ATCA HI Observations of the NGC 6845 Galaxy Group

We present the results of ATCA HI line and 20-cm radio continuum observations of the galaxy Quartet NGC 6845. The HI emission extends over all four galaxies but can only be associated clearly with the two spiral galaxies, NGC 6845A and B, which show signs of strong tidal interaction. We derive a total HI mass of at least 1.8 x 10^10 Msun, most of which is associated with NGC 6845A, the largest galaxy of the group. We investigate the tidal interaction between NGC 6845A and B by studying the kinematics of distinct HI components and their relation to the known HII regions. No HI emission is detected from the two lenticular galaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCA J2001-4659, was detected 4.4' NE from NGC 6845B and has an HI mass of about 5 x 10^8 Msun. No HI bridge is visible between the group and its newly detected companion. Extended 20-cm radio continuum emission is detected in NGC 6845A and B as well as in the tidal bridge between the two galaxies. We derive star formation rates of 15 to 40 Msun/yr.Comment: accepted, to be published in MNRAS, for more details and the full ps-file see http://www.atnf.csiro.au/people/bkoribal/ngc684

Discovery of Pulsed OH Maser Emission Stimulated by a Pulsar

Stimulated emission of radiation has not been directly observed in astrophysical situations up to this time. Here we demonstrate that photons from pulsar B1641-45 stimulate pulses of excess 1720 MHz line emission in an interstellar OH cloud. As this stimulated emission is driven by the pulsar, it varies on a few millisecond timescale, orders of magnitude shorter than the quickest OH maser variations previously detected. Our 1612 MHz spectra are inverted copies of the 1720 MHz spectra. This "conjugate line" phenomenon enables us to constrain the properties of the interstellar OH line-producing gas. We also show that pulsar signals suffer significantly deeper OH absorption than do other background sources; confirming earlier tentative findings that OH clouds are clumpier on small scales than neutral hydrogen clouds.Comment: Accepted by Scienc

HI-deficient galaxies in intermediate density environments

Observations show that spiral galaxies in galaxy clusters tend to have on average less neutral hydrogen (HI) than galaxies of the same type and size in the field. There is accumulating evidence that such HI-deficient galaxies are also relatively frequent in galaxy groups. An important question is, which mechanisms are responsible for the gas deficiency in galaxy groups. To gain a better understanding of how environment affects the gas content of galaxies, we identified a sample of six HI-deficient galaxies from the HI Parkes All Sky Survey (HIPASS) using HI-optical scaling relations. One of the galaxies is located in the outskirts of the Fornax cluster, four are in loose galaxy groups and one is in a galaxy triplet. We present new high resolution HI observations with the Australia Telescope Compact Array (ATCA) of these galaxies. We discuss the possible cause of HI-deficiency in these galaxies based on HI observations and various multi-wavelength data. We find that the galaxies have truncated HI disks, lopsided gas distribution and some show asymmetries in their stellar disks. We conclude that both ram pressure stripping and tidal interactions are important gas removal mechanisms in low density environments.Comment: Accepted to MNRAS, 17 pages, 10 figures, 7 table

Catalogue of HI Parameters (CHIPA)

El Catálogo de parámetros de HI de galaxias (CHIPA, por sus siglas en inglés) es la continuación natural del realizado por M. C. Martin en 1998. CHIPA provee los parámetros más importantes de galaxias cercanas derivados a partir de observaciones de HI. El catálogo contiene datos de unas 1400 galaxias de todo el cielo y de diferentes tipos morfológicos. Algunos de los parámetros presentes en CHIPA son el diámetro óptico, la magnitud en el azul, la distancia, el tipo morfológico, la extensión en HI. Se despliegan, además, para los casos existentes en la literatura los mapas de distribución del HI, de velocidades y de dispersión de velocidades. El principal objetivo de este catálogo es hacer las consultas bibliográficas para astrónomos más fáciles, a través de búsquedas en una base de datos accesibles desde internet que será pública en 2015 (la página web está en construcción). La base de datos fue construida utilizando el código abierto “mysql (sql, Structured Query Language, sistema de gestión de bases de datos relacional)”, mientras que la página web se construyó con “html (Hypertext Markup Language)” y “php (Hypertext Preprocessor)”.The catalog of HI parameters of galaxies HI (CHIPA) is the natural continuation of the compilation by M. C. Martin in 1998. CHIPA provides the most important parameters of nearby galaxies derived from observations of the neutral Hydrogen line. The catalogue contains information of 1400 galaxies across the sky and different morphological types. Parameters like the optical diameter of the galaxy, the blue magnitude, the distance, morphological type, HI extension are listed among others. Maps of the HI distribution, velocity and velocity dispersion can also be display for some cases. The main objective of this catalogue is to facilitate the bibliographic queries, through searching in a database accessible from the internet that will be published in 2015 (the website is under construction). The database was built using the open source “ mysql (SQL, Structured Query Language, management system relational database) ”, while the website was built with “ Html (Hypertext Markup Language) ” and “ PHP (Hypertext Preprocessor)”.Fil: Saponara, Juliana. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Benaglia, Paula. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Koribalski, Baerbel. Australia Telescope National Facility; AustraliaFil: Andruchow, Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaReunión Anual de la Asociación Argentina de AstronomíaCórdobaArgentinaInstituto de Astronomía Teórica y Experimenta

A radio-map of the colliding winds in the very massive binary system HD 93129A

Radio observations are an effective tool to discover particle acceleration regions in colliding-wind binaries, through detection of synchrotron radiation; these regions are natural laboratories for the study of relativistic particles. Wind-collision region (WCR) models can reproduce the radio continuum spectra of massive binaries that contain both thermal and non-thermal radio emission; however, key constraints for models come from high-resolution imaging. Only five WCRs have been resolved to date at radio frequencies at milliarcsec (mas) angular scales. The source HD 93129A, prototype of the very few known O2 I stars, is a promising target for study: recently, a second massive, early-type star about 50 mas away was discovered, and a non-thermal radio source detected in the region. Preliminary long-baseline array data suggest that a significant fraction of the radio emission from the system comes from a putative WCR. We sought evidence that HD 93129A is a massive binary system with colliding stellar winds that produce non-thermal radiation, through spatially resolved images of the radio emitting regions. We completed observations with the Australian Long Baseline Array (LBA) to resolve the system at mas angular resolutions and reduced archival Australia Telescope Compact Array (ATCA) data to derive the total radio emission. We also compiled optical astrometric data of the system in a homogeneous way. We reduced historical Hubble Space Telescope data and obtained absolute and relative astrometry with milliarcsec accuracy. The astrometric analysis leads us to conclude that the two stars in HD 93129A form a gravitationally bound system. The LBA data reveal an extended arc-shaped non-thermal source between the two stars, indicative of a WCR. The wind momentum-rate ratio of the two stellar winds is estimated. The ATCA data show a point source with a change in flux level ...Comment: Accepted in Astronomy and Astrophysic