Star-forming Knots Research Articles

A multi-frequency study of the Wolf-Rayet blue compact dwarf galaxy He2-10

We present preliminary results on multi-wavelength observations of the Wolf-Rayet Blue Compact Dwarf Galaxy He2–10. These observations include Hα and continuum imaging, high-resolution Hα spectroscopy, high-resolution radio-continuum mapping at 6.3 and 3.5 cm and X-ray mapping. The deep Hα image reveals that the galaxy consists of a complex system of different star-forming knots surrounded by kpc-scale bubble-like and filamentary structures. The most interesting structure is a bipolar superbubble centered on the most intense star-formation knot. High-resolution spectroscopy of this structure indicates that it is expanding with a velocity in the range 75–250 km s−1. This kind of outflows is likely to be produced by the mechanical action of stellar winds and supernovae explosions in the intense starbursts that the galaxy hosts. This scenario is consistent with the finding of a very steep radio spectral index in the extended radio continuum emission (α = −0.59) that confirms the presence of a large number of supernova remnants in the galaxy.

High Spatial Resolution Near-IR Tip/Tilt Imaging of “Warm” Ultraluminous Infrared Galaxies

We present results from high spatial resolution (FWHM ≈ 0.3–0.5″) near-IR (1.6 and 2.1μm) imaging of a complete sample of ultraluminous infrared galaxies (ULIGs) chosen to have “warm” mid-IR colors (f25/f60 > 0.2) characteristic of AGN. In conjunction with our WFPC2 imaging program (Surace et al. 1998), we have found that nearly all of these systems are advanced mergers with complex nuclear morphologies. The extended underlying galaxies are detected in each system at H and K′, and are found to have luminosities of a few L∗, similar to quasars (McLeod & Rieke 1994). Many of the circumnuclear star-forming knots seen at optical wavelengths have been detected. Based on model SEDs, their bolometric luminosities appear similar to those of the extended nuclear starbursts seen in other, less-luminous interacting systems (i.e. NGC 4038/9). Each ULIG is increasingly dominated at long wavelengths by a compact source which we identify as a putative active nucleus. The optical/near-IR colors of these putative nuclei are more extreme than the most infrared-active starburst galaxies, yet are identical to “far-IR loud” quasars which are in turn similar to optical quasars with significant hot (800 K) dust emission. Half of the ULIGs have dereddened nuclear near-IR luminosities comparable to those of QSOs, while the others resemble Seyferts; this may be an effect of patchy extinction and scattering. Similarities between the putative ULIG nuclei and QSO nuclei, the underlying host galaxies, and the apparent young age of the ULIGs (as evidenced by their compact star-forming knots) support the evolution of “warm” ULIGs into optical QSOs.

Multiwavelength Observations of Collisional Ring Galaxies. III. Oxygen/Nitrogen Abundances and Star Formation Properties of Ring Knots

This is the third paper in a series examining the multiwavelength properties of a sample of northern ring galaxies, in which we present optical long-slit spectra and broadband BVR and JHK colors of individual star-forming knots embedded in the ring. We present the oxygen and nitrogen abundances of the starburst knots and compare the reddening-corrected colors of individual star clusters with recent models of stellar evolution. We also present kinematic data for one system, LT 41. The star-forming knots in the rings have very similar colors, which implies similar ages in the range 4–80 Myr. These ages are less than the dynamical ages of the rings, which are typically 100–300 Myr. The fact that the implied ages of knots within individual ring galaxies cluster around the same age argues that their formation is recently triggered by a coherent event all around the ring. This strongly supports the triggering of the star formation as being due to the propagation of a radial density wave, as in the classical picture. The ring galaxies are found to have subsolar metallicities in the range one-half to one-fifth solar in [O/H] and [N/H] ratios. There is a suggestion of an increase in the mean nitrogen abundance for the rings of larger linear size, but oxygen abundances show no trend with ring diameter. The uniformity of the oxygen abundances over the sample is consistent with their rather narrow range of K-band luminosities, which suggests that even in strongly disturbed galaxies, when prompt local enrichment is expected to be important, the primary factor governing oxygen metallicity is total luminosity.

Broad Low‐Intensity Wings in the Emission‐Line Profiles of Four Wolf‐Rayet Galaxies

High-resolution spectroscopic observations have been obtained for the Wolf-Rayet galaxies He 2-10, II Zw 40, POX 4, and Tol 35. Several subregions have been selected in each slit position in order to investigate possible spatial variations in the line profiles, radial velocities, and ionization conditions of the gas. The most remarkable feature of the spectra is the presence of asymmetric broad low-intensity wings in the profiles of the brightest emission lines. These spectral features are detected farther out from the star-forming knots, showing linear dimensions between 300 pc and 4.1 kpc. The maximum expansion velocity measured for this gas is between 120 and 340 km s-1 and appears to be quite constant along the slit for all the objects. Additional general properties of the spectra are (1) the quoted emission-line ratios are similar in the narrow and broad components, (2) no systematic differences of the behavior of the broad and narrow components have been found along the major and minor axis of the galaxies, and (3) the spatial distribution of the ionized gas is peaked centrally. Different mechanisms capable of producing the observed broad spectral features are discussed: cloud-cloud collisions in virialized gas, academic superbubbles, champagne flows, and superbubble blowout. It is concluded that superbubble blowout expanding over a cloudy medium can explain the observational properties in a reasonable manner.

The morphology of H II galaxies

We present CCD images of a sample of 39 HII galaxies taken at the Danish 1.54m telescope on La Silla. The images are used to analyse the morphology of these emission line dwarfs, and the structural properties of the knots of star formation and of the underlying galaxy. The sizes of the starbursts are measured. We propose a morphological classification based on the presence or absence of signs of tails, extensions, or distorted outer isophotes. This criterion segregates the objects into two broad morphological types with different physical properties: the more disturbed and extended (type I) HII galaxies having larger luminosities and velocity dispersions than the more compact and regular (type II) objects. The relative position of HII galaxies and of a sample of dwarf elliptical galaxies in the [R -- sigma] diagram support the hypothesis of a possible evolutionary link between the two types of galaxy.

Star Formation Knots in IRAS Galaxies

view Abstract Citations (8) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Star Formation Knots in IRAS Galaxies Hutchings, J. B. Abstract Images of IRAS galaxies with a range of IR properties are examined for bright knots, both within and outside the galaxy. These are found almost exclusively in galaxies with steep IR spectra, but over a wide range of IR luminosity, and usually without strong nuclear activity. In most cases, the knots are likely to be star formation induced by tidal interactions, and are seen in the early stages of such interactions. Detailed photometry is presented of knots in six representative galaxies. The knots appear to have a wide range of colour and luminosity, but it is argued that many are heavily reddened. Knots formed outside the parent galaxy may be a new generation of what later become globular clusters, but they appear to have a wide range of luminosities. Publication: The Astronomical Journal Pub Date: February 1996 DOI: 10.1086/117817 arXiv: arXiv:astro-ph/9511033 Bibcode: 1996AJ....111..712H Keywords: INFRARED: GALAXIES; GALAXIES: STRUCTURE; STARS: FORMATION; GALAXIES: INTERACTIONS; Astrophysics E-Print: 11 pages plain TeX, 5 figures not included but available by request to hutchngs@dao.nrc.ca To appear in the Astronomical Journal. Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html full text sources arXiv | ADS | data products SIMBAD (9) NED (6)

Anatomy of a merger - CO in ARP 299 (IC 694-NGC 3690)

High-resolution (2.4-arcsec) CO observations of the interacting system Arp 299 (Mrk 171: IC 694 and NGC 3690) reveal major gas condensations at the nuclei of both galaxies and in the disk overlap region. The 0.9 x 10 to the 9th solar masses of H2 at the nucleus of NGC 3690 extends to radii of 310 pc and probably sustains a starburst. A compact source (radius not greater than 250 pc) of mass 3.9 x 10 to the 9th solar masses is found at the nucleus of IC 694; this galaxy may harbor an AGN. At least three discrete subcondensations, probably active star-forming knots, are detected in the 1800 x 640 pc overlap region. 24 refs.