Dense and Warm Molecular Gas and Warm Dust in Nearby Galaxies

We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) single-dish observations (beam size ~14"-18") toward nearby starburst and non-starburst galaxies using the Nobeyama 45 m telescope. The 13CO(1-0) and HCN(1-0) emissions were detected from all the seven starburst galaxies, with the intensities of both lines being similar (i.e., the ratios are around unity). On the other hand, for case of the non-starburst galaxies, the 13CO(1-0) emission was detected from all three galaxies, while the HCN(1-0) emission was weakly or not detected in past observations. This result indicates that the HCN/13CO intensity ratios are significantly larger (~1.15+-0.32) in the starburst galaxy samples than the non-starburst galaxy samples (<0.31+-0.14). The large-velocity-gradient model suggests that the molecular gas in the starburst galaxies have warmer and denser conditions than that in the non-starburst galaxies, and the photon-dominated-region model suggests that the denser molecular gas is irradiated by stronger interstellar radiation field in the starburst galaxies than that in the non-starburst galaxies. In addition, HCN/13CO in our sample galaxies exhibit strong correlations with the IRAS 25 micron flux ratios. It is a well established fact that there exists a strong correlation between dense molecular gas and star formation activities, but our results suggest that molecular gas temperature is also an important parameter.Comment: 14 pages, 6 figures. Accepted for publication in PAS

NRO M33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC): II. Dense Gas Formation within Giant Molecular Clouds in M33

We report the results of our observations of the 12CO (J=1-0) and 12CO (J=3-2) line emission of 74 major giant molecular clouds (GMCs) within the galactocentric distance of 5.1 kpc in the Local Group galaxy M33. The observations have been conducted as part of the Nobeyama Radio Observatory M33 All-disk survey of Giant Molecular Clouds project (NRO MAGiC). The spatial resolutions are 80 pc for 12CO (J=1-0) and 100 pc for 12CO (J=3-2). We detect 12CO (J=3-2) emission of 65 GMCs successfully. Furthermore, we find that the correlation between the surface density of the star formation rate, which is derived from a linear combination of Halpha and 24um emissions, and the 12CO (J=3-2) integrated intensity still holds at this scale. This result show that the star-forming activity is closely associated with warm and dense gases that are traced with the 12CO (J=3-2) line, even in the scale of GMCs. We also find that the GMCs with a high star-forming activity tend to show a high integrated intensity ratio (R3-2/1-0). Moreover, we also observe a mass-dependent trend of R3-2/1-0 for the GMCs with a low star-forming activity. From these results, we speculate that the R3-2/1-0 values of the GMCs with a low star-forming activity mainly depend on the dense gas fraction and not on the temperature, and therefore, the dense gas fraction increases with the mass of GMCs, at least in the GMCs with a low star-forming activity.Comment: 17 pages, 5 figures, Accepted for publication in PASJ, 2012, Vol. 64, No.

NRO M33 All Disk Survey of Giant Molecular Clouds (NRO MAGiC): I. HI to H_2 Transition

We present the results of the Nobeyama Radio Observatory (NRO) M33 All Disk (30'x30' or 7.3 kpc x 7.3 kpc) Survey of Giant Molecular Clouds (NRO MAGiC) based on 12CO (1-0) observations using the NRO 45-m telescope. The spatial resolution of the resultant map is 19".3, corresponding to 81 pc, which is sufficient to identify each Giant Molecular Cloud (GMC) in the disk. We found clumpy structures with a typical spatial scale of ~100 pc, corresponding to GMCs, and no diffuse, smoothly distributed component of molecular gas at this sensitivity. Closer inspection of the CO and HI maps suggests that not every CO emission is associated with local HI peaks, particularly in the inner portion of the disk (r < 2 kpc), although most of CO emission is located at the local HI peaks in the outer radii. We found that most uncovered GMCs are accompanied by massive star-forming regions, although the star formation rates (SFRs) vary widely from cloud to cloud. The azimuthally averaged H{\sc i} gas surface density exhibits a flat radial distribution. However, the CO radial distribution shows a significant enhancement within the central 1-2 kpc region, which is very similar to that of the SFR. We obtained a map of the molecular fraction, f_mol = Sigma_H_2/(Sigma_HI+Sigma_H_2, at a 100-pc resolution. This is the first f_mol map covering an entire galaxy with a GMC-scale resolution. We find that f_mol tends to be high near the center. The correlation between f_mol and gas surface density shows two distinct sequences. The presence of two correlation sequences can be explained by differences in metallicity, i.e., higher (~ 2-fold) metallicity in the central region (r< 1.5 kpc) than in the outer parts. Alternatively, differences in scale height can also account for the two sequences, i.e., increased scale height toward the outer disk.Comment: Accepted for publication in PASJ, See http://www.juen.ac.jp/lab/tosaki/paper/astro-ph/2011/tosaki2011.pdf for a version with full resolution figure

Characterizing CO Emitters in the SSA22-AzTEC26 Field

We report the physical characterization of four CO emitters detected near the bright submillimeter galaxy (SMG) SSA22-AzTEC26. We analyze the data from Atacama Large Millimeter/submillileter Array band 3, 4, and 7 observations of the SSA22-AzTEC26 field. In addition to the targeted SMG, we detect four line emitters with a signal-to-noise ratio $>5.2$ in the cube smoothed with 300 km s$^{-1}$ FWHM Gaussian filter. All four sources have NIR counterparts within 1\arcsec. We perform UV-to-FIR spectral energy distribution modeling to derive the photometric redshifts and physical properties. Based on the photometric redshifts, we reveal that two of them are CO(2-1) at redshifts of 1.113 and 1.146 and one is CO(3-2) at $z=2.124$. The three sources are massive galaxies with a stellar mass $\gtrsim10^{10.5}M_\odot$, but have different levels of star formation. Two lie within the scatter of the main sequence (MS) of star-forming galaxies at $z\sim1-2$, and the most massive galaxy lies significantly below the MS. However, all three sources have a gas fraction within the scatter of the MS scaling relation. This shows that a blind CO line search can detect massive galaxies with low specific star formation rates that still host large gas reservoirs and that it also complements targeted surveys, suggesting later gas acquisition and the need for other mechanisms in addition to gas consumption to suppress star formation.Comment: accepted for publication in the Astrophysical Journa

Assignment of CPS1, OTC, CRYD2, ARG2 and ASS genes to the chicken RH map

An attempt was made to assign five genes, CPS1, OTC, ASS, CRYD2, and ARG2, to chicken chromosomes (GGA) by radiation-hybrid mapping. OTC was assigned to GGA1; ARG2 to GGA5; CPS1 to GGA7; and CRYD2 to GGA19. ASS was not, however, assigned to a specific chromosomal position

Revisited cold gas content with atomic carbon [C I] in z=2.5 protocluster galaxies

We revisit the cold gas contents of galaxies in a protocluster at z=2.49 using the lowest neutral atomic carbon transition [CI]$^3$P$_1$-$^3$P$_0$ from Atacama Large Millimeter/submillimeter Array observations. We aim to test if the same gas mass calibration applied in field galaxies can be applied to protocluster galaxies. Five galaxies out of sixteen targeted galaxies are detected in the [CI] line, and these are all previously detected in CO(3-2) and CO(4-3) and three in 1.1 mm dust continuum. We investigate the line luminosity relations between CO and [CI] in the protocluster and compare them with other previous studies. We then compare the gas mass based on three gas tracers of [CI], CO(3-2), and dust if at least one of the last two tracers are available. Using the calibration adopted for field main-sequence galaxies, the [CI]-based gas measurements are lower than or comparable to the CO-based gas measurements by -0.35 dex at the lowest with the mean deviation of -0.14 dex. The differences between [CI]- and the dust- based measurements are relatively mild by up to 0.16 dex with the mean difference of 0.02 dex. Taking these all together with calibration uncertainties, with the [CI] line, we reconfirm our previous findings that the mean gas fraction is comparable to field galaxies for a stellar-mass range of $\log(M_{\rm star}/M_\odot = [10.6, 11.3]$. However, at least for these secure five detections, the depletion time scale decreases more rapidly with stellar mass than field galaxies that might be related to earlier quenching in dense environments.Comment: accepted for publication in Ap