Optical studies of starbursts, AGN and their connections usually leave out galaxies whose emission lines are too weak to warrant reliable measurement and classification. Yet, weak line galaxies abound, and deserve a closer look. We show that these galaxies are either massive, metal rich star-forming systems, or, more often, LINERs. From our detailed stellar population analysis, we find that the...

If galactic halos contain stellar remnants, the infra-red flux from the remnant progenitors would contribute to the opacity of multi-TeV γ-rays. The multi-TeV γ-ray horizon is established to be at a redshift z > 0.034 by the observation of the blazar Mkn501 . By requiring that the optical depth due to γγ −→ ee be less than one for a source at z = 0.034 we limit the cosmological density of stell...

Using a new grism at the Keck Interferometer, we obtained spectrally dispersed (R ∼ 230) interferometric measurements of the Mira star R Vir. These data show that the measured radius of the emission varies substantially from 2.0-2.4 μm. Simple models can reproduce these wavelength-dependent variations using extended molecular layers, which absorb stellar radiation and re-emit it at longer wavel...

Effects of young stellar clusters on their gas and dust environment are probed using mid-infrared (MIR) wavelengths. The strong MIR [NeIII]/[NeII] ratios (∼ 5 to 10) reveal the presence of current massive stars less than 5Myr. Using MIR line ratios along with optical and NIR data from the literature, composite SEDs are constructed for NGC 1569, NGC 1140 and II Zw40. The stellar SEDs are then us...

The most massive black holes, lurking at the centers of large galaxies, must have formed less than a billion years after the big bang, as they are visible today in the form of bright quasars at redshift larger than six. Their early appearance is mysterious, because the radiation pressure, generated by infalling ionized matter, inhibits the rapid growth of these black holes from stellar-mass bla...

We present new Spitzer Space Telescope observations of stars in the young ( 5 Myr) Velorum stellar cluster. Combining optical and 2MASS photometry, we have selected 579 stars as candidate members of the cluster. With the addition of the Spitzermid-infrared data, we have identified five debris disks aroundA-type stars and five to six debris disks around solar-type stars, indicating that the stro...

We present 1.3 millimeter wavelength interferometric observations of two elds containing 6 externally illuminated young stellar objects embedded within the Orion Nebula that have been observed with Hubble Space Telescope. We derive upper bounds on the dust mass from the absence of continuum emission and upper bounds on the gas mass from the lack of CO emission. These limits imply circumstellar ...

Vega and Pictoris are the most prominent A stars surrounded by dust disks. However up to now CO radio observations have not revealed any gas in the circumstellar environment. We present thin hydrostatic equilibrium models for the disks around these stars using ATLAS9 photospheric models (Kurucz 1992) to determine the stellar UV ux and to derive the dust temperature from radiative equilibrium. D...

Vega and β Pictoris are the most prominent A stars surrounded by dust disks. However up to now CO radio observations have not revealed any gas in the circumstellar environment. We present thin hydrostatic equilibrium models for the disks around these stars using ATLAS9 photospheric models (Kurucz 1992) to determine the stellar UV flux and to derive the dust temperature from radiative equilibriu...

We present a series of high-resolution cosmological zoom-in simulations1 of galaxy formation to z = 0, spanning halo masses Mhalo ∼ 108 −1013 M and stellar masses M∗ ∼ 104 −1011 M . Our simulations include a fully explicit treatment of both the multi-phase ISM (molecular through hot) and stellar feedback. The stellar feedback inputs (energy, momentum, mass, and metal fluxes) are taken directly ...