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The Kyoto tridimensional spectrograph II
The Kyoto tridimensional spectrograph II is a multimode spectrograph. Itis so far the only spectrograph with Fabry Perot and/or integral fieldspectrograph (IFS) modes that is mounted on the Subaru Telescope. Itspixel/lenslet sampling matches Subaru’s excellent image quality.This compact spectrograph is also used at the UH 88-inch telescope.Possible merits of lenslet IFS’s are discussed.
| Multiwavelength Star Formation Indicators: Observations
We present a compilation of multiwavelength data on different starformation indicators for a sample of nearby star forming galaxies. Herewe discuss the observations, reductions and measurements of ultravioletimages obtained with STIS on board the Hubble Space Telescope (HST),ground-based Hα, and VLA 8.46 GHz radio images. These observationsare complemented with infrared fluxes, as well as large-apertureoptical, radio, and ultraviolet data from the literature. This databasewill be used in a forthcoming paper to compare star formation rates atdifferent wave bands. We also present spectral energy distributions(SEDs) for those galaxies with at least one far-infrared measurementsfrom ISO, longward of 100 μm. These SEDs are divided in two groups,those that are dominated by the far-infrared emission, and those forwhich the contribution from the far-infrared and optical emission iscomparable. These SEDs are useful tools to study the properties ofhigh-redshift galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| The Active Galactic Nuclei Contribution to the Mid-Infrared Emission of Luminous Infrared Galaxies
We determine the contribution of AGN to the mid-IR emission of luminousinfrared galaxies (LIRGs) at z>0.6 by measuring the mid-IR dustcontinuum slope of 20,039 mid-IR sources. The 24 μm sources areselected from a Spitzer MIPS survey of the NOAO Deep Wide-Field SurveyBoötes field and have corresponding 8 μm data from the IRACShallow Survey. There is a clear bimodal distribution in the 24 to 8μm flux ratio. The X-ray-detected sources fall within the peakcorresponding to a flat spectrum in νfν, implying thatit is populated by AGN-dominated LIRGs, whereas the peak correspondingto a higher 24 to 8 μm flux ratio is likely due to LIRGs whose IRemission is powered by starbursts. The 24 μm emission is increasinglydominated by AGN at higher 24 μm flux densities (f24): theAGN fraction of the z>0.6 sources increases from 9% atf24~0.35 mJy to 74%+/-20% at f24~3 mJy, in goodagreement with model predictions. Deep 24 μm, small-area surveys,like GOODS, will be strongly dominated by starburst galaxies. AGN areresponsible for ~3%-7% of the total 24 μm background.
| Ultraviolet-to-Far-Infrared Properties of Local Star-forming Galaxies
We present the results of a multiwavelength study of nearby galaxiesaimed at understanding the relation between the ultraviolet andfar-infrared emission in star-forming galaxies. The data set comprisesnew ultraviolet (from HST STIS), ground-based Hα, and radiocontinuum observations, together with archival infrared data (from IRASand ISO). The local galaxies are used as benchmarks for comparison ofthe infrared-to-ultraviolet properties with two populations ofhigh-redshift galaxies: the submillimeter star-forming galaxies detectedby SCUBA and the ultraviolet-selected Lyman break galaxies (LBGs). Inaddition, the long wavelength baseline covered by the present dataenables us to compare the star formation rates (SFRs) derived from theobserved ultraviolet, Hα, infrared, and radio luminosities and togauge the impact of dust opacity in the local galaxies. We also derive anew calibration for the nonthermal part of the radio SFR estimator,based on the comparison of 1.4 GHz measurements with a new estimator ofthe bolometric luminosity of the star-forming regions. We find that moreactively star-forming galaxies show higher dust opacities, which is inline with previous results. We find that the local star-forming galaxieshave a lower Fλ(205 μm)/Fλ(UV)ratio by 2-3 orders of magnitude than the submillimeter-selectedgalaxies and may have a similar or somewhat higherFλ(205 μm)/Fλ(UV) ratio thanLBGs. The Fλ(205 μm)/Fλ(UV) ratioof the local galaxy population may be influenced by the cool dustemission in the far-infrared heated by nonionizing stellar populations,which may be reduced or absent in the LBGs.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| SINFONI adaptive optics integral field spectroscopy of the Circinus Galaxy
Aims.We investigate the star formation activity and the gas and stellardynamics on scales of a few parsecs in the nucleus of the CircinusGalaxy. Methods: .Using the adaptive optics near infrared integralfield spectrometer SINFONI on the VLT, we have obtained observations ofthe Circinus galaxy on scales of a few parsecs and at a spectralresolution of 70 km s-1 FWHM. The physical properties of thenucleus are analyzed by means of line and velocity maps extracted fromthe SINFONI datacube. Starburst models are constrained using theBrγ flux, stellar continuum (as traced via the CO absorptionbandheads longward of 2.3 μm), and radio continuum. Results:.The similarity of the morphologies of the H2 1-0 S(1) 2.12 μm andBrγ 2.17 μm lines to the stellar continuum and also theirkinematics, suggest a common origin in star formation. Within 8 pc ofthe AGN we find there has been a recent starburst in the last 100 Myr,which currently accounts for 1.4% of the galaxy's bolometric luminosity.The similarity of the spatial scales over which the stars and gas existindicates that this star formation is occuring within the torus; andcomparison of the gas column density through the torus to the maximumpossible optical depth to the stars implies the torus is a clumpymedium. The coronal lines show asymmetric profiles with a spatiallycompact narrow component and a spatially extended blue wing. Thesecharacteristics are consistent with some of the emission arising inclouds gravitationally bound to the AGN, and some outflowing incloudlets which have been eroded away from the bound clouds.
| Multi-aperture photometry of extended IR sources with ISOPHOT. I. The nature of extended IR emission of planetary Nebulae
Context: .ISOPHOT multi-aperture photometry is an efficient method toresolve compact sources or to detect extended emission down torelatively faint levels with single detectors in the wavelength range 3to 100 μm. Aims: .Using ISOPHOT multi-aperture photometry andcomplementary ISO spectra and IR spectral energy distributions wediscuss the nature of the extended IR emission of the two PNe NGC 6543and NGC 7008. Methods: .In the on-line appendix we describe thedata reduction, calibration and interpretation methods based on asimultaneous determination of the IR source and background contributionsfrom the on-source multi-aperture sequences. Normalized profiles enabledirect comparison with point source and flat-sky references. Modellingthe intensity distribution offers a quantitative method to assess sourceextent and angular scales of the main structures and is helpful inreconstructing the total source flux, if the source extends beyond aradius of 1 arcmin. The photometric calibration is described and typicalaccuracies are derived. General uncertainty, quality and reliabilityissues are addressed, too. Transient fitting to non-stabilised signaltime series, by means of combinations of exponential functions withdifferent time constants, improves the actual average signals andreduces their uncertainty. Results: .The emission of NGC 6543 inthe 3.6 μm band coincides with the core region of the optical nebulaand is homogeneously distributed. It is comprised of 65% continuum and35% atomic hydrogen line emission. In the 12 μm band a resolved butcompact double source is surrounded by a fainter ring structure with allemission confined to the optical core region. Strong line emission of[ArIII] at 8.99 μm and in particular [SIV] at 10.51 μm shapes thisspatial profile. The unresolved 60 μm emission originates from dust.It is described by a modified (emissivity index β = 1.5) blackbodywith a temperature of 85 K, suggesting that warm dust with a mass of 6.4× 10-4 Mȯ is mixed with the ionisedgas. The gas-to-dust mass ratio is about 220. The 25 μm emission ofNGC 7008 is characterised by a FWHM of about 50´´ with anadditional spot-like or ring-like enhancement at the bright rim of theoptical nebula. The 60 μm emission exhibits a similar shape, but isabout twice as extended. Analysis of the spectral energy distributionsuggests that the 25 μm emission is associated with 120 K warm dust,while the 60 μm emission is dominated by a second dust component with55 K. The dust mass associated with this latter component amounts to 1.2× 10-3 Mȯ, significantly higher thanpreviously derived. The gas-to-dust mass ratio is 59 which, compared tothe average value of 160 for the Milky Way, hints at dust enrichment bythis object.
| The Second Byurakan Survey. General Catalogue
The Second Byurakan Survey (SBS) General Catalogue is presented. TheSBS, a continuation of the Markarian survey reaching fainter limitingmagnitudes, is the first survey which combines the search of galaxiesand QSOs. A total area of 991OS#square;degrees of the Northern sky wascovered with the use of three objective prisms in combination withSchott filters. The limited magnitude on the best plates reached B ~19.5.The General Catalogue consists of 3563 objects presented in two parts: aCatalogue of galaxies (1863 objects) and one of stellar objects (1700objects). The Catalogue of SBS AGN consists of 761 objects (155 SyG, 596QSOs, and 10 BLLac). Multi-wavelength data are presented for 1438 SBSobjects identified with X-ray, IRAS and FIRST sources.Spectrophotometric observations obtained over 26 years are available for3132 objects. Redshifts were measured for ~ 2100 extragalactic objects.Spectral classification is presented for ~ 2970 objects. The majority ofthe data is presented here for the first time. The Catalogue presentsnew large homogeneous deep representative complete samples of brightQSOs, AGNs, and faint UVX galaxies in the Northern sky. The SBS sampleis found to be complete at 70% for galaxies and ~ 85% for AGN/QSOs withB ≤ 17.5.
| The SCUBA Local Universe Galaxy Survey - III. Dust along the Hubble sequence
We present new results from the Submillimetre Common-User BolometerArray (SCUBA) Local Universe Galaxy Survey (SLUGS), the first largesystematic submillimetre (submm) survey of the local Universe. Since ourinitial survey of a sample of 104 IRAS-selected galaxies we have nowcompleted a survey of a sample of 81 optically selected galaxies,observed with the SCUBA camera on the James Clerk Maxwell Telescope.Since SCUBA is sensitive to the 90 per cent of dust too cold to radiatesignificantly in the IRAS bands our new sample represents the firstunbiased SCUBA survey of dust in galaxies along the whole length of theHubble sequence.We find little change in the properties of dust in galaxies along theHubble sequence, except a marginally significant trend for early-typegalaxies to be less-luminous submm sources than late types. Wenevertheless detected six out of 11 elliptical galaxies, although someof the emission may possibly be synchrotron rather than dust emission.As in our earlier work on IRAS galaxies we find that the IRAS and submmfluxes are well fitted by a two-component dust model with dustemissivity index β= 2. The major difference from our earlier workis that we find the ratio of the mass of cold dust to the mass of warmdust is much higher for our optically selected galaxies and can reachvalues of ~1000. Comparison of the results for the IRAS and opticallyselected samples shows that there is a population of galaxies containinga large proportion of cold dust that is unrepresented in the IRASsample.We derive local submm luminosity and dust mass functions, both directlyfrom our optically selected SLUGS sample, and by extrapolation from theIRAS Point Source Catalogue Redshift Survey (PSCz) survey using themethod of Serjeant and Harrison (by extrapolating the spectral energydistributions of the IRAS PSCz survey galaxies out to 850μm we probea wider range of luminosities than probed directly by the SLUGSsamples), and find excellent agreement between the two. We find them tobe well fitted by Schechter functions except at the highestluminosities. We find that as a consequence of the omission of coldgalaxies from the IRAS sample the luminosity function presented in ourearlier work is too low by a factor of 2, reducing the amount of cosmicevolution required between the low-z and high-z Universe.
| Properties of FIRBACK-ELAIS 175-μm sources in the ELAIS N2 region
We report on a search for the optical counterparts of 175-μm selectedsources from the Far-Infrared Background (FIRBACK) survey in theEuropean Large Area ISO Survey (ELAIS) N2 field. Applying a likelihoodratio technique to optical catalogues from the Isaac Newton Telescope -Wide Field Survey (INT-WFS), we found optical identifications for 33 outof 55 FIRBACK sources in this field. These were then reassessed in thelight of associations with the ELAIS final catalogue for the N2 field,to yield a final set of 31 associations. We have investigated the natureof this population through a comparison of their observed spectralenergy distributions (SEDs) with predictions from radiative transfermodels which simulate the emission from both cirrus and starburstcomponents. We find the far-infrared sources to be 80 per cent starburstgalaxies with their starburst component at a high optical depth. Theresulting SEDs were used to estimate far-infrared luminosities, starformation rates (SFRs), dust temperatures and dust masses. The N2FIRBACK population is found to consist of four suspected ultraluminousinfrared galaxies (ULIRGs) with LFIR~1012Lsolar and SFRFIR >100Msolaryr-1, a number of luminous infraredgalaxies (LIRGs) with moderate star formation rates and LFIR~1011Lsolar and a population of low-redshiftquiescently star-forming galaxies. We also discuss the implications ofthese results for current evolutionary models.
| High energy gamma ray counterparts of astrophysical sources of ultra-high energy cosmic rays
If ultra-high energy cosmic rays (UHECRs) are accelerated atastrophysical point sources, the identification of such sources can beachieved if there is some kind of radiation at observable wavelengthsthat may be associated with the acceleration and/or propagationprocesses. No radiation of this type has so far been detected or atleast no such connection has been claimed. The process of photopionproduction during the propagation of UHECRs from the sources to theEarth results in the generation of charged and neutral pions. Theneutral (charged) pions in turn decay to gamma quanta and electrons thatinitiate an electromagnetic cascade in the universal photon background.We calculate the flux of this gamma radiation in the GeV TeV energyrange and find that for source luminosities compatible with thoseexpected from small scale anisotropies in the directions of arrival ofUHECRs, the fluxes can be detectable by future Cerenkov gamma raytelescopes, such as VERITAS and HESS, provided the intergalacticmagnetic field is not larger than 10‑10 Gauss andfor source distances comparable with the loss length for photopionproduction.
| Multiple CO lines in SMM J16359+6612 - further evidence for a merger
Using the IRAM 30 m telescope, we report the detection of the CO(3-2),CO(4-3), CO(5-4) and CO(6-5) lines in the gravitational lensed submmgalaxy SMM J16359+6612 at z=2.5. The CO lines have a double peak profilein all transitions. From a Gaussian decomposition of the spectra we showthat the CO line ratios, and therefore the underlying physicalconditions of the gas, are similar for the blue and the redshiftedcomponent. The CO line Spectral Energy Distribution (SED; i.e. fluxdensity vs. rotational quantum number) turns over already at the CO 5-4transition which shows that the molecular gas is less excited than innearby starburst galaxies and high-z QSOs. This difference mainly arisesfrom a lower average H2 density, which indicates that the gas is lesscentrally concentrated than in nuclear starburst regions in localgalaxies. We suggest that the bulk of the molecular gas in SMMJ16359+6612 may arise from an overlap region of two merging galaxies.The low gas density and clear velocity separation may reflect anevolutionary stage of the merger event that is in between those seen inthe Antennae and in the more evolved ultraluminous infrared galaxies(ULIRGs) like e.g. Mrk 231.
| ISO observations and models of galaxies with hidden broad line regions
We present ISO mid-infrared spectrophotometry and far-infraredphotometry of galaxies with Hidden Broad Line Regions (HBLR). We alsopresent radiative transfer models of their spectral energy distributionswhich enable us to separate the contributions from the dusty disc of theAGN and the dusty starbursts. We find that the combination of tapereddiscs (discs whose thickness increases with distance from the centralsource in the inner part but stays constant in the outer part) andstarbursts provide good fits to the data. The tapered discs dominate inthe mid-infrared part of the spectrum and the starbursts in thefar-infrared. After correcting the AGN luminosity for anisotropicemission we find that the ratio of the AGN luminosity to the starburstluminosity, L_AGN/L_sb, ranges from about unity for IRAS 14454-4343 toabout 13 for IRAS 01475-0740. Our results suggest that the warm IRAScolours of HBLR are due to the relatively high L_AGN/L_sb. Our fits areconsistent with the unified model and the idea that the infraredemission of AGN is dominated by a dusty disc in the mid-infrared andstarbursts in the far-infrared.
| VLT narrow-band photometry in the Lyman continuum of two galaxies at z 3. Limits to the escape of ionizing flux
We have performed narrow-band imaging observations with the Very LargeTelescope, aimed at detecting the Lyman continuum (LC) flux escapingfrom galaxies at z3. We do not find any significant LC flux fromour sample of two galaxies in the Hubble Deep Field South, at z=3.170and 3.275. The corresponding lower limits on theF1400/F900 flux density (per Hz) ratio are 15.6and 10.2 (3-σ confidence level). After correction for theintergalactic hydrogen absorption, the resulting limits on the relativeescape fraction of the LC are compared with those obtained by differentapproaches, at similar or lower redshifts. One of our two objects has arelative escape fraction lower than the detection reported by Steidel etal. in a composite spectrum of z3 galaxies. A larger number ofobjects is required to reach a significant conclusion. Our comparisonshows the potential of narrow-band imaging for obtaining the best limiton the relative escape fraction at z3. Stacking a significantnumber of galaxies observed through a narrow-band filter would provideconstraint on the galactic contribution to the cosmic reionization.
| Observational evidence for the presence of PAHs in distant Luminous Infrared Galaxies using ISO and Spitzer
We present ISOCAM 15 μm and MIPS 24 μm photometry of a sample of16 distant Luminous Infrared Galaxies (LIRGs) characterized by a medianluminosity L_IR 2 × 1011~Lȯ andredshift z = 0.7 (distributed from z = 0.1 to 1.2). While some sourcesdisplay 24/15 μm flux ratios also consistent with a featurelesscontinuum dominating their mid-infrared (MIR) spectral energydistributions (SEDs), the presence of prominent emission features suchas the Polycyclic Aromatic Hydrocarbons is clearly required to explainthe observed colors for more than half of the sample. As a result, ageneral good agreement is observed between the data and predictions fromthe local starburst-dominated SEDs that have been used so far toconstrain IR galaxy evolution. This is consistent with the star-formingnature of LIRGs derived from previous works, even though our approachcannot rule out the dominance of an AGN in some cases. Our study alsosupports the possibility of tracing the total IR luminosity of distantgalaxies (up to z 1) from their MIR emission.
| Exceptional H2 emission in the Antennae galaxies: Pre-starburst shocks from the galaxy collision
The collision of gas-rich galaxies is believed to produce strong shocksbetween their gas clouds which cause the onset of the observed bursts ofextended star formation. However, the so far observed shock signaturesin colliding galaxies can be explained essentially by winds from alreadyexisting massive stars and supernovae and thus do not give any evidencefor an outstanding pre-starburst phase. Either pre-starburst gas shocksare too short-lived to be detected or one has to modify our perceptionof colliding galaxies. A dedicated analysis of ISOCAM-CVF mid-infraredspectral maps led us to the discovery of exceptional H2 v = 0-0 S(3)λ = 9.66 μm line emission from the “Antennae”galaxy pair, which is at an early stage of galaxy collision. Its H2 lineluminosity, normalized by the far-infrared luminosity, exceeds that ofall other known galaxies and the strongest H2 emission is spatiallydisplaced from the known starbursts regions. This implies that most ofthe excited H2 gas in the Antennae must be shocked due to the collisionof the two galaxies. These observations indicate that the outstandingphase of pre-starburst shocks exists, and that they might be a key toour understanding of the formation of the first proto-galaxies.Based onobservations with the Infrared Space ObservatoryISO, an ESA project with instrumentsfunded by ESA Member States (especially the PI countries: France,Germany, the Netherlands and the United Kingdom) andwith the participation of ISAS and NASA.
| Predictions for high-frequency radio surveys of extragalactic sources
We present detailed predictions of the contributions of the varioussource populations to the counts at frequencies of tens of GHz. Newevolutionary models are worked out for flat-spectrum radio quasars, BLLac objects, and steep-spectrum sources. Source populationscharacterized by spectra peaking at high radio frequencies, such asextreme GPS sources, ADAF/ADIOS sources and early phases of γ-rayburst afterglows are also dealt with. The counts of differentpopulations of star-forming galaxies (normal spirals, starbursts, high-zgalaxies detected by SCUBA and MAMBO surveys, interpreted asproto-spheroidal galaxies) are estimated taking into account bothsynchrotron and free-free emission, and dust re-radiation. Our analysisis completed by updated counts of Sunyaev-Zeldovich effects in clustersof galaxies and by a preliminary estimate of galactic-scaleSunyaev-Zeldovich signals associated to proto-galactic plasma.
| Cold and warm dust along a merging galaxy sequence
We investigate the cold and warm dust properties during galaxyinteractions using a merging galaxy sample ordered into a chronologicalsequence from pre- to post-mergers. Our sample comprises a total of 29merging systems selected to have far-infrared and submillimetreobservations. The submillimetre data are mainly culled from theliterature, while for five galaxies (NGC 3597, 3690, 6090, 6670 and7252) the submillimetre observations are presented here for the firsttime. We use the 100- to 850-μm flux density ratio,f100/f850, as a proxy for the mass fraction of thewarm and cold dust in these systems. We find evidence for an increase inf100/f850 along the merging sequence from early toadvanced mergers, and interpret this trend as an increase of the warmrelative to the cold dust mass. We argue that the two key parametersaffecting the f100/f850 flux ratio is the starformation rate and the dust content of individual systems relative tothe stars. Using a sophisticated model for the absorption andre-emission of the stellar ultraviolet radiation by dust, we show thatthese parameters can indeed explain both the increase and the observedscatter in f100/f850 along the merging galaxysequence. We also discuss our results under the hypothesis thatelliptical galaxies are formed via disc galaxy mergers.
| Principal component analysis of International Ultraviolet Explorer galaxy spectra
We analyse the UV spectral energy distribution of a sample of normalgalaxies listed in the International Ultraviolet Explorer (IUE) NewlyExtracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principalcomponent analysis. The sample consists of the IUE short-wavelength (SW)spectra of the central regions of 118 galaxies, where the IUE apertureincluded more than 1 per cent of the galaxy size. The principalcomponents are associated with the main components observed in theultraviolet (UV) spectra of galaxies. The first component, accountingfor the largest source of diversity, may be associated with the UVcontinuum emission. The second component represents the UV contributionof an underlying evolved stellar population. The third component issensitive to the amount of activity in the central regions of galaxiesand measures the strength of star-formation events.In all the samples analysed here, the principal component representativeof star-forming activity accounts for a significant percentage of thevariance. The fractional contribution to the spectral energydistribution (SED) by the evolved stars and by the young population aresimilar.Projecting the SEDs on to their eigenspectra, we find that none of thecoefficients of the principal components can outline an internalcorrelation or can correlate with the optical morphological types. In asubsample of 43 galaxies, consisting of almost only compact and BCDgalaxies, the third principal component defines a sequence related tothe degree of starburst activity of the galaxy.
| The impact of broad mid-infrared emission bands on extragalactic surveys - a case study: the unidentified 22-μm feature
The effect of unidentified dust emission features in the mid-infrared(MIR) spectral energy distributions of dusty star-forming galaxies isinvestigated. As a case study, we discuss the broad emission feature at2 μm of Chan & Onaka. By modelling a distribution of featurestrengths using a starburst galaxy template, we speculativelyinvestigate the influence of the feature on galaxy fluxes, colours anddetected numbers. We find that the fluxes and colours of galaxies aresystematically affected by the feature from redshifts 0-3, atwavelengths ranging from 20 to 70 μm by up to factors of ~2,resulting in bluer MIR/far-infrared (FIR) and FIR/MIR colours at localand high redshifts, respectively, as the feature is redshifted in andout of the various observation passbands. Furthermore, we find that ifthe feature is prolific, it will manifest itself in the same manner asevolution in the infrared (IR) galaxy population in a similar way to theunidentified IR bands at shorter wavelengths. We also consider theeffect of the feature on the future IR SIRTF (Spitzer) and ASTRO-F spacemissions. We conclude that although the bulk effects of the feature maybe small, careful consideration will have to be made when discussing thecolours of sources in the relevant bands and redshift ranges affected bythe feature emission.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Warm Molecular Gas in Galaxy-Galaxy Merger NGC 6090
We present Submillimeter Array observations of the CO (2-1) and (3-2)transitions toward the merging galaxies of NGC 6090. The high-resolutionCO data reveal three gas concentrations. The main component is peakingin the overlap region between the two galaxies, where the near-IR andradio continuum emission are weak. The CO (2-1) emission from theface-on galaxy NGC 6090E is somewhat stronger than that from the edge-ongalaxy NGC 6090W. The CO (3-2) emission peaks in the overlap region,similar to the CO (2-1) emission. More than 50% of the CO (3-2) emissionarises from the 2" (1.2 kpc) area of the overlap region. There appearsto be CO (3-2) emission toward the nuclear region and the northwest armof NGC 6090E, while no CO (3-2) emission is detected toward NGC 6090W.Unlike the CO gas, most of the radio continuum emission comes from NGC6090E. The strong CO emission, together with the weak radio continuumemission, suggests that star formation in the overlap region has notproceeded long enough to produce significant numbers of supernovae thatwould be detectable from their radio continuum emission.
| High-Density Molecular Gas in the Infrared-bright Galaxy System VV 114
The new high-resolution CO (3-2) interferometric map of the IR-brightinteracting galaxy system VV 114 observed with the Submillimeter Arrayreveals a substantial amount of warm and dense gas in the IR-bright butoptically obscured galaxy, VV 114E, and the overlap region connectingthe two nuclei. A 1.8×1.4 kpc concentration of CO (3-2) emittinggas with a total mass of 4×109 Msolarcoincides with the peaks of near-IR, mid-IR, and radio continuumemission found previously by others, identifying the dense fuel for theactive galactic nucleus and/or the starburst activity there. ExtensiveCO (2-1) emission is also detected, revealing detailed distribution andkinematics that are consistent with the earlier CO (1-0) results. Thewidely distributed molecular gas traced in CO (2-1) and the distributeddiscrete peaks of CO (3-2) emission suggest that a spatially extendedintense starbursts may contribute significantly to its large IRluminosity. These new observations further support the notion that VV114 is approaching its final stage of merger, when a violent centralinflow of gas triggers intense starburst activity possibly boosting theIR luminosity above the ultraluminous threshold.
| The Submillimeter Array
The Submillimeter Array, a collaborative project of the SmithsonianAstrophysical Observatory and the Academia Sinica Institute of Astronomyand Astrophysics, has begun operation on Mauna Kea in Hawaii. The arraycomprises a total of eight 6 m telescopes, which will cover thefrequency range of 180-900 GHz. All eight telescopes have been deployedand are operational. First scientific results utilizing the threereceiver bands at 230, 345, and 690 GHz have been obtained and arepresented in the accompanying Letters.
| Rapid Large-Scale Metal Enrichment in the Starbursts of an Interacting Galaxy System
By obtaining integral field spectra of the interacting galaxy system NGC6090, we have found a kiloparsec-scale region where active starformation is currently increasing the fraction of heavy elements. Youngmassive starbursts are occurring in regions offset from the galacticcenters, highlighting the present epoch of metal enrichment over theprevious ones usually seen at galactic centers. The short timescale of~107 yr for the starbursts, inferred from the galacticrotation, provides a strong constraint on the origins of themetallicity/abundance enhancements. While oxygen is considered tooriginate in supernovae, the observed nitrogen enhancement is likely tobe caused by winds/mass loss from massive stars rather than being aproduct of intermediate-mass stars.
| C I Emission in Ultraluminous Infrared Galaxies as a Molecular Gas Mass Tracer
We present new sensitive wide-band measurements of the fine-structureline 3P1-->3P0 (J=1-0,492 GHz) of neutral atomic carbon (C I) in the two typical ultraluminousinfrared galaxies (ULIRGs) NGC 6240 and Arp 220. We then use them alongwith several other C I measurements in similar objects found in theliterature to estimate their global molecular gas content under theassumption of a full C I-H2 concomitance. We find excellentagreement between the H2 gas mass estimated with this methodand the standard methods using 12CO. This may provide a newway to measure H2 gas mass in galaxies and one that may bevery valuable in ULIRGs since in such systems the bright 12COemission is known to systematically overestimate the gas mass whiletheir 13CO emission (an often-used alternative) is usuallyvery weak. At redshifts z>=1 the C I J=1-0 line shifts to much morefavorable atmospheric windows and can become a viable alternative tracerof the H2 gas, fueling starburst events in the distantuniverse.
| Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation?
Infrared (IR) emission features at 3.3, 6.2, 7.7, 8.6, and 11.3 μmare generally attributed to IR fluorescence from (mainly)far-ultraviolet (FUV) pumped large polycyclic aromatic hydrocarbon (PAH)molecules. As such, these features trace the FUV stellar flux and arethus a measure of star formation. We examined the IR spectralcharacteristics of Galactic massive star-forming regions and of normaland starburst galaxies, as well as active galactic nuclei (AGNs) andultraluminous infrared galaxies (ULIRGs). The goal of this study is toanalyze whether PAH features are a good qualitative and/or quantitativetracer of star formation, and hence to evaluate the application of PAHemission as a diagnostic tool in order to identify the dominantprocesses contributing to the infrared emission from Seyfert galaxiesand ULIRGs. We develop a new mid-infrared (MIR)/far-infrared (FIR)diagnostic diagram based on our Galactic sample and compare it to thediagnostic tools of Genzel and coworkers and Laurent and coworkers, withthese diagnostic tools also applied to our Galactic sample. This MIR/FIRdiagnostic is derived from the FIR normalized 6.2 μm PAH flux and theFIR normalized 6.2 μm continuum flux. Within this diagram, theGalactic sources form a sequence spanning a range of 3 orders ofmagnitude in these ratios, ranging from embedded compact H II regions toexposed photodissociation regions (PDRs) and the (diffuse) interstellarmedium (ISM). However, the variation in the 6.2 μm PAHfeature-to-continuum ratio is relative small. Comparison of ourextragalactic sample with our Galactic sources revealed an excellentresemblance of normal and starburst galaxies to exposed PDRs. WhileSeyfert 2 galaxies coincide with the starburst trend, Seyfert 1 galaxiesare displaced by at least a factor of 10 in 6.2 μm continuum flux, inaccordance with general orientation-dependent unification schemes forAGNs. ULIRGs show a diverse spectral appearance. Some show a typical AGNhot dust continuum. More, however, either are starburst-like or showsigns of strong dust obscuration in the nucleus. One characteristic ofthe ULIRGs also seems to be the presence of more prominent FIR emissionthan either starburst galaxies or AGNs. We discuss the observedvariation in the Galactic sample in view of the evolutionary state andthe PAH/dust abundance and discuss the use of PAHs as quantitativetracers of star formation activity. Based on these investigations, wefind that PAHs may be better suited as a tracer of B stars, whichdominate the Galactic stellar energy budget, than as a tracer of massivestar formation (O stars).
| Metal Enrichment in Near-Infrared Luminous Galaxies at z~2: Signatures of Proto-elliptical Galaxies?
We present the analysis of the co-added rest-frame UV spectrum (1200Å
| Optical Imaging of Very Luminous Infrared Galaxy Systems: Photometric Properties and Late Evolution
A sample of 19 low-redshift (0.03
| Faint 6.7 Micron Galaxies and Their Contributions to the Stellar Mass Density in the Universe
We discuss the nature of faint 6.7 μm galaxies detected with themid-infrared camera ISOCAM on board the Infrared Space Observatory(ISO). The 23 hr integration on the Hawaii Deep Field SSA13 has provideda sample of 65 sources down to 6 μJy at 6.7 μm. For 57 sources,optical or near-infrared counterparts were found using a statisticalmethod. All four Chandra sources, three SCUBA sources, and one VLA/FIRSTsource in this field were detected at 6.7 μm with high significance.Using their optical to mid-infrared colors, we divided the 6.7 μmsample into three categories: low-redshift galaxies with past historiesof rapid star formation, high-redshift ancestors of these, and otherstar-forming galaxies. Rapidly star-forming systems at high redshiftsdominate the faintest end. Spectroscopically calibrated photometricredshifts were derived from fits to a limited set of template spectralenergy distributions (SEDs). They show a high-redshift tail in theirdistribution with faint (<30 μJy) galaxies at z>1. The 6.7μm galaxies tend to have brighter K magnitudes and redder I-K colorsthan the blue dwarf population at intermediate redshifts. Stellar massesof the 6.7 μm galaxies were estimated from their rest-frame,near-infrared luminosities. Massive galaxies(Mstar~1011 Msolar) were found in theredshift range of z=0.2-3. Epoch-dependent stellar mass functionsindicate a decline of massive galaxies' comoving space densities withredshift. Even with such a decrease, the contributions of the 6.7 μmgalaxies to the stellar mass density in the universe are found to becomparable to those expected from UV bright galaxies detected in deepoptical surveys.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA.
| A Study of the Distribution of Star-forming Regions in Luminous Infrared Galaxies by Means of Hα Imaging Observations
We performed Hα imaging observations of 22 luminous infraredgalaxies to investigate how the distribution of star-forming regions inthese galaxies is related to galaxy interactions. Based on correlationdiagrams between Hα flux and continuum emission for individualgalaxies, a sequence for the distribution of star-forming regions wasfound: very compact (~100 pc) nuclear starbursts with almost nostar-forming activity in the outer regions (type 1), dominant nuclearstarbursts <~1 kpc in size with a negligible contribution from theouter regions (type 2), nuclear starbursts >~1 kpc in size with asignificant contribution from the outer regions (type 3), and extendedstarbursts with relatively faint nuclei (type 4). These classes ofstar-forming regions were found to be strongly related to globalstar-forming properties, such as star formation efficiency, far-infraredcolor, and dust extinction. There was a clear tendency for the objectswith more compact distributions of star-forming regions to show a higherstar formation efficiency and hotter far-infrared color. An appreciablefraction of the sample objects were dominated by extended starbursts(type 4), which is unexpected in the standard scenario ofinteraction-induced starburst galaxies. We also found that thedistribution of star-forming regions was weakly but clearly related togalaxy morphology: severely disturbed objects had a more concentrateddistribution of star-forming regions. This suggests that the propertiesof galaxy interactions, such as dynamical phase and orbital parameters,play a more important role than the internal properties of progenitorgalaxies, such as dynamical structure or gas mass fraction. We alsodiscuss the evolution of the distribution of star-forming regions ininteracting galaxies.
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