arXiv subjects

Guilin Liu

Publications and source records attributed to Guilin Liu.

94 records · Page 6Linked to original sources

arXiv2011

Physical properties of the circumnuclear starburst ring in the barred Galaxy NGC 1097

We report high resolution 12CO(J = 2-1), 13CO(J = 2-1), and 12CO(J = 3-2) imaging of the Seyfert 1/starburst ring galaxy NGC 1097 with the Submillimeter Array to study the physical and kinematic properties of the 1-kpc circumnuclear starburst ring. Individual star clusters as detected in the HST map of Pa_alpha line emission have been used to determine the star formation rate, and are compared with the properties of the molecular gas. The molecular ring has been resolved into individual clumps at GMA-scale of 200--300 pc in all three CO lines. The intersection between the dust lanes and the starburst ring, which is associated with orbit-crowding region, is resolved into two physically/kinematically distinct features in the 1.5x1.0 (105x70 pc) 12CO(J = 2-1) map. The clumps associated with the dust lanes have broader line width, higher surface gas density, and lower star formation rate, while the narrow line clumps associated with the starburst ring have opposite characteristics. Toomre-Q value under unity at the radius of the ring suggests that the molecular ring is gravitationally unstable to fragment at the scale of the GMA. The line widths and surface density of gas mass of the clumps show an azimuthal variation related to the large scale dynamics. The star formation rate, on the other hand, is not significantly affected by the dynamics, but has a correlation with the intensity ratio of 12CO (J = 3-2) and 12CO(J = 2-1), which traces the denser gas associated with star formation. Our resolved CO map, especially in the orbit-crowding region, for the first time demonstrates observationally that the physical/kinematic properties of the GMAs are affected by the large scale bar-potential dynamics in NGC 1097.

astro-ph.CO↗

arXiv2011

The Super-linear Slope of the Spatially-Resolved Star Formation Law in NGC 3521 and NGC 5194 (M51a)

We have conducted interferometric observations with CARMA and an OTF mapping with the 45-m telescope at NRO in the CO (J=1-0) emission line of NGC 3521. Combining these new data, together with CARMA+NRO45 data for M51a and archival SINGS H$α$, 24$μ$m, THINGS H I and GALEX FUV data for both galaxies, we investigate the empirical scaling law that connects the surface density of SFR and cold gas (the Schmidt-Kennicutt law) on a spatially-resolved basis. We argue that plausibly deriving SFR maps of nearby galaxies requires the diffuse stellar/dust background emission to be carefully subtracted. An approach to complete this task is presented and applied in our pixel-by-pixel analysis on both galaxies, showing that the controversial results whether the molecular S-K law is super-linear or basically linear is a result of removing or preserving the local background. In both galaxies, the power index of the molecular S-K law is 1.5-1.9 at the highest available resolution (230 pc), and decreases monotonically for decreasing resolution; while the scatter (mainly intrinsic) increases as the resolution becomes higher, indicating a trend for which the S-K law breaks down below some scale. Both quantities are systematically larger in M51a than in NGC 3521, but when plotted against the de-projected scale (δ_{dp}), they become highly consistent between the two galaxies, tentatively suggesting that the sub-kpc molecular S-K law in spiral galaxies depends only on the considered scale, without varying amongst spiral galaxies. A logarithmic function γ_{H_2}=-1.1 log[δ_{dp}/kpc]+1.4 and a linear relation σ_{H_2}=-0.2 [δ_{dp}/kpc]+0.7 are obtained through fitting to the M51a data, which describes both galaxies impressively well on sub-kpc scales. A larger sample of galaxies with better quality data are required to test the general applicability of these relations.

astro-ph.CO↗

arXiv2010

The Redshift Search Receiver 3 mm Wavelength Spectra of 10 Galaxies

The 3 mm wavelength spectra of 10 galaxies have been obtained at the Five College Radio Astronomy Observatory using a new, very broadband receiver and spectrometer, called the Redshift Search Receiver (RSR). The RSR has an instantaneous bandwidth of 37 GHz covering frequencies from 74 to 111 GHz, and has a spectral resolution of 31 MHz (~100 km/s). During tests of the RSR on the FCRAO 14 m telescope the complete 3 mm spectra of the central regions of NGC 253, Maffei 2, NGC1068, IC 342, M82, NGC 3079, NGC 3690, NGC 4258, Arp 220 and NGC 6240 were obtained. Within the wavelength band covered by the RSR, 20 spectral lines from 14 different atomic and molecular species were detected. Based on simultaneous fits to the spectrum of each galaxy, a number of key molecular line ratios are derived. A simple model which assumes the emission arises from an ensemble of Milky Way-like Giant Nolecular Cloud cores can adequately fit the observed line ratios using molecular abundances based on Galactic molecular cloud cores. Variations seen in some line ratios, such as 13CO/HCN and HCO+/HCN, can be explained if the mean density of the molecular gas varies from galaxy to galaxy. However, NGC 3690, NGC 4258 and NGC 6240 show very large HCO+/HCN ratios and require significant abundance enhancement of HCO+ over HCN, possible due to the proximity to active galactic nucleus activity. Finally, the mass of dense molecular gas is estimated and we infer that 25-85 % of the total molecular gas in the central regions of these galaxies must have densities greater than 10^4 cm^-3.

astro-ph.GA↗

arXiv2010

An Investigation of the Dust Content in the Galaxy pair NGC 1512/1510 from Near-Infrared to Millimeter Wavelengths

We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with archival Spitzer IRAC and MIPS images covering the wavelength range 3.6--160 um from the SINGS project to derive accurate dust masses in each galaxy, and in sub--galactic regions in NGC 1512. The two galaxies form a pair consisting of a large, high--metallicity spiral (NGC 1512) and a low metallicity, blue compact dwarf (NGC 1510). The derived total dust masses are (2.4+/-0.6) 10^7 Msun and (1.7+/-3.6) 10^5 Msun for NGC 1512 and NGC 1510, respectively. The derived ratio of dust mass to H I gas mass for the galaxy pair (0.0034) is much lower than expected, while regions within NGC 1512, specifically the central region and the arms, do not show such unusually low ratios; furthermore, the dust--to--gas ratio is within expectations for NGC 1510. These results suggest that a fraction of the H I included in the determination of the M_d/M_HI ratio of the NGC 1512/1510 pair is not associated with the star forming disks/regions of either galaxy. We also perform simple two--temperature (warm + cold) modified--blackbody fits to the far--infrared/mm data. The warm dust temperature of the low--metallicity NGC 1510 (~36 K) is substantially higher than that of the high--metallicity NGC 1512 (~24 K). In both galaxies, a substantial fraction (>93%) of the total dust mass is in a cool dust component, with temperatures 14--16 K for NGC 1512 and 15--24 K for NGC 1510. In contrast, the warm dust in the arms and central regions of NGC 1512 represents a much larger fraction of the total dust content, in agreement with the fact that all three regions have higher specific star formation rates than the average in the galaxy.

astro-ph.CO↗