Molecular Gas and Dust in Arp 94: The Formation of a Recycled Galaxy in an Interacting System

Lisenfeld, U.; Mundell, C. G.; Schinnerer, E.; Appleton, P. N.; Allsopp, J.

doi:10.1086/590420

Cited by 25 publications

(35 citation statements)

References 51 publications

(99 reference statements)

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“…The star formation efficiency with respect to the molecular gas is normal in the galactic disks, but it is at least a factor of 2 to 3 lower in the bridge region. This decrease in star formation efficiency is very similar to what is observed in the extraplanar gas of the Virgo spiral galaxy NGC 4438 (Vollmer et al 2012b) and in the interacting galaxies NGC 3226/27 (region 2 in Table 1 of Lisenfeld et al 2008). Whereas this decrease is observed at low molecular gas surface densities (∼10 M ) in NGC 4438 and NGC 3226/27, it occurs at a 3 to 5 times higher molecular gas surface density in the Taffy bridge.…”

Section: The Low Star Formation Efficiency In the Bridgesupporting

confidence: 78%

A dynamical model for the Taffy galaxies UGC 12914/5

Vollmer¹,

Braine²,

Soida³

2012

A&A

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The spectacular head-on collision of the two gas-rich galaxies of the Taffy system, UGC 12914/15, gives us a unique opportunity to study the consequences of a direct ISM-ISM collision. To interpret existing multi-wavelength observations, we made dynamical simulations of the Taffy system including a sticky particle component. To compare simulation snapshots to Hi and CO observations, we assume that the molecular fraction of the gas depends on the square root of the gas volume density. For the comparison of our simulations with observations of polarized radio continuum emission, we calculated the evolution of the 3D large-scale magnetic field for our simulations. The induction equations including the time-dependent gas-velocity fields from the dynamical model were solved for this purpose. Our simulations reproduce the stellar distribution of the primary galaxy, UGC 12914, the prominent Hi and CO gas bridge, the offset between the CO and Hi emission in the bridge, the bridge isovelocity vectors parallel to the bridge, the Hi double-line profiles in the bridge region, the large line-widths (∼200 km s −1 ) in the bridge region, the high field strength of the bridge large-scale regular magnetic field, the projected magnetic field vectors parallel to the bridge and the strong total power radio continuum emission from the bridge. The stellar distribution of the secondary model galaxy is more perturbed than observed. The observed distortion of the Hi envelope of the Taffy system is not reproduced by our simulations which use initially symmetric gas disks. The model allows us to define the bridge region in three dimensions. We estimate the total bridge gas mass (Hi, warm and cold H 2 ) to be 5 to 6× 10 9 M , with a molecular fraction M H 2 /M HI of about unity. Despite the enormous mass of molecular gas in the bridge, very little star formation is present, similar to other systems with extraplanar gas and broad CO lines. The structure of the model gas bridge is bimodal: on kpc-scales there is a dense ( 0.01 M pc −3 ) component with a high velocity dispersion >100 km s −1 and a less dense (∼10 −3 M pc −3 ) component with a smaller, but still high, velocity dispersion ∼50 km s −1 . The synchrotron lifetime of relativistic electrons is only long enough to be consistent with the existence of the radio continuum bridge for the less dense component. On the other hand, only the high-density gas undergoes a high enough mechanical energy input to produce the observed strong emission of warm H 2 . We propose that, despite the high local gas densities, this high input of mechanical energy drives strong turbulence and quenches star formation in the bridge gas except for the giant Hii region near UGC 12915. Our model suggests that we observe this galaxy head-on collision near the time of maximum CO and H 2 emission.

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Section: The Low Star Formation Efficiency In the Bridgesupporting

confidence: 78%

A dynamical model for the Taffy galaxies UGC 12914/5

Vollmer¹,

Braine²,

Soida³

2012

A&A

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“…For d = 14.5 Mpc, 1 corresponds to 70.3 pc. This is very similar to the d = 15.1 Mpc assumed by Mundell et al (1995b) based on the redshift of the source, and slightly smaller than d = 20.4 Mpc assumed by Mundell et al (2004) and Lisenfeld et al (2008) relying on the Tully-Fisher relation (Tully 1988).…”

Section: Paper Goals and Structuresupporting

confidence: 75%

“…Using the IRAM 30 m telescope, Lisenfeld et al (2008) demonstrated that this TDG is also rich in molecular gas (M H 2 = 1.5 × 10 8 M , corrected for our distance). In spite of comparable atomic and molecular gas surface densities in the north and south of the cloud, star formation in J1023+1952 is predominantly happening along a 2-kpc-long ridge in the southern half (traced by optical blue colours, Hα, and UV emission, as well as young stellar clusters resolved with HST; see Fig.…”

Section: Our Target: the Tidal Dwarf Galaxy J1023+1952mentioning

confidence: 66%

ALMA resolves giant molecular clouds in a tidal dwarf galaxy

Lelli

Schinnerer

Colombo

et al. 2021

A&A

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Tidal dwarf galaxies (TDGs) are gravitationally bound condensations of gas and stars formed during galaxy interactions. Here we present multi-configuration ALMA observations of J1023+1952, a TDG in the interacting system Arp 94, where we resolve CO(2-1) emission down to giant molecular clouds (GMCs) at 0.64 ∼ 45 pc resolution. We find a remarkably high fraction of extended molecular emission (∼80−90%), which is filtered out by the interferometer and likely traces diffuse gas. We detect 111 GMCs that give a similar mass spectrum as those in the Milky Way and other nearby galaxies (a truncated power law with slope of −1.76 ± 0.13). We also study Larson's laws over the available dynamic range of GMC properties (∼2 dex in mass and ∼1 dex in size): GMCs follow the size-mass relation of the Milky Way, but their velocity dispersion is higher such that the size-linewidth and virial relations appear super-linear, deviating from the canonical values. The global molecular-to-atomic gas ratio is very high (∼1) while the CO(2-1)/CO(1-0) ratio is quite low (∼0.5), and both quantities vary from north to south. Star formation is predominantly taking place in the south of the TDG, where we observe projected offsets between GMCs and young stellar clusters ranging from ∼50 pc to ∼200 pc; the largest offsets correspond to the oldest knots, as seen in other galaxies. In the quiescent north, we find more molecular clouds and a higher molecular-to-atomic gas ratio (∼1.5); atomic and diffuse molecular gas also have a higher velocity dispersion there. Overall, the organisation of the molecular ISM in this TDG is quite different from other types of galaxies on large scales, but the properties of GMCs seem fairly similar, pointing to near universality of the star-formation process on small scales.

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“…Surveys of colliding galaxies with HI-rich tidal tails lead to several other detections [41,141,205]. However the later-on CO mapping of entire tidal tails revealed the presence of molecular clouds outside the HI peaks, leaving open the possibility that the molecular component (or part of it) might have been directly stripped form the colliding galaxies at the same time as the HI and stellar components [74,143]. 9.9 Faint stellar streams wrapping around the spiral galaxy NGC 5907, seen edge-on.…”

Section: Sparse Components: Molecular Clouds Dust and Heavy Elementsmentioning

confidence: 99%

Tides in Astronomy and Astrophysics

2013

Lecture Notes in Physics

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Molecular Gas and Dust in Arp 94: The Formation of a Recycled Galaxy in an Interacting System

Cited by 25 publications

References 51 publications

A dynamical model for the Taffy galaxies UGC 12914/5

A dynamical model for the Taffy galaxies UGC 12914/5

ALMA resolves giant molecular clouds in a tidal dwarf galaxy

Tides in Astronomy and Astrophysics

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