Search Publications
Asymmetric Solar Polar Field Reversals
Svalgaard, Leif; Kamide, Yohsuke
The solar polar fields reverse because magnetic flux from decaying sunspots moves toward the poles, with a preponderance of flux from the trailing spots. If there is a strong asymmetry, in the sense that most activity is in the northern hemisphere, then that excess flux will move toward the north pole and reverse that pole first. If there is more …
A Global Wave-driven Magnetohydrodynamic Solar Model with a Unified Treatment of Open and Closed Magnetic Field Topologies
Gombosi, T. I.; Landi, E.; Jin, M. +3 more
We describe, analyze, and validate the recently developed Alfvén Wave Solar Model, a three-dimensional global model starting from the top of the chromosphere and extending into interplanetary space (out to 1-2 AU). This model solves the extended, two-temperature magnetohydrodynamics equations coupled to a wave kinetic equation for low-frequency Al…
WFC3 GRISM Confirmation of the Distant Cluster Cl J1449+0856 at langzrang = 2.00: Quiescent and Star-forming Galaxy Populations
Finoguenov, A.; Cimatti, A.; Daddi, E. +7 more
We present deep Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) slitless spectroscopic observations of the distant cluster Cl J1449+0856. These cover a single pointing with 18 orbits of G141 spectroscopy and F140W imaging, allowing us to derive secure redshifts down to M 140 ~ 25.5 AB and 3σ line fluxes of ~5 × 10-18 er…
Large Abundances of Polycyclic Aromatic Hydrocarbons in Titan's Upper Atmosphere
López-Puertas, M.; D'Aversa, E.; García-Comas, M. +6 more
In this paper, we analyze the strong unidentified emission near 3.28 µm in Titan's upper daytime atmosphere recently discovered by Dinelli et al. We have studied it by using the NASA Ames PAH IR Spectroscopic Database. The polycyclic aromatic hydrocarbons (PAHs), after absorbing UV solar radiation, are able to emit strongly near 3.3 µm…
A Measurement of the Kinetic Sunyaev-Zel'dovich Signal Toward MACS J0717.5+3745
Pierpaoli, E.; Bock, J.; Egami, E. +18 more
We report our analysis of MACS J0717.5+3745 using 140 and 268 GHz Bolocam data collected at the Caltech Submillimeter Observatory. We detect extended Sunyaev-Zel'dovich (SZ) effect signal at high significance in both Bolocam bands, and we employ Herschel-SPIRE observations to subtract the signal from dusty background galaxies in the 268 GHz data. …
Active Galactic Nucleus Feedback Works Both Ways
Dettmar, R. -J.; Norris, R. P.; Middelberg, E. +1 more
Simulations of galaxy growth need to invoke strong negative feedback from active galactic nuclei (AGNs) to suppress the formation of stars and thus prevent the over-production of very massive systems. While some observations provide evidence for such negative feedback, other studies find either no feedback or even positive feedback, with increased…
Unidentified Infrared Emission Bands: PAHs or MAONs?
Zhang, Yong; Kwok, Sun
We suggest that the carrier of the unidentified infrared emission (UIE) bands is an amorphous carbonaceous solid with mixed aromatic/aliphatic structures, rather than free-flying polycyclic aromatic hydrocarbon molecules. Through spectral fittings of the astronomical spectra of the UIE bands, we show that a significant amount of the energy is emit…
Evidence for a Snow Line beyond the Transitional Radius in the TW Hya Protoplanetary Disk
Pontoppidan, K. M.; Blake, G. A.; Zhang, K. +1 more
We present an observational reconstruction of the radial water vapor content near the surface of the TW Hya transitional protoplanetary disk, and report the first localization of the snow line during this phase of disk evolution. The observations are comprised of Spitzer-IRS, Herschel-PACS, and Herschel-HIFI archival spectra. The abundance structu…
Evidence for Elevated X-Ray Emission in Local Lyman Break Galaxy Analogs
Heckman, Timothy M.; Hornschemeier, Ann E.; Schiminovich, David +6 more
Our knowledge of how X-ray emission scales with star formation at the earliest times in the universe relies on studies of very distant Lyman break galaxies (LBGs). In this paper, we study the relationship between the 2-10 keV X-ray luminosity (L X), assumed to originate from X-ray binaries (XRBs), and star formation rate (SFR) in ultrav…
The HST/ACS+WFC3 Survey for Lyman Limit Systems. II. Science
Prochaska, J. Xavier; Chen, Hsiao-Wen; Madau, Piero +2 more
We present the first science results from our Hubble Space Telescope survey for Lyman limit absorption systems (LLS) using the low dispersion spectroscopic modes of the Advanced Camera for Surveys and the Wide Field Camera 3. Through an analysis of 71 quasars, we determine the incidence frequency of LLS per unit redshift and per unit path length, …