737 research outputs found
Star Formation at z~6: The UDF-Parallel ACS Fields
We report on the i-dropouts detected in two exceptionally deep ACS fields
(B_{435}, V_{606}, i_{775}, and z_{850} with 10 sigma limits of 28.8, 29.0,
28.5, and 27.8, respectively) taken in parallel with the UDF NICMOS
observations. Using an i-z>1.4 cut, we find 30 i-dropouts over 21 arcmin^2 down
to z_AB=28.1, or 1.4 i-dropouts arcmin^{-2}, with significant field-to-field
variation (as expected from cosmic variance). This extends i-dropout searches
some ~0.9^m further down the luminosity function than was possible in the GOODS
field, netting a ~7x increase in surface density. An estimate of the size
evolution for UV bright objects is obtained by comparing the composite radial
flux profile of the bright i-dropouts (z<27.2) with scaled versions of the
HDF-N + HDF-S U-dropouts. The best-fit is found with a (1+z)^{-1.57_{-0.53}
^{+0.50}} scaling in size (for fixed luminosity), extending lower redshift
(1<z<5) trends to z~6. Adopting this scaling and the brighter i-dropouts from
both GOODS fields, we make incompleteness estimates and construct a z~6 LF in
the rest-frame continuum UV (~1350 A) over a 3.5 magnitude baseline, finding a
shape consistent with that found at lower redshift. To evaluate the evolution
in the LF from z~3.8, we make comparisons against different scalings of a lower
redshift B-dropout sample. Though a strong degeneracy is found between
luminosity and density evolution, our best-fit model scales as (1+z)^{-2.8} in
number and (1+z)^0.1 in luminosity, suggesting a rest-frame continuum UV
luminosity density at z~6 which is just 0.38_{-0.07} ^{+0.09}x that at z~3.8.
Our inclusion of size evolution makes the present estimate lower than previous
z~6 estimates.Comment: 5 pages, 5 figures, accepted for publication in the Astrophysical
Journal Letters, labelling to the left-hand axis of Figure 4 correcte
Outlying HII Regions in HI-Selected Galaxies
We present results from the first systematic search for outlying HII regions,
as part of a sample of 96 emission-line point sources (referred to as ELdots -
emission-line dots) derived from the NOAO Survey for Ionization in Neutral Gas
Galaxies (SINGG). Our automated ELdot-finder searches SINGG narrow-band and
continuum images for high equivalent width point sources outside the optical
radius of the target galaxy (> 2 X r25 in the R-band). Follow-up longslit
spectroscopy and deep GALEX images (exposure time > 1000 s) distinguish
outlying HII regions from background galaxies whose strong emission lines
([OIII], Hbeta or [OII]) have been redshifted into the SINGG bandpass. We find
that these deep GALEX images can serve as a substitute for spectroscopic
follow-up because outlying HII regions separate cleanly from background
galaxies in color-color space. We identify seven SINGG systems with outlying
massive star formation that span a large range in Halpha luminosities
corresponding to a few O stars in the most nearby cases, and unresolved dwarf
satellite companion galaxies in the most distant cases. Six of these seven
systems feature galaxies with nearby companions or interacting galaxies.
Furthermore, our results indicate that some outlying HII regions are linked to
the extended-UV disks discovered by GALEX, representing emission from the most
massive O stars among a more abundant population of lower mass (or older) star
clusters. The overall frequency of outlying HII regions in this sample of
gas-rich galaxies is 8 - 11% when we correct for background emission-line
galaxy contamination (~75% of ELdots).Comment: 20 pages, 14 Figures, Accepted by A
Febre Q: uma zoonose de distribuição mundial.
A febre Q é uma zoonose de distribuição mundial causada pelo patógeno Coxiella burnetii, uma bactéria que, além de apresentar resistência e estabilidade ambiental, é um dos agentes mais infecciosos ao ser humano. Sua principal forma de transmissão à população humana ocorre através da inalação de aerossóis contaminados com produtos de animais infectados, principalmente bovinos, caprinos e ovinos. A infecção em humanos apresenta um amplo espectro de manifestações, desde casos assintomáticos até complicações graves e fatais
Local Starbursts in a Cosmological Context
In this contribution I introduce some of the major issues that motivate the
conference, with an emphasis on how starbursts fit into the ``big picture''. I
begin by defining starbursts in several different ways, and discuss the merits
and limitations of these definitions. I will argue that the most physically
useful definition of a starburst is its ``intensity'' (star formation rate per
unit area). This is the most natural parameter to compare local starbursts with
physically similar galaxies at high redshift, and indeed I will argue that
local starbursts are unique laboratories to study the processes at work in the
early universe. I will describe how NASA's GALEX mission has uncovered a rare
population of close analogs to Lyman Break Galaxies in the local universe. I
will then compare local starbursts to the Lyman-Break and sub-mm galaxies high
redshift populations, and speculate that the multidimensional ``manifold'' of
starbursts near and far can be understood largely in terms of the
Schmidt/Kennicutt law and galaxy mass-metallicity relation. I will briefly
summarize he properties of starburst-driven galactic superwinds and their
possible implications for the evolution of galaxies and the IGM. These complex
multiphase flows are best studied in nearby starbursts, where we can study the
the hot X-ray gas that contains the bulk of the energy and newly produced
metals.Comment: Proceedings of the Conference "Starbursts: Fropm 30 Doradus to Lyman
Break Galaxies
Discovery of Globular Clusters in the Proto-Spiral NGC2915: Implications for Hierarchical Galaxy Evolution
We have discovered three globular clusters beyond the Holmberg radius in
Hubble Space Telescope Advanced Camera for Surveys images of the gas-rich dark
matter dominated blue compact dwarf galaxy NGC2915. The clusters, all of which
start to resolve into stars, have M_{V606} = -8.9 to -9.8 mag, significantly
brighter than the peak of the luminosity function of Milky Way globular
clusters. Their colors suggest a metallicity [Fe/H] ~ -1.9 dex, typical of
metal-poor Galactic globular clusters. The specific frequency of clusters is at
a minimum normal, compared to spiral galaxies. However, since only a small
portion of the system has been surveyed it is more likely that the luminosity
and mass normalized cluster content is higher, like that seen in elliptical
galaxies and galaxy clusters. This suggests that NGC2915 resembles a key phase
in the early hierarchical assembly of galaxies - the epoch when much of the old
stellar population has formed, but little of the stellar disk. Depending on the
subsequent interaction history, such systems could go on to build-up larger
elliptical galaxies, evolve into normal spirals, or in rare circumstances
remain suspended in their development to become systems like NGC2915.Comment: ApJ Letters accepted; 6 pages, 2 figures, 3 table
Very blue UV-continuum slopes of low luminosity z~7 galaxies from WFC3/IR: Evidence for extremely low metallicities?
We use the ultra-deep WFC3/IR data over the HUDF and the Early Release
Science WFC3/IR data over the CDF-South GOODS field to quantify the broadband
spectral properties of candidate star-forming galaxies at z~7. We determine the
UV-continuum slope beta in these galaxies, and compare the slopes with galaxies
at later times to measure the evolution in beta. For luminous L*(z=3) galaxies,
we measure a mean UV-continuum slope beta of -2.0+/-0.2, which is comparable to
the beta~-2 derived at similar luminosities at z~5-6. However, for the lower
luminosity 0.1L*(z=3) galaxies, we measure a mean beta of -3.0+/-0.2. This is
substantially bluer than is found for similar luminosity galaxies at z~4, just
800 Myr later, and even at z~5-6. In principle, the observed beta of -3.0 can
be matched by a very young, dust-free stellar population, but when nebular
emission is included the expected beta becomes >~-2.7. To produce these very
blue beta's (i.e., beta~-3), extremely low metallicities and mechanisms to
reduce the red nebular emission are likely required. For example, a large
escape fraction (i.e., f_{esc}>~0.3) could minimize the contribution from this
red nebular emission. If this is correct and the escape fraction in faint z~7
galaxies is >~0.3, it may help to explain how galaxies reionize the universe.Comment: 5 pages, 5 figures, accepted for publication in Astrophysical Journal
Letter
Internal Color Properties of Resolved Spheroids in the Deep HST/ACS field of UGC 10214
(Abridged) We study the internal color properties of a morphologically
selected sample of spheroidal galaxies taken from HST/ACS ERO program of UGC
10214 (``The Tadpole''). By taking advantage of the unprecedented high
resolution of the ACS in this very deep dataset we are able to characterize
spheroids at sub-arcseconds scales. Using the V_606W and I_814W bands, we
construct V-I color maps and extract color gradients for a sample of spheroids
at I_814W < 24 mag. We investigate the existence of a population of
morphologically classified spheroids which show extreme variation in their
internal color properties similar to the ones reported in the HDFs. These are
displayed as blue cores and inverse color gradients with respect to those
accounted from metallicity variations. Following the same analysis we find a
similar fraction of early-type systems (~30%-40%) that show non-homologous
internal colors, suggestive of recent star formation activity. We present two
statistics to quantify the internal color variation in galaxies and for tracing
blue cores, from which we estimate the fraction of non-homogeneous to
homogeneous internal colors as a function of redshift up to z<1.2. We find that
it can be described as about constant as a function of redshift, with a small
increase with redshift for the fraction of spheroids that present strong color
dispersions. The implications of a constant fraction at all redshifts suggests
the existence of a relatively permanent population of evolving spheroids up to
z~1. We discuss the implications of this in the context of spheroidal
formation.Comment: Fixed URL for high resolution version. 13 Pages, 10 Figures. Accepted
for Publication in ApJ. Sep 1st issue. Higher resolution version and complete
table3B at http://acs.pha.jhu.edu/~felipe/e-prints/Tadpol
The Luminosity Function of Early-Type Galaxies at z~0.75
We measure the luminosity function of morphologically selected E/S0 galaxies
from to using deep high resolution Advanced Camera for Surveys
imaging data. Our analysis covers an area of 48\Box\arcmin (8 the
area of the HDF-N) and extends 2 magnitudes deeper ( mag) than was
possible in the Deep Groth Strip Survey (DGSS). At , we find
and , and at
, we find . These luminosity
functions are similar in both shape and number density to the luminosity
function using morphological selection (e.g., DGSS), but are much steeper than
the luminosity functions of samples selected using morphological proxies like
the color or spectral energy distribution (e.g., CFRS, CADIS, or COMBO-17). The
difference is due to the `blue', , E/S0 galaxies, which make up to
of the sample at all magnitudes and an increasing proportion of faint
galaxies. We thereby demonstrate the need for {\it both morphological and
structural information} to constrain the evolution of galaxies.
We find that the `blue' E/S0 galaxies have the same average sizes and Sersic
parameters as the `red', , E/S0 galaxies at brighter luminosities
(), but are increasingly different at fainter magnitudes where
`blue' galaxies are both smaller and have lower Sersic parameters. Fits of the
colors to stellar population models suggest that most E/S0 galaxies have short
star-formation time scales ( Gyr), and that galaxies have formed at an
increasing rate from until after which there has been a
gradual decline.Comment: 39 pages, 21 figures, accepted in A
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