337 research outputs found
Evolutionary models of cold and low-mass planets: Cooling curves, magnitudes, and detectability
Future instruments like NIRCam and MIRI on JWST or METIS at the ELT will be
able to image exoplanets that are too faint for current direct imaging
instruments. Evolutionary models predicting the planetary intrinsic luminosity
as a function of time have traditionally concentrated on gas-dominated giant
planets. We extend these cooling curves to Saturnian and Neptunian planets. We
simulate the cooling of isolated core-dominated and gas giant planets with
masses of 5 Earthmasses to 2 Jupitermasses. The luminosity includes the
contribution from the cooling and contraction of the core and of the H/He
envelope, as well as radiogenic decay. For the atmosphere we use grey,
AMES-Cond, petitCODE, and HELIOS models. We consider solar and non-solar
metallicities as well as cloud-free and cloudy atmospheres. The most important
initial conditions, namely the core-to-envelope ratio and the initial
luminosity are taken from planet formation simulations based on the core
accretion paradigm. We first compare our cooling curves for Uranus, Neptune,
Jupiter, Saturn, GJ 436b, and a 5 Earthmass-planet with a 1% H/He envelope with
other evolutionary models. We then present the temporal evolution of planets
with masses between 5 Earthmasses and 2 Jupitermasses in terms of their
luminosity, effective temperature, radius, and entropy. We discuss the impact
of different post formation entropies. For the different atmosphere types and
initial conditions magnitudes in various filter bands between 0.9 and 30
micrometer wavelength are provided. Using black body fluxes and non-grey
spectra, we estimate the detectability of such planets with JWST. It is found
that a 20 (100) Earthmass-planet can be detected with JWST in the background
limit up to an age of about 10 (100) Myr with NIRCam and MIRI, respectively.Comment: Language corrected version and improved arrangements of figures,
online data at:
http://www.space.unibe.ch/research/research_groups/planets_in_time/numerical_data/index_eng.htm
Quantitative Morphology of Galaxies in the Hubble Deep Field
We measure quantitative structural parameters of galaxies in the Hubble Deep
Field (HDF) on the drizzled F814W images. Our structural parameters are based
on a two-component surface brightness made up of a S\'ersic profile and an
exponential profile. We compare our results to the visual classification of van
den Bergh et al. (1996) and the classification of Abraham et al. (1996a).
Our morphological analysis of the galaxies in the HDF indicates that the
spheroidal galaxies, defined here as galaxies with a dominant bulge profile,
make up for only a small fraction, namely 8% of the galaxy population down to
m = 26.0. We show that the larger fraction of early-type systems
in the van den Bergh sample is primarily due to the difference in
classification of 40% of small round galaxies with half-light radii <
0\arcsecpoint 31. Although these objects are visually classified as elliptical
galaxies, we find that they are disk-dominated with bulge fractions < 0.5.
Given the existing large dataset of HDF galaxies with measured spectroscopic
redshifts, we are able to determine that the majority of distant galaxies
() from this sample are disk-dominated. Our analysis reveals a subset of
HDF galaxies which have profiles flatter than a pure exponential profile.Comment: 35 pages, LaTeX, 18 Postscript Figures, Tables available at
http://astro.berkeley.edu/~marleau/. Accepted for Publication in The
Astrophysical Journa
The stellar content of the halo of NGC 5907 from deep Hubble Space Telescope NICMOS imaging
We present H-band images obtained with NICMOS of a field 75'' (5kpc) above
the plane of the disk of the edge-on spiral galaxy NGC 5907. Ground-based
observations have shown that NGC 5907 has a luminous halo with a shallow radial
profile between 4 and 8 kpc that roughly traces the dark matter distribution of
the galaxy deduced from its rotation curve. Our NICMOS observations were
designed to resolve bright giants in the halo of NGC 5907 to constrain its
stellar composition with the goal of understanding its nature and origin. More
than 100 stars are expected in the NICMOS images if the dwarf-to-giant ratio in
the halo of NGC 5907 is consistent with that expected from standard stellar
initial mass functions, and if ground-based estimates of the distance to NGC
5907 and the integrated colors of its halo are correct. Instead we observe only
one candidate giant star. This apparent discrepancy can be resolved by assuming
either a significantly larger distance than suggested by several studies, or a
halo metallicity much lower than suggested by ground-based colors and as low as
metal-poor Galactic globular clusters. If previous distance and halo color
estimates for NGC 5907 are correct, our NICMOS results suggest that its
extended light is composed of stars that formed with an initial mass function
different than that observed locally, leading to a much higher ratio of dwarfs
to giants. We describe how these three possible explanations for the absence of
bright giants in our NICMOS images of the halo of NGC 5907 might be constrained
by future observations.Comment: Accepted for publication in the Astronomical Journal, 23 pages, 6
figure
Spectroscopic Survey of 1.4 GHz and 24 μm Sources in the Spitzer First Look Survey with WIYN Hydra
We present an optical spectroscopic survey of 24 μm and 1.4 GHz sources, detected in the Spitzer extragalactic First Look Survey (FLS), using the multifiber spectrograph, Hydra, on the WIYN telescope. We have obtained spectra for 772 sources, with flux densities above 0.15 mJy in the infrared and 0.09 mJy in the radio. The redshifts measured in this survey are mostly in the range 0 < z < 0.4, with a distribution peaking at z ~ 0.2. Detailed spectral analysis of our sources reveals that the majority are emission-line star-forming galaxies, with star formation rates in the range 0.2-200 M_☉ yr^(-1). The rates estimated from the Hα line fluxes are found to be on average consistent with those derived from the 1.4 GHz luminosities. For these star-forming systems, we find that the 24 μm and 1.4 GHz flux densities follow an infrared-radio correlation, which can be characterized by a value of q_(24) = 0.83, with a 1 σ scatter of 0.31. Our WIYN Hydra database of spectra nicely complements those obtained by the Sloan Digital Sky Survey in the region at lower redshift, as well as the MMT Hectospec survey by Papovich et al. in 2006, and brings the redshift completeness to 70% for sources brighter than 2 mJy at 24 μm. Applying the classical 1/V_(max) method, we derive new 24 μm and 1.4 GHz luminosity functions, using all known redshifts in the FLS. We find evidence for evolution in both the 1.4 GHz and 24 μm luminosity functions in the redshift range 0 < z < 1. The redshift catalog and spectra presented in this paper are available at the Spitzer FLS Web site
A Spatially Resolved Study of the Cold Dust in NGC 205
We present IRAC and MIPS observations of NGC 205, the dwarf
elliptical companion of M31, obtained with the Spitzer Space Telescope. The
extended dust emission is spatially concentrated in three main emission regions.
Based on our mid-to-far infrared flux density measurements alone, we derive a
total dust mass estimate of the order of 3.2 × 10^4 M_⊙, at a temperature of ~20K.
The gas mass associated with this component matches the predicted mass returned
by the dying stars from the last burst of star formation in NGC 205
(~0.5 Gyr ago). Analysis of the Spitzer data combined with previous 1.1mm
observations over a small central region or “Core” (18" diameter), suggest the
presence of very cold (T ~ 12K) dust and a dust mass 16 times higher than is estimated
from the Spitzer measurements alone. Assuming a gas to dust mass ratio
of 100, these two datasets, i.e. with and without the millimeter observations,
suggest a total gas mass range of 3.2 × 10^6 to 5 × 10^7 M_⊙
Discovery of Highly Obscured Galaxies in the Zone of Avoidance
We report the discovery of twenty-five previously unknown galaxies in the
Zone of Avoidance. Our systematic search for extended extra-galactic sources in
the GLIMPSE and MIPSGAL mid-infrared surveys of the Galactic plane has revealed
two overdensities of these sources, located around l ~ 47 and 55 degrees and
|b| less than 1 degree in the Sagitta-Aquila region. These overdensities are
consistent with the local large-scale structure found at similar Galactic
longitude and extending from |b| ~ 4 to 40 degrees. We show that the infrared
spectral energy distribution of these sources is indeed consistent with those
of normal galaxies. Photometric estimates of their redshift indicate that the
majority of these galaxies are found in the redshift range z = 0.01 - 0.05,
with one source located at z = 0.07. Comparison with known sources in the local
Universe reveals that these galaxies are located at similar overdensities in
redshift space. These new galaxies are the first evidence of a bridge linking
the large-scale structure between both sides of the Galactic plane at very low
Galactic latitude and clearly demonstrate the feasibility of detecting galaxies
in the Zone of Avoidance using mid-to-far infrared surveys.Comment: Accepted for publication in the Astronomical Journal, 28 pages, 5
tables, 11 figure
Infrared Properties of Radio-Selected Submillimeter Galaxies in the Spitzer First Look Survey Verification Field
We report on submillimeter and infrared observations of 28 radio-selected
galaxies in the Spitzer First Look Survey Verification field (FLSV). All of the
radio-selected galaxies that show evidence for emission at 850um with SCUBA
have Spitzer counterparts at 24um, while only half of the radio-selected
galaxies without 850um emission have detectable counterparts at 24um. The data
show a wide range of infrared colors (S70/S24 < 5--30, S8/S3.6 < 0.3--4),
indicative of a mixture of infrared-warm AGN and cooler starburst dominated
sources. The galaxies showing 850um emission have Spitzer flux densities and
flux density ratios consistent with the range of values expected for
high-redshift (z=1--4) ultraluminous infrared galaxies.Comment: Accepted for Spitzer ApJS Special Edition, 12 pages including 4
figures and 1 tabl
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