arXiv subjects

G. Rieke

Publications and source records attributed to G. Rieke.

42 records · Page 3Linked to original sources

arXiv2005

Infrared luminosity functions from the Chandra Deep Field South : the Spitzer view on the history of dusty star formation at 0<z<1

We analyze a sample of ~2600 MIPS/Spitzer 24mic sources brighter than ~80muJy and located in the Chandra Deep Field South to characterize the evolution of the comoving infrared (IR) energy density of the Universe up to z~1. Using published ancillary optical data we first obtain a nearly complete redshift determination for the 24mic objects associated with R<24 counterparts at z<1. We find that the 24mic population at 0.5 10^11 L_IR) are responsible for 70+/-15% of this energy density at z~1. Taking into account the contribution of the UV luminosity evolving as (1+z)^~2.5, we infer that these IR-luminous sources dominate the star-forming activity beyond z~0.7. The uncertainties affecting these conclusions are largely dominated by the errors in the k-corrections used to convert 24mic fluxes into luminosities.

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arXiv2005

An Excess Due to Small Grains Around The Nearby K0V Star HD69830: Asteroid or Cometary Debris?

Spitzer photometry and spectroscopy of the star HD69830 reveal an excess of emission relative to the stellar photosphere between 8 and 35 $μ$m dominated by strong features attributable to crystalline silicates with an emitting surface area more than 1,000 times that of our zodiacal cloud. The spectrum closely resembles that of the comet C/1995 O1 (Hale-Bopp). Since no excess is detected at 70 $μ$m, the emitting material must be quite warm, be confined within a few AU of the star, and originate in grains with low long-wavelength emissivity, i.e. grains much smaller than $70 μ$m$/2π\sim 10 $ $μ$m. The strong mineralogical features are evidence for even smaller, possibly sub-micron sized grains. This small grain size is in direct contrast to the 10-100 $μ$m grains that dominate the relatively featureless spectra of our zodiacal dust cloud and most other main sequence stars with excesses. The upper limit at 70 $μ$m also implies that any Kuiper Belt analog must either be very cold or be less massive than $\sim$ 5 times our own Kuiper Belt. With collisional and Poynting-Robertson drag times of about a thousand years for small grains, the emitting material must either: a) be created through continual grinding down of material in a dense asteroid belt; or b) originate in cometary debris arising from either a single ``super-comet'' or a very large number of individual comets arriving from a distant reservoir. In the case of a cometary origin for the emission, the mass requirements for continuous generation by many individual comets are unreasonable and we favor the capture of a single ``super comet'' into a 0.5-1 AU orbit where it can evolve a large number of small grains over a 2 Myr period.

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arXiv2004

Evolution of the infrared luminosity density and star formation history up to z~1: preliminary results from MIPS

Using deep observations of the Chandra Deep Field South obtained with MIPS at 24mic, we present our preliminary estimates on the evolution of the infrared (IR) luminosity density of the Universe from z=0 to z~1. We find that a pure density evolution of the IR luminosity function is clearly excluded by the data. The characteristic luminosity L_IR* evolves at least by (1+z)^3.5 with lookback time, but our monochromatic approach does not allow us to break the degeneracy between a pure evolution in luminosity or an evolution in both density and luminosity. Our results imply that IR luminous systems (L_IR > 10^11 L_sol) become the dominant population contributing to the comoving IR energy density beyond z~0.5-0.6. The uncertainties affecting our measurements are largely dominated by the poor constraints on the spectral energy distributions that are used to translate the observed 24mic flux into luminosities.

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arXiv2004

The Anatomy of Star Formation in NGC 300

The Spitzer Space Telescope was used to study the mid-infrared to far-infrared properties of NGC 300, and to compare dust emission to Halpha to elucidate the heating of the ISM and the star formation cycle at scales < 100 pc. The new data allow us to discern clear differences in the spatial distribution of 8 micron dust emission with respect to 24 micron dust and to HII regions traced by the Halpha light. The 8 micron emission highlights the rims of HII regions, and the 24 micron emission is more strongly peaked in star forming regions than at 8 microns. We confirm the existence and approximate amplitude of interstellar dust emission at 4.5 microns, detected statistically in Infrared Space Observatory (ISO) data, and conclude it arises in star forming regions. When averaging over regions larger than ~ 1 kpc, the ratio of Halpha to Aromatic Feature emission in NGC 300 is consistent with the values observed in disks of spiral galaxies. The mid-to-far-infrared spectral energy distribution of dust emission is generally consistent with pre-Spitzer models.

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arXiv2002

Probing the Invisible Universe: The Case for Far-IR/Submillimeter Interferometry

The question "How did we get here and what will the future bring?" captures the human imagination and the attention of the National Academy of Science's Astronomy and Astrophysics Survey Commitee (AASC). Fulfillment of this "fundamental goal" requires astronomers to have sensitive, high angular and spectral resolution observations in the far-infrared/submillimeter (far-IR/sub-mm) spectral region. With half the luminosity of the universe and vital information about galaxy, star and planet formation, observations in this spectral region require capabilities similar to those currently available or planned at shorter wavelengths. In this paper we summarize the scientific motivation, some mission concepts and technology requirements for far-IR/sub-mm space interferometers that can be developed in the 2010-2020 timeframe.

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arXiv2001

Gliese 569B: A young multiple brown dwarf system?

The nearby late M star Gliese 569B was recently found by adaptive optics imaging to be a double with separation ~1 AU. To explore the orbital motion and masses, we have undertaken a high resolution (~0.05 arcsec) astrometric study. Images were obtained over 1.5 years with bispectrum speckle interferometry at the 6.5m MMT and 6m SAO telescopes. Our data show motion corresponding to more than half the orbital period, and constrain the total mass to be > 0.115 M_solar, with a most probable value of 0.145 M_solar. Higher masses cannot be excluded without more extended observations, but from statistical analysis we find an 80% probability that the total mass is less than 0.21 M_solar. An infrared spectrum of the blended B double obtained with the MMT has been modeled as a blend of two different spectral types, chosen to be consistent with the measured J and K band brightness difference of a factor ~2. The blended fit is not nearly as good as that to a pure M8.5+ template. Therefore we hypothesize that the brighter component likely has two unresolved components with near equal masses, each the same as the fainter component. If Gl 569B is a triple our dynamical limits suggest each component has a mass of 50 (+23/-4) M_jupiter. We infer an age for the system of 300 Myr, from its kinematic motion which places its as a member of the Ursa Major moving group. All the above parameters are consistent with the latest DUSTY evolutiuon models for brown dwarfs.

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