A Photodissociation Model for the Morphology of Hi near Ob Associations in M33
نویسندگان
چکیده
We present an approach for analysing the morphology and physical properties of Hi features near giant OB associations in M33, in the context of a model whereby the Hi excess arises from photodissociation of the molecular gas in remnants of the parent Giant Molecular Clouds (GMCs). Examples are presented here in the environs of NGC604 and CPSDPZ204, two prominent Hii regions in M33. These are the first results of a detailed analysis of the environs of a large number of OB associations in that galaxy. We present evidence for “diffusion” of the far-UV radiation from the OB association through a clumpy remnant GMC, and show further that enhanced CO(1-0) emission appears preferentially associated with GMCs of higher volume density. Subject headings: galaxies: individual (M33) — galaxies: ISM — ISM: clouds — ISM: molecules — HII regions — ultraviolet: galaxies
منابع مشابه
Testing An Identification Algorithm for Extragalactic OB Associations Using a Galactic Sample
We have used a Galactic sample of OB stars and associations to test the performance of an automatic grouping algorithm designed to identify extragalactic OB associations. The algorithm identifies the known Galactic OB associations correctly when the search radius (78 pc) is defined by the observed stellar surface density, which suggests that the sample of Galactic OB associations constitutes a ...
متن کاملساخت و تحلیل فهرست ستارهای از کهکشان M33
In this study, 1200 images and catalogues of M33 spiral galaxy taken by WFCAM camera at UKIRT telescope in J, H and K bands. Cross correlation methods were employed to identify stars in overlapping regions from among images taken in different dates. Careful astrometric and photometric analysis was made to calibrate stellar positions and magnitudes using their 2MASS near infra red survey. The fi...
متن کاملOn The Origin of HI in Galaxies: The Sizes and Masses of HI Photodissociation Regions
Young stars in the disks of galaxies produce HI from their parent H2 clouds by photodissociation. This paper describes the observational evidence for and the morphology of such HI. Simple estimates of the amount of dissociated gas lead to the startling conclusion that much, and perhaps even all, of the HI in galaxy disks can be produced in this way.
متن کاملA MODEL STUDY OF LASER ISOTOPE SEPARATION BY PHOTOIONIZATION OR PHOTODISSOCIATION PROCESS
In this study, the selective photoexication of isotopic mixtures by laser light is investigated. Atomic and molecular methods are examined and rate equations are derived for both cases. Two and three step photoionization techniques are considered and rate equations are solved for ion yields. The molecular photodissociation process is also studied and the dependence of the dissociation produ...
متن کاملAn Hst Study of Ob Associations and Star Clusters In
The massive stellar content, the OB associations and the star clusters in an HST field in M101 = NGC 5457 are investigated. A clustering algorithm yields 79 putative associations. Their size distribution is similar to that found in the Magellanic Clouds, M31 and M33, with an average size around 90 pc. The V luminosity function for the stars contained within the associations has a slope d logN/d...
متن کامل