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Tidal dwarf galaxies (TDGs) are low-mass objects that form within tidal and/or collisional debris ejected from more massive interacting galaxies. We use CO(1–0) observations from Atacama Large Millimeter/submillimeter Array and integral-field spectroscopy from Multi-Unit Spectroscopic Explorer to study molecular and ionized gas in three TDGs: two around the collisional galaxy NGC 5291 and one in the late-stage merger NGC 7252. The CO and H α emission is more compact than the H  i emission and displaced from the H  i dynamical centre, so these gas phases cannot be used to study the internal dynamics of TDGs. We use CO, H  i , and H α data to measure the surface densities of molecular gas (Σmol), atomic gas (Σatom), and star formation rate (ΣSFR), respectively. We confirm that TDGs follow the same spatially integrated ΣSFR–Σgas relation of regular galaxies, where Σgas = Σmol + Σatom, even though they are H  i dominated. We find a more complex behaviour in terms of the spatially resolved ΣSFR–Σmol relation on subkpc scales. The majority (⁠|$\sim 60~{{\ \rm per\ cent}}$|⁠) of star-forming regions in TDGs lie on the same ΣSFR–Σmol relation of normal spiral galaxies but show a higher dispersion around the mean. The remaining fraction of star-forming regions (⁠|$\sim 40~{{\ \rm per\ cent}}$|⁠) lie in the starburst region and are associated with the formation of massive super star clusters, as shown by Hubble Space Telescope images. We conclude that the local star formation activity in TDGs proceeds in a hybrid fashion, with some regions comparable to normal spiral galaxies and others to extreme starbursts. [ABSTRACT FROM AUTHOR]

We present H  i and radio continuum, narrow-band Hα imaging, IFU spectroscopy, and X-ray observations of the FGC 1287 triplet projected ∼1.8 Mpc west of the galaxy cluster Abell 1367. One triplet member, FGC 1287, displays an exceptionally long, 250 kpc H  i tail and an unperturbed stellar disc which are the typical signatures of ram pressure stripping (RPS). To generate detectable RPS signatures the presence of an Intracluster medium ICM or intragroup medium IGM with sufficient density to produce RPS at a realistic velocity relative to the ICM or IGM is a prerequisite. However, XMM–Newton observations were not able to detect X-ray emission from the triplet, implying that if a hot ICM/IGM is present, its density, ne , is less than 2.6 × 10−5 cm−3. Higher resolution VLA H  i data presented here show FGC 1287's H  i disc is truncated and significantly warped, whereas the H  i tail is clumpy. TNG Hα imaging identified three star-forming clumps projected within 20 kpc of FGC 1287's disc, with VIMOS–IFU data confirming two of these are counterparts to H  i clumps in the tail. The triplet's H  i kinematics, together with Hα and radio continuum imaging suggests an interaction may have enhanced star formation in FGC 1287's disc, but cannot readily account for the origin of the long H  i tail. We consider several scenarios which might reconcile RPS with the non-detection of ICM or IGM X-ray emission but none of these unambiguously explains the origin of the long H  i tail. [ABSTRACT FROM AUTHOR]

Aims. We present the results of three commissioning H I observations obtained with the MeerKAT radio telescope. These observations make up part of the preparation for the forthcoming MHONGOOSE nearby galaxy survey, which is a MeerKAT large survey project that will study the accretion of gas in galaxies and the link between gas and star formation. Methods. We used the available H I data sets, along with ancillary data at other wavelengths, to study the morphology of the MHONGOOSE sample galaxy, ESO 302-G014, which is a nearby gas-rich dwarf galaxy. Results. We find that ESO 302-G014 has a lopsided, asymmetric outer disc with a low column density. In addition, we find a tail or filament of H I clouds extending away from the galaxy, as well as an isolated H I cloud some 20 kpc to the south of the galaxy. We suggest that these features indicate a minor interaction with a low-mass galaxy. Optical imaging shows a possible dwarf galaxy near the tail, but based on the current data, we cannot confirm any association with ESO 302-G014. Nonetheless, an interaction scenario with some kind of low-mass companion is still supported by the presence of a significant amount of molecular gas, which is almost equal to the stellar mass, and a number of prominent stellar clusters, which suggest recently triggered star formation. Conclusions. These data show that MeerKAT produces exquisite imaging data. The forthcoming full-depth survey observations of ESO 302-G014 and other sample galaxies will, therefore, offer insights into the fate of neutral gas as it moves from the intergalactic medium onto galaxies. [ABSTRACT FROM AUTHOR]

Scaling laws of dust, H  i gas, and metal mass with stellar mass, specific star formation rate, and metallicity are crucial to our understanding of the build-up of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass (M H  i / M ⋆) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) – including stellar dust production, grain growth, and dust destruction – within a Bayesian framework to enable a rigorous search of the multidimensional parameter space. We find that these scaling laws for galaxies with −1.0 ≲ log  M H  i / M ⋆ ≲ 0 can be reproduced using closed-box models with high fractions (37–89  |${{\ \rm per\ cent}}$|⁠) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies (ϵ = 30–40), and long dust lifetimes (1–2 Gyr). The models have present-day dust masses with similar contributions from stellar sources (50–80  |${{\ \rm per\ cent}}$|⁠) and grain growth (20–50  |${{\ \rm per\ cent}}$|⁠). Over the entire lifetime of these galaxies, the contribution from stardust (>90  |${{\ \rm per\ cent}}$|⁠) outweighs the fraction of dust grown in the interstellar medium (<10  |${{\ \rm per\ cent}}$|⁠). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth time-scales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium. [ABSTRACT FROM AUTHOR]

The radio and far-infrared luminosities of star-forming galaxies are tightly correlated over several orders of magnitude; this is known as the far-infrared radio correlation (FIRC). Previous studies have shown that a host of factors conspire to maintain a tight and linear FIRC, despite many models predicting deviation. This discrepancy between expectations and observations is concerning since a linear FIRC underpins the use of radio luminosity as a star-formation rate indicator. Using LOFAR  |$\mathrm{150\, MHz}$|  , FIRST  |$\mathrm{1.4\, GHz}$|  , and Herschel  infrared luminosities derived from the new LOFAR/ H -ATLAS catalogue, we investigate possible variation in the monochromatic (  |$\mathrm{250\, \mu}$| m) FIRC at low and high radio frequencies. We use statistical techniques to probe the FIRC for an optically selected sample of 4082 emission-line classified star-forming galaxies as a function of redshift, effective dust temperature, stellar mass, specific star formation rate, and mid-infrared colour (an empirical proxy for specific star formation rate). Although the average FIRC at high radio frequency is consistent with expectations based on a standard power-law radio spectrum, the average correlation at |$\mathrm{150\, MHz}$|  is not. We see evidence for redshift evolution of the FIRC at |$\mathrm{150\, MHz}$|⁠, and find that the FIRC varies with stellar mass, dust temperature, and specific star formation rate, whether the latter is probed using magphys  fitting, or using mid-infrared colour as a proxy. We can explain the variation, to within 1σ, seen in the FIRC over mid-infrared colour by a combination of dust temperature, redshift, and stellar mass using a Bayesian partial correlation technique. [ABSTRACT FROM AUTHOR]

We report on CO (J = 2 → 1) mapping with the IRAM 30-m HEtrodyne Receiver Array (HERA) of CGCG 97-079, an irregular galaxy in the merging galaxy cluster Abell 1367 (z = 0.022). We find that â80 per cent of the detected CO (J = 2 → 1) is projected within a 16 arcsec2 (6.5 kpc2) region to the north and west of the optical/NIR centre, with the intensity maximum offset â10 arcsec (4 kpc) NW of the optical/NIR centre and â7 arcsec (3 kpc) south-east of the HI intensity maximum. Evolutionary synthesis models indicate CGCG 97- 079 experienced a burst of star formation â108 yr ago, most likely triggered by a tidal interaction with CGCG 97-073. For CGCG 97-079 we deduce an infall velocity to the cluster of â1000 km sâ'1 and moderate ram pressure (Pram â 10â'11 dyne cmâ'2). The observed offset in CGCG 97-079 of the highest density HI and CO (J = 2→1) from the stellar components has not previously been observed in galaxies currently undergoing ram pressure stripping, although previous detailed studies of gas morphology and kinematics during ram pressure stripping were restricted to significantly more massive galaxies with deeper gravitational potential wells. We conclude the observed cold gas density maxima offsets are most likely the result of ram pressure and/or the high-speed tidal interaction with CGCG 97-073. However ram pressure stripping is likely to be playing a major role in the perturbation of lower density gas. [ABSTRACT FROM AUTHOR]

Observed Hi accretion around nearby galaxies can only account for a fraction of the gas supply needed to sustain the currently observed star formation rates. It is possible that additional accretion occurs in the form of low column density cold flows, as predicted by numerical simulations of galaxy formation. To constrain the presence and properties of such flows, we present deep Hi observations obtained with the NRAO Green Bank Telescope of an area measuring 4° × 4° around NGC 2403. These observations, with a 5σ detection limit of 2.4 × 1018 cm-2 over a 20 km s-1 linewidth, reveal a low column density, extended cloud outside the main Hi disk, about 17' (∼16 kpc or ∼2 R25) to the NW of the center of the galaxy. The total Hi mass of the cloud is 6.3 × 106 M☉, or 0.15 percent of the total Hi mass of NGC 2403. The cloud is associated with an 8 kpc anomalous-velocity Hi filament in the inner disk, that was previously observed in deep VLA observations. We discuss several scenarios for the origin of the cloud, and conclude that it is either accreting from the intergalactic medium, or is the result of a minor interaction with a neigboring dwarf galaxy. [ABSTRACT FROM AUTHOR]

We present ∼kiloparsec spatial resolution maps of the CO-to-H2 conversion factor (αCO) and dust-to-gas ratio (DGR) in 26 nearby, star-forming galaxies. We have simultaneously solved for αCO and the DGR by assuming that the DGR is approximately constant on kiloparsec scales. With this assumption, we can combine maps of dust mass surface density, CO-integrated intensity, and H I column density to solve for both αCO and the DGR with no assumptions about their value or dependence on metallicity or other parameters. Such a study has just become possible with the availability of high-resolution far-IR maps from the Herschel key program KINGFISH, 12CO J = (2-1) maps from the IRAM 30 m large program HERACLES, and H I 21 cm line maps from THINGS. We use a fixed ratio between the (2-1) and (1-0) lines to present our αCO results on the more typically used 12CO J = (1-0) scale and show using literature measurements that variations in the line ratio do not affect our results. In total, we derive 782 individual solutions for αCO and the DGR. On average, αCO = 3.1 M☼ pc–2 (K km s–1)–1 for our sample with a standard deviation of 0.3 dex. Within galaxies, we observe a generally flat profile of αCO as a function of galactocentric radius. However, most galaxies exhibit a lower αCO value in the central kiloparsec—a factor of ∼2 below the galaxy mean, on average. In some cases, the central αCO value can be factors of 5-10 below the standard Milky Way (MW) value of αCO, MW = 4.4 M☼ pc–2 (K km s–1)–1. While for αCO we find only weak correlations with metallicity, the DGR is well-correlated with metallicity, with an approximately linear slope. Finally, we present several recommendations for choosing an appropriate αCO for studies of nearby galaxies. [ABSTRACT FROM AUTHOR]

Indirect evidence from detailed chemical evolution studies shows that infall of low metallicity gas appears to have proceeded at a rather constant rate during the lifetime of the Galactic disk. We explore two possible implications: (a) the effect of an infalling high velocity cloud (HVC) on interstellar cloud stability leading to enhanced star formation, and (b) the presence of these HVC's around neighbouring galaxies, which would generalize this aspect of the evolution of galaxies in groups. (a) Using a simple analytical model we show how the overpressure produced in the galactic plane by HVC infall reduces the effective Jeans mass of the existing clouds, thus tending to enhance the SFR. (b) Using HI data from the THINGS survey we detect HI "fluff" around 4 galaxies of a total sample of 32 observed. Projecting some of the largest Galactic HVC's to the distances of the THINGS galaxies we produce a useful estimate of the fraction of the HVC masses that we can detect at these distances, finding a value of order 10%, and go on to make tentative estimates about infall rates for nearby galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT 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, H2 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: Mdyn= 5 × 107 M⊙ 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. [ABSTRACT FROM AUTHOR]

ABSTRACT An analysis of large-area CO J= 3-2 maps from the James Clerk Maxwell Telescope for 12 nearby spiral galaxies reveals low velocity dispersions in the molecular component of the interstellar medium. The three lowest luminosity galaxies show a relatively flat velocity dispersion as a function of radius while the remaining nine galaxies show a central peak with a radial fall-off within 0.2-0.4 r25. Correcting for the average contribution due to the internal velocity dispersions of a population of giant molecular clouds, the average cloud-cloud velocity dispersion across the galactic discs is 6.1 ± 1.0 km s −1 (standard deviation of 2.9 km s −1), in reasonable agreement with previous measurements for the Galaxy and M33. The cloud-cloud velocity dispersion derived from the CO data is on average two times smaller than the H i velocity dispersion measured in the same galaxies. The low cloud-cloud velocity dispersion implies that the molecular gas is the critical component determining the stability of the galactic disc against gravitational collapse, especially in those regions of the disc which are H 2 dominated. The cloud-cloud velocity dispersion shows a significant positive correlation with both the far-infrared luminosity, which traces the star formation activity, and the K-band absolute magnitude, which traces the total stellar mass. For three galaxies in the Virgo cluster, smoothing the data to a resolution of 4.5 kpc (to match the typical resolution of high-redshift CO observations) increases the measured velocity dispersion by roughly a factor of 2, comparable to the dispersion measured recently in a normal galaxy at z= 1. This comparison suggests that the mass and star formation rate surface densities may be similar in galaxies from z= 0 to 1 and that the high star formation rates seen at z= 1 may be partly due to the presence of physically larger molecular gas discs. [ABSTRACT FROM AUTHOR]