We present a study of the molecular gas properties in a sample of 98 HI - flux selected spiral galaxies within similar to 25 Mpc, using the CO J = 3 - 2 line observed with the James Clerk Maxwell Telescope. We use the technique of survival analysis to incorporate galaxies with CO upper limits into our results. Comparing the group and Virgo samples, we find a larger mean H-2 mass in the Virgo galaxies, despite their lower mean HI mass. This leads to a significantly higher H-2 to HI ratio for Virgo galaxies. Combining our data with complementary H alpha star formation rate measurements, Virgo galaxies have longer molecular gas depletion times compared to group galaxies, due to their higher H-2 masses and lower star formation rates. We suggest that the longer depletion times may be a result of heating processes in the cluster environment or differences in the turbulent pressure. From the full sample, we find that the molecular gas depletion time has a positive correlation with the stellar mass, indicative of differences in the star formation process between low- and high-mass galaxies, and a negative correlation between the molecular gas depletion time and the specific star formation rate.

We present (CO)-C-12 J = 3 -> 2 maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with (CO)-C-12 J = 1 -> 0 data and find that the computed (CO)-C-12 J = 3 -> 2 to (CO)-C-12 J = 1 -> 0 line ratio (R-31) agrees with values measured in other NGLS field galaxies. We compute the M-H2 value and find that it is robust against the value of R-31 used. Using HI data from The HI Nearby Galaxy Survey, we find a tight correlation between the surface density of H-2 and star formation rate density for NGC 3351 when (CO)-C-12 J = 3 -> 2 data are used. Finally, we compare the (CO)-C-12 J = 3 -> 2 intensity with the polycyclic aromatic hydrocarbon (PAH) 8 mu m surface brightness and find a good correlation in the high surface brightness regions. We extend this study to include all 25 Spitzer Infrared Nearby Galaxies Survey galaxies within the NGLS sample and find a tight correlation at large spatial scales. We suggest that both PAH 8 mu m and (CO)-C-12 J = 3 -> 2 are likely to originate in regions of active star formation.

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an HI-selected sample of 155 galaxies spanning all morphological types with distances less than 25 Mpc. We describe the scientific goals of the survey, the sample selection, and the observing strategy. We also present an atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift which have also been observed in the CO J=3-2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the L(FIR)/L(CO3-2) ratio with the atomic to molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.

NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst ring, a strong large-scale bar, and an active nucleus. We present a detailed study of the spatial variation of the far-infrared (FIR) [CII]158 mu m and [OI]63 mu m lines and mid-infrared H-2 emission lines as tracers of gas cooling, and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the photoelectric heating, using Herschel-PACS and Spitzer-IRS infrared spectral maps. We focus on the nucleus and the ring, and two star-forming regions (Enuc N and Enuc S). We estimated a photoelectric gas heating efficiency ([CII]158 mu m+[OI]63 mu m)/PAH in the ring about 50% lower than in Enuc N and S. The average 11.3/7.7 mu m PAH ratio is also lower in the ring, which may suggest a larger fraction of ionized PAHs, but no clear correlation with [CII]158 mu m/PAH(5.5-14 mu m) is found. PAHs in the ring are responsible for a factor of two more [CII]158 mu m and [OI]63 mu m emission per unit mass than PAHs in the Enuc S. spectral energy distribution (SED) modeling indicates that at most 25% of the FIR power in the ring and Enuc S can come from high-intensity photodissociation regions (PDRs), in which case G(0) similar to 10(2.3) and n(H) similar to 10(3.5) cm(-3) in the ring. For these values of G(0) and n(H), PDR models cannot reproduce the observed H-2 emission. Much of the H-2 emission in the starburst ring could come from warm regions in the diffuse interstellar medium that are heated by turbulent dissipation or shocks.

NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst ring, a strong large-scale bar, and an active nucleus. We present a detailed study of the spatial variation of the far-infrared (FIR) [C ii]158 μm and [O i]63 μm lines and mid-infrared H2 emission lines as tracers of gas cooling, and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the photoelectric heating, using Herschel-PACS and Spitzer-IRS infrared spectral maps. We focus on the nucleus and the ring, and two star-forming regions (Enuc N and Enuc S). We estimated a photoelectric gas heating efficiency ([C ii]158 μm+[O i]63 μm)/PAH in the ring about 50% lower than in Enuc N and S. The average 11.3/7.7 μm PAH ratio is also lower in the ring, which may suggest a larger fraction of ionized PAHs, but no clear correlation with [C ii]158 μm/PAH(5.5–14 μm) is found. PAHs in the ring are responsible for a factor of two more [C ii]158 μm and [O i]63 μm emission per unit mass than PAHs in the Enuc S. spectral energy distribution (SED) modeling indicates that at most 25% of the FIR power in the ring and Enuc S can come from high-intensity photodissociation regions (PDRs), in which case G0 ∼ 102.3 and nH ∼ 103.5 cm−3 in the ring. For these values of G0 and nH, PDR models cannot reproduce the observed H2 emission. Much of the H2 emission in the starburst ring could come from warm regions in the diffuse interstellar medium that are heated by turbulent dissipation or shocks.

The definitive version can be found at: http://onlinelibrary.wiley.com/ Copyright Wiley-Blackwell and Royal Astronomical Society

We present a first complete 12 CO J=3-2 map of M81, observed as part of the Nearby Galaxies Legacy Survey being carried out at the James Clerk Maxwell Telescope. We detect 9 regions of significant CO emission located at different positions within the spiral arms, and confirm that the global CO emission in the galaxy is low. We combine these data with a new H-alpha map obtained using the Isaac Newton Telescope and archival HI, 24 microns and FUV images to uncover a correlation between the molecular gas and star forming regions in M81. For the nine regions detected in CO J=3-2, we combine our CO J=3-2 data with existing CO J=1-0 data to calculate line ratios. We find that the ratio J=(3-2)/(1-0) is in agreement with the range of typical values found in the literature (0.2-0.8). Making reasonable assumptions, this allows us to constrain the hydrogen density to the range (10^3-10^4) cm^{-3}. We also estimated the amount of hydrogen produced in photo-dissociation regions near the locations where CO J=3-2 was detected.

We have made the first map of CO(J = 3-2) emission covering the disc of the edge-on galaxy, NGC 4631, which is known for its spectacular gaseous halo. The strongest emission, which we model with a Gaussian ring, occurs within a radius of 5 kpc. Weaker disc emission is detected out to radii of 12 kpc, the most extensive molecular component yet seen in this galaxy. From comparisons with infrared data, we find that CO(J = 3-2) emission more closely follows the hot dust component, rather than the cold dust, consistent with it being a good tracer of star formation. The first maps of R3-2/1-0, H-2 mass surface density and star formation efficiency (SFE) have been made for the inner 2.4 kpc radius region. Only 20 per cent of the star formation occurs in this region and excitation conditions are typical of galaxy discs, rather than of central starbursts. The SFE suggests long gas consumption time-scales (> 109 yr).The velocity field is dominated by a steeply rising rotation curve in the region of the central molecular ring followed by a flatter curve in the disc. A very steep gradient in the rotation curve is observed at the nucleus, providing the first evidence for a central concentration of mass: M-dyn = 5 x 107 M-circle dot within a radius of 282 pc. The velocity field shows anomalous features indicating the presence of molecular outflows; one of them is associated with a previously observed CO(J = 1-0) expanding shell. Consistent with these outflows is the presence of a thick (z up to 1.4 kpc) CO(J = 3-2) disc. We suggest that the interaction between NGC 4631 and its companion(s) has agitated the disc and also initiated star formation which was likely higher in the past than it is now. These may be necessary conditions for seeing prominent haloes.

We present the first complete 12CO J = 3−2 map of M 81, observed as part of the Nearby Galaxies Legacy Survey being carried out at the James Clerk Maxwell Telescope. We detect nine regions of significant CO emission located at different positions within the spiral arms, and confirm that the global CO emission in the galaxy is low. We combine these data with a new Hα map obtained using the Isaac Newton Telescope and archival H i, 24μm, and FUV images to uncover a correlation between the molecular gas and star forming regions in M 81. For the nine regions detected in CO J = 3−2, we combine our CO J = 3−2 data with existing CO J = 1−0 data to calculate line ratios. We find that the ratio J = (3−2)/(1−0) is in agreement with the range of typical values found in the literature (0.2−0.8). Making reasonable assumptions, this allows us to constrain the hydrogen density to the range (103−104) cm-3. We also estimated the amount of hydrogen produced in photo-dissociation regions near the locations where CO J = 3−2 was detected.

Using photometry of NGC 1097 from the Herschel PACS (Photodetector Array Camera and Spectrometer) instrument, we study the resolved properties of thermal dust continuum emission from a circumnuclear starburst ring with a radius ~ 900 pc. These observations are the first to resolve the structure of a circumnuclear ring at wavelengths that probe the peak (i.e. lambda ~ 100 micron) of the dust spectral energy distribution. The ring dominates the far-infrared (far-IR) emission from the galaxy - the high angular resolution of PACS allows us to isolate the ring's contribution and we find it is responsible for 75, 60 and 55% of the total flux of NGC 1097 at 70, 100 and 160 micron, respectively. We compare the far-IR structure of the ring to what is seen at other wavelengths and identify a sequence of far-IR bright knots that correspond to those seen in radio and mid-IR images. The mid- and far-IR band ratios in the ring vary by less than +/- 20% azimuthally, indicating modest variation in the radiation field heating the dust on ~ 600 pc scales. We explore various explanations for the azimuthal uniformity in the far-IR colors of the ring including a lack of well-defined age gradients in the young stellar cluster population, a dominant contribution to the far-IR emission from dust heated by older (> 10 Myr) stars and/or a quick smoothing of local enhancements in dust temperature due to the short orbital period of the ring. Finally, we improve previous limits on the far-IR flux from the inner ~ 600 pc of NGC 1097 by an order of magnitude, providing a better estimate of the total bolometric emission arising from the active galactic nucleus and its associated central starburst.

NGC 1097 is a nearby SBb galaxy with a Seyfert nucleus and a bright starburst ring. We study the physical properties of the interstellar medium (ISM) in the ring using spatially resolved far-infrared spectral maps of the circumnuclear starburst ring of NGC 1097, obtained with the PACS spectrometer on board the Herschel Space Observatory. In particular, we map the important ISM cooling and diagnostic emission lines of [OI] 63 mu m, [OIII] 88 mu m, [NII] 122 mu m, [CII] 158 mu m and [NII] 205 mu m. We observe that in the [OI] 63 mu m, [OIII] 88 mu m, and [NII] 122 mu m line maps, the emission is enhanced in clumps along the NE part of the ring. We observe evidence of rapid rotation in the circumnuclear ring, with a rotation velocity of similar to 220 km s(-1) (inclination uncorrected) measured in all lines. The [OI] 63 mu m/[CII] 158 mu m ratio varies smoothly throughout the central region, and is enhanced on the northeastern part of the ring, which may indicate a stronger radiation field. This enhancement coincides with peaks in the [OI] 63 mu m and [OIII] 88 mu m maps. Variations of the [NII] 122 mu m/[NII] 205 mu m ratio correspond to a range in the ionized gas density between 150 and 400 cm(-3).

We used 3.6, 8.0, 70, 160 µm Spitzer Space Telescope data, James Clerk Maxwell Telescope HARP-B COJ =(3-2) data, National Radio Astronomy Observatory 12 meter telescope CO J =(1-0) data, and Very Large Array HI data to investigate the relations among PAHs, cold (� 20 K) dust, molecular gas, and atomic gas within NGC 2403, an SABcd galaxy at a distance of 3.13 Mpc. The dust surface density is mainly a function of the total (atomic and molecular) gas surface density and galactocentric radius. The gas-to-dust ratio monotonically increases with radius, varying from � 100 in the nucleus to � 400 at 5.5 kpc. The slope of the gas-to-dust ratio is close to that of the oxygen abunda nce, suggesting that metallicity strongly affects the gas-to-dust ratio within this galaxy. The exponential scale length of the radial profile for the CO J =(3-2) emission is statistically identical to the scale len gth for the stellar continuum-subtracted 8 µm (PAH 8 µm) emission. However, CO J =(3-2) and PAH 8 µm surface brightnesses appear uncorrelated when examining sub-kpc sized regions.

Stellar density and bar strength should affect the temperatures of the cool (T ~ 20-30 K) dust component in the inner regions of galaxies, which implies that the ratio of temperatures in the circumnuclear regions to the disk should depend on Hubble type. We investigate the differences between cool dust temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting models to measurements between 70 and 500 microns. We attempt to quantify temperature trends in nearby disk galaxies, with archival data from Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired during the first phases of the Herschel observations for the KINGFISH (key insights in nearby galaxies: a far-infrared survey with Herschel) sample. We fit single-temperature modified blackbodies to far-infrared and submillimeter measurements of the central and disk regions of galaxies to determine the temperature of the component(s) emitting at those wavelengths. We present the ratio of central-region-to-disk-temperatures of the cool dust component of 13 nearby galaxies as a function of morphological type. We find a significant temperature gradient in the cool dust component in all galaxies, with a mean center-to-disk temperature ratio of 1.15 +/- 0.03. The cool dust temperatures in the central ~3 kpc of nearby galaxies are 23(+/-3)% hotter for morphological types earlier than Sc, and only 9(+/-3)% hotter for later types. The temperature ratio is also correlated with bar strength, with only strongly barred galaxies having a ratio over 1.2. The strong radiation field in the high stellar density of a galactic bulge tends to heat the cool dust component to higher temperatures, at least in early-type spirals with relatively large bulges, especially when paired with a strong bar.

We present the results of large-area CO J=3-2 emission mapping of three nearby field galaxies, NGC 628, NGC 3521, and NGC 3627, completed at the James Clerk Maxwell Telescope as part of the Nearby Galaxies Legacy Survey. These galaxies all have moderate to strong CO J=3-2 detections over large areas of the fields observed by the survey, showing resolved structure and dynamics in their warm/dense molecular gas disks. All three galaxies were part of the Spitzer Infrared Nearby Galaxies Survey sample, and as such have excellent published multi-wavelength ancillary data. These data sets allow us to examine the star formation properties, gas content, and dynamics of these galaxies on sub-kiloparsec scales. We find that the global gas depletion times for dense/warm molecular gas in these galaxies is consistent with other results for nearby spiral galaxies, indicating this may be independent of galaxy properties such as structures, gas compositions, and environments. Similar to the results from the THINGS HI survey, we do not see a correlation of the star formation efficiency with the gas surface density consistent with the Schmidt-Kennicutt law. Finally, we find that the star formation efficiency of the dense molecular gas traced by CO J=3-2 is potentially flat or slightly declining as a function of molecular gas density, the CO J=3-2/J=1-0 ratio (in contrast to the correlation found in a previous study into the starburst galaxy M83), and the fraction of total gas in molecular form.

We present the results of large-area CO J=3-2 emission mapping of three nearby field galaxies, NGC 628, NGC 3521, and NGC 3627, completed at the James Clerk Maxwell Telescope as part of the Nearby Galaxies Legacy Survey. These galaxies all have moderate to strong CO J=3-2 detections over large areas of the fields observed by the survey, showing resolved structure and dynamics in their warm/dense molecular gas disks. All three galaxies were part of the Spitzer Infrared Nearby Galaxies Survey sample, and as such have excellent published multi-wavelength ancillary data. These data sets allow us to examine the star formation properties, gas content, and dynamics of these galaxies on sub-kiloparsec scales. We find that the global gas depletion times for dense/warm molecular gas in these galaxies is consistent with other results for nearby spiral galaxies, indicating this may be independent of galaxy properties such as structures, gas compositions, and environments. Similar to the results from the THINGS HI survey, we do not see a correlation of the star formation efficiency with the gas surface density consistent with the Schmidt-Kennicutt law. Finally, we find that the star formation efficiency of the dense molecular gas traced by CO J=3-2 is potentially flat or slightly declining as a function of molecular gas density, the CO J=3-2/J=1-0 ratio (in contrast to the correlation found in a previous study into the starburst galaxy M83), and the fraction of total gas in molecular form.

We present large-area maps of the CO J = 3-2 emission obtained at the James Clerk Maxwell Telescope for four spiral galaxies in the Virgo Cluster. We combine these data with published CO J = 1-0, 24 mu m, and Ha images to measure the CO line ratios, molecular gas masses, and instantaneous gas depletion times. For three galaxies in our sample (NGC 4254, NGC 4321, and NGC 4569), we obtain molecular gas masses of 7 x 10(8) - 3 x 10(9) M-circle dot and disk-averaged instantaneous gas depletion times of 1.1-1.7 Gyr. We argue that the CO J = 3-2 line is a better tracer of the dense star-forming molecular gas than the CO J = 1-0 line, as it shows a better correlation with the star formation rate surface density both within and between galaxies. NGC 4254 appears to have a larger star formation efficiency (smaller gas depletion time), perhaps because it is on its first passage through the Virgo Cluster. NGC 4569 shows a large-scale gradient in the gas properties traced by the CO J = 3-2/J = 1-0 line ratio, which suggests that its interaction with the intracluster medium is affecting the dense star-forming portion of the interstellar medium directly. The fourth galaxy in our sample, NGC 4579, has weak CO J = 3-2 emission despite having bright 24 mu m emission; however, much of the central luminosity in this galaxy may be due to the presence of a central active galactic nucleus.

Luminous and Ultraluminous infrared galaxies (ULIRGs) contain the most intense regions of star formation in the local universe. Because molecular gas is the fuel for current and future star formation, the physical properties and distribution of the warm, dense molecular gas are key components for understanding the processes and timescales controlling star formation in these merger and merger remnant galaxies. We present new results from a legacy project on the Submillimeter Array which is producing high resolution images of a representative sample of galaxies with log L FIR >11.4 and D<200 Mpc.

We present new data obtained with the Submillimeter Array for a sample of 14 nearby luminous and ultraluminous infrared galaxies. The galaxies were selected to have distances D-L < 200 Mpc and far-infrared luminosities log L-FIR > 11.4. The galaxies were observed with spatial resolutions of order 1 kpc in the COJ = 3-2, COJ = 2-1, (13)COJ = 2-1, and HCO+ J = 4-3 lines as well as the continuum at 880 mu m and 1.3 mm. We have combined our CO and continuum data to measure an average gas-to-dust mass ratio of 120 +/- 28 (rms deviation 109) in the central regions of these galaxies, very similar to the value of 150 determined for the Milky Way. This similarity is interesting given the more intense heating from the starburst and possibly accretion activity in the luminous infrared galaxies compared to the Milky Way. We find that the peak H-2 surface density correlates with the far-infrared luminosity, which suggests that galaxies with higher gas surface densities inside the central kiloparsec have a higher star formation rate. The lack of a significant correlation between total H-2 mass and far-infrared luminosity in our sample suggests that the increased star formation rate is due to the increased availability of molecular gas as fuel for star formation in the central regions. In contrast to previous analyses by other authors, we do not find a significant correlation between central gas surface density and the star formation efficiency, as traced by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that it is the star formation rate, not the star formation efficiency, that increases with increasing central gas surface density in these galaxies.

We present an analysis of the atomic hydrogen and stellar properties of 38 late-type galaxies in the local universe covering a wide range of H I mass-to-light ratios ( M(HI)/ L(B)), stellar luminosities, and surface brightnesses. Combining the results with those of four other well-studied dwarf galaxies known for their unusually large Hi contents, we identified an upper envelope for the MH(I)/ LB as a function of galaxy luminosity. This implies an empirical relation between the minimum amount of stars a galaxy will form and its initial baryonic mass. We also find that the star density systematically decreases with increasing MH I/ LB, making the galaxies optically more elusive. While the stellar mass of a galaxy seems to be only loosely connected to its baryonic mass, the latter quantity is strongly linked to the galaxy's dynamical mass as it is observed in the baryonic Tully-Fisher relation. We find that dwarf irregular galaxies with generally high M(H) (I)/ LB ratios follow the same trend as defined by lower MH (I)/ LB giant galaxies but are underluminous for their rotation velocity to follow the trend in a stellar mass Tully-Fisher relation, suggesting that the baryonic mass of the dwarf galaxies is normal but they have failed to produce a sufficient amount of stars. Finally, we present a three-dimensional equivalent to the morphology-density relation which shows that high M(H) (I)/ LB galaxies preferentially evolve and/or survive in low-density environments. We conclude that an isolated galaxy with a shallow dark matter potential can retain a large portion of its baryonic matter in the form of gas, only producing the minimum quantity of stars necessary to maintain a stable gas disk.