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The Diffuse Ionised Gas in NGC 4449
- C. Muñoz-Tuñón, O. Fuentes-Masip, H. O. Castañeda
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- Journal:
- Publications of the Astronomical Society of Australia / Volume 15 / Issue 1 / 1998
- Published online by Cambridge University Press:
- 16 May 2016, pp. 103-105
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It is now well established that there is a diffuse ionised medium which extends far beyond the disks of spirals. The mechanism responsible for the ionisation is still an issue of debate, and the method of measuring the total luminosity, independently of the observational set-up, has to be defined. Here we analyse the case of the Magellanic irregular NGC 4449, using Fabry–Perot bidimensional mapping of the Hα emission line, at the 4·2 m William Herschel Telescope (WHT) telescope on La Palma, Canary Islands. The total spatial coverage of 80×80 arcsec2 allows most of the star forming regions to be sampled at 0·26 arcsec/pixel spatial resolution. Using 3D spectroscopy, it is possible to define the individual star-forming regions and to produce a luminosity versus size diagram. This can be used to estimate directly the number of photons leaking out from those regions exceeding the thickness of the galactic disc. In the case of NGC 4449 it is shown that the large population of GEHRs can be the source of UV photons ionising the diffuse ionised gas (DIG) of the galaxy, and the logL–R diagram can be used to quantify the number of photons leaking out of the material surrounding the star forming regions. In the case of NGC 4449 it is found that 54% of the total luminosity of the giant star-forming regions is lost to the DIG. This implies a contribution of 3·12×1040 erg s−1 (1 erg s−1 = 10−7 J s−1) which amounts to 30% of the galaxy total Hα luminosity.
New Methods to Measure HII Regions Diameters
- O. Fuentes-Masip, H. O. Castañeda, C. Muñoz-Tuñón
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- Journal:
- International Astronomical Union Colloquium / Volume 149 / 1995
- Published online by Cambridge University Press:
- 12 April 2016, pp. 143-147
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- 1995
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Observations of the giant irregular galaxy NGC 4449 are being used to study the correlations between the diameter or luminosity and the velocity dispersion of its giant HII regions (GHRs), understanding as GHRs those HII regions with supersonic velocity dispersions. In the central part of this galaxy the HII regions overlap, and also there is a strong, morphologically diffuse emission that permeates the main body of NGC 4449, both effects making difficult the detection, identification and separation of HII regions. We have developed new techniques to solve these problems, obtaining HII regions parameters equivalent to the ones that would be got if the HII regions did not overlap and if the diffuse emission did not exist.
Spectroscopical Imaging of Star-Forming Regions
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- By J. M. Mas-Hesse, Laboratorio de Astrofísica Espacial y Física Fundamental, POB 50727, E-28080 Madrid, Spain, C. Muñoz Tuñon, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Spain, J. M. Vilchez, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Spain, H. O. Castañeda, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Spain, D. Carter, Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0EZ, UK
- G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, Tenerife
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- Book:
- Violent Star Formation
- Published online:
- 10 November 2010
- Print publication:
- 22 September 1994, pp 125-130
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Summary
As part of the GEFE collaboration, observations of star-forming regions with high spectral resolution and long-slit sampling are being undertaken. 2D maps of physical parameters like density, excitation, extinction…etc. have been produced with 1″ spatial resolution and 2″ spatial sampling. Some preliminary results on the giant HII Region NGC 5471 and the irregular galaxy NGC 4214 are presented. Very high velocity components have been detected at some particular positions on the nebulae, as well as other peculiar kinematical structures (redshifted secondary emission peaks, line splitting etc.). The whole emitting area of NGC 5471 behaves as a unique entity with respect to excitation, with no correlation with the emitting knots. On the other hand, differentiated star-forming regions can be identified on NGC 4214. Finally, the distribution of dust particles seems to be rather inhomogeneous and anticorrelated with the distribution of emission-line intensities.
Introduction: aim and targets
The ultimate aim of the GEFE collaboration is to determine which are the physical parameters that control the formation of a violent burst of star formation. Within this framework and in order to fulfil this main objective it is important to know the physical properties of star-forming regions with high enough spatial resolution as to determine variations of the measurable parameters within the emitting nebulae. We aim to use measurements of age, excitation degree, velocity dispersion and chemical composition to know whether we are dealing with single star-forming regions or with well differentiated physical entities within a patch of ionized gas, which cause misinterpretation in our understanding of the “physical object” (Muñoz-Tuñón et al. 1993).
A Kinematical Study of NGC 604
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- By N. S. P. Sabalisck, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, H. O. Castañeda, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, C. Muñoz-Tuñón, Instituto de Astroísica de Canarias, E-38200 La Laguna, Tenerife, Spain
- G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, Tenerife
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- Book:
- Violent Star Formation
- Published online:
- 10 November 2010
- Print publication:
- 22 September 1994, pp 39-40
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Summary
We present a kinematical study of NGC 604 in the emission lines of Hα and [OIII] λ5007 Å, based on data obtained with TAURUS-2, a Fabry-Perot imaging spectrograph. The main result is that the global supersonic velocity value is dominated by emission coming from the two maximum brightness peaks covering an area of about 12 arcsec.
NGC 604, located in M33, is one of the most prominent giant extragalactic HII regions (GEHR). It was observed with TAURUS-2 at the 4.2-m William Herschel Telescope (La Palma), with the Image Photon Counting System (IPCS) as detector. Two data cubes, each with an integration time of 3600 sec, were obtained in the emission line of Hα and [OIII] λ5007. The 125-µm etalon was used, which gave a free spectral range for Hα of 17.6 Å (806.6 km s−1) and 10.0 Å (596.1 km s−1) for [OIII]. The velocity resolution (σ of the calibration line) was 23.1 km s−1 for Hα and 19.6 km s−1 for [OIII].
In order to determine the origin of the supersonic mass motion in NGC 604, the kinematics of the region were analyzed by means of individual spectra, applying automatic fitting routines with single Gaussian fits. The measured velocity dispersions were corrected for instrumental and thermal broadening. The thermal velocity dispersion correction was calculated assuming Te = 10,000 K.
Photometric Diagrams of NGC 2366
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- By A. Aparicio, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, J. Cepa, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, H. O. C. Castañeda, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, C. Gallart, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, C. Muñoz-Tuñón, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, E. Telles, Royal Greenwich Observatory, Madingley Road CB3 0EZ, Cambridge, UK, G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
- G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, Tenerife
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- Book:
- Violent Star Formation
- Published online:
- 10 November 2010
- Print publication:
- 22 September 1994, pp 123-124
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Summary
The irregular magellanic galaxy NGC 2366 is usually assumed to belong to the M 81/ NGC 2403 group. (B − V)-V and (V − R)-V photometric diagrams of its stellar content are presented. Using its brightest blue and red stars, its distance is estimated to be about 3.0 Mpc.
Introduction
For some time now, a considerable effort has been devoted to the analysis of the stellar content of nearby galaxies through the photometry of their resolved stars. These data, combined with spectroscopic and radio observations, provide interesting information about the history of the star formation and about the star formation processes in galaxies. The understanding of these processes is relevant, since they define the path followed by the galaxy through its evolution.
Our project is devoted to the analysis of the stellar content in nearby galaxies and is included in the GEFE project.
We present the first results of our photometric analysis of NGC 2366. This galaxy is usually assumed to belong to the M 81–NGC 2403 group. Table 1, summarizes the global parameters of NGC 2366.
Data and results
Observations of the stellar content of NGC 2366 were carried out in 1992 using the 1150 × 1250 EEV5 chip at the prime focus of the 2.5-m Isaac Newton Telescope of the Observatory of Roque de los Muchachos in La Palma (Canary Islands, Spain). The limiting magnitudes, are about B = 22.1, V = 23.2 and R = 22.9 (defined as those for which 50% of the stars are lost).
A Study on the HII Regions of NGC 4449
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- By O. Fuentes-Masip, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, H. O. Castañeda, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain, C. Muñoz-Tuñón, Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
- G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, Tenerife
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- Book:
- Violent Star Formation
- Published online:
- 10 November 2010
- Print publication:
- 22 September 1994, pp 131-132
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Summary
Observations in the line of Hα and of [OIII] λ5007 of the galaxy NGC 4449 taken at the William Herschel Telescope of the Observatorio del Roque de los Muchachos with TAURUS-2, a Fabry-Perot interferometer, are being used to study the correlation between the diameter or flux and the velocity dispersion of its HII regions. Two different catalogues of HII regions are being compared. In the first we consider each flux relative maximum as a differentiated HII region, while in the second sample we use kinematical criteria to identify the different regions.
Introduction
In 1981, Terlevich and Melnick established a correlation between the diameter or the luminosity of giant HII regions and the turbulent width of their emission lines, which represented a chance to improve present extragalactic distance estimations. To study the possible existence of similar correlations for HII regions in a single galaxy, we have chosen NGC 4449, a giant irregular type I galaxy. It is located 5 Mpc away from the Milky Way and is very rich in HII regions. New criteria to identify HII regions are explored and compared with the samples and measurements already present in the literature. Detailed information will be presented in Fuentes-Masip et al. (1994, in preparation).
Data analysis
The product of the calibrated Fabry-Perot observations was a three dimensional set where the X-Y axes were the spatial coordinates, and the Z axis was wavelength calibrated (the dispersion direction).