2016A&A...588A..23A


C.D.S. - SIMBAD4 rel 1.7 - 2020.02.24CET12:58:25

2016A&A...588A..23A - Astronomy and Astrophysics, volume 588A, 23-23 (2016/4-1)

Molecular gas in low-metallicity starburst galaxies: Scaling relations and the CO-to-H2 conversion factor.

AMORIN R., MUNOZ-TUNON C., AGUERRI J.A.L. and PLANESAS P.

Abstract (from CDS):

Context. Tracing the molecular gas-phase in low-mass star-forming galaxies becomes extremely challenging due to significant UV photo-dissociation of CO molecules in their low-dust, low-metallicity ISM environments.
Aims. We aim to study the molecular content and the star-formation efficiency of a representative sample of 21 blue compact dwarf galaxies (BCDs), previously characterized on the basis of their spectrophotometric properties.
Methods. We present CO (1-0) and (2-1) observations conducted at the IRAM-30m telescope. These data are further supplemented with additional CO measurements and multiwavelength ancillary data from the literature. We explore correlations between the derived CO luminosities and several galaxy-averaged properties.
Results. We detect CO emission in seven out of ten BCDs observed. For two galaxies these are the first CO detections reported so far. We find the molecular content traced by CO to be correlated with the stellar and Hi masses, star formation rate (SFR) tracers, the projected size of the starburst, and its gas-phase metallicity. BCDs appear to be systematically offset from the Schmidt-Kennicutt (SK) law, showing lower average gas surface densities for a given σSFR, and therefore showing extremely low (<=0.1Gyr) H2 and H2+HI depletion timescales. The departure from the SK law is smaller when considering H2+HI rather than H2 only, and is larger for BCDs with lower metallicity and higher specific SFR. Thus, the molecular fraction (σH2/σHI) and CO depletion timescale (σH2/σSFR) of BCDs is found to be strongly correlated with metallicity. Using this, and assuming that the empirical correlation found between the specific SFR and galaxy-averaged H2 depletion timescale of more metal-rich galaxies extends to lower masses, we derive a metallicity-dependent CO-to-H2 conversion factor αCO,Z∝(Z/Z☉)-y, with y=1.5(±0.3)in qualitative agreement with previous determinations, dust-based measurements, and recent model predictions. Consequently, our results suggest that in vigorously star-forming dwarfs the fraction of H2 traced by CO decreases by a factor of about 40 from Z∼Z☉ to Z∼0.1Z☉, leading to a strong underestimation of the H2 mass in metal-poor systems when a Galactic αCO,MW is considered. Adopting our metallicity-dependent conversion factor αCO,Z we find that departures from the SK law are partially resolved.
Conclusions. Our results suggest that starbursting dwarfs have shorter depletion gas timescales and lower molecular fractions compared to normal late-type disc galaxies, even accounting for the molecular gas not traced by CO emission in metal-poor environments, raising additional constraints to model predictions.

Abstract Copyright: © ESO, 2016

Journal keyword(s): galaxies: ISM - radio lines: ISM - galaxies: starburst - galaxies: evolution - galaxies: general

Simbad objects: 28

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Number of rows : 28

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 Mrk 960 bCG 00 48 35.430 -12 42 59.77   15.5       ~ 102 0
2 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9232 1
3 NGC 1036 G 02 40 28.982 +19 17 49.48   13.5       ~ 107 0
4 SBSG 0335-052 bCG 03 37 44.04 -05 02 38.5     16.65     ~ 426 1
5 NGC 1741 IG 05 01 38.3 -04 15 25   13.7   13.02 13.6 ~ 248 0
6 IC 399 EmG 05 01 44.083 -04 17 19.28   15.0 14.8     ~ 65 0
7 NAME Ori A MoC 05 38 -07.1           ~ 2639 0
8 UGCA 116 H2G 05 55 42.645 +03 23 32.23 10.74 11.68 11.46   11.82 ~ 494 0
9 Mrk 5 H2G 06 42 15.9 +75 37 40   17.0       ~ 108 0
10 NGC 2415 bCG 07 36 56.730 +35 14 31.04   12.5       ~ 120 1
11 NGC 2537 IG 08 13 14.643 +45 59 23.25 12.18 12.50 11.69 11.66   ~ 266 1
12 NGC 2893 G 09 30 16.9562425723 +29 32 23.883900204   13.6 13.11     ~ 106 1
13 Mrk 116 PaG 09 34 02.1 +55 14 25           ~ 985 1
14 IRC +10216 C* 09 47 57.40632 +13 16 43.5648     10.96     C9,5e 2115 0
15 Mrk 33 IG 10 32 31.956 +54 24 03.53 13.29 13.66 13.13 12.71 12.27 ~ 320 1
16 NGC 3353 AGN 10 45 22.390 +55 57 37.36 12.90 13.25 12.79     ~ 316 1
17 Mrk 36 SBG 11 04 58.298 +29 08 16.54   15.50 15.29     ~ 215 0
18 Mrk 1307 Sy1 11 52 37.19 -02 28 09.9   14.79   14.09 14.9 ~ 156 0
19 Mrk 829 GiP 14 50 56.495 +35 34 18.27   14.5 14.83     ~ 194 0
20 UGC 9562 GiP 14 51 14.3970867139 +35 32 32.933386615   14.2       ~ 147 0
21 NGC 5860 EmG 15 06 33.73 +42 38 29.2   14.2       ~ 83 0
22 Mrk 487 bCG 15 37 04.237 +55 15 47.60   15.2       ~ 126 0
23 NGC 6052 IG 16 05 12.8707837896 +20 32 32.613940524 13.01 13.44 13.00     ~ 330 2
24 [WBN74] W 51 IRS 2 SFR 19 23 40.05 +14 31 07.1           ~ 252 0
25 NGC 7468 bCG 23 02 59.172 +16 36 16.20   14.0       ~ 153 0
26 NGC 7625 IG 23 20 30.132 +17 13 32.16 13.31 13.23 11.98 11.25   ~ 239 0
27 Mrk 324 G 23 26 32.783 +18 16 00.07   15.5       ~ 63 0
28 LEDA 71605 EmG 23 30 09.7 +25 31 56   15.0       ~ 52 0

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2020.02.24-12:58:25

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