6 research outputs found
Extended Tidal Structure In Two Lyman Alpha-Emitting Starburst Galaxies
We present new VLA C-configuration HI imaging of the Lyman Alpha-emitting
starburst galaxies Tol 1924-416 and IRAS 08339+6517. The effective resolution
probes neutral gas structures larger than 4.7 kpc in Tol 1924-416, and larger
than 8.1 kpc in IRAS 08339+6517. Both systems are revealed to be tidally
interacting: Tol 1924-416 with ESO 338-IG04B (6.6 arcminutes = 72 kpc minimum
separation), and IRAS 08339+6517 with 2MASX J08380769+6508579 (2.4 arcminutes =
56 kpc minimum separation). The HI emission is extended in these systems, with
tidal tails and debris between the target galaxies and their companions. Since
Lyman Alpha emission has been detected from both of these primary systems,
these observations suggest that the geometry of the ISM is one of the factors
affecting the escape fraction of Lyman Alpha emission from starburst
environments. Furthermore, these observations argue for the importance of
interactions in triggering massive star formation events.Comment: ApJ, in press; 11 pages, 2 color figure
The First Deep ACS Lyman alpha Images of Local Starburst Galaxies
We report the first results from a deep Lya imaging program of local
starburst galaxies with the Advanced Camera for Surveys (ACS) of the Hubble
Space Telescope. The two observed galaxies ESO 350-IG038 and SBS 0335-052 have
luminosities similar to those of the Magellanic Clouds but differ in their
chemical composition. ESO 350-IG038 has an oxygen abundance of 1/8 solar,
whereas SBS 0335-052 is known to have one of the lowest abundances among blue
galaxies (~1/30). The ACS imaging reveals a complex Lya morphology, with
sometimes strong offsets between the emission of Lya and the location of
stellar light, ionized gas traced by Halpha, and the neutral gas. Overall, more
Lya photons escape from the more metal- and dust-rich galaxy ESO 350-IG038. The
absence of clear SBS 0335-052 Lya emission over all observed knots, whatever
their dust content or/and color indices, contradicts model expectations of a
lower escape fraction from dust-rich gas due to destruction of Lya photons by
dust grains. Rather, the results are in qualitative agreement with models
suggesting the kinematic properties of the gas as the dominant Lya escape
regulator. If the properties of the two observed galaxies are representative
for starburst galaxies in general, Lya will be difficult to interpret as a
star-formation indicator, in particular if based on Lya imaging at low spatial
resolution.Comment: 6 pages, 2 figures (1 in color) New version of Fig
The Lyman alpha morphology of local starburst galaxies: release of calibrated images
We present reduced and calibrated high resolution Lyman-alpha (Lya) images
for a sample of 6 local star forming galaxies. Targets were selected to
represent a range in luminosity and metallicity and to include both known Lya
emitters and non-emitters. Far ultraviolet imaging was carried out with the
Solar Blind Channel of the ACS on HST in the F122M (Lya on-line) and F140LP
(continuum) filters. The resulting Lya images are the product of careful
modeling of both the stellar and nebular continua, facilitated by supporting
HST imaging in Ha and 5 continuum bands, combined with Starburst99 evolutionary
synthesis models, and prescriptions for dust extinction on the continuum. In
all, the resulting morphologies in Lya, Ha, and UV-continuum are qualitatively
very different and we show that the bulk of Lya emerges in a diffuse component
resulting from resonant scattering events. Lya escape fractions, computed from
integrated Ha luminosities and recombination theory, are found never to exceed
14%. Internal dust extinction is estimated in each pixel and used to correct
Lya fluxes. However, the extinction corrections are far too small (factors from
2.6 to infinity) to reconcile the global Lya luminosities with recombination
theory. Surprisingly, when comparing the global equivalent widths of Lya and
Ha, the two quantities appear anti-correlated, which may be due to the
evolution of mechanical feedback. This calls for caution in the interpretation
of Lya observations. The images presented have a physical resolution 3 orders
of magnitude better than attainable at high-z from the ground with current
instrumentation and our images may therefore serve as useful templates for
comparing with observations and modeling of primeval galaxy formation. We
therefore provide the reduced Lya, Ha, and continuum images to the community.Comment: Accepted by the Astronomical Journal. See also
http://ttt.astro.su.se/projects/Lyman-alpha
The North Galactic Pole +30° Zone Galaxies. I. A Comparative Study of Galaxies with Different Nuclear Activity
International audienceA database containing 618 active and star-forming (A/SF) galaxies and 564 normal galaxies in a 120° à 6° wide strip crossing the north Galactic pole was constructed in order to compare the global properties of "active" galaxies against a control sample of "normal" galaxies. This database combines a literature and catalog search with new optical measurements from the Fpg (red) and Jpg (blue) band images of the STScI Digitized Sky Survey (DSS). We provide alternative names, accurate coordinates, morphological type, activity classes, red and blue apparent magnitudes, 2MASS near-infrared J-H and H-K colors, apparent diameters, axial ratios, position angles, and number counts of neighboring objects in a circle of radius 50 kpc. We also present an atlas of 103 interacting and merging systems among these galaxies. The integrated properties of A/SF and normal galaxies in this sample are compared using a multivariate factor analysis, which reveals that A/SF galaxies are objects with relatively late morphological types, and are more inclined and have bluer optical colors than normal galaxies. In this sample, all merging and interacting galaxies are A/SF objects. Star-forming galaxies are objects with relatively late morphological types, lower absolute luminosities and linear sizes, bluer colors, and higher inclination than sample X-ray or radio sources, as well as Seyfert galaxies. The near-infrared colors of the sample galaxies are independent parameters and do not correlate with activity level or any other parameter of the galaxies