A multiscale approach to environment

Physical processes influencing the properties of galaxies can be traced by the dependence and evolution of galaxy properties on their environment. A detailed understanding of this dependence can only be gained through comparison of observations with models, with an appropriate quantification of the rich parameter space describing the environment of the galaxy. We present a new, multiscale parameterization of galaxy environment which retains an observationally motivated simplicity whilst utilizing the information present on different scales. We examine how the distribution of galaxy (u-r) colours in the Sloan Digital Sky Survey (SDSS), parameterized using a double gaussian (red plus blue peak) fit, depends upon multiscale density. This allows us to probe the detailed dependence of galaxy properties on environment in a way which is independent of the halo model. Nonetheless, cross-correlation with the group catalogue constructed by Yang et al, 2007 shows that galaxy properties trace environment on different scales in a way which mimics that expected within the halo model. This provides independent support for the existence of virialized haloes, and important additional clues to the role played by environment in the evolution of the galaxy population. This work is described in full by Wilman et al., 2010, MNRAS, acceptedComment: A brief summary of the work presented by Wilman et al., 2010, MNRAS, accepted; LaTeX, 4 pages, 2 figures. To appear in "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista & C.C. Popescu, AIP Conference Serie

Galaxy Evolution in Groups and Clusters

In this thesis, we investigate the extent to which galaxy evolution is driven by processes common to the group and cluster environments. A bimodality of galaxy properties such as star formation, strongly dependent upon the local overdensity of galaxies, suggests that the passive, early type galaxies common to groups and clusters originate in transformation processes, which are nurtured by the environment. This can only be important to global galaxy evolution if transformations are common in groups, which contain z 50% of the local galaxy population. We present deep Magellan spectroscopy and HST ACS imaging of our group and field samples at 0.3 ˂ z ˂ 0.55, selected from the CN0C2 survey by Carlberg et al. (2001b). We find that these groups contain significantly more passive galaxies than the field, with excesses of S0, elliptical and passive spiral galaxy types. The morphological composition is closely matched to that of irregular and X-ray-faint clusters at a similar epoch. In contrast with a low-redshift group sample selected from 2dFGRS (Eke et al, 2004), we find that the fraction of passive galaxies, fp， is strongly evolving in the group environment, with parallel evolution in the field population. Simple models confirm that galaxy transformations are required to match the evolution of both group and field populations. Qualitatively similar evolution and dependence on environment is found in physically-motivated simulations. However, these do not quantitatively match the environmental nor luminosity dependence in the evolution of fp. We also present a complementary method using photometric redshifts to identify infalling groups in the outskirts of clusters with Wide Field Imaging (WFI) technology. Finally, we identify the key developments which will help to unravel the history of galaxy evolution in coming years

More than just halo mass: Modelling how the red galaxy fraction depends on multiscale density in a HOD framework

The fraction of galaxies with red colours depends sensitively on environment, and on the way in which environment is measured. To distinguish competing theories for the quenching of star formation, a robust and complete description of environment is required, to be applied to a large sample of galaxies. The environment of galaxies can be described using the density field of neighbours on multiple scales - the multiscale density field. We are using the Millennium simulation and a simple HOD prescription which describes the multiscale density field of Sloan Digital Sky Survey DR7 galaxies to investigate the dependence of the fraction of red galaxies on the environment. Using a volume limited sample where we have sufficient galaxies in narrow density bins, we have more dynamic range in halo mass and density for satellite galaxies than for central galaxies. Therefore we model the red fraction of central galaxies as a constant while we use a functional form to describe the red fraction of satellites as a function of halo mass which allows us to distinguish a sharp from a gradual transition. While it is clear that the data can only be explained by a gradual transition, an analysis of the multiscale density field on different scales suggests that colour segregation within the haloes is needed to explain the results. We also rule out a sharp transition for central galaxies, within the halo mass range sampled.Comment: 24 pages, 21 figures, accepted for publication by MNRA

The Hierarchical Origins of Observed Galaxy Morphology

Galaxies grow primarily via accretion-driven star formation in discs and merger-driven growth of bulges. These processes are implicit in semi-analytical models of galaxy formation, with bulge growth in particular relating directly to the hierarchical build-up of halos and their galaxies. In this paper, we consider several implementations of two semi-analytical models. Focusing on implementations in which bulges are formed during mergers only, we examine the fractions of elliptical galaxies and both passive and star-forming disk galaxies as functions of stellar and halo mass, for central and satellite systems. This is compared to an observational cross-matched SDSS+RC3 z ~ 0 sample of galaxies with accurate visual morphological classifications and M_{stellar} > 10^10.5 M_{sol}. The models qualitatively reproduce the observed increase of elliptical fraction with stellar mass, and with halo mass for central galaxies, supporting the idea that observed ellipticals form during major mergers. However, the overall elliptical fraction produced by the models is much too high compared with the z ~ 0 data. Since the "passive" -- i.e. non-star-forming -- fractions are approximately reproduced, and since the fraction which are star-forming disc galaxies is also reproduced, the problem is that the models overproduce ellipticals at the expense of passive S0 and spiral galaxies. Bulge-growth implementations (tuned to reproduce simulations) which allow the survival of residual discs in major mergers still destroy too much of the disc. Increasing the lifetime of satellites, or allowing significant disc regrowth around merger remnants, merely increases the fraction of star-forming disc galaxies. Instead, it seems necessary to reduce the mass ratios of merging galaxies, so that most mergers produce modest bulge growth in disc-galaxy remnants instead of ellipticals. [Abridged]Comment: latex, 20 pages, 13 figures. Accepted by Monthly Notices. Source package includes full version of Table 1 from paper (file sdssrc3_table_for_paper.tab

Propuesta para la captación y uso de agua lluvia en las instalaciones de la Universidad Católica de Colombia a partir de un modelo de recolección de agua

Trabajo de InvestigaciónEl presente trabajo se propone la captación y uso de agua lluvia en las instalaciones de la Universidad Católica de Colombia a partir de un modelo físico de recolección de agua, teniendo en cuenta que se puede utilizar como una alternativa para abastecer la demanda de agua, en alguna de las actividades cotidianas en el bloque R de la Universidad Católica de Colombia.INTRODUCCIÓN. 1. GENERALIDADES. 2. PLANIFICACIÓN DEL SISTEMA. 3. DATOS OBTENIDOS SOBRE LA CAPTACIÓN. 4. COMPARATIVO PROPIEDADES FÍSICAS Y QUIMICAS. 5. RUTA CRÍTICA. 6. CONCLUSIONES. 7. RECOMENDACIONES. BIBLIOGRAFÍA - ANEXOSPregradoIngeniero Civi

On the influence of environment on star forming galaxies

We use our state-of-the-art semi analytic model for GAlaxy Evolution and Assembly (GAEA), and observational measurements of nearby galaxies to study the influence of the environment on the gas content and gaseous/stellar disc sizes of star-forming galaxies. We analyse the origin of differences between physical properties of satellites and those of their central counterparts, identified by matching the Vmax of their host haloes at the accretion time of the satellites. Our model reproduces nicely the differences between centrals and satellites measured for the HI mass, size of the star-forming region, and stellar radii. In contrast, our model predicts larger differences with respect to data for the molecular gas mass and star formation rate. By analysing the progenitors of central and satellite model galaxies, we find that differences in the gas content arise after accretion, and can be entirely ascribed to the instantaneous stripping of the hot gas reservoir. The suppression of cold gas replenishment via cooling and star formation leads to a reduction of the cold gas and of its density. Therefore, more molecular gas is lost than lower density HI gas, and model satellites have less molecular gas and lower star formation rates than observed satellites. We argue that these disagreements could be largely resolved with the inclusion of a proper treatment for ram-pressure stripping of cold gas and a more gradual stripping of the hot gas reservoir. A more sophisticated treatment of angular momentum exchanges, accounting for the multi-phase nature of the gaseous disc is also required.Comment: 15 pages, 9 figures, accepted for publication in MNRA

What determines the fraction of elliptical galaxies in clusters?

We study the correlation between the morphological mix of cluster galaxies and the assembly history of the parent cluster by taking advantage of two independently developed semi-analytic models for galaxy formation and evolution. In our models, both the number of cluster members and that of elliptical members increase as a function of cluster mass, in such a way that the resulting elliptical fractions are approximately independent of cluster mass. The population of cluster ellipticals exhibit a marked bimodal distribution as a function of galaxy stellar mass, with a dip at masses $\sim 10^{10}\,{\rm M}_{\odot}$. In the framework of our models, this bimodality originates from the combination of a strongly decreasing number of galaxies with increasing stellar mass, and a correspondingly increasing probability of experiencing major mergers. We show that the correlation between the measured elliptical fraction and the assembly history of the parent cluster is weak, and that it becomes stronger in models that adopt longer galaxy merger times. We argue that this results from the combined effect of a decreasing bulge production due to a reduced number of mergers, and an increasing survival probability of pre-existing ellipticals, with the latter process being more important than the former.Comment: 8 pages, 3 figures, accepted for publication in MNRA

The GEEC2 spectroscopic survey of Galaxy Groups at 0.8<z<10.8<z<1

We present the data release of the Gemini-South GMOS spectroscopy in the fields of 11 galaxy groups at $0.8<z<1$, within the COSMOS field. This forms the basis of the Galaxy Environment Evolution Collaboration 2 (GEEC2) project to study galaxy evolution in haloes with $M\sim 10^{13}M_\odot$ across cosmic time. The final sample includes $162$ spectroscopically--confirmed members with $R50$ per cent complete for galaxies within the virial radius, and with stellar mass $M_{\rm star}>10^{10.3}M_\odot$. Including galaxies with photometric redshifts we have an effective sample size of $\sim 400$ galaxies within the virial radii of these groups. We present group velocity dispersions, dynamical and stellar masses. Combining with the GCLASS sample of more massive clusters at the same redshift we find the total stellar mass is strongly correlated with the dynamical mass, with $\log{M_{200}}=1.20\left(\log{M_{\rm star}}-12\right)+14.07$. This stellar fraction of $~\sim 1$ per cent is lower than predicted by some halo occupation distribution models, though the weak dependence on halo mass is in good agreement. Most groups have an easily identifiable most massive galaxy (MMG) near the centre of the galaxy distribution, and we present the spectroscopic properties and surface brightness fits to these galaxies. The total stellar mass distribution in the groups, excluding the MMG, compares well with an NFW profile with concentration $4$, for galaxies beyond $\sim 0.2R_{200}$. This is more concentrated than the number density distribution, demonstrating that there is some mass segregation.Comment: Accepted for publication in MNRAS. The appendix is omitted due to large figures. The full version will be available from the MNRAS website and from http://quixote.uwaterloo.ca/~mbalogh/papers/GEEC2_data.pdf. Long data tables are available from MNRAS or by contacting the first autho