The Size Distribution of HII Regions as a New Variant to Determine the Distances of Galaxies

Es wurden die scheinbaren Radien einiger HII-Gebiete in den Galaxien NGC 224, 2403, 300, 598 und 1313 bestimmt und deren Größenverteilung untersucht. Zur Entfernungsbestimmung dieser Galaxien wurden zwei Varianten angenommen, deren Zuverlässigkeit durch Vergleich mit auf andere Weise bestimmten Entfernungen gezeigt wird.     

The Evolution of HII Regions

Here we review some recent results on the observed properties of UCH IIregions, and on the new class of Super-ultra-compact H II regions, and describe the theoretical scheme for H II region expansion, from star-forming cloud cores to the more diffuse external medium. High-pressure cores can stop the expansion on relatively short time scales, of the order of 3× 10⁴ yr, and the resulting pressure equilibrium UCH II regions have small sizes and large ion densities. If the ionization front enters into the decreasing density gradient of the cloud core, the expansion is accelerated and the H II region“pops” out of the core and becomes a “blister”-like region. The properties of the outflows depend on the cloud density structure, and a variety of different shocks can be formed. Density inhomogeneities inside photoionized regions are smoothed out on short time scales, but new clumps are continuously created at the cool shell generated by the shock front. Instabilities in both the ionization and shock fronts cause the fragmentation of the shell, maintaining the presence of clumps during the whole evolution. This revised version was published online in July 2006 with corrections to the Cover Date.     

类星体光度函数

对前人在类星体光度函数研究中的工作作了详细的介绍。在前人工作的基础上,提出两个新的研究方法和一个新的统计方法。第一为分类研究法。将类星体分作若干子类,每一子类的光度演化形式可以通过相关分析求出,而数密度则可由简单计数求得。第二为平均星等法,定义平均星等Ｍ。研究表明,对于纯密度演化模型,Ｍ与红移ｚ无关;而对于纯光度演化模型,Ｍ与光度演化形式（Ｍｚ－Ｍ）成线性关系。提出的新的统计方法为ｎ／ｎｍａｘ检验法,它是传统的Ｖ／Ｖｍａｘ和Ｖ′／Ｖ′ｍａｘ检验法的推广。与传统方法不同,它能适用于任何光度函数模型。若所采用的光度函数正确,则样品的ｎ／ｎｍａｘ值应均匀分布于数域［０,１］     

Density structure of the giant HII region NGC 2363

We perform a detailed measurement of the electron density along two slit position angles in the bright, low metallicity extragalactic HII region NGC 2363. A comparison of the density structures obtained with the two independent diagnostics given by [AIV]4711/4740 and [SII]6716/6731, show that they present both different absolute values and different radial dependencies, with the [AIV] densities reaching up to 1000 cm^-3. We explore the implications for the computation of the He abundance.     

Virgo星系团的光度函数和质量函数

本文对Ｖｉｒｇｏ星系团中央６°天区内的成员星系作了光度函数和质量函数的研究。成员星系是以视向速度作为判据并合理地考虑了密度分布因素后确定的。研究表明，该天区全部成员星系的光度函数为Ｓｃｈｅｃｈｔｅｒ型，而各类Ｓ星系的光度函数则为Ｇａｕｓｓ型，且峰值位置按Ｓａ→Ｓｄ序列向暗端移动，宽度亦逐渐变宽；Ｖｉｒｇｏ团质量函数与恒星质量函数一样可以用指数形式来描述，文中还利用光度函数和质量函数对该团的形态和质量分层进行了讨论，并计算了该天区团的总光度。     

Distances of Galaxies from the Apparent Size Distribution of Dark Clouds. II NGC 224, NGC 2841 and NGC 7331

The distances of three Sb galaxies NGC 224, NGC 2841 and NGC 7331 have been determined using the apparent size distribution of dark interstellar clouds in each of them. The distances of NGC 224, NGC 2841, NGC 7331 were found to be 727.7 ± 63 kpc, 8.07 ± 0.16 Mpc and 7.22 ± 0.15 Mpc, respectively.     

Study of the HII regions in the spiral galaxy NGC6384

The galaxy NGC6384 has been observed with an IPCS through Hα and [NII] narrow-band interference filters for direct imagery with the 2.6-m Byurakan telescope. We studied the main physical parameters of the identified 98 HII regions, their diameter and luminosity functions, as well the [NII]/Hα ratio distribution. The integrated distribution function of the HII region diameters can be well fitted by the exponential function. The characteristic diameter has the value (Do = 217 pc) predicted for a galaxy of its measured luminosity. The luminosity function of HII regions has a double power law profile with relatively shallow slope at low luminosities (α = −0.4), an abrupt turnover at logL(Hα) ≈ 38.75, and sharper slope at higher luminosities (α = −2.3). The correlation between the luminosity and diameter of HII regions confirms that in general they are constant density, radiation-bound systems. [NII]/Hα ratio data for the HII regions show that there is a negative radial gradient of [NII]/Hα. In the central region of the galaxy, nitrogen abundance is higher than in the periphery. The properties of the HII region population of this AGN galaxy do not differ significantly from the properties of the HII region population of the “normal” galaxies. Reexamining the location of the type Ia SN 1971L in the galaxy, we confirm that it lies on the spiral arm at about 8″.6 far from the closest HII region N 53 (F81). Such a location can be taken as proof that the progenitor of this SN does not belong to an old, evolved stellar population. Published in Astrofizika, Vol. 50, No. 4, pp. 519–533 (November 2007).     

Nonisothermal Wave Motions in the HII Regions

The propagation of the linear and nonlinear waves in the HII regions is considered. The relaxation processes to the temperature and ionization fraction are taken into account. It is shown, that the essential damping of the waves takes place. The motion at long wavelengths is not isothermal and the velocity perturbations should be accompanied with the noticeable temperature variations. Instability of the traveling waves in the partially ionized hydrogen is possible. This effect may be important in the gas layer between ionization and shock fronts. It is found out, that the nonlinear waves can be generated by the ionization-shock front. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinematics of Giant HII Regions in Nearby Galaxies

We present optical high-spectral-resolution long-slit observationsof massive star formation regions in the nearby galaxies M101, NGC2403, and M33 obtained with the WHT. We have constructed velocity,line dispersion and intensity maps using between 6 and 12 parallelslits in each case. We will present the data for seven regions:NGC 5455, NGC 5461, NGC 5471 in M101; three regions in NGC 2403;and NGC 595 in M33. We will also present a detailed study of thedifferent profiles found across the regions, paying specialattention to the presence of supersonic profiles and multiplecomponents.     

类星体的光度函数

主要讨论了光学选类星体的光度函数有其演化的达几年中的进展，目前在小红移范围已取得比较一致的结论，对ｚ〉２．２，由于类星样品的限制，对类星体光度函数的演化还存在着很大的分岐，在文中还比较了类星体光学，射电，Ｘ射线的光度函数的性质。     

Nonlinear Dynamics of Ionization Fronts in HII Regions

Hydrodynamic instability of an accelerating ionization front (IF) is investigated with 2D hydrodynamic simulations, including absorption of incident photoionizing photons, recombination in the HII region, and radiative molecular cooling. When the amplitude of the perturbation is large enough, nonlinear dynamics of the IF triggered by the separation of the IF from the cloud surface is observed. This causes the second harmonic of the imposed perturbation to appear on the cloud surfaces, whereas the perturbation in density of ablated gas in the HII region remains largely single mode. This mismatch of modes between the IF and the density perturbation in the HII region prevents the strong stabilization effect seen in the linear regime. Large growth of the perturbation caused by Rayleigh-Taylor-like instability is observed late in time.     

Luminosity and colour distribution in the interacting system NGC 7770-71

Detailed surface photometry for the SB(s)a galaxy NGC 7771 has been carried out in the blue spectral band. Isophotes, luminosity profiles, and photometric parameters are obtained from photographs collected with the 74 inch telescope of Kottamia Observatory, Egypt. The total apparent magnitudem _T =13.08 with maximum dimensions 3.6±0.5×2.7±0.5 (at threshold µ _m = 27.38 mag s^–2). The absolute magnitude isM _T =–21.70 if the distance is =90.2 Mpc. The major axis is in position angle =69°.5±1° and the mean axis ratio of the outer regionsq=b/a=0.45 corresponds to an inclinationi=66°. The equivalent effective radiusr _e ^* =0.29 and the effective surface brightness µ _e = 22.30 mag s^–2.The equivalent luminosity distribution has been decomposed into two main components, anr ^1/4 spheroid and an exponential disk. The total apparent magnitudes of the spheroidal and disk components are 14.36 and 13.48, which correspond to contributions of 31 and 69% to the total blue luminosity, respectively.     

The Internal Kinematics of Complete Sets of HII Regions in Disc Galaxies

We analyse spectral images across the full emission line in H_αof the discs of M100 and M101, extracting for each HII region its spectrum, and for the more luminous and extended, spectra over a range of circular apertures. The principal components of these spectra are presented in log–log plots of luminosity vs. turbulent line-width. These plots are apparently scatter diagrams, with no convincing linear fits, e.g. with slope ∼ 4 as predicted for a population of virialized systems. Both plots do show, however, clean linear lower envelopes in turbulent width. We interpret these as the loci of HII regions in virial equilibrium. The emissions with greater widths (the great majority), show the effects of not yet fully damped kinematic inputs from stellar winds and supernovae. As expected, a greater fraction of the most luminous regions, which are the most massive, lie on or near the virial envelopes. The slopes of these envelopes are in fact 2.6,not 4, which is explicable if the most luminous regions are density bounded, so that a fraction of their ionizing luminosity, (increasing with luminosity above a critical value) is not registered in H_α.The regions on the envelopes are also those of greatest surface brightness, as predicted for density bounded regions. The masses of the regions on the envelopes, computed via the virial expression, agree well with masses estimated via their emission measures and assuming density bounding. This revised version was published online in July 2006 with corrections to the Cover Date.     

年轻星团光度函数的演化

利用已发表的Ｔｒａｐｅｚｉｕｍ星团和ＩＣ３４８星团的Ｋ波段光度函数和作者获得的ＮＧＣ６６３Ｉ波段的光度函数，将它们分别与不同年龄一次形成或分批形成的模型计算结果作了比较，认为Ｔｒａｐｅｚｉｕｍ星团的年龄为５×１０５年，ＩＣ３４８则为４－６×１０６年，且它们的成员星可能是持续产生的．ＮＧＣ６６３的年龄据推算在１－３×１０７年之间．     

The Global, Local and Cluster Galaxy Luminosity Function

We review selected measurements of the galaxy luminosity function including the field, the local group, the local sphere, nearby clusters (Virgo, Coma and Fornax) and clusters in general. We conclude that, excluding the super-luminous cD and D galaxies, the overall cluster luminosity function is fully consistent with the field luminosity function over the magnitude range in common (–22 ≤ M _B –5log _{h 0.68} ≤ –17). We find that only in the core regions of clusters (r ≤ 300 kpc) does the overall form of the luminosity function show significant variation. However when the luminosity function is subdivided by spectral type some further variations are seen. We argue that these results imply: substantial late infall, efficient star-formation suppression, and the confinement of mass-changing evolutionary processes to the core regions only. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Correlation between Optical Spectral Index and Continuum Luminosity Variation in the Seyfert 1 Galaxy NGC 5548

Using the archived optical spectra of NGC 5548 between 1989 and 2001, we derived the optical spectral index by fitting the spectra in wavelength windows unaffected by strong emission lines. We found that the index is anti-correlated with the continuum luminosity at 5100 A with a correlation coefficient of -0.8. Based on the standard thin accretion disk model, we investigated whether the correlation is related to the variations of the dimensionless accretion rate m (mass accretion rate in Eddington unit), or the inner radius of the accretion disk Rin, or both. The correlation can be modeled well using a co-variable mode of Rin/Rs = 12.5m-0.8 (Rs is Schwarzschild radius). As luminosity increases, m increases from 0.05 to 0.16 and at the same time Rin decreases from 133.9.RS to 55.5.RS, consistent with the prediction for a transition radius within which an ADAF structure exists. We concluded that the change of both inner accretion radius and the dimensionless accretion rate are key factors for the variation     

Discovery of Three Large HII Regions in the Galactic Plane

We discovered three large HII regions:G148.8 2.3,G149.5 0.0 and G169.9 2.0 in the Sino-German λ6 cm polarization survey of the Galactic plane.They have been identi fied based on the flat spectral indexes and the strong infrared emission properties.