423 research outputs found
Breaking the Curve with CANDELS: A Bayesian Approach to Reveal the Non-Universality of the Dust-Attenuation Law at High Redshift
Dust attenuation affects nearly all observational aspects of galaxy
evolution, yet very little is known about the form of the dust-attenuation law
in the distant Universe. Here, we model the spectral energy distributions
(SEDs) of galaxies at z = 1.5--3 from CANDELS with rest-frame UV to near-IR
imaging under different assumptions about the dust law, and compare the amount
of inferred attenuated light with the observed infrared (IR) luminosities. Some
individual galaxies show strong Bayesian evidence in preference of one dust law
over another, and this preference agrees with their observed location on the
plane of infrared excess (IRX, ) and UV slope
(). We generalize the shape of the dust law with an empirical model,
where
is the dust law of Calzetti et al. (2000), and show that there
exists a correlation between the color excess and tilt with
+ . Galaxies with high
color excess have a shallower, starburst-like law, and those with low color
excess have a steeper, SMC-like law. Surprisingly, the galaxies in our sample
show no correlation between the shape of the dust law and stellar mass,
star-formation rate, or . The change in the dust law with color excess
is consistent with a model where attenuation is caused by by scattering, a
mixed star-dust geometry, and/or trends with stellar population age,
metallicity, and dust grain size. This rest-frame UV-to-near-IR method shows
potential to constrain the dust law at even higher () redshifts.Comment: 20 pages, 18 figures, resubmitted to Ap
The SFR-M <sub>∗</sub> Correlation Extends to Low Mass at High Redshift
To achieve a fuller understanding of galaxy evolution, SED fitting can be
used to recover quantities beyond stellar masses (M) and star formation
rates (SFRs). We use Star Formation Histories (SFHs) reconstructed via the
Dense Basis method of Iyer \& Gawiser (2017) for a sample of galaxies
at in the CANDELS GOODS-S field to study the nature and evolution of
the SFR-M correlation. The reconstructed SFHs represent trajectories in
SFR-M space, enabling us to study galaxies at epochs earlier than observed
by propagating them backwards in time along these trajectories. We study the
SFR-M correlation at using both direct fits to galaxies
observed at those epochs and SFR-M trajectories of galaxies observed at
lower redshifts. The SFR-M correlations obtained using the two approaches
are found to be consistent with each other through a KS test. Validation tests
using SFHs from semi-analytic models and cosmological hydrodynamical
simulations confirm the sensitivity of the method to changes in the slope,
normalization and shape of the SFR-M correlation. This technique allows us
to further probe the low-mass regime of the correlation at high-z by
dex and over an effective volume of larger than possible with
just direct fits. We find that the SFR-M correlation is consistent with
being linear down to M at . The evolution of the
correlation is well described by , where is the age of the universe in Gyr.Comment: 22 pages, 10 figures. Accepted for publication in Ap
Stellar Mass--Gas-phase Metallicity Relation at : A Power Law with Increasing Scatter toward the Low-mass Regime
We present the stellar mass ()--gas-phase metallicity relation (MZR)
and its scatter at intermediate redshifts () for 1381 field
galaxies collected from deep spectroscopic surveys. The star formation rate
(SFR) and color at a given of this magnitude-limited ( AB)
sample are representative of normal star-forming galaxies. For masses below
, our sample of 237 galaxies is 10 times larger than those
in previous studies beyond the local universe. This huge gain in sample size
enables superior constraints on the MZR and its scatter in the low-mass regime.
We find a power-law MZR at :
. Our MZR
shows good agreement with others measured at similar redshifts in the
literature in the intermediate and massive regimes, but is shallower than the
extrapolation of the MZRs of others to masses below . The SFR
dependence of the MZR in our sample is weaker than that found for local
galaxies (known as the Fundamental Metallicity Relation). Compared to a variety
of theoretical models, the slope of our MZR for low-mass galaxies agrees well
with predictions incorporating supernova energy-driven winds. Being robust
against currently uncertain metallicity calibrations, the scatter of the MZR
serves as a powerful diagnostic of the stochastic history of gas accretion, gas
recycling, and star formation of low-mass galaxies. Our major result is that
the scatter of our MZR increases as decreases. Our result implies that
either the scatter of the baryonic accretion rate or the scatter of the
-- relation increases as decreases. Moreover, our
measures of scatter at appears consistent with that found for local
galaxies.Comment: 18 pages, 10 figures. Accepted by ApJ. Typos correcte
CANDELS Multi-wavelength Catalogs: Source Detection and Photometry in the GOODS-South Field
We present a UV-to-mid infrared multi-wavelength catalog in the
CANDELS/GOODS-S field, combining the newly obtained CANDELS HST/WFC3 F105W,
F125W, and F160W data with existing public data. The catalog is based on source
detection in the WFC3 F160W band. The F160W mosaic includes the data from
CANDELS deep and wide observations as well as previous ERS and HUDF09 programs.
The mosaic reaches a 5 limiting depth (within an aperture of radius
0.17 arcsec) of 27.4, 28.2, and 29.7 AB for CANDELS wide, deep, and HUDF
regions, respectively. The catalog contains 34930 sources with the
representative 50% completeness reaching 25.9, 26.6, and 28.1 AB in the F160W
band for the three regions. In addition to WFC3 bands, the catalog also
includes data from UV (U-band from both CTIO/MOSAIC and VLT/VIMOS), optical
(HST/ACS F435W, F606W, F775W, F814W, and F850LP), and infrared (HST/WFC3 F098M,
VLT/ISAAC Ks, VLT/HAWK-I Ks, and Spitzer/IRAC 3.6, 4.5, 5.8, 8.0 m)
observations. The catalog is validated via stellar colors, comparison with
other published catalogs, zeropoint offsets determined from the best-fit
templates of the spectral energy distribution of spectroscopically observed
objects, and the accuracy of photometric redshifts. The catalog is able to
detect unreddened star-forming (passive) galaxies with stellar mass of
10^{10}M_\odot at a 50% completeness level to z3.4 (2.8), 4.6 (3.2), and
7.0 (4.2) in the three regions. As an example of application, the catalog is
used to select both star-forming and passive galaxies at z2--4 via the
Balmer break. It is also used to study the color--magnitude diagram of galaxies
at 0<z<4.Comment: The full resolution article is now published in ApJS (2013, 207, 24).
22 pages, 21 figures, and 5 tables. The catalogue is available on the CANDELS
website: http://candels.ucolick.org/data_access/GOODS-S.html MAST:
http://archive.stsci.edu/prepds/candels and Rainbow Database:
https://arcoiris.ucolick.org/Rainbow_navigator_public and
https://rainbowx.fis.ucm.es/Rainbow_navigator_publi
Recent Synthetic Studies Leading to Structural Revisions of Marine Natural Products
Because of the highly unique structures of marine natural products, there are many examples of structures that were originally proposed based on spectral analyses but later proven incorrect. In many cases, the total syntheses of the originally proposed structures of marine natural products has confirmed their incorrectness and the subsequent total syntheses of the newly proposed structures proved the revised structures. This review will show such cases appearing after 2005 and demonstrate how the true structures were elucidated
Neurophysiology
Contains reports on twenty research projects.Bell Laboratories (Grant)National Institutes of Health (Grant 5 R01 EY01149-03S2)National Institutes of Health (Grant 5 TO1 EY00090-04)National Institutes of Health (Grant 5 RO1 NS12307-03)National Institutes of Health (Grant K04 NS00010)National Multiple Sclerosis Society (Grant RG-1133-A-1)Health Sciences Fund (Grant 78-10
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