Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
The impact of the visibility of the [OIII]λ4363 line on the general properties of HII galaxies in the Local Universe
We present a statistical study of a very large sample of HII galaxiestaken from the literature. We focus on the differences in severalproperties between galaxies that show the auroral line[OIII]λ4363 and those that do not present this feature in theirspectra. It turns out that objects without this auroral line are moreluminous, are more metal-rich and present a lower ionization degree. Theunderlying population is found to be much more important for objectswithout the [OIII]λ4363 line, and the effective temperature ofthe ionizing star clusters of galaxies not showing the auroral line isprobably lower. We also study the subsample of HII galaxies whoseproperties most closely resemble the properties of theintermediate-redshift population of luminous compact blue galaxies(LCBGs). The objects from this subsample are more similar to the objectsnot showing the [OIII]λ4363 line. It might therefore be expectedthat the intermediate-redshift population of LCBGs is powered by verymassive, yet somewhat aged, star clusters. The oxygen abundance of LCBGswould be greater than the average oxygen abundance of local HIIgalaxies.
| A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds
We present a Far Ultraviolet Spectroscopic Explorer survey of highlyionized high-velocity clouds (HVCs) in 66 extragalactic sight lines with(S/N)1030>8. We search the spectra for high-velocity (100km s-1<|vLSR|<400 km s-1) O VIabsorption and find a total of 63 absorbers, 16 with 21 cm emitting H Icounterparts and 47 ``highly ionized'' absorbers without 21 cm emission.The highly ionized HVC population is characterized by =38+/-10 km s-1 and =13.83+/-0.36, with negative-velocity clouds generally found atl<180deg and positive-velocity clouds found atl>180deg. Eleven of these highly ionized HVCs arepositive-velocity wings (broad O VI features extending asymmetrically tovelocities of up to 300 km s-1). We find that 81% (30 of 37)of highly ionized HVCs have clear accompanying C III absorption, and 76%(29 of 38) have accompanying H I absorption in the Lyman series. Wepresent the first (O VI selected) sample of C III and H I absorptionline HVCs and find =30+/-8 km s-1,logNa(C III) ranges from <12.5 to >14.4, =22+/-5 km s-1, and log Na(H I) ranges from<14.7 to >16.9. The lower average width of the high-velocity H Iabsorbers implies the H I lines arise in a separate, lower temperaturephase than the O VI. The ratio Na(C III)/Na(O VI)is generally constant with velocity in highly ionized HVCs, suggestingthat at least some C III resides in the same gas as the O VI.Collisional ionization equilibrium models with solar abundances canexplain the O VI/C III ratios for temperatures near1.7×105 K; nonequilibrium models with the O VI ``frozenin'' at lower temperatures are also possible. Photoionization models arenot viable since they underpredict O VI by several orders of magnitude.The presence of associated C III and H I strongly suggests the highlyionized HVCs are not formed in the hotter plasma that gives rise to OVII and O VIII X-ray absorption. We find that the shape of the O VIpositive-velocity wing profiles is well reproduced by a radiativelycooling, vertical outflow moving with ballistic dynamics, withT0=106 K, n0~2×10-3cm-3, and v0~250 km s-1. However, theoutflow has to be patchy and out of ionization equilibrium to explainthe sky distribution and the simultaneous presence of O VI, C III, and HI. We found that a spherical outflow can produce high-velocity O VIcomponents (as opposed to the wings), showing that the possible range ofoutflow model results is too broad to conclusively identify whether ornot an outflow has left its signature in the data. An alternative model,supported by the similar multiphase structure and similar O VIproperties of highly ionized and 21 cm HVCs, is one where the highlyionized HVCs represent the low N(H I) tail of the HVC population, withthe O VI formed at the interfaces around the embedded H I cores.Although we cannot rule out the possibility that some highly ionizedHVCs exist in the Local Group or beyond, we favor a Galactic origin.This is based on the recent evidence that both H I HVCs and themillion-degree gas detected in X-ray absorption are Galactic phenomena.Since the highly ionized HVCs appear to trace the interface betweenthese two Galactic phases, it follows that highly ionized HVCs areGalactic themselves. However, the nondetection of high-velocity O VI inhalo star spectra implies that any Galactic high-velocity O VI exists atz distances beyond a few kpc.
| Multiwavelength Star Formation Indicators: Observations
We present a compilation of multiwavelength data on different starformation indicators for a sample of nearby star forming galaxies. Herewe discuss the observations, reductions and measurements of ultravioletimages obtained with STIS on board the Hubble Space Telescope (HST),ground-based Hα, and VLA 8.46 GHz radio images. These observationsare complemented with infrared fluxes, as well as large-apertureoptical, radio, and ultraviolet data from the literature. This databasewill be used in a forthcoming paper to compare star formation rates atdifferent wave bands. We also present spectral energy distributions(SEDs) for those galaxies with at least one far-infrared measurementsfrom ISO, longward of 100 μm. These SEDs are divided in two groups,those that are dominated by the far-infrared emission, and those forwhich the contribution from the far-infrared and optical emission iscomparable. These SEDs are useful tools to study the properties ofhigh-redshift galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| Dynamical Masses in Luminous Infrared Galaxies
We have studied the dynamics and masses of a sample of 10 nearbyluminous and ultraluminous infrared galaxies (LIRGs and ULIRGs,respectively) using 2.3 μm 12CO-absorption linespectroscopy and near-infrared H- and Ks-band imaging. Bycombining velocity dispersions derived from the spectroscopy, disk scalelengths obtained from the imaging, and a set of likely model densityprofiles, we calculate dynamical masses for each LIRG. For the majorityof the sample, it is difficult to reconcile our mass estimates with thelarge amounts of gas derived from millimeter observations and from astandard conversion between 12CO emission and H2mass. Our results imply that LIRGs do not have huge amounts of moleculargas (1010-1011 Msolar) at their centersand support previous indications that the standard conversion of12CO to H2 probably overestimates the gas massesand cannot be used in these environments. This in turn suggests muchmore modest levels of extinction in the near-infrared for LIRGs thanpreviously predicted (AV~10-20 vs. AV~100-1000).The lower gas mass estimates indicated by our observations imply thatthe star formation efficiency in these systems is very high and istriggered by cloud-cloud collisions, shocks, and winds rather than bygravitational instabilities in circumnuclear gas disks.Observations reported here were obtained at the MMT Observatory, a jointfacility of the University of Arizona and the Smithsonian Institution.
| Magnetic Fields in Starburst Galaxies and the Origin of the FIR-Radio Correlation
We estimate minimum energy magnetic fields (Bmin) for asample of galaxies with measured gas surface densities, spanning morethan four orders of magnitude in surface density, from normal spirals toluminous starbursts. We show that the ratio of the minimum energymagnetic pressure to the total pressure in the ISM decreasessubstantially with increasing surface density. For the ultraluminousinfrared galaxy Arp 220, this ratio is ~10-4. Therefore, ifthe minimum energy estimate is applicable, magnetic fields in starburstsare dynamically weak compared to gravity, in contrast to normalstar-forming spiral galaxies. We argue, however, that rapid cooling ofrelativistic electrons in starbursts invalidates the minimum energyestimate. We assess a number of independent constraints on the magneticfield strength in starburst galaxies. In particular, we argue that theexistence of the FIR-radio correlation implies that the synchrotroncooling timescale for cosmic-ray electrons is much shorter than theirescape time from the galactic disk; this in turn implies that the truemagnetic field in starbursts is significantly larger thanBmin. The strongest argument against such large fields isthat one might expect starbursts to have steep radio spectra indicativeof strong synchrotron cooling, which is not observed. However, we showthat ionization and bremsstrahlung losses can flatten the nonthermalspectra of starburst galaxies even in the presence of rapid cooling,providing much better agreement with observed spectra. We furtherdemonstrate that ionization and bremsstrahlung losses are likely to beimportant in shaping the radio spectra of most starbursts at GHzfrequencies, thereby preserving the linearity of the FIR-radiocorrelation. We thus conclude that magnetic fields in starbursts aresignificantly larger than Bmin. We highlight severalobservations that can test this conclusion.
| Ultraviolet-to-Far-Infrared Properties of Local Star-forming Galaxies
We present the results of a multiwavelength study of nearby galaxiesaimed at understanding the relation between the ultraviolet andfar-infrared emission in star-forming galaxies. The data set comprisesnew ultraviolet (from HST STIS), ground-based Hα, and radiocontinuum observations, together with archival infrared data (from IRASand ISO). The local galaxies are used as benchmarks for comparison ofthe infrared-to-ultraviolet properties with two populations ofhigh-redshift galaxies: the submillimeter star-forming galaxies detectedby SCUBA and the ultraviolet-selected Lyman break galaxies (LBGs). Inaddition, the long wavelength baseline covered by the present dataenables us to compare the star formation rates (SFRs) derived from theobserved ultraviolet, Hα, infrared, and radio luminosities and togauge the impact of dust opacity in the local galaxies. We also derive anew calibration for the nonthermal part of the radio SFR estimator,based on the comparison of 1.4 GHz measurements with a new estimator ofthe bolometric luminosity of the star-forming regions. We find that moreactively star-forming galaxies show higher dust opacities, which is inline with previous results. We find that the local star-forming galaxieshave a lower Fλ(205 μm)/Fλ(UV)ratio by 2-3 orders of magnitude than the submillimeter-selectedgalaxies and may have a similar or somewhat higherFλ(205 μm)/Fλ(UV) ratio thanLBGs. The Fλ(205 μm)/Fλ(UV) ratioof the local galaxy population may be influenced by the cool dustemission in the far-infrared heated by nonionizing stellar populations,which may be reduced or absent in the LBGs.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| Is HCN a True Tracer of Dense Molecular Gas in Luminous and Ultraluminous Infrared Galaxies?
We present the results of the first HCO+ survey probing thedense molecular gas content of a sample of 16 luminous and ultraluminousinfrared galaxies (LIRGs and ULIRGs). Previous work, based on HCN (1-0)observations, had shown that LIRGs and ULIRGs possess a significantlyhigher fraction of dense molecular gas compared to normal galaxies.While the picture issued from HCO+ partly confirms thisresult, we have discovered an intriguing correlation between the HCN(1-0)/HCO+ (1-0) luminosity ratio and the IR luminosity ofthe galaxy (LIR). This trend casts doubts on the use of HCNas an unbiased quantitative tracer of the dense molecular gas content inLIRGs and ULIRGs. A plausible scenario explaining the observed trendimplies that X-rays coming from an embedded active galactic nucleus mayplay a dominant role in the chemistry of molecular gas atLIR>=1012 Lsolar. We discuss theimplications of this result for the understanding of LIRGs, ULIRGs, andhigh-redshift gas-rich galaxies.
| Late-Time Radio Observations of 68 Type Ibc Supernovae: Strong Constraints on Off-Axis Gamma-Ray Bursts
We present late-time radio observations of 68 local Type Ibc supernovae,including six events with broad optical absorption lines(``hypernovae''). None of these objects exhibit radio emissionattributable to off-axis gamma-ray burst jets spreading into our line ofsight. Comparison with our afterglow models reveals the followingconclusions. (1) Less than ~10% of Type Ibc supernovae are associatedwith typical gamma-ray bursts initially directed away from our line ofsight; this places an empirical constraint on the GRB beaming factor of<~104, corresponding toan average jet opening angle, θj>~0.8d. (2) Thisholds in particular for the broad-lined supernovae (SNe 1997dq, 1997ef,1998ey, 2002ap, 2002bl, and 2003jd), which have been argued to host GRBjets. Our observations reveal no evidence for typical (or evensubenergetic) GRBs and rule out the scenario in which every broad-linedSN harbors a GRB at the 84% confidence level. Their large photosphericvelocities and asymmetric ejecta (inferred from spectropolarimetry andnebular spectroscopy) appear to be characteristic of the nonrelativisticSN explosion and do not necessarily imply the existence of associatedGRB jets.
| Extragalactic H_2O masers and X-ray absorbing column densities
Having conducted a search for the λ 1.3 cm (22 GHz) water vaporline towards galaxies with nuclear activity, large nuclear columndensities or high infrared luminosities, we present H2O spectra for NGC2273, UGC 5101, and NGC 3393 with isotropic luminosities of 7, 1500, and400 Lȯ. The H2O maser in UGC 5101 is by far the mostluminous yet found in an ultraluminous infrared galaxy. NGC 3393 revealsthe classic spectrum of a "disk maser", represented by three distinctgroups of Doppler components. As in all other known cases except NGC4258, the rotation velocity of the putative masing disk is well below1000 km s-1. Based on the literature and archive data, X-rayabsorbing column densities are compiled for the 64 galaxies withreported maser sources beyond the Magellanic Clouds. For NGC 2782 andNGC 5728, we present Chandra archive data that indicate the presence ofan active galactic nucleus in both galaxies. Modeling the hard nuclearX-ray emission, NGC 2782 is best fit by a high energy reflectionspectrum with NH 1024 cm-2. ForNGC 5728, partial absorption with a power law spectrum indicatesNH 8 × 1023 cm-2. Thecorrelation between absorbing column and H2O emission is analyzed. Thereis a striking difference between kilo- and megamasers with megamasersbeing associated with higher column densities. All kilomasers (L_H_2O< 10 Lȯ) except NGC 2273 and NGC 5194 areCompton-thin, i.e. their absorbing columns are <1024cm-2. Among the H{2}O megamasers, 50% arise fromCompton-thick and 85% from heavily obscured (>1023cm-2) active galactic nuclei. These values are not larger butconsistent with those from samples of Seyfert 2 galaxies not selected onthe basis of maser emission. The similarity in column densities can beexplained by small deviations in position between maser spots andnuclear X-ray source and a high degree of clumpiness in thecircumnuclear interstellar medium.
| Hydrogen and helium traces in type Ib-c supernovae
Aims.To investigate the spectroscopic properties of a selected opticalphotospheric spectra of core collapse supernovae (CCSNe). Specialattention is devoted to traces of hydrogen at early phases. The impacton the physics and nature of their progenitors is emphasized.Methods: .The CCSNe-sample spectra are analyzed with the parameterizedsupernova synthetic spectrum code "SYNOW" adopting some simplifyingapproximations. Results: .The generated spectra are found to matchthe observed ones reasonably well, including a list of only 23 candidateions. Guided by SN Ib 1990I, the observed trough near 6300 Å isattributed to Hα in almost all type Ib events, although in someobjects it becomes too weak to be discernible, especially at laterphases. Alternative line identifications are discussed. Differences inthe way hydrogen manifests its presence within CCSNe are highlighted. Intype Ib SNe, the Hα contrast velocity (i.e. line velocity minusthe photospheric velocity) seems to increase with time at early epochs,reaching values as high as 8000 km s-1 around 15-20 daysafter maximum and then remains almost constant. The derived photosphericvelocities, indicate a lower velocity for type II SNe 1987A and 1999emas compared to SN Ic 1994I and SN IIb 1993J, while type Ib eventsdisplay a somewhat larger variation. The scatter, around day 20, ismeasured to be ~5000 km s-1. Following two simple approaches,rough estimates of ejecta and hydrogen masses are given. A mass ofhydrogen of approximately 0.02 M_ȯ is obtained for SN 1990I, whileSNe 1983N and 2000H ejected ~0.008 M_ȯ and ~0.08 M_ȯ ofhydrogen, respectively. SN 1993J has a higher hydrogen mass, ~0.7M_ȯ with a large uncertainty. A low mass and thin hydrogen layerwith very high ejection velocities above the helium shell, is thus themost likely scenario for type Ib SNe. Some interesting and curiousissues relating to oxygen lines suggest future investigations.
| Radio properties of FIR-megamaser nuclei
Aims.Radio data on the nuclear emissions have been used to characterizethe dominant nuclear activity in a sample of FIR (ultra-) luminousgalaxies and the subgroup of known OH Megamasers. This study complementsan earlier study of the optical classification of these Megamasernuclei.Methods.Classification of the radio activity in the nuclei isbased on three critical parameters: the radio brightness temperature,the radio spectral index, and the ratio of FIR and radio fluxes. A firstmethod gives equal weight to the three parameters and a second methoduses a weighted function to classify the nuclei.Results.The presentsample shows that only 43% of the sample shows some - weak or strong -AGN characteristics. About 66% of the OH-MM sample and 81% of thenon-OH-MM sample can be actually classified as Starburst-dominatedsources. Radio diagnostic diagrams using these diagnostic parametersshow a continuous distribution ranging between AGN-dominated andSBN-dominated sources. The diagnostic diagrams also support the notionthat AGNs and starbursts coexist in the nuclei.Conclusions.A comparisonof the radio and optical classifications shows a consistency in theextreme cases of clear SBN and AGNs. A significant part of the sourceswith optical AGN-like activity have an SBN classification in the radio.The discrepant classifications are discussed in order to arrive at afinal classification of the dominant power source in the nucleus.
| Dense and Warm Molecular Gas between Double Nuclei of the Luminous Infrared Galaxy NGC 6240
High spatial resolution observations of the 12CO (1-0),HCN(1-0), HCO+(1-0), and 13CO(1-0) molecular linestoward the luminous infrared merger NGC 6240 have been performed usingthe Nobeyama Millimeter Array and the RAINBOW Interferometer. All of theobserved molecular emission lines are concentrated in the region betweenthe double nuclei of the galaxy. However, the distributions of both HCNand HCO+ emissions are more compact compared with that of12CO, and they are not coincident with the star-formingregions. The HCN/12CO line intensity ratio is 0.25; thissuggests that most of the molecular gas between the double nuclei isdense. A comparison of the observed high HCN/13CO intensityratio, 5.9, with large velocity gradient calculations suggests that themolecular gas is dense [n(H2) = 104--6cm-3] and warm (Tkin > 50 K). The observedstructure in NGC 6240 may be explained by time evolution of themolecular gas and star formation, which was induced by an almost head-oncollision or very close encounter of the two galactic nuclei accompaniedwith the dense gas and star-forming regions.
| On the X-ray properties of OH megamaser sources: Chandra snapshot observations
We present Chandra snapshot observations for a sample of seven sourcesselected from the Arecibo OH megamaser (OHM) survey at z~ 0.13-0.22 andwith far-infrared (FIR) luminosities in excess of1011Lsolar. In contrast with the knownH2O megamasers, which are mostly associated with powerfulactive galactic nuclei (AGN), the situation is far less clear for OHMs,which have been poorly studied in the X-ray band thus far. All of theobserved sources are X-ray weak, with only one OHM, IRAS FSC 03521+0028(z= 0.15), being detected by Chandra (with five counts). The resultsfrom this pilot programme indicate that the X-ray emission, withluminosities of less than ~1042ergs-1, isconsistent with that from star formation (as also suggested in somecases by the optical spectra) and low-luminosity active galactic nuclei(LLAGN) emission. If an AGN is present, its contribution to thebroad-band emission of OHM galaxies is likely modest. Under reasonableassumptions about the intrinsic X-ray spectral shape, the observed countdistribution from stacking analysis suggests absorption of~1022cm-2.
| The XMM-Newton Needles in the Haystack Survey: the local X-ray luminosity function of `normal' galaxies
In this paper we estimate the local (z < 0.22) X-ray luminosityfunction of `normal' galaxies derived from the XMM-Newton Needles in theHaystack Survey. This is an on-going project that aims to identifyX-ray-selected normal galaxies (i.e. non-AGN dominated) in the localUniverse. We are using a total of 70 XMM-Newton fields covering an areaof 11 deg2 which overlap with the Sloan Digital Sky SurveyData Release 2. Normal galaxies are selected on the basis of theirresolved optical light profile, their low X-ray-to-optical flux ratio[log(fx/fo) < - 2] and soft X-ray colours. Wefind a total of 28 candidate normal galaxies to the 0.5-8keV band fluxlimit of ~2 × 10-15ergcm-2s-1.Optical spectra are available for most sources in our sample (82 percent). These provide additional evidence that our sources are bona fidenormal galaxies with X-ray emission coming from diffuse hot gas emissionand/or X-ray binaries rather than a supermassive black hole. 16 of ourgalaxies have narrow emission lines or a late-type spectral energydistribution (SED) while the remaining 12 present only absorption linesor an early-type SED. Combining our XMM-Newton sample with 18 local (z< 0.22) galaxies from the Chandra Deep Field North and South surveys,we construct the local X-ray luminosity function of normal galaxies.This can be represented with a Schechter form with a break atL*~ 3+1.4-1.0×1041ergs-1 and a slope of α~ 1.78 +/- 0.12.Using this luminosity function and assuming pure luminosity evolution ofthe form ~(1 +z)3.3 we estimate a contribution to the X-raybackground from normal galaxies of ~10-20 per cent (0.5-8keV). Finally,we derive, for the first time, the luminosity functions for early- andlate-type systems separately.
| Infrared mergers and infrared quasi-stellar objects with galactic winds - III. Mrk 231: an exploding young quasi-stellar object with composite outflow/broad absorption lines (and multiple expanding superbubbles)
We present a study of outflow (OF) and broad absorption line (BAL)systems in Mrk 231, and in similar infrared (IR) quasi-stellar objects(QSOs). This study is based mainly on one-dimensional andtwo-dimensional spectroscopy (obtained at La Palma/William HerschelTelescope, Hubble Space Telescope, International Ultraviolet Explorer,European Southern Observatory/New Technology Telescope, Kitt PeakNational Observatory, Apache Point Observatory and Complejo AstronomicoEl Leoncito observatories) plus Hubble Space Telescope images. For Mrk231, we report evidence that the extreme nuclear OF process has at leastthree main components on different scales, which are probably associatedwith: (i) the radio jet, at parsec scale; (ii) the extreme starburst atparsec and kiloparsec scale. This OF has generated at least fourconcentric expanding superbubbles and the BAL systems.Specifically, inside and very close to the nucleus the two-dimensionalspectra show the presence of an OF emission bump in the blendHα+[NII], with a peak at the same velocity of the main BAL-Isystem (VEjectionBAL-I~-4700 km s-1). This bumpwas more clearly detected in the area located at 0.6-1.5 arcsec(490-1220 pc), to the south-west of the nucleus core, showing a strongand broad peak. In addition, in the same direction [at position angle(PA) ~-120°, i.e. close to the PA of the small-scale radio jet] at1.7-2.5 arcsec, we also detected multiple narrow emission-linecomponents, with `greatly' enhanced [NII]/Hα ratio (very similarto the spectra of jets bow shocks). These results suggest that the BAL-Isystem is generated in OF clouds associated with the parsec-scale jet.The Hubble Space Telescope images show four (or possibly five) nuclearsuperbubbles or shells with radii r~ 2.9, 1.5, 1.0, 0.6 and 0.2 kpc. Forthese bubbles, the two-dimensional Hα velocity field map andtwo-dimensional spectra show the following. (i) At the border of themore extended bubble (S1), a clear expansion of the shell withblueshifted velocities (with circular shape and at a radius r~ 5.0arcsec). This bubble shows a rupture arc - to the south - suggestingthat the bubble is in the blowout phase. The axis of this rupture orejection (at PA ~ 00°) is coincident with the axis of theintermediate and large-scale structures detected at radio wavelengths.(ii) In addition, in the three more external bubbles (S1, S2, S3), thetwo-dimensional William Herschel Telescope spectra show multipleemission-line components with OF velocities, of S1, S2 and S3 =[-(650 - 420) +/- 30], [-500+/- 30] and [-230 +/- 30] km s-1. (iii) In the wholecircumnuclear region (1.8 < r < 5 arcsec), the [NII]/Hα and[SII]/Hα narrow emission-line ratios show high values (>0.8),which are consistent with low-ionization nuclear emission-line region/OFprocesses associated with fast velocity shocks. Therefore, we suggestthat these giant bubbles are associated with the large-scale nuclear OFcomponent, which is generated - at least in part - by the extremenuclear starburst: giant supernova/hypernova explosions.The variability of the short-lived BAL-III NaI D system was studied,covering almost all the period in which this system appeared (between~1984 and 2004). We have found that the BAL-III light curve is clearlyasymmetric with a steep increase, a clear maximum and an exponentialfall (similar to the shape of a supernova light curve). The origin ofthis BAL-III system is discussed, mainly in the framework of an extremeexplosive event, probably associated with giant supernova/hypernovaexplosions.Finally, the IR colour diagram and the ultraviolet BAL systems of IR +GW/OF + FeII QSOs are analysed. This study shows two new BAL IR QSOs andsuggests/confirms that these objects could be nearby young BAL QSOs,similar to those detected recently at z~ 6.0. We propose that the phaseof young QSOs is associated with accretion of a large amount of gas (bythe supermassive black hole) + extreme starbursts + extreme compositeOFs/BALs.
| XMM-Newton observations of the interacting galaxy pairs NGC 7771/0 and NGC 2342/1
We present XMM-Newton X-ray observations of the interacting galaxy pairsNGC 7771/7770 and NGC 2342/2341. In NGC 7771, for the first time we areable to resolve the X-ray emission into a bright central source plus twobright (LX > 1040 erg s-1)ultraluminous X-ray sources (ULXs) located either end of the bar. In thebright central source (LX~ 1041 ergs-1), the soft emission is well-modelled by a two-temperaturethermal plasma with kT= 0.4/0.7 keV. The hard emission is modelled witha flat absorbed power-law (Γ~ 1.7, NH~ 1022cm-2), and this together with a low-significance (1.7σ)~ 300 eV equivalent width emission line at ~6 keV are the firstindications that NGC 7771 may host a low-luminosity AGN. For the barULXs, a power-law fit to X-1 is improved at the 2.5σ level withthe addition of a thermal plasma component (kT~ 0.3 keV), while X-2 isimproved only at the 1.3σ level with the addition of a discblackbody component with Tin~ 0.2 keV. Both sources arevariable on short time-scales implying that their emission is dominatedby single accreting X-ray binaries (XRBs). The three remaining galaxies,NGC 7770, NGC 2342 and NGC 2341, have observed X-ray luminosities of0.2, 1.8 and 0.9 × 1041 erg s-1,respectively (0.3-10 keV). Their integrated spectra are alsowell-modelled by multi-temperature thermal plasma components with kT=0.2-0.7 keV, plus power-law continua with slopes of Γ= 1.8-2.3that are likely to represent the integrated emission of populations ofXRBs as observed in other nearby merger systems. A comparison with otherisolated, interacting and merging systems shows that all four galaxiesfollow the established correlations for starburst galaxies betweenX-ray, far-infrared and radio luminosities, demonstrating that theirX-ray outputs are dominated by their starburst components.
| Two-dimensional warm gas kinematics in interacting galaxy systems
Gas reservoirs, internal or acquired, play an important role in thesecular evolution of interacting galaxies, since they are able toenhance/trigger star formation episodes and, probably, feed the activityof active galactic nuclei. Using Fabry-Perot observations, we havemapped, in the Hα line, the warm (T~ 104) gasdistribution and the velocity fields of the galaxy members of fiveinteracting, gas-rich galaxy systems. We investigated two M51-likesystems (Arp 70 and Arp 74), two systems containing highly disruptedmembers (WBL 366 and RR 24) and a case of merging in progress (Arp 299,one of the nearest luminous infrared objects).We detected gas motions following the elongated arm/tail of Arp 70b,while in the fainter member of the pair of galaxies, Arp 70a, the gasdistribution is off-centred with respect to the stellar isophotes,suggesting an external acquisition. Our kinematic data highlightednon-circular motions in the velocity field of one of the members of Arp74 (Arp 74a). The two galaxies of the RR 24 system are connected by onetidal tail, through which the kinematically disturbed component RR 24bseems to supply warm gas to RR 24a. In spite of the nearly irregular gasdistribution and perturbed morphology, WBL 366a (the star-forming galaxyVV-523) and WBL 366b have nearly regular velocity fields. The velocityfield in the Arp 299 system is irregular, and gas flow between the twonuclei is detected.The present observations, discussed in the light of model predictionsand complementary observations from the literature, suggest that allthese systems are still probably in an early phase of the encounter.However, the ionized gas distribution and kinematics are stronglyinfluenced by tidal forces. In particular, cross-fuelling mechanismsbetween galaxies are in action. In Arp 299 the warm and cold gaseouscomponents show similar kinematic properties, although the cold gasseems to maintain a still better organized motion with respect to thewarm gas.
| Arp 299
IAUC 8477 available at Central Bureau for Astronomical Telegrams.
| Mega-Masers and Galaxies
In the Galaxy, microwave radiation can be amplified in the interstellarmedium in the immediate neighborhood of young stellar objects, orcircumstellar envelopes around evolved stars, resulting in cosmic maseremission. Cosmic masers exist because, in contrast to terrestrialconditions, the interstellar gas density is very low so that levelpopulation in molecules is typically not in thermal equilibrium, andsometimes inverted. In the nuclear regions of external galaxies, thereexist very powerful OH ( 18 cm) and H2O ( 1.35 cm) cosmicmasers with line luminosities of 102 104Lȯ, 106 times more luminous than typicalGalactic maser sources. These are the "mega-masers," found inhigh-density molecular gas located within parsecs of active galacticnuclei in the case of H2O mega-masers, or within the central100 pc of nuclear star-burst regions in the case of OH mega-masers.H2O mega-masers are most frequently found in galactic nucleiwith Seyfert2 or LINER spectral characteristics, in spiral and someelliptical galaxies. OH mega-masers are found in ultra-luminous IRgalaxies (ULIRG) with the warmest IR colors, and importantly, the OHluminosity is observed to increase with the IR luminosity:LOH L1.2IR. Because of the extremelyhigh-surface brightness, H2O mega-maser emission can bemapped at sub-milli-arc-second resolution by Very Long BaselineInterferometry (VLBI), providing a powerful tool to probe spatial andkinematic distributions of molecular gas in distant galactic nuclei atscales below one parsec. An excellent example is the active galaxy, NGC4258, in which mapping of the H2O mega-maser emission hasprovided the first direct evidence in an active galactic nucleus for theexistence of a thin Keplerian accretion disk with turbulence, as well ashighly compelling evidence for the existence of a massive black hole.The NGC 4258 mega-maser has also provided a geometric distancedetermination of extremely high precision. H2O mega-maseremission is also found to arise from postshocked gas from the impact ofnuclear jets or outflows on the surrounding molecular clouds.High-resolution observations have shown that OH mega-masers originatefrom the molecular gas medium in 100-pc scale nuclear star-burstregions. It is proposed that such extreme star-burst regions, withextensive high-density gas bathed in a very high far-IR radiation field,are conducive to the formation of a very large number of OH masersources that collectively produce the OH mega-maser emission. In theearly Universe, galaxies or mergers could go through a very luminousphase, powered by intensive star-bursts and AGN formation, and couldhave extremely large OH and H2O maser luminosities, possiblyproducing giga-masers. With the increasing sensitivity of new telescopesand receivers, surveys and high-resolution studies of mega-masers andgiga-masers will be very important tracers and high-resolution probes ofactive galactic nuclei, dust embedded star-bursts in the earliestgalaxies and galaxy mergers in the epoch of very active star formationat z 2 and beyond. Distance determination of giga-masers at z 1 2can provide on independent measure of how fast the universe isexpanding.
| Deconstructing NGC 7130
Observations of the Seyfert 2 and starburst galaxy NGC 7130 with theChandra X-Ray Observatory illustrate that both of these phenomenacontribute significantly to the galaxy's detectable X-ray emission. Theactive galactic nucleus (AGN) is strongly obscured, buried beneathcolumn density NH>1024cm-2, and itis most evident in a prominent Fe Kα emission line with equivalentwidth greater than 1 keV. The AGN accounts for most (60%) of theobserved X-rays at energy E>2 keV, with the remainder due tospatially extended star formation. The soft X-ray emission is strong andpredominantly thermal on both small and large scales. We attribute thethermal emission to stellar processes. In total, the AGN is responsiblefor only one-third of the observed 0.5-10 keV luminosity of3×1041ergss-1 of this galaxy and less thanhalf of its bolometric luminosity. Starburst/AGN composite galaxies likeNGC 7130 are truly common, and similar examples may contributesignificantly to the high-energy cosmic X-ray background while remaininghidden at lower energies, especially if they are distant.
| Some Features of the X-Ray and Radio Emission from OH Megamaser Galaxies
The properties of OH megamaser galaxies in the x-ray and radio rangesare discussed. Based on a sample of OH megamaser galaxies it is shownthat the x-ray emission and the width of the OH radio line are closelyrelated. The line width is also related to the radio emission frommegamasers, but it depends only weakly on the infrared emission and thisrelationship is statistically less significant. The OH line width andthe radio and x-ray emissions depend on the central mass of megamasers.There is a weak correlation between the radio and x-ray emissions owingto multiple scattering of synchrotron photons and bursts from thegalactic nucleus. These results indicate that an active nucleus can bedominant in OH megamaser galaxies.
| Properties of OH megamaser galaxies in the radio continuum. I. Observational data
Radio observations with the VLA-A radio telescope of 30 OH megamasergalaxies at a frequency of 1.49 GHz are discussed. Radio emission wasdetected from all 30 of these galaxies. Radio emission was detected from5 of the 30 objects for the first time. Important results were obtainedfor 12 galaxies that had previously been little studied in the radiocontinuum. Additional data at 1.49 GHz were obtained for the remaining13 objects. The core component of the continuum radio emissionpredominates in the OH megamaser galaxies.
| Active and Star-forming Galaxies and Their Supernovae
To investigate the extent to which nuclear starbursts or other nuclearactivity may be connected with enhanced star formation activity in thehost galaxy, we perform a statistical investigation of supernovae (SNe)discovered in host galaxies from four samples: the Markarian galaxiessample, the Second Byurakan Survey (SBS) sample, the north Galactic pole(NGP) sample of active or star-forming galaxies, and the NGP sample ofnormal galaxies. Forty-seven SNe in 41 Mrk galaxies, 10 SNe in six SBSgalaxies, 29 SNe in 26 NGP active or star-forming galaxies, and 29 SNein 26 NGP normal galaxies have been studied. We find that the rate ofSNe, particularly core-collapse (Types Ib/c and II) SNe, is higher inactive or star-forming galaxies in comparison with normal galaxies.Active or star-forming host galaxies of SNe are generally of latermorphological type and have lower luminosity and smaller linear sizethan normal host galaxies of SNe. The radial distribution of SNe inactive and star-forming galaxies shows a higher concentration toward thecenter of the active host galaxy than is the case for normal hostgalaxies, and this effect is more pronounced for core-collapse SNe.Ib/c-type SNe have been discovered only in active and star-forminggalaxies of our samples. About 78% of these SNe are associated with H IIregions or are located very close to the nuclear regions of these activegalaxies, which are in turn hosting AGNs or starburst nuclei. Besidesthese new results, our study also supports the conclusions of severalother earlier papers. We find that Type Ia SNe occur in all galaxytypes, whereas core-collapse SNe of Types Ib/c and II are found only inspiral and irregular galaxies. The radial distribution of Type Ib SNe intheir host galaxies is more centrally concentrated than that of Type IIand Ia SNe. The radial distances of Types Ib/c and II SNe, from thenuclei of their host galaxies, is larger for barred spiral hosts.Core-collapse SNe are concentrated in spiral arms and are often close toor in the H II regions, whereas Type Ia SNe show only a looseassociation with spiral arms and no clear association with H II regions.
| New H2O masers in Seyfert and FIR bright galaxies
Using the Effelsberg 100-m telescope, detections of four extragalacticwater vapor masers are reported. Isotropic luminosities are ~50, 1000, 1and 230 Lȯ for Mrk 1066 (UGC 2456), Mrk 34, NGC 3556 andArp 299, respectively. Mrk 34 contains by far the most distant and oneof the most luminous water vapor megamasers so far reported in a Seyfertgalaxy. The interacting system Arp 299 appears to show two maserhotspots separated by approximately 20´´. With these newresults and even more recent data from Braatz et al. (2004, ApJ, 617,L29), the detection rate in our sample of Seyferts with known jet-NarrowLine Region interactions becomes 50% (7/14), while in star forminggalaxies with high (S100~μ m>50 Jy) far infrared fluxesthe detection rate is 22% (10/45). The jet-NLR interaction sample maynot only contain “jet-masers” but also a significant numberof accretion “disk-masers” like those seen in NGC 4258. Astatistical analysis of 53 extragalactic H2O sources (excluding theGalaxy and the Magellanic Clouds) indicates (1) that the correlationbetween IRAS Point Source and H2O luminosities, established forindividual star forming regions in the galactic disk, also holds forAGN-dominated megamaser galaxies; (2) that maser luminosities are notcorrelated with 60 μm/100 μm color temperatures; and (3) that onlya small fraction of the luminous megamasers (L_H_2O > 100Lȯ) detectable with 100-m sized telescopes have so farbeen identified. The H2O luminosity function (LF) suggests that thenumber of galaxies with 1 Lȯ < L_H_2O < 10Lȯ, the transition range between“kilomasers” (mostly star formation) and“megamasers” (active galactic nuclei), is small. The overallslope of the LF, ~-1.5, indicates that the number of detectable masersis almost independent of their luminosity. If the LF is not steepeningat very high maser luminosities and if it is possible to find suitablecandidate sources, H2O megamasers at significant redshifts should bedetectable even with present day state-of-the-art facilities.
| Radio recombination lines from the starburst galaxy NGC 3256
We have detected the radio recombination lines H91α and H92αwith rest frequencies of 8.6 GHz and 8.3 GHz from the starburst nucleusNGC 3256 at an angular resolution of 16.4'' × 9.6'' using theAustralia Telescope Compact Array and at an angular resolution of 12.0''× 2.9'' using the VLA. The line was detected at ~1 mJybeam-1 peak with a width of 160 km s-1 with theATCA and at ~0.5 mJy beam-1 peak with a width of 114 kms-1 with the VLA. Modelling the line emitting region as acollection of H II regions, we derive constraints on the required numberof H II regions, their temperature, density, and distribution. We findthat a collection of 10 to 300 H II regions with temperatures of 5000 K,densities of 1000 cm-3 to 5000 cm-3 and diametersof 15 pc produced good matches to the line and continuum emmission. TheLyman continuum production rate required to maintain the ionization is 2× 1052~s-1 to 6 ×1053~s-1, which requires 600 to 17 000 O5 stars tobe produced in the starburst.
| Radio sources in low-luminosity active galactic nuclei. IV. Radio luminosity function, importance of jet power, and radio properties of the complete Palomar sample
We present the completed results of a high resolution radio imagingsurvey of all ( 200) low-luminosity active galactic nuclei (LLAGNs) andAGNs in the Palomar Spectroscopic Sample of all ( 488) bright northerngalaxies. The high incidences of pc-scale radio nuclei, with impliedbrightness temperatures ≳107 K, and sub-parsec jetsargue for accreting black holes in ≳50% of all LINERs andlow-luminosity Seyferts; there is no evidence against all LLAGNs beingmini-AGNs. The detected parsec-scale radio nuclei are preferentiallyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). The radio luminosity function (RLF) of PalomarSample LLAGNs and AGNs extends three orders of magnitude below, and iscontinuous with, that of “classical” AGNs. We find marginalevidence for a low-luminosity turnover in the RLF; nevertheless LLAGNsare responsible for a significant fraction of present day massaccretion. Adopting a model of a relativistic jet from Falcke &Biermann, we show that the accretion power output in LLAGNs is dominatedby the kinetic power in the observed jets rather than the radiatedbolometric luminosity. The Palomar LLAGNs and AGNs follow the samescaling between jet kinetic power and narrow line region (NLR)luminosity as the parsec to kilo-parsec jets in powerful radio galaxies.Eddington ratios {l_Edd} (=L_Emitted/L_Eddington) of≤10-1{-}10-5 are implied in jet models of theradio emission. We find evidence that, in analogy to Galactic black holecandidates, LINERs are in a “low/hard” state (gas poornuclei, low Eddington ratio, ability to launch collimated jets) whilelow-luminosity Seyferts are in a “high” state (gas richnuclei, higher Eddington ratio, less likely to launch collimated jets).In addition to dominating the radiated bolometric luminosity of thenucleus, the radio jets are energetically more significant thansupernovae in the host galaxies, and are potentially able to depositsufficient energy into the innermost parsecs to significantly slow thegas supply to the accretion disk.
| Exceptional H2 emission in the Antennae galaxies: Pre-starburst shocks from the galaxy collision
The collision of gas-rich galaxies is believed to produce strong shocksbetween their gas clouds which cause the onset of the observed bursts ofextended star formation. However, the so far observed shock signaturesin colliding galaxies can be explained essentially by winds from alreadyexisting massive stars and supernovae and thus do not give any evidencefor an outstanding pre-starburst phase. Either pre-starburst gas shocksare too short-lived to be detected or one has to modify our perceptionof colliding galaxies. A dedicated analysis of ISOCAM-CVF mid-infraredspectral maps led us to the discovery of exceptional H2 v = 0-0 S(3)λ = 9.66 μm line emission from the “Antennae”galaxy pair, which is at an early stage of galaxy collision. Its H2 lineluminosity, normalized by the far-infrared luminosity, exceeds that ofall other known galaxies and the strongest H2 emission is spatiallydisplaced from the known starbursts regions. This implies that most ofthe excited H2 gas in the Antennae must be shocked due to the collisionof the two galaxies. These observations indicate that the outstandingphase of pre-starburst shocks exists, and that they might be a key toour understanding of the formation of the first proto-galaxies.Based onobservations with the Infrared Space ObservatoryISO, an ESA project with instrumentsfunded by ESA Member States (especially the PI countries: France,Germany, the Netherlands and the United Kingdom) andwith the participation of ISAS and NASA.
| A catalogue of ultraluminous X-ray sources in external galaxies
We present a catalogue of ultraluminous X-ray sources (ULXs) in externalgalaxies. The aim of this catalogue is to provide easy access to theproperties of ULXs, their possible counterparts at other wavelengths(optical, IR, and radio), and their host galaxies. The cataloguecontains 229 ULXs reported in the literature until April 2004. Most ULXsare stellar-mass-black hole X-ray binaries, but it is not excluded thatsome ULXs could be intermediate-mass black holes. A small fraction ofthe candidate ULXs may be background Active Galactic Nuclei (AGN) andSupernova Remnants (SNRs). ULXs with luminosity above 1040ergs s-1 are found in both starburst galaxies and in thehalos of early-type galaxies.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/1125
| The observations and studies of OH megamasers associated with external galaxies
During the thirty years since the first discovery of OH megamaserassociated with external galaxies, a great progress of observations andstudies for OH megamasers associated with external galaxies has beenproceeded. So far 106 OH megamasers associated with external galaxieshave been found, including 59 higher red-shifted ones. The observationsand studies of the OH megamasers associated with AGN and starburstgalaxies are the very efficient tools to investigate characteristics oftheir central sources and circumnuclear discs. A review on the currentprogress concerning surveys, observations and theoretical investigationson extragalactic OH megamaser sources is given in this paper.
| Infrared mergers and infrared quasi-stellar objects with galactic winds - II. NGC5514: two extranuclear starbursts with LINER properties and a supergiant bubble in the rupture phase
A study of the morphology, kinematics and ionization structure of theinfrared (IR) merger NGC5514 is presented. This study is based mainly onINTEGRAL two-dimensional (2D) spectroscopy (obtained at the 4.2-mWilliam Herschel Telescope, WHT), plus optical and near-IR images. Clearevidence of two extranuclear starbursts with young outflows (OFs) andlow-ionization nuclear emission region (LINER) activity are reported.One of these OFs has generated a supergiant bubble and the other isassociated with an extended complex of HII regions.In the galactic bubble it was found that: (i) the [SII], Hα,[NII], [OI] and [OIII] emission-line maps show a bubble with a distortedellipsoidal shape, with major and minor axes of ~6.5 kpc [13.6 arcsec;at position angle (PA) = 120°+/- 10°] and ~4.5 kpc (9.6 arcsec);(ii) these maps depict four main knots, a very strong one and threeothers more compact and located at the border; (iii) the centre of thebubble is located at ~4.1 kpc (8.5 arcsec) to the west of the mainnucleus; (iv) the WHT spectra show, in this area, two strong components:blue and red emission-line systems, probably associated with emissionfrom the near and far side of the external shell, for which the mean OFvelocities were measured as VOFblue= (-320 +/- 20)kms-1 and VOFred= (+265 +/- 25) kms-1(v) these two components depict LINER properties, probably associatedwith large-scale OF + shocks; (vi) at the east border, the kinematics ofthe ionized gas and the [SII] emission-line maps show an extendedejection of 4 kpc aligned with the PA of the major axis; (vii) threeother ejections were found, two of them perpendicular to the extendedone. Each ejection starts in one of the knots. These results suggestthat the bubble is in the rupture phase.For the complex of giant HII regions it was found that: (i) theHα, [NII] and [SII] emission-line maps show a compact strongemission area (peaking at ~810 pc ~1.7 arcsec, to the east of the secondnucleus) and faint extended emission with an elongated shape, and majorand minor axes of ~5.1 kpc (10.8 arcsec; at PA ~20°) and ~2.9 kpc(6.0 arcsec); (ii) inside this complex, the spectra show HII region andtransition LINER/HII characteristics; (iii) at the border of thisextended HII area the spectra have outflow components and LINERproperties.INTEGRAL 2D [NII], Hα, [SII] and [OIII] velocity fields (VFs) arepresented. These VF maps show results consistent with an expansion ofthe bubble, plus four ejections of ionized gas. The U, B, V, I, J, H andKS images show a pre-merger morphology, from which faintfilaments of emission emerge, centred on the bubble. The ionizationstructure and the physical conditions were analysed using the following2D emission-line ratio and width maps: [SII]/Hα, [NII]/Hα,[OI]/Hα, [OIII]/Hβ and FWHM-[NII]. In the region of thebubble, 100 per cent of the [NII]/Hα and [SII]/Hα ratiosshow very high values (>0.8) consistent with LINER processesassociated with high-velocity shocks. These new results support theprevious proposition that extreme nuclear and `extranuclear' starburstswith galactic winds + shocks play an important role in the evolution ofIR mergers/quasi-stellar objects.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
Katalógusok és elnevezések:
|
