Evolutionary algorithms and other meta-heuristics have been employed widely to solve optimization problems in many different fields over the past few decades. Their performance in finding optimal ...solutions often depends heavily on the parameterization of the algorithm's search operators, which affect an algorithm's balance between search diversification and intensification. While many parameter-adaptive algorithms have been developed to improve the searching ability of meta-heuristics, their performance is often unsatisfactory when applied to real-world problems. This is, at least in part, because available computational budgets are often constrained in such settings due to the long simulation times associated with objective function and/or constraint evaluation, thereby preventing convergence of existing parameter-adaptive algorithms. To this end, this paper proposes an innovative parameter-adaptive strategy for ant colony optimization (ACO) algorithms based on controlling the convergence trajectory in decision space to follow any prespecified path, aimed at finding the best possible solution within a given, and limited, computational budget. The utility of the proposed convergence trajectory controlled ACO (ACO CTC ) algorithm is demonstrated using six water distribution system design problems (WDSDPs, a difficult type of combinatorial problem in water resources) with varying complexity. The results show that the proposed ACO CTC successfully enables the specified convergence trajectories to be followed by automatically adjusting the algorithm's parameter values. Different convergence trajectories significantly affect the algorithm's final performance (solution quality). The trajectory with a slight bias toward diversification in the first half and more emphasis on intensification during the second half of the search exhibits substantially improved performance compared to the best available ACO variant with the best parameterization (no convergence control) for all WDSDPs and computational scenarios considered. For the two large-scale WDSDPs, new best-known solutions are found by the proposed ACO CTC .
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 for a sample of 17,873 galaxies at 0.5 < z < 6 in the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey 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 backward in time along these trajectories. We study the SFR-M* correlation at z = 1, 2, 3, 4, 5, 6 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 K-S 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 ∼1 dex and over an effective volume of ∼10× larger than possible with just direct fits. We find that the SFR-M* correlation is consistent with being linear down to M* ∼ 106 M at z > 4. The evolution of the correlation is well described by , where tuniv is the age of the universe in Gyr.
Using the CANDELS photometric catalogs for the Hubble Space Telescope/ACS and WFC3, we identified massive evolved galaxies at 3 < z < 4.5 employing three different selection methods. We find the ...comoving number density of these objects to be ∼2 × 10−5 and 8 × 10−6 Mpc−3 after correction for completeness for two redshift bins centered at z = 3.4, 4.7. We quantify a measure of how much confidence we should have for each candidate galaxy from different selections and what the conservative error estimates propagated into our selection are. Then we compare the evolution of the corresponding number densities and their stellar mass density with numerical simulations, semianalytical models, and previous observational estimates, which shows slight tension at higher redshifts as the models tend to underestimate the number and mass densities. By estimating the average halo masses of the candidates (Mh 4.2, 1.9, and 1.3 × 1012 M for redshift bins centered at z = 3.4, 4.1, and 4.7), we find them to be consistent with halos that were efficient in turning baryons to stars, relatively immune to the feedback effects, and on the verge of transition into hot-mode accretion. This can suggest the relative cosmological starvation of the cold gas followed by an overconsumption phase in which the galaxy rapidly consumes the available cold gas as one of the possible drivers for the quenching of the massive evolved population at high redshift.
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 5σ limiting depth (within an aperture of radius 0farcs17) of 27.4, 28.2, and 29.7 AB for CANDELS wide, deep, and HUDF regions, respectively. The catalog contains 34,930 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 μm) observations. The catalog is validated via stellar colors, comparison with other published catalogs, zero-point 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(exp 10) M(sub ☉) at a 50% completeness level to z ~ 3.4 (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 z ~ 2-4 via the Balmer break. It is also used to study the color-magnitude diagram of galaxies at 0 < z < 4.
ABSTRACT 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 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 (β). We generalize the shape of the dust law with an empirical model, where kλ is the dust law of Calzetti et al., and show that there exists a correlation between the color excess and tilt δ 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 β. The change in the dust law with color excess is consistent with a model where attenuation is caused 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 ( ).
ABSTRACT We present the stellar mass ( M * )-gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts ( 0.5 ≤ z ≤ 0.7 ) for 1381 field galaxies collected from deep spectroscopic ...surveys. The star formation rate (SFR) and color at a given M * of this magnitude-limited ( R 24 AB) sample are representative of normal star-forming galaxies. For masses below 109 M , 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 108 M < M * < 10 11 M : 12 + log ( O / H ) = ( 5.83 0.19 ) + ( 0.30 0.02 ) log ( M * / M ) . At 109 M < M * < 10 10.5 M , our MZR shows agreement with others measured at similar redshifts in the literature. Our power-law slope is, however, shallower than the extrapolation of the MZRs of others to masses below 109 M . 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 M * decreases. Our result implies that either the scatter of the baryonic accretion rate ( M ˙ ) or the scatter of the M * - M halo relation ( SHMR ) increases as M * decreases. Moreover, our measure of scatter at z = 0.7 appears consistent with that found for local galaxies. This lack of redshift evolution constrains models of galaxy evolution to have both M ˙ and SHMR remain unchanged from z = 0.7 to z = 0.
We present the stellar mass (M-*)-gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts (0.5 \textless= z \textless= 0.7) for 1381 field galaxies collected from deep ...spectroscopic surveys. The star formation rate (SFR) and color at a given M-* of this magnitude-limited (R less than or similar to 24 AB) sample are representative of normal star-forming galaxies. For masses below 10(9) M-circle dot, our sample of 237 galaxies is similar to 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 10(8) M-circle dot \textless M-* \textless 10(11) M-circle dot: 12 + log (O/H) = (5.83 +/- 0.19)+(0.30 +/- 0.02) log (M-*/M-circle dot). At 10(9) M-circle dot \textless M-* \textless 10(10.5) M-circle dot, our MZR shows agreement with others measured at similar redshifts in the literature. Our power-law slope is, however, shallower than the extrapolation of the MZRs of others to masses below 10(9) M-circle dot. 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 M-* decreases. Our result implies that either the scatter of the baryonic accretion rate (sigma((M) over dot)) or the scatter of the M-*-M-halo relation (sigma(SHMR)) increases as M-* decreases. Moreover, our measure of scatter at z = 0.7 appears consistent with that found for local galaxies. This lack of redshift evolution constrains models of galaxy evolution to have both sigma((M) over dot) and sigma(SHMR) remain unchanged from z = 0.7 to z = 0.
Using the CANDELS photometric catalogs for the HST/ACS and WFC3, we
identified massive evolved galaxies at $3 < z < 4.5$, employing three different
selection methods. We find the comoving number ...density of these objects to be
$\sim 2 \times 10^{-5}$ and $8 \times 10^{-6}Mpc^{-3}$ after correction for
completeness for two redshift bins centered at $z=3.4, 4.7$. We quantify a
measure of how much confidence we should have for each candidate galaxy from
different selections and what are the conservative error estimates propagated
into our selection. Then we compare the evolution of the corresponding number
densities and their stellar mass density with numerical simulations,
semi-analytical models, and previous observational estimates, which shows
slight tension at higher redshifts as the models tend to underestimate the
number and mass densities. By estimating the average halo masses of the
candidates ($M_h \approx 4.2, 1.9, 1.3 \times 10^{12} M_\odot$ for redshift
bins centered at $z=3.4, 4.1, 4.7$), we find them to be consistent with halos
that were efficient in turning baryons to stars and were relatively immune to
the feedback effects and on the verge of transition into hot-mode accretion.
This can suggest the relative cosmological starvation of the cold gas followed
by an overconsumption phase in which the galaxy consumes the available cold gas
rapidly as one of the possible drivers for the quenching of the massive evolved
population 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 \(17,873\) galaxies at \(0.5<z<6\) 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 \(z=1,2,3,4,5,6\) 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 \(\sim 1\) dex and over an effective volume of \(\sim 10\times\) larger than possible with just direct fits. We find that the SFR-M\(_*\) correlation is consistent with being linear down to M\(_*\sim 10^7 M_\odot\) at \(z>4\). The evolution of the correlation is well described by \(\log SFR= (0.80\pm 0.029 - 0.017\pm 0.010\times t_{univ})\log M_*\) \(- (6.487\pm 0.282-0.039\pm 0.008\times t_{univ})\), where \(t_{univ}\) is the age of the universe in Gyr.
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