417 research outputs found
Description of Drip-Line Nuclei within Relativistic Mean-Field Plus BCS Approach
Recently it has been demonstrated, considering Ni and Ca isotopes as
prototypes, that the relativistic mean-field plus BCS (RMF+BCS) approach
wherein the single particle continuum corresponding to the RMF is replaced by a
set of discrete positive energy states for the calculation of pairing energy
provides a good approximation to the full relativistic Hartree-Bogoliubov (RHB)
description of the ground state properties of the drip-line neutron rich
nuclei. The applicability of RMF+BCS is essentially due to the fact that the
main contribution to the pairing correlations is provided by the low-lying
resonant states. General validity of this approach is demonstrated by the
detailed calculations for the ground state properties of the chains of isotopes
of O, Ca, Ni, Zr, Sn and Pb nuclei. The TMA and NL-SH force parameter sets have
been used for the effective mean-field Lagrangian. Comprehensive results for
the two neutron separation energy, rms radii, single particle pairing gaps and
pairing energies etc. are presented. The Ca isotopes are found to exhibit
distinct features near the neutron drip line whereby it is found that further
addition of neutrons causes a rapid increase in the neutron rms radius with
almost no increase in the binding energy, indicating the occurrence of halos. A
comparison of these results with the available experimental data and with the
recent continuum relativistic Hartree-Bogoliubov (RCHB) calculations amply
demonstrates the validity and usefulness of this fast RMF+BCS approach.Comment: 59 pages, 40 figure
Discovery of a dark, massive, ALMA-only galaxy at z~5-6 in a tiny 3-millimeter survey
We report the serendipitous detection of two 3 mm continuum sources found in
deep ALMA Band 3 observations to study intermediate redshift galaxies in the
COSMOS field. One is near a foreground galaxy at 1.3", but is a previously
unknown dust-obscured star-forming galaxy (DSFG) at probable ,
illustrating the risk of misidentifying shorter wavelength counterparts. The
optical-to-mm spectral energy distribution (SED) favors a grey
attenuation curve and results in significantly larger stellar mass and SFR
compared to a Calzetti starburst law, suggesting caution when relating
progenitors and descendants based on these quantities. The other source is
missing from all previous optical/near-infrared/sub-mm/radio catalogs
("ALMA-only"), and remains undetected even in stacked ultradeep optical
( AB) and near-infrared ( AB) images. Using the ALMA position as
a prior reveals faint measurements in stacked IRAC 3.6+4.5,
ultradeep SCUBA2 850m, and VLA 3GHz, indicating the source is real. The
SED is robustly reproduced by a massive M and
M, highly obscured , star forming
Myr galaxy at redshift 1.1. The
ultrasmall 8 arcmin survey area implies a large yet uncertain
contribution to the cosmic star formation rate density CSFRD(z=5)
M yr Mpc, comparable to all
ultraviolet-selected galaxies combined. These results indicate the existence of
a prominent population of DSFGs at , below the typical detection limit of
bright galaxies found in single-dish sub-mm surveys, but with larger space
densities Mpc, higher duty cycles ,
contributing more to the CSFRD, and potentially dominating the high-mass galaxy
stellar mass function.Comment: Accepted for publication in ApJ. 2 galaxies, too many pages, 8
figures, 2 table
Constraints for the X17 boson from compacts objects observations
We investigate the hypothetical X17 boson on neutron stars and Quark Stars
(QSs) using various hadronic Equation of States (EoSs) with phenomenological or
microscopic origin. Our aim is to set realistic constraints on its coupling
constant and the mass scaling, with respect to causality and various possible
upper mass limits and the dimensionless tidal deformability . In
particular, we pay special attention on two main phenomenological parameters of
the X17, the one is related to the coupling constant that it has
with hadrons or quarks and the other with the in-medium effects through the
regulator . Both are very crucial concerning the contribution on
the total energy density and pressure. In the case of considering the X17 as a
carrier of nuclear force in Relativistic Mean Field (RMF) theory, an admixture
into vector boson segment was constrained by 20\% and 30\%. In our
investigation, we came to the general conclusion that the effect of the
hypothetical X17 both on neutron and QSs constrained mainly by the causality
limit, which is a specific property of each EoS. Moreover, it depends on the
interplay between the main two parameters that is the interaction coupling
and the in-medium effects regulator . These effects
are more pronounced in the case of QSs concerning all the bulk properties.Comment: 12 pages, 14 figures, 2 table
How to Measure Galaxy Star Formation Histories. II. Nonparametric Models
Nonparametric star formation histories (SFHs) have long promised to be the
`gold standard' for galaxy spectral energy distribution (SED) modeling as they
are flexible enough to describe the full diversity of SFH shapes, whereas
parametric models rule out a significant fraction of these shapes {\it a
priori}. However, this flexibility is not fully constrained even with
high-quality observations, making it critical to choose a well-motivated prior.
Here, we use the SED-fitting code \texttt{Prospector} to explore the effect of
different nonparametric priors by fitting SFHs to mock UV-IR photometry
generated from a diverse set of input SFHs. First, we confirm that
nonparametric SFHs recover input SFHs with less bias and return more accurate
errors than do parametric SFHs. We further find that, while nonparametric SFHs
robustly recover the overall shape of the input SFH, the primary determinant of
the size and shape of the posterior star formation rate (SFR) as a function of
time is the choice of prior, rather than the photometric noise. As a practical
demonstration, we fit the UV-IR photometry of 6000 galaxies from the GAMA
survey and measure inter-prior scatters in mass (0.1 dex), SFR (0.8 dex), and mass-weighted ages (0.2 dex), with the bluest
star-forming galaxies showing the most sensitivity. An important distinguishing
characteristic for nonparametric models is the characteristic timescale for
changes in SFR(t). This difference controls whether galaxies are assembled in
bursts or in steady-state star formation, corresponding respectively to
(feedback-dominated/accretion-dominated) models of galaxy formation and to
(larger/smaller) confidence intervals derived from SED-fitting. High-quality
spectroscopy has the potential to further distinguish between these proposed
models of SFR(t).Comment: replacing with ApJ accepted versio
ZFOURGE: Extreme 5007 emission may be a common early-lifetime phase for star-forming galaxies at
Using the \prospector\ spectral energy distribution (SED) fitting code, we
analyze the properties of 19 Extreme Emission Line Galaxies (EELGs) identified
in the bluest composite SED in the \zfourge\ survey at .
\prospector\ includes a physical model for nebular emission and returns
probability distributions for stellar mass, stellar metallicity, dust
attenuation, and nonparametric star formation history (SFH). The EELGs show
evidence for a starburst in the most recent 50 Myr, with the median EELG having
a specific star formation rate (sSFR) of 4.6 Gyr and forming 15\% of its
mass in this short time. For a sample of more typical star-forming galaxies
(SFGs) at the same redshifts, the median SFG has a sSFR of 1.1 Gyr and
forms only of its mass in the last 50 Myr. We find that virtually all of
our EELGs have rising SFHs, while most of our SFGs do not. From our analysis,
we hypothesize that many, if not most, star-forming galaxies at
undergo an extreme H+[\hbox{{\rm O}\kern 0.1em{\sc iii}}] emission
line phase early in their lifetimes. In a companion paper, we obtain
spectroscopic confirmation of the EELGs as part of our {\sc MOSEL} survey. In
the future, explorations of uncertainties in modeling the UV slope for galaxies
at are needed to better constrain their properties, e.g. stellar
metallicities.Comment: 11 pages, 5 figures (main figure is fig 5), accepted for publication
in Ap
SPECULATOR: Emulating stellar population synthesis for fast and accurate galaxy spectra and photometry
We present SPECULATOR - a fast, accurate, and flexible framework for emulating stellar population synthesis (SPS) models for predicting galaxy spectra and photometry. For emulating spectra, we use principal component analysis to construct a set of basis functions, and neural networks to learn the basis coefficients as a function of the SPS model parameters. For photometry, we parameterize the magnitudes (for the filters of interest) as a function of SPS parameters by a neural network. The resulting emulators are able to predict spectra and photometry under both simple and complicated SPS model parameterizations to percent-level accuracy, giving a factor of - speed up over direct SPS computation. They have readily-computable derivatives, making them amenable to gradient-based inference and optimization methods. The emulators are also straightforward to call from a GPU, giving an additional order-of-magnitude speed-up. Rapid SPS computations delivered by emulation offers a massive reduction in the computational resources required to infer the physical properties of galaxies from observed spectra or photometry and simulate galaxy populations under SPS models, whilst maintaining the accuracy required for a range of applications
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale
We present the properties of NGC 4993, the host galaxy of GW170817, the first
gravitational wave (GW) event from the merger of a binary neutron star (BNS)
system and the first with an electromagnetic (EM) counterpart. We use both
archival photometry and new optical/near-IR imaging and spectroscopy, together
with stellar population synthesis models to infer the global properties of the
host galaxy. We infer a star formation history peaked at Gyr ago,
with subsequent exponential decline leading to a low current star formation
rate of 0.01 M yr, which we convert into a binary merger
timescale probability distribution. We find a median merger timescale of
Gyr, with a 90% confidence range of Gyr. This
in turn indicates an initial binary separation of R,
comparable to the inferred values for Galactic BNS systems. We also use new and
archival images to measure a projected offset of
the optical counterpart of kpc (0.64) from the center of NGC 4993
and to place a limit of mag on any pre-existing emission,
which rules out the brighter half of the globular cluster luminosity function.
Finally, the age and offset of the system indicates it experienced a modest
natal kick with an upper limit of km s. Future GWEM
observations of BNS mergers will enable measurement of their population delay
time distribution, which will directly inform their viability as the dominant
source of -process enrichment in the Universe.Comment: 9 Pages, 3 Figures, 2 Tables, ApJL, In Press. Keywords: GW170817, LV
3D-HST+CANDELS : the evolution of the galaxy size-mass distribution since z=3
Spectroscopic+photometric redshifts, stellar mass estimates, and rest-frame colors from the 3D-HST survey are combined with structural parameter measurements from CANDELS imaging to determine the galaxy size-mass distribution over the redshift range 0 < z < 3. Separating early- and late-type galaxies on the basis of star-formation activity, we confirm that early-type galaxies are on average smaller than late-type galaxies at all redshifts, and we find a significantly different rate of average size evolution at fixed galaxy mass, with fast evolution for the early-type population, R eff∝(1 + z)–1.48, and moderate evolution for the late-type population, R eff∝(1 + z)-0.75Peer reviewedFinal Accepted Versio
How to Measure Galaxy Star Formation Histories. I. Parametric Models
Parametric models for galaxy star-formation histories (SFHs) are widely used,
though they are known to impose strong priors on physical parameters. This has
consequences for measurements of the galaxy stellar-mass function (GSMF),
star-formation-rate density (SFRD) and star-forming main sequence (SFMS). We
investigate the effects of the exponentially declining, delayed exponentially
declining, lognormal and double power law SFH models using BAGPIPES. We
demonstrate that each of these models imposes strong priors on specific
star-formation rates (sSFRs), potentially biasing the SFMS, and also imposes a
strong prior preference for young stellar populations. We show that stellar
mass, SFR and mass-weighted age inferences from high-quality mock photometry
vary with the choice of SFH model by at least 0.1, 0.3 and 0.2 dex
respectively. However the biases with respect to the true values depend more on
the true SFH shape than the choice of model. We also demonstrate that
photometric data cannot discriminate between SFH models, meaning it is
important to perform independent tests to find well-motivated priors. We
finally fit a low-redshift, volume-complete sample of galaxies from the Galaxy
and Mass Assembly (GAMA) Survey with each model. We demonstrate that our
stellar masses and SFRs at redshift, are consistent with other
analyses. However, our inferred cosmic SFRDs peak at , approximately
6 Gyr later than direct observations suggest, meaning our mass-weighted ages
are significantly underestimated. This makes the use of parametric SFH models
for understanding mass assembly in galaxies challenging. In a companion paper
we consider non-parametric SFH models.Comment: 20 pages, 12 figures, ApJ accepte
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