Galactic winds are essential to the regulation of star formation in galaxies. To study the distribution and dynamics of molecular gas in wind, we imaged the nearby starburst galaxy NGC 1482 in CO (J ...= 1 → 0) at a resolution of 1″ ( 100 pc) using the Atacama Large Millimeter/submillimeter Array. Molecular gas is detected in a nearly edge-on disk with a radius of 3 kpc and a biconical outflow emerging from the central 1 kpc starburst and extending to at least 1.5 kpc perpendicular to the disk. In the outflow, CO gas is distributed approximately as a cylindrically symmetrical envelope surrounding the warm and hot ionized gas traced by H and soft X-rays. The velocity, mass outflow rate, and kinetic energy of the molecular outflow are , , and , respectively. is comparable to the star formation rate ( ) and Ew is ∼1% of the total energy released by stellar feedback in the past , which is the dynamical timescale of the outflow. The results indicate that the wind is starburst driven.
We describe the construction of a database of extremely metal-poor (EMP) stars in the Galaxy. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, ...photometry, and binarity status, compiled from papers in the literature that report on studies of EMP halo stars with Fe/H
$\;\le\;$
$-$
2.5. The compilation procedures for this database were designed to assemble data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria and illustrations to explore relationships between stored variables. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering relevant papers published by 2007 December. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with Fe/H
$\;\le\;$
$-$
2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amounts to
$\sim\;$
30% for Fe/H
$\;\le\;$
$-$
2.5. We find that known binaries exhibit different distributions of the orbital period, according to whether they are giants or dwarfs, and also as a function of the metallicity, although the total sample of such stars is still quite small.
We conduct spectral line survey observations in the 3 mm band toward a spiral arm, a bar-end, and a nuclear region of the nearby barred spiral galaxy NGC 3627 with the IRAM 30 m telescope and the ...Nobeyama 45 m telescope. Additional observations are performed toward the spiral arm and the bar-end in the 2 mm band. We detect 8, 11, and 9 molecular species in the spiral arm, the bar-end, and the nuclear region, respectively. Star formation activities are different among the three regions, and in particular, the nucleus of NGC 3627 is known as a low-ionization nuclear emission region/Seyfert 2 type nucleus. In spite of these physical differences, the chemical composition shows impressive similarities among the three regions. This result means that the characteristic chemical composition associated with these regions is insensitive to the local physical conditions such as star formation rate, because such local effects are smeared out by extended quiescent molecular gas on scales of 1 kpc. Moreover, the observed chemical compositions are also found to be similar to those of molecular clouds in our Galaxy and the spiral arm of M51, whose elemental abundances are close to those in NGC 3627. Therefore, this study provides us with a standard template of the chemical composition of extended molecular clouds with the solar metallicity in nearby galaxies.
MOLECULAR DISTRIBUTION IN THE SPIRAL ARM OF M51 Watanabe, Yoshimasa; Sakai, Nami; Sorai, Kazuo ...
Astrophysical journal/The Astrophysical journal,
03/2016, Letnik:
819, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT Molecular line images of 13CO, C18O, CN, CS, CH3OH, and HNCO are obtained toward the spiral arm of M51 at a resolution with the Combined Array for Research in Millimeter-wave Astronomy. ...Distributions of the molecules averaged over a 300 pc scale are found to be almost similar to one another and to essentially trace the spiral arm. However, the principal component analysis shows a slight difference of distributions among molecular species, particularly for CH3OH and HNCO. These two species do not correlate well with the star formation rate, implying that they are not enhanced by local star formation activities but by galactic-scale phenomena such as spiral shocks. Furthermore, the distributions of HNCO and CH3OH are found to be slightly different, and their origins deserve further investigation. The present results provide us with an important clue for understanding the 300 pc scale chemical composition in the spiral arm and its relation to galactic-scale dynamics.
ABSTRACT
Photometric surveys have provided incredible amounts of astronomical information in the form of images. However, astronomical images often contain artifacts that can critically hinder ...scientific analysis by misrepresenting intensities or contaminating catalogs as artificial objects. These affected pixels need to be masked and dealt with in any data reduction pipeline. We present a flexible, iterative algorithm to recover (unmask) astronomical images where some pixels are lacking. We demonstrate the application of the method on some intensity calibration source images in the CO Multi-line Imaging of Nearby Galaxies (COMING) project conducted using the 45 m telescope at Nobeyama Radio Observatory. The proposed algorithm restored artifacts due to a detector error in the intensity calibration source images. The restored images were used to calibrate 11 out of 147 observed galaxy maps in the survey. The tests show that the algorithm can restore measured intensities at sub 1% error even for noisy images (S/N = 2.4), despite lacking a significant part of the image. We present the formulation of the reconstruction algorithm, discuss its possibilities and limitations for extensions to other astronomical signals, and examine the results of the COMING application.
Abstract
We present simultaneous mappings of J = 1–0 emission of 12CO, 13CO, and C18O molecules toward the whole disk (8′ × 5′ or 20.8 kpc × 13.0 kpc) of the nearby barred spiral galaxy NGC 2903 with ...the Nobeyama Radio Observatory 45 m telescope at an effective angular resolution of 20″ (or 870 pc). We detected 12CO(J = 1–0) emission over the disk of NGC 2903. In addition, significant 13CO(J = 1–0) emission was found at the center and bar-ends, whereas we could not detect any significant C18O(J = 1–0) emission. In order to improve the signal-to-noise ratio of CO emission and to obtain accurate line ratios of 12CO(J = 2–1)/12CO(J = 1–0) (R
2−1/1−0) and 13CO(J = 1–0)/12CO(J = 1–0) (R
13/12), we performed the stacking analysis for our 12CO(J = 1–0), 13CO(J = 1–0), and archival 12CO(J = 2–1) spectra with velocity axis alignment in nine representative regions of NGC 2903. We successfully obtained the stacked spectra of the three CO lines, and could measure averaged R
2−1/1−0 and R
13/12 with high significance for all the regions. We found that both R
2−1/1−0 and R
13/12 differ according to the regions, which reflects the difference in the physical properties of molecular gas, i.e., density (
$n_{\rm H_2}$
) and kinetic temperature (T
K). We determined
$n_{\rm H_2}$
and T
K using R
2−1/1−0 and R
13/12 based on the large velocity gradient approximation. The derived
$n_{\rm H_2}$
ranges from ∼1000 cm−3 (in the bar, bar-ends, and spiral arms) to 3700 cm−3 (at the center) and the derived T
K ranges from 10 K (in the bar and spiral arms) to 30 K (at the center). We examined the dependence of star formation efficiencies (SFEs) on
$n_{\rm H_2}$
and T
K, and found a positive correlation between SFE and
$n_{\rm H_2}$
with correlation coefficient for the least-squares power-law fit R
2 of 0.50. This suggests that molecular gas density governs the spatial variations in SFEs.
We report systematic variations in the emission line ratio of the CO J = 2-1 and J = 1-0 transitions (R sub(2-1/1-0)) in the grand-design spiral galaxy M51. The R sub(2-1/1-0) ratio shows clear ...evidence for the evolution of molecular gas from the upstream interarm regions into the spiral arms and back into the downstream interarm regions. Analysis of the molecular excitation using a Large Velocity Gradient radiative transfer calculation provides insight into the changes in the physical conditions of molecular gas between the arm and interarm regions: cold and low-density gas (lap10 K, lap300 cm super(-3)) is required for the interarm GMCs, but this gas must become warmer and/or denser in the more active star-forming spiral arms. The systematic enhancement of the CO(2-l) line relative to CO(l-O) in luminous star-forming regions suggests that some caution is needed when using CO(2-l) as a tracer of bulk molecular gas mass, especially when galactic structures are resolved.
Abstract
We investigate the molecular gas properties of galaxies across the main sequence of star-forming (SF) galaxies in the local Universe using 12CO(J = 1–0), hereafter 12CO, and 13CO(J = 1–0), ...hereafter 13CO, mapping data of 147 nearby galaxies obtained in the COMING project, a legacy project of the Nobeyama Radio Observatory. In order to improve the signal-to-noise ratios of both lines, we stack all the pixels where 12CO emission is detected after aligning the line center expected from the first-moment map of 12CO. As a result, 13CO emission is successfully detected in 80 galaxies with a signal-to-noise ratio larger than three. The error-weighted mean of the integrated-intensity ratio of 12CO to 13CO lines (R1213) of the 80 galaxies is 10.9, with a standard deviation of 7.0. We find that (1) R1213 positively correlates to specific star-formation rate (sSFR) with a correlation coefficient of 0.46, and (2) both the flux ratio of IRAS 60 μm to 100 μm (f60/f100) and the inclination-corrected linewidth of 12CO stacked spectra ($\sigma _{{\rm ^{12}CO},i}$) also correlate with sSFR for galaxies with the R1213 measurement. Our results support the scenario where R1213 variation is mainly caused by changes in molecular gas properties such as temperature and turbulence. The consequent variation of the CO-to-H2 conversion factor across the SF main sequence is not large enough to completely extinguish the known correlations between sSFR and Mmol/Mstar (μmol) or star-formation efficiency (SFE) reported in previous studies, while this variation would strengthen (weaken) the sSFR–SFE (sSFR–μmol) correlation.
We present results of 12CO (1-0) and 13CO (1-0) observations of the northeastern spiral arm segment of IC 342 with a ~50 pc resolution carried out with the Nobeyama Millimeter Array. Zero-spacing ...components were recovered by combining with existing data taken with the Nobeyama 45 m telescope. The principal objective of this study is to investigate the variation of cloud properties across the spiral arm with a resolution comparable to the size of giant molecular clouds (GMCs). The observations cover a 1 kpc X 1.5 kpc region located ~2 kpc away from the galactic center, where a giant molecular association is located at the trailing side and associated star-forming regions at the leading side. The spiral arm segment was resolved into a number of clouds, whose size, temperature, and surface mass density are comparable to typical GMCs in the Galaxy. Twenty-six clouds were identified from the combined data cube, and the identified clouds followed the linewidth-size relation of Galactic GMCs. The identified GMCs were divided into two categories according to whether they are associated with star formation activity or not. Comparison between the two categories indicated that the active GMCs are more massive, have smaller line width, and are closer to virial equilibrium than the quiescent GMCs. These variations of the GMCs' properties suggest that dissipation of excess kinetic energy of GMCs is a required condition for the onset of massive star formation.
Abstract
We examined radial variations in molecular-gas based star formation efficiency (SFE), which is defined as star formation rate per unit molecular gas mass, for 80 galaxies selected from the ...CO Multi-line Imaging of Nearby Galaxies project (Sorai et al. 2019, PASJ, 71, S14). The radial variations in SFE for individual galaxies are typically a factor of 2–3, which suggests that SFE is nearly constant along the galactocentric radius. We found an averaged SFE in 80 galaxies of (1.69 ± 1.1) × 10−9 yr−1, which is consistent with Leroy et al. (2008, AJ, 136, 2782) if we consider the contribution of helium to the molecular gas mass evaluation and the difference in the assumed initial mass function between the two studies. We compared SFE among different morphological (i.e., SA, SAB, and SB) types, and found that SFE within the inner radii (r/r25 < 0.3, where r25 is the B-band isophotal radius at 25 mag arcsec−2) of SB galaxies is slightly higher than that of SA and SAB galaxies. This trend can be partly explained by the dependence of SFE on global stellar mass, which probably relates to the CO-to-H2 conversion factor through the metallicity. For two representative SB galaxies in our sample, NGC 3367 and NGC 7479, the ellipse of r/r25 = 0.3 seems to cover not only the central region but also the inner part of the disk, mainly the bar. These two galaxies show higher SFE in the bar than in the spiral arms. However, we found an opposite trend in NGC 4303; SFE is lower in the bar than in the spiral arms, which is consistent with earlier studies (e.g., Momose et al. 2010, ApJ, 721, 383). These results suggest a diversity of star formation activities in the bar.
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