arXiv subjects

Hector Hernandez Toledo

Publications and source records attributed to Hector Hernandez Toledo.

6 recordsLinked to original sources

arXiv2018

The Fifteenth Data Release of the Sloan Digital Sky Surveys: First Release of MaNGA Derived Quantities, Data Visualization Tools and Stellar Library

Twenty years have passed since first light for the Sloan Digital Sky Survey (SDSS). Here, we release data taken by the fourth phase of SDSS (SDSS-IV) across its first three years of operation (July 2014-July 2017). This is the third data release for SDSS-IV, and the fifteenth from SDSS (Data Release Fifteen; DR15). New data come from MaNGA - we release 4824 datacubes, as well as the first stellar spectra in the MaNGA Stellar Library (MaStar), the first set of survey-supported analysis products (e.g. stellar and gas kinematics, emission line, and other maps) from the MaNGA Data Analysis Pipeline (DAP), and a new data visualisation and access tool we call "Marvin". The next data release, DR16, will include new data from both APOGEE-2 and eBOSS; those surveys release no new data here, but we document updates and corrections to their data processing pipelines. The release is cumulative; it also includes the most recent reductions and calibrations of all data taken by SDSS since first light. In this paper we describe the location and format of the data and tools and cite technical references describing how it was obtained and processed. The SDSS website (www.sdss.org) has also been updated, providing links to data downloads, tutorials and examples of data use. While SDSS-IV will continue to collect astronomical data until 2020, and will be followed by SDSS-V (2020-2025), we end this paper by describing plans to ensure the sustainability of the SDSS data archive for many years beyond the collection of data.

astro-ph.IM↗

arXiv2015

Halpha3: an Halpha imaging survey of HI selected galaxies from ALFALFA. V: The Coma Supercluster survey completion

Neutral hydrogen represents the major observable baryonic constituent of galaxies that fuels the formation of stars through the transformation in molecular hydrogen. The emission of the hydrogen recombination line Halpha is the most direct tracer of the process that transforms gas (fuel) into stars. We continue to present Halpha3 (acronym for Halpha-alpha-alpha), an extensive Halpha+[NII] narrow-band imaging campaign of galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA), using the instrumentation available at the San Pedro Martir observatory (Mexico). In only four years since 2011 we were able to complete in 48 nights the Halpha imaging observations of 724 galaxies in the region of the Coma supercluster 10^h < R.A. <16^h; 24^o < Dec. <28^o and 3900<cz<9000 kms^{-1}. Of these, 603 are selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) and constitute a 97% complete sample. They provide for the first time a complete census of the massive star formation properties of local gas-rich galaxies belonging to different environments (cluster vs filaments), morphological type (spirals vs dwarf Irr), over a wide range of stellar mass (10^{8}-10^{11.5} Modot) in the Coma Supercluster. The present Paper V provides the Halpha data and the derived star formation rates for the observed galaxies.

astro-ph.GA↗

arXiv2013

Halpha3: an Halpha imaging survey of HI selected galaxies from ALFALFA. III. Nurture shapes up the Hubble sequence in the Great Wall

We present the analysis of Halpha3, an Halpha imaging survey of galaxies selected from the HI ALFALFA Survey in the Coma Supercluster. By using the Halpha line as a tracer of the "instantaneous" star formation, complemented with optical colors from SDSS we explore the hypothesis that a morphological sequence of galaxies of progressively earlier type, lower gas-content exists in the neighborhood of the Coma cluster, with specific star formation activity decreasing with increasing local galaxy density and velocity dispersion. In the dwarf regime (8.5<\log(M*)< 9.5) we identify a 4-step sequence of galaxies with progressively redder colors, i.e. of decreasing specific star formation, from (1) HI-rich Late-Type Galaxies belonging to the blue-cloud exhibiting extended plus nuclear star formation, (2) HI-poor LTGs with nuclear star formation only, (3) HI-poor galaxies with no star formation either extended or nuclear, but with nuclear Post-Star-Burst signature,(4) Early-type Galaxies in the red-sequence, with no gas or star formation on all scales. Along this sequence the quenching of the star formation proceeds radially outside-in. The progression toward redder colors found along this "morphological" (gas content) sequence is comparable to the one obtained increasing the local galaxy density, from the cosmic filaments (1,2), to the rich clusters (2,3,4). In the dwarf regime we find evidence for evolution of HI-rich LTGs into ETGs, passing through HI-poor and PSB galaxies, driven by the environment. We identify ram-pressure as the mechanism most likely responsible for this transformation. We conclude that infall of low-mass galaxies has proceeded for the last 7.5 Gyr building up the Coma cluster at a rate of approximately 100 galaxies per Gyr.

astro-ph.CO↗

arXiv2013

Halpha3: an Halpha imaging survey of HI selected galaxies from ALFALFA. IV. Structure of galaxies in the Local and Coma Superclusters

We present the analysis of the galaxy structural parameters from Halpha3, an Halpha narrow-band imaging follow-up survey of ~800 galaxies selected from the HI ALFALFA Survey in the Local and Coma Superclusters. Taking advantage of Halpha3 which provides the complete census of the recent star-forming, HI-rich galaxies in the local universe, we aim to investigate the structural parameters of both the young (<10 Myr) and the old (>1 Gyr) stellar populations. By comparing the sizes of these stellar components we investigated the spatial scale on which galaxies are growing at the present cosmological epoch and the role of the environment in quenching the star-formation activity. We computed the concentration, asymmetry, and clumpiness structural parameters. To quantify the sizes we computed half-light radii and a new parameter dubbed EW/r. The concentration index computed in the r band depends on the stellar mass and on the Hubble type, these variables being related since most massive galaxies are bulge dominated thus most concentrated. Going toward later spirals and irregulars both the concentration index and the stellar mass decrease. Blue Compact dwarfs represent an exception since they have similar stellar mass but they are more concentrated than dwarf irregulars. The asymmetry and the clumpiness increase along the spiral sequence then they decrease going into the dwarf regime, where the light distribution is smooth and more symmetric. When measured on Halpha images, the CAS parameters do not exhibit obvious correlations with Hubble type. We found that the concentration index is the main parameter that describes the current growth of isolated galaxies but, for a fixed concentration, the stellar mass plays a second order role. At the present epoch, massive galaxies are growing inside-out, conversely the dwarfs are growing on the scale of their already assembled mass.

astro-ph.CO↗

arXiv2000

Color Correlations in (S+S) Binary Galaxies I. The Holmberg Effect

Relying on his photometry of galaxies, Holmberg (1958) found, more than 40 years ago, that the color indices of paired galaxies were closely correlated. Our deep broad-band BVRI CCD photometry of 45 (S+S) pairs from the Karachentsev (1972) catalogue (see Hernandez Toledo and Puerari, this volume), and additional (B-V) color information from the literature (50 extra (S+S) pairs), help us to confirm the effect. This "Holmberg Effect" has long been remained unverified and not explained yet.

astro-ph↗

arXiv2000

BVRI Surface Photometry of (S+S) Binary Galaxies

We report the first results of our multicolour broad-band BVRI photometry for a statistically well defined sample of interacting pairs, drawn from the Catalogue of Isolated Pairs of Galaxies in the Northern Hemisphere Karachentsev (1972). At present, the details of photometric structure of disk-disk (S+S) galaxies are just beginning to be studied because of their intrinsic difficulties. We take advantage of the statistical properties of this well defined sample of interacting galaxies to try to isolate the main structural components of galaxies. Due to their environmental simplicity (compared to groups and clusters), the sample provides an unique opportunity to peform a photometric study of galaxies and their structural components in a non-equilibrium configuration. In this contribution, the first results of a deep multicolour (BVRI) photometric study of a sample of 45 (S+S) isolated pairs of galaxies is presented. Our attention is focused on the morphology and the global photometric properties (integrated magnitudes, colours and mean surface brightness profiles).

astro-ph↗