Hector O. Castaneda

Building the cosmic infrared background brick by brick with Herschel/PEP

The cosmic infrared background (CIB) includes roughly half of the energy radiated by all galaxies at all wavelengths across cosmic time, as observed at the present epoch. The PACS Evolutionary Probe (PEP) survey is exploited here to study the CIB and its redshift differential, at 70, 100 and 160 μm, where the background peaks. Combining PACS observations of the GOODS-S, GOODS-N, Lockman Hole and COSMOS areas, we define number counts spanning over more than two orders of magnitude in flux: from ∼ 1m Jy to few hundreds mJy. Stacking of 24 μm sources and P(D) statistics extend the analysis down to ∼0.2 mJy. Taking advantage of the wealth of ancillary data in PEP fields, differential number counts d 2 N/dS /dz and CIB are studied up to z = 5. Based on these counts, we discuss the effects of confusion on PACS blank field observations and provide confusion limits for the three bands considered. While most of the available backward evolution models predict the total PACS number counts with reasonable success, the consistency to redshift distributions and CIB derivatives can still be significantly improved. The new high-quality PEP data highlight the need to include redshift-dependent constraints in future modeling. The total CIB surface brightness emitted above PEP 3σ flux limits is νIν = 4.52 ± 1.18, 8.35 ± 0.95 and 9.49 ± 0.59 [nW m −2 sr −1 ] at 70, 100, and 160 μm, respectively. These values correspond to 58 ± 7% and 74± 5% of the COBE/DIRBE CIB direct measurements at 100 and 160 μm. Employing the P(D) analysis, these fractions increase to ∼65% and ∼89%. More than half of the resolved CIB was emitted at redshift z ≤ 1. The 50%-light redshifts lie at z = 0.58, 0.67 and 0.73 at the three PACS wavelengths. The distribution moves towards earlier epochs at longer wavelengths: while the 70 μ mC IB is mainly produced by z ≤ 1.0 objects, the contribution of z > 1.0 sources reaches 50% at 160 μm. Most of the CIB resolved in the three PACS bands was emitted by galaxies with infrared luminosities in the range 10 11 −10 12 L� .

Violent star formation in NGC 2363

This is an electronic version of an article published in The Astrophysical Journal. Gonzalez-Delgado, R.M. et al. Violent star formation in NGC 2363. The Astrophysical Journal 437 (1994): 239-261

Study of star-forming galaxies in SDSS up to redshift 0.4 - II. Evolution from the fundamental parameters: mass, metallicity and star formation rate

To understand the formation and evolution of galaxies, it is important to have a full comprehension of the role played by the metallicity, star formation rate (SFR), morphology, and color. The interplay of these parameters at different redshifts will substantially affect the evolution of galaxies and, as a consequence, the evolution of them will provide important clues and constraints on the galaxy evolution models. In this work we focus on the evolution of the SFR, metallicity of the gas, and morphology of galaxies at low redshift in search of signs of evolution. We use the S2N2 diagnostic diagram as a tool to classify star--forming, composite, and AGN galaxies. We analyzed the evolution of the three principal BPT diagrams, estimating the SFR and specific SFR (SSFR) for our samples of galaxies, studying the luminosity and mass-metallicity relations, and analyzing the morphology of our sample of galaxies through the g-r color, concentration index, and SSFR. We found that the S2N2 is a reliable diagram to classify star--forming, composite, and AGNs galaxies. We demonstrate that the three principal BPT diagrams show an evolution toward higher values of [OIII]5007/Hb due to a metallicity decrement. We found an evolution in the mass-metallicity relation of ~ 0.2 dex for the redshift range 0.3 < z < 0.4 compared to our local one. From the analysis of the evolution of the SFR and SSFR as a function of the stellar mass and metallicity, we discovered a group of galaxies with higher SFR and SSFR at all redshift samples, whose morphology is consistent with those of late-type galaxies. Finally, the comparison of our local (0.04<z<0.1) with our higher redshift sample (0.3<z<0.4), show that the metallicity, the SFR and morphology, evolve toward lower values of metallicity, higher SFRs, and late--type morphologies for the redshift range 0.3<z<0.4

OSIRIS tunable imager and spectrograph for the GTC. Instrument status

OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the optical Day One instrument for the 10.4m Spanish telescope GTC to be installed in the Observatorio del Roque de Los Muchachos (La Palma, Spain). This instrument, operational in mid-2004, covers from 360 up to 1000 nm. OSIRIS observing modes include direct imaging with tunable and conventional filters, long slit and multiple object spectroscopy and fast spectrophotometry. The OSIRIS wide field of view, high efficiency and the new observing modes (tunable imaging and fast spectrophotometry) for 8-10m class telescopes will provide GTC with a powerful tool for their scientific exploitation. The present paper provides an updated overview of the instrument development, of some of the scientific projects that will be tackled with OSIRIS and of the general requirements driving the optical and mechanical design.

STUDY OF THE LARGEST MULTIWAVELENGTH CAMPAIGN OF THE MICROQUASAR GRS 1915+105

We present the results from a multiwavelength campaign of GRS 1915+105 performed from 2000 April 16 to April 25. This is one of the largest coordinated set of observations ever performed for this source, covering the wide energy band in radio (13.3–0.3 cm), near-infrared (J, H, and K bands), X-rays, and gamma rays (from 1 keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the ‘‘ plateau ’’ (or low/ hard) state but sometimes showed soft X-ray oscillations: before April 20.3, rapid, quasi-periodic (’45 minutes) flare-dip cycles were observed. In the spectral energy distribution in the plateau state, optically thick synchrotron emission and Comptonization is dominant in the radio and X- to gamma-ray bands, respectively. The small luminosity in the radio band relative to that in X-rays indicates that GRS 1915+105 falls in the regime of ‘‘ radio-quiet ’’ microquasars. In three epochs we detected faint flares in the radio or infrared bands with amplitudes of 10–20 mJy. The radio flares observed on April 17 shows frequency-dependent peak delay, consistent with an expansion of synchrotron-emitting region starting at the transition from the harddip to the soft-flare states in X-rays. On the other hand, infrared flares on April 20 appear to follow (or precede) the beginning of X-ray oscillations with an inconstant time delay of ’5–30 minutes. This implies that the infrared-emitting region is located far from the black hole by e10 13 cm, while its size is d10 12 cm constrained from the time variability. We find a good correlation between the quasi-steady flux level in the near-infrared band and in the X-ray band. From this we estimate that the reprocessing of X-rays, probably occurring in the outer parts of the accretion disk, accounts for about 20%–30% of the observed K magnitude in the plateau state. The OSSE spectrum in the 0.05–10 MeV band is represented by a single power law with a photon index of 3.1 extending to � 1 MeV with no cutoff. We can model the combined GIS-PCA-HEXTE spectra covering 1–200 keV by a sum of the multicolor disk model, a broken power law modified with a highenergy cutoff, and a reflection component. The power-law slope above � 30 keV is found to be very similar between different states in spite of large flux variations in soft X-rays, implying that the electron energy distribution is not affected by the change of the state in the accretion disk. Subject headings: accretion, accretion disks — black hole physics — infrared: stars — radio continuum: stars — stars: individual (GRS 1915+105) — X-rays: individual (GRS 1915+105) — X-rays: stars

Evidence for turbulence in H II regions

The results of extensive velocity mapping across the face of Galactic H II regions are used to make an accurate determination of velocity dispersions and structure functions for a number of nebulae. A dependence of random velocities upon scale, indicating the presence of turbulence, is found. These relationships are compared with the predictions of models for Kolmogorov turbulence in H II regions, and poor agreement is found. A more general formulation shows that there is no single power law for the velocity-distance relation that fits the observations. From the variations in the shape of the observed structure function, it is concluded that the turbulent energy enters the nebulae at several different scales. It is also found that velocity broadening of the observed lines is significantly greater than would be inferred from the velocity scatter across the face of the nebulae. 19 references.

ISOPHOT { Photometric calibration of point sources

All observations by the aperture photometer (PHT-P) and the far-infrared (FIR) camera section of ISOPHOT included reference measurements against stable internal fine calibration sources (FCS) to correct for temporal drifts in detector responsivities. The FCSs were absolutely calibrated in-orbit against stars, asteroids and planets, covering wavelengths from 3.2 to 240 μm. We present the calibration concept for point sources within a flux-range from 60 mJy up to 4500 Jy for staring and raster observations in standard configurations and discuss the requisite measurements and the uncertainties involved. In this process we correct for instrumental effects like nonlinearities, signal transients, time variable dark current, misalignments and diffraction effects. A set of formulae is developed that describes the calibration from signal level to flux densities. The scatter of 10 to 20% of the individual data points around the derived calibration relations is a measure of the consistency and typical accuracy of the calibration. The reproducibility over longer periods of time is better than 10%. The calibration tables and algorithms have been implemented in the final versions of the software for offline processing and interactive analysis.

On the Size and Luminosity versus Velocity Dispersion Correlations from the Giant H II Regions in the Irregular Galaxy NGC 4449

Here we present the size and luminosity versus velocity dispersion empirical correlations for the giant H II regions in the large irregular galaxy NGC 4449. We show that correlations only hold for nebulae with a surface brightness higher than 2 × 1035 ergs s-1 pc-2 in Hα and with a supersonic single-line Gaussian profile. The exponents of the fits are consistent with virial mechanisms. A comparison with the results from other studies that have only used first-ranked giant H II regions from a variety of star-forming galaxies is also given.

Two-dimensional metallicity distribution of the ionized gas in NGC 628 and NGC 6946

Aims. We present here two H II region catalogues with azimuthal resolution for the two grand design galaxies NGC 628 and NGC 6946. With the help of these catalogues, we study several properties of the star-forming processes occurring in spiral galaxies. Methods. We obtained direct imaging in the narrow-band filters centred at Hα ,H β, [O II]λ3727, and [O III]λλ4959, 5007 and their respective continua. After the calibration and correction of the data, we obtained for each H II region the de-reddened fluxes in the aforementioned lines, the size, the Hα equivalent width, and, using two different empirical calibrations, the metallicity. Employing a method based on the Delaunay triangulation, a two-dimensional (2D) representation of the metallicity was obtained. Results. Data for 209 H II regions of NGC 628 and 226 H II regions of NGC 6946 are obtained. The radial behaviours of the Hα equivalent width, the excitation, and the oxygen abundance are derived. Two-dimensional representations of the metallicity and the excitation are calculated for the galaxies in the study. The two empirical calibrations of the metallicity are compared. Conclusions. The behaviours of the extinction and the Hα equivalent width are similar to those presented in the literature. The oxygen abundance gradients obtained in this study agree with previously published values. However, more regions were examined than in previous studies. We find a difference of about 0.6 dex between the two empirical calibrations employed. Finally, the 2D representations of the metallicity reveal high metallicity knots in NGC 628, and for NGC 6946 a high metallicity azimuthal structure is discovered. These high metallicity regions seem to be linked to the arms of the galaxies and are probably produced by an increase in the temperature of the ionizing clusters in the H II regions, which may be linked to variations in the initial mass functions of the galaxies between the arm and interarm regions.

Study of star-forming galaxies in SDSS up to redshift 0.4 I. Metallicity evolution

Context. The chemical composition of the gas in galaxies over cosmic time provides a very important tool for understanding galaxy evolution. Although there are many studies at high redshift, they are rather scarce at lower redshifts. However, low redshift studies can provide important clues about the evolution of galaxies, furnishing the required link between the local and high redshift universe. In this work, we focus on the metallicity of the gas of star-forming galaxies at low redshift, looking for signs of chemical evolution. Aims. We aim to analyze the metallicity contents star-forming galaxies of similar luminosities and masses at different redshifts. With this purpose, we present a study of the metallicity of relatively massive (log(Mstar/M� ) 10.5) star forming galaxies from SDSS–DR5 (Sloan Digital Sky Survey-data release 5), using different redshift intervals from 0.04 to 0.4. Methods. We used data processed with the STARLIGHT spectral synthesis code, correcting the fluxes for dust extinction, estimating metallicities using the R23 method, and segregating the samples with respect to the value of the [N ii] λ6583/[O ii] λ3727 line ratio in order to break the R23 degeneracy selecting the upper branch. We analyze the luminosity and mass-metallicity relations, and the effect of the Sloan fiber diameter looking for possible biases. Results. By dividing our redshift samples in intervals of similar magnitude and comparing them, significant signs of metallicity evolution are found. Metallicity correlates inversely with redshift: from redshift 0 to 0.4 a decrement of ∼0.1 dex in 12 + log(O/H) is found.