High resolution NaI and CaII absorption observations towards M13, M15 and M33

TL;DR

This study uses high-resolution interstellar absorption line measurements towards stars in M13, M15, and M33 to analyze the kinematics and physical conditions of gas clouds, revealing multiple IVCs and HVCs with detailed velocity structures.

Contribution

The paper provides detailed high-resolution profiles of NaI and CaII lines towards multiple sight-lines, identifying and characterizing various intermediate and high velocity clouds in the Milky Way and M33.

Findings

Identification of 4 IVC components towards M13 with T=1000 K.

Detection of complex velocity structure in IVCs towards M15.

Discovery of multiple cloud components in M33, including potential HVCs.

Abstract

We present high resolution (R = 60,000) measurements of the NaI D1 and D2 (5890 A) and CaII K (3933 A) interstellar absorption line profiles recorded towards several post-AGB stars located within the M13 and M15 globular clusters, supplemented with a lower resolution spectrum of the CaII K-line observed in absorption towards an Ofpe/WN9 star in the central region of the M33 galaxy. The normalized interstellar absorption profiles have been fit with cloud component velocities, doppler widths and column densities in order to investigate the kinematics and physical conditions of the neutral and partially ionized gas observed along each sight-line. Our CaII observations towards M13 have revealed 4 absorption components that can be identified with galactic Intermediate Velocity Clouds (IVCs) spanning the -50 > Vlsr > -80 km/s range. The NaI/CaII ratio for these IVC's is<0.3, which characterizes the gas as being warm (T=1000 K) and partially ionized. Similar observations towards two stars within M15 have revealed absorption due to a galactic IVC at Vlsr=+65 km/s. This IVC is revealed to have considerable velocity structure, requiring at least 3 cloud components to fit the observed NaI and CaII profiles. CaII K-line observations of a sight-line towards the center of the M33 galaxy have revealed at least 10 cloud components. A cloud at Vlsr=-130 km/s is either an IVC associated with the M33 galaxy occurring at +45 km/s with respect to the M33 local standard of rest, or it is a newly discovered HVC associated with our own Galaxy. In addition, 4 clouds have been discovered in the -165 > Vlsr > -205 km/s range. Three of these clouds are identified with the disk gas of M33, whereas a component at - 203 km/s could be IVC gas in the surrounding halo of M33.