Dense Molecular Gas And That Correlated With Infrared Characteristics In NGC 1068

Star formation is the key to the study of galaxy formation and evolution,as well as the foundation of our understanding of the universe.In this MS thesis,we study the dense molecular gas and that correlated with infrared characteristics in the nearby galaxy NGC 1068.The research content is mainly divided into two parts:Firstly,we study the HCN 4-3 and HCO+4-3 data from the MALATANG(Mapping the dense molecular gas in the strongest star-forming galaxies)project,which are compared with ancillary data including CO 1-0 from Nobeyama 45-m,CO 3-2 from JCMT,and infrared photometric data from Herschel/PACS.We explore the correlations between dense molecular gas and infrared characteristics,discuss the star formation under the assumption that the study regions are dominated by star formation.Secondly,we use the multi-spectral lines from ALMA with high-resolution combined with continuum data to study the link between physical environments and molecular gas in the nuclear region of NGC 1068 systematically.We present HCN 4-3 and HCO+4-3 maps of NGC 1068,which cover a large area(～1.5’×1.5’)in the central region.We adopted an improved data reduced method by combining STARLINK with CLASS to do the reduction.The signal-to-noise ratio of spectra maps was improved.The dense molecular gas traced by HCN 4-3 or HCO+43 shows a compact morphology,while the CO 3-2 and CO 1-0 maps are much more extended.The HCN 4-3 and HCO+4-3 emission are detected at～3-8 sigma levels in the outer disk region(～2.2-3.2 kpc radial distance)by stacking.We use the estimated 70μm/100μm flux ratio as a proxy of warm-dust temperature(Tdust),and find an increasing trend between the LIR/L’dense ratio and Tdust,as well as a weak correlation between Tdust and the CO 3-2/CO 1-0 integrated intensity ratio(R31).The spatially resolved LIR-L’dense correlations show a slope β=1.03±0.15 for HCN 4-3 and a slope β=1.33±0.11 for HCO+4-3 under the assumption of star formation dominance,suggesting that the dense-gas SF law is also valid on sub-kpc scales in the individual galaxy.In addition,the HCN 4-3/HCO+4-3 integrated intensity ratio shows an increasing trend with star formation rate surface densities(ΣSFR).The more linear correlation with LIR and relatively stronger correlation with ΣSFR presented in HCN 4-3,might suggest that it is more relevant to dense gas that is related to star formation than HCO+4-3 on sub-kpc scales.Furthermore,we find the the dense-gas fraction(fdense,traced by the HCN 4-3/CO 1-0 and HCO+4-3/CO 1-0 integrated intensity ratios)shows a positive correlation with the star formation efficiency of total molecular gas(SFEmol)while independent of the star formation efficiency of dense gas(SFEdense),which suggests a constant SFEdense on sub-kpc scales.The high-resolution(～0.2″-0.7″)spectral lines from ALMA we used include CO 1-0,CO 2-1,CO 3-2,HCN 1-0,HCO+ 1-0,HCN 3-2,HCO+ 3-2,HCN 4-3 and HCO+ 4-3.The circumnuclear disk(CND)shows an asymmetric ring structure with a size of～300 pc in the velocity-integrated intensity images.All the molecular lines show stronger emission and larger velocities at the eastern knot(E-knot)than at the western knot(W-knot)of the CND.Furthermore.the fdense and dense gas ratios(HCN/HCO+integrated intensity ratios)are higher at the E-knot.The R31 show much higher values at the E-knot,suggesting that there is molecular excitation enhancement caused by the extreme physical environment.The spectral lines show that the flux ratios between Eknot and W-knot are～1.8-3.9.These differences implying that the E and W knots have different physical environments or chemical compositions.In addition,the CO 21.CO 1-0 and HCO+ 1-0 spectra show absorption features in the active galactic nucleus(AGN),which could be caused by the strong background of continuum emissions.