Systematic Variations of CO J=2-1/1-0 Ratio and Their Implications in The Nearby Barred Spiral Galaxy M83

We present spatial variations of the CO J = 2−1/1–0 line ratio (R_(21/10)) in the barred spiral galaxy M83 using Total Power Array (single-dish telescopes) data from the Atacama Large Millimeter/submillimeter Array. While the intensities of these two lines correlate tightly, R_(21/10) varies over the disk, with a disk average ratio of 0.69, and shows the galactic center and a two-arm spiral pattern. It is high (>̰0.7) in regions of high molecular gas surface density (Σ_(mol)), but ranges from low to high ratios in regions of low Σ_(mol). The ratio correlates well with the spatial distributions and intensities of far-ultraviolet (FUV) and infrared (IR) emissions, with FUV being the best correlated. It also correlates better with the ratio of specific intensities at 70 and 350 μm, a proxy for dust temperature, than with the IR intensities. Taken together, these results suggest either a direct or indirect link between the dust heating by the interstellar radiation field and the condition of giant molecular clouds (GMCs), even though no efficient mechanism is known for a thermal coupling of dust and bulk gas in GMCs. We speculate that the large spread of R_(21/10)in low Σ_(mol) regions, mostly at the downstream sides of spiral arms, may be due to the evolution of massive stars after spiral arm passage. Having in a late phase escaped from the spiral arms and their parental clouds, they may contribute to the dust heating by FUV and gas heating by cosmic rays produced by supernovae

MEGARA. High-precision alignment system for gluing fibers and microlenses

MEGARA is the multi-object medium-resolution spectrograph for the GTC 10m telescope. MEGARA offers two observing modes, the LCB mode, a large central IFU; and a MOS mode composed by 92 robotic positioners carrying 7 fibers minibundles. Microlens are required to fit the GTC f/17 to the f/3 at the fiber entrance, where pupil image is oversized to have a fiber-to-fiber flux variation better than 10%. This tight requirement imposed manufacturing tolerances for the different components and required the development of a gluing station to provide a centering precision better than 5μm. We present the overview of the optical bundles, the gluing station and the final performance obtained during the integration and tests

Recent star formation in nearby galaxies from galaxy evolution explorer imaging: M101 and M51

The Galaxy Evolution Explorer (GALEX) Nearby Galaxies Survey is providing deep far-UV and near-UV imaging for a representative sample of galaxies in the local universe. We present early results for M51 and M101, from GALEX UV imaging and Sloan Digital Sky Survey optical data in five bands. The multiband photometry of compact stellar complexes in M101 is compared to population synthesis models, to derive ages, reddening, reddening-corrected luminosities, and current/initial masses. The GALEX UV photometry provides a complete census of young compact complexes on a ≈160 pc scale. A galactocentric gradient of the far-UV/near-UV color indicates younger stellar populations toward the outer parts of the galaxy disks, the effect being more pronounced in M101 than in M51

An Empirical Connection between the UV Color of Early Type Galaxies and the Stellar Initial Mass Function

Using new UV magnitudes for a sample of early-type galaxies, ETGs, with published stellar mass-to-light ratios, Upsilon_*, we find a correlation between UV color and Upsilon_* that is tighter than those previously identified between Upsilon_* and either the central stellar velocity dispersion, metallicity, or alpha enhancement. The sense of the correlation is that galaxies with larger Upsilon_* are bluer in the UV. We conjecture that differences in the lower mass end of the stellar initial mass function, IMF, are related to the nature of the extreme horizontal branch populations that are generally responsible for the UV flux in ETGs. If so, then UV color can be used to identify ETGs with particular IMF properties and to estimate Upsilon_*.Comment: Submitted for publication in ApJ Letter

Polishing techniques for MEGARA pupil elements optics

MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the new integral-field and multi-object optical spectrograph for the 10.4m Gran Telescopio Canarias.. It will offer RFWHM ~6,000, 12,000 and 18,700 for the low- , mid- and high-resolution, respectively in the wavelength range 3650-9700Å. .The dispersive elements are volume phase holographic (VPH) gratings, sandwiched between two flat Fused Silica windows of high optical precision in large apertures. The design, based in VPHs in combination with Ohara PBM2Y prisms allows to keep the collimator and camera angle fixed. Seventy three optical elements are being built in Mexico at INAOE and CIO. For the low resolution modes, the VPHs windows specifications in irregularity is 1 fringe in 210mm x 170mm and 0.5 fringe in 190mm x 160mm. for a window thickness of 25 mm. For the medium and high resolution modes the irregularity specification is 2 fringes in 220mm x 180mm and 1 fringe in 205mm x 160mm, for a window thickness of 20mm. In this work we present a description of the polishing techniques developed at INAOE optical workshop to fabricate the 36 Fused Silica windows and 24 PBM2Y prisms that allows us to achieve such demanding specifications. We include the processes of mounting, cutting, blocking, polishing and testing

Cinemática y poblaciones estelares en galaxias compactas azules

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Astrofísica y Ciencias de la Atmósfera, leída el 19-06-2000En esta tesis doctoral se ha estudiado la historia de la formación estelar en la galaxia Mrk 86 como propotipo de la sgalaxias compactas azules o galaxias BCD. Se obtuvieron imágenes en diferentes bandas asó como espectros ópticos de resolución intermida y alta e imágenes de interferomtría Fabry-Pérot. La existencia de un gran número de regiones de formaciónestelar en esta galaxia nos permitió indagar sobre los posibles mecanismos de activacióny propagación de la formacióne stelar en las galaxias BCD. En primer lugar se desrrollaron un conjunto de modelos de síntesis evolutiva que incluyen la contribución de una población subyacente y un brote de formacióne stelar reciente. Se desarrolló así mismo un novedoso procedimiento de comparación entre nuestros observables y las predicciones de los modelos de síntesis evlutiva basado en el uso combinado de simulaciones de Monte Carlo, un estimador de máxima verosimilitud, análisis de agrupamiento y análisis de la componente principal PCA. Lea medida de los colores y flujos de líneas de emisión y su posterior comparación con nuestros modelos siguiendo dicho procedimiento de análisis nos permitieron derivar las edades, fuerzas de brote, abundancias metálicas y masas estelares de las regiones de formacióne stelar de esta galaxia. Se estudiaron también las propiedades de la población estelar subyacente a partir del análisis de los perfiles de color. Finanlmente, mediante las observaciones de espectroscopía óptica y de interferometría Fabry-Pérot se obtuvo el campo de velocidad radial y de dispersiónde velocidades del objeto. A partir de este campo de velocidad radial y del perfil de masa reconstuido para esta galaxia, se extrajeron improtantes conclusiones respecto a la distribución del gas ionizado. Estos resultados nos permitieron ahondar en las compresión de la historia de estas galaxias.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu