Shock-ionization in the Extended Emission-Line Region of 3C~305. The last piece of the (optical) puzzle

We present new Gemini spectroscopical data of the Extended Emission-Line Region of 3C~305 radio galaxy in order to achieve the final answer of the long-standing question about the ionizing mechanism. The spectra show strong kinematic disturbances within the most intense line-emitting region. The relative intensities amongst the emission lines agree with the gas being shocked during the interaction of the powerful radio jets with the ambient medium. The emission from the recombination region acts as a very effective cooling mechanism, which is supported by the presence of a neutral outflow. However, the observed intensity is almost an order of magnitude lower than expected in a pure shock model. So auto-ionizing shock models, in low-density and low-abundance regime, are required in order to account for the observed emission within the region. This scenario also supports the hypothesis that the optical emitting gas and the X-ray plasma are in pressure balance.Comment: 13 pages, 6 figures. To be published in MNRA

Identification and analysis of the young population in the starburst galaxy NGC 253

We present a study of the young population in the starburst galaxy NGC 253. In particular, we focused our attention on searching young star groups, obtaining their main properties and studying their hierarchical organization. For this task, we used multiband images and their corresponding photometric data obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST).We have first derived the absorption affecting the different regions of the galaxy. Then, we applied an automatic and objective searching method over the corrected data in order to detect young star groups. We complemented this result with the construction of the stellar density map for the blue young population. A statistical procedure to decontaminate the photometric diagrams from field stars was applied over the detected groups and we estimated their fundamental parameters.As a result, we built a catalog of 875 new identified young groups with their main characteristics, including coordinates, sizes, estimated number of members, stellar densities, luminosity function (LF) slopes and galactocentric distances. We observed these groups delineate different structures of the galaxy, and they are the last step in the hierarchical way in which the young population is organized. From their size distribution, we found they have typical radius of ∼ 40 − 50 pc. These values are consistent with those ones found in others nearby galaxies. We estimated a mean value of the LF slope of 0.21 and an average density of 0.0006 stars/pc³ for the identified young groups taking into account stars earlier than B6.Fil: Rodriguez, Maria Jimena. 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; ArgentinaFil: Baume, Gustavo Luis. 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; ArgentinaFil: Feinstein Baigorri, Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

The interaction between jets and clouds in the 3CR galaxies

From the HST/WFPC2 3CR Snapshot Survey, data taken with the filter F555W, F702W and narrow-ramp, a set of galaxies with noticeable extended structure were selected (e.g. 3C 79, 3C 135, 3C 234, etc). All of these objects show large regions of [OIII] λ 5007˚A emission (narrow ramp filter) and the broad-band filters data show similar structures indicating the presence of strong emission in several lines over these regions. The morphology observed seems to be related (e.g. same position angle, direct overlapping or similar shape) with the radio-jet. For some candidates with these properties GMOS/Gemini spectroscopy was taken. These data (both HST direct imaging and Gemini spectroscopy) can be tested with diagnostic diagrams and total UV photons budget to understand the source of energy that is ionizing the gas. This source of ionization was commonly believed to be the UV photons emitted by the powerful active galactic nuclei (AGN), but several of these objects show clearly that shocks produced by the radio jet are the main cause of the observed gas line emission. We show in this work, the results obtained over some of these radio-galaxies: 3C 135, 3C 180, 3C 234 and 3C 284.Fil: Hägele, G. F.. Universidad Autónoma de Madrid; EspañaFil: Feinstein Baigorri, Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Macchetto, D. F.. Space Telescope Science Institute; Estados UnidosFil: Montero, F.. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Shock ionization in the extended emission-line region of 3C 305: the last piece of the (optical) puzzle

We present new Gemini spectroscopical data of the extended emission-line region of the 3C 305 radio galaxy in order to achieve a final answer to the long-standing question about the ionizing mechanism. The spectra show strong kinematic disturbances within the most intense line-emitting region. The relative intensities of the emission lines agree with the hypothesis that the gas is shocked during the interaction of powerful radio jets with the ambient medium. The emission from the recombination region acts as a very effective cooling mechanism, which is supported by the presence of a neutral outflow. However, the observed intensity is almost an order of magnitude lower than expected in a pure shock model. So, autoionizing shock models, in low-density and low-abundance regimes, are required in order to account for the observed emission within the region. This scenario also supports the hypothesis that the optical emitting gas and the X-ray plasma are in pressure balance.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

The fingerprints of photoionization and shock-ionization in two CSS sources

We investigate the ionization state of the extended emission-line regions (EELRs) around two compact steep-spectrum (CSS) radio galaxies, 3C 268.3 and 3C 303.1, in order to identify the contribution of photoionization and shock-ionization. We perform a new spectroscopical (long-slit) analysis with GMOS/Gemini with the slit oriented in the radio-jet direction, where outflows are known to exist. The [Ne V] λ3426 emission is the most interesting feature of the spectra and the one key to breaking the degeneracy between the models: since this emission-line is more extended than He II, it challenges the ionization structure proposed by any photoionization model, also its intensity relative to H β does not behave as expected with respect to the ionization parameter U in the same scenario. On the contrary, when it is compared to the intensity of [O II] λ3727/H β and all these results are joined, the whole scenario is plausible to be explained as emission coming from the hot, compressed, shocked gas in shock-ionization models. Although the model fitting is strongly sensitive to the chosen line ratios, it argues for the presence of external and strong ionizing fields, such as the precursor field created by the shock or/and the AGN radiation field. In this paper, we show how AGN photoionization and shock-ionization triggered by jet–cloud interaction work together in these EELRs in order to explain the observed trends and line-ratio behaviours in a kinematically acceptable way.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Note on the Ca II Emission in Cepheids

It has been shown by O.Wilson and V. Bappu^that a strong con 3 nation exists between the absolute magnitude of late type stars and the strength of their Call emissions. We have felt that this relation could also hold for Cepheid variables. Prom our plate material of Cepheids, taken with the 60" reflector of the Bosque Alegre station of the Cordoba Observatory (dispersion 42 A/mm) we have selected all plates showing double emission in the H and/or K lines. The position of each emission wing was measured, and the difference between both measurements (in Km/sec) was taken as the width "W" of the emission. It is well known that the emission features in Cepheids are usually stronger in the H than in the K line; for this reason the results are based on the emissions in H alone.Asociación Argentina de Astronomí

Searching for evidence of jet-cloud interaction in radio galaxies : First results for 3C 381

We present results of Gemini spectroscopy and Hubble Space Telescope imaging of the 3C 381 radio galaxy. Possible ionizing mechanisms for the extended emission-line region were studied through state-of-the-art diagnostic analysis employing line ratios. Photoionization from the central engine as well as mixed medium photoionization models fail in reproducing both the strengths and the behaviour of the highest excitation lines, such as [Ne v]λ3424, He ii and [O iii]λ5007, which are measured at very large distances from the active galactic nucleus. Shock-ionization models provide a better fit to the observation. Expanding shocks with velocities higher than 500 km s-1 are capable of reaching the observed intensity ratios for lines with different ionization states and excitation degrees. This model also provides a direct explanation of the mechanical energy input needed to explain the high-velocity line-splitting observed in the velocity field.Facultad de Ciencias Astronómicas y Geofísica

The fingerprints of photoionization and shock-ionization in two CSS sources

We investigate the ionization state of the extended emission-line regions (EELRs) around two compact steep-spectrum (CSS) radio galaxies, 3C 268.3 and 3C 303.1, in order to identify the contribution of photoionization and shock-ionization. We perform a new spectroscopical (long-slit) analysis with GMOS/Gemini with the slit oriented in the radio-jet direction, where outflows are known to exist. The [Ne V] λ3426 emission is the most interesting feature of the spectra and the one key to breaking the degeneracy between the models: since this emission-line is more extended than He II, it challenges the ionization structure proposed by any photoionization model, also its intensity relative to H β does not behave as expected with respect to the ionization parameter U in the same scenario. On the contrary, when it is compared to the intensity of [O II] λ3727/H β and all these results are joined, the whole scenario is plausible to be explained as emission coming from the hot, compressed, shocked gas in shock-ionization models. Although the model fitting is strongly sensitive to the chosen line ratios, it argues for the presence of external and strong ionizing fields, such as the precursor field created by the shock or/and the AGN radiation field. In this paper, we show how AGN photoionization and shock-ionization triggered by jet–cloud interaction work together in these EELRs in order to explain the observed trends and line-ratio behaviours in a kinematically acceptable way.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Optical polarization study in the open cluster NGC 6250

We present (UBVRI) multicolour linear polarimetric data for 32 of the brightest stars in the area of the open cluster NGC 6250, with the aim of studying the properties of the interstellar medium (ISM) towards the cluster. Our data yield a mean polarization P¯V = 1.83 per cent, close to the polarization value produced by the ISM with normal efficiency for a mean colour excess of EB−V = 0.37. Our analysis indicates that the observed visual absorption in NGC 6250 is caused by a nearby dust layer (within 300 pc) producing a polarization with an angle close to the Galactic plane (θGP ∼ 38◦). In addition, there are at least two more dust layers along the line of sight between the Sun and the cluster producing a change in the observed polarization, making our results compatible with Neckel and Klare’s results. The observations show differences between the orientation of the local magnetic field of the nearby dust layer and the one that is polarizing along the way to the cluster (θ v = 20◦). The internal dispersion of the polarization values for the members of NGC 6250 seems to be compatible with the presence of intracluster dust. The majority of observed stars do not present evidence of intrinsic polarization in their light. In this work, we also show (as in several previous papers) how polarimetry is an excellent technique for identifying non-member stars.Fil: Feinstein Baigorri, Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. 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; ArgentinaFil: Vergne, Maria Marcela. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. 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; ArgentinaFil: Martinez, Ruben Enrique. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. 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; ArgentinaFil: Orsatti, Ana Maria. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. 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; ArgentinaFil: Vergne, Maria Marcela. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. 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; Argentin

La ciencia en la ciencia ficción : Relaciones entre científicos, escritores y sus temas en el caso de las ciencias del espacio

En esta charla trataremos el caso de la comunicación entre escritores y científicos, pero no sólo desde el punto de vista de los logros que se han realizado desde el punto de buscar que la CF sea predictiva, sino al revés donde la ciencia es la que inspira la CF, Para entender este panorama trataremos primero una serie de pautas que nos permiten evaluar el contexto en que se realiza esta comunicación.Facultad de Ingenierí