Infrared studies of the structure of the galaxy

A simple three-component model of the Galaxy is presented. The Galaxy is represented by (1) a disk whose stellar density decreases exponentially with distance from the galactic centre as well as perpendicularly as a function of height above or below the galactic plane; plus a (2) ring with a radius of R₀sin25 kpc considered to be an enhancement of the disk and finally by (3) an oblate de Vaucouleurs spheroid meant to represent the galactic bulge. The absorbing material is also assumed to be distributed as an exponential layer. The model is used to fit the 2.4 μm integrated flux observations of the Galaxy, which it does remarkably well, and to determine some of the model constants such as the radial length scale for the disk and the central densities for the bulge and ring components. Based on this model and the derived values of the constants, a series of stellar count predictions for the Km agnitude (2.2 μm) were made. These predictions were com pared to those made by the Bahcall and Soneira model of the Galaxy. The model predicts an almost complete dominance of the bright K-magnitude (K ≤ 14-15) realm by the disk population. At fainter magnitudes the bulge population dominates. A transition region at which disk and bulge contributions are similar occurs at different K -m agnitudes and depends on galactic longitude (from K ~ +9.5 at l ~ 0 to K ~ +20 at l ~ 180). Stellar counts along the galactic plane in the range 220 ≤ l ≤ 60 have been obtained, and have been fitted to the galactic model described above. The model constants utilised in fitting the stellar counts are those derived from the model fit to the 2.4 μm observed integrated flux. Considering the general nature of the model (same constants for all regions), the agreement between the model predictions and the observations is remarkable. The slight discrepancies which have arisen between theory and observations have been interpreted, in most cases, as inhomogeneities in the absorbing material. In the longitude range 0 ≤ l ≤ 60, there appears to be a slight theoretical excess over the observed counts at bright magnitudes. A carefully chosen alteration of the absolute K-magnitude of all the stars in the Luminosity Function (LF) may be necessary to produce a perfect fit between predicted and observed Cumulative Counts Functions (CCF’s). A low absorption window in the direction l — 0, 6 ~ -4, known as Baade’s Window (BW) has been observed photometrically as well as spectroscopically. A K-scan of this region provided an observational CCF which, with the aid of the model discussed above, was decomposed into possible disk plus bulge contributions. The following results were obtained: • At bright K-magnitudes the slope of the disk CCF is different from that of the bulge CCF. This suggests the presence of two radically different stellar populations within a radius of ± 3 kpc from the galactic centre. • Possible similarities between the real BW bulge population and globular clusters stars is suggested from the similar slope of both stellar populations’ CCF’s. • A significant spread in the (J-H) vs. (H-K), as well as in the CO vs. (J-K) diagram suggests an intrinsic spread in the colour of the sources, which may indicate a possible spread in the metallicity of the objects observed in BW. • What may be identified as the brightest infrared (IR) magnitude locus for stars in BW, is composed of young (2 x 10⁹ years) Asymptotic Giant Branch (AGB) stars with a luminosity of the order ~ 10⁴Lʘ. • In BW ‘true’ bulge members appear to be CO-poor as opposed to ‘true’ disk members which seem to have higher CO-index values. This suggests there is a difference in metallicity of the stars in the disk and the bulge. ‘True’ bulge members appear to be more metal poor than 47-Tuc. There is a hint of kinematical differences between CO-weak and CO-strong stars which is consistent with our picture of ‘true’ bulge and ‘true’ disk populations respectively. Further photometric, spectroscopic and kinematical studies of IR sources in low absorption regions will help to confirm the points put forward in this thesis

Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939

We have searched and reviewed all multi- wavelength data available for the region towards the gamma-ray source 2FGL J2056.7+4939 in order to con- strain its possible counterpart at lower energies. As a result, only a point-like optical/infrared source with flat-spectrum radio emission is found to be consistent with all X-ray and gamma-ray error circles. Its struc- ture is marginally resolved at radio wavelengths at the sub-arcsecond level. An extragalactic scenario appears to be the most likely interpretation for this object.Comment: 5 pages, 3 figures, 1 tabl

Virial masses of late-type galaxies from the SDSS DR16

Motivated by the challenges of calculating the dynamical masses of late-type galaxies (LTGs) and the enormous amount of data from the Sloan Digital Sky Survey (SDSS), we calculate virial masses of a sample of approximately 126 000 LTGs from the sixteenth data release of the SDSS. The virial mass estimations were made considering Newtonian mechanics, virial equilibrium and velocity dispersion from stars and gas. The procedure gave as a result seven mass estimations for each galaxy. The calculated masses were calibrated using a sample of spiral galaxies with velocity rotation curves. Considering the results from the calibration, we find that the correlation between virial and dynamical (rotation curve) masses is stronger for high inclination values. Therefore, the calibration relies more on the available data for higher inclination angle galaxies. We also show that if we have a heterogeneous sample of galaxies one must take into consideration the size and colour of these galaxies by using the following variables: Sersic index n, concentration index, and colour of the stars. For relatively smaller and bluer LTGs, the gas velocity dispersion provides a more consistent mass calculation, while for LTGs that are relatively larger and redder the stellar velocity dispersion provides a better correlated mass calculation.Fil: Nigoche Netro, A.. Universidad de Guadalajara; México. Instituto de Astronomía y Meteorologia de la Universidad de Guadalajara; MéxicoFil: De La Fuente, E.. Universidad de Guadalajara; México. University of Tokyo; JapónFil: Diaz, Ruben Joaquin. United States Gemini Office; Estados Unidos. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Agüero, Maria Paz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Kemp, S. N.. Instituto de Astronomía y Meteorologia de la Universidad de Guadalajara; MéxicoFil: Marquez Lugo, R. A.. Instituto de Astronomía y Meteorologia de la Universidad de Guadalajara; MéxicoFil: Lagos, P.. Centro de Astrofísica Da Universidade Do Porto; PortugalFil: Ruelas Mayorga, A.. Universidad Nacional Autónoma de México; MéxicoFil: López Contreras, N. L.. Instituto de Astronomía y Meteorologia de la Universidad de Guadalajara; Méxic

A major star formation region in the receding tip of the stellar Galactic bar

We present an analysis of the optical spectroscopy of 58 stars in the Galactic plane at $l=27$\arcdeg, where a prominent excess in the flux distribution and star counts have been observed in several spectral regions, in particular in the Two Micron Galactic Survey (TMGS) catalog. The sources were selected from the TMGS, to have a $K$ magnitude brighter than +5 mag and be within 2 degrees of the Galactic plane. More than 60% of the spectra correspond to stars of luminosity class I, and a significant proportion of the remainder are very late giants which would also be fast evolving. This very high concentration of young sources points to the existence of a major star formation region in the Galactic plane, located just inside the assumed origin of the Scutum spiral arm. Such regions can form due to the concentrations of shocked gas where a galactic bar meets a spiral arm, as is observed at the ends of the bars of face-on external galaxies. Thus, the presence of a massive star formation region is very strong supporting evidence for the presence of a bar in our Galaxy.Comment: 13 pages (latex) + 4 figures (eps), accepted in ApJ Let

Simultaneous multiwavelength observations of the Low/Hard State of the X-ray transient source SWIFT J1753.5-0127

We report the results of simultaneous multiwavelength observations of the X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL, RXTE, NTT, REM and VLA on 2005 August 10-12. The source, which underwent an X-ray outburst since 2005 May 30, was observed during the INTEGRAL Target of Opportunity program dedicated to new X-ray novae located in the Galactic Halo. Broad-band spectra and fast timing variability properties of SWIFT J1753.5-0127 are analyzed together with the optical, near infra-red and radio data. We show that the source was significantly detected up to 600 keV with Comptonization parameters and timing properties typical of the so-called Low/Hard State of black hole candidates. We build a spectral energy distribution and we show that SWIFT J1753.5-0127 does not follow the usual radio/X-ray correlation of X-ray binaries in the Low/Hard State. We give estimates of distance and mass. We conclude that SWIFT J1753.5-0127 belongs to the X-ray nova class and that it is likely a black hole candidate transient source of the Galactic Halo which remained in the Low/Hard State during its main outburst. We discuss our results within the context of Comptonization and jet models.Comment: Accepted for publication in ApJ, 25 pages, 4 tables, 11 figures (3 in color

The optical/NIR counterpart of the INTEGRAL obscured source IGR J16318-4848 : a sgB[e] in a HMXB ?

The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL. The high energy spectrum exhibits such a high column density that the source is undetectable in X-rays below 2 keV. We used the NTT telescope of ESO to obtain optical and near-infrared (NIR) observations. We confirm the already proposed NIR counterpart and for the first time extended detection into optical. We report here photometric measurements in the R, I, J, bands, upper flux limits in the Bb and V bands, lower flux limits in the H and Ks bands. We also obtain NIR spectroscopy, revealing a large number of emission lines, including forbidden iron lines and P-Cygni profiles, and showing a strong similarity with CI Cam, another strongly absorbed source. These data point to a high luminosity, high temperature source, with an intrinsic optical-NIR absorption greater than the interstellar absorption, but two orders of magnitude below the X-ray absorption. We propose that the source is a High Mass X-ray binary (HMXB) at a distance between 0.9 and 6.2 kpc, the optical/NIR counterpart corresponds to the mass donor, which is an early-type star, maybe a sgB[e] star, surrounded by a dense and absorbing circumstellar material. This would make the second HMXB with a sgB[e] star as the mass donor after CI Cam. Such sources may represent a different evolutionary state of X-ray binaries previously undetected with the lower energy space telescopes ; if it is so, a new class of strongly absorbed X-ray binaries is being unveiled by INTEGRAL.Comment: 42 pages, 12 figures, accepted in Ap.

Astroclimate at San Pedro M\'artir I: 2004-2008 Seeing Statistics from the TMT Site Testing Data

We present comprehensive seeing statistics for the San Pedro M\'artir site derived from the Thirty Meter Telescope site selection data. The observations were obtained between 2004 and 2008 with a Differential Image Motion Monitor (DIMM) and a Multi Aperture Scintillation Sensor (MASS) combined instrument (MASS--DIMM). The parameters that are statistically analised here are: whole atmosphere seeing -measured by the DIMM-; free atmosphere seeing --measured by the MASS--; and ground-layer seeing (GL) --difference between the total and free-atmosphere seeing--. We made a careful data coverage study along with statistical distributions of simultaneous MASS--DIMM seeing measurements, in order to investigate the nightly, monthly, seasonal, annual and global behaviour, as well as possible hourly seeing trends. Although this campaign covers five years, the sampling is uneven, being 2006 and 2007 the best sampled years in terms of seasonal coverage. The overall results yield a median seeing of 0.78 (DIMM), 0.37 (MASS) and 0.59 arcsec (GL). The strongest contribution to the whole atmosphere seeing comes, therefore, from a strong ground layer. We find that the best season is summer, while the worst one is winter, in accordance with previous studies. It is worth noting that the best yearly results are correlated with the best sampled years. The hourly analysis shows that there is no statistically significant tendency of seeing degradation towards dawn. The seeing values are slightly larger than those reported before. This may be caused by climate changes.Comment: Accepted for publication (2012 June 14) in MNRAS, 15 pages, 16 Figures, 8 Table