THE JAMES CLERK MAXWELL TELESCOPE NEARBY GALAXIES LEGACY SURVEY. II. WARM MOLECULAR GAS AND STAR FORMATION IN THREE FIELD SPIRAL GALAXIES

Context. The global Schmidt law of star formation provides a power-law relation between the surface densities of star-formation rate (SFR) and gas, and successfully explains plausible scenarios of galaxy formation and evolution. However, star formation being a multi-scale process, requires spatially-resolved analysis for a better understanding of the physics of star formation. Aims. It has been shown that the removal of a diffuse background from SFR tracers, such as Hα, far-ultraviolet (FUV), infrared, leads to an increase in the slope of the sub-galactic Schmidt relation. We reinvestigate the local Schmidt relations in nine nearby spiral galaxies taking into account the effect of inclusion and removal of diffuse background in SFR tracers as well as in the atomic gas. Methods. We used multiwavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey, Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel, The H I Nearby Galaxy Survey, and HERA CO-Line Extragalactic Survey. Making use of a novel split of the overall light distribution as a function of spatial scale, we subtracted the diffuse background in the SFR tracers as well as the atomic gas. Using aperture photometry, we study the Schmidt relations on background subtracted and unsubtracted data at physical scales varying between 0.5–2 kpc. Results. The fraction of diffuse background varies from galaxy to galaxy and accounts to ∼34% in Hα, ∼43% in FUV, ∼37% in 24 μm, and ∼75% in H I on average. We find that the inclusion of diffuse background in SFR tracers leads to a linear molecular gas Schmidt relation and a bimodal total gas Schmidt relation. However, the removal of diffuse background in SFR tracers leads to a super-linear molecular gas Schmidt relation. A further removal of the diffuse background from atomic gas results in a slope ∼1.4 ± 0.1, which agrees with dynamical models of star formation accounting for flaring effects in the outer regions of galaxies.

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Gas, dust and star formation in nearby galaxies as seen with the JCMT

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313005310 ◽

2012 ◽

Vol 8 (S295) ◽

pp. 338-338

Author(s):

José Ramón Sánchez-Gallego ◽

Johan H. Knapen

Keyword(s):

Star Formation ◽

Spectral Line ◽

Observational Data ◽

Massive Star ◽

Molecular Gas ◽

Massive Star Formation ◽

James Clerk Maxwell ◽

Nearby Galaxies

We presented results using the Nearby Galaxies Legacy Survey (NGLS), which is being carried out with the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in Hawai'i. We have obtained CO J=3−2 data for 155 nearby galaxies to trace the dense molecular gas in which stars are believed to be born. The sample of this survey covers a wide morphological range and has been selected to include galaxies that have been thoroughly studied in the literature, and for which abundant observational data are available. In parallel, we have observed the same sample of galaxies using the Hα spectral line, which traces massive star formation.

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5.12. High-resolution CO (1-0) observations of the ringed galaxy NGC 4736

Symposium - International Astronomical Union ◽

10.1017/s0074180900084746 ◽

1998 ◽

Vol 184 ◽

pp. 235-236

Author(s):

Tony Wong ◽

Tamara Helfer ◽

Leo Blitz

Keyword(s):

Star Formation ◽

High Resolution ◽

Spiral Galaxies ◽

Molecular Gas ◽

H Ii Regions ◽

Nearby Galaxies ◽

Initial Results

It is well known that the radial distributions of atomic and molecular gas differ markedly in spiral galaxies, including our own (e.g. Burton & Gordon 1978, Sofue et al. 1995). We have recently begun a program to obtain multifrequency observations of several nearby galaxies in order to determine whether H I is needed to replenish the H2 consumed by star formation and, if so, how this might be accomplished. Here we present initial results on the nearby RSab galaxy NGC 4736, known for its bright ring of H II regions and recently shown to have a central stellar bar (Möllenhoff et al. 1995). We have mapped the distribution of CO (1-0) emission within r=1′ (1.8 kpc at D=6.2 Mpc) with the BIMA interferometer at ~5″ resolution, and added data from the NRAO 12-m telescope to recover zero-spacing information.

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The JCMT Nearby Galaxies Legacy Survey – XI. Environmental variations in the atomic and molecular gas radial profiles of nearby spiral galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx345 ◽

2017 ◽

Vol 467 (4) ◽

pp. 4282-4292 ◽

Cited By ~ 9

Author(s):

Angus Mok ◽

C. D. Wilson ◽

J. H. Knapen ◽

J. R. Sánchez-Gallego ◽

E. Brinks ◽

...

Keyword(s):

Spiral Galaxies ◽

Molecular Gas ◽

Radial Profiles ◽

Environmental Variations ◽

Nearby Galaxies

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SKA studies of nearby galaxies: star-formation, accretion processes and molecular gas across all environments

10.22323/1.215.0070 ◽

2015 ◽

Cited By ~ 1

Author(s):

Rob J. Beswick ◽

Elias Brinks ◽

Miguel Perez-Torres ◽

Anita Richards ◽

Susanne Aalto ◽

...

Keyword(s):

Star Formation ◽

Molecular Gas ◽

Nearby Galaxies

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Environmental Effects on the ISM and Star Formation Properties of Nearby Spiral Galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316008188 ◽

2015 ◽

Vol 11 (S315) ◽

Author(s):

Angus Mok ◽

Christine Wilson

Keyword(s):

Star Formation ◽

Environmental Effects ◽

Spiral Galaxies ◽

Star Formation Rate ◽

Formation Rate ◽

Molecular Gas ◽

Turbulent Pressure ◽

Cluster Environment ◽

Gas Properties

AbstractWe studied molecular gas properties in a sample of 98 Hi - flux selected spiral galaxies within ~ 25 Mpc using the CO J = 3 − 2 line, observed with the JCMT, and subdivided into isolated, group, and Virgo subsamples. We find a larger mean H2 mass in the Virgo galaxies compared to group galaxies, despite their lower mean Hi mass. Combining our data with complementary Hα star formation rate measurements, Virgo galaxies have a longer molecular gas depletion times compared to group galaxies, perhaps due to heating processes in the cluster environment or differences in the turbulent pressure.

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High-J CO Intensity Measurements for Galaxies Observed by the Herschel FTS

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007201 ◽

2015 ◽

Vol 11 (S315) ◽

pp. 26-29

Author(s):

Julia Kamenetzky ◽

Naseem Rangwala ◽

Jason Glenn ◽

Philip Maloney ◽

Alex Conley

Keyword(s):

Star Formation ◽

Galaxy Evolution ◽

Raw Material ◽

Molecular Gas ◽

Star Forming ◽

Star Forming Regions ◽

J 13 ◽

Systematic Effects ◽

Nearby Galaxies ◽

Co Emission

AbstractMolecular gas is the raw material for star formation and is commonly traced by the carbon monoxide (CO) molecule. The atmosphere blocks all but the lowest-J transitions of CO for observatories on the ground, but the launch of the Herschel Space Observatory revealed the CO emission of nearby galaxies from J = 4−3 to J = 13−12. Herschel showed that mid- and high-J CO lines in nearby galaxies are emitted from warm gas, accounting for approximately 10% of the molecular mass, but the majority of the CO luminosity. The energy budget of this warm, highly-excited gas is a significant window into the feedback interactions among molecular gas, star formation, and galaxy evolution. Likely, mechanical heating is required to explain the excitation. Such gas has also been observed in star forming regions within our galaxy.We have examined all ~300 spectra of galaxies from the Herschel Fourier Transform Spectrometer and measured line fluxes or upper limits for the CO J = 4−3 to J = 13−12, [CI], and [NII] 205 micron lines in ~200 galaxies, taking systematic effects of the FTS into account. We will present our line fitting method, illustrate trends available so far in this large sample, and preview the full 2-component radiative transfer likelihood modeling of the CO emission using an illustrative sample of 20 galaxies, including comparisons to well-resolved galactic regions. This work is a comprehensive study of mid- and high-J CO emission among a variety of galaxy types, and can be used as a resource for future (sub)millimeter studies of galaxies with ground-based instruments.

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Head-on collisions: how to bring large quantities of gas out of inner disks

Symposium - International Astronomical Union ◽

10.1017/s0074180900198079 ◽

2004 ◽

Vol 217 ◽

pp. 420-421

Author(s):

Jonathan Braine ◽

U. Lisenfeld ◽

P.-A. Duc

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Intergalactic Medium ◽

Spiral Galaxies ◽

Molecular Gas ◽

Hii Region ◽

Neutral Gas ◽

Dense Cores ◽

Clear Cases ◽

Formation Efficiency

Head-on collisions of spiral galaxies can bring large quantities of gas out of spiral disks and into the intergalactic medium. Only two clear cases (UGC 12914/5 and UGC 813/6) of such collisions are known (Condon et al. 1993, 2002) and in both cases several 109 M⊙ of neutral gas is found in the bridge between the two galaxies which are now separating. About half of the gas is molecular. The gas, atomic or molecular, is brought out by collisions between clouds, which then acquire an intermediate velocity and end up between the galaxies. The bridges contain no old stars and in each case only one HII region despite the large masses of molecular gas, such that the star formation efficiency is very low in the bridges. The collisions occurred 20 – 50 million years ago, much greater than the collapse time for dense cores. We (Braine et al. 2003, 2004) show that collisions between molecular clouds, and not only between atomic gas clouds, bring gas into the bridges. It is not currently known whether the galaxies and bridges are bound or whether they will continue to separate, releasing several 109 M⊙ of neutral gas into the intergalactic medium.

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