Context. M 33 is a gas rich spiral galaxy of the Local Group. Its vicinity allows us to study its interstellar medium (ISM) on linear scales corresponding to the sizes of individual giant molecular clouds. Aims. We investigate the relationship between the two major gas cooling lines and the total infrared (TIR) dust continuum. Methods. We mapped the emission of gas and dust in M 33 using the far-infrared lines of [C ii] and [O i](63 µm) and the total infrared continuum. The line maps were observed with the PACS spectrometer on board the Herschel Space Observatory. These maps have 50 pc resolution and form a ∼370 pc wide stripe along its major axis covering the sites of bright H ii regions, but also more quiescent arm and inter-arm regions from the southern arm at 2 kpc galacto-centric distance to the south out to 5.7 kpc distance to the north. Full-galaxy maps of the continuum emission at 24 µm from Spitzer/MIPS, and at 70 µm, 100 µm, and 160 µm from Herschel/PACS were combined to obtain a map of the TIR. Results. TIR and [C ii] intensities are correlated over more than two orders of magnitude. The range of TIR translates to a range of far ultraviolet (FUV) emission of G0,obs ∼ 2 to 200 in units of the average Galactic radiation field. The binned [C ii]/TIR ratio drops with rising TIR, with large, but decreasing scatter. The contribution of the cold neutral medium to the [C ii] emission, as estimated from VLA H i data, is on average only 10%. Fits of modified black bodies to the continuum emission were used to estimate dust mass surface densities and total gas column densities. A correction for possible foreground absorption by cold gas was applied to the [O i] data before comparing it with models of photon dominated regions. Most of the ratios of [C ii]/[O i] and ([C ii]+[O i])/TIR are consistent with two model solutions. The median ratios are consistent with one solution at n ∼ 2 × 102 cm−3 , G0 ∼ 60, and a second low-FUV solution at n ∼ 104 cm−3 , G0 ∼ 1.5. Conclusions. The bulk of the gas along the lines-of-sight is represented by a low-density, high-FUV phase with low beam filling factors ∼1. A fraction of the gas may, however, be represented by the second solution. ; Spanish Ministerio de Economia y Competitividad AYA2014-53506-P AYA2017-84897-P ; Junta de Andalucia FQM108 ; Junta de Andalucia ; European Union (EU) SOMM17/6105/UGR ; Spanish Ministry of Economy and Competitiveness (MINECO) AYA2016-76219-P ; European Union (EU)
We sincerely thank the referee (Erik Rosolowsky) for the careful reading and useful comments to improve our manuscript. We would also like to show our gratitude to him for the kind assistance with the usage of CPROPS in the early stages of this work. REM was supported by the ALMA Japan Research Grant of NAOJ ALMA Project, NAOJ-ALMA-222. DE was supported by JSPS KAKENHI grant number JP 17K14254. DE was supported by the ALMA Japan Research Grant of NAOJ ALMA Project, NAOJ-ALMA-0093. MINK was supported by JSPS KAKENHI grant number JP 15J04974. KK was supported by JSPS KAKENHI grant number JP17H06130 and the NAOJ ALMA Scientific Research grant number 2017-06B. SV acknowledges support by the research projects AYA2014-53506-P and AYA2017-84897-P from the Spanish Ministerio de Economia y Competitividad, and by the Consejer ' ia de Conocimiento, Investigaci ' on y Universidad, Junta de Andaluc ' ia (FQM108) and European Regional Development Fund (ERDF)". This study has been partially financed by the Consejer ' ia de Conocimiento, Investigaci ' on y Universidad, Junta de Andaluc ' ia and European Regional Development Fund (ERDF), ref. SOMM17/6105/UGR. Part of this work was achieved using the grant of Visiting Scholars Program supported by the Research Coordination Committee, National Astronomical Observatory of Japan (NAOJ), National Institutes ofNatural Sciences (NINS). SM would like to thank the Ministry of Science and Technology (MOST) of Taiwan, MOST 107-2119-M-001-020. This research has made use of NASA's Astrophysics Data System. This research has made use of Astropy, a community-developed core PYTHON (http://www.python.org) package for Astronomy (Astropy Collaboration 2013, 2018); IPYTHON (Perez & Granger 2007); MATPLOTLIB (Hunter 2007); APLPY, an open-source plotting package for PYTHON (Robitaille & Bressert 2012), and NUMPY (van derWalt, Colbert & Varoquaux 2011). Data analysis was in part carried out on the open use data analysis computer system at the Astronomy Data Center, ADC, of the National Astronomical Observatory of Japan. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00803.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic ofKorea), in cooperationwith theRepublic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The NationalRadio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. ; We present the first census of giant molecular clouds (GMCs) complete down to 106M and within the inner 4 kpc of the nearest giant elliptical and powerful radio galaxy, Centaurus A. We identified 689 GMCs using CO(1–0) data with 1 arcsec spatial resolution (∼20 pc) and 2 kms−1 velocity resolution obtained with the Atacama Large Millimeter/submillimeter Array. The I(CO)-N(H2) conversion factor based on the virial method is XCO = (2 ± 1) × 1020 cm−2(K km s−1)−1 for the entire molecular disc, consistent with that of the discs of spiral galaxies including the Milky Way, and XCO = (5 ± 2) × 1020 cm−2(K km s−1)−1 for the circumnuclear disc (CND; within a galactocentric radius of 200 pc). We obtained the GMC mass spectrum distribution and find that the best truncated power-law fit for the whole molecular disc, with index γ −2.41 ± 0.02 and upper cut-off mass ∼1.3 × 107M , is also in agreement with that of nearby disc galaxies. A trend is found in the mass spectrum index from steep to shallow as we move to inner radii. Although the GMCs are in an elliptical galaxy, the general GMC properties in the molecular disc are as in spiral galaxies. However, in the CND, large offsets in the line-width-size scaling relations (∼0.3 dex higher than those in the GMCs in the molecular disc), a different XCO factor, and the shallowest GMC mass distribution shape (γ = −1.1 ± 0.2) all suggest that there the GMCs are most strongly affected by the presence of the active galactic nucleus and/or shear motions. ; ALMA Japan Research Grant of NAOJ ALMA Project NAOJ-ALMA-222 NAOJ-ALMA-0093 ; Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science ; Grants-in-Aid for Scientific Research (KAKENHI) JP 17K14254 JP 15J04974 JP17H06130 ; NAOJ ALMA Scientific Research grant 2017-06B ; Spanish Government AYA2014-53506-P AYA2017-84897-P ; Junta de Andalucia FQM108 ; European Commission SOMM17/6105/UGR ; Research Coordination Committee, National Astronomical Observatory of Japan (NAOJ), National Institutes ofNatural Sciences (NINS) ; Ministry of Science and Technology, Taiwan MOST 107-2119-M-001-020 2013.1.00803.S
We thank the anonymous referee for a constructive and detailed report. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska Curie grant agreement No 893673. We acknowledge financial support from the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No 721463 to the SUNDIAL ITN network, from the State Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation under the grant "The structure and evolution of galaxies and their central regions" with reference PID2019-105602GBI00/10.13039/501100011033, and from IAC project P/300724, financed by the Ministry of Science and Innovation, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community. SDG acknowledges support from the Spanish Public Employment Service (SEPE). Furthermore, we acknowledge support by the research project AYA2017-84897-P from the Spanish Ministerio de Economia y Competitividad, from the European Regional Development Funds (FEDER) and the Junta de Andalucia (Spain) grants FQM108. DE acknowledges support from a Beatriz Galindo senior fellowship (BG20/00224) from the Ministry of Science and Innovation. LVM acknowledges financial support from the grants AYA2015-65973-C3-1-R and RTI2018096228-B-C31 (MINECO/FEDER, UE), as well as from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709). This research makes use of python (http://www.python.org), Matplotlib (Hunter 2007), and Astropy (Astropy Collaboration 2013, 2018). We acknowledge the usage of the HyperLeda database (http://leda.univ-lyon1.fr).We thank Alexandre Bouquin for providing us with the GALEX FUV and NUV images used in this work. We thank Stephane Courteau, Estrella Florido, Raul Infante-Sainz, Tom Jarrett, Johan H. Knapen, Heikki Salo, and Miguel Querejeta for useful discussions. We thank Sebastien Comeron and Facundo D. Moyano for valuable comments on the manuscript. Facilities: GALEX, WISE, Spitzer (IRAC). ; Context. While some galactic bars show recent massive star formation (SF) along them, some others do not. Whether bars with low level of SF are a consequence of low star formation efficiency, low gas inflow rate, or dynamical effects remains a matter of debate. Aims. In order to study the physical conditions that enable or prevent SF, we perform a multi-wavelength analysis of 12 strongly barred galaxies with total stellar masses log(10)(M-*/M-circle dot)is an element of[10.2,11], chosen to host different degrees of SF along the bar major axis without any prior condition on gas content. We observe the CO(1-0) and CO(2-1) emission within bars with the IRAM-30 m telescope (beam sizes of 1.7-3.9 kpc and 0.9-2.0 kpc, respectively; 7-8 pointings per galaxy on average). Methods. We estimated molecular gas masses (M-mol) from the CO(1-0) and CO(2-1) emissions. SF rates (SFRs) were calculated from GALEX near-ultraviolet (UV) and WISE 12 mu m images within the beam-pointings, covering the full bar extent (SFRs were also derived from far-UV and 22 mu m). Results. We detect molecular gas along the bars of all probed galaxies. Molecular gas and SFR surface densities span the ranges log(10)(sigma(mol)/[M-circle dot pc(-2)]) is an element of [0.4,2.4] and log(10)(sigma(SFR)/[M-circle dot pc(-1) kpc(-2)]]) is an element of [-3.25, -0.75], respectively. The star formation efficiency (SFE; i.e., SFR/M-mol) in bars varies between galaxies by up to an order of magnitude (SFE is an element of[0.1,1.8] Gyr(-1)). On average, SFEs are roughly constant along bars. SFEs are not significantly different from the mean value in spiral galaxies reported in the literature (similar to 0.43 Gyr(-1)), regardless of whether we estimate M-mol from CO(1-0) or CO(2-1). Interestingly, the higher the total stellar mass of the host galaxy, the lower the SFE within their bars. In particular, the two galaxies in our sample with the lowest SFE and sigma(SFR) (NGC 4548 and NGC 5850, SFE less than or similar to 0.25 Gyr(-1), sigma(SFR)less than or similar to 10(-2.25)M(circle dot) yr(-1) kpc(-2), M greater than or similar to 10(10.7)M(circle dot)) are also those hosting massive bulges and signs of past interactions with nearby companions. Conclusions. We present a statistical analysis of the SFE in bars for a sample of 12 galaxies. The SFE in strong bars is not systematically inhibited (either in the central, middle, or end parts of the bar). Both environmental and internal quenching are likely responsible for the lowest SFEs reported in this work. ; European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska Curie 893673 ; European Commission 721463 ; State Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation under the grant "The structure and evolution of galaxies and their central regions" - Ministry of Science and Innovation P/300724 PID2019-105602GBI00 ; Spanish Public Employment Service (SEPE) ; Spanish Ministerio de Economia y Competitividad, from the European Regional Development Funds (FEDER) AYA2017-84897-P ; Junta de Andalucia ; European Commission FQM108 ; Spanish Government BG20/00224 ; State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award SEV-2017-0709 ; Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community ; MINECO/FEDER, UE AYA2015-65973-C3-1-R RTI2018096228-B-C31
