Query : 2016A&A...594A..70K

2016A&A...594A..70K - Astronomy and Astrophysics, volume 594A, 70-70 (2016/10-1)

Deep ALMA imaging of the merger NGC 1614. Is CO tracing a massive inflow of non-starforming gas?


Abstract (from CDS):

Aims. Observations of the molecular gas over scales of ∼0.5 to several kpc provide crucial information on how molecular gas moves through galaxies, especially in mergers and interacting systems, where it ultimately reaches the galaxy center, accumulates, and feeds nuclear activity. Studying the processes involved in the gas transport is one of the important steps forward to understand galaxy evolution.
Methods. 12CO, 13CO, and C18O 1-0 high-sensitivity ALMA observations (∼4''x2'') were used to assess the properties of the large-scale molecular gas reservoir and its connection to the circumnuclear molecular ring in the merger NGC 1614. Specifically, the role of excitation and abundances were studied in this context. We also observed the molecular gas high-density tracers CN and CS.
Results. The spatial distributions of the detected 12CO 1-0 and 13CO 1-0 emission show significant differences. 12CO traces the large-scale molecular gas reservoir, which is associated with a dust lane that harbors infalling gas, and extends into the southern tidal tails. 13CO emission is for the first time detected in the large-scale dust lane. In contrast to 12CO, its line emission peaks between the dust lane and the circumnuclear molecular ring. A 12CO-to-13CO 1-0 intensity ratio map shows high values in the ring region (∼30) that are typical for the centers of luminous galaxy mergers and even more extreme values in the dust lane (>45). Surprisingly, we do not detect C18O emission in NGC 1614, but we do observe gas emitting the high-density tracers CN and CS.
Conclusions. We find that the 12CO-to-13CO 1-0 line ratio in NGC 1614 changes from >45 in the 2kpc dust lane to ∼30 in the starburst nucleus. This drop in ratio with decreasing radius is consistent with the molecular gas in the dust lane being kept in a diffuse, unbound state while it is being funneled toward the nucleus. This also explains why there are no (or very faint) signs of star formation in the dust lane, despite its high 12CO luminosity. In the inner 1.5kpc, the gas is compressed into denser and most likely self-gravitating clouds (traced by CN and CS emission), allowing it to power the intense central starburst. We find a high 16O-to-18O abundance ratio in the starburst region (≥900), typical of quiescent disk gas. This is surprising because by now, the starburst is expected to have enriched the nuclear interstellar medium in 18O relative to 16O. We suggest that the massive inflow of gas may be partially responsible for the low 18O/16O abundance since it will dilute the starburst enrichment with unprocessed gas from greater radial distances. The 12CO-to-13CO abundance of >90 we infer from the line ratio is consistent with this scenario. It suggests that the nucleus of NGC 1614 is in a transient phase of its evolution where the starburst and the nuclear growth is still being fuelled by returning gas from the minor merger event.

Abstract Copyright: © ESO, 2016

Journal keyword(s): galaxies: evolution - galaxies: individual: NGC 1614 - galaxies: starburst - galaxies: active - radio lines: galaxies - ISM: molecules

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 QSO B0336-0156 QSO 03 39 30.93778633 -01 46 35.8041892   18.96 18.41 17.33   ~ 540 1
2 QSO B0420-0127 QSO 04 23 15.80072217 -01 20 33.0656073   17.50 17.00 16.28   ~ 1174 3
3 NGC 1614 AGN 04 34 00.027 -08 34 44.57   14.66 13.99     ~ 658 0
4 NGC 3690 IG 11 28 31.0 +58 33 41   13.19 12.86     ~ 966 4
5 NGC 4355 Sy2 12 26 54.6206739120 -00 52 39.421212996   14.21 13.37     ~ 474 2
6 Mrk 231 Sy1 12 56 14.2341182928 +56 52 25.238373852   14.68 13.84     ~ 1956 3
7 M 51 GiP 13 29 52.698 +47 11 42.93   9.26 8.36 8.40   ~ 4247 4
8 Z 49-57 GiC 15 13 13.0927 +07 13 31.850   15.5       ~ 232 1
9 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13888 0

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