Observations
Observations
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The following are the projects that I am currently leading as the principal investigator.
Revealing the morphology and kinematics of molecular gas in double-barred galaxies using the ALMA telescope
Bars are one of the most common non-axisymmetric structures in disk galaxies and affect the evolution of galaxies dramatically by redistributing mass and angular momentum. The major focus of my research is to understand the formation, evolution and effects of bars in galaxies. Specifically, I investigate the galaxies which have two bars, that is an inner secondary bar embedded within an outer primary bar. They are so-called double-barred galaxies. Fig. 1 is an example showing the morphology of the double-barred galaxy NGC 3504. The investigation of double-barred galaxies is especially important as the inner bar is expected to drive gas inflow towards the nucleus of galaxies to feed supermassive black holes and therefore significantly change the evolution of galaxies (Shlosman et al. 1989). To verify this scenario, our project aims to reveal the morphology and kinematics of molecular gas in double-barred galaxies using modern telescopes.
Figure 1: (a) SDSS g-band image of the double-barred galaxy NGC 3504. The white arrows indicate the dust lanes on the outer bar. (b) The HST/WFC3 F160W image, showing the central 2.4 kpc region of NGC 3504. The contour levels are 10, 20, 30, 40, 60, 100, 200 and 600 electrons/s. The blue line represents the major axis of the inner bar with a length of 5.2 arcsec and position angle of 172 degree.
I and my collaborators successfully carried out observations of the double-barred galaxy NGC 3504 with the ALMA telescope. Our observations reveal an inner molecular gas bar, a nuclear ring, and four inner spiral arm-like structures in the central 1-kpc region, as shown in Fig. 2. Furthermore, we found clear evidence for radial gas motions in the central 0.3 kpc. Our results give a new example of an inner gas bar within a gas-rich double-barred galaxy and support the scenario for the gas inflow driven by the inner bar (Wu et al. 2021).
Figure 2: CO (J=2-1) integrated intensity map of the central ~2.4 kpc region of NGC 3504 with the contours at 0.35, 0.8, 2.0, 4.0, 10.0, and 15.0 Jy/beam km/s. The red arrow indicates the gaseous inner bar. The black dashed and dotted lines are the identified nuclear ring and spiral structures from the channel maps (shown in Wu et al. 2021).
Systematically measuring molecular gas mass in double-barred galaxies using the ALMA telescope
Molecular gas is one of the crucial components in galaxies. It plays a major role in the formation of double-barred galaxies and the evolution of the black holes in the galaxies (Friedli & Martinet 1993). However, previous studies cannot provide reliable results on the properties of molecular gas due to the problems of identifying true double-barred galaxies and having adequate sensitivity and spatial resolution to probe gas in the whole galaxy as well as in the inner bar region.
To provide reliable constraints on theories and shed light on the formation and evolution of double-barred galaxies, I am currently leading a pilot survey to observe a sample of double-barred galaxies using the ALMA telescope. Our first goal is to systematically measure molecular gas mass in the double-barred galaxies. Our data is expected to allow us to provide constraints on the formation scenarios of double-barred galaxies, and will also serve as a basis for future studies attempting to investigate a variety of gas properties in the double-barred galaxies.
Our sample:
Figure 3: SDSS g-band ((a), (c), (e) and (f)) and Spitzer 4.5μm images ((b), (d) and (g)) of the galaxies in our sample. The white squares indicate the observing areas we request for the ALMA observations.
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