Search Publications
The Inner Jet of the Radio Galaxy M87
Kellermann, K. I.; Kovalev, Y. Y.; Lister, M. L. +1 more
We report new 2 cm VLBA images of the inner radio jet of M87 showing a limb-brightened structure and unambiguous evidence for a faint 3 mas long counterfeature which also appears limb brightened. Multiepoch observations of seven separate jet features show typical speeds of less than a few percent of the speed of light, despite the highly asymmetri…
The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
Anderson, Jay; Dotter, Aaron; Majewski, Steven R. +11 more
As part of the ACS Survey of Galactic Globular Clusters, we present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showin…
Coronal Pseudostreamers
Sheeley, N. R., Jr.; Wang, Y. -M.; Rich, N. B.
In a recent study of the 2006 solar eclipse, we noted that there are two kinds of coronal streamers: ``helmet streamers,'' which separate coronal holes of opposite magnetic polarity, and ``pseudostreamers,'' which overlie twin loop arcades and separate holes of the same polarity. It is well known that the heliospheric plasma and current sheets rep…
Emergence of Small-Scale Magnetic Loops in the Quiet-Sun Internetwork
Kubo, M.; Ichimoto, K.; Tsuneta, S. +11 more
We study the emergence of magnetic flux at very small spatial scales (less than 2") in the quiet-Sun internetwork. To this aim, a time series of spectropolarimetric maps was taken at disk center using the instrument SP/SOT on board Hinode. The LTE inversion of the full Stokes vector measured in the Fe I 6301 and 6302 Å lines allows us to retrieve …
A Wide-Field Survey of Two z ~ 0.5 Galaxy Clusters: Identifying the Physical Processes Responsible for the Observed Transformation of Spirals into S0s
Smith, Graham P.; Treu, Tommaso; Smail, Ian +3 more
We present new results from our comparative survey of two massive, intermediate-redshift galaxy clusters, Cl 0024+17 (z=0.39) and MS 0451-03 (z=0.54). Combining optical and UV imaging with spectroscopy of member galaxies, we identify and study several key classes of ``transition objects'' whose stellar populations or dynamical states indicate a re…
The Multiplicity of the Subgiant Branch of ω Centauri: Evidence for Prolonged Star Formation
Recio-Blanco, A.; Anderson, J.; Cool, A. M. +9 more
We combine spectroscopic and photometric data for subgiant stars of ω Cen to extract results that neither data set could have provided on its own. GIRAFFE@VLT spectra of 80 stars at R=6400 give metallicities for all of them and abundances of C, N, Ca, Ti, and Ba for a subset of them. The photometric data, which have unusually high accuracy, come f…
The Compact, Conical, Accretion-Disk Warm Absorber of the Seyfert 1 Galaxy NGC 4051 and Its Implications for IGM-Galaxy Feedback Processes
Elvis, Martin; Nicastro, Fabrizio; Mathur, Smita +4 more
Using a 100 ks XMM-Newton exposure of NGC 4051, we show that the time evolution of the ionization state of the X-ray absorbers in response to the rapid and highly variable X-ray continuum constrains all the main physical and geometrical properties of an AGN ``warm absorber'' wind. The absorber consists of two different ionization components, with …
Hα Tail, Intracluster H II Regions, and Star Formation: ESO 137-001 in Abell 3627
Sun, M.; Donahue, M.; Voit, G. M.
We present the discovery of a 40 kpc Hα tail and at least 29 emission-line objects downstream of a star-forming galaxy, ESO 137-001, in the rich, nearby cluster A3627. The galaxy is known to possess a dramatic 70 kpc X-ray tail. The detected Hα tail coincides positionally with the X-ray tail. The Hα emission in the galaxy is sharply truncated on t…
A New Population of High-Redshift Short-Duration Gamma-Ray Bursts
Cenko, S. B.; Peterson, B. A.; Price, P. A. +23 more
The redshift distribution of the short-duration gamma-ray bursts (GRBs) is a crucial, but currently fragmentary, clue to the nature of their progenitors. Here we present optical observations of nine short GRBs obtained with Gemini, Magellan, and the Hubble Space Telescope. We detect the afterglows and host galaxies of two short bursts, and host ga…
Leo A: A Late-blooming Survivor of the Epoch of Reionization in the Local Group
Dolphin, Andrew E.; Skillman, Evan D.; Cole, Andrew A. +8 more
As part of a major program to use isolated Local Group dwarf galaxies as near-field probes of cosmology, we have obtained deep images of the dwarf irregular galaxy Leo A with the Advanced Camera for Surveys aboard the Hubble Space Telescope. From these images we have constructed a color-magnitude diagram (CMD) reaching apparent [absolute] magnitud…