275 research outputs found
Localized starbursts in dwarf galaxies produced by impact of low metallicity cosmic gas clouds
Models of galaxy formation predict that gas accretion from the cosmic web is
a primary driver of star formation over cosmic history. Except in very dense
environments where galaxy mergers are also important, model galaxies feed from
cold streams of gas from the web that penetrate their dark matter haloes.
Although these predictions are unambiguous, the observational support has been
indirect so far. Here we report spectroscopic evidence for this process in
extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of
localized starbursts associated with gas having low metallicity. Detailed
abundance analyses based on Gran Telescopio Canarias (GTC) optical spectra of
ten XMPs show that the galaxy hosts have metallicities around 60 % solar on
average, while the large star-forming regions that dominate their integrated
light have low metallicities of some 6 % solar. Because gas mixes azimuthally
in a rotation timescale (a few hundred Myr), the observed metallicity
inhomogeneities are only possible if the metal-poor gas fell onto the disk
recently. We analyze several possibilities for the origin of the metal-poor
gas, favoring the metal-poor gas infall predicted by numerical models. If this
interpretation is correct, XMPs trace the cosmic web gas in their surroundings,
making them probes to examine its properties.Comment: Accepted for publication in ApJ
AVOCADO: A Virtual Observatory Census to Address Dwarfs Origins
Dwarf galaxies are by far the most abundant of all galaxy types, yet their
properties are still poorly understood -especially due to the observational
challenge that their intrinsic faintness represents. AVOCADO aims at
establishing firm conclusions on their formation and evolution by constructing
a homogeneous, multiwavelength dataset for a statistically significant sample
of several thousand nearby dwarfs (-18 < Mi < -14). Using public data and
Virtual Observatory tools, we have built GALEX+SDSS+2MASS spectral energy
distributions that are fitted by a library of single stellar population models.
Star formation rates, stellar masses, ages and metallicities are further
complemented with structural parameters that can be used to classify them
morphologically. This unique dataset, coupled with a detailed characterization
of each dwar's environment, allows for a fully comprehensive investigation of
their origins and to track the (potential) evolutionary paths between the
different dwarf types.Comment: 4 pages, 1 figure. To appear in the proceedings of IAU Symposium 277,
"Tracing the Ancestry of Galaxies on the Land of our Ancestors", Carignan,
Freeman, and Combes, ed
First Results from the KMOS Lens-Amplified Spectroscopic Survey (KLASS): Kinematics of Lensed Galaxies at Cosmic Noon
We present the first results of the KMOS Lens-Amplified Spectroscopic Survey
(KLASS), a new ESO Very Large Telescope (VLT) large program, doing multi-object
integral field spectroscopy of galaxies gravitationally lensed behind seven
galaxy clusters selected from the HST Grism Lens-Amplified Survey from Space
(GLASS). Using the power of the cluster magnification we are able to reveal the
kinematic structure of 25 galaxies at , in four
cluster fields, with stellar masses . This sample includes 5 sources at with lower stellar masses
than in any previous kinematic IFU surveys. Our sample displays a diversity in
kinematic structure over this mass and redshift range. The majority of our
kinematically resolved sample is rotationally supported, but with a lower ratio
of rotational velocity to velocity dispersion than in the local universe,
indicating the fraction of dynamically hot disks changes with cosmic time. We
find no galaxies with stellar mass in our sample
display regular ordered rotation. Using the enhanced spatial resolution from
lensing, we resolve a lower number of dispersion dominated systems compared to
field surveys, competitive with findings from surveys using adaptive optics. We
find that the KMOS IFUs recover emission line flux from HST grism-selected
objects more faithfully than slit spectrographs. With artificial slits we
estimate slit spectrographs miss on average 60% of the total flux of emission
lines, which decreases rapidly if the emission line is spatially offset from
the continuum.Comment: Accepted for publication in Ap
O vírus da queima do broto da soja no Brasil: etiologia, epidemiologia e controle.
Caracteristicas do virus; Modo de transmissao; Sintomas; Epidemiologia e controle; Distribuicao no Brasil e plantas hospedeiras; Danos e controle.bitstream/item/60659/1/Documentos-85.pd
Índice de estresse hídrico da cultura do feijoeiro irrigado.
A determinacao das necessidades hidricas de culturas, em seus diferentes estadios de desenvolvimento, e uma etapa importante para o manejo de irrigacao. Entre os metodos usualmente utilizados, destacam-se o metodo gravimetrico, medidas do potencial de agua na folha, tensiometros e climatologicos. A utilizacao de tecnicas de sensoriamento remoto apresenta-se como uma alternativa importante por permitir a deteccao do status de agua da planta, em funcao da emitancia radiante da superficie da cultura. Dentre os equipamentos usados destaca-se o termometro a infravermelho por sua praticidade de uso. Neste estudo utilizou-se a termometria infravermelha, associada ao balanco de energia para obtencao de um indice de estresse hidrico da cultura (IEHC) do feijoeiro (Phaseolus vulgaris L.) que possibilitasse ao irrigante saber em tempo real, nos diferentes estadios de desenvolvimento da cultura, quando irrigar. Os valores do IEHC variaram de -0,06 a 0,053; -0,041 a 0,221 e -0,038 a 0,108, respectivamente, para os niveis de tensao de umidade do solo de 0,04; 0,06 e 0,08 MPa. Embora os indices obtidos nao tenham apresentado diferencas acentuadas entre os tratamentos, os resultados evidenciam o potencial do metodo para realizacao do manejo de irrigacao
Hubble imaging of the ionizing radiation from a star-forming galaxy at z=3.2 with fesc>50%
Star-forming galaxies are considered to be the leading candidate sources that
dominate the cosmic reionization at z>7, and the search for analogs at moderate
redshift showing Lyman continuum (LyC) leakage is currently a active line of
research. We have observed a star-forming galaxy at z=3.2 with Hubble/WFC3 in
the F336W filter, corresponding to the 730-890A rest-frame, and detect LyC
emission. This galaxy is very compact and also has large Oxygen ratio
[OIII]5007/[OII]3727 (>=10). No nuclear activity is revealed from
optical/near-infrared spectroscopy and deep multi-band photometry (including
the 6Ms X-ray, Chandra). The measured escape fraction of ionizing radiation
spans the range 50-100\%, depending on the IGM attenuation. The LyC emission is
detected at S/N=10 with m(F336W)=27.57+/-0.11 and it is spatially unresolved,
with effective radius R_e<200pc. Predictions from photoionization and radiative
transfer models are in line with the properties reported here, indicating that
stellar winds and supernova explosions in a nucleated star-forming region can
blow cavities generating density-bounded conditions compatible with optically
thin media. Irrespective to the nature of the ionizing radiation, spectral
signatures of these sources over the entire electromagnetic spectrum are of
central importance for their identification during the epoch of reionization,
when the LyC is unobservable. Intriguingly, the Spitzer/IRAC photometric
signature of intense rest-frame optical emissions ([OIII]+Hbeta) observed
recently at z~7.5-8.5 is similar to what is observed in this galaxy. Only the
James Webb Space Telescope will measure optical line ratios at z>7 allowing a
direct comparison with lower redshift LyC emitters, as reported here.Comment: 6 pages, 5 figures, ApJ submitted (comments welcome
Identification of z~>2 Herschel 500 micron sources using color-deconfusion
We present a new method to search for candidate z~>2 Herschel 500{\mu}m
sources in the GOODS-North field, using a S500{\mu}m/S24{\mu}m "color
deconfusion" technique. Potential high-z sources are selected against
low-redshift ones from their large 500{\mu}m to 24{\mu}m flux density ratios.
By effectively reducing the contribution from low-redshift populations to the
observed 500{\mu}m emission, we are able to identify counterparts to high-z
500{\mu}m sources whose 24{\mu}m fluxes are relatively faint. The recovery of
known z~4 starbursts confirms the efficiency of this approach in selecting
high-z Herschel sources. The resulting sample consists of 34 dusty star-forming
galaxies at z~>2. The inferred infrared luminosities are in the range
1.5x10^12-1.8x10^13 Lsun, corresponding to dust-obscured star formation rates
(SFRs) of ~260-3100 Msun/yr for a Salpeter IMF. Comparison with previous SCUBA
850{\mu}m-selected galaxy samples shows that our method is more efficient at
selecting high-z dusty galaxies with a median redshift of z=3.07+/-0.83 and 10
of the sources at z~>4. We find that at a fixed luminosity, the dust
temperature is ~5K cooler than that expected from the Td-LIR relation at z<1,
though different temperature selection effects should be taken into account.
The radio-detected subsample (excluding three strong AGN) follows the
far-infrared/radio correlation at lower redshifts, and no evolution with
redshift is observed out to z~5, suggesting that the far-infrared emission is
star formation dominated. The contribution of the high-z Herschel 500{\mu}m
sources to the cosmic SFR density is comparable to that of SMG populations at
z~2.5 and at least 40% of the extinction-corrected UV samples at z~4
(abridged).Comment: 33 pages in emulateapj format, 24 figures, 2 tables, accepted for
publication in the ApJ
T-PHOT: A new code for PSF-matched, prior-based, multiwavelength extragalactic deconfusion photometry
We present T-PHOT, a publicly available software aimed at extracting accurate
photometry from low-resolution images of deep extragalactic fields, where the
blending of sources can be a serious problem for the accurate and unbiased
measurement of fluxes and colours. T-PHOT has been developed within the
ASTRODEEP project and it can be considered as the next generation to TFIT,
providing significant improvements above it and other similar codes. T-PHOT
gathers data from a high-resolution image of a region of the sky, and uses it
to obtain priors for the photometric analysis of a lower resolution image of
the same field. It can handle different types of datasets as input priors: i) a
list of objects that will be used to obtain cutouts from the real
high-resolution image; ii) a set of analytical models; iii) a list of
unresolved, point-like sources, useful e.g. for far-infrared wavelength
domains. We show that T-PHOT yields accurate estimations of fluxes within the
intrinsic uncertainties of the method, when systematic errors are taken into
account (which can be done thanks to a flagging code given in the output).
T-PHOT is many times faster than similar codes like TFIT and CONVPHOT (up to
hundreds, depending on the problem and the method adopted), whilst at the same
time being more robust and more versatile. This makes it an optimal choice for
the analysis of large datasets. In addition we show how the use of different
settings and methods significantly enhances the performance. Given its
versatility and robustness, T-PHOT can be considered the preferred choice for
combined photometric analysis of current and forthcoming extragalactic optical
to far-infrared imaging surveys. [abridged]Comment: 23 pages, 20 figures, 2 table
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