We investigate the oxygen and nitrogen abundance distributions across the optical disks of 130 nearby late-type galaxies using around 3740 published spectra of H II regions. We use these data in order to provide homogeneous abundance determinations for all objects in the sample, including H II regions in which not all of the usual diagnostic lines were measured. Examining the relation between N and O abundances in these galaxies we find that the abundances in their centers and at their isophotal R {sub 25} disk radii follow the same relation. The variation in N/H at a given O/H is around 0.3 dex. We suggest that the observed spread in N/H may be partly caused by the time delay between N and O enrichment and the different star formation histories in galaxies of different morphological types and dimensions. We study the correlations between the abundance properties (central O and N abundances, radial O and N gradients) of a galaxy and its morphological type and dimension.

https://iopscience.iop.org/article/10.1088/0004-6256/147/6/131/pdf

The abundance properties of nearby late-type galaxies. i. the data

We present a search for outlying H II regions in the extended gaseous outskirts of nearby (D < 40 Mpc) galaxies and subsequent multi-slit spectroscopy used to obtain the H II region nebular oxygen abundances. The galaxies in our sample have extended H I disks and/or interaction-related H I features that extend well beyond their primary stellar components. We report oxygen abundance gradients out to 2.5 times the optical radius for these galaxies which span a range of morphologies and masses. We analyze the underlying stellar and neutral H I gas distributions in the vicinity of the H II regions to understand the physical processes that give rise to the observed metal distributions in galaxies. These measurements, for the first time, convincingly show flat abundance distributions out to large radii in a wide variety of systems and have broad implications for galaxy chemodynamical evolution.

/pdf/metal-transport-to-the-gaseous-outskirts-of-galaxies-1llcdt3ym2.pdf

Metal transport to the gaseous outskirts of galaxies

We present a search for outlying HII regions in the extended gaseous outskirts of nearby (D < 40 Mpc) galaxies, and subsequent multi-slit spectroscopy used to obtain the HII region nebular oxygen abundances. The galaxies in our sample have extended HI disks and/or interaction-related HI features that extend well beyond their primary stellar components. We report oxygen abundance gradients out to 2.5 times the optical radius for these galaxies which span a range of morphologies and masses. We analyze the underlying stellar and neutral HI gas distributions in the vicinity of the HII regions to understand the physical processes that give rise to the observed metal distributions in galaxies. These measurements, for the first time, convincingly show flat abundance distributions out to large radii in a wide variety of systems, and have broad implications for galaxy chemodynamical evolution.

/pdf/metal-transport-to-the-gaseous-outskirts-of-galaxies-2w07nitjmg.pdf

Metal Transport to the Gaseous Outskirts of Galaxies

Long tails and streams of stars are the most noticeable upshots of galaxy collisions. Their origin as gravitational, tidal, disturbances has however been recognized only less than fifty years ago and more than ten years after their first observations. This Review describes how the idea of galactic tides emerged, in particular thanks to the advances in numerical simulations, from the first ones that included tens of particles to the most sophisticated ones with tens of millions of them and state-of-the-art hydrodynamical prescriptions. Theoretical aspects pertaining to the formation of tidal tails are then presented. The third part of the review turns to observations and underlines the need for collecting deep multi-wavelength data to tackle the variety of physical processes exhibited by collisional debris. Tidal tails are not just stellar structures, but turn out to contain all the components usually found in galactic disks, in particular atomic / molecular gas and dust. They host star-forming complexes and are able to form star-clusters or even second-generation dwarf galaxies. The final part of the review discusses what tidal tails can tell us (or not) about the structure and content of present-day galaxies, including their dark components, and explains how tidal tails may be used to probe the past evolution of galaxies and their mass assembly history. On-going deep wide-field surveys disclose many new low-surface brightness structures in the nearby Universe, offering great opportunities for attempting galactic archeology with tidal tails.

Tides in colliding galaxies

Accurate techniques that allow for the derivation of the spatial density in star formation regions are rare. A technique that has found application for the derivation of spatial densities in Galactic star formation regions utilizes the density-sensitive properties of the K-doublet transitions of formaldehyde (H{sub 2}CO). In this paper, we present an extension of our survey of the formaldehyde 1{sub 10}-1{sub 11} ({lambda} = 6.2 cm) and 2{sub 11}-2{sub 12} ({lambda} = 2.1 cm) K-doublet transitions of H{sub 2}CO in a sample of 56 starburst systems. We have extended the number of galaxies in which both transitions have been detected from 5 to 13. We have improved our spatial density measurements by incorporating kinetic temperatures based upon NH{sub 3} measurements of 11 of the galaxies with a total of 14 velocity components in our sample. Our spatial density measurements lie in a relatively narrow range from 10{sup 4.5} to 10{sup 5.5} cm{sup -3}. This implies that the Schmidt-Kennicutt relation between L{sub IR} and M{sub dense} (1) is an indication of the dense gas mass reservoir available to form stars and (2) is not directly dependent upon a higher average density driving the star formation process in the most luminous starburstmore » galaxies. We have also used our H{sub 2}CO measurements to derive two separate measures of the dense gas mass which are generally smaller, in many cases by a factor of 10{sup 2}-10{sup 3}, than those derived using HCN. This disparity suggests that H{sub 2}CO traces a denser, more compact component of the giant molecular clouds in our starburst galaxy sample. We also report measurements of the rotationally excited {lambda} = 6.3 cm {sup 2}{Pi}{sub 1/2} J = 1/2 state of OH and the H111{alpha} radio recombination line taken concurrently with our H{sub 2}CO 1{sub 10}-1{sub 11} measurements.« less

Formaldehyde densitometry of starburst galaxies: density-independent global star formation

We present new results for the molecular gas, dust emission and the ionized gas in J1023+1952, an HI rich intergalactic star-forming tidal dwarf galaxy candidate. It is located at the projected intersection of two faint stellar tidal streams wrapped around the interacting pair of galaxies NGC 3227/6 (Arp~94). Using the IRAM 30m telescope, emission from CO(1-0) and CO(2-1) was detected across the entire extent of the neutral hydrogen cloud associated with J1023+1952, a region of the size of 8.9$ x 5.9 kpc, as well as in the nuclear region and outer disk of NGC 3227. The molecular gas is found to be abundant over the entire HI cloud, with H2-to-HI gas mass ratios between 0.5 and 1.7. New Spitzer mid-infrared observations at 3.6, 4.5, 5.8, 8.0, 15 and 24mu show that young SF is restricted to the southern part of the cloud. Despite the relatively uniform H$_2$ and HI column density across the cloud, young SF occurs only where the velocity dispersion in the CO and HI is a factor of $\sim$two lower (FWHM of 30 - 70 \kms) than elsewhere in the cloud (FWHM of 80 - 120 \kms). Thus the kinematics of the gas, in addition to its column density, seems to be a crucial factor in triggering SF. Optical/infrared spectral energy distributions (SEDs) and Halpha photometry confirm that all the knots are young, with a tentative age sequence from the south-west (oldest knots) to the north-east (youngest). Optical spectroscopy of the brightest SF region allowed us to determine the metallicity (12+log(O/H) = 8.6 +- 0.2) and the extinction ($A_B$=2.4). This shows that J1023+1952 is made from metal-enriched gas which is inconsistent with the hypothesis that it represents a pre-existing dwarf galaxy. Instead, it must be formed from recycled, metal-enrichd gas, expelled from NGC 3227 or NGC 3226 in a previous phase of the interaction.

/pdf/molecular-gas-and-dust-in-arp-94-the-formation-of-a-recycled-2wj99qoqco.pdf

Molecular gas and dust in Arp 94: The formation of a recycled galaxy in an interacting system

We present new results for the molecular gas, dust emission, and the ionized gas in J1023+1952, an H I-rich intergalactic star-forming tidal dwarf galaxy candidate. It is located at the projected intersection of two faint stellar tidal streams wrapped around the interacting pair of galaxies NGC 3227/6 (Arp 94). Using the IRAM 30 m telescope, emission from (CO)-C-12(1-0) and (CO)-C-12(2-1) was detected across the entire extent of the neutral hydrogen cloud associated with J1023+1952, a region of the size of 8.9 x 5.9 kpc. The molecular gas is found to be abundant over the entire H I cloud, with H-2-to-H I gas mass ratios between 0.5 and 1.7. New Spitzer mid-infrared observations at 3.6, 4.5, 5.8, 8.0, 15, and 24 mu m show that young SF is restricted to the southern part of the cloud. Despite the relatively uniform H-2 and H I column density across the cloud, young SF occurs only in those regions where the velocity dispersion in the CO and H I is a factor of similar to 2 lower (FWHM of 30-70 km s^(-1)) than elsewhere in the cloud (FWHM of 80-120 km s(-1)). Thus, the kinematics of the gas, in addition to its column density, seems to be a crucial factor in triggering SF. Optical/infrared spectral energy distributions (SEDs) and Hα photometry confirm that all the knots are young. Optical spectroscopy of the brightest SF region allowed us to determine the metallicity [12 + log (O/H) = 8.6 +/- 0.2] and the extinction (A(B) = 2.4). This shows that J1023+1952 is made from metal-enriched gas which is inconsistent with the hypothesis that it represents a preexisting dwarf galaxy. Instead, it must be formed from recycled, metal-enriched gas, expelled from NGC 3227 or NGC 3226 in a previous phase of the interaction.

/pdf/molecular-gas-and-dust-in-arp-94-the-formation-of-a-recycled-2o16nfx0tj.pdf

Molecular gas and dust in arp 94: the formation of a recycled galaxy in an interacting system

Molecular gas in Arp 94: Implications for intergalactic star formation

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Molecular gas and dust in Arp 94: The formation of a recycled galaxy in an interacting system

Molecular gas and dust in arp 94: the formation of a recycled galaxy in an interacting system

Molecular gas in Arp 94: Implications for intergalactic star formation