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Gaspar Galaz

Publications and source records attributed to Gaspar Galaz.

At least 55 records · Page 3Linked to original sources
arXiv2015

Deep optical images of Malin 1 reveal new features

We present Megacam deep optical images (g and r) of Malin 1 obtained with the 6.5m Magellan/Clay telescope, detecting structures down to ~ 28 B mag arcsec-2. In order to enhance galaxy features buried in the noise, we use a noise reduction filter based on the total generalized variation regularizator. This method allows us to detect and resolve very faint morphological features, including spiral arms, with a high visual contrast. For the first time, we can appreciate an optical image of Malin 1 and its morphology in full view. The images provide unprecedented detail, compared to those obtained in the past with photographic plates and CCD, including HST imaging. We detect two peculiar features in the disk/spiral arms. The analysis suggests that the first one is possibly a background galaxy, and the second is an apparent stream without a clear nature, but could be related to the claimed past interaction between Malin 1 and the galaxy SDSSJ123708.91 + 142253.2. Malin 1 exhibits features suggesting the presence of stellar associations, and clumps of molecular gas, not seen before with such a clarity. Using these images, we obtain a diameter for Malin 1 of 160 kpc, ~ 50 kpc larger than previous estimates. A simple analysis shows that the observed spiral arms reach very low luminosity and mass surface densities, to levels much lower than the corresponding values for the Milky Way.

astro-ph.GA↗
arXiv2015

UBVRIz Light Curves of 51 Type II Supernovae

We present a compilation of UBV RIz light curves of 51 type II supernovae discovered during the course of four different surveys during 1986 to 2003: the Cerro Tololo Supernova Survey, the Calan/Tololo Supernova Program (C&T), the Supernova Optical and Infrared Survey (SOIRS), and the Carnegie Type II Supernova Survey (CATS). The photometry is based on template-subtracted images to eliminate any potential host galaxy light contamination, and calibrated from foreground stars. This work presents these photometric data, studies the color evolution using different bands, and explores the relation between the magnitude at maximum brightness and the brightness decline parameter (s) from maximum light through the end of the recombination phase. This parameter is found to be shallower for redder bands and appears to have the best correlation in the B band. In addition, it also correlates with the plateau duration, being thus shorter (longer) for larger (smaller) s values.

astro-ph.SR↗
arXiv2015

Unveiling a Rich System of Faint Dwarf Galaxies in the Next Generation Fornax Survey

We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded $u, g$ and $i$-band image obtained with the DECam wide-field camera mounted on the 4-meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the {\it Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii $0.1\!<\!r_e\!<\!2.8$ kpc and average effective surface brightness values $22.0\!<\!μ_i\!<\!28.0$ mag arcsec$^{-2}$. We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters.~We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of $M_i\!=\!-8.0$\,mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of $>\!75\%$ at luminosities brighter than $M_i\!\simeq\!-15.0$ mag to $0\%$ at luminosities fainter than $M_i\!\simeq\!-10.0$ mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below $\sim\!100$ kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.

astro-ph.GA↗
arXiv2014

Extended HCN and HCO$^{+}$ emission in the starburst galaxy M82

We mapped 3 mm continuum and line emission from the starburst galaxy M82 using the Combined Array for Research in Millimeter-wave Astronomy. We targeted the HCN, HCO$^{+}$, HNC, CS and HC$_{3}$N lines, but here we focus on the HCN and HCO$^{+}$ emission. The map covers a field of 1.2' with a ~5" resolution. The HCN and HCO$^{+}$ observations are combined with single dish images. The molecular gas in M82 had been previously found to be distributed in a molecular disk, coincident with the central starburst, and a galactic scale outflow which originates in the central starburst. With the new short spacings-corrected maps we derive some of the properties of the dense molecular gas in the base of the outflow. From the HCN and HCO$^{+}$ J=(1-0) line emission, and under the assumptions of the gas being optically thin and in local thermodynamic equilibrium, we place lower limits to the amount of dense molecular gas in the base of the outflow. The lower limits are $7\times10^{6}$ $M_{\odot}$ and $21\times10^{6}$ $M_{\odot}$, or $\gtrsim2\%$ of the total molecular mass in the outflow. The kinematics and spatial distribution of the dense gas outside the central starburst suggests that it is being expelled through chimneys. Assuming a constant outflow velocity, the derived outflow rate of dense molecular gas is $\geq0.3$ $M_{\odot}$ yr$^{-1}$, which would lower the starburst lifetime by $\geq5\%$. The energy required to expel this mass of dense gas is $(1-10)\times10^{52}$ erg.

astro-ph.GA↗
arXiv2010

Low Surface Brightness Galaxies in the SDSS: the link between environment, star-forming properties and AGN

Using the Sloan Digital Sky Survey (SDSS) data release 4 (DR 4), we investigate the spatial distribution of low and high surface brightness galaxies (LSBGs and HSBGs, respectively). In particular, we focus our attention on the influence of interactions between galaxies on the star formation strength in the redshift range $0.01 < z < 0.1$. With cylinder counts and projected distance to the first and fifth-nearest neighbor as environment tracers, we find that LSBGs tend to have a lack of companions compared to HSBGs at small scales ($<2$ Mpc). Regarding the interactions, we have evidence that the fraction of LSBGs with strong star formation activity increases when the distance between pairs of galaxies ($r_{p}$) is smaller than about four times the Petrosian radius ($r_{90}$) of one of the components. Our results suggest that, rather than being a condition for their formation, the isolation of LSBGs is more connected with their survival and evolution. The effect of the interaction on the star formation strength, measured by the average value of the birthrate parameter $b$, seems to be stronger for HSBGs than for LSBGs. The analysis of our population of LSBGs and HSBGs hosting an AGN show that, regardless of the mass range, the fraction of LSBGs having an AGN is lower than the corresponding fraction of HSBGs with an AGN. Also, we observe that the fraction of HSBGs and LSBGs having an AGN increases with the bulge luminosity. These results, and those concerning the star-forming properties of LSBGs as a function of the environment, fit with the scenario proposed by some authors where, below a given threshold of surface mass density, low surface brightness disks are unable to propagate instabilities, preventing the formation and evolution of massive black holes in the centers of LSBGs.

astro-ph.CO↗
arXiv2009

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.

astro-ph.IM↗
arXiv2009

Spectral Classification of Galaxies using the Principal Component Analysis: a Web Based Tool

We have developed a web tool to perform Principal Component Analysis (PCA, Murtagh & Heck 1987; Kendall 1980) onto spectral data. The method is especially designed to perform spectral classification of galaxies from a sample of input spectra, giving the set of orthonormal vectors called Principal Components (PCs) and the corresponding projections. The first two projections of the galaxy spectra onto the PCs are known to correlate with the morphological type (Connolly et al. 1995) and, following Galaz & de Lapparent (1998), we use the parameters δand θwhich define a spectral classification sequence of typical galaxies from ellipticals to late spirals and star-forming galaxies. The program runs in the website http://azul.astro.puc.cl/PCA/ and can be used without downloading any binary files or building archives of any kind.

astro-ph.GA↗
arXiv2008

12CO(3-2) Emission in Spiral Galaxies: Warm Molecular Gas in Action?

Using the APEX sub-millimeter telescope we have investigated the 12CO(3-2) emission in five face-on nearby barred spiral galaxies, where three of them are high surface brightness galaxies (HSBs) lying at the Freeman limit, and two are low surface brightness galaxies (LSBs). We have positive detections for two of three HSB spirals and non-detections for the LSBs. For the galaxies with positive detection (NGC0521 and PGC070519), the emission is confined to their bulges, with velocity dispersions of ~90 and ~73 km/s and integrated intensities of 1.20 and 0.76 K/km/s, respectively. For the non-detections, the estimated upper limit for the integrated intensity is ~0.54 K/km/s. With these figures we estimate the H2 masses as well as the atomic-to-molecular mass ratios. Although all the galaxies are barred, we observe 12CO(3-2) emission only for galaxies with prominent bars. We speculate that bars could dynamically favor the 12CO(3-2) emission, as a second parameter after surface brightness. Therefore, secular evolution could play a major role in boosting collisional transitions of molecular gas, such as 12CO(3-2), especially in LSBs.

astro-ph↗
arXiv2006

Bulge evolution in face-on spirals and low surface brightness galaxies

It is an observational fact that bulges of spiral galaxies contain a high fraction of old and metal-rich stars. Following this observational fact, we have investigated colors of 21 bulges hosted by a selected sample of high surface brightness spirals and low surface brightness galaxies observed in B and R optical bands and in J and Ks near-IR bands. Using structural parameters derived from these observations we obtain evidence that bulges could be formed by pure disk evolution (secular evolution), in agreement with the suggestion by some authors. The color profiles, especially the near-IR ones show null or almost null color gradients, supporting the hypothesis that the disk stellar populations are similar to those present in the bulge, and/or some bulges can be understood as disks with enhanced stellar density (or pseudobulges). In the optical, half of the galaxies present an inverse color gradient, giving additional evidence in favor of secular evolution for the sample investigated. The comparison of the observed colors with those obtained from spectrophotometric models of galaxy evolution suggests that bulges of the selected sample have solar and subsolar metallicity, and are independent of the current stellar formation rate. Also, we obtain evidence suggesting that galaxies hosting small bulges tend to be systematically metal poor compared to those with larger bulges. These results are being checked more carefully with high S/N spectroscopy.

astro-ph↗
arXiv2005

SN 2005bf: A Possible Transition Event Between Type Ib/c Supernovae and Gamma Ray Bursts

We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first ~100 days following discovery. The u'g'BV light curves displayed a double-peaked morphology, which is among Type Ib/Ic supernovae. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u'g'BV was accompanied by the presence in the spectrum of high velocity absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations which attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 x 10^{51} erg), asymmetric explosion of a massive (8.3 M_sun) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of 1) a polar explosion containing a small fraction of the total mass and moving at high velocity, and 2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically-thin, revealing the slower-moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and gamma ray bursts.

astro-ph↗
arXiv2004

The Nature of Blue Cores in Spheroids: a Possible Connection with AGN and Star Formation

We investigate the physical nature of blue cores in early-type galaxies through the first multi-wavelength analysis of a serendipitously discovered field blue-nucleated spheroid in the background of the deep ACS/WFC griz multicolor observations of the cluster Abell 1689. The resolved g-r, r-i and i-z color maps reveal a prominent blue core identifying this galaxy as a ``typical'' case study, exhibiting variations of 0.5-1.0 mag in color between the center and the outer regions, opposite to the expectations of reddened metallicity induced gradients in passively evolved ellipticals. From a Magellan-Clay spectrum we secure the galaxy redshift at $z=0.624$. We find a strong X-ray source coincident with the spheroid galaxy. Spectral features and a high X-ray luminosity indicate the presence of an AGN in the galaxy. However, a comparison of the X-ray luminosity to a sample derived from the Chandra Deep Field South displays Lx to be comparable to Type I/QSO galaxies while the optical flux is consistent with a normal star-forming galaxy. We conclude that the galaxy's non-thermal component dominates at high-energy wavelengths while we associate the spheroid blue light with the stellar spectrum of normal star-forming galaxies. We argue about a probable association between the presence of blue cores in spheroids and AGN activity.

astro-ph↗
arXiv2004

The ESO-Sculptor Survey: Evolution of late-type galaxies at redshifts 0.1-0.5

[ABRIDGED] Using the Gaussian+Schechter composite luminosity functions measured from the ESO-Sculptor Survey (de Lapparent et al. 2003), we obtain evidence for evolution in the late spectral class containing late-type Spiral (Sc+Sd) and dwarf Irregular (dI) galaxies. This evolution is detected as an increase of the Sc+Sd+dI galaxy density which can be modeled as either n(z)~1+3(z-0.15) or n(z) ~ (1+z)^2 using the currently favored cosmological parameters Omega_m=0.3 and Omega_Lambda=0.7, with an uncertainty in both evolution rates of order of unity. For Omega_m=1.0 and Omega_Lambda=0.0, the linear and power-law evolution rates are 4 and 2.5 resp. Both models yield a good match to the ESS BVRc redshift distributions to 21-22 mag and to the number-counts to 23-23.5 mag, which probe the galaxy distribution to redshifts z~0.5 and z~1.0 resp. This analysis illustrates how Gaussian+Schechter composite luminosity functions provide more robust constraints on the evolution rate than pure Schechter functions. The detected density evolution indicates that mergers could play a significant role in the evolution of late-type Spiral and dwarf Irregular galaxies. However, the ESO-Sculptor density increase with redshift could also be caused by a ~1 mag brightening of the Sc+Sd+dI galaxies at z~0.5 and a ~1.5-2.0 mag brightening at z~1, which is compatible with the expected passive brightening of Sc galaxies at these redshifts. Distinguishing between luminosity and density evolution is a major difficulty as these produce the same effect on the redshift and magnitude distributions. The detected evolution rate of the ESO-Sculptor Sc+Sd+dI galaxies is nevertheless among the range of measured values from the other existing analyses, whether they provide evidence for density or luminosity evolution.

astro-ph↗
arXiv2003

The ESO-Sculptor Survey: Luminosity functions of galaxies per spectral type at redshifts 0.1-0.5

[ABRIDGED] We present the first statistical analysis of the complete ESO-Sculptor redshift survey (ESS). The flux-calibrated sample of 617 galaxy spectra with R_c<20.5 is separated into 3 spectral classes (early, intermediate, and late). We report in detail on the spectral classification, the polynomial K-corrections, and all sources of corresponding random and systematic errors. The derived luminosity functions (LF) in the Johnson-Cousins B and Rc bands are in agreement with the results from the comparable CNOC2 survey (Lin et al. 1999), whereas the ESS provides the first estimates of LFs per spectral type in the Johnson V band. A renewed interpretation of the galaxy LFs from a redshift survey are obtained by fitting the ESS LFs with composite functions based on the local LFs per morphological type (Sandage, Binggeli & Tammann 1985; Jerjen & Tammann 1997). As good or better fits than with pure Schechter functions are obtained using: for the early-type LF, a two-wing Gaussian; for the intermediate-type LF, the sum of a Gaussian modeling the Spiral galaxies and a steep Schechter function (alpha=-1.5) representing the dwarf elliptical galaxies; for the late-type LF, a similar composite function with a flat or weaker slope (-0.8 0.1 which separates the giant and dwarf galaxy populations.

astro-ph↗
arXiv2002

Properties of Low Surface Brightness Galaxies and Normal Spirals in the Near-IR

(Abridged) We present results for J and Ks near-IR imaging data on a large sample of 88 galaxies drawn from the catalogue of Impey et al. (1996). The near-IR data unveils many features of LSBGs not seen before in the optical. First, a high fraction of the observed LSBGs are very luminous in the near-IR, indicating that they have a well developed old stellar population, and that older LSBGs are more frequent in the universe than data from optical bands suggested. Second, the near-IR morphologies are often quite different than seen in the optical. Third, we find significant trends between the near-IR morphologies of the galaxies and their ratio of HI mass to near-IR luminosity. Fourth, we find no trend in disk surface brightness with absolute magnitude, but significant correlations when the bulge surface brightness is used. Finally, we find that the formation of a bulge requires a galaxy to have a total baryonic mass above ~ 10**10 Msun. A wide variety of other correlations are explored for the sample. The strongest of our correlations are with the ratio of HI mass to total baryonic mass, MHI/Mbaryonic, which tracks the evolutionary state of the galaxies as they convert gas into stars, and which ranges from 0.05 up to nearly 1 for the galaxies in our sample. We see also trends between MHI/Mbaryonic and central surface density, suggesting that increased star formation efficiency with increasing gas surface density strongly drives the conversion of gas into stars.

astro-ph↗
arXiv2000

Near-IR Imaging of LSB Galaxies: the High and Low HI Content Cases

Recently acquired near-IR imaging (J and Ks) of low surface brightness galaxies is presented. The data includes 52 galaxies with log[MHI/Msolar] < 9.0 and 58 galaxies with log[MHI/Msolar] > 9.5. These galaxies have been selected from the catalogue of Impey et al. (1996), and all of them are observable from both hemispheres. The principal goal of this research is to investigate the poorly understood giant and old stellar content of these galaxies. Current work includes total and isophotal photometry, and comparison with spectrophotometric models of galaxy evolution, including the role of age and metallicity. Already allocated observing time at Las Campanas Observatory will provide high S/N B and I imaging.

astro-ph↗
arXiv2000

E+A galaxies in the near-IR: Broad band photometry

(Abridged) We present near-IR photometry of a selected sample of southern hemisphere E+A galaxies. The sample includes 50 galaxies from nearby and distant clusters as well as E+A galaxies from the field. The photometry includes J, H and Ks apparent magnitudes and colors. Observed colors are obtained from the apparent total magnitudes and compared to spectrophotometric models of galaxy evolution GISSEL96. There is an overall agreement between integrated colors of models and observed ones, for both the E+A located in clusters and in the field, at z~0.1. However, large differences are found between colors predicted from models and those observed in E+A galaxies located in more distant clusters. We investigate systematic properties of the E+A sample as a function of their environment. Results seem to indicate that cluster E+As (at low redshift) are bluer than field E+As at z~0.1. Even this conclusion does not depend whether we use comoving or rest-frame colors, nor on the models used to obtain rest-frame colors; the difference is not significant enough, considering color dispersions between the samples. If differences are real, they could imply different stellar content for the E+A galaxies located in the field, compared to the cluster E+A.

astro-ph↗
arXiv1999

E+A Galaxies in the near-IR: Field and Clusters

I present near-IR photometry of a selected sample of E+A galaxies observed in the southern hemisphere. The sample includes 50 galaxies from nearby clusters (z ~ 0.05) and distant clusters (z ~ 0.31) as well as E+A galaxies from the field (z ~ 0.15). I have also observed 13 normal early-type galaxies from the field and from clusters, to be compared with the E+A sample. The photometry includes J, H and Ks apparent magnitudes and colors. I investigate systematic properties of the E+A sample as a function of their environment, contrasting the observed colors with spectrophotometric models of galaxy evolution.

astro-ph↗