Maria Paz Aguero

Infrared mergers and infrared quasi-stellar objects with galactic winds – II. NGC 5514: two extranuclear starbursts with LINER properties and a supergiant bubble in the rupture phase

A study of the morphology, kinematics and ionization structure of the IR merger NGC5514, is here presented. This study is based mainly on INTEGRAL twodimensional (2D) spectroscopy (obtained at the 4.2 m William Herschel Telescope, WHT), plus optical and near IR images. Clear evidence of two extra-nuclear starbursts with young outflows (OFs) and LINER activity are reported. One of these OFs has generated a supergiant bubble and the other is associated with an extended complex of H ii region. In the galactic bubble it was found that: (i) the [S ii], H�, [N ii], [O i] and [O iii] emission line maps show a bubble with a distorted ellipsoidal shape, with major and minor axes of �6.5 kpc (13.

The nearest extreme starburst: bubbles, young star clusters and outflow in the merger NGC 3256

We have studied the extreme starburst in the infrared merger NGC 3256. We detect four galactic bubbles (using ESO New Technology Telescope and Hubble Space Telescope WFPC2 Hα images). These shells would be associated with previous supernova explosions. The first analysis of the spatial distribution of young star cluster candidates shows that more than 90 per cent of them are located in a complex starburst structure, including some of the bubble walls, three nuclei and three blue asymmetrical spiral arms. We have made a kinematic study of the ionized gas in the core of the main optical nucleus, performed with HST STIS spectra. The shape of the rotation curve and the emission-line profile can be explained by the presence in the core of young star clusters with outflow. Any low-luminosity active galactic nucleus associated with this core would have a mass less than 107 M⊙. It is also probable that the compact X-ray and radio emission of ULX(7)N – the source coincident with the main optical nucleus – is the result of a few recent supernova remnants.

Light Cores Behind Dark Masks

The dusty circumnuclear environments of many spiral galaxies hide important clues for understanding the tight correlation between the supermassive black hole and the host galaxy bulge mass. Two of the nearest spiral galaxies with nuclear starburst host off-centered compact cores associated with the peak of the infrared emission.These compact objects are lightweight, up to a few million solar masses. Their locations imply that they are triggering the present star formation within the circumnuclear disk. Numerical modeling implies that the giant star clusters formed in the process evaporate in a few system revolutions (due to the strong asymmetric gravitational potential). Therefore the off-center compact object scenario provides a model in which the dynamically cold gaseous component is rapidly converted into a dynamically hot stellar component. Meanwhile only a small fraction of the gas contributes to the growth of the off-centered compact object.

The Ying and Yang of the M 83 Nucleus

The spiral galaxy M 83, an SB(rs)b at only 4.5 Mpc, is a privileged case for study of the detailed physics on spatial scales of a tenth of a parsec. With 3-D spectroscopic observations using CIRPASS on Gemini-S, we studied the ionized gas properties in J -band with spatial resolution of 0.″5 (Figure 1). The Paβ velocity field shows two dynamical centers, neither of them coincident with the bulge center, identified with the optical nucleus (ON) and the hidden nucleus (HN), with masses, within a radius of 10 pc, of M ON = (1.8±0.4)× 10 7 M ⊙ and M HN = (1.0±0.4)× 10 7 M ⊙ . Using the Paβ equivalent width together with population synthesis models, we are able to estimate the ages of both mass concentrations, T ON = 8 Myr and T HN =6–7 Myr. Adding complexity to this puzzling scenario, we used GMOS+Gemini imaging and spectroscopy to study the radio source J133658.3–295105 (Dottori et al . 2008) and find that Hα emission at the position of this source is redshifted by ~130 km s −1 with respect to an M 83 H II region, leading us to face the possibility of that we are witnessing the ejection of an object by gravitational recoil from the M 83 nucleus. A fit to the X-ray spectrum obtained Chandra supports the association between this source and the disk of M 83 by the presence of the Fe Kα line at 6.7 keV.

AGNs vs. circumnuclear rings

We have analyzed the frequency and properties of the nuclear activity in two samples of galaxies, with and without circumnuclear rings and spirals (CNRs). We discuss the relevance of the results in the framework of the AGN feeding processes and some results are: (i) bright companion galaxies seem not to be important for the appearance of CNRs, therefore these would be more related to intrinsic properties of the host galaxies or to minor merger processes; (ii) the proportion of strong bars in AGN galaxies with a CNR is higher than the expected rate of strongly barred AGN galaxies from the sample of Ho and co-workers; (iii) the incidence of Seyfert activity coeval with CNRs is clearly larger than the expected rate from the morphological distribution of the host galaxies; (iv) the rate of Sy 2 to Sy 1 in galaxies with CNRs is larger than the expected proportion for galaxies without CNRs; this proportion would be in the opposite sense as expected from the geometric paradigm of the classical unified model for AGNs, but supports a scenario where Sy 2 activity is linked to circumnuclear star formation.