Galáxias post-starburst no universo local

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2014Galáxias post-starburst (PSB) apresentam espectros com fortes linhas de absorção na série de Balmer e fracas linhas de emissão associadas a formação estelar, indicando uma predominância de populações estelares jovens e nenhum sinal de formação estelar atual. Combinando dados do Sloan Digital Sky Survey comos resultados da aplicação de um método de síntese espectral, selecionamos 427 galáxias PSB a partir de uma amostra limitada em volume de 162 538 objetos com redshift entre 0,04 e 0,095. Nossos resultados mostram que galáxias post-starburst têm um desenvolvimento extremamente tardio quando comparadas com outras galáxias. Suas massas estelares atuais são comparáveis às de galáxias star-forming. Por outro lado, enquanto galáxias star-forming formam sua massa de maneira contínua, galáxias PSB apresentam uma forte descontinuidade em sua taxa deformação estelar por volta de 3 Ganos atrás, formando até 40% de sua massa no período entre 3 bilhões e 150 milhões de anos atrás e cessando sua formação estelar em seguida. A alta quantidade de massa formada nos últimos 3 Ganos pode indicar que estas galáxias são remanescentes de fusões com galáxias de massa comparável, o que é verificado em redshifts mais altos. Dados morfológicos do Galaxy Zoo mostram que apenas 14,5% das galáxias PSB em nossa amostra apresentam vestígios de fusões e menos de 1% apresentam sinais evidentes de fusões. Uma justificativa para este resultado é que o tempo característico para que o espectro de uma galáxia apresente características PSB após uma fusão é maior do que o tempo necessário para o desaparecimento dos vestígios desta fusão. Esta hipótese é compatível coma baixa incidência de galáxias espirais em nossa amostra de galáxias PSB.Abstract: Post-starburst (PSB) galaxies are characterized by strong Balmer absorption lines and weak emission lines associated with star formation in their spectra. These characteristics indicate a predominance of young stellar populations and no ongoing star formation. Combining data from the Sloan Digital Sky Survey (SDSS) with results from a spectral synthesis code, we selected 427 PSB galaxies in a volume limited sample containing 162 538 objects from the SDSS DR7 with redshift between 0.04 and 0.095. From the spectral synthesis we recovered the star formation histories (SFH) of these galaxies, showing that they assembled stellar mass later than the average galaxy population (in a % basis). Stellar masses of PSB galaxies are comparable to those of star-forming galaxies, but while star-forming galaxies assemble their stellar mass in a continuous way, PSB galaxies show a strong slope in their SFH, forming up to 40% of their stellar mass in the period between 150 Myrand 3 Gyr ago. This strong slope can be associated to major-mergers, although these events are not detectable using Galaxy Zoo data. According to Galaxy Zoo, only 14.5% of PSB galaxies show traces of mergers and less than 1% show strong morphological evidences of mergers. We briefly discuss the timescales involved in merger induced star formation and the lifetime of merger features, showing that the PSB phenomena may in fact be merger related, but by the time we detect the PSB spectral features, the merger evidences are already undetectable in SDSS photometry. This idea is compatible with the low incidence of spiral galaxies in the PSB sample

Evidence for enhanced star formation rates in z~0.35 cluster galaxies undergoing ram pressure stripping

Ram pressure stripping (RPS) is one of the most invoked mechanisms to explain the observed differences between cluster and field galaxies. In the local Universe, its effect on the galaxy star forming properties has been largely tackled and the general consensus is that this process first compresses the gas available in the galaxy disks, boosting the star formation for a limited amount of time, and then removes the remaining gas leading to quenching. Much less is known on the effect and preponderance of RPS at higher redshift, due to the lack of statistical samples. Exploiting VLT/MUSE observations of galaxies at 0.2<z<0.55 and the catalog of ram pressure stripped galaxies by Moretti et al., we compare the global star formation rate-mass (SFR-M*) relation of 29 cluster galaxies undergoing RPS to that of 26 field and cluster undisturbed galaxies that constitute our control sample. Stripping galaxies occupy the upper envelope of the control sample SFR-M* relation, showing a systematic enhancement of the SFR at any given mass. The boost is >3sigma when considering the SFR occurring in both the tail and disk of galaxies. The enhancement is retrieved also on local scales: considering spatially resolved data, ram pressure stripped galaxies overall have large {\Sigma}SFR values, especially for Sigma_*>10^7.5M_sun kpc~2. RPS seems to leave the same imprint on the SFR-M* and Sigma_SFR-Sigma_* relations both in the Local Universe and at z~0.35.Comment: A&A in pres

The star formation histories of z ∼ 1 post-starburst galaxies

Funding: LTA acknowledges support from the Ministry of Higher Education and Scientific Research (MOHESR), Iraq. AW acknowledges financial support from the Royal Society Newton Fund (grant NAF/R1/180403, PI Natalia Vale Asari) and Fundação de à Amparo Pesquisa do Estado de São Paulo (FAPESP) process number 2019/01768-6.We present the star formation histories of 39 galaxies with high-quality rest-frame optical spectra at 0.5 <z <1.3 selected to have strong Balmer absorption lines and/or Balmer break, and compare to a sample of spectroscopically selected quiescent galaxies at the same redshift. Photometric selection identifies a majority of objects that have clear evidence for a recent short-lived burst of star formation within the last 1.5 Gyr, i.e. 'post-starburst' galaxies, however we show that good quality continuum spectra are required to obtain physical parameters such as burst mass fraction and burst age. Dust attenuation appears to be the primary cause for misidentification of post-starburst galaxies, leading to contamination in spectroscopic samples where only the [O II] emission line is available, as well as a small fraction of objects lost from photometric samples. The 31 confirmed post-starburst galaxies have formed 40-90 per cent of their stellar mass in the last1-1.5 Gyr. We use the derived star formation histories to find that the post-starburst galaxies are visible photometrically for 0.5-1 Gyr. This allows us to update a previous analysis to suggest that 25-50 per cent of the growth of the red sequence at z ∼ 1 could be caused by a starburst followed by rapid quenching. We use the inferred maximum historical star formation rates of several 100-1000 M⊙yr-1 and updated visibility times to confirm that sub-mm galaxies are likely progenitors of post-starburst galaxies. The short quenching time-scales of 100-200 Myr are consistent with cosmological hydrodynamic models in which rapid quenching is caused by the mechanical expulsion of gas due to an acive galactic neucleus.Publisher PDFPeer reviewe

The star formation histories of z~1 post-starburst galaxies

We present the star formation histories of 39 galaxies with high quality rest-frame optical spectra at 0.5<z<1.3 selected to have strong Balmer absorption lines and/or Balmer break, and compare to a sample of spectroscopically selected quiescent galaxies at the same redshift. Photometric selection identifies a majority of objects that have clear evidence for a recent short-lived burst of star formation within the last 1.5 Gyr, i.e. "post-starburst" galaxies, however we show that good quality continuum spectra are required to obtain physical parameters such as burst mass fraction and burst age. Dust attenuation appears to be the primary cause for misidentification of post-starburst galaxies, leading to contamination in spectroscopic samples where only the [OII] emission line is available, as well as a small fraction of objects lost from photometric samples. The 31 confirmed post-starburst galaxies have formed 40-90% of their stellar mass in the last 1-1.5 Gyr. We use the derived star formation histories to find that the post-starburst galaxies are visible photometrically for 0.5-1 Gyr. This allows us to update a previous analysis to suggest that 25-50% of the growth of the red sequence at z~1 could be caused by a starburst followed by rapid quenching. We use the inferred maximum historical star formation rates of several 100-1000 Msun/yr and updated visibility times to confirm that sub-mm galaxies are likely progenitors of post-starburst galaxies. The short quenching timescales of 100-200 Myr are consistent with cosmological hydrodynamic models in which rapid quenching is caused by the mechanical expulsion of gas due to an AGN.Comment: 24 pages, 16 figures, MNRAS accepted 06/03/202

UV and Hα\alpha HST observations of 6 GASP jellyfish galaxies

Star-forming, H$\alpha$-emitting clumps are found embedded in the gaseous tails of galaxies undergoing intense ram-pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a unique opportunity to study star formation under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination of broad-band filters and a narrow-band H{\alpha} filter. HST observations are needed to study the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will be used to study the clump scaling relations, the universality of the star formation process and verify whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations, data reduction strategy, and some general results based on the preliminary data analysis: the UVIS high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions of the galaxies and of the substructures in the galaxy disks; we found clear signatures of stripping in regions very close in projection to the galactic disk; the star-forming regions in the stripped tails are extremely bright and compact while we did not detect a significant number of star-forming clumps outside those detected by MUSE. The paper finally presents the development plan for the project.Comment: 17 pages, 7 figures. Accepted for publication in Ap

Recovering the origins of the lenticular galaxy NGC 3115 using multiband imaging

A detailed study of the morphology of lenticular galaxies is an important way to understand how this type of galaxy is formed and evolves over time. Decomposing a galaxy into its components (disc, bulge, bar, ...) allows recovering the colour gradients present in each system, its star formation history, and its assembly history. We use GALFITM to perform a multiwavelength structural decomposition of the closest lenticular galaxy, NGC 3115, resulting in the description of its stellar light into several main components: a bulge, a thin disc, a thick disc, and also evidence of a bar. We report the finding of central bluer stellar populations in the bulge, as compared to the colour of the galaxy outskirts, indicating either the presence of an active galactic nucleus (AGN) and/or recent star formation activity. From the spectral energy distribution results, we show that the galaxy has a low luminosity AGN component, but even excluding the effect of the nuclear activity, the bulge is still bluer than the outer-regions of the galaxy, revealing a recent episode of star formation. Based on all of the derived properties, we propose a scenario for the formation of NGC 3115 consisting of an initial gas-rich merger, followed by accretions and feedback that quench the galaxy, until a recent encounter with the companion KK084 that reignited the star formation in the bulge, provoked a core displacement in NGC 3115 and generated spiral-like features. This result is consistent with the two-phase formation scenario, proposed in previous studies of this galaxy

Analysis of SDSS spectra and GALEX photometry with STARLIGHT: stellar populations and dust attenuation in local galaxies

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2019.O software de síntese espectral STARLIGHT é uma ferramenta que permite a extração de propriedades físicas de galáxias ajustando suas componentes estelares usando uma combinação de espectros de populações estelares. Nesta tese, apresentamos uma nova versão do código que permite a combinação de dados espectroscópicos e fotométricos, permitindo melhores estimativas de propriedades de galáxias. O código é aplicado a dados do Sloan Digital Sky Survey (SDSS) e do Galaxy Evolution Explorer (GALEX) para uma análise simultânea de espectros ópticos e fotometria ultravioleta em uma amostra de 231643 galáxias usando modelos do estado da arte para populações estelares. Desenvolvemos um novo método para estimar a fotometria do GALEX em aberturas compatíveis com espectros do SDSS. Nosso método é confiável quando aplicado a amostras grandes e compatível com outro método encontrado na literatura. Em concordância com experiências anteriores baseadas em espectros integrados do CALIFA, nossos resultados mostram que a adição de dados ultravioleta leva a um aumento moderado nas frações de luz atribuídas a populações estelares de 10 a 100 milhões de anos; também é possível identificar uma concomitante diminuição nas frações de luz das populações mais jovens e mais velhas. Quando analisamos estas tendências em um espaço de cor-magnitude, percebemos que as mudanças são mais dramáticas em galáxias da chamada nuvem azul (NUV-r6 (sequência vermelha superior) a emissão ultravioleta é dominada por populações velhas que contribuem mais para o FUV do que populações de idade intermediária. A contribuição de populações estelares para a luz ultravioleta é usada para evidenciar as diferenças entre galáxias aposentadas com e sem linhas de emissão detectáveis. Em concordância com trabalhos anteriores, mostramos que o primeiro grupo apresenta um excesso em populações estelares de idade intermediária quando comparado com o segundo grupo, evidenciando que a ionização em galáxias aposentadas está conectada com diferentes históricos de formação. Por fim, comparamos os resultados obtidos com duas prescrições diferentes para os efeitos da poeira em uma sub-amostra composta apenas por galáxias espirais. Nosso conjunto de dados é mais bem representado pela lei de atenuação de galáxias starburst, apesar de os resultados assumindo a lei de extinção da Via-Láctea como modelo de atenuação melhoram conforme a profundidade óptica da poeira diminui, especialmente em galáxias cujos discos são vistos em alta inclinação, indicando que estas galáxias podem ser mais bem representadas com leis de atenuação de formas similares à curva de extinção da Via-Láctea, mas com características menos acentuadas. Verificamos que os modelos de populações estelares usados neste trabalho, que atribuem o UV upturn apenas a estrelas post-AGB, reproduzem a emissão FUV de galáxias com UV upturn em nossa amostra com margem de 0.25 magnitudes em 62% dos casos. Esse resultado indica que fontes adicionais de emissão são necessárias para explicar as magnitudes FUV de uma fração considerável destes objetos.Abstract : The STARLIGHT spectral synthesis code is a tool that extracts physical information of galaxies by fitting their stellar component using a combination of stellar population spectra. In this thesis, we present a new version of the code, which allows the combination of spectroscopic and photometric information to better constrain galaxy properties. The code is applied to data from the Sloan Digital Sky Survey (SDSS) and the Galaxy Evolution Explorer (GALEX) to simultaneously analyze optical spectra and ultraviolet photometry of 231643 galaxies using state-of-the-art stellar population models. A new method was developed to estimate GALEX photometry in the SDSS spectroscopic aperture. The method proves itself reliable when applied to large samples and is compatible to another method found in the literature. We find that, in agreement with previous experiments based on CALIFA data, the addition of UV constraints leads to a moderate increase on the light fraction of populations with 10 to 100 million years; we also find a concomitant decrease of younger and older components. In color magnitude space, changes are most relevant for galaxies at the faint end of the blue cloud. We investigate the contribution of different stellar populations to the fraction of light in GALEX and SDSS bands across the UV-optical color-magnitude diagram, showing that young stellar populations contribute significantly to UV emission up to the green valley (4<NUV-r<5) and to a smaller extent in the faint end of the lower red sequence (5<NUV-r<6). In the upper red sequence, UV emission is dominated by old stellar populations that contribute more to FUV emission than intermediate age populations. As an example application, we use this wavelength dependence to highlight differences between retired galaxies with and without emission lines. In agreement with previous work, we find that the former show an excess of intermediate age populations when compared to the later. Testing the suitability of two different prescriptions for dust in a subsample of spiral galaxies, we find that our data-set is best fitted using the attenuation law of starburst galaxies. However, results assuming the Milky Way extinction curve as an attenuation model improve with decreasing V-band optical depth, especially for galaxies viewed edge-on, indicating that highly inclined galaxies may exhibit attenuation curves with shapes similar to the one of the Milky Way extinction curve, although with less prominent features. We find that the models used in this work, on which the UV upturn phenomenon is solely due to post-AGB stars, can reproduce FUV emission within 0.25 magnitudes in 62% of UV upturn galaxies in our sample. This indicates the need for additional UV sources to reproduce the FUV magnitudes of a significant portion of these objects

UV and Hα HST Observations of Six GASP Jellyfish Galaxies

Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a unique opportunity to study star formation under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medium. Yet, a comprehensive, high-spatial-resolution study of these systems is missing. We obtained UVIS/Hubble Space Telescope (HST) data to observe the first statistical sample of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination of broadband (UV to I) filters and a narrowband Hα filter. HST observations are needed to study the sizes, stellar masses, and ages of the clumps and their clustering hierarchy. These observations will be used to study the clump scaling relations and the universality of the star formation process, and to verify whether a disk is irrelevant, as hinted at by results from jellyfish galaxies. This paper presents the observations, data reduction strategy, and some general results based on the preliminary data analysis. The high spatial resolution of UVIS gives an unprecedentedly sharp view of the complex structure of the inner regions of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails are extremely bright and compact and we did not detect a significant number of star-forming clumps in regions where MUSE did not detect any. The paper finally presents the development plan for the project.</p

Locations and Morphologies of Jellyfish Galaxies in A2744 and A370

International audienceWe present a study of the orbits, environments, and morphologies of 13 ram-pressure stripped galaxies in the massive, intermediate redshift (z ~ 0.3-0.4) galaxy clusters A2744 and A370, using MUSE integral-field spectroscopy and Hubble Space Telescope imaging from the Frontier Fields Program. We compare different measures of the locations and morphologies of the stripped sample with a sample of six post-starburst galaxies identified within the same clusters, as well as the general cluster population. We calculate the phase-space locations of all cluster galaxies and carry out a substructure analysis, finding that the ram-pressure stripped galaxies in A370 are not associated with any substructures, but are likely isolated infalling galaxies. In contrast, the ram-pressure stripped galaxies in A2744 are strictly located within a high-velocity substructure, moving through a region of dense X-ray emitting gas. We conclude that their ram-pressure interactions are likely to be the direct result of the merger between two components of the cluster. Finally, we study the morphologies of the stripped and post-starburst galaxies, using numerical measures to quantify the level of visual disturbances. We explore any morphological deviations of these galaxies from the cluster population, particularly the weaker cases that have been confirmed via the presence of ionized gas tails to be undergoing ram-pressure stripping, but are not strongly visually disturbed in the broadband data. We find that the stripped sample galaxies are generally divergent from the general cluster sample, with post-starburst galaxies being intermediary in morphology between stripped galaxies and red passive cluster members