Carbon monoxide (CO) is the best tracer of Galactic molecular hydrogen H_2_. Its lowest rotational emission lines are in the radio regime, and thanks to Galactic rotation, emission at different distances is Doppler shifted. For a given gas flow model, the observed spectra can thus be deprojected along the line of sight to infer the gas distribution. We used the CO-line survey of Dame et al. (2001ApJ...547..792D) to reconstruct the three-dimensional density of H_2_. We considered the deprojection as a Bayesian variational inference problem. The posterior distribution of the gas densities allowed us to estimate the mean and uncertainty of the reconstructed density. Unlike most of the previous attempts, we took the correlations of gas on a variety of scales into account, which allowed us to correct for some of the well-known pathologies, such as finger-of-god effects. The two gas flow models that we adopted incorporate a Galactic bar that induces radial motions in the inner few kiloparsecs and thus offers spectral resolution towards the Galactic centre. We compared our gas maps with those of earlier studies and characterise their statistical properties, for instance the radial profile of the average surface mass density. We have made our three-dimensional gas maps and their uncertainties available to the community here and at https://dx.doi.org/10.5281/zenodo.5501196.
We perform an extensive test of theoretical stellar models for main-sequence (MS) stars in ugriz, using cluster fiducial sequences obtained in the previous paper of this series. We generate a set of isochrones using the Yale Rotating Evolutionary Code with updated input physics, and derive magnitudes and colors in ugriz from MARCS model atmospheres. These models match cluster MSs over a wide range of metallicity within the errors of the adopted cluster parameters. However, we find a large discrepancy of model colors at the lower MS (T_eff_<~4500K) for clusters at and above solar metallicity. We also reach similar conclusions using the theoretical isochrones of Girardi et al. and Dotter et al., but our new models are generally in better agreement with the data. Using our theoretical isochrones, we also derive MS-fitting distances and turnoff ages for five key globular clusters, and demonstrate the ability to derive these quantities from photometric data in the Sloan Digital Sky Survey. In particular, we exploit multiple color indices (g-r, g-i, and g-z) in the parameter estimation, which allows us to evaluate internal systematic errors. Our distance estimates, with an error of {sigma}_(m-M)_=0.03-0.11mag for individual clusters, are consistent with Hipparcos-based subdwarf-fitting distances derived in the Johnson-Cousins or Stromgren photometric systems.
Galaxies Chemical and photometric evolution models
Short Name:
VI/147
Date:
21 Oct 2021
Publisher:
CDS
Description:
We summarize the updated set of multiphase chemical evolution models performed with 44 theoretical radial mass initial distributions and 10 possible values of efficiencies to form molecular clouds and stars. We present the results about the infall rate histories, the formation of the disk, and the evolution of the radial distributions of diffuse and molecular gas surface density, stellar profile, star formation rate surface density, and elemental abundances of C, N, O, and Fe, finding that the radial gradients for these elements begin steeper and flatten with increasing time or decreasing redshift, although the outer disks always show a certain flattening for all times. With the resulting star formation and enrichment histories, we calculate the spectral energy distributions (SEDs) for each radial region by using the ones for single stellar populations resulting from the evolutive synthesis model POPSTAR. With these SEDs we may compute finally the broad band magnitudes and colors radial distributions in the Johnson and in the SLOAN/SDSS systems which are the main result of this work. We present the evolution of these brightness and color profiles with the redshift.
We present a catalogue of 2D, point spread function-corrected de Vacouleurs, Sersic, de Vacouleurs+Exponential, and Sersic+Exponential fits of ~7x10^5^ spectroscopically selected galaxies drawn from the Sloan Digital Sky Survey (SDSS) Data Release 7. Fits are performed for the SDSS r band utilizing the fitting routine galfit and analysis pipeline pymorph. We compare these fits to prior catalogues. Fits are analysed using a physically motivated flagging system. The flags suggest that more than 90 percent of two-component fits can be used for analysis. We show that the fits follow the expected behaviour for early and late galaxy types. The catalogues provide a robust set of structural and photometric parameters for future galaxy studies. We show that some biases remain in the measurements, e.g. the presence of bars significantly affect the bulge measurements although the bulge ellipticity may be used to separate barred and non-barred galaxies, and about 15 percent of bulges of two-component fits are also affected by resolution. The catalogues are available in electronic format. We also provide an interface for generating postage stamp images of the 2D model and residual as well as the 1D profile. These images can be generated for a user-uploaded list of galaxies on demand.
Cosmic Dawn II (CoDa II) is a new, fully-coupled radiation-hydrodynamics simulation of cosmic reionization and galaxy formation and their mutual impact, to redshift z<6. With 4096^3^ particles and cells in a 94Mpc box, it is large enough to model global reionization and its feedback on galaxy formation while resolving all haloes above 10^8^M_{sun}_. Using the same hybrid CPU-GPU code RAMSES-CUDATON as CoDa I in Ocvirk et al. (2016MNRAS.463.1462O), CoDa II modified and re-calibrated the subgrid star-formation algorithm, making reionization end earlier, at z>~6, thereby better matching the observations of intergalactic Lyman-alpha opacity from quasar spectra and electron-scattering optical depth from cosmic microwave background fluctuations. CoDa II predicts a UV continuum luminosity function in good agreement with observations of high-z galaxies, especially at z=6. As in CoDa I, reionization feedback suppresses star formation in haloes below ~2x10^9^M_{sun}_, though suppression here is less severe, a possible consequence of modifying the star-formation algorithm. Suppression is environment-dependent, occurring earlier (later) in overdense (underdense) regions, in response to their local reionization times. Using a constrained realization of {LAMBDA}CDM constructed from galaxy survey data to reproduce the large-scale structure and major objects of the present-day Local Universe, CoDa II serves to model both global and local reionization. In CoDa II, the Milky Way and M31 appear as individual islands of reionization, i.e. they were not reionized by the progenitor of the Virgo cluster, nor by nearby groups, nor by each other. Description: The galaxy catalogs for redshifts z=10 down to z=6 (the simulation ended at z=5.8) are provided. Galaxies are identified as Friends-of-Friends dark matter haloes with a linking length ll=0.2. Stars are associated to each halo if they are within a sphere of radius r200. Magnitudes are computed using a BPASS stellar population model, as detailed in the article. No dust opacity is considered.
We measure the mass functions for generically red and blue galaxies, using a z<0.12 sample of logM_*_>8.7 field galaxies from the Galaxy And Mass Assembly (GAMA) survey. Our motivation is that, as we show, the dominant uncertainty in existing measurements stems from how "red" and "blue" galaxies have been selected/defined. Accordingly, we model our data as two naturally overlapping populations, each with their own mass function and colour-mass relation, which enables us characterize the two populations without having to specify a priori which galaxies are "red" and "blue". Our results then provide the means to derive objective operational definitions for the terms "red" and "blue", which are based on the phenomenology of the colour-mass diagrams. Informed by this descriptive modelling, we show that (1) after accounting for dust, the stellar colours of "blue" galaxies do not depend strongly on mass; (2) the tight, flat "dead sequence" does not extend much below logM_*_~10.5; instead, (3) the stellar colours of "red" galaxies vary rather strongly with mass, such that lower mass "red" galaxies have bluer stellar populations; (4) below logM_*_~9.3, the "red" population dissolves into obscurity, and it becomes problematic to talk about two distinct populations; as a consequence, (5) it is hard to meaningfully constrain the shape, including the existence of an upturn, of the "red" galaxy mass function below logM_*_~9.3. Points 1-4 provide meaningful targets for models of galaxy formation and evolution to aim for.
In our classical grid of multiphase chemical evolution models, star formation in the disc occurs in two steps: first, molecular gas forms, and then stars are created by cloud-cloud collisions or interactions of massive stars with the surrounding molecular clouds. The formation of both molecular clouds and stars are treated through the use of free parameters we refer to as efficiencies. In this work, we modify the formation of molecular clouds based on several new prescriptions existing in the literature, and we compare the results obtained for a chemical evolution model of the Milky Way Galaxy regarding the evolution of the Solar region, the radial structure of the Galactic disc and the ratio between the diffuse and molecular components, H I/H_2_. Our results show that the six prescriptions we have tested reproduce fairly consistent most of the observed trends, differing mostly in their predictions for the (poorly constrained) outskirts of the Milky Way and the evolution in time of its radial structure. Among them, the model proposed by Ascasibar et al. (in preparation), where the conversion of diffuse gas into molecular clouds depends on the local stellar and gas densities as well as on the gas metallicity, seems to provide the best overall match to the observed data.
Cluster strong lensing cosmography is a promising probe of the background geometry of the Universe and several studies have emerged thanks to the increased quality of observations using space- and ground-based telescopes. For the first time, we used a sample of five cluster strong lenses to measure the values of cosmological parameters and combine them with those from classical probes. In order to assess the degeneracies and the effectiveness of strong-lensing cosmography in constraining the background geometry of the Universe, we adopted four cosmological scenarios. We found good constraining power on the total matter density of the Universe ({OMEGA}_m_) and the equation of state of the dark energy parameter w. For a flat wCDM cosmology, we found {OMEGA}_m_=0.30^+0.09^_0.11_ and w=-1.12^+0.17^_0.32_ from strong lensing only. Interestingly, we show that the constraints from the cosmic microwave background (CMB) are improved by factors of 2.5 and 4.0 on {OMEGA}_m_ and w, respectively, when combined with our posterior distributions in this cosmological model. In a scenario where the equation of state of dark energy evolves with redshift, the strong lensing constraints are compatible with a cosmological constant (i.e. {OMEGA}_m_=-1). In a curved cosmology, our strong lensing analyses can accommodate a large range of values for the curvature of the Universe of {OMEGA}_k_=0.28^+0.16^_0.21_. In all cosmological scenarios, we show that our strong lensing constraints are complementary and in good agreement with measurements from the CMB, baryon acoustic oscillations, and Type Ia supernovae. Our results show that cluster strong lensing cosmography is a potentially powerful probe to be included in the cosmological analyses of future surveys.
We study how optical galaxy morphology depends on mass and star formation rate (SFR) in the Illustris Simulation. To do so, we measure automated galaxy structures in 10808 simulated galaxies at z=0 with stellar masses 109.7<M*/M_{sun}_< 1012.3. We add observational realism to idealized synthetic images and measure non-parametric statistics in rest-frame optical and near-IR images from four directions. We find that Illustris creates a morphologically diverse galaxy population, occupying the observed bulge strength locus and reproducing median morphology trends versus stellar mass, SFR, and compactness. Morphology correlates realistically with rotation, following classification schemes put forth by kinematic surveys. Type fractions as a function of environment agree roughly with data. These results imply that connections among mass, star formation, and galaxy structure arise naturally from models matching global star formation and halo occupation functions when simulated with accurate methods. This raises a question of how to construct experiments on galaxy surveys to better distinguish between models. We predict that at fixed halo mass near 10^12^M_{sun}_, disc-dominated galaxies have higher stellar mass than bulge-dominated ones, a possible consequence of the Illustris feedback model. While Illustris galaxies at M*~10^11^M_{sun}_ have a reasonable size distribution, those at M*~10^10^M_{sun}_ have half-light radii larger than observed by a factor of 2. Furthermore, at M*~10^10.5^-10^11^M_{sun}_, a relevant fraction of Illustris galaxies have distinct 'ring-like' features, such that the bright pixels have an unusually wide spatial extent.
We apply the modified acceleration law obtained from Einstein gravity coupled to a massive skew-symmetric field F_{mu}{nu}{lambda}_ to the problem of explaining galaxy rotation curves without exotic dark matter. Our sample of galaxies includes low surface brightness (LSB) and high surface brightness (HSB) galaxies and an elliptical galaxy. In those cases for which photometric data are available, a best fit via the single parameter (M/L)_stars_ to the luminosity of the gaseous (HI plus He) and luminous stellar disks is obtained. In addition, a best fit to the rotation curves of galaxies is obtained in terms of a parametric mass distribution (independent of luminosity observations) - a two-parameter fit to the total galactic mass (or mass-to-light ratio M/L) and a core radius associated with a model of the galaxy cores - using a nonlinear least-squares fitting routine including estimated errors. The fits are compared to those obtained using Milgrom's phenomenological MOND model and to the predictions of the Newtonian/Kepler acceleration law.
