Search Publications
High-Resolution Measurements of the Dark Matter Halo of NGC 2976: Evidence for a Shallow Density Profile
Bolatto, Alberto D.; Simon, Joshua D.; Blitz, Leo +1 more
We have obtained two-dimensional velocity fields of the dwarf spiral galaxy NGC 2976 in Hα and CO. The high spatial (~75 pc) and spectral (13 and 2 km s-1, respectively) resolution of these observations, along with our multicolor optical and near-infrared imaging, allows us to measure the shape of the density profile of the dark matter …
Star formation rate in galaxies from UV, IR, and Hα estimators
Buat, V.; Inoue, A. K.; Hirashita, H.
Infrared (IR) luminosity of galaxies originating from dust thermal emission can be used as an indicator of the star formation rate (SFR). Inoue et al. (\cite{inoue00}, IHK) have derived a formula for the conversion from dust IR luminosity to SFR by using the following three quantities: the fraction of Lyman continuum luminosity absorbed by gas (f)…
Reprocessing the Hipparcos data of evolved stars. III. Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
Jorissen, A.; Pourbaix, D.; Platais, I. +1 more
We analyze the K band luminosities of a sample of galactic long-period variables using parallaxes measured by the Hipparcos mission. The parallaxes are in most cases re-computed from the Hipparcos Intermediate Astrometric Data using improved astrometric fits and chromaticity corrections. The K band magnitudes are taken from the literature and from…
Identifying Lenses with Small-Scale Structure. I. Cusp Lenses
Keeton, Charles R.; Gaudi, B. Scott; Petters, A. O.
The inability of standard models to explain the flux ratios in many four-image gravitational lens systems has been presented as evidence for significant small-scale structure in lens galaxies. That claim has generally relied on detailed lens modeling, so it is both model dependent and somewhat difficult to interpret. We present a more robust and g…
Circumnuclear Dust in Nearby Active and Inactive Galaxies. I. Data
Pogge, Richard W.; Mulchaey, John S.; Martini, Paul +1 more
The detailed morphology of the interstellar medium (ISM) in the central kiloparsec of galaxies is controlled by pressure and gravitation. The combination of these forces shapes both circumnuclear star formation and the growth of the central, supermassive black hole. We present visible and near-infrared Hubble Space Telescope images and color maps …
The Magnetic Helicity Budget of Solar Active Regions and Coronal Mass Ejections
Zhang, H.; Zhang, J.; Nindos, A.
We compute the magnetic helicity injected by transient photospheric horizontal flows in six solar active regions associated with halo coronal mass ejections (CMEs) that produced major geomagnetic storms and magnetic clouds (MCs) at 1 AU. The velocities are computed using the local correlation tracking (LCT) method. Our computations cover time inte…
The Effects of UV Continuum and Lyα Radiation on the Chemical Equilibrium of T Tauri Disks
Herczeg, Gregory J.; Calvet, Nuria; Bergin, Edwin +1 more
We show in this Letter that the spectral details of the far-ultraviolet (FUV) radiation fields have a large impact on the chemistry of protoplanetary disks surrounding T Tauri stars. We show that the strength of a realistic stellar FUV field is significantly lower than typically assumed in chemical calculations and that the radiation field is domi…
Evidence of a Significant Intermediate-Age Population in the M31 Halo from Main-Sequence Photometry
Ferguson, Henry C.; Brown, Thomas M.; Rich, R. Michael +5 more
We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M31), 51' (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at mV=30.7 mag. The CMD, c…
Discovery of Interacting Molecular Gas toward the TeV Gamma-Ray Peak of the SNR G 347.3--0.5
Takahashi, Tadayuki; Uchiyama, Yasunobu; Fukui, Yasuo +10 more
Supernova remnants ( = SNR) are suggested to be sites of cosmic-ray acceleration. In particular, it has been an issue of keen interest whether cosmic ray protons are being accelerated in a SNR which emits TeV γ-rays. A crucial observational test for this is to find dense molecular gas towards the SNR, because such molecular gas can best verify the…
The Initial Helium Content of Galactic Globular Cluster Stars from the R-Parameter: Comparison with the Cosmic Microwave Background Constraint
Salaris, Maurizio; Cassisi, Santi; Irwin, Alan W.
Recent precise determinations of the primordial He abundance (Yp) from cosmic microwave background (CMB) analyses and cosmological nucleosynthesis computations provide Yp=0.248+/-0.001. On the other hand, recent works on the initial He abundance of Galactic globular cluster (GGC) stars, making use of the R-parameter as an He …