Dark matter in dwarf irregular galaxies, DDO 210 and DDO 169

It has been proposed that dwarf irregular galaxies can be separated into two classes based on their formation mechanism; that they are the result of the collapse of a primordial gas cloud or that they are the product of condensation of gas in the tidal tails of interacting galaxies. Simulations of galaxy interactions indicate that one can differentiate between these two scenarios by the dark matter content, with a low dark matter content indicating a fossil tidal dwarf. The purpose of this dissertation was to explore the dark matter distribution of two dwarf irregular galaxies using optical and neutral atomic hydrogen data. For DDO 210, the method of mass-modelling was used to determine its dark matter. About 64% of the galaxy mass was calculated to be in the form of dark matter and hence it is unlikely to be a fossil tidal dwarf. The method of mass-modelling could not be used for DDO 169 as the galaxy shows evidence of being tidally disrupted and hence, has a disturbed velocity field. Instead, the suggestion that dark matter might be responsible for a pressure anomaly in DDO 169 was tested to determine its dark matter content. According to this method, a pressure anomaly does exist but without a concrete value for the scale-height, it is unclear whether the anomaly is due to the presence of dark matter. Hence one cannot say how much dark matter might actually be present in DDO 169. A rotation curve would be required to do this. ^

The H I chronicles of LITTLE THINGS blue compact dwarf galaxies

Star formation occurs when the gas (mostly atomic hydrogen; H I) in a galaxy becomes disturbed, forming regions of high density gas, which then collapses to form stars. In dwarf galaxies it is still uncertain which processes contribute to star formation and how much they contribute to star formation. Blue compact dwarf (BCD) galaxies are low mass, low shear, gas rich galaxies that have high star formation rates when compared to other dwarf galaxies. What triggers the dense burst of star formation in BCDs but not other dwarfs is not well understood. It is often suggested that BCDs may have their starburst triggered by gravitational interactions with other galaxies, dwarf-dwarf galaxy mergers, or consumption of intergalactic gas. However, there are BCDs that appear isolated with respect to other galaxies, making an external disturbance unlikely.^ Here, I study six apparently isolated BCDs from the LITTLE THINGS sample in an attempt to understand what has triggered their burst of star formation. LITTLE THINGS is an H I survey of 41 dwarf galaxies. Each galaxy has high angular and velocity resolution H I data from the Very Large Array (VLA) telescope and ancillary stellar data. I use these data to study the detailed morphology and kinematics of each galaxy, looking for signatures of starburst triggers. In addition to the VLA data, I have collected Green Bank Telescope data for the six BCDs. These high sensitivity, low resolution data are used to search the surrounding area of each galaxy for extended emission and possible nearby companion galaxies.^ The VLA data show evidence that each BCD has likely experienced some form of external disturbance despite their apparent isolation. These external disturbances potentially seen in the sample include: ongoing/advanced dwarf-dwarf mergers, an interaction with an unknown external object, and external gas consumption. The GBT data result in no nearby, separate H I companions at the sensitivity of the data. These data therefore suggest that even though these BCDs appear isolated, they have not been evolving in isolation. It is possible that these external disturbances may have triggered the starbursts that defines them as BCDs.^

Correspondências científicas como uma relação didática entre história e ensino de matemática: o exemplo das cartas de Euler a uma princesa da Alemanha

Lettres àune Princesse d'Allemagne sur divers sujets de physique et de philosophie (Letters to a Princess of Germany on various topics of physics and philosophy) is the work taken as an object of study of this thesis. It is a literary success written in the eighteenth century by the Swiss mathematician and physicist Leonhard Paul Euler (1707-1783) in order to meet a request from the Prussian king, Frederick II, the Great (1712-1786) to accept to guide the intellectual education of his niece, the young princess Anhalt-Dessau (1745-1808). The method of teaching and learning through letters elected to the education of the German monarch resulted in a collection of 234 matches in which Euler theory is about music, Philosophy, Mechanics, Optics, Astronomy, Theology and Ethics among others. The research seeks to point out mathematical content contained in this reference work based on the exploitation and adaptation of original historical works as an articulator of development activities for teaching mathematics in basic education and in accordance with the National Curriculum Parameters of Mathematics (NCP) work. The general objective point out the limits and didactic potential of Lettres à une Princesse d'Allemagne sur divers sujets de physique et de philosophie as a source of support for teachers of basic education in developing activities for teaching mathematics. The discussions raised point to concrete possibilities of entanglement between the extracted mathematical content of the bulge of the work with current teaching methodologies from resizing the use of letters according to Freire's pedagogical perspective of the correspondence, and especially the use of new communication channels in the century XXI, both aimed at dialogue and approximation between those who write and those who read.

Struttura e cinematica della Via Lattea

In questa tesi si vuole fornire una descrizione delle proprietà morfologiche delle galassie per poi passare ad una analisi dettagliata della struttura e della cinematica della Via Lattea. Il primo capitolo è basato sulle informazioni generali che caratterizzano e classificano le galassie, partendo dalla classificazione di Hubble per poi analizzare nel dettaglio i diversi tipi di galassie. Il secondo capitolo si concentra in particolar modo sulla struttura della Via Lattea, descrivendo in modo dettaglio tutte le componenti morfologiche che la costituiscono. Il terzo ed ultimo capitolo si concentra sugli aspetti cinematici delle galassia a spirale applicati alla Via Lattea.

Heavily obscured AGN: an ideal laboratory to study the early co-evolution of galaxies and black holes

Obscured AGN are a crucial ingredient to understand the full growth history of super massive black holes and the coevolution with their host galaxies, since they constitute the bulk of the BH accretion. In the distant Universe, many of them are hosted by submillimeter galaxies (SMGs), characterized by a high production of stars and a very fast consumption of gas. Therefore, the analysis of this class of objects is fundamental to investigate the role of the ISM in the early coevolution of galaxies and black holes. We present a multiwavelength study of a sample of six obscured X-ray selected AGN at z>2.5 in the CDF-S, detected in the far-IR/submm bands. We performed the X-ray spectral analysis based on the 7Ms Chandra dataset, which provides the best X-ray spectral information currently available for distant AGN. We were able to place constraints on the obscuring column densities and the intrinsic luminosities of our targets. Moreover, we built up the UV to FIR spectral energy distributions (SEDs) by combining the broad-band photometry from CANDELS and the Herschel catalogs, and analyzed them by means of an SED decomposition technique. Therefore, we derived important physical parameters of both the host galaxy and the AGN. In addition, we obtained, through an empirical calibration, the gas mass in the host galaxy and assessed the galaxy sizes in order to estimate the column density associated with the host ISM. The comparison of the ISM column densities with the values measured from the X-ray spectral analysis pointed out that the contribution of the host ISM to the obscuration of the AGN emission can be substantial, ranging from ~10% up to ~100% of the value derived from the X-ray spectra. The absorption may occur at different physical scales in these sources and, in particular, the medium in the host galaxy is an ingredient that should be taken into account, since it may have a relevant role in driving the early co-evolution of galaxies with their black holes.

First science with SHARDS: emission line galaxies

SHARDS is an unbiased ultra-deep spectro-photometric survey with GTC@OSIRIS aimed at selecting and studying massive passively evolving galaxies at z=1.0-2.3 using a set of 24 medium-band filters (FWHM~17 nm) at 500-950 nm in GOODS-N. Our observing strategy is optimized to detect at z>1 the prominent Mg absorption feature at rest-frame ~ 280 nm, a distinctive, necessary, and sufficient feature of evolved stellar populations. Nonetheless, the data quality allow a plethora of studies on galaxy populations, including Emission Lines Galaxies (ELGs) about which we have started our first science verification project presented in this contribution.

Spectrophotometric study in the near-ir of a sample of MIPS selected galaxies at Z~2

Our main objective is to determine what kind of galaxies dominate the cosmic SFR density at z~2. Our sample consists of 24 galaxies in Chandra Deep Field South, a unique field for the study of galaxy evolution (12 observed with GNIRS/GEMINI and 12 with ISAAC/VLT). We use H alpha together with the already merged X-ray, ultraviolet, optical, near and mid-infrared imaging data to obtain estimations of SFRs, metallicities, stellar and dynamical masses, AGN activity, and extinction properties. We have obtained 15 Hα detections, 4 rotation curves, and SFR relationship for 7 galaxies. The metallicities obtained for 8 galaxies of the sample are compatible with the metallicities of local galaxies.

Exploring the star forming regions in vigorous star forming galaxies at Z=0.84

We analyze the properties of star forming regions in a sample of star forming galaxies at z = 0.84. Star forming regions are extracted from B band ACS-HST images. Previously we have substracted a model of the galaxy, fitting a bulged+disk model to the whole galaxy. Special care has been taken masking the star forming regions in the model fitting procedure, yielding more reliable results. We present here the properties of these star forming regions.

Discovery of "Warm Dust" galaxies in clusters at z ~ 0.3: evidence for stripping of cool dust in the dense environment?

Using far-infrared imaging from the "Herschel Lensing Survey," we derive dust properties of spectroscopically confirmed cluster member galaxies within two massive systems at z ~ 0.3: the merging Bullet Cluster and the more relaxed MS2137.3-2353. Most star-forming cluster sources (~90%) have characteristic dust temperatures similar to local field galaxies of comparable infrared (IR) luminosity (T_dust ~ 30 K). Several sub-luminous infrared galaxy (LIRG; L_IR < 10^11 L_☉) Bullet Cluster members are much warmer (T_dust > 37 K) with far-infrared spectral energy distribution (SED) shapes resembling LIRG-type local templates. X-ray and mid-infrared data suggest that obscured active galactic nuclei do not contribute significantly to the infrared flux of these "warm dust" galaxies. Sources of comparable IR luminosity and dust temperature are not observed in the relaxed cluster MS2137, although the significance is too low to speculate on an origin involving recent cluster merging. "Warm dust" galaxies are, however, statistically rarer in field samples (>3σ), indicating that the responsible mechanism may relate to the dense environment. The spatial distribution of these sources is similar to the whole far-infrared bright population, i.e., preferentially located in the cluster periphery, although the galaxy hosts tend toward lower stellar masses (M_* < 10^10 M_☉). We propose dust stripping and heating processes which could be responsible for the unusually warm characteristic dust temperatures. A normal star-forming galaxy would need 30%-50% of its dust removed (preferentially stripped from the outer reaches, where dust is typically cooler) to recover an SED similar to a "warm dust" galaxy. These progenitors would not require a higher IR luminosity or dust mass than the currently observed normal star-forming population.

Satellites around massive galaxies since z∼ 2

The accretion of minor satellites has been postulated as the most likely mechanism to explain the significant size evolution of massive galaxies over cosmic time. Using a sample of 629 massive (M_star~ 10^11 M_⊙) galaxies from the near-infrared Palomar/DEEP-2 survey, we explore what fraction of these objects have satellites with 0.01 < M_sat/M_central < 1 (1:100) up to z= 1 and what fraction have satellites with 0.1 < M_sat/M_central < 1 (1:10) up to z= 2 within a projected radial distance of 100 kpc. We find that the fraction of massive galaxies with satellites, after background correction, remains basically constant and close to 30 per cent for satellites with a mass ratio down to 1:100 up to z= 1, and close to 15 per cent for satellites with a 1:10 mass ratio up to z= 2. The family of spheroid-like massive galaxies presents a 2–3 times larger fraction of objects with satellites than the group of disc-like massive galaxies. A crude estimation of the number of 1:3 mergers a massive spheroid-like galaxy has experienced since z~2 is around 2. For a disc-like galaxy this number decreases to ~1.

Far-infrared constraints on the contamination by dust-obscured galaxies of high-z dropout searches

The spectral energy distributions (SED) of dusty galaxies at intermediate redshift may look similar to very high-redshift galaxies in the optical/near infrared (NIR) domain. This can lead to the contamination of high-redshift galaxy searches based on broad-band optical/NIR photometry by lower redshift dusty galaxies because both kind of galaxies cannot be distinguished. The contamination rate could be as high as 50%. This work shows how the far-infrared (FIR) domain can help to recognize likely low-z interlopers in an optical/NIR search for high-z galaxies. We analyze the FIR SEDs of two galaxies that are proposed to be very high-redshift (z > 7) dropout candidates based on deep Hawk-I/VLT observations. The FIR SEDs are sampled with PACS/Herschel at 100 and 160 μm, with SPIRE/Herschel at 250, 350 and 500 μm and with LABOCA/APEX at 870 μm. We find that redshifts > 7 would imply extreme FIR SEDs (with dust temperatures >100 K and FIR luminosities >10^13 L_⊙). At z ~ 2, instead, the SEDs of both sources would be compatible with those of typical ultra luminous infrared galaxies or submillimeter galaxies. Considering all available data for these sources from visible to FIR we re-estimate the redshifts and find z ~ 1.6–2.5. Owing to the strong spectral breaks observed in these galaxies, standard templates from the literature fail to reproduce the visible-to-near-IR part of the SEDs even when additional extinction is included. These sources strongly resemble dust-obscured galaxies selected in Spitzer observations with extreme visible-to-FIR colors, and the galaxy GN10 at z = 4. Galaxies with similar SEDs could contaminate other high-redshift surveys.

The AGN, star-forming, and morphological properties of luminous ir-bright/optically-faint galaxies

We present the active galactic nucleus (AGN), star-forming, and morphological properties of a sample of 13 MIR-luminous (∫_24 700 μJy) IR-bright/optically-faint galaxies (IRBGs, ∫_24/f_R≲ 1000). While these z ∼ 2 sources were drawn from deep Chandra fields with >200 ks X-ray coverage, only seven are formally detected in the X-ray and four lack X-ray emission at even the 2σ level. Spitzer InfraRed Spectrograph (IRS) spectra, however, confirm that all of the sources are AGN-dominated in the mid-IR, although half have detectable polycyclic aromatic hydrocarbon (PAH) emission responsible for ∼25% of their mid-infrared flux density. When combined with other samples, this indicates that at least 30%–40% of luminous IRBGs have star formation rates in the ultraluminous infrared galaxy (ULIRG) range (∼100–2000 M_⨀ yr^−1). X-ray hardness ratios and MIR to X-ray luminosity ratios indicate that all members of the sample contain heavily X-ray obscured AGNs, 80% of which are candidates to be Compton thick. Furthermore, the mean X-ray luminosity of the sample, log L_2–10 keV(erg s^−1) ∼44.6, indicates that these IRBGs are Type 2 QSOs, at least from the X-ray perspective. While those sources most heavily obscured in the X-ray are also those most likely to display strong silicate absorption in the mid-IR, silicate absorption does not always accompany X-ray obscuration. Finally, ∼70% of the IRBGs are merger candidates, a rate consistent with that of sub-mm galaxies (SMGs), although SMGs appear to be physically larger than IRBGs. These characteristics are consistent with the proposal that these objects represent a later, AGN-dominated, and more relaxed evolutionary stage following soon after the star-formation-dominated one represented by the SMGs.

The Herschel Lensing Survey (HLS): Overview

The Herschel Lensing Survey (HLS) will conduct deep PACS and SPIRE imaging of ~40 massive clusters of galaxies. The strong gravitational lensing power of these clusters will enable us to penetrate through the confusion noise, which sets the ultimate limit on our ability to probe the Universe with Herschel. Here we present an overview of our survey and a summary of the major results from our science demonstration phase (SDP) observations of the Bullet cluster (z = 0.297). The SDP data are rich and allow us to study not only the background high-redshift galaxies (e. g., strongly lensed and distorted galaxies at z = 2.8 and 3.2) but also the properties of cluster-member galaxies. Our preliminary analysis shows a great diversity of far-infrared/submillimeter spectral energy distributions (SEDs), indicating that we have much to learn with Herschel about the properties of galaxy SEDs. We have also detected the Sunyaev-Zel'dovich (SZ) effect increment with the SPIRE data. The success of this SDP program demonstrates the great potential of the Herschel Lensing Survey to produce exciting results in a variety of science areas.

The far-infrared/submillimeter properties of galaxies located behind the Bullet cluster

The Herschel Lensing Survey (HLS) takes advantage of gravitational lensing by massive galaxy clusters to sample a population of high-redshift galaxies which are too faint to be detected above the confusion limit of current far-infrared/submillimeter telescopes. Measurements from 100-500 μm bracket the peaks of the far-infrared spectral energy distributions of these galaxies, characterizing their infrared luminosities and star formation rates. We introduce initial results from our science demonstration phase observations, directed toward the Bullet cluster (1E0657-56). By combining our observations with LABOCA 870 μm and AzTEC 1.1 mm data we fully constrain the spectral energy distributions of 19 MIPS 24 μm-selected galaxies which are located behind the cluster. We find that their colors are best fit using templates based on local galaxies with systematically lower infrared luminosities. This suggests that our sources are not like local ultra-luminous infrared galaxies in which vigorous star formation is contained in a compact highly dust-obscured region. Instead, they appear to be scaled up versions of lower luminosity local galaxies with star formation occurring on larger physical scales.

First detection of the Sunyaev Zel'dovich effect increment at λ < 650 μm

The Sunyaev-Zel'dovich (SZ) effect is a spectral distortion of the cosmic microwave background as observed through the hot plasma in galaxy clusters. This distortion is a decrement in the CMB intensity for λ > 1.3 mm, an increment at shorter wavelengths, and small again by λ ~ 250 μm. As part of the Herschel Lensing Survey (HLS) we have mapped 1E0657–56 (the Bullet cluster) with SPIRE with bands centered at 250, 350 and 500 μm and have detected the SZ effect at the two longest wavelengths. The measured SZ effect increment central intensities are ΔI_0 = 0.097 ± 0.019 MJy sr^-1 at 350 μm and ΔI_0 = 0.268 ± 0.031 MJy sr^-1 at 500 μm, consistent with the SZ effect spectrum derived from previous measurements at 2 mm. No other diffuse emission is detected. The presence of the finite temperature SZ effect correction is preferred by the SPIRE data at a significance of 2.1σ, opening the possibility that the relativistic SZ effect correction can be constrained by SPIRE in a sample of clusters. The results presented here have important ramifications for both sub-mm measurements of galaxy clusters and blank field surveys with SPIRE.