Search

Relic galaxies are massive compact quiescent galaxies that formed at high-redshift and remained almost unchanged since then. In this work, we search for analogues to relic galaxies in the TNG50 cosmological simulations to understand relic formation and test the ability of TNG50 to reproduce such rare objects. Using stellar mass, age, radius, quiescence, and stellar assembly criteria, we find five subhaloes in TNG50 that could be potential relic analogues. We compare their properties with other constraints imposed by a sample of 13 observed relic galaxies. We find one analogue in TNG50 that simultaneously satisfies most of the available observational constraints, such as metallicity and morphology. It also shows similarities to the confirmed relic NGC 1277, regarding environment and dark matter fraction. By taking into account a degree of relicness, a second relic analogue may also be considered. However, the central parts of the brightness and density profiles of the analogues are less steep than that of real relic galaxies, possibly due to limited numerical resolution. We identify two formation pathways of relic analogues in TNG50 depending on their environment: they either have their remaining gas stripped during the infall into a cluster at z 1.2 or consume it before z > 1.5. They are then deprived of significant star formation, leaving their stellar populations almost unaltered during the last 9 Gyr. We also find that the analogue progenitors at z ∼ 4 inhabit more massive haloes than progenitors of quiescent galaxies with similar stellar mass at z ∼ 0.

We characterized the kinematics, morphology, and stellar population (SP) properties of a sample of massive compact quiescent galaxies (MCGs, 10 log M /M 11 and re ∼ 1–3 kpc) in the MaNGA Survey, with the goal of constraining their formation, assembly history, and assessing their relation with non-compact quiescent galaxies. We compared their properties with those of a control sample of median-sized quiescent galaxies (re ∼ 4–8 kpc) with similar effective velocity dispersions. MCGs have elevated rotational support, as evidenced by a strong anticorrelation between the Gauss–Hermite moment h3 and V/σ. In contrast, 30 per cent of control sample galaxies (CSGs) are slow rotators, and fast-rotating CSGs generally show a weak h3–V/σ anticorrelation. MCGs and CSGs have similar ages, but MCGs are more metal-rich and α-enhanced. Both MCGs and CSGs have shallow negative metallicity gradients and flat [α/Fe] gradients. On average, MCGs and CSGs have flat age gradients, but CSGs have a significantly larger dispersion of gradient values. The kinematics and SP properties of MCGs suggest that they experienced highly dissipative gas-rich events, such as mergers, followed by an intense, short, and centrally concentrated burst of star formation, between 4 and 10 Gyr ago (z ∼ 0.4–2), and had a quiet accretion history since then. This sequence of events might be analogous to, although less extreme than, the compaction events that formed compact quiescent galaxies at z ∼ 2. The small sizes of MCGs, and the high efficiency and short duration of their last star formation episode suggest that they are descendants of compact post-starburst galaxies.

The so-called ultraviolet (UV) upturn of elliptical galaxies is a phenomenon characterised by the up-rise of their fluxes in bluer wavelengths, typically in the 1,200-2,500A range. This work aims at estimating the rate of occurrence of the UV upturn over the entire red-sequence population of galaxies that show significant UV emission. This assessment is made considering it as function of three parameters: redshift, stellar mass, and -- what may seem counter-intuitive at first -- emission-line classification. We built a multiwavelength spectro-photometric catalogue from the Galaxy Mass Assembly survey, together with aperture-matched data from Galaxy Evolution Explorer Medium-Depth Imaging Survey (MIS) and Sloan Digital Sky Survey, covering the redshift range between 0.06 and 0.40. From this sample, we analyse the UV emission among UV bright galaxies, by selecting those that occupy the red-sequence locus in the (NUV-r) x (FUV-NUV) chart; then, we stratify the sample by their emission-line classes. To that end, we make use of emission-line diagnostic diagrams, focusing the analysis in retired/passive lineless galaxies. Then, a Bayesian logistic model was built to simultaneously deal with the effects of all galaxy properties (including emission-line classification or lack thereof). The main results show that retired/passive systems host an up-rise in the fraction of UV upturn or redshifts between 0.06 and 0.25, followed by an in-fall up to 0.35. Additionally, we show that the fraction of UV upturn hosts rises with increasing stellar mass., 17 pages, 19 figures, accepted for publication in MNRAS

Com o objetivo de entender as limitações de modelos de população estelar no infravermelho próximo (NIR), realizamos na presente tese um teste extensivo de bibliotecas de modelos de populações estelares simples no NIR em comparação com o óptico. Tal estudo foi feito ajustando o espectro inteiro com o programa starlight e através da comparação de índices espectrais. Os principais resultados obtidos foram (i) bibliotecas de modelos NIR com baixa resolução espectral produzem resultados que dependem da escolha da biblioteca estelar e não produzem resultados consistentes entre si (ii) de maneira geral, bibliotecas no NIR com baixa resolucão espectral tendem a superestimar a extinção por poeira e a quantidade de população estelar jovem e (iii) para bibliotecas com alta resolução espectral, este cenário é consideravelmente melhor, com as duas bibliotecas testadas produzindo resultados mais compátíveis com os resultados encontrados no óptico. Com a metodologia consolidada, utilizamos cubos de dados no óptico e no NIR, ambos obtidos com o telescópio Gemini, para mapearmos a população estelar da galáxia elíptica NGC1052. A partir dos dados ópticos, a galáxia NGC1052 apresenta população estelar velha em todos os pontos do cubo de dados. No entanto, a partir de dados no NIR, os mesmos pontos apresentam uma contribuição de população estelar de idade intermediária. Afim de detectar populações sensíveis aos dois intervalos de comprimento de onda, combinamos os dois conjuntos de dados em um único cubo de dados, analisando assim simultaneamente o óptico e o NIR. Os resultados obtidos nesta análise pancromática mostram que a população estelar que domina a luz desta galáxia é predominantemente velha. Argumentamos que a divergência entre os resultados ópticos e NIR pode ser explicada pela baixa razão sinal-ruído da banda J e a ausência de dados na banda H, a qual contém grande parte das absorções estelares no NIR. Também mapeamos as propriedades do gás desta galáxia, encontrando 5 componentes cinemáticas nas linhas de emissão: (1 e 2) Duas componentes espacialmente não resolvidas, sendo uma componente larga em Hα, com um FWHM~de 3200kms-¹ e uma componente intermediária-larga no dubleto [Oiii] λλ4959,5007; (3) uma componente estendida de largura intermediária com 280

We map optical and near-infrared (NIR) stellar population properties of the inner 320 × 535 pc2 of the elliptical galaxy NGC 1052. The optical and NIR spectra were obtained using the Gemini Integral Field Units of the GMOS instrument and NIFS, respectively. By performing stellar population synthesis in the optical alone, we find that this region of the galaxy is dominated by old (t > 10 Gyr) stellar populations. Using the NIR, we find the nucleus to be dominated by old stellar populations, and a circumnuclear ring with younger (~2.5 Gyr) stars. We also combined the optical and NIR datacubes and performed a panchromatic spatially resolved stellar population synthesis, which resulted in a dominance of older stellar populations, in agreement with optical results. We argue that the technique of combining optical and NIR data might be useful to isolate the contribution of stellar population ages with strong NIR absorption bands. We also derive the stellar kinematics and find that the stellar motions are dominated by a high (~240 km s−1) velocity dispersion in the nucleus, with stars also rotating around the centre. Lastly, we measure the absorption bands, both in the optical and in the NIR, and find a nuclear drop in their equivalent widths. The favoured explanation for this drop is a featureless continuum emission from the low luminosity active galactic nucleus.

Recovering the origins of lenticular galaxies can shed light on the understanding of galaxy formation and evolution, since they present properties that can be found in both elliptical and spiral galaxies. In this work we study the kinematics of the globular cluster (GC) systems of three lenticular galaxies located in low density environments (NGC 2768, NGC 3115 and NGC 7457), and compare them with the kinematics of planetary nebulae (PNe). The PNe and GC data come from the Planetary Nebulae Spectrograph and the SLUGGS Surveys. Through photometric spheroid-disc decomposition and PNe kinematics we find the probability for a given GC to belong to either the spheroid or the disc of its host galaxy or be rejected from the model. We find that there is no correlation between the components that the GCs are likely to belong to and their colours. Particularly, for NGC 2768 we find that its red GCs display rotation preferentially at inner radii (Re, 13 pages, 10 figures, Accepted for publication in MNRAS

In the hierarchical two-phase formation scenario, the extended halos of early type galaxies (ETGs) are expected to have different physical properties from those of the galaxies' central regions. This work aims at characterizing the kinematic properties of ETG halos using planetary nebulae (PNe) as tracers, which allow us to overcome the limitations of absorption line spectroscopy of continuum at low surface brightness. We present two-dimensional velocity and velocity dispersion fields for 33 ETGs, including both fast (FRs) and slow rotators (SRs), making this the largest kinematic survey to-date of extragalactic PNe. The velocity fields extend out to a median 5.6 effective radii (Re), with a range [3Re-13Re] for the PN.S ETGs. We complemented the PN kinematics with absorption line data from the literature. We find that ETGs typically show a kinematic transition between inner regions and halo. Estimated transition radii in units of Re anticorrelate with stellar mass. SRs have increased but still modest rotational support at large radii, while most of the FRs show a decrease in rotation, due to the fading of the stellar disk in the outer, more slowly rotating spheroid. 30% of the FRs are dominated by rotation also at large radii. Most ETGs have flat or slightly falling halo velocity dispersion profiles, but 15% of the sample have steeply falling profiles. 40% of the FRs show kinematic twists, misalignments, or rotation along two axes, indicating that they turn from oblate at the center to triaxial in the halo, consistently with the distribution of isophote twists from extended photometry. ETGs have more diverse kinematic properties in their halos than in the central regions. The observed kinematic transition to the halo and its dependence on stellar mass is consistent with LambdaCDM simulations and supports a two-phase formation scenario. [abridged], Comment: Accepted for publication in A&A, 52 pages, 30 figures

No presente trabalho zemos uso do espectr ografo multi-objeto do Gemini (GMOS) no modo de unidade de campo integral para mapear a popula c~ao estelar, a distribui c~ao do uxo das linhas de emiss~ao e a cinem atica do g as no kpc mais interno da gal axia NGC 5044. A partir da s ntese de popula c~ao estelar encontramos que a emiss~ao do cont nuo e dominada por estrelas velhas de alta metalicidade (13 Gyr, 2,5 Z ). Tamb em encontramos que a emiss~ao nuclear dessa gal axia e dilu da por uma emiss~ao n~ao t ermica, a qual atribu mos a presen ca de um n ucleo ativo gal actico (AGN) fraco. Al em disso, registramos pela primeira vez uma componente alargada (FWHM 3000 kms1) na emiss~ao da linha de H na regi~ao nuclear de NGC 5044. Por meio de diagramas de diagn ostico de raz~oes de linhas de emiss~ao encontramos que coexistem dois processos de ioniza c~ao dominantes, enquanto a regi~ao nuclear (200 pc mais internos) e ionizada por um AGN de baixa luminosidade, as estruturas lamentares s~ao consistentes com excita c~ao por choques. O campo de velocidade de H mostra evid^encias de um disco em rota c~ao, o qual tem uma amplitude de velocidade de 240 km s1a 136 pc do n ucleo. Assumindo uma aproxima c~ao Kepleriana estimamos que a massa dentro desse raio e 1; 9 0; 9 109M , o qual est a de acordo com o valor obtido utilizando a rela c~ao M- , MSMBH=1,8 1; 6 109M . Modelando o campo de velocidade do g as ionizado por uma componente de disco em rota c~ao mais in ows em dire c~ao ao n ucleo ao longo das estruturas lamentares, obtivemos uma taxa de massa de in ow de 0,4 M . Essa taxa de in ow e su ciente para acionar o AGN central na NGC 5044. We used Gemini Multi-Object Spectrograph (GMOS) in the Integral Field Unit mode to map the stellar population, emission line ux distributions and gas kinematics in the inner kpc of NGC 5044. From the stellar populations synthesis we found that the continuum emission is dominated by old high metallicity stars (13 Gyr, 2.5 Z ). Also, its nuclear emission is diluted by a non thermal emission, which we attribute to the presence of a weak active galactic nuclei (AGN). In addition, we report for the rst time a broad component (FWHM 3000 km s1) in the H emission line in the nuclear region of NGC 5044. By using emission line ratio diagnostic diagrams we found that two dominant ionization processes coexist, while the nuclear region (inner 200 pc) is ionized by a low luminosity AGN, being the lamentary structures consistent with excited by shocks. The H velocity eld shows evidence of a rotating disk, which has a velocity amplitude of 240 km s1at 136 pc from the nucleus. Assuming a Keplerian approach we estimated that the mass inside this radius is 1:9 0:9 109M , which is in agreement with the value obtained through the M- relation, MSMBH=1.8 1:6 109M . Modelling the ionized gas velocity eld by a rotating disk component plus in ows towards the nucleus along lamentary structures, we obtain a mass in ow rate of 0.4 M . This in ow rate is enough to power the central AGN in NGC 5044.

We study the internal gradients of stellar population properties within $1.5\;R_{\rm e}$ for a representative sample of 721 galaxies with stellar masses ranging between $10^{9}\;M_{\odot}$ to $10^{11.5}\;M_{\odot}$ from the SDSS-IV MaNGA IFU survey. Through the use of our full spectral fitting code FIREFLY, we derive light and mass-weighted stellar population properties and their radial gradients, as well as full star formation and metal enrichment histories. We also quanfify the impact that different stellar population models and full spectral fitting routines have on the derived stellar population properties, and the radial gradient measurements. In our analysis, we find that age gradients tend to be shallow for both early-type and late-type galaxies. {\em Mass-weighted} age gradients of early-types are positive ($\sim 0.09\; {\rm dex}/R_{\rm e}$) pointing to "outside-in" progression of star formation, while late-type galaxies have negative {\em light-weighted} age gradients ($\sim -0.11\; {\rm dex}/R_{\rm e}$), suggesting an "inside-out" formation of discs. We detect negative metallicity gradients in both early and late-type galaxies, but these are significantly steeper in late-types, suggesting that radial dependence of chemical enrichment processes and the effect of gas inflow and metal transport are far more pronounced in discs. Metallicity gradients of both morphological classes correlate with galaxy mass, with negative metallicity gradients becoming steeper with increasing galaxy mass. The correlation with mass is stronger for late-type galaxies, with a slope of $d(\nabla [Z/H])/d(\log M)\sim -0.2\pm 0.05\;$, compared to $d(\nabla [Z/H])/d(\log M)\sim -0.05\pm 0.05\;$ for early-types. This result suggests that the merger history plays a relatively small role in shaping metallicity gradients of galaxies., 31 pages, 22 figures, 5 tables. Resubmitted to MNRAS including referees comments

Globular clusters (GCs) can be considered discrete, long-lived, dynamical tracers that retain crucial information about the assembly history of their parent galaxy. In this paper, we present a new catalogue of GC velocities and colours for the lenticular galaxy NGC 1023, we study their kinematics and spatial distribution, in comparison with the underlying stellar kinematics and surface brightness profile, and we test a new method for studying GC properties. Specifically, we decompose the galaxy light into its spheroid (assumed to represent the bulge+halo components) and disc components and use it to assign to each GC a probability of belonging to one of the two components. Then we model the galaxy kinematics, assuming a disc and spheroidal component, using planetary nebulae and integrated stellar light. We use this kinematic model and the probability previously obtained from the photometry to recalculate for each GC its likelihood of being associated with the disc, the spheroid, or neither. We find that the reddest GCs are likely to be associated with the disc, as found for faint fuzzies in this same galaxy, suggesting that the disc of this S0 galaxy originated at z 2. The majority of blue GCs are found likely to be associated with the spheroidal (hot) component. The method also allows us to identify objects that are unlikely to be in equilibrium with the system. In NGC 1023 some of the rejected GCs form a substructure in phase space that is connected with NGC 1023 companion galaxy.

The power of jets from black holes are expected to depend on both the spin of the black hole and the structure of the accretion disk in the region of the last stable orbit. We investigate these dependencies using two different physical models for the jet power: the classical Blandford-Znajek (BZ) model and a hybrid model developed by Meier. In the BZ case, the jets are powered by magnetic fields directly threading the spinning black hole while in the hybrid model, the jet energy is extracted from both the accretion disk as well as the black hole via magnetic fields anchored to the accretion flow inside and outside the hole's ergosphere. The hybrid model takes advantage of the strengths of both the Blandford-Payne and BZ mechanisms, while avoiding the more controversial features of the latter. We develop these models more fully to account for general relativistic effects and to focus on advection-dominated accretion flows (ADAF) for which the jet power is expected to be a significant fraction of the accreted rest mass energy. We apply the models to elliptical galaxies, in order to see if these models can explain the observed correlation between the Bondi accretion rates and the total jet powers. For typical values of the disk viscosity parameter alpha~0.04-0.3 and mass accretion rates consistent with ADAF model expectations, we find that the observed correlation requires j>0.9; i.e., it implies that the black holes are rapidly spinning. Our results suggest that the central black holes in the cores of clusters of galaxies must be rapidly rotating in order to drive jets powerful enough to heat the intracluster medium and quench cooling flows., 12 pages, 4 figures, accepted for publication in MNRAS

En esta Tesis Doctoral se presenta un estudio en gran escala de propiedades fotométricas de la población de galaxias del Cúmulo de Antlia. En el mismo, se incluyen galaxias de tipo temprano, desde elípticas gigantes hasta enanas elípticas y esferoidales, incluyendo zonas periféricas, aledañas a la parte central del cúmulo, no analizadas hasta la fecha. Este trabajo involucra aproximadamente 180 galaxias, entre las cuales se encuentran las ya catalogadas previamente sobre placas fotográficas por Ferguson y Sandage (1990) sumadas a 77 nuevas galaxias descubiertas. El material observacional que se utilizó en este trabajo consiste en imágenes CCD de 4 campos del cúmulo de Antlia, incluyendo entre ellos la zona central. Las imágenes han sido obtenidas con el telescopio Víctor Blanco de 4−m del Observatorio Interamericano de Cerro Tololo (CTIO-Chile), con la cámara MOSAICII de 8 CCDs y los filtros R de Kron-Cousins y C del sistema de Washington. Cada imagen tipo mosaico cubre un área proyectada sobre el plano del cielo de 36' ×36', con lo que la cobertura total del cúmulo es aproximadamente de 1.5 grados cuadrados. Se ha realizado fotometría superficial para cada objeto en forma individual. Se obtuvieron los perfiles de brillo superficial mediante la tarea ellipse del paquete IRAF y se realizaron ajustes a tales perfiles, utilizando un modelo de Sérsic, mediante la tarea nfit1d. Los perfiles teóricos se integraron numéricamente hasta infinito para calcular magnitudes totales. De este modo, para cada galaxia se obtuvieron magnitudes y colores integrados, brillos superficiales, radios efectivos, índices de Sérsic, y demás parámetros estructurales. Posteriormente, se analizaron las correlaciones entre tales parámetros galácticos que caracterizan los diferentes tipos y/o morfologías presentes en el entorno de un cúmulo de galaxias. Se estudió la relación color-magnitud de las galaxias de tipo temprano, que se encuentra en buen acuerdo con relaciones análogas para otros cúmulos, y muestra un suave quiebre en la parte brillante, que se explica mediante resultados de modelos. Se construyeron relaciones de escala estructurales y fotométricas entre las magnitudes totales integradas, los brillos superficiales central, efectivo y efectivo promedio, el radio efectivo, etc., las que además se han comparado con otros cúmulos de galaxias. Se encuentra un buen acuerdo global, principalmente en la zona de bajo brillo superficial. Finalmente, se analizaron tales relaciones de escala a fin de determinar si están presentes distintas secuencias para distinto tipo de galaxias tempranas, mostrando separaciones o dicotomías, o si es posible representar distintos tipos de galaxias tempranas con correlaciones únicas. En función de estas opciones, e incluyendo los datos de otros grupos y cúmulos, resulta factible interpretar el origen y/o evolución de las galaxias de tipo temprano, brillantes y enanas, a partir de procesos diferentes, dado que los ajustes realizados mediante dos secuencias diferentes para cada subpoblación parecen ser los más apropiados., Facultad de Ciencias Astronómicas y Geofísicas

We investigate interaction effects on the dynamics and morphology of the galaxy pairs AM\,2058-381 and AM\,1228-260. This work is based on $r'$ images and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the Gemini South Telescope. The luminosity ratio between the main (AM\,2058A) and secondary (AM\,2058B) components of the first pair is a factor of $\sim$ 5, while for the other pair, the main (AM\,1228A) component is 20 times more luminous than the secondary (AM\,1228B). The four galaxies have pseudo-bulges, with a S��rsic index $n, 20 pages, 10 figures, accepted for publication in MNRAS

Besides its major objective tuned to the detection of the stellar galactic population the Gaia mission experiment will also observe a large number of galaxies. In this work we intend to evaluate the number and the characteristics of the galaxies that will effectively pass the onboard selection algorithm of Gaia. The detection of objects in Gaia will be performed in a section of the focal plane known as the Sky Mapper. Taking into account the Video Processing Algorithm criterion of detection and considering the known light profiles of discs and bulges galaxies we assess the number and the type of extra-galactic objects that will be observed by Gaia. We show that the stellar disk population of galaxies will be very difficult to be observed. On the contrary the spheroidal component of elliptical galaxies and bulges having higher central surface brightness and steeper brightness profile will be more easy to be detected. We estimate that most of the 20 000 elliptical population of nearby galaxies inside the local region up to 170 Mpc are in condition to be observed by Gaia. A similar number of bulges could also be observed although the low luminosity bulges should escape detection. About two thirds of the more distant objects up to 600 Mpc could also be detected increasing the total sample to half a million objects including ellipticals and bulges. The angular size of the detected objects will never exceed 4.72 arcsec which is the size of the largest transmitted windows. An heterogeneous population of elliptical galaxies and bulges will be observable by Gaia. This nearby Universe sample of galaxies should constitute a very rich and interesting sample to study their structural properties and their distribution., Comment: 6 figures, 22 pages

In a former paper, we have presented spectra of 64 active, nine normal and five starburst galaxies in the region around the near-infrared calcium triplet (CaT) absorption lines and the [S III]λ9069 line. In the present paper, we analyse the CaT strength (WCaT) and kinematical products derived in that study, namely stellar (σ) and ionized gas (σgas) velocity dispersions. Our main results may be summarized as follows. (1) Type 2 Seyfert galaxies show no sign of dilution in WCaT with respect to the values spanned by normal galaxies, even when optical absorption lines such as the Ca II K band at 3933 Å are much weaker than in old, bulge-like stellar populations. (2) The location of type 2 Seyfert galaxies in the WCaT–WCaK plane is consistent with evolutionary synthesis models. The implication is that the source responsible for the dilution of optical lines in these active galactic nuclei (AGN) is a young stellar population, rather than an AGN featureless continuum, confirming the conclusion of the pioneer study of Terlevich, Díaz & Terlevich. (3) In type 1 Seyfert galaxies, both W[S III] and WCaT tend to be diluted due to the presence of a non-stellar component, in agreement with the unification paradigm. (4) A comparison of σ with σgas (obtained from the core of the [S III] emitting line) confirms the existence of a correlation between the typical velocities of stars and clouds of the narrow line region. The strength and scatter around this correlation are similar to those previously obtained from the [O III]λ5007 linewidth.

Context. Luminous elliptical galaxies generally display a rich star cluster system, whose properties provide strong constraints on the physics of galaxy formation and evolution. Star cluster system studies, however, concentrate on galaxies located in nearby or rich galaxy clusters. Aims. We acquired deep B and I images of NGC 1600, a luminous elliptical in a galaxy group to study its star cluster system. The images were obtained with the Optical Imager at the Southern Telescope for Astrophysical Research for an exposure time of 1.66 h in each filter. Methods. The sample selection incompleteness was assessed as a function of magnitude and image background level. Source counts were measured for different elliptical annuli from the centre of NGC 1600, background subtracted, and fitted with a Gaussian function. Colour distributions were derived as a function of galactocentric distance for sources measured successfully in both filters. Typical ages and metallicities were estimated based on single stellar population models. Results. A clear excess of point sources around NGC 1600 was found in relation to the nearby field. The source counts were consistent with a Gaussian distribution typical of other luminous ellipticals. The luminosity function fits provided an estimate of the density of clusters at the different annuli that could be integrated in solid angle, resulting in an estimated total population of NGC -~ 2850 star clusters. This yielded a specific frequency of SN -~ 1.6. The colour distributions show a hint of bimodality, especially at 20 -~ kpc from the centre. Clusters in this region may be associated with a ring or shell perturbation. Finally, the star cluster candidates were crosscorrelated to discrete X-ray sources and a coincidence rate of -~ 40% was found. These are likely to be globular clusters harboring low-mass X-ray binaries. Conclusions.

The stellar population, metallicity distribution and ionized gas in the elliptical galaxies NGC6868 and 5903 are investigated in this paper by means of long-slit spectroscopy and stellar population synthesis. Lick indices in both galaxies present a negative gradient indicating an overabundance of Fe, Mg, Na and TiO in the central parts with respect to the external regions. We found that Mg2 correlates both with Fe I λ5270 and Fe I λ5335, suggesting that these elements probably underwent the same enrichment process in NGC 6868. However, only a marginal correlation of Mg2 and Fe I λ5270 occurs in NGC5903. The lack of correlation between computed galaxy mass and the Mg2 gradient suggests that these elliptical galaxies were formed by merger events. The stellar population synthesis shows the presence of at least two populations with ages of 13 and 5 Gyr old in both galaxies. We have estimated the metallicity of the galaxies using single-aged stellar population (SSP) models. The central region of NGC6868 (|R| 0.5 < ~ kpc) presents a deficiency of alpha elements with respect to iron and solar metallicity. The external parts present a roughly uniform distribution of [α/Fe] ratios and metallicities ranging from [Z/Zʘ] = − 0.33 and solar. A similar conclusion applies to NGC5903. Concerning the emitting gas conspicuously detected in NGC6868, we test three hypotheses as ionizing source: an H II region, post-AGB (asymptotic giant branch) stars and an active galactic nucleus (AGN). Diagnostic diagrams involving the ratios ([N II] λ6584)/(Hα), ([O I] λ6300)/(Hα) and ([S II] λλ6717, 6731)/(Hα) indicate that values measured in the central region of NGC6868 are typical of LINERs (Low-Ionization Nuclear Emission-Line Regions). Together with the stellar population synthesis, this result suggests that the main source of gas ionization in NGC6868 is non-thermal, produced by a low-luminosity AGN, probably with some contribution of shocks to explain ionization at distances of ~ 3.5 kpc from the nucleus.

Early-type galaxies (ETGs) are known to be enhanced in alpha elements, in accordance with their old ages and short formation timescales. In this contribution we aim to resolve the enrichment histories of ETGs. This means we study the abundance of Fe ([Fe/H]) and the alpha-element groups ([alpha/Fe]) separately for stars older than 9.5 Gyr ([Fe/H]o, [alpha/Fe]o) and for stars between 1.5 and 9.5 Gyr ([Fe/H]i, [alpha/Fe]i). Through extensive simulation we show that we can indeed recover the enrichment history per galaxy. We then analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS selected to be ETGs. We separate out those galaxies for which the abundance of iron in stars grows throughout the lifetime of the galaxy, i.e. in which [Fe/H]o < [Fe/H]i. We confirm earlier work where the [Fe/H] and [alpha/Fe] parameters are correlated with the mass and velocity dispersion of ETGs. We emphasize that the strongest relation is between [alpha/Fe] and age. This relation falls into two regimes, one with a steep slope for old galaxies and one with a shallow slope for younger ETGs. The vast majority of ETGs in our sample do not show the 'knee' in the plot of [Fe/H] vs. [alpha/Fe] commonly observed in local group galaxies. This implies that for the vast majority of ETGs, the stars younger than 9.5 Gyrs are likely to have been accreted or formed from accreted gas. The properties of the intermediate-age stars in accretion-dominated ETGs indicate that mass growth through late (minor) mergers in ETGs is dominated by galaxies with low [Fe/H] and low [alpha/Fe]. The method of reconstructing the stellar enrichment histories of ETGs introduced in this paper promises to constrain the star formation and mass assembly histories of large samples of galaxies in a unique way., 22 pages, 25 figures, accepted for publication by A&A

The stellar population of the central region of the galaxy NGC 720 has been investigated through longslit optical spectroscopy. The velocity dispersion and 13 Lick indices were obtained as a function of the radius along the semimajor axis of the galaxy. The Mg₂ index presents a gradient of d Mg₂ / d log r = −0.079 which behaves similarly to the Fe I lines, indicating no enhancement of Mg₂ in relation to Fe I. The stellar population ages and metallicities were derived by a population synthesis method using available evolutive spectrophotometric models. The synthesis indicates a strong age gradient along the semimajor axis of NGC 720. In the central region a 13 Gyr and solar metallicity stellar population dominates the flux at 5870 Å; the contribution of this component vanishes at a radius of 0.73 kpc, where the total flux is accounted for by a younger, 5 Gyr and solar metallicity stellar population. For distances larger than 1 kpc a 2.5 Gyr component becomes very important. Moreover, NGC 720 is probably overabundant in CN in the center with respect to the solar abundance. The estimated total mass (3.29×10¹¹ Mѳ) and theMg₂ gradient values suggest that this galaxy might have undergone a merger event. The correspondence between the J-band brightness profile decomposition and the result of the spectral synthesis shows that this galaxy is formed by an old (13–5 Gyr), bulge-like, small-scale and massive spheroid and a younger (5–2.5Gyr), large-scale disk component. We discuss our results in comparison with available numerical simulations and propose that the merger event must have occurred about 4 Gyr ago.

In this paper we discuss the reason why the parameters of the Sersic model best-fitting the major axis light profile of elliptical galaxies can differ significantly from those derived for the minor axis profile. We show that this discrepancy is a natural consequence of the fact that the isophote eccentricity varies with the radius of the isophote and present a mathematical transformation that allows the minor axis Sersic model to be calculated from the major axis model, provided that the elliptical isophotes are aligned and concentric and that their eccentricity can be represented by a well behaved, though quite general, function of the radius. When there is no variation in eccentricity only the effective radius changes in the Sersic model, while for radial-dependent eccentricity the transformation which allows the minor axis Sersic model to be calculated from the major axis model is given by the Lerch Phi transcendental function. The proposed transformation was tested using photometric data for 28 early-type galaxies., Comment: 16 pages, 14 figures, LaTex with mn2e.cls. Accepted to MNRAS

This paper discusses the stellar population content of distant (5 000kms−1 VR 16 000kms−1) galaxies with enhanced star-formation activity. Distinction is made between isolated galaxies and galaxies morphologically disturbed, with clear signs of interaction such as mergers. In these galaxies the International Ultraviolet Explorer (IUE) large aperture samples most of the galaxy’s body. Consequently, the resulting integrated spectra arise primarily from blue stellar populations of different ages together with significant contributions from intermediate and old age components, subject to varying reddening amounts. Instead of analysing individual, usually lowSignal-to- Noise ratio (S/N) spectra, our approach is to coadd the spectra of objects with similar spectral properties in the UV, considering as well their properties in the visible/near-infrared ranges. Consequently, the resulting high (S/N) template spectra contain the average properties of a rather uniform class of objects, and information on spectral features can now be analysed with more precision. Three groups have been found for the interacting galaxies, corresponding to a red, blue and very blue continuum. Isolated galaxies have been separated into two groups, one with a flat/red continuum and the other with a blue continuum. For comparison, we also include in the present analysis two groups of nearby disturbed galaxies. Stellar populations are analysed by means of a synthesis algorithm based on star cluster spectral components of different ages which fit the observed spectra both in terms of continuum distribution and spectral features. Flux fractions of the different age groups found in the synthesis have been transformed into mass fractions, allowing inferences on the star formation histories. Young stellar populations (age < 500 Myr) are the main flux contributors, except for the groups with a red spectrum not due to extinction, arising from the intermediate (age 1−2 Gyr) and old age populations.We also study the reddening values and the extinction law: a Small Magellanic Cloud-like extinction law is appropriate for all cases. As compared to nearby galaxies with enhanced star-formation, the distant starburst galaxy spectral groups exhibit larger contributions from the intermediate and old age populations. This effect is mainly accounted for by the larger spatial area sampled by the IUE slit in the distant galaxies, including not only the entire bulge but also evolved disk populations. The present results provide a quantitative measure of the star-forming activity in interacting galaxies, compared to isolated galaxies.

We present BV RI CCD surface photometry for 4 elliptical and 2 S0 galaxies that show bright emission lines in their nuclear spectra. We obtained isophote maps, luminosity profiles, and basic photometric parameters. We also obtained continuum subtracted Hα +[NII] images for 5 galaxies in our sample, but only in two of them, NGC 6858 and ESO 185-54, we detected emission gas. We used the standard technique of ellipse fitting to determine the radial variation of surface brightness, color, ellipticity, position angle and the fourth order Fourier coefficient of the deviations from elliptical shape to look for isophotal twists, color gradients and fine structure variations. We have fitted an r1=n S´ersic law to the light profiles, finding that it provides a better fit to the light profiles of the ellipticals than the traditional r1/4 law. However, this lawdoes not provide a good fit for SO galaxies.

We study the UV turnup in early-type galaxies from coadded IUE spectra reaching an unprecedented signal to noise ratio. Some spectral groups resulted with strong or moderate UV turnup, while in others it is very weak or absent. We study the relationships of the UV turn up intensity with absolute magnitude, X-ray and Hα luminosities. Galaxies in the strong UV turnup groups are systematically bright, and have high X-ray and Hα luminosities; however, some other galaxies with the latter properties do not exhibit a significant UV turn up. The spectral groups with an important intermediate age component are far-UV weak. The contribution from an intermediate age population with varying strength might explain why some red stellar population early-type galaxies present the UV turn up while others do not. The available spectral groups have been further coadded into one with strong UV turnup and another one without it, and we analyse their difference. We compare the spectral slope of the isolated UV turnup with IUE spectra of various hot sources which had been proposed in previous studies to explain it. We conclude that only very hot stars like sdO and sdB subdwarfs, some nuclei of planetary nebulae or DO white dwarfs, have the proper slope to explain the UV turnup. The UV turnup as detected through the IUE aperture is not featureless: it presents absorptions similar to those observed in the galaxies with weak far-UV flux. These features appear to be the λ1400 Å and λ1600 Å ones, characteristic of moderately cool white dwarfs (DA 5), which indicates that these stars are dominant flux contributors between λ1300 - 2000 Å in the farUV weak groups.The cooling time of DA 5 stars together with the evolutionary time since they left the main sequence, imply that they evolved from low-mass stars possibly associated with the initial burst of star formation in early-type galaxies and/or merger events at intermediate ages. On the other hand, two possible scenari are discussed for the origin of the hot component which causes the UV turn up, one related to late stages of normal evolution of low-mass stars, and another related to past nuclear activity events and jets which might have blown away the atmospheres of red giants in the central parts of the galaxies, exposing the hot stellar cores and mimicking a spectral distribution like that of the hottest stars observed.

In order to gain a better understanding of starburst and merger events, we have extended to dwarf galaxies our previous spectral simulations of burst evolution over 3 Gyr, superimposed on an old underlying stellar population. We have used a library of star cluster and galaxy integrated spectra in the 3700-9700 Å wavelength range. Two kinds of galaxy spectra representing the underlying red stellar populations have been considered: (i) an average spectrum of the central regions of NGC 3056 and 4476, for which previous population syntheses have shown a maximum metallicity of [Z/Z̛0 ]= -0.5, and (ii) a combination of globular cluster spectra in the range - 2≤s;[Z/Z̛] ≤ -1, which could represent the old stellar population in the transition between dwarf ellipticals and dwarf spheroidals. These spectra were combined with those of Large Magellanic Cloud (LMC) and Galactic disc star clusters in the 3-Myr to 3-Gyr age range, in order to simulate starburst events in dwarf galaxies and model the subsequent spectral evolution of the composite system. The star cluster spectra have been properly scaled to represent starburst-to-galaxy mass fractions of 1O, 1 and 0.1 per cent. The resulting models forma spectral atlas for comparisons with observa­ tions. Rest-frame BVRI magnitudes and the related colours have been derived from these models, as well as the equivalent widths for a set of metallic and Balmer features. The behaviour of these índices is analysed as a function of the burst age and strength. The results can be used to study the properties of star-forming events in galaxies.

We present evidence for a young stellar population component in the early-type member of the E+S galaxy pair AM 0327-285. This young population is consistent with the occurrence of cross-fueling in this interacting system. We used spectroscopy, optical imaging, IRAS data, and stellar population synthesis to study the stellar content in the early-type galaxy. We also attempted to date episodes of star formation in its nuclear region, from population synthesis and basic dynamical considerations. The dominant population is old and metal-rich ([Z/Z]Θ=0.3) while ~ 10% of the flux at 5870 Å arises from a superimposed young stellar population with age

The star clusters G 158 and G 177, located at projected distances smaller than 1.5 kpc from the semi-stellar nucleus of M 31, show spectra extreme in absorption-line strengths, comparable to those from the nuclei of giant ellipticals or from the M 31 nucleus itself. A synthesis has been performed of the integrated spectrum of the Galactic globular cluster 47 Tucanae ([Fe/H]= –0.7) with a solar neighbourhood stellar library: as expected, lines of elements like Mg and Fe are stronger in the solar metallicity model. In turn, 47 Tuc presents a blue-violet blanketing excess which, from a detailed study of the spectral residuais (47 Tuc-model) using laboratory molecular patterns, was found to arise from molecules containing C, N and O. In this Research Note we discuss, at a much higher metallicity level, a very similar blanketing excess observed in G 177 with respect to G 158. We suggest that G 177 is an inner bulge cluster, whereas G 158 is an inner disc one, in analogy with the difference found between the halo cluster 47 Tuc and the model which simulates an old cluster with disc stars. In this scenario the [O/Fe] overabundance, known to exist in metal poor Galactic halo stars as compared to the disc, would persist through the bulge and inner bulge. The inner disc stars might have in common with solar neighbourhood ones the solar CNO/Fe ratio.

We have linked available ultraviolet observations to the visible and near infrared spectra of some objects from our star cluster and galaxy nucleus samples. We have analyzed the nature of the UV turn-up in giant elliptical galaxies (gE) in the light of our recent population synthesis results which are based upon a library of star cluster integrated spectra in the visible and near infrared. We also investigate how star clusters can provide in­ formation on the frequency of occurrence of particular types of stars with respect to the associated populations of a given age and metallicity. We definitely exclude the possibility that the UV turn-up in gE is caused by blue horizontal branch (BHB) stars associated with metal-poor components: even if they were a major contributor to the optical spectrum, their UV turn-up would be unable to account for that observed in gE, simply because it is not steep enough. Furthermore, our previous visible­ near infrared synthesis has shown that only 10% of the flux originates from low metallicity components. On the contrary we find strong evidence that this UV turn-up is a result of on-going star formation in gE nuclei. Indeed, young blue clusters and/or H 11 region spectra match the UV turn-up quite well, without affecting much the optical range where their contribution is less than 2% at 5870 Å. Another possibility would be that the UV turn-up in gE is caused by post AGB stars from metal-rich components: data presently available about their frequency of occurrence in metal-rich galactic clusters, as well as about that of planetary nebulae in the bulge of M31 do not favour this inter­ pretation however.

In the equivalent width (W) vs absolute magnitude (Mʙ) diagram corresponding to the best metallic features in the visible range, CN and Mg + MgH, field giant E and S0 galaxies are shifted towards weaker line-strengths with respect to galaxies belonging to the Virgo and Fornax clusters. We find evidence that this is a genuine stellar population effect. For part of the deviating galaxies it results from an aperture effect, galaxies at larger redshifts including more of the metal poor component outside their nucleus. For the rest, the shift is due to a variable content of intermediate age components in the range 4-10 Gyr, superimposed on the very old underlying population.

Se discuten las propiedades de las galaxias elípticas y se demuestra que probablemente existan dos clases. Se discute el diagrama Masa-Densidad para las galaxias y se construye un modelo que lo interpreta como resultado de la fragmentación de sistemas esferoidales masivos., Asociación Argentina de Astronomía