The surface brightness and colour-magnitude relations for Fornax cluster galaxies

We present BVI photometry of 190 galaxies in the central 4 x 3 deg(2) region of the Fornax cluster observed with the Michigan Curtis Schmidt Telescope. Results from the Fornax Cluster Spectroscopic Survey (FCSS) and the Flair-II Fornax Surveys have been used to confirm the membership status of galaxies in the Fornax Cluster Catalogue (FCC). In our catalogue of 213 member galaxies, 92 (43 per cent) have confirmed radial velocities. In this paper, we investigate the surface brightness-magnitude relation for Fornax cluster galaxies. Particular attention is given to the sample of cluster dwarfs and the newly discovered ultracompact dwarf galaxies (UCDs) from the FCSS. We examine the reliability of the surface brightness-magnitude relation as a method for determining cluster membership and find that at surface brightnesses fainter than 22 mag arcsec(-2), it fails in its ability to distinguish between cluster members and barely resolved background galaxies. Cluster members exhibit a strong surface brightness-magnitude relation. Both elliptical (E) galaxies and dwarf elliptical (dE) galaxies increase in surface brightness as luminosity decreases. The UCDs lie off the locus of the relation. B-V and V-I colours are determined for a sample of 113 cluster galaxies and the colour-magnitude relation is explored for each morphological type. The UCDs lie off the locus of the colour-magnitude relation. Their mean V - I colours (similar to1.09) are similar to those of globular clusters associated with NGC 1399. The location of the UCDs on both surface brightness and colour-magnitude plots supports the 'galaxy threshing' model for infalling nucleated dwarf elliptical (dE, N) galaxies.

The HIPASS catalogue - II. Completeness reliability and parameter accuracy

The H I Parkes All Sky Survey (HIPASS) is a blind extragalactic H I 21-cm emission-line survey covering the whole southern sky from declination -90degrees to +25degrees. The HIPASS catalogue (HICAT), containing 4315 H I-selected galaxies from the region south of declination +2degrees, is presented in Meyer et al. (Paper I). This paper describes in detail the completeness and reliability of HICAT, which are calculated from the recovery rate of synthetic sources and follow-up observations, respectively. HICAT is found to be 99 per cent complete at a peak flux of 84 mJy and an integrated flux of 9.4 Jy km. s(-1). The overall reliability is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy or integrated flux >8.2 Jy km s(-1). Expressions are derived for the uncertainties on the most important HICAT parameters: peak flux, integrated flux, velocity width and recessional velocity. The errors on HICAT parameters are dominated by the noise in the HIPASS data, rather than by the parametrization procedure.

The Little Galaxies That Could Reionize the Universe

Thesis (Ph.D.)--University of Washington, 2016-08

Space density distribution of galaxies in the absolute magnitude - rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA stellar kinematics

We measured the distribution in absolute magnitude - circular velocity space for a well-defined sample of 199 rotating galaxies of the Calar Alto Legacy Integral Field Area Survey (CALIFA) using their stellar kinematics. Our aim in this analysis is to avoid subjective selection criteria and to take volume and large-scale structure factors into account. Using stellar velocity fields instead of gas emission line kinematics allows including rapidly rotating early-type galaxies. Our initial sample contains 277 galaxies with available stellar velocity fields and growth curve r-band photometry. After rejecting 51 velocity fields that could not be modelled because of the low number of bins, foreground contamination, or significant interaction, we performed Markov chain Monte Carlo modelling of the velocity fields, from which we obtained the rotation curve and kinematic parameters and their realistic uncertainties. We performed an extinction correction and calculated the circular velocity v_circ accounting for the pressure support of a given galaxy. The resulting galaxy distribution on the M-r - v(circ) plane was then modelled as a mixture of two distinct populations, allowing robust and reproducible rejection of outliers, a significant fraction of which are slow rotators. The selection effects are understood well enough that we were able to correct for the incompleteness of the sample. The 199 galaxies were weighted by volume and large-scale structure factors, which enabled us to fit a volume-corrected Tully-Fisher relation (TFR). More importantly, we also provide the volume-corrected distribution of galaxies in the M_r - v_circ plane, which can be compared with cosmological simulations. The joint distribution of the luminosity and circular velocity space densities, representative over the range of -20 > M_r > -22 mag, can place more stringent constraints on the galaxy formation and evolution scenarios than linear TFR fit parameters or the luminosity function alone.

Investigating stellar mixing processes through the study of the Red-Giant Branch bump

Extra mixing at the borders of convective zones in stellar interiors takes on an important role in the chemical evolution of stars and galaxies through the transport of chemical elements towards the stellar surface: knowing the overshooting mechanism can therefore lead to a better understanding of the observed chemical abundances in stellar photospheres. The comprehension of this phenomenon is quite uncertain and currently object of many studies. In particular, concerning low mass stars, in the past decades several works highlighted a discrepancy between the observed luminosity of the Red-Giant Branch bump and its prediction from simulations, which can be fixed including overshooting at the base of the convective envelope. This work, studying the Red-Giant Branch bump and using it as a diagnostic for extra mixing processes, tries to classify two different types of overshooting, instantaneous and diffusive, using both simulations from stellar models and Globular Clusters’ data. The aim is to understand which one of the two mixing processes is the most suitable in reproducing the observed stellar behaviour and, in case both of them provide reliable results, what are the conditions under which they produce the same effects on the Red-Giant Branch bump luminosity function and are consequently indistinguishable. Finally, possible dependences of overshooting efficiency on stellar parameters, such as chemical composition, are analysed.

The clusters Abell 222 and Abell 223: a multi-wavelength view

Context. The Abell 222 and 223 clusters are located at an average redshift z similar to 0.21 and are separated by 0.26 deg. Signatures of mergers have been previously found in these clusters, both in X-rays and at optical wavelengths, thus motivating our study. In X-rays, they are relatively bright, and Abell 223 shows a double structure. A filament has also been detected between the clusters both at optical and X-ray wavelengths. Aims. We analyse the optical properties of these two clusters based on deep imaging in two bands, derive their galaxy luminosity functions (GLFs) and correlate these properties with X-ray characteristics derived from XMM-Newton data. Methods. The optical part of our study is based on archive images obtained with the CFHT Megaprime/Megacam camera, covering a total region of about 1 deg(2), or 12.3 x 12.3 Mpc(2) at a redshift of 0.21. The X-ray analysis is based on archive XMM-Newton images. Results. The GLFs of Abell 222 in the g' and r' bands are well fit by a Schechter function; the GLF is steeper in r' than in g'. For Abell 223, the GLFs in both bands require a second component at bright magnitudes, added to a Schechter function; they are similar in both bands. The Serna & Gerbal method allows to separate well the two clusters. No obvious filamentary structures are detected at very large scales around the clusters, but a third cluster at the same redshift, Abell 209, is located at a projected distance of 19.2 Mpc. X-ray temperature and metallicity maps reveal that the temperature and metallicity of the X-ray gas are quite homogeneous in Abell 222, while they are very perturbed in Abell 223. Conclusions. The Abell 222/Abell 223 system is complex. The two clusters that form this structure present very different dynamical states. Abell 222 is a smaller, less massive and almost isothermal cluster. On the other hand, Abell 223 is more massive and has most probably been crossed by a subcluster on its way to the northeast. As a consequence, the temperature distribution is very inhomogeneous. Signs of recent interactions are also detected in the optical data where this cluster shows a ""perturbed"" GLF. In summary, the multiwavelength analyses of Abell 222 and Abell 223 are used to investigate the connection between the ICM and the cluster galaxy properties in an interacting system.

Quasars from a complete spectroscopic survey

With the advent of multi-fibre spectrographs such as the 'Two-Degree Field' (2dF) instrument at the Angle-Australian Telescope, quasar surveys that are free of any preselection of candidates and any biases this implies have become possible for the first time. The first of these is that which is being undertaken as part of the Fornax Spectroscopic Survey, a survey of the area around the Fornax Cluster of galaxies, and aims to obtain the spectra of all objects in the magnitude range 16.5 < b(j) < 19.7. To date, 3679 objects in the central pi -deg(2) area have been successfully identified from their spectral characteristics. Of these, 71 are found to be quasars, 61 with redshifts 0.3 < z < 2.2 and 10 with redshifts z > 2.2. Using this complete quasar sample, a new determination of quasar number counts is made, enabling an independent check of existing quasars surveys. Cumulative counts per square degree at a magnitude limit of b(j) < 19.5 are found to be 11.5 +/- 2.2 for 0.3 < z < 2.2, 2.22 +/- 0.93 for z > 2.2 and 13.7 +/- 3.1 for z > 0.3. Given the likely detection of extra quasars in the Fornax survey, we make a more detailed examination of existing quasar selection techniques. First, looking at the use of a stellar criterion, four of the 71 quasars are 'non-stellar' on the basis of the automated plate measuring facility (APM) b(j) classification, however inspection shows all are consistent with stellar, but misclassified due to image confusion. Examining the ultraviolet excess and multicolour selection techniques, for the selection criteria investigated, ultraviolet excess would find 69 +/- 6 per cent of our 0.3 < z < 2.2 quasars and only 50(-18)(+14), per cent of our z > 2.2 quasars, while the completeness level for multicolour selection is found to be 90(-4)(+3) per cent for 0.3 < z < 2.2 quasars and 80(-12)(+14) per cent for z > 2.2 quasars. The extra quasars detected by our all-object survey thus have unusually red star-like colours, and this appears to be a result of the continuum shape rather than any emission features. An intrinsic dust extinction model may, at least partly, account for the red colours.

The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy

Observations of the extraordinarily bright optical afterglow (OA) of GRB 991208 started 2.1 d after the event. The flux decay constant of the OA in the R-band is -2.30 +/- 0.07 up to 5 d, which is very likely due to the jet effect, and after that it is followed by a much steeper decay with constant -3.2 +/- 0.2, the fastest one ever seen in a GRB OA. A negative detection in several all-sky films taken simultaneously to the event implies either a previous additional break prior to 2 d after the occurrence of the GRB (as expected from the jet effect). The existence of a second break might indicate a steepening in the electron spectrum or the superposition of two events. Once the afterglow emission vanished, contribution of a bright underlying SN is found, but the light curve is not sufficiently well sampled to rule out a dust echo explanation. Our determination of z = 0.706 indicates that GRB 991208 is at 3.7 Gpc, implying an isotropic energy release of 1.15 x 10E53 erg which may be relaxed by beaming by a factor > 100. Precise astrometry indicates that the GRB coincides within 0.2' with the host galaxy, thus given support to a massive star origin. The absolute magnitude is M_B = -18.2, well below the knee of the galaxy luminosity function and we derive a star-forming rate of 11.5 +/- 7.1 Mo/yr. The quasi-simultaneous broad-band photometric spectral energy distribution of the afterglow is determined 3.5 day after the burst (Dec 12.0) implying a cooling frequency below the optical band, i.e. supporting a jet model with p = -2.30 as the index of the power-law electron distribution.

Étude spectroscopique d'étoiles naines blanches riches en hélium de type DB et DBA

De nouveaux modèles d'atmosphère sont présentés, incluant les profils de raie d'hélium neutre améliorés de Beauchamp (1995) et le formalisme de probabilité d'occupation pour ce même atome. Ces modèles sont utilisés pour calculer une grille de spectres synthétiques correspondant à des atmosphères riches en hélium et contenant des traces d'hydrogène. Cette grille est utilisée pour déterminer les paramètres atmosphériques principaux des étoiles de notre échantillon, soient la température effective, la gravité de surface et l'abondance d'hydrogène. Notre échantillon contient des spectres visibles de haut rapport signal-sur-bruit pour 102 naines blanches riches en hélium, dont 29 ont été observés au cours de ce projet, ce qui en fait le plus grand échantillon de spectres de qualité de naines blanches riches en hélium. Des spectres synthétiques ont été calculés en utilisant différentes valeurs du paramètre α de la théorie de la longueur de mélange dans le but de calibrer empiriquement la valeur de ce paramètre pour les DB. Afin d'améliorer la précision sur les paramètres atmosphériques de quelques étoiles, nous avons utilisé des spectres couvrant la raie Hα pour mieux déterminer l'abondance d'hydrogène. Finalement, nous avons calculé la distribution de masse de notre échantillon et la fonction de luminosité des DB. La distribution de masse montre une coupure à 0.5 fois la masse solaire qui est prédite par les modèles d'évolution stellaire et dévoile une masse moyenne significativement plus élevée pour les étoiles de type DBA. La masse moyenne de l'ensemble des DB et DBA est très proche de celle des DA. La fonction de luminosité nous permet de calculer que le rapport du nombre de DB sur le nombre de DA vaut environ 25%.

Relevé spectroscopique et étude des propriétés physiques des étoiles naines blanches à moins de 40 parsecs du Soleil

Les étoiles naines blanches représentent la fin de l’évolution de 97% des étoiles de notre galaxie, dont notre Soleil. L’étude des propriétés globales de ces étoiles (distribution en température, distribution de masse, fonction de luminosité, etc.) requiert l’élaboration d’ensembles statistiquement complets et bien définis. Bien que plusieurs relevés d’étoiles naines blanches existent dans la littérature, la plupart de ceux-ci souffrent de biais statistiques importants pour ce genre d’analyse. L’échantillon le plus représentatif de la population d’étoiles naines blanches demeure à ce jour celui défini dans un volume complet, restreint à l’environnement immédiat du Soleil, soit à une distance de 20 pc (∼ 65 années-lumière) de celui-ci. Malheureusement, comme les naines blanches sont des étoiles intrinsèquement peu lumineuses, cet échantillon ne contient que ∼ 130 objets, compromettant ainsi toute étude statistique significative. Le but de notre étude est de recenser la population d’étoiles naines blanches dans le voisinage solaire a une distance de 40 pc, soit un volume huit fois plus grand. Nous avons ainsi entrepris de répertorier toutes les étoiles naines blanches à moins de 40 pc du Soleil à partir de SUPERBLINK, un vaste catalogue contenant le mouvement propre et les données photométriques de plus de 2 millions d’étoiles. Notre approche est basée sur la méthode des mouvements propres réduits qui permet d’isoler les étoiles naines blanches des autres populations stellaires. Les distances de toutes les candidates naines blanches sont estimées à l’aide de relations couleur-magnitude théoriques afin d’identifier les objets se situant à moins de 40 pc du Soleil, dans l’hémisphère nord. La confirmation spectroscopique du statut de naine blanche de nos ∼ 1100 candidates a ensuite requis 15 missions d’observations astronomiques sur trois grands télescopes à Kitt Peak en Arizona, ainsi qu’une soixantaine d’heures allouées sur les télescopes de 8 m des observatoires Gemini Nord et Sud. Nous avons ainsi découvert 322 nouvelles étoiles naines blanches de plusieurs types spectraux différents, dont 173 sont à moins de 40 pc, soit une augmentation de 40% du nombre de naines blanches connues à l’intérieur de ce volume. Parmi ces nouvelles naines blanches, 4 se trouvent probablement à moins de 20 pc du Soleil. De plus, nous démontrons que notre technique est très efficace pour identifier les étoiles naines blanches dans la région peuplée du plan de la Galaxie. Nous présentons ensuite une analyse spectroscopique et photométrique détaillée de notre échantillon à l’aide de modèles d’atmosphère afin de déterminer les propriétés physiques de ces étoiles, notamment la température, la gravité de surface et la composition chimique. Notre analyse statistique de ces propriétés, basée sur un échantillon presque trois fois plus grand que celui à 20 pc, révèle que nous avons identifié avec succès les étoiles les plus massives, et donc les moins lumineuses, de cette population qui sont souvent absentes de la plupart des relevés publiés. Nous avons également identifié plusieurs naines blanches très froides, et donc potentiellement très vieilles, qui nous permettent de mieux définir le côté froid de la fonction de luminosité, et éventuellement l’âge du disque de la Galaxie. Finalement, nous avons aussi découvert plusieurs objets d’intérêt astrophysique, dont deux nouvelles étoiles naines blanches variables de type ZZ Ceti, plusieurs naines blanches magnétiques, ainsi que de nombreux systèmes binaires non résolus.

Open cluster survival within the solar circle: Teutsch 145 and Teutsch 146 star

Teutsch 145 and Teutsch 146 are shown to be open clusters (OCs) orbiting well inside the solar circle, a region where several dynamical processes combine to disrupt most OCs on a time-scale of a few 108 yr. BVI photometry from the GALILEO telescope is used to investigate the nature and derive the fundamental and structural parameters of the optically faint and poorly known OCs Teutsch 145 and 146. These parameters are computed by means of field-star-decontaminated colour-magnitude diagrams and stellar radial density profiles (RDPs). Cluster mass estimates are made based on the intrinsic mass functions (MFs). We derive the ages 200+100(-50) and 400 +/- 100 Myr, and the distances from the Sun d(circle dot) = 2.7 +/- 0.3 and 3.8 +/- 0.2 kpc, respectively, for Teutsch 145 and 146. Their integrated apparent and absolute magnitudes are m(V) approximate to 12.4 and 13.3 and M(V) approximate to -5.6 and -5.3. The MFs (detected for stars with m greater than or similar to 1 M(circle dot)) have slopes similar to Salpeter`s initial mass function. Extrapolated to the H-burning limit, the MFs would produce total stellar masses of similar to 1400 M(circle dot), typical of relatively massive OCs. Both OCs are located deep into the inner Galaxy and close to the Crux-Scutum arm. Since cluster-disruption processes are important, their primordial masses must have been higher than the present-day values. The conspicuous stellar density excess observed in the innermost bin of both RDPs might reflect the dynamical effects induced by a few 108 yr of external tidal stress.

Probing the cosmic distance-duality relation with the Sunyaev-Zel'dovich effect, X-ray observations and supernovae Ia

Context. The angular diameter distances toward galaxy clusters can be determined with measurements of Sunyaev-Zel'dovich effect and X-ray surface brightness combined with the validity of the distance-duality relation, D-L(z)(1 + z)(2)/D-A(z) = 1, where D-L(z) and D-A(z) are, respectively, the luminosity and angular diameter distances. This combination enables us to probe galaxy cluster physics or even to test the validity of the distance-duality relation itself. Aims. We explore these possibilities based on two different, but complementary approaches. Firstly, in order to constrain the possible galaxy cluster morphologies, the validity of the distance-duality relation (DD relation) is assumed in the Lambda CDM framework (WMAP7). Secondly, by adopting a cosmological-model-independent test, we directly confront the angular diameters from galaxy clusters with two supernovae Ia (SNe Ia) subsamples (carefully chosen to coincide with the cluster positions). The influence of the different SNe Ia light-curve fitters in the previous analysis are also discussed. Methods. We assumed that eta is a function of the redshift parametrized by two different relations: eta(z) = 1 +eta(0)z, and eta(z) = 1 + eta(0)z/(1 + z), where eta(0) is a constant parameter quantifying the possible departure from the strict validity of the DD relation. In order to determine the probability density function (PDF) of eta(0), we considered the angular diameter distances from galaxy clusters recently studied by two different groups by assuming elliptical and spherical isothermal beta models and spherical non-isothermal beta model. The strict validity of the DD relation will occur only if the maximum value of eta(0) PDF is centered on eta(0) = 0. Results. For both approaches we find that the elliptical beta model agrees with the distance-duality relation, whereas the non-isothermal spherical description is, in the best scenario, only marginally compatible. We find that the two-light curve fitters (SALT2 and MLCS2K2) present a statistically significant conflict, and a joint analysis involving the different approaches suggests that clusters are endowed with an elliptical geometry as previously assumed. Conclusions. The statistical analysis presented here provides new evidence that the true geometry of clusters is elliptical. In principle, it is remarkable that a local property such as the geometry of galaxy clusters might be constrained by a global argument like the one provided by the cosmological distance-duality relation.

Is there a Population II analogy to the F star lithium dip?

Observers have found a small number of lithium-depleted halo stars in the temperature range of the Spite plateau. The current status of the mass-loss hypothesis for producing the observed lithium dip in Population (Pop) I stars is briefly discussed and extended to Pop II stars as a possible explanation for these halo objects. Based on detections of F-type main-sequence variables, mass loss is assumed to occur in a narrow temperature region corresponding to this “instability strip.” As Pop II main-sequence stars evolve to the blue, they enter this narrow temperature region, then move back through the lower temperature area of the Spite plateau. If 0.05 M⊙ (solar mass) or more have been lost, they will show lithium depletion. This hypothesis affects the lithium-to- beryllium abundance, the ratio of high- to low-lithium stars, and the luminosity function. Constraints on the mass-loss hypothesis due to these effects are discussed. Finally, mass loss in this temperature range would operate in stars near the turnoff of metal-poor globular clusters, resulting in apparent ages 2 to 3 Gyr (gigayears) older than they actually are.

Emission-line galaxy surveys with GTC: The Hα Universe

Emission line galaxies are the most easily detected and studied objects in the high redshift Universe. They are being used to trace the evolution of critical observables of the Universe such as Star Formation Rate densities, starburst properties and abundances. Most of the research is being done using [OII]3727 and UV lines, but Hα is still one the best tracers for Star Formation Rate and physical properties of current star-forming galaxies. As a complementary contribution to studies of galaxy evolution, our team has focused into a long-term project to study the population of Hα-selected star-forming galaxies of the Universe at different redshifts. In 1995 we first determined the local Hα luminosity function, and from it the Star Formation Rate density (SFRd) of the local Universe. We then, using narrow-band imaging in the optical, extended this measurement to z ≃ 0.24 and z ≃ 0.4. Working in the near-infrared, GTC will be a very powerful tool to study the evolution of the Hα emission-line galaxy populations at different redshifts. We will both quantify the SFRd evolution and characterize the star-forming galaxy populations by directly comparing the same observables at all redshifts up to z ≃ 2.5.

The molecular gas content of star-forming galaxies in the ALPINE fields.

In this thesis, I aim to study the evolution with redshift of the gas mass fraction of a sample of 53 sources (from z ∼ 0.5 to z > 5) serendipitously detected in ALMA band 7 as part of the ALMA Large Program to INvestigate C II at Early Times (ALPINE). First, I used SED-fitting software CIGALE, which is able to implement energy balancing between the optical and the far infrared part, to produce a best-fit template of my sources and to have an estimate of some physical properties, such as the star formation rate (SFR), the total infrared luminosity and the total stellar mass. Then, using the tight correlation found by Scoville et al. (2014) between the ISM molecular gas mass and the rest-frame 850 μm luminosity, I used the latter, extrapolating it from the best-fit template using a code that I wrote in Python, as a tracer for the molecular gas. For my sample, I then derived the most important physical properties, such as molecular gas mass, gas mass fractions, specific star formation rate and depletion timescales, which allowed me to better categorize them and find them a place within the evolutionary history of the Universe. I also fitted our sources, via another code I wrote again in Python, with a general modified blackbody (MBB) model taken from the literature (Gilli et al. (2014), D’Amato et al. (2020)) to have a direct method of comparison with similar galaxies. What is evident at the end of the paper is that the methods used to derive the physical quantities of the sources are consistent with each other, and these in turn are in good agreement with what is found in the literature.