Showing papers by "Stuart D. Ryder published in 2008"

A SINFONI View of Galaxy Centers: Morphology and Kinematics of Five Nuclear Star Formation-Rings

Abstract: We present near-infrared (H- and K-band) integral-field observations of the circumnuclear star formation rings in five nearby spiral galaxies. The data, obtained at the Very Large Telescope with the SINFONI spectrograph, are used to construct maps of various emission lines that reveal the individual star forming regions ("hot spots") delineating the rings. We derive the morphological parameters of the rings, and construct velocity fields of the stars and the emission line gas. We propose a qualitative, but robust, diagnostic for relative hot spot ages based on the intensity ratios of the emission lines Brγ, He I, and [Fe II]. Application of this diagnostic to the data presented here provides tentative support for a scenario in which star formation in the rings is triggered predominantly at two well-defined regions close to, and downstream from, the intersection of dust lanes along the bar with the inner Lindblad resonance.

The ultraluminous X-ray source NGC 1313 X-2. Its optical counterpart and environment

Abstract: NGC 1313 X-2 is one of the brightest ultraluminous X-ray sources in the sky, at both X-ray and optical wavelengths; therefore, quite a few studies of available ESO VLT and HST data have appeared in the literature. Here, we present our analysis of VLT/FORS1 and HST/ACS photometric data, confirming the identification of the B ∼ 23 mag blue optical counterpart. We show that the system is part /

Deep Near-Infrared Surface Photometry of 57 Galaxies in the Local Sphere of Influence

Abstract: We present H-band (165 μm) surface photometry of 57 galaxies drawn from the Local Sphere of Influence (LSI), with distances of less than 10 Mpc from the Milky Way The images, with a typical surface brightness limit 4 mag fainter than the Two Micron All Sky Survey (2MASS) (245 mag arcsec–2 < μlim < 26 mag arcsec–2), have been obtained with the Infrared Imager and Spectrograph 2 on the 39 m Anglo-Australian Telescope A total of 22 galaxies that remained previously undetected in the near-infrared (NIR), and potentially could have been genuinely young galaxies, were found to have an old stellar population with a star density 1-2 mag below the 2MASS detection threshold The cleaned NIR images reveal the morphology and extent of many of the galaxies for the first time For all program galaxies, we derive radial luminosity profiles, ellipticities, and position angles, together with global parameters such as total magnitude, mean effective surface brightness, and half-light radius Our results show that 2MASS underestimates the total magnitude of galaxies with μ H eff between 18 and 21 mag arcsec–2 by up to 25 mag The Sersic parameters that best describe the observed surface brightness profiles are also presented By adopting accurate galaxy distances and an H-band mass-to-light ratio of H * = 10 ± 04, the LSI galaxies are found to cover a stellar-mass range of The results are discussed along with previously obtained optical data Our sample of low-luminosity galaxies is found to closely follow the optical-infrared B-versus-H luminosity relation defined by brighter galaxies, with a slope of 114 ± 002 and a scatter of 03 mag Finally, we analyze the luminosity-surface brightness relation to determine an empirical mass-to-light ratio of H * = 078 ± 008 for late-type galaxies in the H band

Discovery of a Very Highly Extinguished Supernova in a Luminous Infrared Galaxy

Abstract: We report the discovery of a confirmed supernova (SN) and a supernova candidate in near-infrared images from the ALTAIR/NIRI adaptive optics system on the Gemini-North Telescope and NICMOS on the Hubble Space Telescope. The Gemini images were obtained as part of a near-infrared K-band search for highly obscured SNe in the nuclear regions of luminous infrared galaxies. SN 2008cs, apparent in the Gemini images, is the first SN discovered using laser guide star adaptive optics. It is located at 1500 pc projected distance from the nucleus of the luminous infrared galaxy IRAS 17138–1017. The SN luminosity, JHK colors, and light curve are consistent with a core-collapse event suffering from a very high host galaxy extinction of -->15.7 ± 0.8 mag in the V-band, which is to our knowledge the highest yet measured for a SN. The core-collapse nature of SN 2008cs is confirmed by its radio detection at 22.4 GHz using our Very Large Array observations 28 days after the SN discovery, indicating a prominent interaction of the SN ejecta with the circumstellar medium. An unconfirmed SN apparent in the NICMOS images from 2004 is located in the same galaxy at 660 pc projected distance from the nucleus and has a lower extinction.

Adaptive optics imaging and optical spectroscopy of a multiple merger in a luminous infrared galaxy

Abstract: We present near-infrared (NIR) adaptive optics imaging obtained with VLT/NACO and optical spectroscopy from the Southern African Large Telescope of a luminous IR galaxy (LIRG) IRAS 19115-2124. Thes ...

Discovery of a very highly extinguished supernova in a luminous infrared galaxy

Abstract: We report the discovery of a confirmed supernova (SN) and a supernova-candidate in near-infrared images from the ALTAIR/NIRI adaptive optics system on the Gemini-North Telescope and NICMOS on the Hubble Space Telescope. The Gemini images were obtained as part of a near-infrared K-band search for highly-obscured SNe in the nuclear regions of luminous infrared galaxies. SN 2008cs apparent in the Gemini images is the first SN discovered using laser guide star adaptive optics. It is located at 1500 pc projected distance from the nucleus of the luminous infrared galaxy IRAS 17138-1017. The SN luminosity, JHK colors and light curve are consistent with a core-collapse event suffering from a very high host galaxy extinction of 15.7 +- 0.8 magnitudes in V-band which is to our knowledge the highest yet measured for a SN. The core-collapse nature of SN 2008cs is confirmed by its radio detection at 22.4 GHz using our Very Large Array observations 28 days after the SN discovery, indicating a prominent interaction of the SN ejecta with the circumstellar medium. An unconfirmed SN apparent in the NICMOS images from 2004 is located in the same galaxy at 660 pc projected distance from the nucleus and has a lower extinction.

A Pair of Leading Spiral Arms in a Luminous Infrared Galaxy

Abstract: Leading spiral arms are a rare phenomenon. We present here one of the very few convincing candidates of spiral arms opening counterintuitively in the same direction as the galaxy disk is rotating. This detection in the luminous IR galaxy (LIRG) IRAS 18293–3413 is based on near-infrared (NIR) adaptive optics imaging with the Very Large Telescope and long-slit NIR spectroscopy with the Anglo-Australian Telescope. We discuss the orientation of the galaxy based on imaging and derive rotation curves from both emission and absorption features in the spectrum. The galaxy is strongly star-forming and has a minor companion in a high-velocity encounter. The fact that the arms of IRAS 18293–3413 are not easily traceable from optical images suggests that larger samples of high-quality NIR imaging of interacting systems and LIRGs might uncover further cases of leading arms, placing constraints on spiral arm theories and retrogade encounters, and especially on the relationship between disk masses and dark matter halo masses.

Deepest Near-IR Surface Photometry of Galaxies in the Local Sphere of Influence

Abstract: Summary. We present near-IR, deep (4 mag deeper than 2MASS) imaging of 56 Local Volume galaxies. Global parameters such as total magnitudes and stellar masses have been derived and the new near-IR data combined with existing 21cm and optical B-band data. We present multiwavelength relations such as the H i mass-to-light ratio and investigate the maximum total baryonic mass a galaxy can have.

Discovery of Large-Scale Gravitational Infall in a Massive Protostellar Cluster

Abstract: We report Mopra (ATNF), Anglo-Australian Telescope, and Atacama Submillimeter Telescope Experiment observations of a molecular clump in Carina, BYF73 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the clump has mass ~ 2 x 10^4 Msun, luminosity ~ 2-3 x 10^4 Lsun, and diameter ~ 0.9 pc. From radiative transfer modelling, we derive a mass infall rate ~ 3.4 x 10^-2 Msun yr-1. If confirmed, this rate for gravitational infall in a molecular core or clump may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact HII region and IR cluster surrounded by a shell-like photodissociation region showing H2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H2 emission. The combination of these features is very unusual and we suggest they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.

Discovery of Large-Scale Gravitational Infall in a Possible Massive Protostellar Cluster

Abstract: We report Mopra (ATNF), Anglo-Australian Telescope, and Atacama Submillimeter Telescope Experiment observations of a molecular core in Carina, BY72 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the core has mass ∼ 5,000 M⊙, luminosity ∼ 2–3×10 4 L⊙, diameter ∼ 0.9 pc, and mass infall rate ∼ 2.4×10 M⊙yr . If confirmed, this rate for gravitational infall in a molecular core may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact HII region and IR cluster surrounded by a shell-like photodissociation region showing H2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H2 emission. The combination of these features is very unusual and we suggest they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation. Subject headings: astrochemistry — infrared: ISM — ISM: kinematics and dynamics — ISM: molecules — radio lines: ISM — stars:formation

A pair of leading spiral arms in a luminous infrared galaxy

Abstract: Leading spiral arms are a rare phenomenon. We present here one of the very few convincing candidates of spiral arms opening counter-intuitively in the same direction as the galaxy disk is rotating. This detection in a luminous IR galaxy (LIRG) IRAS 18293-3134 is based on near infrared (NIR) adaptive optics imaging with the Very Large Telescope and long-slit NIR spectroscopy with the Anglo-Australian Telescope. We discuss the orientation of the galaxy based on imaging and derive rotation curves from both emission and absorption features in the spectrum. The galaxy is strongly star-forming and has a minor companion in a high-velocity encounter. The fact that the arms of IRAS 18293-3134 are not easily traceable from optical images suggests that larger samples of high-quality NIR imaging of interacting systems and LIRGs might uncover further cases of leading arms, placing constraints on spiral arm theories and retrograde encounters, and especially on the relationship between disk masses and dark matter halo masses.