Properties of Galaxies with Counter-rotating Stellar Disks in the MaNGA Survey

Abstract

Gas accretion process can fuel both star formation and black hole activity, playing a critical role in galaxy evolution. The counter-rotating structures are believed to originate from gas accretion, serving as an ideal laboratory for studying its impact on galaxy evolution. Based on the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we built a sample of 147 galaxies with counter-rotating stellar disks (CRDs). This is the largest CRD sample to date, accounting for $\sim$1.5% of the MaNGA survey. For a subset of 138 CRDs, global stellar mass ($M_\ast$) and star formation rate (SFR) were measured in reference. We constructed a control sample with similar $M_\ast$ and SFR but lacking counter-rotating structures. The CRDs relatively exhibit more bulge-dominated morphology, lower molecular gas mass fraction and reside in less dense environment, supporting the hypothesis that they primarily originate from gas accretion. We classified 96 out of 138 CRDs into four types based on their stellar and gas kinematics following the criteria from Bao et al. (2022). There are two additional CRD types: 8 CRDs show misalignment between both stellar disks and gas disk, indicating multiple gas accretion events with differing angular momentum directions; 34 CRDs lack ionized gas emission, showing the highest $M_\ast$ among all the CRD types, which may represent a final stage of CRD evolution. We compared the radial gradients of gas-phase metallicity and stellar population properties between CRD types, and found that the impact of gas accretion on galaxy evolution primarily depends on the abundance of pre-existing gas in progenitors.

Figures (9)

• Figure 1: Two examples of our sample selection. (a) The stellar velocity dispersion field in polar coordinate. The black solid and dashed lines show the photometric major and minor axes. (b) Normalized $\sigma_{\ast}$ as a function of $\theta$. The black circle represents the median $\sigma_{\ast}$ in each sector, with the black vertical bar showing the $\pm 1 \sigma$ scattering range. The black curve shows the best-fitting double Gaussian model. The vertical blue lines and grey-shaded areas mark the directions of two peaks and corresponding errors. The vertical orange dashed lines mark $\theta = 90^{\circ}$ and $\theta = 270^{\circ}$, the photometric major axis. (c) The stellar velocity field. The black solid and dashed lines show the photometric major and minor axes. (d) $v_\ast$ along major axis. The black circles show the $v_\ast$ as a function of radius, with the black vertical bar showing the $v_\ast$ error. The black curve shows the best result of polynomial fitting. The horizontal grey dashed line marks $v_\ast = 0~\rm km~s^{-1}$. The vertical gray dashed line marks the radius of central velocity-zero point. The vertical blue solid lines mark the radii of the other two velocity-zero points.
• Figure 2: Examples of different types of CRDs. (a) Type NO-EML, where the gas emission can be neglected. (b) Type MIS, where both stellar disks are misaligned with the gas disk. (c) Type CO, where one stellar disk overshines the other, with the brighter stellar disk co-rotating with the gas disk. (d) Type CT, where one stellar disk overshines the other, with the brighter stellar disk counter-rotating with the gas disk. (e) Type IN, where the inner stellar disk is co-rotating with the gas disk. (f) Type OUT, where the outer stellar disk is co-rotating with the gas disk. In all the panels, three subplots sequentially represent stellar velocity dispersion field, stellar velocity field, and gas velocity field traced by H$\alpha$. The black solid line in each stellar velocity dispersion field represents the photometric major axis.
• Figure 3: Distribution of CRD sample in the $\log M_\ast$ - $\log \rm SFR$ plane. (a) The grey contour shows the distribution of SDSS spectroscopic galaxy sample from 2015ApJS..219....8C catalog. The blue, green, red and black circles show the distributions of Type CO+IN, Type CT+OUT, Type MIS and Type NO-EML, respectively. The black dashed line classifies galaxies into SF and QS sequence. (b) Distribution of stellar mass. (c) Distribution of star formation rate. In panels (b) and (c), the blue, green, red and black histograms show the $M_\ast$ and SFR distributions of Type CO+IN, Type CT+OUT, Type MIS and Type NO-EML, respectively. The blue, green, red and black vertical lines show the corresponding median values.
• Figure 4: The distributions of bulge-to-total ratio. Four panels sequentially display the B/T distributions for Type CO+IN, Type CT+OUT, Type NO-EML, Type MIS and their control samples. The colorful histograms show the B/T distributions for different CRD types. The grey histograms show the B/T distributions for their control samples. The colorful and grey vertical lines show the corresponding median values.
• Figure 5: The distributions of molecular gas mass fraction. Three panels sequentially display the $\log(M_{\rm mol} / M_\ast)$ distributions for Type CO+IN, Type CT+OUT, Type MIS and their control samples. The colorful histograms show the $\log(M_{\rm mol} / M_\ast)$ distributions for different CRD types. The grey histograms show the $\log(M_{\rm mol} / M_\ast)$ distributions for their control samples. The colorful and grey vertical lines show the corresponding median values.