Photometry and dynamics of the minor mergers AM\,1228-260 and AM\,2058-381

We investigate interaction effects on the dynamics and morphology of the galaxy pairs AM\,2058-381 and AM\,1228-260. This work is based on $r'$ images and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the Gemini South Telescope. The luminosity ratio between the main (AM\,2058A) and secondary (AM\,2058B) components of the first pair is a factor of $\sim$ 5, while for the other pair, the main (AM\,1228A) component is 20 times more luminous than the secondary (AM\,1228B). The four galaxies have pseudo-bulges, with a S\'ersic index $n<2$. Their observed radial velocities profiles (RVPs) present several irregularities. The receding side of the RVP of AM\,2058A is displaced with respect to the velocity field model, while there is a strong evidence that AM\,2058B is a tumbling body, rotating along its major axis. The RVPs for AM\,1228A indicate a misalignment between the kinematic and photometric major axes. The RVP for AM\,1228B is quite perturbed, very likely due to the interaction with AM\,1228A. NFW halo parameters for AM\,2058A are similar to those of the Milky Way and M\,31. The halo mass of AM\,1228A is roughly 10\% that of AM\,2058A. The mass-to-light (M/L) of AM\,2058 agrees with the mean value derived for late-type spirals, while the low M/L for AM\,1228A may be due to the intense star formation ongoing in this galaxy.Comment: 20 pages, 10 figures, accepted for publication in MNRA

LIINUS/SERPIL: a design study for interferometric imaging spectroscopy at the LBT

LIINUS/SERPIL is a design study to augment LBTs interferometric beam combiner camera LINC-NIRVANA with imaging spectroscopy. The FWHM of the interferometric main beam at 1.5 micron will be about 10 mas, offering unique imaging and spectroscopic capabilities well beyond the angular resolution of current 8-10m telescopes. At 10 mas angular scale, e.g., one resolution element at the distance of the Galactic Center corresponds to the average diameter of the Pluto orbit (79 AU), hence the size of the solar system. Taking advantage of the LBT interferometric beam with an equivalent maximum diameter of 23 m, LIINUS/SERPIL is an ideal precursor instrument for (imaging) spectrographs at extremely large full aperture telescopes. LIINUS/SERPIL will be built upon the LINC-NIRVANA hardware and LIINUS/SERPIL could potentially be developed on a rather short timescale. The study investigates several concepts for the optical as well as for the mechanical design. We present the scientific promises of such an instrument together with the current status of the design study.Comment: 12 pages, SPIE conference proceeding, Orlando, 200

A first study of the galaxy HRG 2304 and its companion AM 1646-795 (NED01)

Aims. We report the first study of the peculiar ring-like galaxy HRG 2304 (NED02),which was previously classified as a ring galaxy with an elliptical smooth ring. This object was selected to prove that it is a candidate for the Solitaire-type ring galaxies in an early stage of ring formation. The main goal of this work is to provide the spectral characteristics of the current object and its companion AM 1646-795 (NED01). Methods. The study is based on spectroscopic observations in the optical band to highlight the characteristics of this interacting galaxy. To investigate the star formation history of HRG 2304 we used the stellar population synthesis code STARLIGHT. The direct V and B broad band images were used to enhance some fine structures. Results. Along the entire long-slit signal, the spectra of HRG 2304 and its companion resemble that of an early-type galaxy. We estimated a heliocentric systemic redshift of z = 0.0415, corresponding to heliocentric velocities of 12449 km s-1 for HRG 2304 (NED02) and 12430 km s-1 for AM1646-795 (NED01). The spatial variation in the contribution of the stellar population components for both objects are dominated by an old stellar population 2x10^9 < t < 13x10^9 yr. The observed radial-velocity distribution and the fine structures around HRG 2304 suggest an ongoing tidal interaction of both galaxies. Conclusions.The spectroscopic results and the morphological peculiarities of HRG 2304 can be adequately interpreted as an ongoing interaction with the companion galaxy. Both galaxies are early-type, the companion is elliptical, and the smooth distribution of the material around HRG 2304 and its off-center nucleus in the direction of AM1646-795 (NED01) characterize HRG 2304 as a Solitaire-type galaxy candidate in an early stage of ring formation.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 10 figures and 3 table

Sulphur abundance determinations in star-forming regions-I: Ionization Correction Factor

In the present work we used a grid of photoionization models combined with stellar population synthesis models to derive reliable Ionization Correction Factors (ICFs) for the sulphur in star-forming regions. These models cover a large range of nebular parameters and yielding ionic abundances in consonance with those derived through optical and infrared observational data of star-forming regions. From our theoretical ICFs, we suggested an {\alpha} value of 3.27 in the classical Stasinska formulae. We compared the total sulphur abundance in the gas phase of a large sample of objects by using our Theoretical ICF and other approaches. In average, the differences between the determinations via the use of the different ICFs considered are similar to the uncertainties in the S/H estimations. Nevertheless, we noted that for some objects it could reach up to about 0.3 dex for the low metallicity regime. Despite of the large scatter of the points, we found a trend of S/O ratio to decrease with the metallicity, independently of the ICF used to compute the sulphur total abundance.Comment: Accepted for publication in MNRAS, 21 pages, 8 figures, 5 table

FM 047-02: a collisional pair of galaxies with a ring

Aims. We investigate the nature of the galaxy pair FM 047-02, which has been proposed as an archetype of the Solitaire types of peculiar (collisional) ring galaxies. Methods. The study is based on long-slit spectrophotometric data in the range of 3500-9500 angstrons obtained with the Gemini Multi-ObjectComment: 07 pages, 06 figures, 02 tables. arXiv admin note: text overlap with arXiv:1206.071

Interaction effects on galaxy pairs with Gemini/GMOS- II: Oxygen abundance gradients

In this paper we derived oxygen abundance gradients from HII regions located in eleven galaxies in eight systems of close pairs. Long-slit spectra in the range 4400-7300A were obtained with the Gemini Multi-Object Spec- trograph at Gemini South (GMOS). Spatial profiles of oxygen abundance in the gaseous phase along galaxy disks were obtained using calibrations based on strong emission-lines (N2 and O3N2). We found oxygen gradients signifi- cantly flatter for all the studied galaxies than those in typical isolated spiral galaxies. Four objects in our sample, AM1219A, AM1256B, AM 2030A and AM2030B, show a clear break in the oxygen abundance at galactocentric radius R/R25 between 0.2 and 0.5. For AM1219A and AM1256B we found negative slopes for the inner gradients, and for AM2030B we found a positive one. In all these three cases they show a flatter behaviour to the outskirts of the galaxies. For AM2030A, we found a positive-slope outer gradient while the inner one is almost compatible with a flat behaviour. A decrease of star forma- tion efficiency in the zone that corresponds to the oxygen abundance gradient break for AM1219A and AM2030B was found. For the former, a minimum in the estimated metallicities was found very close to the break zone that could be associated with a corotation radius. On the other hand, AM1256B and AM2030A, present a SFR maximum but not an extreme oxygen abundance value. All the four interacting systems that show oxygen gradient breakes the extreme SFR values are located very close to break zones. Hii regions lo- cated in close pairs of galaxies follow the same relation between the ionization parameter and the oxygen abundance as those regions in isolated galaxies.Comment: 30 pages, 14 figures, accepted MNRAS, (Figs. 1 and 2 are in low resolution

Field galaxies at intermediate redshift (0.2 < z < 0.8) in the direction of the galaxy cluster LCDCS-S001

We present spectroscopic and photometric analysis for eight field galaxies in the direction of the galaxy cluster LCDCS-S001. The spectra were obtained with the GMOS instrument in the Gemini South Observatory. The objects were selected in an i' band image and the multi-object spectroscopic observations were centered at 7500 A. For the galaxies ID 440 and ID 461 we have determined redshifts of z=0.7464 and z=0.7465, respectively. For the other six galaxies we have confirmed the redshift calculated by Rembold & Pastoriza (2006). The redshifts of the field galaxies are in the range of 0.2201 < z < 0.7784. We determined the blue and visual luminosities and they are brighter than M_B=-18.64. The galaxies ID 180, ID 266, ID 461 follow the Faber-Jackson relation of the Coma and Virgo early-type galaxies, and therefore do not present a brightening of the B luminosity as observed in galaxies at higher redshifts. The stellar velocity dispersion was measured for five galaxies and estimated to be in the range of 200 < sigma < 346 km/s. Lick indices were measured and used to determine the stellar population properties of galaxies ID 120 and ID 146, by means of spectral synthesis. The first galaxy, ID 120, presents in its spectrum absorption and emission lines, and we have found that the main contribution in the flux at lambda 5870 A is of a 0.1 Gyr stellar population of solar metallicity. For ID 146, the dominant flux contribution at lambda 4200 A, is provided by a stellar population of 10 Gyr of subsolar metallicity. From stellar population synthesis we estimated reddening values of E(B-V)=0.90 and E(B-V)=0.82 for ID 120 and ID 146, respectively. According to classical diagnostic diagrams the emission lines present in the spectrum of ID 120 indicate that it is a starburst galaxy.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical. 6 Figures and 4 table

Is there a Supermassive Black Hole at the Center of the Milky Way?

This review outlines the observations that now provide an overwhelming scientific case that the center of our Milky Way Galaxy harbors a supermassive black hole. Observations at infrared wavelength trace stars that orbit about a common focal position and require a central mass (M) of 4 million solar masses within a radius of 100 Astronomical Units. Orbital speeds have been observed to exceed 5,000 km/s. At the focal position there is an extremely compact radio source (Sgr A*), whose apparent size is near the Schwarzschild radius (2GM/c^2). This radio source is motionless at the ~1 km/s level at the dynamical center of the Galaxy. The mass density required by these observations is now approaching the ultimate limit of a supermassive black hole within the last stable orbit for matter near the event horizon.Comment: Invited review submitted to International Journal of Modern Physics D; 23 pages; 10 figure