Effects of mergers and galaxy interactions at intermediate densities in the SDSS-DR4

Recently, several observational works have provided evidence in favor of a pre-processing of galaxies at moderate environments. These evidences show that the transition of galaxies onto the red-sequence could take place in galaxy groups in the outskirt of clusters or in the infalling populations. Based on the evidence that interacting and merging systems are priviledged found at intermediate densities, we use the SDSSDR4 data to analyse the role of mergers and close galaxy interactions as environmental processes to lead to evolutionary transformations. We explore the properties of galaxy pairs and merging systems at different local and global density environments, comparing them with those of isolated galaxies in an unbiased control sample.Recientemente varios autores han aportado evidencia observacional que sugerir´ıa que las galaxias son pre-procesadas en regiones de densidad intermedia, produciendo una gran transformacion en las mismas. Estos resultados observacionales muestran que la transicion de las galaxias hacia la secuencia roja se producir´ıa en regiones perifericas de los cumulos de galaxias. Por otra parte, existe evidencia tanto teorica como observacional que indicar´ıa que las interacciones y fusiones de galaxias son particularmente frecuentes en estas regiones. En este trabajo analizamos el rol de las interacciones y colisiones de galaxias en regiones de densidad intermedia, utilizando para tal efecto galaxias del cat´alogo SDSS-DR4.Facultad de Ciencias Astronómicas y GeofísicasConsejo Nacional de Investigaciones Científicas y Técnica

Effects of mergers and galaxy interactions at intermediate densities in the SDSS-DR4

Recently, several observational works have provided evidence in favor of a pre-processing of galaxies at moderate environments. These evidences show that the transition of galaxies onto the red-sequence could take place in galaxy groups in the outskirt of clusters or in the infalling populations. Based on the evidence that interacting and merging systems are priviledged found at intermediate densities, we use the SDSSDR4 data to analyse the role of mergers and close galaxy interactions as environmental processes to lead to evolutionary transformations. We explore the properties of galaxy pairs and merging systems at different local and global density environments, comparing them with those of isolated galaxies in an unbiased control sample.Recientemente varios autores han aportado evidencia observacional que sugerir´ıa que las galaxias son pre-procesadas en regiones de densidad intermedia, produciendo una gran transformacion en las mismas. Estos resultados observacionales muestran que la transicion de las galaxias hacia la secuencia roja se producir´ıa en regiones perifericas de los cumulos de galaxias. Por otra parte, existe evidencia tanto teorica como observacional que indicar´ıa que las interacciones y fusiones de galaxias son particularmente frecuentes en estas regiones. En este trabajo analizamos el rol de las interacciones y colisiones de galaxias en regiones de densidad intermedia, utilizando para tal efecto galaxias del cat´alogo SDSS-DR4.Facultad de Ciencias Astronómicas y GeofísicasConsejo Nacional de Investigaciones Científicas y Técnica

Triplets of Quasars at high redshift I: Photometric data

We have conducted an optical and infrared imaging in the neighbourhoods of 4 triplets of quasars. R, z', J and Ks images were obtained with MOSAIC II and ISPI at Cerro Tololo Interamerican Observatory. Accurate relative photometry and astrometry were obtained from these images for subsequent use in deriving photometric redshifts. We analyzed the homogeneity and depth of the photometric catalog by comparing with results coming from the literature. The good agreement shows that our magnitudes are reliable to study large scale structure reaching limiting magnitudes of R = 24.5, z' = 22.5, J = 20.5 and Ks = 19.0. With this catalog we can study the neighbourhoods of the triplets of quasars searching for galaxy overdensities such as groups and galaxy clusters.Comment: The paper contains 12 figures and 3 table

Low X-Ray Luminosity Galaxy Clusters: Main goals, sample selection, photometric and spectroscopic observations

We present the study of nineteen low X-ray luminosity galaxy clusters (L$_X \sim$ 0.5--45 $\times$ $10^{43}$ erg s$^{-1}$), selected from the ROSAT Position Sensitive Proportional Counters (PSPC) Pointed Observations (Vikhlinin et al. 1998) and the revised version of Mullis et al. (2003) in the redshift range of 0.16 to 0.7. This is the introductory paper of a series presenting the sample selection, photometric and spectroscopic observations and data reduction. Photometric data in different passbands were taken for eight galaxy clusters at Las Campanas Observatory; three clusters at Cerro Tololo Interamerican Observatory; and eight clusters at the Gemini Observatory. Spectroscopic data were collected for only four galaxy clusters using Gemini telescopes. With the photometry, the galaxies were defined based on the star-galaxy separation taking into account photometric parameters. For each galaxy cluster, the catalogues contain the PSF and aperture magnitudes of galaxies within the 90\% completeness limit. They are used together with structural parameters to study the galaxy morphology and to estimate photometric redshifts. With the spectroscopy, the derived galaxy velocity dispersion of our clusters ranged from 507 km~s$^{-1}$ for [VMF98]022 to 775 km~s$^{-1}$ for [VMF98]097 with signs of substructure. Cluster membership has been extensively discussed taking into account spectroscopic and photometric redshift estimates. In this sense, members are the galaxies within a projected radius of 0.75 Mpc from the X-ray mission peak and with cluster centric velocities smaller than the cluster velocity dispersion or 6000 km~s$^{-1}$, respectively. These results will be used in forthcoming papers to study, among the main topics, the red cluster sequence, blue cloud and green populations; the galaxy luminosity function and cluster dynamics.Comment: 13 pages, 6 tables, 9 figures. Uses emulateapj. Accepted for publication in The Astronomical Journal. Some formatting errors fixe

Observations of the First Electromagnetic Counterpart to a Gravitational-wave Source by the TOROS Collaboration

We present the results of prompt optical follow-up of the electromagnetic counterpart of the gravitational-wave event GW170817 by the Transient Optical Robotic Observatory of the South Collaboration. We detected highly significant dimming in the light curves of the counterpart (Δg = 0.17 ± 0.03 mag, Δr = 0.14 ± 0.02 mag, Δi = 0.10 ± 0.03 mag) over the course of only 80 minutes of observations obtained ∼35 hr after the trigger with the T80-South telescope. A second epoch of observations, obtained ∼59 hr after the event with the EABA 1.5 m telescope, confirms the fast fading nature of the transient. The observed colors of the counterpart suggest that this event was a \ blue kilonova\ relatively free of lanthanides

The intrinsic shape of galaxy bulges

The knowledge of the intrinsic three-dimensional (3D) structure of galaxy components provides crucial information about the physical processes driving their formation and evolution. In this paper I discuss the main developments and results in the quest to better understand the 3D shape of galaxy bulges. I start by establishing the basic geometrical description of the problem. Our understanding of the intrinsic shape of elliptical galaxies and galaxy discs is then presented in a historical context, in order to place the role that the 3D structure of bulges play in the broader picture of galaxy evolution. Our current view on the 3D shape of the Milky Way bulge and future prospects in the field are also depicted.Comment: Invited Review to appear in "Galactic Bulges" Editors: Laurikainen E., Peletier R., Gadotti D. Springer Publishing. 24 pages, 7 figure

The Mice at play in the CALIFA survey: A case study of a gas-rich major merger between first passage and coalescence

We present optical integral field spectroscopy (IFS) observations of the Mice, a major merger between two massive (>10^11Msol) gas-rich spirals NGC4676A and B, observed between first passage and final coalescence. The spectra provide stellar and gas kinematics, ionised gas properties and stellar population diagnostics, over the full optical extent of both galaxies. The Mice provide a perfect case study highlighting the importance of IFS data for improving our understanding of local galaxies. The impact of first passage on the kinematics of the stars and gas has been significant, with strong bars likely induced in both galaxies. The barred spiral NGC4676B exhibits a strong twist in both its stellar and ionised gas disk. On the other hand, the impact of the merger on the stellar populations has been minimal thus far: star formation induced by the recent close passage has not contributed significantly to the global star formation rate or stellar mass of the galaxies. Both galaxies show bicones of high ionisation gas extending along their minor axes. In NGC4676A the high gas velocity dispersion and Seyfert-like line ratios at large scaleheight indicate a powerful outflow. Fast shocks extend to ~6.6kpc above the disk plane. The measured ram pressure and mass outflow rate (~8-20Msol/yr) are similar to superwinds from local ULIRGs, although NGC4676A has only a moderate infrared luminosity of 3x10^10Lsol. Energy beyond that provided by the mechanical energy of the starburst appears to be required to drive the outflow. We compare the observations to mock kinematic and stellar population maps from a merger simulation. The models show little enhancement in star formation during and following first passage, in agreement with the observations. We highlight areas where IFS data could help further constrain the models.Comment: 23 pages, 13 figures, accepted to A&A. A version with a complete set of high resolution figures is available here: http://www-star.st-and.ac.uk/~vw8/resources/mice_v8_astroph.pd

Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)

This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands