Spectrophotometric Study of the Region of the Sky Around the Galaxies Markarian 261 and 262

Results are presented from a detailed spectrophotometric study of a unique system of physically coupled galaxies whose spectra contain identical emission lines. This system consists of four galaxies, three of which have a double or multiple structure in their central portions and are, by definition, galaxies with two or multiple nuclei. Two of these objects are the galaxies with an ultraviolet excess (UVE), Mark 261 and Mark 262, while one is a galaxy made up of two identical starlike nuclei that are referred to as the “twin objects.” In the DSS2 charts, the latter show up as two adjacent stars without any surroundings. However, there are two condensations between these starlike nuclei. The fourth object has a triplet structure. It is shown here that all these objects have the same emission (line) spectra and red shifts. All the physical characteristics that can be determined from the spectra are determined: red shifts, relative intensities of emission lines, their equivalent widths, distances to the galaxies, etc. It is concluded that the members of this system have a common origin, more or less consistent with Ambartsumyan's idea of the fragmentation of an isolated, high density body. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 503–514 (November 2005).     

New Galaxies with UV Excess. VI

A list is presented of 122 new galaxies with UV excess observed on plates obtained using the 40″ Schmidt telescope at the Byurakan Observatory with a 1°.5 objective prism. It is shown that the relative number of galaxies with a strong UV excess (classes 1 and 2) listed in Table 1 is roughly 55.7%. This is 6.7% higher than for the previously observed galaxies. These samples also differ in terms of the morphology of the spectra. The largest deviation, approximately 9.9%, occurs for type “sd.”__________Published in Astrofizika, Vol. 48, No. 3, pp. 393–408 (August 2005).     

Spectroscopic Study of Multiple IRAS Galaxies

Spectroscopic observations by the 2.6 m BAO telescope of IRAS galaxies identified on the basis of the First Byurakan Survey (BIG objects) are reported. Slit spectra were obtained for 16 objects, including components of 7 multiple systems and 2 individual galaxies. The red shifts were measured, and the radial velocities, distances, absolute stellar magnitudes, and infrared and far infrared luminosities were calculated. A diagnostic diagram has been constructed based on the intensity ratios of emission lines and the activity types of the objects have been determined. Two LINERs, five galaxies with composite spectra (Comp, one of which has Sy2 features) and seven HII regions were found. Two objects are ultraluminous IR galaxies (ULIG). It is shown that all the multiple systems are physical pairs or groups. The observed high IR luminosity confirms the view that ULIG/HLIGs may be associated with interactions of galaxies.     

Spectroscopic Observations of New Galaxies with a UV Excess. III

The results of the spectroscopic observation of 23 galaxies with a UV excess from Kazarian's lists are presented. The spectra were obtained on the 2.6-m telescope of Byurakan Observatory with a Byu FOSC-2 camera. Two grisms, red and green, were used in the observations. Emission lines are observed in the spectra of 21 of the galaxies.     

A Study of 2MASS Low Surface Brightness Galaxies

A study is being made of a sample of about 4,000 Low Surface Brightness (LSB) galaxies detected in the 2MASS all-sky near-infrared survey. These objects have similar central K-band surface brighnesses as optically selected LSBs. About 1,000 of them were observed in HI, and one third of these were detected. BVRI CCD photometry was obtained of 65 objects. These multi-wavelength data provide us with important information on a large, homogenous sample of LSB galaxies (e.g., colors, gas content). They will be used to construct models of the star formation histories and evolution of LSBs, and for a study of their Tully-Fisher (TF) relation, particularly to search for deviations from the ‘classical’ TF relation. This revised version was published online in September 2006 with corrections to the Cover Date.     

Soft X—ray Properties of Ultraluminous IRAS Galaxies

We report on the results of cross-correlation of a sample of 903 Utraluminous IRAS galaxies (ULIRGs) with the ROSAT-All Sky Survey Bright Source Catalogue and the ROSAT archived pointing observations. The sample of ULIRGs has been compiled from the recently released PSCz redshift survey. In total,35 ULIRGs are securely detected by the ROSAT All-Sky Survey and pointing observations, five of which are blazars. The statistical properties of these sources in the soft X-ray band are determined and compared with their properties on other wavebands. We find that the ratio of the soft X-ray to the far-infrared flux spans about five orders of magnitude and reaches values of about unity. This ratio is a good indicator of the main energy source of ULIRGs. Those with soft X-ray to far-infrared flux exceeding 0.01 are probably powered by accretion onto central supermassive black holes while those with ratios smaller than 0.001 are probably powered by starbursts or other heating processes, or are Compton thick sources. Some ULIRGs have energy contributions from both. This ratio is low for most ULIRGs and hyperluminous infrared galaxies, which explains their low detection rate by ROSAT and ASCA.We also find that some ULIRGs have a similar soft X-ray luminosity vs. temperature relation to that for groups of galaxies and elliptical galaxies,suggesting a common origin of these systems. Our study also reveals a tight correlation between the hardness ratio and the soft X-ray luminosity for Seyfert 1s/QSOs.     

棒对星系核区恒星形成活动的影响

利用SDSS光谱,研究了IRAS卫星亮红外源星表中的盘状星系中的恒星形成性质,并着重探讨了棒对星系核区恒星形成活动的影响.利用星族合成的方法得到了每个样本星系核区的恒星组成性质、恒星形成活动的强度等信息,并比较了星系整体和核区恒星形成性质的差异.得到的结论:除去相互作用,样本中的棒星系显示出比非棒旋星系更强的核区恒星形成活动和更多的年轻星族成分.     

Merging Massive Star Clusters as Building Blocks of Dwarf Galaxies?

Recent spectroscopic observations of galaxies in the Fornax-Cluster reveal nearly unresolved ‘star-like’ objects with red-shifts appropriate to the Fornax-Cluster. These objects have intrinsic sizes of ≈ 100 pc and absolute B-band magnitudes in the range - 14 < M_B < -11.5 mag and lower limits for the central surface brightness μ_B ≥ 23 mag/arcsec² (Phillipps et al., 2001, Hilker et al., 1999), and so appear to constitute a new population of ultra-compact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar super-clusters (= clusters of star clusters; not to confuse with super stellar clusters (SSC)) by P. Kroupa (1998), which are rich aggregates of young massive star clusters (YMCs) that can form in collisions between gas-rich galaxies. Here we present the evolution of super-clusters in a tidal field. The YMCs merge on a few super-cluster crossing times. Super-clusters that are initially as concentrated and massive as Knot S in the interacting Antennae galaxies (Whitmore et al., 1999) evolve to merger objects that are long-lived and show properties comparable to the newly discovered UCDs. This revised version was published online in September 2006 with corrections to the Cover Date.     

New insights into the photometric structure of Blue Compact Dwarf Galaxies from a deep Near-Infrared study

We present deep Near-Infrared (NIR) imaging of Blue Compact Dwarf Galaxies (BCDs), allowing for the first time to derive and systematize the NIR structural properties of their stellar low-surface brightness (LSB) host galaxies. Compared to optical data, NIR images, being less contamined by the extended stellar and ionized gas emission from the starburst, permit to study the LSB host galaxy closer to its center. We find that radial surface brightness profiles (SBPs) of the LSB hosts show at large radii a mostly exponential intensity distribution, in agreement with previous optical studies. At small to intermediate radii, however, the NIR data reveal an inwards flattening with respect to the outer exponential slope (`type V SBPs', Binggeli and Cameron, 1991) in the LSB component of more than one half of the sample BCDs. This result may constitute an important observational constraint to the dynamics and evolution of BCDs. We apply a modified exponential fitting function (Papaderos et al., 1996a) to parametrize and systematically study type V profiles in BCDs. A Sérsic law is found to be less suitable for studying the LSB component of BCDs, since it yields very uncertain solutions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interacting Galaxies — the X-ray View

We have selected a complete, flux-limited sample of bright point-like sources with absorbed X-ray spectra from the ROSAT All-Sky survey, the ROSAT Hard Survey (RHS). The sample is drawn from the high-galactic latitude sky, |b^II| > ±30°, and avoids the general direction of the Magellanic Clouds and the Virgo Cluster. It comprises a total of 182 objects of which 118 were previosly catalogued objects and 64 were new AGN candidates. Through optical follow-up studies at La Silla, Calar Alto and the 6m Zelentchuk telescope we could identify 56 of the new objects, thus achieving a spectrscopic completeness of 96% of the sample. The selection strategy turned out to be extremely useful. Out of the new identifications, 84% are indeed active galaxies or emission line galaxies. While 14 objects are new BL Lac candidates 33 of the new AGN are Seyfert galaxies with a redshift distribution in the range 0.021–0.63, peaking at around 0.06, i.e. relatively local. Surprisingly, about 40% of the X-ray selected Seyfert galaxies seem to reside in interacting systems. With smaller selection uncertainties this fraction exceeds the number of paired galaxies in optically selected samples and therefore gives strong support to the idea that AGN activity is triggered by interaction.     

The Effect of Bar on Star-forming Activities in Nuclear Regions of Nearby Spiral Galaxies

By using the SDSS spectra, we have studied the star formation properties of the nearby spiral galaxies selected from the Revised Bright Galaxy Sample, and tried to find the effect of bar structure on the star formation activity in the nuclear regions of nearby galaxies. The stellar population composition and the intensity of star formation activities of each sample galaxy are acquired by using the stellar population synthesis code—STARLIGHT, and the star formation properties of nuclear regions are compared with those of integral sample galaxies. We find that the star formation in barred spiral galaxies is more active than that of unbarred spirals, and that barred spirals have younger stellar populations.     

Spectral observations of galaxies with UV excess

Spectral observations of 19 galaxies with UV-excesses from Kazarian’s list are reported. The spectra were obtained with the 2.6-m telescope at the Byurakan Observatory using the SCORPIO spectral camera. A grism was used to obtain spectra in the wavelength interval λλ7420-3920 Å. 43 spectra in which emission lines are mainly observed were obtained from the 19 galaxies, except for the spectra of Kaz 21, Kaz 178, Kaz 183, and Kaz 184. The spectra of Kaz 17, Kaz 151, Kaz 153, and Kaz 357 have type Sy2 galactic features. In the spectra of the galaxies Kaz 17, Kaz 151, and Kaz 153, absorption lines are observed along with high excitation emission lines such as HeI λ5876 Å and HeII λ4686 Å. No lines were observed within the interval λλ7420-3920 Å in the spectra of the galaxies Kaz 183 and Kaz 184. __________ Translated from Astrofizika, Vol. 49, No. 3, pp. 351–358 (August 2006).     

Head-on Collision of Disk–Sphere Galaxies

Numerical simulations are performed to study the tidal effects of non-merging rapid head-on collision between a disk galaxy and a spherical galaxy. The disk consists of three components – a disk, a bulge and a halo – and the spherical galaxy is a Plummer model. The galaxies have the same dimensions with different mass ratios viz., 2, 1 and 0.5. They move in a rectilinear orbit with a relative velocity of 1000 km s⁻¹. None of the simulations leads to the merger of the galaxies by tidal capture. The results of our simulations indicate that although tidal effects are sensitive to both the mass ratio and the inclination of the disk to the orbital plane, it is the mass ratio which is more important in producing tidal damage to the less massive galaxy. The spherical galaxy undergoes considerable tidal effects if the mass of the disk is same or larger. On the other hand the collisions in which the mass of the spherical galaxy is more, result in the formation of a ring structure after the closest approach and the structure disappears by the end of the simulations.     

Properties of Galaxies in the Second Byurakan Survey. II. Characteristic Features of a Separate Sample of Galaxies

Some features of a sample of galaxies from the Second Byurakan Survey are discussed. Most of them are small galaxies with star formation. It is shown that different types of galaxies are in the Survey, with high, medium, and low levels of excitation and continua ranging from blue to relatively red. Many of the galaxies have absorption lines in their spectra; their continua are formed by stars in later spectral classes.     

OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系

利用66个OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系,得到log L(OH)=1.71log L(IR)-17.67,即L(OH)α[L(IR)]1。71.这个结果介于Baan所得到的L(OH)α[L(IR)]2和Kandalian所得到的L(OH)α[L(IR)]1.38的结果之间.由于统计时所取的样本数最多,因此结果更能反映实际情况.进一步,可把这66个OH megamaser分为两类;第一类为L(OH)<102L(?)的小光度OH megamaser,小光度OH megamaser包含了14个OH megamaser;第二类为L(OH)≥102L的大光度OH megamaser,大光度OH megamaser包含了52个OHmegamaser.研究结果表明,小光度OH megamaser的光度和它们的宿主星系的红外光度之间相关关系为L(OH)α[L(IR)]1.43,与Kandalia所得到的结果相接近.大光度OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系为L(OH)α[L(IR)]2,与Baan所得到的结果相一致.     

旋涡星系密度波理论中Poisson积分的简化及应用

本文给出了旋涡星系密度波理论中Poisson积分的一种简化方法。这一简化的最重要应用在于利用它计算旋涡模式时可节省大量计算机时。此外本文还利用这种简化方法对一系列密度——引力势渐近关系进行了系统的数值检验。 用这一简化方法计算核函数比用未简化的核函数形式直接计算节省机时八十四倍。当在数值模式理论研究中大量计算Poisson积分时,应用本文提出的简化将有效地提高计算效率并保证足够高的精度。     

南银极区星系与类星体候选者的相关性研究

对南银极区的亮星系样本和类星体候选者样本进行了两点交叉相关函数分析,最邻近间距分析和Kolmogorov-Smirnov检验;结果表明这两个样本之间不存在显著性相关。     

Measurements of the Stellar Velocity Dispersions of Seyfert Galaxies

The close relation between the mass of the central black hole of galaxy and the stellar velocity dispersion of bulge indicates that it is of especial importance to accurately measure the stellar velocity dispersion for determining the mass of the central black hole of galaxy. A method which uses the spectra of SDSS (Sloan Digital Sky Survey) to measure the velocity dispersion and its uncertainty is provided in this paper. Through fitting four different spectral regions which contain remarkable characteristic absorption lines in pixel space, the spectral regions used to accurately measure the stellar velocity dispersion σ are obtained. In this paper, the absorption lines which are mainly contained in these four fitted bands are Ca II K, Mg I b triplet (with wavelengths of 5 167.5, 5 172.7, 5 183.6 Å) and CaT (Ca II triplet with wavelengths of 8 498.0, 8 542.1, 8 662.1 Å). As indicated by the results in different regions, the values of σ obtained by fitting the Mg I b region are small because this region is affected by the emission lines of iron group; the spectral line in the Ca II K line region is easily restricted to the searching algorithm of least square method because its strength is very weak; the stellar velocity dispersions obtained in the combined region of CaT and Ca II K are equivalent to the results given by calculating only the CaT region. This method is used to test a sample of Seyfert galaxies whose redshifts are less than 0.05. It is found that the CaT region is the best spectral region for measuring the stellar velocity dispersion.