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SINFONI observations of starclusters in starburst galaxies
We have used ESO’s new NIR IFS SINFONI during its ScienceVerification period to observe the central regions of local starburstgalaxies. Being Science Verification observations, the aim was 2-fold:to demonstrate SINFONI’s capabilities while obtaining informationon the nature of starclusters in starburst galaxies. The targets choseninclude a number of the brighter clusters in NGC1808 and NGC253. Here wepresent first results.
| Nuclear embedded star clusters in NGC 7582*
We report on the discovery of several compact regions of mid-infraredemission in the star-forming circumnuclear disc of the starburst/Seyfert2 galaxy NGC 7582. The compact sources do not have counterparts in theoptical and near-infrared, suggesting that they are deeply embedded indust. We use the [NeII] 12.8-μm line emission to estimate theemission measure of the ionized gas, which in turn is used to assess thenumber of ionizing photons. Two of the brighter sources are found tohave ionizing fluxes of ~2.5 × 1052, whereas thefainter ones have ~1 × 1052 photon s-1.Comparing with a 1-Myr-old starburst, we derive stellar masses in therange 3-5 × 105Msolar and find that thenumber of O stars in each compact source is typically 0.6-1.6 ×103. We conclude that the compact mid-infrared sources arelikely to be young, embedded star clusters, of which only a few areknown so far. Our observation highlights the need for high-resolutionmid-infrared imaging to discover and study embedded star clusters in theproximity of active galactic nuclei.
| Lifetime of nuclear velocity dispersion drops in barred galaxies
We have made hydro/N-body simulations with and without star formation toshed some light on the conditions under which a central kinematicallycold stellar component (characterized by a velocity dispersion drop orσ-drop) could be created in a hot medium (e.g. a bulge) andsurvive enough time to be observed. We found that the time-scale for aσ-drop formation could be short (less than 500 Myr), whereas itslifetime could be long (more than 1 Gyr) provided that the centralregion is continuously or regularly fed by fresh gas which leads to acontinuous star formation activity. Star formation in the centralregion, even at a low rate as 1Msolaryr-1, ismandatory to sustain a permanent σ-drop by replacing heatedparticles by new low-σ ones. We moreover show that as soon as starformation is switched off, the σ-drop begins to disappear.
| HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| Modelling galaxy spectra in presence of interstellar dust - I. The model of interstellar medium and the library of dusty single stellar populations
The advent of modern infrared astronomy has brought into evidence therole played by the interstellar dust in galaxy formation and evolution.Therefore, to fully exploit modern data, realistic spectrophotometricmodels of galaxies must include this important component of theinterstellar medium (ISM).In this paper, the first of a series of two devoted to modelling thespectra of galaxies of different morphological type in the presence ofdust, we present our description of the dust both in the diffuse ISM andin the molecular clouds (MCs).Our galaxy model contains three interacting components: the diffuse ISM,made of gas and dust, the large complexes of MCs in which active starformation occurs and, finally, the populations of stars that are nolonger embedded in the dusty environment of their parental MCs.Our model for the dust takes into account three components, i.e.graphite, silicates and polycyclic aromatic hydrocarbons (PAHs). Weconsider and adapt to our aims two prescriptions for the sizedistribution of the dust grains and two models for the emission of thedusty ISM. We cross-check the emission and extinction models of the ISMby calculating the extinction curves and the emission for the typicalenvironments of the Milky Way (MW) and the Large and Small MagellanicClouds (LMC and SMC) and by comparing the results with the observationaldata. The final model we have adopted is a hybrid one which stems fromcombining the analysis of Guhathakurta & Draine for the emission ofgraphite and silicates and Puget, Leger & Boulanger for the PAHemission, and using the distribution law of Weingartner & Draine andthe ionization model for PAHs of Weingartner & Draine.We apply the model to calculate the spectral energy distribution (SED)of single stellar populations (SSPs) of different age and chemicalcomposition, which may be severely affected by dust at least in twotypes of stars: the young, massive stars while they are still embeddedin their parental MCs and the intermediate- and low-mass asymptoticgiant branch (AGB) stars when they form their own dust shell around.We use the `ray-tracing' method to solve the problem of radiativetransfer and to calculate extended libraries of SSP SEDs. Particularcare is taken to model the contribution from PAHs, introducing differentabundances of C in the population of very small carbonaceous grains(VSGs) and different ionization states in PAHs. The SEDs of young SSPsare then compared with observational data of star-forming regions offour local galaxies successfully reproducing their SEDs from theultraviolet (UV)-optical regions to the mid- and far-infrared region(MIR and FIR, respectively).
| The Survey for Ionization in Neutral Gas Galaxies. I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG),a census of star formation in H I-selected galaxies. The survey consistsof Hα and R-band imaging of a sample of 468 galaxies selected fromthe H I Parkes All Sky Survey (HIPASS). The sample spans three decadesin H I mass and is free of many of the biases that affect otherstar-forming galaxy samples. We present the criteria for sampleselection, list the entire sample, discuss our observational techniques,and describe the data reduction and calibration methods. This paperfocuses on 93 SINGG targets whose observations have been fully reducedand analyzed to date. The majority of these show a single emission linegalaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs ina single field. All of the targets in this sample are detected inHα, indicating that dormant (non-star-forming) galaxies withMHI>~3×107 Msolar are veryrare. A database of the measured global properties of the ELGs ispresented. The ELG sample spans 4 orders of magnitude in luminosity(Hα and R band), and Hα surface brightness, nearly 3 ordersof magnitude in R surface brightness and nearly 2 orders of magnitude inHα equivalent width (EW). The surface brightness distribution ofour sample is broader than that of the Sloan Digital Sky Survey (SDSS)spectroscopic sample, the EW distribution is broader than prism-selectedsamples, and the morphologies found include all common types ofstar-forming galaxies (e.g., irregular, spiral, blue compact dwarf,starbursts, merging and colliding systems, and even residual starformation in S0 and Sa spirals). Thus, SINGG presents a superior censusof star formation in the local universe suitable for further studiesranging from the analysis of H II regions to determination of the localcosmic star formation rate density.
| Mapping Large-Scale Gaseous Outflows in Ultraluminous Infrared Galaxies with Keck II ESI Spectra: Spatial Extent of the Outflow
The kinematics of neutral gas and warm ionized gas have been mappedacross ultraluminous starburst galaxies using the Na Iλλ5890, 5896 absorption-line and Hα emission-lineprofiles, respectively, in Keck II ESI spectra. Blueshifted,interstellar absorption is found over extended regions, exceeding 15 kpcin several systems. An outflow diverging from the nuclear starburstwould have to reach large heights to cover this area in projection. Thescale height of the absorbing material could be lower, however, if theoutflow emanates from a larger region of the galaxy. The large velocitygradient discovered across several outflows is inconsistent with a flowdiverging from the nuclear starburst. Widespread star formation,triggered by the merger, probably drives these extended outflows viamechanical feedback from supernovae, although shocks generated by thegalaxy-galaxy merger may also contribute to the formation of a hot wind.In a typical ULIG, the mass carried by the cool phase of the outflow is~108 Msolar i.e., a few percent of the dynamicalmass in the starburst region. Assuming the starburst activity haspersisted for 10 Myr, the kinetic energy of the cool outflows is a fewpercent of the supernova energy. The cool wind is expected to beaccelerated by momentum deposition, possibly from radiation pressure aswell as the ram pressure of the hot, supernova-induced wind. Theturnaround radii of the cool outflows are at least ~30-90 kpc, whichpresents a significant Na I absorption cross section. If mostL>0.1L* galaxies pass through a luminous starburst phase,then relics of cool outflows will create a significant redshift-pathdensity. Galaxy formation models should include this cool phase of theoutflow in addition to a hot wind in feedback models.Data presented herein were obtained at the W. M. Keck Observatory, whichis operated as a scientific partnership among the California Instituteof Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| 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.
| Star Formation and Extinction in Redshift z~2 Galaxies: Inferences from Spitzer MIPS Observations
We use very deep Spitzer MIPS 24 μm observations to examine thebolometric luminosities (Lbol) and UV extinction propertiesof more than 200 spectroscopically identified, optically selected(UnGR) z~2 galaxies, supplemented with near-IR-selected(``BzK'' and ``DRG'') and submillimeter galaxies at similar redshifts,in the GOODS-N field. Focusing on redshifts 1.51012 Lsolar, with a mean~=2×1011 Lsolar. Using24 μm observations as an independent probe of dust extinction, wefind that, as in the local universe, the obscurationLIR/L1600 is strongly dependent on Lboland ranges in value from <1 to ~1000 within the sample considered.However, the obscuration is generally ~10 times smaller at a givenLbol at z~2 than at z~0. We show that the values ofLIR and obscuration inferred from the UV spectral slopeβ generally agree well with the values inferred fromL5-8.5μm for Lbol<1012Lsolar. Using the specific SFRs of galaxies as a proxy forcold gas fraction, we find a wide range in the evolutionary state ofgalaxies at z~2, from galaxies that have just begun to form stars tothose that have already accumulated most of their stellar mass and areabout to become, or already are, passively evolving.Based, in part, on data obtained at the W. M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California, and NASA and was made possibleby the generous financial support of the W. M. Keck Foundation. Alsobased in part on observations made with the Spitzer Space Telescope,which is operated by the Jet Propulsion Laboratory, California Instituteof Technology, under a contract with NASA.
| Discovery of PAHs in the halo of NGC 5907
We have used sensitive archival data from the Infrared Space Observatory(ISO) to make maps of the edge-on low SFR galaxy, NGC 5907, in 6different MIR bands: LW2, LW5, LW6, LW7, LW8, and LW10, covering thespectrum from 6.5 to 15.0 μm and including several narrow bands thatisolate the infrared aromatic spectral features commonly referred to asPAHs. Most of the MIR emission is dominated by PAHs and it is likelythat emission from VSGs contribute only negligibly except in the broadIRAS-equivalent band. The flux ratios are typical of galaxies with lowSFRs or quiesent regions within galaxies (e.g. M 83) and a very highPAH/continuum ratio is observed. The PAH emission follows the COdistribution and also shows some correlation within the disk with theλ850 μm distribution. However, the PAH emission also reacheslarger galactocentric radii than the CO and other correlations suggestthat the PAHs are also more widespread. A significant new discovery isthe presence of PAHs in the halo of the galaxy. In the narrow bands thatisolate single PAH features, the emission shows structure similar tohigh latitude features seen in other galaxies in other tracers. Thefeatures extend as far as 6.5 kpc from the plane but scale heights of3.5 kpc are more typical. The λ11.3/λ7.7 ratio alsoappears to increase with distance from the major axis. To our knowledge,this is the first time PAHs have been seen in the halo of an externalgalaxy. Just as significantly, they are seen in a low SFR galaxy,suggesting that strong SNe and winds are not necessary for these largemolecules to reach high latitudes.
| The evolution of actively star-forming galaxies in the mid-infrared
In this paper we analyze the evolution of actively star-forming galaxiesin the mid-infrared (MIR). This spectral region, characterized bycontinuum emission by hot dust and by the presence of strong emissionfeatures generally ascribed to polycyclic aromatic hydrocarbon (PAH)molecules, is the most strongly affected by the heating processesassociated with star formation and/or active galactic nuclei (AGNs).Following the detailed observational characterization of galaxies in theMIR by the Infrared Space Observatory (ISO), we have updated themodelling of this spectral region in our spectrophotometric modelGRASIL. In the diffuse component we have updated the treatment of PAHsaccording to the model by Li & Draine. As for the dense phase of theinterstellar medium associated with the star-forming regions, themolecular clouds, we strongly decrease the abundance of PAHs as comparedto that in the cirrus, based on the observational evidence of the lackor weakness of PAH bands close to the newly formed stars, possibly dueto the destruction of the molecules in strong ultraviolet fields. Therobustness of the model is checked by fitting near-infrared to radiobroad-band spectra and the corresponding detailed MIR spectra of a largesample of galaxies, at once. With this model, we have analyzed thelarger sample of actively star-forming galaxies by Dale et al. We showthat the observed trends of galaxies in the ISO-IRAS-radio colour-colourplots can be interpreted in terms of the different evolutionary phasesof star formation activity, and the consequent different dominance inthe spectral energy distribution of the diffuse or dense phase of theISM. We find that the observed colours indicate a surprising homogeneityof the starburst phenomenon, allowing only a limited variation of themost important physical parameters, such as the optical depth of themolecular clouds, the time-scale of the escape of young stars from theirfor mation sites, and the gas consumption time-scale. In this paper wedo not attempt to reproduce the far-infrared coolest region in thecolour-colour plots, as we concentrate on models meant to reproduceactive star-forming galaxies, but we discuss possible requirements of amore complex modelling for the coldest objects.
| An atlas of calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering theregion around the λλ8498, 8542, 8662 calcium triplet(CaT). The sample comprises 78 objects, divided into 43 Seyfert 2s, 26Seyfert 1s, three starburst and six normal galaxies. The spectra pertainto the inner ~300 pc in radius, and thus sample the central kinematicsand stellar populations of active galaxies. The data are used to measurestellar velocity dispersions (σ*) with bothcross-correlation and direct fitting methods. These measurements arefound to be in good agreement with each other and with those in previousstudies for objects in common. The CaT equivalent width is alsomeasured. We find average values and sample dispersions ofWCaT of 4.6 +/- 2.0, 7.0 +/- 1.0 and 7.7 +/- 1.0 Å forSeyfert 1s, Seyfert 2s and normal galaxies, respectively. We furtherpresent an atlas of [SIII]λ9069 emission-line profiles for asubset of 40 galaxies. These data are analysed in a companion paperwhich addresses the connection between stellar and narrow-line regionkinematics, the behaviour of the CaT equivalent width as a function ofσ*, activity type and stellar population properties.
| Neutral hydrogen gas in interacting galaxies: the NGC 1511 galaxy group
We present HI line and 20-cm radio continuum observations of the NGC1511 galaxy group obtained with the Australia Telescope Compact Array.The data reveal an extended, rather disturbed HI distribution for thepeculiar starburst galaxy NGC 1511 and a narrow bridge to its smallcompanion galaxy, NGC 1511B, which has been severely distorted by theinteraction/collision between the two galaxies. No stellar counterpartto the gaseous bridge has been detected. In addition, we find that thepeculiar optical ridge to the east of NGC 1511 is probably the stellarremnant of a galaxy completely disrupted by interactions with NGC 1511.The slightly more distant neighbour, NGC 1511A, shows a regular HIvelocity field and no obvious signs of interactions.Radio continuum emission from NGC 1511 reveals three prominent sourceson top of a more diffuse, extended distribution. We derive an overallstar formation rate of 7Msolaryr-1. The mostenhanced star formation is found in the south-eastern part of the disc,coincident with several bright HII regions, and closest to the peculiaroptical ridge. No continuum emission was detected in the companions, butNGC 1511B appears to show an HII region at its faint western edge,closest to NGC 1511. The group displays a prime example ofinteraction-induced star formation activity.
| Dust in spiral galaxies: global properties
We present and analyse high-quality Submillimetre Common-User BolometerArray (SCUBA) 850- and 450-μm images of 14 local spiral galaxies,including the detection of dust well out into the extended disc in manycases. We use these data in conjunction with published far-infrared fluxdensities from IRAS and ISO, and millimetre-wave measurements fromground-based facilities to deduce the global properties of the dust inthese galaxies, in particular temperature and mass. We find that simpletwo-temperature greybody models of fixed dust emissivity index β= 2and with typical temperatures of 25 < Twarm < 40 K and10 < Tcold < 20 K provide good fits to the overallspectral energy distributions. The dust mass in the cold componentcorrelates with the mass in atomic hydrogen and the mass in the warmcomponent correlates with the mass in molecular hydrogen. These resultsthus fit the simple picture in which the cold dust is heatedpredominantly by the interstellar radiation field, while the hot dust isheated predominantly by OB stars in more active regions, although weargue that there is some mixing. The mean gas-to-dust mass ratio is 120+/- 60, very similar to that found within our own galaxy and roughly afactor of 10 lower than that derived from IRAS data alone. Thegas-to-dust mass ratios in the warm, molecular component are on averagehigher than those in the cold, atomic component. We compare ourmodelling results with similar results for more luminous spiral galaxiesselected at far-infrared wavelengths by the SCUBA Local Universe GalaxySurvey. We find that whilst the total dust mass distributions of the twosamples are indistinguishable, they have significantly different dusttemperature distributions in both the warm and cold components. Wesuggest that this difference might be related to the level of starformation activity in these systems, with the more active galaxieshaving more intense interstellar radiation fields and higher dusttemperatures.
| A radio study of the superwind galaxy NGC 1482
We present multifrequency radio continuum as well as HI observations ofthe superwind galaxy NGC 1482, with both the Giant Metrewave RadioTelescope (GMRT) and the Very Large Array (VLA). This galaxy has aremarkable hourglass-shaped optical emission-line outflow as well asbipolar soft X-ray bubbles on opposite sides of the galactic disc. Thelow-frequency, lower-resolution radio observations show a smoothstructure. From the non-thermal emission, we estimate the availableenergy in supernovae, and examine whether this would be adequate todrive the observed superwind outflow. The high-frequency,high-resolution radio image of the central starburst region located atthe base of the superwind bi-cone shows one prominent peak and moreextended emission with substructure. This image has been compared withthe infrared, optical red continuum, Hα, and soft and hard X-rayimages from Chandra to understand the nature and relationship of thevarious features seen at different wavelengths. The peak of the infraredemission is the only feature that is coincident with the prominent radiopeak, and possibly defines the centre of the galaxy.The HI observations with the GMRT show two blobs of emission on oppositesides of the central region. These are rotating about the centre of thegalaxy and are located at ~2.4 kpc from it. In addition, theseobservations also reveal a multicomponent HI absorption profile againstthe central region of the radio source, with a total width of ~250 kms-1. The extreme blue- and redshifted absorption componentsare at 1688 and 1942 km s-1, respectively, while the peakabsorption is at 1836 km s-1. This is consistent with theheliocentric systemic velocity of 1850 +/- 20 km s-1,estimated from a variety of observations. We discuss possibleimplications of these results.
| A wide-field HI study of the NGC 1566 group
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.
| An Analytic Model of Galactic Winds and Mass Outflows
Galactic winds and mass outflows are observed both in nearby starburstgalaxies and in high-redshift star-forming galaxies. We develop a simpleanalytic model to understand the observed superwind phenomenon with adiscussion of the model uncertainties. Our model is built upon the modelof McKee & Ostriker for the interstellar medium. It allows one topredict how properties of a superwind, such as wind velocity and massoutflow rate, are related to properties of its star-forming host galaxy,such as size, gas density and star formation rate. The model predicts athreshold of star formation rate density for the generation ofobservable galactic winds. Galaxies with more concentrated starformation activities produce superwinds with higher velocities. Thepredicted mass outflow rates are comparable to (or slightly larger than)the corresponding star formation rates. We apply our model to both localstarburst galaxies and high-redshift Lyman break galaxies, and find itspredictions to be in good agreement with current observations. Our modelis simple and so can be easily incorporated into numerical simulationsand semi-analytical models of galaxy formation.
| Galactic Winds
Galactic winds are the primary mechanism by which energy and metals arerecycled in galaxies and are deposited into the intergalactic medium.New observations are revealing the ubiquity of this process,particularly at high redshift. We describe the physics behind thesewinds, discuss the observational evidence for them in nearbystar-forming and active galaxies and in the high-redshift universe, andconsider the implications of energetic winds for the formation andevolution of galaxies and the intergalactic medium. To inspire futureresearch, we conclude with a set of observational and theoreticalchallenges.
| Outflows in Active Galactic Nucleus/Starburst-Composite Ultraluminous Infrared Galaxies1,
Galactic superwinds occur in almost all infrared-luminous galaxies withstar formation rates (SFRs) above 10 Msolar yr-1,as shown by studies of the Na I D interstellar absorption line. Wedemonstrate that this result also applies to ultraluminous infraredgalaxies (ULIRGs) that host an active galactic nucleus (AGN) embedded ina strong starburst (SFR>~100 Msolar yr-1) bystudying a sample of 26 Seyfert ULIRGs in Na I D. The infraredluminosity of these galaxies is powered jointly by the AGN andstarburst. We find that there are hints of the influence of the AGN onoutflows in Seyfert 2/starburst composites, but the evidence is not yetstatistically conclusive. The evidence we find is lower wind detectionrates (i.e., wind opening angles) in Seyfert 2 ULIRGs than in galaxiesof comparable LIR, higher velocities than in galaxies ofcomparable SFR, and correlations between the neutral gas and the ionizedgas in the extended narrow-line region. Although the AGN probablycontributes to the outflows in Seyfert 2 ULIRGs, its momentum and energyinjection is equal to or less than that of the starburst. Similarly, theoutflow mechanical luminosity (energy outflow rate) per unit radiativeluminosity is the same for starburst and Seyfert 2 ULIRGs. In the nucleiof Seyfert 1 ULIRGs, we observe small-scale outflows that are poweredsolely by the AGN. However, in Mrk 231, we observe both a high-velocity,small-scale and low-velocity, extended outflow. The latter may bepowered by a starburst or radio jet. These large-scale, lower velocityoutflows certainly exist in other Seyfert 1 ULIRGs, but they are washedout by the light of the nucleus.Some of the observations reported here were obtained at the MMTObservatory, which is a joint facility of the Smithsonian Institutionand the University of Arizona.Some of the observations reported here were obtained at the Kitt PeakNational Observatory, National Optical Astronomy Observatory, which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under cooperative agreement with the National ScienceFoundation.
| On the Maximum Luminosity of Galaxies and Their Central Black Holes: Feedback from Momentum-driven Winds
We investigate large-scale galactic winds driven by momentum deposition.Momentum injection is provided by (1) radiation pressure produced by thecontinuum absorption and scattering of photons on dust grains and (2)supernovae (momentum injection by supernovae is important even if thesupernova energy is radiated away). Radiation can be produced by astarburst or active galactic nucleus (AGN) activity. We argue thatmomentum-driven winds are an efficient mechanism for feedback during theformation of galaxies. We show that above a limiting luminosity,momentum deposition from star formation can expel a significant fractionof the gas in a galaxy. The limiting, Eddington-like luminosity isLM~=(4fgc/G)σ4, where σ isthe galaxy velocity dispersion and fg is the gas fraction;the subscript M refers to momentum driving. A starburst that attainsLM moderates its star formation rate and its luminosity doesnot increase significantly further. We argue that elliptical galaxiesattain this limit during their growth at z>~1 and that this is theorigin of the Faber-Jackson relation. We show that Lyman break galaxiesand ultraluminous infrared galaxies have luminosities nearLM. Since these starbursting galaxies account for asignificant fraction of the star formation at z>~1, this supports ourhypothesis that much of the observed stellar mass in early-type galaxieswas formed during Eddington-limited star formation. Star formation isunlikely to efficiently remove gas from very small scales in galacticnuclei, i.e., scales much smaller than that of a nuclear starburst. Thisgas is available to fuel a central black hole (BH). We argue that a BHclears gas out of its galactic nucleus when the luminosity of the BHitself reaches ~LM. This shuts off the fuel supply to the BHand may also terminate star formation in the surrounding galaxy. As aresult, the BH mass is fixed to beMBH~=(fgκes/πG2)σ4,where κes is the electron scattering opacity. Thislimit is in accord with the observed MBH-σ relation.
| X-ray emission from NGC 1808: more than a complex starburst
Earlier observations of NGC 1808 in various wavebands (X-ray, optical,near-infrared, radio) provided evidence for the existence of either astarburst or a Seyfert 2 nucleus. We here present the results ofmultiwavelength XMM-Newton and Chandra observations, which directlyprove the co-existence of thermal diffuse plasma and non-nuclearunresolved point-like sources associated with the starburst activity,along with a Low Luminosity Active Galactic Nucleus (LLAGN) or an UltraLuminous X-ray source (ULX). The broad bandwidth of XMM-Newton allows usto show that the unresolved nuclear source in NGC 1808 dominates thehard X-ray spectrum, while the emission in the soft regime, below 1 keV,is dominated by a thermal component associated to an extended starburst.Both EPIC and RGS data provide reliable detections of a number ofemission lines from heavy elements, with abundances ranging from roughly0.7 to 2.2 Z_ȯ for different elements. However, no 6.4 keV FeKα fluorescence line emission was detected. The analysis of thenuclear region of NGC 1808 allows us to detect and disentangle thecontribution of an unresolved nuclear X-ray source and the starburstregion, but the exact nature of the nucleus remains unknown. Theobserved luminosity of NGC 1808 is L2{-10keV}=(1.61±0.06)×1040 erg s-1. Acomparison of our OM 212 nm image with a CTIO 4-m telescope Hαframe shows a good general correspondence between the emission frommassive stars and warm ionized gas, with minor deviations near the endsof the bar in NGC 1808. An aditional, very soft thermal spectralcomponent with kT≃ 0.1 keV has been discovered in the XMM-Newtonspectral analysis, which most likely originates from the halo of NGC1808.
| Mid-infrared imaging of active galaxies. Active nuclei and embedded star clusters
High resolution, mid-infrared (MIR) images of nine nearby activegalaxies are presented. The data were obtained with the TIMMI 2instrument mounted at the ESO 3.6 m telescope using a set of N-bandnarrow filters. The resulting images have an angular resolution of0.6´´-1´´. The MIR emission has been resolved infour galaxies: NGC 253, NGC 1365, NGC 1808 and NGC 7469. The images showa circumnuclear population of unknown MIR sources in NGC 1365 and NGC1808, coincident with radio sources. These MIR/radio sources areinterpreted in terms of embedded young star clusters. A high-resolutionMIR map of NGC 253 is also presented, and enables the identification ofa previously unknown MIR counterpart to the radio nucleus. Extended MIRemission is detected in NGC 7469, and concurs with previous observationsin the NIR and radio. For this source, an interesting morphologicaldifference between the 10.4 μ m and the 11.9 μ m emission isobserved, suggesting the presence of a dust-rich micro-bar. Our MIRimages of Circinus do not show resolved emission from the nucleus downto an angular scale of 0.5´´. In the case of NGC 2992, anupper limit to the extended MIR emission can be set. We provide new MIRflux measurements for the unresolved AGN in NGC 5995, IZw1 and IIZw136.
| 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.
| PAH emission variations within the resolved starbursts of NGC 253 and NGC 1808
In order to better characterise the usefulness of PAH emission as atracer of star formation, we have undertaken a programme of 3 μmnarrowband imaging of a sample of nearby template galaxies covering awide range of metallicity, star formation activity, and nuclearactivity. In the present paper we present first results of thisprogramme: high spatial resolution images of PAH feature emission andthe adjacent continuum emission from the central regions of the nearbystarburst galaxies NGC 253 and NGC 1808, taken with ISAAC at theVLT-UT1. Globally, the feature emission is seen to peak on the centralstarburst regions of both sources. On smaller scales, however, we see nogeneral spatial correlation or anti-correlation between the PAH featureemission and the location of sites of recent star formation, suggestingthat the degree to which PAH feature emission traces starburst activityis more complicated than previously hypothesized based on results fromdata with lower spatial resolution. We do find spatial correlations,though, when we consider the feature-to-continuum ratio, which is low atthe positions of known super star clusters in NGC 1808 as well as at theposition of the IR peak in NGC 253. We take this to imply a decrease inthe efficiency of PAH emission induced by the star formation, causedeither by mechanical energy input into the ISM, photoionisation of thePAH molecules, or photodissociation of the PAH molecules. All threehypotheses are discussed. In addition, for the first time we presentobservations of PAH feature emission in the superwind of a starburstingsystem (NGC 253), providing strong support that winds are heavilymass-loaded and entrain substantial amounts of ambient ISM. We have alsofound a plausible connection between observed NaD absorption, H2, andPAHs above the plane of NGC 253. This observation has importantimplications for enriching galaxy halos and possibly the intergalacticmedium with small dust grains.Based on observations made with ESO Telescopes at the ParanalObservatory under programme ID 68.B-0264(A).
| Multi-density model of the ionised gas in NGC 253 using radio recombination lines
We have imaged the H92α (8.3 GHz), H75α (15 GHz), andH166α (1.4 GHz) Radio Recombination Lines (RRLs) from NGC 253 atresolutions of 4.5 pc (0.4'') , 2.5 pc (0.2'') and 53 pc (4.5'')respectively. The H92α line arises from individual compactsources, most of which possess radio continuum counterparts. The linewidths range from ~200 km s-1 for the sources near the radionucleus to 70-100 km s-1 for the extranuclear ones. Theselines are emitted by gas at a density ~104 cm-3.The remainder of the cm-wave RRLs arise in lower density gas (~500cm-3) with a higher area filling factor and with ten timeshigher mass. A third component of higher density gas (>104cm-3) is required to explain the mm-wave RRLs.Appendix A is only available in electronic form athttp://www.edpsciences.org
| Cosmic magnetic fields - as observed in the Universe, in galactic dynamos, and in the Milky Way
Cosmic magnetism has that exotic ``Je ne sais quoi''! Magnetism has beenobserved in various objects, located near the edge of the Universe andall the way down to the Milky Way's center. The observed magnetic fieldcan take the cell-type shape in randomly-oriented large blobs found inintracluster gas or outside of clusters of galaxies, the helix shape insynchrotron jets, the longitudinal shape in ram-pressured shocks inradio lobes near elliptical galaxies, the spiral shape of logarithmicarms in spiral galaxies, or the egg shape of an enlarged interstellarbubble. In strength, the magnetic field varies from 0.1 nG(cosmological), to 20 μG (galaxies, jets, superbubbles), and to 1 mGin the Milky Way filaments.Magnetism plays a small physical role in the formation of largestructures. It acts as a tracer of the dynamical histories ofcosmological and intracluster events, it guides the motion of theinterstellar ionised gas, and it aligns the charged dust particles.Batteries and dynamos are often employed in models to create and amplifyseed magnetic fields. Starting soon after the Big Bang (redshiftz>2000), this review covers the cosmological background surface(z~1100, distance ~4.3 Gpc), the epoch of first stars (z~20 distance~4.1 Gpc), the currently observable Universe (z~10, distance ~3.9 Gpc),superclusters of galaxies (size ~50 Mpc), intracluster gas (size ~10Mpc), galaxies (~30 kpc), spiral arms (~10 kpc), interstellarsuperbubbles (~100 pc), synchrotron filaments (~10 pc), and the MilkyWay's center.
| Extragalactic embedded clusters: exploring star formation.
Not Available
| Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.
| The GEMS project: X-ray analysis and statistical properties of the group sample
The Group Evolution Multiwavelength Study (GEMS) involves amultiwavelength study of a sample of 60 galaxy groups, chosen to span awide range of group properties. Substantial ROSAT Position SensitiveProportional Counter (PSPC) observations, available for all of thesegroups, are used to characterize the state of the intergalactic mediumin each. We present the results of a uniform analysis of these ROSATdata and a statistical investigation of the relationship between X-rayand optical properties across the sample. Our analysis improves inseveral respects on previous work: (i) we distinguish between systems inwhich the hot gas is a group-scale medium and those in which it appearsto be just a hot halo associated with a central galaxy; (ii) weextrapolate X-ray luminosities to a fixed overdensity radius(r500) using fitted surface brightness models, in order toavoid biases arising from the fact that cooler systems are detectable tosmaller radii, and (iii) optical properties have been rederived in auniform manner from the NASA Extragalactic Database, rather than relyingon the data in the disparate collection of group catalogues from whichour systems are drawn.The steepening of the LX-TX relation in the groupregime reported previously is not seen in our sample, which fits well onto the cluster trend, albeit with large non-statistical scatter. Anumber of biases affect the fitting of regression lines under thesecircumstances, and until the impact of these has been thoroughlyinvestigated it seems best to regard the slope of the groupLX-TX relation as being poorly determined. Asignificant problem in comparing the properties of groups and clustersis the derivation of system radii, to allow different systems to becompared within regions having the same overdensity. We find evidencethat group velocity dispersion (σv) provides a veryunreliable measure of system mass (and hence radius), with a number ofgroups having remarkably low values of σv, given thatthey appear from their X-ray properties to be collapsed systems. Weconfirm that the surface brightness profiles of groups are significantlyflatter than those of clusters - the maximum value of theβfit parameter for our sample is 0.58, lower than thetypical value of 0.67 seen in clusters - however, we find no significanttendency within our sample for cooler groups to show flatter profiles.This result is inconsistent with simple universal pre-heating models.The morphology of the galaxies in the GEMS groups is correlated to theirX-ray properties in a number of ways: we confirm the very strongrelationship between X-ray emission and a dominant early-type centralgalaxy, which has been noted since the early X-ray studies of groups,and also find that spiral fraction is correlated with the temperature ofthe hot gas and hence the depth of the gravitational potential. A classof spiral-rich groups with little or no X-ray emission probablycorresponds to groups that have not yet fully collapsed.
| LX-SFR relation in star-forming galaxies
We compare the results of Grimm, Gilfanov & Sunyaev and Ranalli,Comastri & Seti on the LX-SFR (X-ray luminosity-starformation rate) relation in normal galaxies. Based on theLX-stellar mass dependence for low-mass X-ray binaries(LMXBs), we show that low-SFR (<~1 Msolar yr-1)galaxies in the Ranalli et al. sample are contaminated by the X-rayemission from LMXBs, unrelated to the current star formation activity.However, the most important conclusion from our comparison is that,after the data are corrected for the `LMXB contamination', the two datasets become consistent with each other, despite differences in theircontent, variability effects, adopted source distances, X-ray fluxes andSFR determinations, and also in the cosmological parameters used ininterpreting the Hubble Deep Field North (HDF-N) data. They also agreewell, both in the low- and high-SFR regimes, with the predictedLX-SFR dependence derived from the parameters of the`universal' high-mass X-ray binary (HMXB) luminosity function. Thisencouraging result emphasizes the potential of the X-ray luminosity asan independent SFR indicator for normal galaxies.
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