1,240 research outputs found
Debris Disks around Solar-Type Stars: Observations of the Pleiades with Spitzer Space Telescope
We present Spitzer MIPS observations at 24 um of 37 solar-type stars in the
Pleiades and combine them with previous observations to obtain a sample of 71
stars. We report that 23 stars, or 32 +/- 6.8%, have excesses at 24 um at least
10% above their photospheric emission. We compare our results with studies of
debris disks in other open clusters and with a study of A stars to show that
debris disks around solar-type stars at 115 Myr occur at nearly the same rate
as around A-type stars. We analyze the effects of binarity and X-ray activity
on the excess flux. Stars with warm excesses tend not to be in equal-mass
binary systems, possibly due to clearing of planetesimals by binary companions
in similar orbits. We find that the apparent anti-correlations in the incidence
of excess and both the rate of stellar rotation and also the level of activity
as judged by X-ray emission are statistically weak.Comment: 34 pages; accepted for publication in ApJ; new version included
corrections of typos, etc to match published versio
Spitzer Observations of Low Luminosity Isolated and Low Surface Brightness Galaxies
We examine the infrared properties of five low surface brightness galaxies
(LSBGs) and compare them with related but higher surface brightness galaxies,
using Spitzer Space Telescope images and spectra. All the LSBGs are detected in
the 3.6 and 4.5um bands, representing the stellar population. All but one are
detected at 5.8 and 8.0um, revealing emission from hot dust and aromatic
molecules, though many are faint or point-like at these wavelengths. Detections
of LSBGs at the far-infrared wavelengths, 24, 70, and 160um, are varied in
morphology and brightness, with only two detections at 160um, resulting in
highly varied spectral energy distributions. Consistent with previous
expectations for these galaxies, we find that detectable dust components exist
for only some LSBGs, with the strength of dust emission dependent on the
existence of bright star forming regions. However, the far-infrared emission
may be relatively weak compared with normal star-forming galaxies.Comment: 20 pages, 8 figures, accepted to Ap
Mid-Infrared Emission from E+A Galaxies in the Coma Cluster
We have used ISO to observe at 12m seven E+A galaxies plus an additional
emission line galaxy, all in the Coma cluster. E+A galaxies lacking narrow
emission lines have 2.2m to 12m flux density ratios or limits similar
to old stellar populations (typical of early-type galaxies). Only galaxies with
emission lines have enhanced 12m flux density. Excess 12m emission is
therefore correlated with the presence of on-going star formation or an active
galactic nucleus (AGN).
By comparing the current star formation rates with previous rates estimated
from the Balmer absorption features, we divide the galaxies into two groups:
those for which star formation has declined significantly following a dramatic
peak 1 Gyr ago; and those with a significant level of ongoing star
formation or/and an AGN. There is no strong difference in the spatial
distribution on the sky between these two groups. However, the first group has
systemic velocities above the mean cluster value and the second group below
that value. This suggests that the two groups differ kinematically.
Based on surveys of the Coma cluster in the radio, the IRAS sources, and
galaxies detected in H emission, we sum the far infrared luminosity
function of galaxies in the cluster. We find that star formation in late type
galaxies is probably the dominant component of the Coma cluster far infrared
luminosity. The presence of significant emission from intracluster dust is not
yet firmly established. The member galaxies also account for most of the far
infrared output from nearby rich clusters in general.Comment: AAS Latex, accepted for publication in Ap
AEGIS: Infrared Spectral Energy Distributions of MIPS 70micron selected sources
We present 0.5 -160 micron Spectral Energy Distributions (SEDs) of galaxies,
detected at 70microns with the Multiband Imaging Photometer for Spitzer (MIPS),
using broadband imaging data from Spitzer and ground-based telescopes.
Spectroscopic redshifts, in the range 0.2<z<1.5, have been measured as part of
the Deep Extragalactic Evolutionary Probe2 (DEEP2) project. Based on the SEDs
we explore the nature and physical properties of the sources. Using the optical
spectra we derive Hbeta and [OII]-based Star Formation Rates (SFR) which are
10-100 times lower than SFR estimates based on IR and radio. The median offset
in SFR between optical and IR is reduced by a factor of ~3 when we apply a
typical extinction corrections. We investigate mid-to-far infrared correlations
for low redshift (>0.5) and high redshift (0.5<z<1.2) bins. Using this unique
``far-infrared'' selected sample we derive an empirical mid to far-infrared
relationship that can be used to estimate the infrared energy budget of
galaxies in the high-redshift universe. Our sample can be used as a template to
translate far-infrared luminosities into bolometric luminosities for high
redshift objects.Comment: 4 pages, 5 figures, accepted for publication in AEGIS ApJL Special
Issu
The Star-formation History of the Universe as Revealed from Deep Radio Observations of the 13^H XMM-Newton/Chandra Deep Field
Discerning the exact nature of the faint (sub-mJy) radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep observations from Chandra/XMM-Newton/Spitzer and ground based follow up we are able to disentangle the AGN and star-
forming populations for the first time in a deep multi-frequency GMRT/VLA/MERLIN Survey. The many diagnostics include radio luminosity, morphology, radio to mid-IR flux density ratios, radio to optical flux density ratios and
radio spectral indices. Further diagnostics, e.g. optical spectra, X-ray spectra/hardness ratios, IR colours indicate the presence of the AGN independent of whether the radio emission is powered by AGN or star-formation. We are able to
examine the star-formation history of the universe up to z = 2.5 in a unique way based on an unbiased star-formation rate indicator, radio luminosity. This work provides an alternative perspective on the distribution of star-formation by mass, “downsizing” and allows us to examine the prevalence of AGN in star-bursts
The Variability of Seyfert 1.8 and 1.9 Galaxies at 1.6 microns
We present a study of Seyfert 1.5-2.0 galaxies observed at two epochs with
the Hubble Space Telescope (HST) at 1.6 microns. We find that unresolved
nuclear emission from 9 of 14 nuclei varies at the level of 10-40% on
timescales of 0.7-14 months, depending upon the galaxy. A control sample of
Seyfert galaxies lacking unresolved sources and galaxies lacking Seyfert nuclei
show less than 3% instrumental variation in equivalent aperture measurements.
This proves that the unresolved sources are non-stellar and associated with the
central pc of active galactic nuclei. Unresolved sources in Seyfert 1.8 and 1.9
galaxies are not usually detected in HST optical surveys, however high angular
resolution infrared observations will provide a way to measure time delays in
these galaxies.Comment: accepted by ApJLetters (emulateapj latex
Spitzer/MIPS Limits on Asteroidal Dust in the Pulsar Planetary System PSR B1257+1
With the MIPS camera on Spitzer, we have searched for far-infrared emission
from dust in the planetary system orbiting pulsar PSR 1257+12. With accuracies
of 0.05 mJy at 24 um and 1.5 mJy at 70 um, photometric measurements find no
evidence for emission at these wavelengths. These observations place new upper
limits on the luminosity of dust with temperatures between 20 and 1000 K. They
are particularly sensitive to dust temperatures of 100-200 K, for which they
limit the dust luminosity to below of the pulsar's spin-down
luminosity, three orders of magnitude better than previous limits. Despite
these improved constraints on dust emission, an asteroid belt similar to the
Solar System's cannot be ruled out
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