HI 21 cm observation and mass models of the extremely thin galaxy FGC 1440

TL;DR

This study investigates the neutral hydrogen distribution and mass models of the superthin galaxy FGC 1440, revealing a warped HI disc, a dark matter halo with a pseudo-isothermal profile, and properties similar to normal spiral galaxies despite its extreme thinness.

Contribution

First detailed HI kinematic and mass modeling of the superthin galaxy FGC 1440, demonstrating its dark matter halo profile and consistency with typical spiral galaxy properties.

Findings

FGC 1440 has an asymptotic rotational velocity of 141.8 km/s.

The HI disc is warped but may have a central thick component.

The dark matter halo fits a pseudo-isothermal profile with R_c/R_d < 2.

Abstract

We present observations and models of the kinematics and distribution of neutral hydrogen (HI) in the superthin galaxy FGC 1440 with an optical axial ratio $a/b = 20.4$. Using the Giant Meterwave Radio telescope (GMRT), we imaged the galaxy with a spectral resolution of 1.7 $\rm kms^{-1}$ and a spatial resolution of $15" \times 13.5"$. We find that FGC 1440 has an asymptotic rotational velocity of 141.8 $\rm kms^{-1}$ . The structure of the HI disc in FGC 1440 is that of a typical thin disc warped along the line of sight, but we can not rule out the presence of a central thick HI disc. We find that the dark matter halo in FGC 1440 could be modeled by a pseudo-isothermal (PIS) profile with $\rm R_{c}/ R_{d} <2$, where $R_{c}$ is the core radius of the PIS halo and $R_{d}$ the exponential stellar disc scale length. We note that in spite of the unusually large axial ratio of FGC 1440, the ratio of the rotational velocity to stellar vertical velocity dispersion, $\frac{V_{Rot}}{\sigma_{z}} \sim 5 - 8$, which is comparable to other superthins. Interestingly, unlike previously studied superthin galaxies which are outliers in the $log_{10}(j_{*}) - log_{10}(M_{*})$ relation for ordinary bulgeless disc galaxies, FGC 1440 is found to comply with the same. The values of $j$ for the stars, gas and the baryons in FGC 1440 are consistent with those of normal spiral galaxies with similar mass.