79 research outputs found
Chemo-Archaeological Downsizing in a Hierarchical Universe: Impact of a Top Heavy IGIMF
We make use of a semi-analytical model of galaxy formation to investigate the
origin of the observed correlation between [a/Fe] abundance ratios and stellar
mass in elliptical galaxies. We implement a new galaxy-wide stellar initial
mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in
the semi-analytic model SAG and evaluate its impact on the chemical evolution
of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key
to reproducing the correct [a/Fe]-stellar mass relation. Massive galaxies reach
higher [a/Fe] abundance ratios because they are characterized by more top-heavy
IMFs as a result of their higher SFR. As a consequence of our analysis, the
value of the minimum embedded star cluster mass and of the slope of the
embedded cluster mass function, which are free parameters involved in the
TH-IGIMF theory, are found to be as low as 5 solar masses and 2, respectively.
A mild downsizing trend is present for galaxies generated assuming either a
universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass,
older galaxies (with formation redshifts > 2) are formed in shorter time-scales
(< 2 Gyr), thus achieving larger [a/Fe] values. Hence, the time-scale of galaxy
formation alone cannot explain the slope of the [a/Fe]-galaxy mass relation,
but is responsible for the big dispersion of [a/Fe] abundance ratios at fixed
stellar mass.We further test the hyphothesis of a TH-IGIMF in elliptical
galaxies by looking into mass-to-light ratios, and luminosity functions. Models
with a TH-IGIMF are also favoured by these constraints. In particular,
mass-to-light ratios agree with observed values for massive galaxies while
being overpredicted for less massive ones; this overprediction is present
regardless of the IMF considered.Comment: 24 pages, 15 figures, 2 tables. (Comments most welcome). Summited to
MNRA
Calibration of semi-analytic models of galaxy formation using Particle Swarm Optimization
We present a fast and accurate method to select an optimal set of parameters
in semi-analytic models of galaxy formation and evolution (SAMs). Our approach
compares the results of a model against a set of observables applying a
stochastic technique called Particle Swarm Optimization (PSO), a self-learning
algorithm for localizing regions of maximum likelihood in multidimensional
spaces that outperforms traditional sampling methods in terms of computational
cost. We apply the PSO technique to the SAG semi-analytic model combined with
merger trees extracted from a standard CDM N-body simulation. The
calibration is performed using a combination of observed galaxy properties as
constraints, including the local stellar mass function and the black hole to
bulge mass relation. We test the ability of the PSO algorithm to find the best
set of free parameters of the model by comparing the results with those
obtained using a MCMC exploration. Both methods find the same maximum
likelihood region, however the PSO method requires one order of magnitude less
evaluations. This new approach allows a fast estimation of the best-fitting
parameter set in multidimensional spaces, providing a practical tool to test
the consequences of including other astrophysical processes in SAMs.Comment: 11 pages, 4 figures, 1 table. Accepted for publication in ApJ.
Comments are welcom
The ALMA Frontier Fields Survey - IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223
[abridged] Characterizing the number counts of faint, dusty star-forming
galaxies is currently a challenge even for deep, high-resolution observations
in the FIR-to-mm regime. They are predicted to account for approximately half
of the total extragalactic background light at those wavelengths. Searching for
dusty star-forming galaxies behind massive galaxy clusters benefits from strong
lensing, enhancing their measured emission while increasing spatial resolution.
Derived number counts depend, however, on mass reconstruction models that
properly constrain these clusters. We estimate the 1.1 mm number counts along
the line of sight of three galaxy clusters, i.e. Abell 2744, MACSJ0416.1-2403
and MACSJ1149.5+2223, which are part of the ALMA Frontier Fields Survey. We
perform detailed simulations to correct these counts for lensing effects. We
use several publicly available lensing models for the galaxy clusters to derive
the intrinsic flux densities of our sources. We perform Monte Carlo simulations
of the number counts for a detailed treatment of the uncertainties in the
magnifications and adopted source redshifts. We find an overall agreement among
the number counts derived for the different lens models, despite their
systematic variations regarding source magnifications and effective areas. Our
number counts span ~2.5 dex in demagnified flux density, from several mJy down
to tens of uJy. Our number counts are consistent with recent estimates from
deep ALMA observations at a 3 level. Below 0.1 mJy, however,
our cumulative counts are lower by 1 dex, suggesting a flattening in
the number counts. In our deepest ALMA mosaic, we estimate number counts for
intrinsic flux densities 4 times fainter than the rms level. This
highlights the potential of probing the sub-10 uJy population in larger samples
of galaxy cluster fields with deeper ALMA observations.Comment: 19 pages, 14 figures, 3 tables. Accepted for publication in A&
Properties of Submillimeter Galaxies in a Semi-analytic Model using the "Count Matching" Approach: Application to the ECDF-S
We present a new technique for modeling submillimeter galaxies (SMGs): the
"Count Matching" approach. Using lightcones drawn from a semi-analytic model of
galaxy formation, we choose physical galaxy properties given by the model as
proxies for their submillimeter luminosities, assuming a monotonic
relationship. As recent interferometric observations of the Extended Chandra
Deep Field South show that the brightest sources detected by single-dish
telescopes are comprised by emission from multiple fainter sources, we assign
the submillimeter fluxes so that the combined LABOCA plus bright-end ALMA
observed number counts for this field are reproduced. After turning the model
catalogs given by the proxies into submillimeter maps, we perform a source
extraction to include the effects of the observational process on the recovered
counts and galaxy properties. We find that for all proxies, there are lines of
sight giving counts consistent with those derived from LABOCA observations,
even for input sources with randomized positions in the simulated map.
Comparing the recovered redshift, stellar mass and host halo mass distributions
for model SMGs with observational data, we find that the best among the
proposed proxies is that in which the submillimeter luminosity increases
monotonically with the product between dust mass and SFR. This proxy naturally
reproduces a positive trend between SFR and bolometric IR luminosity. The
majority of components of blended sources are spatially unassociated.Comment: 21 pages, 20 figures, 5 tables. Accepted for publication in MNRA
The evolution of Balmer jump selected galaxies in the ALHAMBRA survey
We present a new color-selection technique, based on the Bruzual & Charlot
models convolved with the bands of the ALHAMBRA survey, and the redshifted
position of the Balmer jump to select star-forming galaxies in the redshift
range 0.5 < z < 1.5. These galaxies are dubbed Balmer jump Galaxies BJGs. We
apply the iSEDfit Bayesian approach to fit each detailed SED and determine
star-formation rate (SFR), stellar mass, age and absolute magnitudes. The mass
of the haloes where these samples reside are found via a clustering analysis.
Five volume-limited BJG sub-samples with different mean redshifts are found to
reside in haloes of median masses slightly
increasing toward z=0.5. This increment is similar to numerical simulations
results which suggests that we are tracing the evolution of an evolving
population of haloes as they grow to reach a mass of at z=0.5. The likely progenitors of our samples at z3 are Lyman
Break Galaxies, which at z2 would evolve into star-forming BzK galaxies,
and their descendants in the local Universe are elliptical galaxies.Hence, this
allows us to follow the putative evolution of the SFR, stellar mass and age of
these galaxies. From z1.0 to z0.5, the stellar mass of the volume
limited BJG samples nearly does not change with redshift, suggesting that major
mergers play a minor role on the evolution of these galaxies. The SFR evolution
accounts for the small variations of stellar mass, suggesting that star
formation and possible minor mergers are the main channels of mass assembly.Comment: 14 pages, 10 figures. Submitted to A&A. It includes first referee's
comments. Abstract abridged due to arXiv requirement
Persistent and occasional: searching for the variable population of the ZTF/4MOST sky using ZTF data release 11
We present a variability, color and morphology based classifier, designed to
identify transients, persistently variable, and non-variable sources, from the
Zwicky Transient Facility (ZTF) Data Release 11 (DR11) light curves of extended
and point sources. The main motivation to develop this model was to identify
active galactic nuclei (AGN) at different redshift ranges to be observed by the
4MOST ChANGES project. Still, it serves as a more general time-domain astronomy
study. The model uses nine colors computed from CatWISE and PS1, a morphology
score from PS1, and 61 single-band variability features computed from the ZTF
DR11 g and r light curves. We trained two versions of the model, one for each
ZTF band. We used a hierarchical local classifier per parent node approach,
where each node was composed of a balanced random forest model. We adopted a
17-class taxonomy, including non-variable stars and galaxies, three transient
classes, five classes of stochastic variables, and seven classes of periodic
variables. The macro averaged precision, recall and F1-score are 0.61, 0.75,
and 0.62 for the g-band model, and 0.60, 0.74, and 0.61, for the r-band model.
When grouping the four AGN classes into one single class, its precision,
recall, and F1-score are 1.00, 0.95, and 0.97, respectively, for both the g and
r bands. We applied the model to all the sources in the ZTF/4MOST overlapping
sky, avoiding ZTF fields covering the Galactic bulge, including 86,576,577
light curves in the g-band and 140,409,824 in the r-band. Only 0.73\% of the
g-band light curves and 2.62\% of the r-band light curves were classified as
stochastic, periodic, or transient with high probability ().
We found that, in general, more reliable results are obtained when using the
g-band model. Using the latter, we identified 384,242 AGN candidates, 287,156
of which have .Comment: Accepted for publication in Astronomy & Astrophysics. Abstract
shortened for arXiv. Tables containing the classifications and features for
the ZTF g and r bands, and the labeled sets will be available at CDS.
Individual catalogs per class and band, as well as the labeled set catalogs,
can be downloaded at Zenodo DOI:10.5281/zenodo.782604
Multiwavelength monitoring of the nucleus in PBC J2333.9-2343: the giant radio galaxy with a blazar-like core
PBC J2333.9-2343 is a giant radio galaxy at z = 0.047 with a bright central
core associated to a blazar nucleus. If the nuclear blazar jet is a new phase
of the jet activity, then the small orientation angle suggest a dramatic change
of the jet direction. We present observations obtained between September 2018
and January 2019 (cadence larger than three days) with Effeslberg, SMARTS-1.3m,
ZTF, ATLAS, Swift, and Fermi-LAT, and between April-July 2019 (daily cadence)
with SMARTS-1.3m and ATLAS. Large (>2x) flux increases are observed on
timescales shorter than a month, which are interpreted as flaring events. The
cross correlation between the SMARTS-1.3m monitoring in the NIR and optical
shows that these data do not show significant time lag within the measured
errors. A comparison of the optical variability properties between non-blazars
and blazars AGN shows that PBC J2333.9-2343 has properties more comparable to
the latter. The SED of the nucleus shows two peaks, that were fitted with a one
zone leptonic model. Our data and modelling shows that the high energy peak is
dominated by External Compton from the dusty torus with mild contribution from
Inverse Compton from the jet. The derived jet angle of 3 degrees is also
typical of a blazar. Therefore, we confirm the presence of a blazar-like core
in the center of this giant radio galaxy, likely a Flat Spectrum Radio Quasar
with peculiar properties.Comment: Accepted for publication in MNRAS. 15 pages, 6 figures, 2 appendix
including tables and figure
An ALMA survey of submillimetre galaxies in the COSMOS field: The extent of the radio-emitting region revealed by 3 GHz imaging with the Very Large Array
We determine the radio size distribution of a large sample of 152 SMGs in
COSMOS that were detected with ALMA at 1.3 mm. For this purpose, we used the
observations taken by the VLA-COSMOS 3 GHz Large Project. One hundred and
fifteen of the 152 target SMGs were found to have a 3 GHz counterpart. The
median value of the major axis FWHM at 3 GHz is derived to be kpc.
The radio sizes show no evolutionary trend with redshift, or difference between
different galaxy morphologies. We also derived the spectral indices between 1.4
and 3 GHz, and 3 GHz brightness temperatures for the sources, and the median
values were found to be and K. Three of the
target SMGs, which are also detected with the VLBA, show clearly higher
brightness temperatures than the typical values. Although the observed radio
emission appears to be predominantly powered by star formation and supernova
activity, our results provide a strong indication of the presence of an AGN in
the VLBA and X-ray-detected SMG AzTEC/C61. The median radio-emitting size we
have derived is 1.5-3 times larger than the typical FIR dust-emitting sizes of
SMGs, but similar to that of the SMGs' molecular gas component traced through
mid- line emission of CO. The physical conditions of SMGs probably render
the diffusion of cosmic-ray electrons inefficient, and hence an unlikely
process to lead to the observed extended radio sizes. Instead, our results
point towards a scenario where SMGs are driven by galaxy interactions and
mergers. Besides triggering vigorous starbursts, galaxy collisions can also
pull out the magnetised fluids from the interacting disks, and give rise to a
taffy-like synchrotron-emitting bridge. This provides an explanation for the
spatially extended radio emission of SMGs, and can also cause a deviation from
the well-known IR-radio correlation.Comment: 32 pages (incl. 5 appendices), 17 figures, 7 tables; accepted for
publication in A&A; abstract abridged for arXi
Tris(diphenylthiophosphinoyl)methanide as tripod ligand in rhodium(III), iridium(III) and ruthenium(II) complexes. Crystal structures of [(η5-C5Me5)Ir{η3-(SPPh2)3C-S,SâČ,Sâł}]BF4 and [(η6-MeC6H4Pri)Ru{η3-(SPPh2)3C-S,SâČ,Sâł}]BPh4
Reaction of the complex [{(η5-C5Me5)RhCl2}2], in CH2Cl2 solution, with AgBF4 (1:2 molar ratio) and (SPPh2)3CH leads to the cationic compound [(η5-C5Me5)RhCl{η2-(SPPh2)2CH(SPPh2)-S,SâČ}]BF4 (1) which is deprotonated by thallium(I) pyrazolate affording [(η5-C5Me5)Rh{η3-(SPPh2)3CâS,SâČ,Sâł}]BF4 (2a). The iridium dimer [(η5-C5Me5)IrCl2}2] reacts with silver salts and (SPPh2)3CH, in CH2Cl2 or Me2CO, under analogous conditions, affording mixtures of [(η5-C5Me5)IrCl{η2-(SPPh2)2)-S,SâČ}]+ and [(η5-C5Me5)Ir{η3-(SPPh2)3C-S,SâČ,Sâł}]A [A=BF4â (3a), PF6â (3b). Addition of Et3N to the mixture gives pure complexes 3. The ruthenium complexes [{η6j6-arene)RuCl2}2] (arene = C6Me6, p-MeC6H4Pri) react with (SPPh2)3CH, in the presence of AgA (A = PF6â or BF4â) or Na BPh4, in CH2Cl2 or Me2CO, yielding only the deprotonated complexes [(η6-arene)Ru{η3-(SPPH2)3CâS,SâČ,Sâł}]A [arene = C6Me6, A = BF4; arene = p-MeC6H4Pri, A - BPh4 (4a), PF6 (4b)]. The crystal structures of 3a and 4a were established by X-ray crystallography. Compound 3a crystallizes in the orthorhombic space group Pna21, with lattice parameters a-41.477(6), b = 10.6778(11), c = 20.162(3) Ă
and Z=8. Complex 4a crystallizes in a monoclinic lattice, space group P21/n, with a = 20.810(4), b = 12.555(3), c = 23.008(4) Ă
, ÎČ = 95.82(2)° and Z = 4. Both cationic complexes exhibit analogous pseudo-octahedml molecular structures with the anionic (SPPh2)3Câ ligand bonded via the three sulphur atoms in a tripodal, tridentate fashion. Each metal centre completes its coordination environment with a η5-C5Me5 (3a) or a η6-MeC6H4Pri group (4a). A quite interesting result concerns the non-planarity of the methanide carbon which display PâCâP angles in the range 112.6â114.4(5)° in 3a and 111.9â113.6(4)° in 4a. The redox chemistry of the complexes was investigated by cyclic voltammetry. The Rh(III) complexes are quasi-reversibly reduced to Rh(I) and the Ir(III) complex is irreversibly reduced to IKD in acetonitrile solutions. The Ru(II) complex undergoes a quasi-reversible reduction to Ru(I) and a reversible oxidation to Ru(III).We thank the 'Fondo de Desarrollo Cientifico y Tecnologico, Chile' (Grant No. 460/93-95), Direccion
de Investigacion y Postgrado, Pontificia Universidad Catolica de Chile (DlPUC), Fundacion Andes, Chile,
and the Instituto de Cooperacion Iberoamericano, Spain, for financial support.Peer reviewe
Multi-scale stamps for real-time classification of alert streams
In recent years, automatic classifiers of image cutouts (also called
"stamps") have shown to be key for fast supernova discovery. The upcoming Vera
C. Rubin Observatory will distribute about ten million alerts with their
respective stamps each night, which it is expected to enable the discovery of
approximately one million supernovae each year. A growing source of confusion
for these classifiers is the presence of satellite glints, sequences of
point-like-sources produced by rotating satellites or debris. The currently
planned Rubin stamps will have a size smaller than the typical separation
between these point sources. Thus, a larger field of view image stamp could
enable the automatic identification of these sources. However, the distribution
of larger field of view stamps would be limited by network bandwidth
restrictions. We evaluate the impact of using image stamps of different angular
sizes and resolutions for the fast classification of events (AGNs, asteroids,
bogus, satellites, SNe, and variable stars), using available data from the
Zwicky Transient Facility survey. We compare four scenarios: three with the
same number of pixels (small field of view with high resolution, large field of
view with low resolution, and a proposed multi-scale strategy) and a scenario
with the full ZTF stamp that has a larger field of view and higher resolution.
Our multi-scale proposal outperforms all the scenarios, with a macro f1-score
of 87.39. We encourage Rubin and its Science Collaborations to consider the
benefits of implementing multi-scale stamps as a possible update to the alert
specification.Comment: Submitted to ApJ
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