Nuclei Of Spiral Galaxies Research Articles

A MULTIWAVELENGTH VIEW OF A MASS OUTFLOW FROM THE GALACTIC CENTER

The Galactic center (GC) lobe is a degree-tall shell of gas that spans the central degree of our Galaxy. It has been cited as evidence for a mass outflow from our GC region, which has inspired diverse models for its origin. However, most work has focused on the morphology of the GC lobe, which has made it difficult to draw strong conclusions about its nature. Here, I present a coherent, multiwavelength analysis of new and archival observations of the GC lobe. Radio continuum emission shows that the GC lobe has a magnetized layer with a diameter of 110 pc and an equipartition field strength ranging from 40 to 100 $\mu$G. Recombination line emission traces an ionized shell nested within the radio continuum with diameter of 80 pc and height 165 pc. Mid-infrared maps at 8 and 15 $\mu$m show that the GC lobe has a third layer of warm dust and PAH-emission that surrounds the radio continuum shell with a diameter of 130 pc. Assuming adiabatic expansion of the gas in the GC lobe, its formation required an energy input of about $5\times10^{52}$ ergs. I compare the physical conditions of the GC lobe to several models and find best agreement with the canonical starburst outflow model. The formation of the GC lobe is consistent with the currently observed pressure and star formation rate in the central tens of parsecs of our Galaxy. Outflows of this scale are more typical of dwarf galaxies and would not be easily detected in nearby spiral galaxies. Thus, the existence of such an outflow in our own Galaxy may indicate that it is relatively common phenomenon in the nuclei of spiral galaxies. (Abridged)

New active galactic nuclei among the INTEGRAL and SWIFT X-ray sources

We present the results of our optical identifications of a set of X-ray sources from the INTEGRAL and SWIFT all-sky surveys. The optical data have been obtained with the 1.5-m Russian-Turkish Telescope (RTT-150). Nine X-ray sources have been identified with active galactic nuclei (AGNs). Two of them are located in the nearby spiral galaxies MCG-01-05-047 and NGC 973 seen almost edge-on. One source, IGR J16562-3301, is probably a BL Lac object (blazar). The remaining AGNs are observed as the starlike nuclei of spiral galaxies whose spectra exhibit broad emission lines. The relation between the hard X-ray (17–60 keV) luminosity and the [O III] 5007 line luminosity, log Lx/L[O III] ≈ 2.1, holds good for most of the AGNs detected in hard X rays. However, the luminosities of some AGNs deviate from this relation. The fraction of such objects can reach ∼20%. In particular, the [O III] line flux is lower for two nearby edge-on spiral galaxies. This can be explained by the effect of absorption in the galactic disks.

Molecular clouds in the center of M 81

We investigate the molecular gas content and the excitation and fragmentation properties in the central region of the spiral galaxy Messier 81 in both the 12CO(1–0) and 12CO(2–1) transitions. We have recently observed the two transitions of CO in the M 81 center with A, B, and HERA receivers of the IRAM 30-m telescope. We find no CO emission in the inner ~300 pc and a weak molecular gas clump structure at a distance of around 460 pc from the nucleus. Observations of the first two CO transitions allowed us to compute the line ratio, and the average ratio is 0.68 for the M 81 center. This low value, atypical both of the galactic nuclei of spiral galaxies and of interacting systems, is probably associated to diffuse gas with molecular hydrogen density that is not high enough to excite the CO molecules. After analyzing the clumping properties of the molecular gas in detail, we identify very massive giant molecular associations (GMAs) in CO(2–1) emission with masses of ~105 and diameters of ~250 pc. The deduced N(H2)/ICO ratio for the individually resolved GMAs, assumed to be virialized, is a factor of ~15 higher than the standard Galactic value, showing – as suspected – that the X ratio departs significantly from the mean for galaxies with an unusual physics of the molecular gas.

Nuclear Stellar Populations in theInfrared Space ObservatoryAtlas of Bright Spiral Galaxies

To understand the nuclear stellar populations and star formation histories of the nuclei of spiral galaxies, we have obtained K-band nuclear spectra for 41 galaxies and H-band spectra for 20 galaxies in the ISO Atlas of Bright Spiral Galaxies. In the vast majority of the subsample (80%), the near-infrared spectra suggest that evolved red stars completely dominate the nuclear stellar populations and that hot young stars are virtually non-existent. The signatures of recent star formation activity are only found in 20% of the subsample, even though older red stars still dominate the stellar populations in these galaxies. Given the dominance of evolved stars in most galaxy nuclei and the nature of the emission lines in the galaxies where they were detected, we suggest that nuclear star formation proceeds in the form of instantaneous bursts. The stars produced by these bursts comprise only ~2% of the total nuclear stellar mass in these galaxies, but we demonstrate how the nuclear stellar populations of normal spiral galaxies can be built up through a series of these bursts. The bursts were detected only in Sbc galaxies and later, and both bars and interactions appeared to be sufficient but not necessary triggers for the nuclear star formation activity. The vast majority of galaxies with nuclear star formation were classified as HII galaxies. With one exception, LINERs and transition objects were dominated by older red stars, which suggested that star formation was not responsible for generating these galaxies' optical line emission.

Massive black holes in the nuclei of spiral galaxies - M31 and the problem on the initial conditions

The formation of a stationary black hole is constrained by the conditions M > 3 M ⊙ and cJ/GM 2 ≡ a/m < 1, J and M being the total angular momentum and mass of the configuration which has collapsed to the hole. Recent observations indicate that some spiral galaxies, like M31, harbor a massive black hole in their center. In the case of M31, for example, the mass of the hole is estimated to be of the order of 10 6 -10 7 M ⊙ . The a/m content of a fluid model for the bulge of a spiral galaxy is calculated and a search for the limiting mass and angular momentum distributions which would be compatible with the formation of a massive black hole in the center is realized

The activity of the nuclei of spiral galaxies and IR-emission

It is shown that the brightness of the spiral galactic nuclei at 10μ depends on the Byurakan type of galaxies: the brightness is higher in the case of galaxies of types 5, 2s, 4, and 2 with optical signs of activity in comparison with galaxies of types 3 and 1 without optical signs of activity. The noted difference is larger when nonstellar emission at 10μ is considered. The obtained results confirm conclusions made earlier on the activity of the nuclei of galaxies of types 5, 2s, 4, and 2.

Detailed spectrophotometric investigation of the galaxy Mark. 307

Spectra obtained with the 6-m telescope of the Special Astrophysical Observatory have been used to make a detailed spectrophotometric investigation of the spiral galaxy Mark. 307. For the nuclear region and five condensations in the spiral arms, the relative intensities of the emission lines have been used to estimate the values of T/sub e/ and n/sub e/, the abundances of the elements O, N, and S, the masses and volumes of ionized gas, and the number of 09 stars. On the basis of its parameters, the nuclear region of the galaxy is identical to the nuclei of spiral galaxies. One giant H II region is distinguished among the condensations by all its physical parameters; the scale of star formation in it probably exceeds that of the nuclear region of the galaxy.

Evidence for a central massive component in late-type spirals

view Abstract Citations (20) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for a Central Massive Component in Late-Type Spirals Rubin, Vera C. ; Graham, J. A. Abstract New rotation curves have been obtained for the purpose of probing the distribution of matter at small radial distances from the nuclei of spiral galaxies. Four Sc galaxies, NGC 2742, 3198, 5676, and 6643, have rotation velocities that remain high at the first measured point, which is generally within 250 pc of the nucleus. Elementary modeling applied to one galaxy, NGC 2742, shows that a significant central mass concentration (about 10 to the 8th solar masses interior to 250 pc) is present. The new data confirm that the rotation curve as a whole is an excellent criterion of absolute magnitude and one which can be used to investigate anisotropies in the Hubble flow. Intrinsically broad nuclear emission lines are found for the first time in NGC 5985 and are observed again in some previously reported examples (NGC 2639, 4594, 5506, and 6764). NGC 4845 shows an interesting boxlike morphology and an emission-line inner velocity field which cannot arise froma simple rotating disk. Publication: The Astrophysical Journal Pub Date: May 1987 DOI: 10.1086/184894 Bibcode: 1987ApJ...316L..67R Keywords: Galactic Nuclei; Galactic Rotation; Hubble Diagram; Spiral Galaxies; Legendre Functions; Random Sampling; Seyfert Galaxies; Astrophysics; GALAXIES: NUCLEI; GALAXIES: INTERNAL MOTIONS full text sources ADS | data products SIMBAD (10) NED (10)

Study of the radiation emitted by the nuclei of spiral galaxies

The distribution of the U - B, B - V, J - H, and H - K colors of the central regions of galaxies with different estimates of the Byurakan classification is studied. It is shown that in the nuclear regions of many galaxies with estimates 5 and 2s, and also 2 and 4, there is an ultraviolet excess. In the nuclear regions of galaxies with estimates 5, 4, and 2s there is also excess infrared radiation.

Radio Continuum Emission and Optical Emission-Line Activity in the Nuclei of Spirals

As a step towards the understanding of the phenomena occurring in galactic nuclei, we find that the ratio between the radio continuum emission of the nuclei of spiral galaxies and their optical luminosity is related to optical signs of nuclear activity, such as the emission line strengths of the H∝ and [NII] λ6584 lines.

Spectrophotometry of the galaxies Markaryan 367, 449, and 1119

Spectra obtained with the 6-m telescope of the Special Astrophysical Observatory have been used to make a spectrophotometric investigation of the central regions of the galaxies Mark. 367, 449, and 1119. The relative intensities of the emission lines have been used to estimate T/sub e/ and n/sub e/, the abundances of the elements O and N, the masses and volumes of ionized gas, and the number of 07 stars. The galaxy Mark. 1119 recalls blue compact galaxies with a powerful burst of star formation. The central regions of Mark. 367 and 449 have the characteristics of the nuclei of spiral galaxies with a burst of star formation

Infrared characteristics of the nuclei of normal galaxies

view Abstract Citations (90) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Characteristics of the Nuclei of Normal Galaxies Devereux, Nicholas A. ; Becklin, E. E. ; Scoville, Nick Abstract A study of the infrared emission for a sample of 191 spiral, S0, and elliptical galaxies was performed in order to determine the level of nuclear star formation and investigate the factors that may modulate it. The near-infrared luminosity was found to be a tracer of the mass for the nuclei of normal galaxies. A mean of 0.7 solar mass/solar luminosity was obtained from the combination of near-infrared and nuclear velocity dispersion data. The 1-2 micron luminosity function exhibits an exceptionally sharp cutoff which is independent of Hubble type and corresponds to a limiting stellar mass density of about 200 solar mass/cu pc over the central 500 pc. Ten micron emission was observed in the nuclei of spiral galaxies of all Hubble types, but with no obvious dependence on the cluster environment, the presence of a stellar bar, or the depth of the central potential. The data showed that the level of far-infrared emission in late-type spirals is typically twice that of the early types and that there is little difference between the Virgo and field spiral galaxies. Publication: The Astrophysical Journal Pub Date: January 1987 DOI: 10.1086/164899 Bibcode: 1987ApJ...312..529D Keywords: Astronomical Spectroscopy; Galactic Nuclei; Galactic Structure; Infrared Spectra; Mass To Light Ratios; Astronomical Catalogs; Barred Galaxies; Elliptical Galaxies; Star Distribution; Astrophysics; GALAXIES: NUCLEI; GALAXIES: PHOTOMETRY; GALAXIES: STELLAR CONTENT; INFRARED: SOURCES full text sources ADS | data products NED (191) SIMBAD (189)

A comparative study of the stellar content in normal and active nuclei of spiral galaxies

We present spectrophotometry andUBV photometry of the central region of spiral galaxies. The sample consists of the Seyfert galaxies NGC 1566, 3783 and IC 4329A; NGC 1097, 2997, and 5236 containing peculiar nucleus and NGC 5530, 5643, and 6699 with normal nucleus.

Multiaperture infrared photometry of the nuclei of spiral galaxies

view Abstract Citations (20) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiaperture infrared photometry of the nuclei of spiral galaxies. Cizdziel, P. J. ; Wynn-Williams, C. G. ; Becklin, E. E. Abstract Results of a multiaperture, 2.2- and 10-micron photometric survey of the nuclei of 25 nearby, low-inclination spiral galaxies are presented. The 10-micron nuclear luminosities, attributed to thermal reradiation by dust in regions of active star formation, and 10-micron/2.2-micron nuclear flux ratios, are examined as a function of the slope of 2.2-micron growth curve. No correlation is seen, suggesting that the contribution of young, red giants and supergiants to the near-infrared light of spiral nuclei is small. These results indicate that the 2.2-micron light of galaxies in the present sample is not radically altered by starbursts. Publication: The Astronomical Journal Pub Date: May 1985 DOI: 10.1086/113780 Bibcode: 1985AJ.....90..731C Keywords: Astronomical Photometry; Galactic Nuclei; Infrared Astronomy; Spiral Galaxies; Stellar Luminosity; Thermal Radiation; Far Infrared Radiation; H Alpha Line; Molecular Clouds; Red Giant Stars; Stellar Evolution; Stellar Flares; Astrophysics full text sources ADS | data products SIMBAD (27) NED (27)

A 10 micron survey of star formation in galactic nuclei Virgo spiral galaxies

A survey for 10 micron emission in the nuclei of spiral galaxies in the Virgo cluster is reported. It is found that the nuclei of most luminous spiral galaxies are active 10 micron emitters, and that the luminosity function for the sample can be represented by a simple power law over the entire range sampled. The most luminous sources at 10 microns show only a weak correlation with total optical luminosity, and no correlation with morphological type or location in the cluster. It is argued that the 10 micron flux from the Virgo galaxies arises from active star formation regions. A mean far-IR luminosity of two billion solar luminosities is inferred for the galactic nuclei; the required rate of massive star formation is 0.1 solar masses/yr. The results suggest that the rate of star formation in galactic nuclei has little relationship to the size of the nuclear bulge or the gravitational potential near the center.

Optical spectroscopy of the radio-loud nuclei of spiral galaxies - Starbursts or monsters?

view Abstract Citations (80) References (68) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical spectroscopy of the radio-cloud nuclei of spiral galaxies : starbursts or monsters ? Heckman, T. M. ; van Breugel, W. ; Miley, G. K. ; Butcher, H. R. Abstract Optical spectroscopic data pertaining to the physical state, kinematics and spatial extent of emission line gas near the radio-loud nuclei of spiral galaxies are combined with published optical, radio and IR data, in an examination of the Condon et al (1982) suggestion that the nuclear radio emission in galaxies of this class is produced by multiple SNRs generated by a nuclear starburst. It is found that only about 1/3 of the spiral galaxies examined have optical spectroscopic properties consistent with those of 'extranuclear starbursts'. Evidence is adduced for the view that the putative nuclear starbursts must differ significantly from extranuclear starbursts. While giant H II regions generally have thermal radio emission, the radio-loud nuclei exhibit nonthermal radio emission whose spectrum is much steeper than that of SNRs. Publication: The Astronomical Journal Pub Date: August 1983 DOI: 10.1086/113397 Bibcode: 1983AJ.....88.1077H Keywords: Astronomical Spectroscopy; Galactic Nuclei; Radio Sources (Astronomy); Spiral Galaxies; Bursts; Galactic Structure; H Ii Regions; Infrared Astronomy; Nonthermal Radiation; Optical Emission Spectroscopy; Starburst Galaxies; Supernova Remnants; Astronomy full text sources ADS | data products SIMBAD (43) NED (38)

The distribution of ionized gas in the nuclei of spiral galaxies

view Abstract Citations (67) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The distribution of ionized gas in the nuclei of spiral galaxies. Keel, W. C. Abstract Narrow-band digital images have been obtained for a sample of spiral galaxies selected to contain low-ionization emission regions in their nuclei. The images have been processed to yield pure H-alpha + forbidden N II images. These show that the optically emitting gas is usually concentrated in a nearly spherical core of half-intensity diameter typically 200 pc, often surrounded by a disk, in the galactic plane, traceable over a 600-900 pc diameter. This gas disk is not present in several cases in which it is expected by comparison with others of similar luminosity in emission, showing that some morphological variety exists among these emission regions. Publication: The Astrophysical Journal Pub Date: May 1983 DOI: 10.1086/160985 Bibcode: 1983ApJ...268..632K Keywords: Galactic Nuclei; Interstellar Gas; Ionized Gases; Mass Distribution; Spiral Galaxies; Astronomical Maps; Emission Spectra; Fine Structure; Line Spectra; Astrophysics full text sources ADS | data products SIMBAD (35) NED (35)

Observations of ultraviolet spectra of H II regions and galaxies with IUE

The ultraviolet spectra, obtained with the International Ultraviolet Explorer, of a sample of H II regions and the nuclear regions of spiral and elliptical galaxies are described. The star formation rates in the nuclei of spiral galaxies are similar to the star formation rate in the solar neighbourhood. The data indicate that the current thinking on the synthesis of carbon and nitrogen in galaxies has to be revised and the K-corrections determined from the ultraviolet spectra of galaxies when compared with the photometry of distant galaxies suggests colour evolution of galaxies at z > 0.3.

Stellar Populations in the Nuclei of Spiral Galaxies

Spiral galaxies are a composite of two dynamical population types: the spheroidal and disk populations. These can be studied in isolation in E and Irr galaxies, respectively. It is natural to expect that the combination in a spiral of a dense spheroidal population, having a deep central potential well, with a repository of interstellar gas and dust in the disk gives rise to special conditions not usually found in E or Irr galaxies. And in fact, we find spectacular concentrations of star forming regions in some spiral nuclei.In this review, I will limit most of the discussion to later spiral types which are classified as “intermediate” in the Yerkes system (Morgan and Osterbrock 1969). Types earlier than Sbc usually have “k-nuclei,” where the spheroidal population dominates; excellent reviews are available for these types (van den Bergh 1975, Faber 1977).

Further comments on the radio emission of the nuclei of spiral galaxies

The results of new radio observations of spiral galaxies [6] confirm the reality of the correlation found earlier [l-S] between radio emission of galaxies and optical signs of activity of their nuclei, namely, central; compact radio sources are found mainly in the galaxies which are observed to have split, starlike, or semistellar nuclei~ It is also shown that the surface brightnesses of galaxies with bright central condensations of relas large diameter (designated S in the Byurakan classification) are on the average higher if the galaxies have central compact radio sources~ It is suggested that the higher surface brightnesses of galaxies with central radio sources are due in all probability to the existence of not too bright starlike nuclei which cannot be distinguished on the background of the bright central parts of these galaxies.