Search Publications
Evidence for a Long-standing Top-heavy Initial Mass Function in the Central Parsec of the Galaxy
Genzel, R.; Martins, F.; Salaris, M. +10 more
We classify 329 late-type giants within 1 pc of Sgr A*, using the adaptive optics integral field spectrometer SINFONI on the VLT. These observations represent the deepest spectroscopic data set so far obtained for the Galactic center, reaching a 50% completeness threshold at the approximate magnitude of the helium-burning red clump (KS~…
The Role of Galaxy Interactions and Mergers in Star Formation at z<=1.3: Mid-Infrared Properties in the Spitzer First Look Survey
Helou, G.; Armus, L.; Appleton, P. N. +8 more
By combining the 0.12 deg2 F814W Hubble Space Telescope (HST) and Spitzer MIPS 24 µm imaging in the First Look Survey (FLS), we investigate the properties of interacting and merging mid-infrared bright and faint sources at 0.2<=z<=1.3. We find a marginally significant increase in the pair fraction for MIPS 24 µm detect…
The Low-Mass X-Ray Binary and Globular Cluster Connection in Virgo Cluster Early-Type Galaxies: Optical Properties
Sarazin, Craig L.; Jordán, Andrés; Côté, Patrick +6 more
LMXBs form efficiently in GCs. By combining Chandra and HST ACS observations of 11 massive early-type galaxies in the Virgo Cluster, we use the most accurate identification of LMXBs and GCs to date to explore the optical properties of 270 GCs with LMXBs and 6488 GCs without detectable X-ray emission. More massive, redder, and more compact GCs are …
The Optical Extragalactic Background Light: Revisions and Further Comments
Bernstein, Rebecca A.
We revise the measurements in our previous work of foreground zodiacal light (ZL) and diffuse Galactic light (DGL) that were used to measure the extragalactic background light (EBL). These changes result in a decrease of 8 and an increase of 0.3 in units of 10-9 ergs s-1 cm-2 sr-1 Å-1 (``cgs''…
Swift and XMM-Newton Observations of the Extraordinary Gamma-Ray Burst 060729: More than 125 Days of X-Ray Afterglow
Sakamoto, Takanori; Cummings, Jay; Gronwall, Caryl +24 more
We report the results of the Swift and XMM-Newton observations of the Swift -discovered GRB 060729 (T90=115 s). The afterglow of this burst was exceptionally bright in X-rays as well as at UV/optical wavelengths, showing an unusually long slow decay phase (α=0.14+/-0.02), suggesting a larger energy injection phase at early times than in…
GRB 061121: Broadband Spectral Evolution through the Prompt and Afterglow Phases of a Bright Burst
Troja, E.; Sakamoto, T.; Melandri, A. +33 more
Swift triggered on a precursor to the main burst of GRB 061121 (z=1.314), allowing observations to be made from the optical to gamma-ray bands. Many other telescopes, including Konus-Wind, XMM-Newton, ROTSE, and the Faulkes Telescope North, also observed the burst. The gamma-ray, X-ray, and UV/optical emission all showed a peak ~75 s after the tri…
A Morphological Study of Gamma-Ray Burst Host Galaxies
Berger, E.; Penprase, B. E.; Wainwright, C.
We present a comprehensive study of the morphological properties of 42 γ-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope in the optical band. The purpose of this study is to understand the relation of GRBs to their macroenvironments and to compare the GRB-selected galaxies to other high-redshift samples. We perform both qualit…
The Coronal Heating Paradox
Peter, Hardi; Aschwanden, Markus J.; Winebarger, Amy +1 more
The ``coronal heating problem'' has been with us over 60 years, and hundreds of theoretical models have been proposed without an obvious solution in sight. In this paper we point out that observations show no evidence for local heating in the solar corona, but rather for heating below the corona in the transition region and upper chromosphere, wit…
Super Star Cluster Velocity Dispersions and Virial Masses in the M82 Nuclear Starburst
Graham, James R.; McCrady, Nate
We use high-resolution near-infrared spectroscopy from Keck Observatory to measure the stellar velocity dispersions of 19 super star clusters (SSCs) in the nuclear starburst of M82. The clusters have ages on the order of 10 Myr, which is many times longer than the crossing times implied by their velocity dispersions and radii. We therefore apply t…
Why Haven't Loose Globular Clusters Collapsed Yet?
Paresce, Francesco; De Marchi, Guido; Pulone, Luigi
We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c=log(rt/rc), i.e., the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of 20 Gal…