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|An upper limit to polarized submillimetre emission in Arp 220|
We report the results of pointed observations of the prototypicalultraluminous infrared galaxy (ULIRG) Arp 220 at 850μm using thepolarimeter on the Submillimetre Common User Bolometer Array instrumenton the James Clerk Maxwell Telescope. We find a Bayesian 99 per centconfidence upper limit on the polarized emission for Arp 220 of 1.54 percent, averaged over the 15-arcsec beam-size. Arp 220 can serve as aproxy for other, more distant such galaxies. This upper limit constrainsthe magnetic field geometry in Arp 220 and also provides evidence thatpolarized ULIRGs will not be a major contaminant for next-generationcosmic microwave background polarization measurements.
|A NICMOS search for obscured supernovae in starburst galaxies|
The detection of obscured supernovae (SNe) in near-infrared monitoringcampaigns of starburst galaxies has shown that a significant fraction ofSNe is missed by optical surveys. However, the number of SNe detected inground-based near-IR observations is still significantly lower than thenumber of SNe extrapolated from the FIR luminosity of the hosts. Apossibility is that most SNe occur within the nuclear regions, where thelimited angular resolution of ground-based observations prevents theirdetection. This issue prompted us to exploit the superior angularresolution of NICMOS-HST to search for obscured SNe within the first kpcfrom the nucleus of strong starbursting galaxies. A total of 17 galaxieswere observed in SNAPSHOT mode. Based on their FIR luminosity, we didnot expect to detect fewer than ~ 12 SNe. However, no confirmed SN eventwas found. From our data we derived an observed nuclear SN rate <0.5SN/yr per galaxy. The shortage of SN detections can be explained by acombination of several effects. The most important are: i) the existenceof a strong extinction, A_V 11; ii) most SNe occur within the first0.5 arcsec (which corresponds in our sample to about 500 pc) where evenNICMOS is unable to detect SN events.Based on observations made with the NASA/ESA Hubble Space Telescopeassociated with program 9726,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555,and on data obtained at the VLT through the ESO program 272.D-5043.
|The great Milky Way -Andromeda collision.|
|Mid-Infrared All-Sky Survey with the Infrared Camera (IRC) on Board the ASTRO-F Satellite|
An all-sky survey in two mid-infrared bands covering wavelengths from 6to 12 and 14 to 26 μm, with a spatial resolution of ~9.4"-10", willbe performed with the Infrared Camera (IRC) on board the ASTRO-Finfrared astronomical satellite. The expected detection limit for pointsources is 80-130 mJy (5 σ). The all-sky survey will provide datawith a detection limit and a spatial resolution an order of magnitudedeeper and higher, respectively, than those of the Infrared AstronomicalSatellite survey. The IRC is optimally designed for deep imaging instaring observations. It employs 256 × 256 Si:As IBC infraredfocal plane arrays for the two mid-infrared channels. In order to makeobservations with the IRC during the scanning observations for theall-sky survey, a new method of operation for the arrays has beendeveloped-``scan mode'' operation. In the scan mode, only 256 pixels ina single row aligned in the cross-scan direction on the array are usedas the scan detector, and they are sampled every 44 ms. Special care hasbeen taken to stabilize the temperature of the array in scan mode, whichenables the user to achieve a low readout noise, comparable to that inthe imaging mode (20-30 e-). The accuracy of the positiondetermination and the flux measurement for point sources is examinedboth in computer simulations and laboratory tests with the flight modelcamera and moving artificial point sources. In this paper we present thescan mode operation of the array, the results of the computer simulationand the laboratory performance test, and the expected performance of theIRC all-sky survey observations.
|Deep Extragalactic Surveys around the Ecliptic Poles with AKARI (ASTRO-F)|
AKARI (formerly ASTRO-F) is an infrared space telescope designed for anall-sky survey at 10-180 μm, and deep pointed surveys of selectedareas at 2-180 μm. The deep pointed surveys with AKARI willsignificantly advance our understanding of galaxy evolution, thestructure formation of the universe, the nature of buried AGNs, and thecosmic infrared background. We describe here the importantcharacteristics of the AKARI mission, the orbit, and attitude controlsystem, and investigate the optimum survey area based on the updatedpre-flight sensitivities of AKARI, taking into account the cirrusconfusion noise as well as the surface density of bright stars. TheNorth Ecliptic Pole is concluded to be the best area for 2-26μm deepsurveys, while the low-cirrus noise regions around the South EclipticPole are worth considering for 50-180μm pointed surveys to highsensitivities limited by the galaxy confusion noise. Currentobservational plans concerning these pointed surveys are described indetail. Comparing these surveys with deep surveys using the SpitzerSpace Telescope, the AKARI deep surveys are particularly unique inrespect of their continuous wavelength coverage over the 2-26μm rangein broad-band deep imaging, and their slitless spectroscopy mode overthe same wavelength range.
|X-ray observations of three young, early-type galaxies|
Massive haloes of hot plasma exist around some, but not all ellipticalgalaxies. There is evidence that this is related to the age of thegalaxy. In this paper, new X-ray observations are presented for threeearly-type galaxies that show evidence of youth, in order to investigatetheir X-ray components and properties. NGC 5363 and NGC 2865 were foundto have X-ray emission dominated by purely discrete stellar sources.Limits are set on the mass distribution in one of the galaxies observedwith XMM-Newton, NGC 4382, which contains significant hot gas. We detectthe X-ray emission in NGC 4382 out to 4re. The mass-to-lightratio is consistent with a stellar origin in the inner regions but risessteadily to values indicative of some dark matter by 4re.These results are set in context with other data drawn from theliterature, for galaxies with ages estimated from dynamical orspectroscopic indicators. Ages obtained from optical spectroscopyrepresent central luminosity-weighted stellar ages. We examine the X-rayevolution with age, normalized by B- and K-band luminosities. Low valuesof Log(LX/LB) and Log(LX/LK)are found for all galaxies with ages between 1 and 4 Gyr. Luminous X-rayemission only appears in older galaxies. This suggests that theinterstellar medium is removed and then it takes several gigayears forhot gas haloes to build up, following a merger. A possible mechanism forgas expulsion might be associated with feedback from an active nucleustriggered during a merger.
|A population of high-redshift type 2 quasars - I. Selection criteria and optical spectra|
We discuss the relative merits of mid-infrared and X-ray selection oftype 2 quasars. We describe the mid-infrared, near-infrared and radioselection criteria used to find a population of redshift z ~ 2 type 2quasars which we previously argued suggests that most supermassive blackhole growth in the Universe is obscured. We present the optical spectraobtained from the William Herschel Telescope, and we compare the narrowemission-line luminosity, radio luminosity and maximum size of jets tothose of objects from radio-selected samples. This analysis suggeststhat these are genuine radio-quiet type 2 quasars, albeit theradio-bright end of this population. We also discuss the possibility oftwo different types of quasar obscuration, which could explain how the~2-3:1 ratio of type 2 to type 1 quasars preferred by modelling ourpopulation can be reconciled with the ~1:1 ratio predicted by unifiedschemes.
|Modelling galaxy spectra in presence of interstellar dust - II. From the ultraviolet to the far-infrared|
In this paper, we present spectrophotometric models for galaxies ofdifferent morphological type whose spectral energy distributions (SEDs)take into account the effect of dust in absorbing ultraviolet-optical(UV-optical) light and re-emitting it in the infrared. The modelscontain three main components: (i) the diffuse interstellar medium (ISM)composed of gas and dust, (ii) the large complexes of molecular clouds(MCs) in which new stars are formed and (iii) the stars of any age andchemical composition.The galaxy models stand on a robust model of chemical evolution thatassuming a suitable prescription for gas infall, initial mass function,star formation rate and stellar ejecta provides the total amounts of gasand stars present at any age together with their chemical history. Thechemical models are tailored in such a way to match the gross propertiesof galaxies of different morphological type. In order to describe theinteraction between stars and ISM in building up the total SED of agalaxy, one has to know the spatial distribution of gas and stars. Thisis made adopting a simple geometrical model for each type of galaxy. Thetotal gas and star mass provided by the chemical model are distributedover the whole volume by means of suitable density profiles, one foreach component and depending on the galaxy type (spheroidal, disc anddisc plus bulge). The galaxy is then split in suitable volume elementsto each of which the appropriate amounts of stars, MCs and ISM areassigned. Each elemental volume bin is at the same time source ofradiation from the stars inside and absorber and emitter of radiationfrom and to all other volume bins and the ISM in between. They are theelemental seeds to calculate the total SED.Using the results for the properties of the ISM and the single stellarpopulations presented by Piovan et al. we derive the SEDs of galaxies ofdifferent morphological type. First, the technical details of the methodare described and the basic relations driving the interaction betweenthe physical components of the galaxy are presented. Secondly, the mainparameters are examined and their effects on the SED of three prototypegalaxies (a disc, an elliptical and a starburster) are highlighted. Thefinal part of the paper is devoted to assess the ability of our galaxymodels in reproducing the SEDs of a few real galaxies of the localuniverse.
|The Hubble Deep Field-North SCUBA Super-map - IV. Characterizing submillimetre galaxies using deep Spitzer imaging|
We present spectral energy distributions (SEDs), Spitzer colours, andinfrared (IR) luminosities for 850-μm selected galaxies in the GreatObservatories Origins Deep Survey Northern (GOODS-N) field. Using thedeep Spitzer Legacy images and new data and reductions of the Very LargeArray-Hubble Deep Field (VLA-HDF) radio data, we find statisticallysecure counterparts for 60 per cent (21/35) of our submillimetre (submm)sample, and identify tentative counterparts for another 12 objects. Thisis the largest sample of submm galaxies with statistically securecounterparts detected in the radio and with Spitzer. Half of the securecounterparts have spectroscopic redshifts, while the other half havephotometric redshifts. We find that in most cases the 850-μm emissionis dominated by a single 24-μm source, with a median flux density of241μJy, leading to a median 24-to-850-μm flux density ratio of0.040. A composite rest-frame SED shows that the submm sources peak atlonger wavelengths than those of local ultraluminous infrared galaxies(ULIRGs). Using a basic grey-body model, 850-μm selected galaxiesappear to be cooler than local ULIRGs of the same luminosity. Thisdemonstrates the strong selection effects, both locally and at highredshift, which may lead to an incomplete census of the ULIRGpopulation. The SEDs of submm galaxies are also different from those oftheir high-redshift neighbours, the near-IR selected BzK galaxies, whosemid-IR-to-radio SEDs are more like those of local ULIRGs. Using24-μm, 850-μm and 1.4-GHz observations, we fit templates that spanthe mid-IR through radio to derive the integrated IR luminosity (LIR) ofthe submm galaxies and find a median value ofLIR(8-1000μm) = 6.0 × 1012Lsolar. By themselves, 24-μm and radio fluxes are able topredict LIR reasonably well because they are relativelyinsensitive to temperature. However, the submm flux by itselfconsistently overpredicts LIR when using spectral templateswhich obey the local ULIRG temperature-luminosity relation. The shorterSpitzer wavelengths sample the stellar bump at the redshifts of thesubmm sources, and we find that the Spitzer photometry alone provides amodel-independent estimate of the redshift, σ[Δz/(1 + z)] =0.07. The median redshift for our secure submm counterparts is 2.0.Using X-ray and mid-IR data, only 5 per cent of our secure counterparts(1/21) show strong evidence for an active galactic nucleus dominatingthe LIR.
|Luminosity functions for galaxies and quasars in the Spitzer Wide-area Infrared Extragalactic Legacy Survey|
We construct rest-frame luminosity functions (LFs) at 3.6, 4.5, 5.8, 8and 24 μm over the redshift range 0 < z < 2 for galaxies and 0< z < 4 for optical quasi-stellar objects (QSOs), using opticaland infrared (IR) data from the Spitzer Wide-area Infrared Extragalactic(SWIRE) Survey. The 3.6- and 4.5-μm galaxy LFs show evidence formoderate positive luminosity evolution up to z ~ 1.5, consistent withthe passive ageing of evolved stellar populations. Their comovingluminosity density was found to evolve passively, gradually increasingout to z ~ 0.5-1 but flattening, or even declining, at higher redshift.Conversely, the 24-μm galaxy LF, which is more sensitive to obscuredstar formation and/or active galactic nuclei (AGN) activity, undergoesstrong positive evolution, with the derived IR energy density and starformation rate (SFR) density ~ (1 + z)γ with γ =4.5+0.7-0.6 and the majority of this evolutionoccurring since z ~ 1. Optical QSOs, however, show positive luminosityevolution in all bands, out to the highest redshifts (3 < z < 4).Modelling as L* ~ (1 + z)γ gave γ =1.3+0.1-0.1 at 3.6μm,γ =1.0+0.1-0.1 at 4.5μm and stronger evolution atthe longer wavelengths (5.8, 8 and 24μm), of γ ~ 3. Comparisonof the galaxy LFs to predictions from a semi-analytic model based oncold dark matter (CDM) indicates that an initial mass function (IMF)skewed towards higher mass star formation in bursts compared to locallybe preferred. As a result, the currently inferred massive SFRs indistant submm sources may require substantial downwards revision.
|Millimetric properties of gamma-ray burst host galaxies|
We present millimetre (mm) and submillimetre (submm) photometry of asample of five host galaxies of gamma-ray bursts (GRBs), obtained usingthe Max Planck Millimetre Bolometer (MAMBO2) array and SubmillimetreCommon-User Bolometer Array (SCUBA). These observations were obtained aspart of an ongoing project to investigate the status of GRBs asindicators of star formation. Our targets include two of the mostunusual GRB host galaxies, selected as likely candidate submm galaxies:the extremely red (R - K ~ 5) host of GRB 030115, and the extremelyfaint (R > 29.5) host of GRB 020124. Neither of these galaxies isdetected, but the deep upper limits for GRB 030115 impose constraints onits spectral energy distribution, requiring a warmer dust temperaturethan is commonly adopted for submillimetre galaxies (SMGs).As a framework for interpreting these data, and for predicting theresults of forthcoming submm surveys of Swift-derived host samples, wemodel the expected flux and redshift distributions based on luminosityfunctions of both submm galaxies and GRBs, assuming a directproportionality between the GRB rate density and the global starformation rate density. We derive the effects of possible sources ofuncertainty in these assumptions, including (1) introducing ananticorrelation between GRB rate and the global average metallicity, and(2) varying the dust temperature.
|The 1-1000μm spectral energy distributions of far-infrared galaxies|
Galaxies selected at 170μm by the Infrared Space Observatory (ISO)Far-IR BACKground (FIRBACK) survey represent the brightest ~10 per centof the cosmic infrared background. Examining their nature in detail istherefore crucial for constraining models of galaxy evolution. Here, wecombine Spitzer archival data with previous near-infrared (near-IR),far-IR, and submillimetre (submm) observations of a representativesample of 22 FIRBACK galaxies spanning three orders of magnitude in IRluminosity. We fit a flexible, multicomponent, empirical SED model ofstar-forming galaxies designed to model the entire ~1-1000μmwavelength range. The fits are performed with a Markov Chain Monte Carlo(MCMC) approach, allowing for meaningful uncertainties to be derived.This approach also highlights degeneracies such as between Tdand β, which we discuss in detail. From these fits and standardrelations we derive: LIR, LPAH, star formationrate (SFR), τV, M*, Mdust,Td, and β. We look at a variety of correlations betweenthese and combinations thereof in order to examine the physical natureof these galaxies. Our conclusions are supplemented by morphologicalexamination of the sources, and comparison with local samples. We findthe bulk of our sample to be consistent with fairly standard size andmass disc galaxies with somewhat enhanced star formation relative tolocal spirals, but likely not bona fide starbursts. A few higher-zluminous infrared galaxies (LIGs) and ultraluminous infrared galaxies(ULIGs) are also present, but contrary to expectation, they are weakmid-IR emitters and overall are consistent with star formation over anextended cold region rather than concentrated in the nuclear regions. Wediscuss the implications of this study for understanding populationsdetected at other wavelengths, such as the bright 850-μmSubmillimetre Common-User Bolometer Array (SCUBA) sources or the faintSpitzer 24-μm sources.
|Far-infrared detection limits - II. Probing confusion including source confusion|
We present a comprehensive analysis for the determination of theconfusion levels for the current and the next generation of far-infraredsurveys assuming three different cosmological evolutionary scenarios. Weinclude an extensive model for diffuse emission from infrared cirrus inorder to derive absolute sensitivity levels taking into account thesource confusion noise due to point sources, the sky confusion noise dueto the diffuse emission, and instrumental noise. We use our derivedsensitivities to suggest best survey strategies for the current and thefuture far-infrared space missions Spitzer, AKARI (ASTRO-F), Herscheland SPICA. We discuss whether the theoretical estimates are realisticand the competing necessities of reliability and completeness. We findthe best estimator for the representation of the source confusion andproduce predictions for the source confusion using far-infrared sourcecount models. From these confusion limits considering both source andsky confusions, we obtain the optimal, confusion limited redshiftdistribution for each mission. Finally, we predict the cosmicfar-infrared background (CFIRB), which includes information about thenumber and distribution of the contributing sources.
|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).
|Revisiting the infrared spectra of active galactic nuclei with a new torus emission model|
We describe improved modelling of the emission by dust in atoroidal-like structure heated by a central illuminating source withinactive galactic nuclei (AGNs). We have chosen a simple but realistictorus geometry, a flared disc, and a dust grain distribution functionincluding a full range of grain sizes. The optical depth within thetorus is computed in detail taking into account the differentsublimation temperatures of the silicate and graphite grains, whichsolves previously reported inconsistencies in the silicate emissionfeature in type 1 AGNs. We exploit this model to study the spectralenergy distributions (SEDs) of 58 extragalactic (both type 1 and type 2)sources using archival optical and infrared data. We find that both AGNand starburst contributions are often required to reproduce the observedSEDs, although in a few cases they are very well fitted by a pure AGNcomponent. The AGN contribution to the far-infrared luminosity is foundto be higher in type 1 sources, with all the type 2 requiring asubstantial contribution from a circumnuclear starburst. Our resultsappear in agreement with the AGN unified scheme, because thedistributions of key parameters of the torus models turn out to becompatible for type 1 and type 2 AGNs. Further support to theunification concept comes from comparison with medium-resolutioninfrared spectra of type 1 AGNs by the Spitzer observatory, showingevidence for a moderate silicate emission around 10 μm, which ourcode reproduces. From our analysis we infer accretion flows in the innernucleus of local AGNs characterized by high equatorial optical depths(AV~= 100), moderate sizes (Rmax < 100 pc) andvery high covering factors (f~= 80 per cent) on average.
|Unveiling the nature of Ultraluminous Infrared Galaxies with 3-4μm spectroscopy*|
We present the results of L-band spectroscopical observations of localbright Ultraluminous Infrared Galaxies (ULIRGs), performed with theInfrared Spectrometer And Array Camera (ISAAC) at the Very LargeTelescope. The excellent sensitivity of the telescope and of theinstrument provided spectra of unprecedented quality for this class ofobjects, which allowed a detailed study of the active galactic nucleus(AGN)/starburst contribution to the energy output, and of thecomposition of the circumnuclear absorber. We discuss the L-bandspectral features of seven single sources, and the statisticalproperties of a complete sample of 15 sources obtained combining ourobservations with other published 3-4 μm spectra. Our main resultsare as follows. (i) When a spectral indicator suggesting the presenceof an AGN (low equivalent width of the 3.3-μm emission line, steepλ-fλ spectrum, presence of an absorptionfeature at 3.4 μm) is found, the AGN is always confirmed byindependent analysis at other wavelengths. Conversely, in all known AGNsat least one of the above indicators is present. (ii) Two newdiagnostic diagrams are proposed combining the above indicators, inwhich starbursts and AGNs are clearly and completely separated. (iii)The above diagnostic techniques are possible with spectra of relativelylow quality, which can be obtained for several tens of ULIRGs withcurrently available telescopes. This makes L-band spectroscopy thecurrent best tool to disentangle AGN and starburst contributions inULIRGs. (iv) The L-band properties of ULIRGs are heterogeneous.However, we show that all the spectral differences among ULIRGs can bereproduced starting from pure intrinsic AGN and starburst spectra andtwo varying parameters: the amount of dust extinction of the AGNcomponent, and the relative AGN/starburst contribution to the bolometricluminosity. (v) Using the above decomposition model, we show that AGNsin ULIRGs have a low dust-to-gas ratio and a dust extinction curvedifferent from Galactic. (vi) The estimate of the presence andcontribution of AGNs in a complete sample shows that AGNs are hosted byapproximately two-thirds of ULIRGs, but their energetic contribution isrelevant (>30 per cent of the bolometric luminosity) only in ~20 percent of the sample.
|Nuclear starbursts and AGN fueling|
We argue that radiation pressure from star formation can support agalactic disk against its own self-gravity. This model is appropriatewhen the disk is optically thick to its own infrared radiation, as inthe central regions of Ultraluminous Infrared Galaxies and in the outerparts of accretion disks in Active Galactic Nuclei. We review theproperties of radiation-pressure supported disks and discuss theconditions under which AGN can be fueled by gas stored in an outerstarburst disk.
|Star Formation Rates and Stellar Masses in z ~ 1 Gamma-Ray Burst Hosts|
We analyze 4.5, 8, and 24 μm band Spitzer images of six gamma-rayburst host galaxies at redshifts close to 1. We constrain their starformation rates (SFRs) based on the entire available spectral energydistribution rather than the 24 μm band only. Further, we estimatetheir stellar masses (M*) based on rest-frame K-bandluminosities. Our sample spans a wide range of galaxy properties:derived SFRs range from less than 10 to a few hundred solar masses peryear; values of M* range from 109 to1010 Msolar with a median of5.6×109 Msolar. Comparing the specific starformation rate (φ≡SFR/M*) of our sample as afunction of M* to other representative types of galaxies(distant red galaxies, Lyα emitters, Lyman break galaxies,submillimeter galaxies, and z~2 galaxies from the Great ObservatoriesOrigins Deep Survey-North field), we find that gamma-ray burst hosts areamong those with the highest φ.This work is based in part on observations made with the Spitzer SpaceTelescope, which is operated by the Jet Propulsion Laboratory,California Institute of Technology, under a contract with NASA.
|The Spitzer View of Low-Metallicity Star Formation. I. Haro 3|
We present Spitzer observations of the blue compact dwarf galaxy Haro 3,with an oxygen abundance of 12+log(O/H)=8.32. These data are part of alarger study of star formation and dust in low-metallicity environments.The IRS spectrum of Haro 3 shows strong narrow PAH emission, with highequivalent widths. Gaseous nebular fine-structure lines are also seen.Despite the absence of optical high-excitation lines, a fainthigh-ionization O IV line at 25.89 μm indicates the presence ofradiation as hard as 54.9 eV. A CLOUDY model suggests that the MIR linesoriginate in two regions: a low-extinction optically emitting region,and an optically invisible one with much higher extinction. Themorphology of Haro 3 changes with wavelength. IRAC 4.5 μm tracesextended stellar photospheric emission from the body of the galaxy andhot dust continuum coming mainly from star-forming regions, 8 μmprobes extended PAH emission coming mainly from the general ISM, MIPS 24and 70 μm images map compact small-grain warm dust emissionassociated with active star formation, and 160 μm reflects coolerextended dust associated with older stellar populations. We have derivedthe optical-to-radio SED of the brightest star-forming region A in Haro3. The best-fit DUSTY model of the SED gives a total luminosity of2.8×109 Lsolar and a mass of2.8×106 Msolar for the ionizing clusters. Weinfer an extinction AV<~3, intermediate between theoptical AV~0.5 and the radio AV~8, consistent withthe picture that longer wavelength observations probe more deeply intostar-forming regions.
|The Evolution of Obscuration in Active Galactic Nuclei|
In order to study the evolution of the relative fraction of obscuredactive galactic nuclei (AGNs), we constructed the largest sample to dateof AGNs selected in hard X-rays. The full sample contains 2341X-ray-selected AGNs, roughly 4 times the largest previous samplesstudied in this connection. Of these, 1229 (53%) have opticalcounterparts for which redshifts are available; these span the redshiftrange z=0-4. The observed fraction of obscured AGNs declines onlyslightly with redshift. Correcting for selection bias, we find that theintrinsic fraction of obscured AGNs must actually increase withredshift, as (1+z)α, with α~=0.4+/-0.1. Thisevolution is consistent with the integrated X-ray background, whichprovides the strongest constraints at relatively low redshift, z~1.Summing over all AGNs, we estimate the bolometric AGN light to be 3.8 nWm-2 sr-1, or <~8% of the total extragalacticlight. Together with the observed black hole mass density in the localuniverse, this implies an accretion efficiency of η~0.1-0.2,consistent with the values typically assumed.
|Hidden Trigger for the Giant Starburst Arc in M83?|
The huge star formation events that occur at some galactic centers donot provide enough clues as to their origin, since the morphologicalsignatures of the triggering mechanism are smeared out in the timescaleof a few orbital revolutions of the galaxy core. Our high spatialresolution three-dimensional near-infrared spectroscopy for the firsttime reveals that a previously known hidden mass concentration islocated exactly at the youngest end of a giant star-forming arc. Thislocation, the inferred average cluster ages, and the dynamical timesclearly indicate that the interloper has left behind a spur of violentstar formation in M83, in a transient event lasting less than oneorbital revolution. The study of the origin (bar funneling orcannibalized satellite) and fate (black hole merging or giant stellarcluster) of this system could provide clues to the question of coregrowing and morphological evolution in grand-design spiral galaxies. Inparticular, our TreeSPH numerical modeling suggests that the two nucleicould coalesce, forming a single massive core in about 60 million yearsor less. This work is based on observations made at the Gemini SouthTelescope.
|Dynamical Properties of Ultraluminous Infrared Galaxies. II. Traces of Dynamical Evolution and End Products of Local Ultraluminous Mergers|
We present results from our Very Large Telescope large program to studythe dynamical evolution of local ultraluminous infrared galaxies(ULIRGs) and QSOs. This paper is the second in a series presenting thestellar kinematics of 54 ULIRGs, derived from high-resolution, long-slitH- and K-band spectroscopy. The data presented here, includingobservations of 17 new targets, are mainly focused on sources that havecoalesced into a single nucleus. The stellar kinematics, extracted fromthe CO ro-vibrational band heads in our spectra, indicate that ULIRGremnants are dynamically heated systems with a mean dispersion of 161 kms-1. The combination of kinematic, structural, andphotometric properties of the remnants indicate that they mostlyoriginate from major mergers and that they result in the formation ofsystems supported by random motions, i.e., elliptical galaxies. The peakof the velocity dispersion distribution and the locus of ULIRGs on thefundamental plane of early-type galaxies indicate that the end productsof ultraluminous mergers are typically moderate-mass ellipticals (ofstellar mass ~1010-1011 Msolar).Converting the host dispersion into black hole mass with the aid of theMBH-σ relation yields black hole mass estimates of theorder 107-108 Msolar and high accretionrates with Eddington efficiencies often >0.5.Based on observations at the European Southern Observatory (ESO)(171.B-044).
|Effects of a Supermassive Black Hole Binary on a Nuclear Gas Disk|
We study the influence of a galactic central supermassive black hole(SMBH) binary on gas dynamics and star formation activity in a nucleargas disk with three-dimensional tree+SPH simulations. Because of theorbital motions of the SMBHs, there are various resonances between thegas motion and SMBH binary motion. We show that these resonances createcharacteristic structures of gas in the nuclear gas disk, for example,elongated or filament structures, gaseous spiral arms, and/or small gasdisks around the SMBHs. In these dense gaseous regions, active starformation is induced, and as a result, many starbursts are formed in thenuclear region.
|Spitzer IRS Spectra of Optically Faint Infrared Sources with Weak Spectral Features|
Spectra have been obtained with the low-resolution modules of theInfrared Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for58 sources having fν(24 μm)>0.75 mJy. Sources werechosen from a survey of 8.2 deg2 within the NOAO DeepWide-Field Survey region in Boötes (NDWFS) using the MultibandImaging Photometer (MIPS) on Spitzer. Most sources are optically veryfaint (I>24 mag). Redshifts have previously been determined for 34sources, based primarily on the presence of a deep 9.7 μm silicateabsorption feature, with a median z of 2.2. Spectra are presented forthe remaining 24 sources for which we were previously unable todetermine a confident redshift because the IRS spectra show no strongfeatures. Optical photometry from the NDWFS and infrared photometry withMIPS and the Infrared Array Camera on Spitzer (IRAC) are given, with Kphotometry from the Keck I telescope for some objects. The sourceswithout strong spectral features have overall spectral energydistributions (SEDs) and distributions among optical and infrared fluxesthat are similar to those for the sources with strong absorptionfeatures. Nine of the 24 sources are found to have feasible redshiftdeterminations based on fits of a weak silicate absorption feature.Results confirm that the ``1 mJy'' population of 24 μm Spitzersources that are optically faint is dominated by dusty sources withspectroscopic indicators of an obscured AGN rather than a starburst.There remain 14 of the 58 sources observed in Boötes for which noredshift could be estimated, and 5 of these sources are invisible at alloptical wavelengths.
|SHARC-2 350 μm Observations of Distant Submillimeter-selected Galaxies|
We present 350 μm observations of 15 Chapman et al. submillimetergalaxies (SMGs) with radio counterparts and optical redshifts. We detect12 and obtain sensitive upper limits for three, providing direct,precise measurements of their far-infrared luminosities andcharacteristic dust temperatures. With these, we verify the linearradio-far-infrared correlation at redshifts of z~1-3 and luminosities of1011-1013 Lsolar, with a power-lawindex of 1.02+/-0.12 and rms scatter of 0.12 dex. However, either thecorrelation constant q or the dust emissivity index β is lower thanmeasured locally. The best-fitting q~=2.14 is consistent with SMGs beingpredominantly starbust galaxies, without significant AGN contribution,at far-infrared wavelengths. Gas-to-dust mass ratios are estimated at54+14-11(κ850μm/0.15m2 kg-1), depending on the absoption efficiencyκν, with intrinsic dispersion ~=40% around the meanvalue. Dust temperatures consistent with 34.6+/-3 K(1.5/β)0.71, at z~1.5-3.5, suggest that far-infraredphotometric redshifts may be viable, and perhaps accurate to10%<~dz/(1+z), for up to 80% of the SMG population in this range, ifthe above temperature characterizes the full range of SMGs. However,observed temperature evolution of Td~(1+z) is also plausibleand could result from selection effects. From the observedluminosity-temperature (L-T) relation,L~T2.82+/-0.29obs, we derive scaling relations fordust mass versus dust temperature, and we identify expressions tointerrelate the observed quantities. These suggest that measurements ata single wavelength, in the far-infrared, submillimeter, or radio wavebands, might constrain dust temperatures and far-infrared luminositiesfor most SMGs with redshifts at z~0.5-4.
|A Search for H2O in the Strongly Lensed QSO MG 0751+2716 at z = 3.2|
We present a search for 183 GHz H2O(313-->220) emission in the infrared-luminousquasar MG 0751+2716 with the NRAO Very Large Array (VLA). Atz=3.200+/-0.001, this water emission feature is redshifted to 43.6 GHz.Unlike the faint rotational transitions of HCN (the standardhigh-density tracer at high z), H2O(313-->220) is observed with high maseramplification factors in Galactic star-forming regions. It thereforeholds the potential to trace high-density star-forming regions in thedistant universe. If indeed all star-forming regions in massivelystar-forming galaxies at z>3 have physical properties similar tothose of, e.g., the Orion or W49N molecular cloud cores, the flux ratiobetween the maser-amplified H2O(313-->220) and the thermally excited12CO (J=1-->0) transitions may be as high as factor of 20(but has to be corrected by their relative filling factor). MG 0751+2716is a strong 12CO (J=4-->3) emitter, and therefore one ofthe most suitable targets to search for H2O(313-->220) at cosmological redshifts. Oursearch resulted in an upper limit in line luminosity ofL'H2O<0.6×109 K kms-1 pc2. Assuming a brightness temperature ofTb(H2O)~=500 K for the maser emission and COproperties from the literature, this translates to a H2O(313-->220)/12CO (J=4-->3) areafilling factor of less than 1%. However, this limit is not valid if theH2O (313-->220) maser emission isquenched, i.e., if the line is only thermally excited. We conclude that,if our results were to hold for other high-z sources, H2Odoes not appear to be a more luminous alternative to HCN to detecthigh-density gas in star-forming environments at high redshift.
|Probing the Coevolution of Supermassive Black Holes and Galaxies Using Gravitationally Lensed Quasar Hosts|
In the present-day universe, supermassive black hole masses(MBH) appear to be strongly correlated with theirgalaxy's bulge luminosity, among other properties. In this study weexplore the analogous relationship between MBH, derivedusing the virial method, and the stellar R-band bulge luminosity(LR) or stellar bulge mass (M*) at epochs of1<~z<~4.5, using a sample of 31 gravitationally lensed AGNs and 20nonlensed AGNs. At redshifts z>1.7 (10-12 Gyr ago), we find that theobserved MBH-LR relation is nearly the same(to within ~0.3 mag) as it is today. When the observed LR arecorrected for luminosity evolution, this means that the black holes grewin mass faster than their hosts, with theMBH/M* mass ratio being a factor of>~4+2-1 times larger at z>1.7 than it istoday. By the redshift range 1<~z<~1.7 (8-10 Gyr ago), theMBH/M* ratio is at most 2 times higherthan today, but it may be consistent with no evolution. Combining theresults, we conclude that the ratioMBH/M* rises with look-back time,although it may saturate at ~6 times the local value. Scenarios in whichmoderately luminous quasar hosts at z>~1.7 were fully formed bulgesthat passively faded to the present epoch are ruled out.Based on observations with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated byAURA, Inc., under NASA contract NAS5-26555.
|A Spitzer Space Telescope Infrared Spectrograph Survey of Warm Molecular Hydrogen in Ultraluminous Infrared Galaxies|
We have conducted a survey of ultraluminous infrared galaxies (ULIRGs)with the Infrared Spectrograph on the Spitzer Space Telescope, obtainingspectra from 5.0 to 38.5 μm for 77 sources with 0.022 Jy.The average warm molecular gas mass is ~2×108Msolar. High extinction, inferred from the 9.7 μm silicateabsorption depth, is not observed along the line of sight to themolecular gas. The derived H2 mass does not depend onF25μm/F60μm, which has been used to infereither starburst or AGN dominance. Similarly, the molecular mass doesnot scale with the 25 or 60 μm luminosities. In general, theH2 emission is consistent with an origin in photodissociationregions associated with star formation. We detect the S(0) 28.22 μmemission line in a few ULIRGs. Including this line in the model fitstends to lower the temperature by ~50-100 K, resulting in a significantincrease in the gas mass. The presence of a cooler component cannot beruled out in the remainder of our sample, for which we do not detect theS(0) line. The measured S(7) 5.51 μm line fluxes in six ULIRGsimplies ~3×106 Msolar of hot (~1400 K)H2. The warm gas mass is typically less than 1% of the coldgas mass derived from 12CO observations.Based on observations obtained with the Spitzer Space Telescope, whichis operated by the Jet Propulsion Laboratory, California Institute ofTechnology, for the National Aeronautics and Space Administration.
|Far-Ultraviolet and X-Ray Observations of VV 114: Feedback in a Local Analog to Lyman Break Galaxies|
We have analyzed Far Ultraviolet Spectroscopic Explorer (FUSE),XMM-Newton, and Chandra observations of VV 114, a local galaxy mergerwith strong similarities to typical high-redshift Lyman break galaxies(LBGs). Diffuse thermal X-ray emission encompassing VV 114 has beenobserved by Chandra and XMM-Newton. This region of hot (kT~0.59 keV) gashas an enhanced α/Fe element ratio relative to solar abundancesand follows the same relations as typical starbursts between itsproperties (luminosity, size, and temperature) and those of thestarburst galaxy (star formation rate, dust temperature, and galaxymass). These results are consistent with the X-ray gas having beenproduced by shocks driven by a galactic superwind. The FUSE observationsof VV 114 show strong, broad interstellar absorption lines with apronounced blueshifted component (similar to what is seen in LBGs). Thisimplies an outflow of material moving at ~300-400 km s-1relative to VV 114. The properties of the strong O VI absorption lineare consistent with radiative cooling at the interface between the hotoutrushing gas seen in X-rays and the cooler material seen in the otheroutflowing ions in the FUSE data. We show that the wind in VV 114 has not created a ``tunnel'' that enables more than a small fraction(
|Systematic Survey of Extended Lyα Sources over z ~ 3-5|
Spatially extended Lyα sources that are faint and compact incontinuum are candidates for extremely young (<~107 yr)galaxies at high redshifts. We carried out a systematic survey forextended Lyα sources, using deep intermediate-band imaging datataken with the Suprime-Cam on the Subaru Telescope. Our survey covers afield of view of 33'×25' and a redshiftrange of 3.24<~z<~4.95, down to a Lyα flux of~1×10-17 ergs cm-2 s-1. Weidentified 41 extended Lyα sources. The redshift distribution ofthese sources shows that this kind of object is common in the earlyuniverse over the surveyed redshift range. The identified objects havetypical sizes of ~10-15 kpc and luminosities of ~1042 ergss-1. Follow-up spectroscopy made for 7 of the 41 objectsshowed that our sample suffers from little contamination. All 7 objectshave large equivalent widths of Lyα emission line, all but oneexceeding 240 Å in the rest frame. The large equivalent widthssuggest that their extended Lyα emissions are unlikely to be dueto normal starbursts, but possibly originate from very young galaxies.All 41 objects in our sample have much smaller Lyα luminositiesthan the two Lyα blobs (LABs) found at a z~=3.1 protocluster, inspite of our much larger survey volume. This suggests that large andluminous extended Lyα objects like the two LABs are very rare andare clustered in overdense regions.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
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