117960870
Simulations and modelling of the ISM in galaxies
The latest observations of molecular gas and the atomic hydrogen content of local and high-redshift galaxies, coupled with how these correlate with star formation activity, have revolutionized our ideas about how to model star formation in a galactic context. A successful theory of galaxy formation has to explain some key facts: (i) high-redshift galaxies have higher molecular gas fractions and star formation rates than local galaxies, (ii) scaling relations show that the atomic-to-stellar mass ratio decreases with stellar mass in the local Universe, and (iii) the global abundance of atomic hydrogen evolves very weakly with time. We review how modern cosmological simulations of galaxy formation attempt to put these pieces together and highlight how approaches simultaneously solving dark matter and gas physics, and approaches first solving the dark matter N-body problem and then dealing with gas physics using semi-analytic models, differ and complement each other. We review the observable predictions, what we think we have learned so far and what still needs to be done in the simulations to allow robust testing by the new observations expected from telescopes such as ALMA, PdBI, LMT, JVLA, ASKAP, MeerKAT, SKA.
56451522
PROBABILITY FRIENDS-OF-FRIENDS (PFOF) GROUP FINDER: PERFORMANCE STUDY AND OBSERVATIONAL DATA APPLICATIONS ON PHOTOMETRIC SURVEYS
In tandem with observational data sets, we utilize realistic mock catalogs, based on a semi-analytic galaxy formation model, constructed specifically for Pan-STARRS1 Medium Deep Surveys to assess the performance of the Probability Friends-of-Friends (PFOF) group finder, and aim to develop a grouping optimization method applicable to surveys like Pan-STARRS1. Producing mock PFOF group catalogs under a variety of photometric redshift accuracies (), we find that catalog purities and completenesses from "good" ( 0.01) to "poor" ( 0.07) photo-zs gradually degrade from 77% and 70% to 52% and 47%, respectively. A "subset optimization" approach is developed by using spectroscopic-redshift group data from the target field to train the group finder for application to that field and demonstrated using zCOSMOS groups for PFOF searches within PS1 Medium Deep Field04 (PS1MD04) and DEEP2 EGS groups in PS1MD07. With four data sets spanning the photo-z accuracy range from 0.01 to 0.06, we find purities and completenesses agree with their mock analogs. Further tests are performed via matches to X-ray clusters. We find PFOF groups match ∼85% of X-ray clusters identified in COSMOS and PS1MD04, lending additional support to the reliability of the detection algorithm. In the end, we demonstrate, by separating red and blue group galaxies in the EGS and PS1MD07 group catalogs, that the algorithm is not biased with respect to specifically recovering galaxies by color. The analyses suggest the PFOF algorithm shows great promise as a reliable group finder for photometric galaxy surveys of varying depth and coverage. © 2014. The American Astronomical Society. All rights reserved..
53507114
Modelling redshift space distortions in hierarchical cosmologies
Galaxy redshift surveys allow us to study the 3D spatial distribution of galaxies and clusters. In a homogeneous universe, redshift measurements would probe only the Hubble flow and would provide accurate radial distances for galaxies. In reality, peculiar velocities are gravitationally induced by inhomogeneous structure and distort the measured distances.
489993
The Infrared Side of Galaxy Formation. I. The Local Universe in the Semianalytical Framework
We present a new evolutionary model for predicting the far-UV-to-submillimeter properties of the galaxy population. This combines a semianalytic galaxy formation model based on hierarchical clustering (GALFORM) with a spectrophotometric code that includes dust reprocessing (GRASIL). The former provides the star formation and metal enrichment histories, together with the gas mass and various geometrical parameters, for a representative sample of galaxies formed in different density environments. These quantities, together with a few other assumptions concerning the spatial distribution of dust and its optical properties, allow us to model the spectral energy distributions (SEDs) of galaxies, taking into account stellar emission and also dust extinction (absorption plus scattering) and reemission. In the spectrophotometric code, dust is considered only in the disk, but the general radiation field is contributed by both the disk and the bulge components with their own distinct age and metallicity distributions. Two phases are considered for the dust: molecular cloud complexes, where stars are assumed to be born, and the diffuse interstellar medium. The model includes both galaxies forming stars quiescently in disks and starbursts triggered by galaxy mergers. We test our models against the observed spectrophotometric properties of galaxies in the local universe, assuming a cold dark matter cosmology with Ω0 = 0.3 and Λ0 = 0.7. The models reproduce fairly well the SEDs of normal spirals and starbursts from the far-UV to the submillimeter and their internal extinction properties. The starbursts follow the observed relationship between the far-IR-to-UV luminosity ratio and the slope of the UV continuum. They also reproduce the observed starburst attenuation law. This result is remarkable because we use a dust mixture that reproduces the Milky Way extinction law. It suggests that the observed attenuation law is closely related to the geometry of the stars and dust. We compute galaxy luminosity functions over a wide range of wavelengths, which turn out to be in good agreement with observational data in the UV (2000 A), in the B and K bands, and in the IR (12-100 μm). Finally, we investigate the reliability of some star formation indicators that are based on the properties of the continuum SEDs of galaxies. The UV continuum turns out to be a poor star formation indicator for our models, while the infrared luminosity is much more reliable.
15222238
Predictions for the intrinsic UV continuum properties of star-forming galaxies and the implications for inferring dust extinction
The observed ultraviolet continuum (UVC) slope is potentially a powerful diagnostic of dust obscuration in star-forming galaxies. However, the intrinsic slope is also sensitive to the form of the stellar initial mass function and to the recent star formation and metal enrichment histories of a galaxy. Using the GALFORM semi-analytical model of galaxy formation, we investigate the intrinsic distribution of UVC slopes. For star-forming galaxies, we find that the intrinsic distribution of UVC slopes at z= 0, parametrized by the power-law index β, has a standard deviation of σβ≃ 0.30. This suggests an uncertainty on the inferred ultraviolet (UV) attenuation of Afuv≃ 0.7 (assuming a Calzetti attenuation curve) for an individual object, even with perfect photometry. Furthermore, we find that the intrinsic UVC slope correlates with star formation rate, intrinsic UV luminosity, stellar mass and redshift. These correlations have implications for the interpretation of trends in the observed UVC slope with these quantities irrespective of the sample size or quality of the photometry. Our results suggest that in some cases the attenuation by dust has been incorrectly estimated.
119413594
Can the faint sub-mm galaxies be explained in the Lambda-CDM model?
We present predictions for the abundance of sub-mm galaxies (SMGs) and Lyman-break galaxies (LBGs) in the $\Lambda$CDM cosmology. A key feature of our model is the self-consistent calculation of the absorption and emission of radiation by dust. The new model successfully matches the LBG luminosity function, as well reproducing the properties of the local galaxy population in the optical and IR. The model can also explain the observed galaxy number counts at $850\mum$, but only if we assume a top-heavy IMF for the stars formed in bursts. The predicted redshift distribution of SMGs depends relatively little on their flux over the range 1-$10\mjy$, with a median value of $z\approx 2.0$ at a flux of $5\mjy$, in very good agreement with the recent measurement by Chapman et al The counts of SMGs are predicted to be dominated by ongoing starbursts. However, in the model these bursts are responsible for making only a few per cent of the stellar mass locked up in massive ellipticals at the present day.
945316
Intragroup diffuse light in compact groups of galaxies – II. HCG 15, 35 and 51
This continuing study of intragroup light in compact groups of galaxies aims to establish new constraints to models of formation and evolution of galaxy groups, specially of compact groups, which are a key part in the evolution of larger structures, such as clusters. In this paper we present three additional groups (HCG 15, 35 and 51) using deep wide-field B- and R-band images observed with the LAICA camera at the 3.5-m telescope at the Calar Alto observatory (CAHA). This instrument provides us with very stable flat-fielding, a mandatory condition for reliably measuring intragroup diffuse light. The images were analysed with the OV_WAV package, a wavelet technique that allows us to uncover the intragroup component in an unprecedented way. We have detected that 19,15 and 26 per cent of the total light of HCG 15, 35 and 51, respectively, are in the diffuse component, with colours that are compatible with old stellar populations and with mean surface brightness that can be as low as 28.4 B mag arcsec -2 . Dynamical masses, crossing times and mass-to-light ratios were recalculated using the new group parameters. Also tidal features were analysed using the wavelet technique.