arXiv subjects

F. Combes

Publications and source records attributed to F. Combes.

At least 307 records · Page 17Linked to original sources

arXiv2011

The Herschel M33 extended survey (HerM33es): PACS spectroscopy of the star forming region BCLMP 302

Context: The emission line of [CII] at 158 micron is one of the strongest cooling lines of the interstellar medium (ISM) in galaxies. Aims: Disentangling the relative contributions of the different ISM phases to [CII] emission, is a major topic of the HerM33es program, a Herschel key project to study the ISM in the nearby spiral galaxy M33. Methods: Using PACS, we have mapped the emission of [CII] 158 micron, [OI] 63 micron, and other FIR lines in a 2'x2' region of the northern spiral arm of M33, centered on the HII region BCLMP302. At the peak of H-alpha emission, we have observed in addition a velocity resolved [CII] spectrum using HIFI. We use scatterplots to compare these data with PACS 160 micron continuum maps, and with maps of CO and HI data, at a common resolution of 12 arcsec or 50 pc. Maps of H-alpha and 24 micron emission observed with Spitzer are used to estimate the SFR. We have created maps of the [CII] and [OI] 63 micron emission and detected [NII] 122 micron and NIII 57 micron at individual positions. Results: The [CII] line observed with HIFI is significantly broader than that of CO, and slightly blue-shifted. In addition, there is little spatial correlation between [CII] observed with PACS and CO over the mapped region. There is even less spatial correlation between [CII] and the atomic gas traced by HI. Detailed comparison of the observed intensities towards the HII region with models of photo ionization and photon dominated regions, confirms that a significant fraction, 20--30%, of the observed [CII] emission stems from the ionized gas and not from the molecular cloud. The gas heating efficiency, using the ratio between [CII] and the TIR as a proxy, varies between 0.07 and 1.5%, with the largest variations found outside the HII region.

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arXiv2011

On the absence of molecular absorption in high redshift millimetre-band searches

We have undertaken a search for millimetre-wave band absorption (through the CO and HCO+ rotational transitions) in the host galaxies of reddened radio sources (z = 0.405-1.802). Despite the colour selection (optical-near infrared colours of V - K > 5 in all but one source), no absorption was found in any of the eight quasars for which the background continuum flux was detected. On the basis of the previous (mostly intervening) H2 and OH detections, the limits reached here and in some previous surveys should be deep enough to detect molecular absorption according to their V - K colours. However, our survey makes the assumption that the reddening is associated with dust close to the emission redshift of the quasar and that the narrow millimetre component of this emission is intercepted by the compact molecular cores. By using the known millimetre absorbers to define the colour depth and comparing this with the ultra-violet luminosities of the sources, we find that, even if these assumptions are valid, only twelve of the forty objects (mainly from this work) are potentially detectable. This is assuming an excitation temperature of 10 K at z=0, with the number decreasing with increasing temperatures (to zero detectable at 100 K).

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arXiv2011

SMA/PdBI multiple line observations of the nearby Seyfert2 galaxy NGC 1068: Shock related gas kinematics and heating in the central 100pc?

We present high angular resolution (0.5-2.0") observations of the mm continuum and the 12CO(J=3-2), 13CO(J=3-2), 13CO(J=2-1), C18O(J=2-1), HCN(J=3-2), HCO+(J=4-3) and HCO+(J=3-2) line emission in the circumnuclear disk (r=100pc) of the proto-typical Seyfert type-2 galaxy NGC1068, carried out with the Submillimeter Array. We further include in our analysis new 13CO(J=1-0) and improved 12CO(J=2-1) observations of NGC1068 at high angular resolution (1.0-2.0") and sensitivity, conducted with the IRAM Plateau de Bure Interferometer. Based on the complex dynamics of the molecular gas emission indicating non-circular motions in the central ~100pc, we propose a scenario in which part of the molecular gas in the circumnuclear disk of NGC1068 is radially blown outwards as a result of shocks. This shock scenario is further supported by quite warm (Tkin>=200K) and dense (nH2=10^4cm^-3) gas constrained from the observed molecular line ratios. The HCN abundance in the circumnuclear disk is found to be [HCN]/[12CO]=10^-3.5. This is slightly higher than the abundances derived for galactic and extragalactic starforming/starbursting regions. This results lends further support to X-ray enhanced HCN formation in the circumnuclear disk of NGC1068, as suggested by earlier studies. The HCO+ abundance ([HCO+]/[12CO]=10^-5) appears to be somewhat lower than that of galactic and extragalactic starforming/starbursting regions. When trying to fit the cm to mm continuum emission by different thermal and non-thermal processes, it appears that electron-scattered synchrotron emission yields the best results while thermal free-free emission seems to over-predict the mm continuum emission.

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arXiv2011

A very extended molecular web around NGC 1275

We present the first detection of CO emission lines in the Halpha filaments at distances as far as 50 kpc from the centre of the galaxy NGC 1275. This gas is probably dense (>=10E3 cm-3). However, it is not possible to accurately determine the density and the kinetic temperature of this relatively warm gas (Tkin~20-500K) with the current data only. The amount of molecular gas in the filaments is large 10E9 Msun (assuming a Galactic N(H2)/Ico ratio). This is 10% of the total mass of molecular gas detected in this cD galaxy. This gas has large-scale velocities comparable to those seen in Halpha. The origin of the filaments is still unclear, but their formation is very likely linked to the AGN positive feedback (Revaz et al., 2008) that regulates the cooling of the surrounding X-ray-emitting gas as suggested by numerical simulations. We also present high-resolution spectra of the galaxy core. The spatial characteristics of the double-peaked profile suggest that the molecular web of filaments and streamers penetrates down to radii of less than 2 kpc from the central AGN and eventually feed the galaxy nucleus. The mass of gas inside the very central region is ~10E^9 Msun, and is similar to the mass of molecular gas found in the filaments.

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arXiv2011

HCOOCH3 as a probe of temperature and structure of Orion-KL

We studied the O-bearing molecule HCOOCH3 to characterize the physical conditions of the different molecular source components in Orion-KL. We identify 28 methyl formate emission peaks throughout the 50" field of observations. The two strongest peaks are in the Compact Ridge (MF1) and in the SouthWest of the Hot Core (MF2). Spectral confusion is still prevailing as half of the expected transitions are blended over the region. Assuming that the transitions are thermalized, we derive the temperature at the five main emission peaks. At the MF1 position we find a temperature of 80K in a 1.8"x0.8" beam size and 120K on a larger scale (3.6" x2.2"), suggesting an external source of heating, whereas the temperature is about 130K at the MF2 position on both scales. Transitions of HCOOCH3 in vt=1 are detected as well and the good agreement of the positions on the rotational diagrams between the vt=0 and the vt=1 transitions suggests a similar temperature. The velocity of the gas is between 7.5 and 8.0km/s depending on the positions and column density peaks vary from 1.6x10^16 to 1.6x10^17cm^-2. A second velocity component is observed around 9-10 km/s in a North-South structure stretching from the Compact Ridge up to the BN object; this component is warmer at the MF1 peak. The two other C2H4O2 isomers are not detected and the derived upper limit for the column density is <3x10^14cm^-2 for glycolaldehyde and <2x10^15cm^-2 for acetic acid. From the 223GHz continuum map, we identify several dust clumps with associated gas masses in the range 0.8 to 5.8Msun. Assuming that the HCOOCH3 is spatially distributed as the dust, we find relative abundances of HCOOCH3 in the range <0.1x10^-8 to 5.2x10^-8. We suggest a relation between the methyl formate distribution and shocks as traced by 2.12 mum H2 emission.

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arXiv2011

Molecular gas in NUclei of GAlaxies (NUGA) XV. Molecular gas kinematics in the inner 3kpc of NGC6951

Within the NUclei of GAlaxies project we have obtained IRAM PdBI and 30m 12CO(1-0) and 12CO(2-1) observations of the spiral galaxy NGC 6951. Previous work shows that there is indirect evidence of gas inflow from 3 kpc down to small radii: a large-scale stellar bar, a prominent starburst ring (r~580 pc) and a LINER/Seyfert 2 nucleus. In this paper we study the gas kinematics as traced by the CO line emission in detail. We quantify the influence of the large-scale stellar bar by constructing an analytical model of the evolution of gas particles in a barred potential. From this model gravitational torques and mass accumulation rates are computed. We compare our model-based gravitational torque results with previous observationally-based ones. The model also shows that the large-scale stellar bar is indeed the dominant force for driving the gas inward, to the starburst ring. Inside the ring itself a nuclear stellar oval might play an important role. Detailed analysis of the CO gas kinematics there shows that emission arises from two co-spatial, but kinematically distinct components at several locations. The main emission component can always be related to the overall bar-driven gas kinematics. The second component exhibits velocities that are larger than expected for gas on stable orbits, has a molecular gas mass of 1.8x10^6Msun, is very likely connected to the nuclear stellar oval, and is consistent with inflowing motion towards the very center. This may form the last link in the chain of gas inflow towards the active galactic nucleus in NGC 6951.

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arXiv2011

Gas inflows, star formation and metallicity evolution in galaxy pairs

It has been known since many decades that galaxy interactions can induce star formation (hereafter SF) enhancements and that one of the driving mechanisms of this enhancement is related to gas inflows into the central galaxy regions, induced by asymmetries in the stellar component, like bars. In the last years many evidences have been accumulating, showing that interacting pairs have central gas-phase metallicities lower than those of field galaxies, by {\sim} 0.2-0.3 dex on average. These diluted ISM metallicities have been explained as the result of inflows of metal-poor gas from the outer disk to the galaxy central regions. A number of questions arises: What's the timing and the duration of this dilution? How and when does the SF induced by the gas inflow enrich the circumnuclear gas with re-processed material? Is there any correlation between the timing and strength of the dilution and the timing and intensity of the SF? By means of Tree-SPH simulations of galaxy major interactions, we have studied the effect that gas inflows have on the ISM dilution, and the effect that the induced SF has, subsequently, in re-enriching the nuclear gas. In this contribution, we present the main results of this study.

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arXiv2011

Molecular Gas and Star Formation in Local Early-Type Galaxies

The molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the Atlas3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation, following the standard Schmidt-Kennicutt law but not the far infrared-radio correlation. This may suggest a greater diversity in star formation processes than observed in disk galaxies. Using multiple molecular tracers, we are thus starting to probe the physical conditions of the cold gas in early-types.

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arXiv2011

Galaxy Evolution and Star Formation Efficiency at 0.2 < z < 0.6

We present the results of a CO line survey of 30 galaxies at moderate redshift (z \sim 0.2-0.6), with the IRAM 30m telescope, with the goal to follow galaxy evolution and in particular the star formation efficiency (SFE) as defined by the ratio between far-infrared luminosity and molecular gas mass (LFIR/M(H2)). The sources are selected to be ultra-luminous infrared galaxies (ULIRGs), with LFIR larger than 2.8 10^{12} Lsol, experiencing starbursts; adopting a low ULIRG CO-to-H2 conversion factor, their gas consumption time-scale is lower than 10^8 yr. To date only very few CO observations exist in this redshift range that spans nearly 25% of the universe's age. Considerable evolution of the star formation rate is already observed during this period. 18 galaxies out of our sample of 30 are detected (of which 16 are new detections), corresponding to a detection rate of 60%. The average CO luminosity for the 18 galaxies detected is L'CO = 2 10^{10} K km/s pc^2, corresponding to an average H2 mass of 1.6 10^{10} Msol. The FIR luminosity correlates well with the CO luminosity, in agreement with the correlation found for low and high redshift ULIRGs. Although the conversion factor between CO luminosity and H2 mass is uncertain, we find that the maximum amount of gas available for a single galaxy is quickly increasing as a function of redshift. Using the same conversion factor, the SFEs for z\sim 0.2-0.6 ULIRGs are found to be significantly higher, by a factor 3, than for local ULIRGs, and are comparable to high redshift ones. We compare this evolution to the expected cosmic H2 abundance and the cosmic star formation history.

astro-ph.CO↗

arXiv2011

Molecular gas in galaxies at all redshifts

I review some recent results about the molecular content of galaxies, obtained essentially from the CO lines, but also dense tracers, or the dust continuum emission. New results have been obtained on molecular cloud physics, and their efficiency to form stars, shedding light on the Kennicutt-Schmidt law as a function of surface density and galaxy type. Large progress has been made on galaxy at moderate and high redshifts, allowing to interprete the star formation history and star formation efficiency as a function of gas content, or galaxy evolution. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. ALMA observations will allow the study of more normal galaxies at high z with higher spatial resolution and sensitivity.

astro-ph.CO↗

arXiv2011

Molecular Gas in NUclei of GAlaxies (NUGA) XIV. The barred LINER/Seyfert 2 galaxy NGC 3627

We present CO(1-0) and CO(2-1) maps of the interacting barred LINER/Seyfert 2 galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of 2.1" x 1.3" and 0.9" x 0.6", respectively. The molecular gas emission shows a nuclear peak, an elongated bar-like structure of ~18" (~900 pc) diameter in both CO maps and, in CO(1-0), a two-arm spiral feature from r~9" (~450 pc) to r~16" (~800 pc). The inner ~18" bar-like structure, with a north/south orientation (PA = 14°), forms two peaks at the extremes of this elongated emission region. The kinematics of the inner molecular gas shows signatures of non-circular motions associated both with the 18" bar-like structure and the spiral feature detected beyond it. The 1.6 micron H-band 2MASS image of NGC 3627 shows a stellar bar with a PA = -21°, different from the PA (= 14°) of the CO bar-like structure, indicating that the gas is leading the stellar bar. The torques computed with the HST-NICMOS F160W image and our PdBI maps are negative down to the resolution limit of our images, ~60 pc in CO(2-1). If the bar ends at ~3 kpc, coincident with corotation (CR), the torques are negative between the CR of the bar and the nucleus, down to the resolution limit of our observations. This scenario is compatible with a recently-formed rapidly rotating bar which has had insufficient time to slow down because of secular evolution, and thus has not yet formed an inner Lindblad resonance (ILR). The presence of molecular gas inside the CR of the primary bar, where we expect that the ILR will form, makes NGC 3627 a potential smoking gun of inner gas inflow. The gas is fueling the central region, and in a second step could fuel directly the active nucleus.

astro-ph.CO↗

arXiv2011

Radial migration in galactic disks caused by resonance overlap of multiple patterns: Self-consistent simulations

We have recently identified a new radial migration mechanism resulting from the overlap of spiral and bar resonances in galactic disks. Here we confirm the efficiency of this mechanism in fully self-consistent, Tree-SPH simulations, as well as high-resolution pure N-body simulations. In all barred cases we clearly identify the effect of spiral-bar resonance overlap by measuring a bimodality in the changes of angular momentum in the disk, dL, whose maxima are near the bar's corotation and outer Lindblad resonance. This contrasts with the smooth distribution of dL for a simulation with no stable bar present, where strong radial migration is induced by multiple spirals. The presence of a disk gaseous component appears to increase the rate of angular momentum exchange by about 20%. The efficiency of this mechanism is such that galactic stellar disks can extend to over 10 scale-lengths within 1-3 Gyr in both Milky Way size and low-mass galaxies (circular velocity ~100 km/s). We also show that metallicity gradients can flatten in less than 1 Gyr rendering mixing in barred galaxies an order of magnitude more efficient than previously thought.

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arXiv2010

Discovery of an extremely bright submillimeter galaxy at z=3.93

Serendipitously we have discovered a rare, bright submillimeter galaxy (SMG) with a flux density of 30 +/- 2 mJy at lambda=1.2mm, using MAMBO2 at the IRAM 30-meter millimeter telescope. Although no optical counterpart is known for MM18423+5938, we were able to measure the redshift z=3.92960 +/- 0.00013 from the detection of CO lines using the IRAM Eight MIxer Receiver (EMIR). In addition, by collecting all available photometric data in the far-infrared and radio to constrain its spectral energy distribution, we derive the FIR luminosity 4.8 10^14/m Lsol and mass 6.0 10^9/m Msol for its dust, allowing for a magnification factor m caused by a probable gravitational lens. The corresponding star-formation rate is 8.3 10^4/m Msol/yr. The detection of three lines of the CO rotational ladder, and a significant upper limit for a fourth CO line, allow us to estimate an H2 mass of between 1.9 10^11/m Msol and 1.1 10^12/m Msol. The two lines CI(3p1-3p0) and CI(3p2-3p1) were clearly detected and yield a [CI]/[H2] number abundance between 1.4 10^-5 and 8.0 10^-5. Upper limits are presented for emission lines of HCN, HCO^+, HNC, H_2O and other molecules observed. The moderate excitation of the CO lines is indicative of an extended starburst, and excludes the dominance of an AGN in heating this high-redshift SMG.

astro-ph.CO↗

arXiv2010

High-resolution mapping of the physical conditions in two nearby active galaxies based on 12CO(1-0), (2-1) and (3-2) lines

We present a detailed analysis of high resolution observations of the three lowest CO transitions in two nearby active galaxies, NGC4569 and NGC4826. The CO(1-0) and (2-1) lines were observed with the Plateau de Bure Interferometer and the CO(3-2) line with the Submillimeter Array. Combining these data allows us to compare the emission in the three lines and to map the line ratios, R21=I_{CO(2-1)}/I_{CO(1-0)} and R32=I_{CO(3-2)}/I_{CO(1-0)} at a resolution of ~2", i.e., a linear resolution of 160 pc for NGC4569 and 40 pc for NGC4826. In both galaxies the emission in the three lines is similarly distributed spatially and in velocity, and CO is less excited (R32<0.6) than in the Galactic Center or the centers of other active galaxies studied so far. According to a pseudo-LTE model the molecular gas in NGC4569 is cold and mainly optically thick in the CO(1-0) and (2-1) lines; less than 50% of the gas is optically thin in the CO(3-2) line. LVG modeling suggests the presence of an elongated ring of cold and dense gas coinciding with the ILR of the stellar bar. More excited gas is resolved in the circumnuclear disk of NGC4826. According to our pseudo-LTE model this corresponds to warmer gas with a ~50% of the CO(3-2) emission being optically thin. LVG modeling indicates the presence of a semicircular arc of dense and cold gas centered on the dynamical center and ~70 pc in radius. The gas temperature increases and its density decreases toward the center. A near side/far side asymmetry noticeable in the CO, R32 and Pa-alpha maps suggests that opacity effects play a role. Examining published CO maps of nearby active galaxies we find similar asymmetries suggesting that this could be a common phenomenon in active galaxies. These mainly qualitative results open new perspectives for the study of active galaxies with the future Atacama Large Millimeter/submillimeter Array.

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arXiv2010

Reionization by UV or X-ray sources

We present simulations of the 21-cm signal during the epoch of reionization. We focus on properly modeling the absorption regime in the presence of inhomogeneous Wouthuysen-Field effect and X-ray heating. We ran radiative transfer simulations for three bands in the source spectrum (Lyman, UV, and X-ray) to fully account for these processes. We find that the brightness temperature fluctuation of the 21 cm signal has an amplitude greater than 100 mK during the early reionization, up to 10 times greater than the typical amplitude of a few 10 mK obtained during the later emission phase. More importantly, we find that even a rather high contribution from QSO-like sources only damps the absorption regime without erasing it. Heating the IGM with X-ray takes time. Our results show that observations of the early reionization will probably benefit from a higher signal-to-noise value than during later stages. After analyzing the statistical properties of the signal (power spectrum and PDF) we find three diagnostics to constrain the level of X-ray, hence the nature of the first sources.

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arXiv2010

The Energetics of Molecular Gas in NGC 891 from H2 and FIR Spectroscopy

We have studied the molecular hydrogen energetics of the edge-on spiral galaxy NGC\,891, using a 34-position map in the lowest three pure rotational H$_2$ lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1), and S(2) lines are bright with an extinction corrected total luminosity of $\sim2.8 \times 10^{7}$ L$_{\odot}$, or 0.09\% of the total-infrared luminosity of NGC\,891. The H$_2$ line ratios are nearly constant along the plane of the galaxy -- we do not observe the previously reported strong drop-off in the S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so we find no evidence for the very massive cold CO-free molecular clouds invoked to explain the past observations. The H$_2$ level excitation temperatures increase monotonically indicating more than one component to the emitting gas. More than 99\% of the mass is in the lowest excitation (T$_{ex}$ $\sim$125 K) ``warm'' component. In the inner galaxy, the warm H$_2$ emitting gas is $\sim$15\% of the CO(1-0)-traced cool molecular gas, while in the outer regions the fraction is twice as high. This large mass of warm gas is heated by a combination of the far-UV photons from stars in photo-dissociation regions (PDRs) and the dissipation of turbulent kinetic energy. Including the observed far-infrared [OI] and [CII] fine-structure line emission and far-infrared continuum emission in a self-consistent manner to constrain the PDR models, we find essentially all of the S(0) and most (70\%) of the S(1) line arises from low excitation PDRs, while most (80\%) of the S(2) and the remainder of the S(1) line emission arises from low velocity microturbulent dissipation.

astro-ph.CO↗

arXiv2010

The dilution peak, metallicity evolution, and dating of galaxy interactions and mergers

Strong inflows of gas from the outer disk to the inner kiloparsecs are induced during the interaction of disk galaxies. This inflow of relatively low-metallicity gas dilutes the metallicity of the circumnuclear gas. We have investigated several aspects of the process as the timing and duration of the dilution and its correlation with the induced star formation. We analysed major (1:1) gas-rich interactions and mergers, spanning a range of initial orbital characteristics. Star formation and metal enrichment from SNe are included in our model. Our results show that the strongest trend is between the star formation rate and the dilution of the metals in the nuclear region; i.e., the more intense the central burst of star formation, the more the gas is diluted. This trend comes from strong inflows of relatively metal-poor gas from the outer regions of both disks, which fuels the intense star formation and lowers the overall metallicity for a time. The strong inflows happen on timescales of about 10^8 years or less, and the most intense star formation and lowest gas phase metallicities are seen generally after the first pericentre passage. As the star formation proceeds and the merger advances, the dilution reduces and enrichment becomes dominant - ultimately increasing the metallicity of the circumnuclear gas to a level higher than the initial metallicities of the merging galaxies. The "fly-bys" - pairs that interact but do not merge - also cause some dilution. We even see some dilution early in the merger or in the "fly-bys" and thus do not observe a strong trend between the nuclear metallicities and separation in our simulations until the merger is well advanced. We also analyse the O and Fe enrichment of the ISM, and show that the evolution of the alpha/Fe ratios, as well as the dilution of the central gas metallicity, can be used as a clock for "dating" the interaction.

astro-ph.CO↗

arXiv2010

Molecular and Atomic Gas in the Local Group Galaxy M33

We present high resolution large scale observations of the molecular and atomic gas in the Local Group Galaxy M33. The observations were carried out using the HERA at the 30m IRAM telescope in the CO(2-1) line achieving a resolution of 12"x2.6 km/s, enabling individual GMCs to be resolved. The observed region mainly along the major axis out to a radius of 8.5 kpc, and covers the strip observed with HIFI/PACS Spectrometers as part of the HERM33ES Herschel key program. The achieved sensitivity in main beam temperature is 20-50 mK at 2.6 km/s velocity resolution. The CO(2-1) luminosity of the observed region is 1.7\pm0.1x10^7 Kkm/s pc^2, corresponding to H2 masses of 1.9x10^8 Msun (including He), calculated with a NH2/ICO twice the Galactic value due to the half-solar metallicity of M33. HI 21 cm VLA archive observations were reduced and the mosaic was imaged and cleaned using the multi-scale task in CASA, yielding a series of datacubes with resolutions ranging from 5" to 25". The HI mass within a radius of 8.5 kpc is estimated to be 1.4x10^9 Msun. The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9\pm0.1 kpc whereas the atomic gas surface density is constant at Sigma_HI=6\pm2 Msun/pc^2 deprojected to face-on. The central kiloparsec H_2 surface density is Sigma_H2=8.5\pm0.2 Msun/pc^2. The star formation rate per unit molecular gas (SF Efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to Halpha and FIR brightness, is constant with radius. The SFE appears 2-4 times greater than of large spiral galaxies. A morphological comparison of molecular and atomic gas with tracers of star formation shows good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8 kpc from the galaxy center, are presented.

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