaging Spectrograph echelle observations of 47 sight lines extending up to 6.5 kpc through the Galactic disk. These paths probe a variety of interstellar environments, covering ranges of nearly 4 orders of magnitude in molecular hydrogen fraction f(H2…
The ACS Virgo Cluster Survey. XI. The Nature of Diffuse Star Clusters in Early-Type Galaxies
Jordán, Andrés; Tonry, John L.; Côté, Patrick +7 more
We use HST ACS imaging of 100 early-type galaxies in the ACS Virgo Cluster Survey to investigate the nature of diffuse star clusters (DSCs). Compared to globular clusters (GCs), these star clusters have low luminosities (MV>-8) and a broad distribution of sizes (3<rh<30 pc), but they are principally characterized by …
Three-dimensional Inversion of Sound Speed below a Sunspot in the Born Approximation
Kosovichev, A. G.; Birch, A. C.; Couvidat, S.
We revise the inversion of acoustic travel times for the three-dimensional sound-speed structure below the solar NOAA Active Region 8243 of 1998 June. We benefit from recent progress in time-distance helioseismology that provides us with more reliable tools to infer subsurface solar properties. Among the improvements we implement here are the use …
Why X-Ray-selected Active Galactic Nuclei Appear Optically Dull
Rigby, J. R.; Rieke, G. H.; Pérez-González, P. G. +2 more
We investigate why half of X-ray-selected active galactic nuclei (AGNs) in deep surveys lack signs of accretion in their optical spectra. The majority of these ``optically dull'' AGNs are no more than ~6 times fainter than their host galaxies in rest-frame R band; as such, AGN lines are unlikely to be overwhelmed by stellar continuum in at least h…
The UV Scattering Halo of the Central Source Associated with η Carinae
Weis, K.; Sonneborn, G.; Smith, Nathan +8 more
We have made an extensive study of the UV spectrum of η Carinae and find that we do not directly observe the star and its wind in the UV. Because of dust along our line of sight, the UV light that we observe arises from bound-bound scattering at large impact parameters. We obtain a reasonable fit to the UV spectrum by using only the flux that orig…
ACS Photometry of Extended, Luminous Globular Clusters in the Outskirts of M31
Mackey, A. D.; Tanvir, N. R.; Ferguson, A. M. N. +6 more
A new population of extended, luminous globular clusters has recently been discovered in the outskirts of M31. These objects have luminosities typical of classical globular clusters, but much larger half-light radii. We report the first results from deep ACS imaging of four such clusters, one of which is a newly discovered example lying at a proje…