Cold gas accretion in galaxies

By R. Sancisi, Filippo Fraternali, T. Oosterloo, T. Hulst. 2008

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Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing or recent accretion: (1) A large number of galaxies are accompanied by gas-rich dwarfs or are surrounded by HI cloud complexes, tails and filaments. This suggests ongoing minor mergers and recent arrival of external gas. It may be regarded, therefore, as direct evidence of cold gas accretion in the local universe. It is probably the same kind of phenomenon of material infall as the stellar streams observed in the halos of our galaxy and M 31. (2) Considerable amounts of extra-planar HI have been found in nearby spiral galaxies. While a large fraction of this gas is undoubtedly produced by galactic fountains, it is likely that a part of it is of extragalactic origin. Also the Milky Way has extra-planar gas complexes: the Intermediate- and High-Velocity Clouds (IVCs and HVCs). (3) Spirals are known to have extended and warped outer layers of HI. It is not clear how these have formed, and how and for how long the warps can be sustained. Gas infall has been proposed as the origin. (4) The majority of galactic disks are lopsided in their morphology as well as in their kinematics. Also here recent accretion has been advocated as a possible cause. In our view, accretion takes place both through the arrival and merging of gas-rich satellites and through gas infall from the intergalactic medium (IGM). The new gas could be added to the halo or be deposited in the outer parts of galaxies and form reservoirs for replenishing the inner parts and feeding star formation. The infall may have observable effects on the disk such as bursts of star formation and lopsidedness. We infer a mean “visible” accretion rate of cold gas in galaxies of at least $${0.2\, M_{\odot} year^{-1}}$$ . In order to reach the accretion rates needed to sustain the observed star formation ($${\approx 1 M_{\odot} year^{-1}}$$), additional infall of large amounts of gas from the IGM seems to be required.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/4131947a39d9a87bbc676f1e3833f4f2cbedd799

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Citations in the corpus

GASP. I. Gas Stripping Phenomena in Galaxies with MUSE (2017, background): “…observed (e.g., Cantalupo et al. 2012, 2014), pure-gas accretion onto galaxies is very difficult to probe observationally, and direct observational evidence is still rare (e.g., Sancisi et al. 2008; Bouché et al. 2013), except in specific cases such asX-ray cooling flows (Peterson & Fabian 2006).”
MORPHOLOGICAL QUENCHING OF STAR FORMATION: MAKING EARLY-TYPE GALAXIES RED (2009, background): “This is above the average accretion rate expected from z ∼ 1 to z ∼ 0 for a typical galaxy with the mass of the MilkyWay (Kereš et al. 2009), and above the typical observed gas infall rates, too (Sancisi et al. 2008).”
The Sydney-AAO Multi-object Integral field spectrograph (2011, background): “Whether gas enters the galaxy potential in a hot phase and then cools down (Binney, Nipoti & Fraternali 2009), as a warm rain (Bland-Hawthorn et al. 2007), or as an HI complex like the high velocity clouds in the Galactic halo (Sancisi et al. 2008), or all of the above, is unclear.”
The ATLAS3D project – III. A census of the stellar angular momentum within the effective radius of early‐type galaxies: unveiling the distribution of fast and slow rotators (2011, background): “Accretion of gas from external sources, either via the large-scale filaments (e.g. Sancisi et al. 2008; Dekel et al. 2009; Khochfar & Silk 2009) or extracted by tidal forces from a gas-rich galaxy passing by, thus contributing to an increase in λR if the gas is corotating with the main existing…”
Gaseous Galaxy Halos (2012, background): “There are some non-detections of Hα emission for HVCs, but it is possible they will be detected in the future if the cloud is fully mapped to deep levels.”
Star formation sustained by gas accretion (2014, background): “Other recent reviews covering cosmic gas accretion from different perspectives are in Sancisi et al. (2008), Silk & Mamon (2012), Combes (2014), Fraternali (2014), Conselice et al. (2013) (observationally oriented), Shlosman (2013), Benson (2010) (theoretically oriented), and Madau & Dickinson…”
The ATLAS3D project - XIII. Mass and morphology of H I in early-type galaxies as a function of environment (2011, background): “In spirals, gas in these regions often exhibits warps and unsettled morphology and kinematics, and is taken as a signature of the on-going accretion of gas on the host galaxy (Sancisi et al. 2008).”
The baryonic assembly of dark matter haloes (2011, result): “The high ISM metallicities that would result at z = 0 if most star formation were fuelled by stellar mass loss are, however, in tension with the measured ones, which argue for substantial recent accretion of metal-poor intergalactic gas (e.g. Sancisi et al. 2008).”
TOWARD A UNIFICATION OF STAR FORMATION RATE DETERMINATIONS IN THE MILKY WAY AND OTHER GALAXIES (2011, background): “Also (assuming the Galactic SFR has been roughly constant throughout the history of the Milky Way), a larger amount of fresh un-processed 15 ISM material would be required to infall onto the Galactic disk to explain stellar abundance patterns and sustain star formation (e.g., Sancisi et al. 2008).”
Cold gas properties of the Herschel Reference Survey - II. Molecular and total gas scaling relations (2014, background): “…to the molecular gas component (Bigiel et al. 2008), the global star formation history of late-type galaxies is instead driven by the total gas content, which inludes a large portion of gas not directly participating to the starformation process (Sancisi et al. 2008; Fraternali & Tomassetti 2012).”
Chemical evolution with radial mixing (2008, background): “Moreover, both the short time-scale for the current ISM to be consumed by star formation and direct manifestations of infalling gas (Sancisi et al. 2008) argue strongly for the existence of infall.”
Misaligned angular momentum in hydrodynamic cosmological simulations: warps, outer discs and thick discs (2010, background): “The general conclusion is that observed sources of H I gas do not account for sufficient accretion rates to sustain current observed SFRs (Sancisi et al. 2008).”