5,966 research outputs found
Star Formation Rate Distributions: Inadequacy of the Schechter Function
In this paper we posit that galaxy luminosity functions (LFs) come in two
fundamentally different types depending on whether the luminosity traces galaxy
stellar mass or its current star formation rate (SFR). Mass function types
reflect the older stars and therefore the stellar mass distribution, while SFR
function types arise from the young stars and hence the distribution of SFRs.
Optical and near-infrared LFs are of the mass function type, and are well fit
by a Schechter function (power law with an exponential cutoff at the bright
end). In contrast, LFs of the SFR function type are of a different form, one
that cannot be adequately described by a Schechter function. We demonstrate
this difference by generating SFR distributions for mock samples of galaxies
drawn from a Schechter stellar mass distribution along with established
empirical relations between the SFR and stellar mass. Compared with the
Schechter function, SFR distributions have a shallower decline at the bright
end, which can be traced to the large intrinsic scatter of SFRs at any given
stellar mass. A superior description of SFR distributions is given by the
"Saunders" function, which combines a power law with a Gaussian at the high
end. We show that the Schechter-like appearance of UV and H alpha LFs, although
they are LFs of SFR function type, results when luminosities are not corrected
for dust, or when average statistical corrections are used because individual
attenuation measurements are not available. We thus infer that the
non-Schechter form of the far-IR LFs is a true reflection of the underlying SFR
distribution, rather than the purported artifact of AGN contamination.Comment: Revised after a referee report. Submitted to ApJ. Compatible with B/W
printers. Comments are welcom
Dust Attenuation Curves in the Local Universe: Demographics and New Laws for Star-forming Galaxies and High-redshift Analogs
We study dust attenuation curves of 230,000 individual galaxies in the local
universe, ranging from quiescent to intensely star-forming systems, using
GALEX, SDSS, and WISE photometry calibrated on Herschel-ATLAS. We use a new
method of constraining SED fits with infrared luminosity (SED+LIR fitting), and
parameterized attenuation curves determined with the CIGALE SED fitting code.
Attenuation curve slopes and UV bump strengths are reasonably well constrained
independently from one another. We find that attenuation
curves exhibit a very wide range of slopes that are on average as steep as the
SMC curve slope. The slope is a strong function of optical opacity. Opaque
galaxies have shallower curves - in agreement with recent radiate transfer
models. The dependence of slopes on the opacity produces an apparent dependence
on stellar mass: more massive galaxies having shallower slopes. Attenuation
curves exhibit a wide range of UV bump amplitudes, from none to MW-like; with
an average strength 1/3 of the MW bump. Notably, local analogs of high-redshift
galaxies have an average curve that is somewhat steeper than the SMC curve,
with a modest UV bump that can be to first order ignored, as its effect on the
near-UV magnitude is 0.1 mag. Neither the slopes nor the strengths of the UV
bump depend on gas-phase metallicity. Functional forms for attenuation laws are
presented for normal star-forming galaxies, high-z analogs and quiescent
galaxies. We release the catalog of associated SFRs and stellar masses
(GSWLC-2).Comment: Accepted to ApJ. GSWLC-2 catalog of SED+LIR SFRs and M* to be
released Jun 1 at http://pages.iu.edu/~salims/gswlc
On the Mass-Metallicity-Star Formation Rate Relation for Galaxies at
Recent studies have shown that the local mass-metallicity (M-Z) relation
depends on the specific star formation rate (SSFR). Whether such a dependence
exists at higher redshifts, and whether the resulting M-Z-SFR relation is
redshift invariant, is debated. We re-examine these issues by applying the
non-parametric techniques of Salim et al. (2014) to ~130 galaxies
with N2 and O3 measurements from KBSS (Steidel et al. 2014). We find that the
KBSS M-Z relation depends on SSFR at intermediate masses, where such dependence
exists locally. KBSS and SDSS galaxies of the same mass and SSFR ("local
analogs") are similarly offset in the BPT diagram relative to the bulk of local
star-forming galaxies, and thus we posit that metallicities can be compared
self-consistently at different redshifts as long as the masses and SSFRs of the
galaxies are similar. We find that the M-Z-SFR relation of galaxies is
consistent with the local one at , but is offset up to -0.25 dex
at higher masses, so it is altogether not redshift invariant. This high-mass
offset could arise from a bias that high-redshift spectroscopic surveys have
against high-metallicity galaxies, but additional evidence disfavors this
possibility. We identify three causes for the reported discrepancy between N2
and O3N2 metallicities at : (1) a smaller offset that is also present
for SDSS galaxies, which we remove with new N2 calibration, (2) a genuine
offset due to differing ISM condition, which is also present in local analogs,
(3) an additional offset due to unrecognized AGN contamination.Comment: ApJ accepted. 14 pages. Comments welcom
Dynamics of O(N) Model in a Strong Magnetic Background Field as a Modified Noncommutative Field Theory
In the presence of a strong magnetic field, the effective action of a
composite scalar field in an scalar O(N) model is derived using two different
methods. First, in the framework of worldline formalism, the 1PI n-point vertex
function for the composites is determined in the limit of strong magnetic
field. Then, the n-point effective action of the composites is calculated in
the regime of lowest Landau level dominance. It is shown that in the limit of
strong magnetic field, the results coincide and an effective field theory
arises which is comparable with the conventional noncommutative field theory.
In contrast to the ordinary case, however, the UV/IR mixing is absent in this
modified noncommutative field theory.Comment: Latex file, 19 pp, no figur
High-Resolution Imaging and Optical Control of Bose-Einstein Condensates in an Atom Chip Magnetic Trap
A high-resolution projection and imaging system for ultracold atoms is
implemented using a compound silicon and glass atom chip. The atom chip is
metalized to enable magnetic trapping while glass regions enable high numerical
aperture optical access to atoms residing in the magnetic trap about 100
microns below the chip surface. The atom chip serves as a wall of the vacuum
system, which enables the use of commercial microscope components for
projection and imaging. Holographically generated light patterns are used to
optically slice a cigar-shaped magnetic trap into separate regions; this has
been used to simultaneously generate up to four Bose-condensates. Using
fluorescence techniques we have demonstrated in-trap imaging resolution down to
2.5 micronsComment: 4 pages, 5 figures, 12 reference
Backyard lobster fattening unit Economic feasibility analysis
Lobsters form an important fishery
all along the coastline of India. The
lobster resource potential of Indian
EEZ is 50,000 mt (Vijayakumaran and
Radhakrishnan, 2000). Against this,
lobster production of India in the year
20.00 was 2,387 t, consisting of spiny
lobsters, sand lobsters, and deep-sea
lobsters. While lobster fishery occurs
round the year along the Indian coast
and its island territories , th ere are
peak seasons depending on the
hydrographic conditions and natural
fishery dist ribution of the regions
concerned
Design challenges facing clinical trials of the effectiveness of new HIV prevention technologies
Recent successes of antiretroviral pre-exposure prophylaxis (PrEP) in preventing HIV infection have raised questions whether further placebo controlled trials of new HIV-prevention technologies are ethically justifiable. A trial with active agent(s) in the comparator group can be designed either as a superiority or non-inferiority trial. In a non-inferiority trial the hypothesis tested is that the intervention is not inferior to, by a predefined clinically relevant amount, or at least as effective as, the comparator. Non-inferiority trials pose challenges in data interpretation.Firstly it is possible to show equivalence of two non-effective interventions. If the active comparator intervention is ineffective, the new intervention would be shown to be non-inferior to this inactive intervention, while neither intervention is superior to placebo or no intervention. The second challenge is that any effect that dilutes the true efficacy of an intervention in a trial, such as non-adherence, loss to follow-up or protocol violations, makes it easier for the two interventions to be declared equivalent. Non-differential low adherence is unlikely to lead to the conclusion that an inferior intervention is non-inferior. However, differential adherence between study arms, which is more likely in non-blinded trials, is likely to bias the results and lead to incorrect conclusions. Investigators conducting non-inferiority trials will have to pay special attention to supporting, measuring and maintaining high adherence. The goal in future non-inferiority trials should be to maintain similar levels of high adherence in all study arms, but at a minimum to reduce the likelihood of differential adherence across study arms
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