Catalog of Interstellar HI Shells Discovered in the SETHI Database

Shauna Sallmen¹, Eric J. Korpela², Brooke B. Bellehumeur^1,3, Elizabeth M. Tennyson^1,4, Kurt Grunwald¹, Cheuk Man Lo^1,5

SETHI Data

Both the raw SETHI data cubes and the larger cubes used for this search are available

Acknowledgement: If your use of these data leads to a publication, please cite Sallmen, S.M. et al. 2015, AJ, 149, 189

• SETHI survey parameters:
  • Sky Coverage: 7.2^o < Declination < 29.7^o
  • Angular resolution: 0.1^o
  • Spectral resolution: 0.25 km/s.
  • Sensitivity: 0.25 K
• Raw data cubes: (produced by Kevin Douglas)
  • 7.68^o x 7.68^o x 410 km/s.
  • Pixels: 0.03^o = 1.8 arcmin and 0.26 km/s
  • Naming convention: sethi_raHH.H_decDD.D.fits identifies center of maps in RA decimal hours and Declination decimal degrees
• Larger data cubes used in search:
  • 22.5^o x 22.5^o x 410 km/s.
  • Pixels: 0.03^o = 1.8 arcmin and 1.55 km/s
  • Naming convention: RAhh.hDdd.d.fits identifies center of maps in RA decimal hours and Declination decimal degrees

Tables

• Note: In all tables, click on the Shell ID to go to a page containing detailed information on each shell.

Contains basic parameters for the 74 shells currently in the catalog

Contains the following columns:

• Shell ID: GSHlll+bb+vvv
  • (lll,bb are Galactic coordinates of shell center at velocity vvv)
  • Click on Shell ID for detailed info on each shell
• RA (hh mm), Dec (deg): Equatorial coordinates of shell center
• V_ref: LSR Velocity at which feature is most "shell-like"
• ∆RA (hh mm), ∆Dec (deg): Angular extent of shell at reference velocity
• V₁ and V₂: Min / Max velocities at which object appears "shell-like"
• ∆Θ (deg): Mean Angular Diameter of shell at reference velocity
• Shape parameter s: Based on major / minor axis measurements (0 for a line, 1 for circular object)
• Quality parameter Q: Based on
  • Fragmentation of shell walls (undesirable)
  • consistency and persistence of shell-like feature across velocity range (desirable)
  • regularity of shape (desirable)
• Expansion Quality Parameter Q_exp: Higher if
  • Shell smaller towards velocity extremes, larger near central velocity
  • Signs of foreground / background walls at velocity slices outside "shell-like" range
  • Signs of expansion in position-velocity space
• Flag: An asterisk (*) in this column indicates the presence of a comment about the shell on its individual website.

Table of Kinematic Distances (Download .csv)

Contains Kinematic Distances for 27 shells with |b| < 15 degrees, using rotation curve of Brand & Blitz (1993)

Contains the following columns:

• Shell ID: GSHlll+bb+vvv
• Galactic Coordinates l & b in degrees
• D_ref, D_min, D_max (kpc)
  • Kinematic Distances corresponding to reference velocity, with lower and upper limits based on velocity range at which object appears "shell-like"
• S_ref, S_min, S_max (pc)
  • Sizes derived from mean angular diameter and kinematic distance estimates
• D_ref2, D_min2, D_max2 (kpc) and S_ref2, S_min2, S_max2 (pc)
  • Second distance / size option for inner galaxy
• Dashes for a value indicate that no solution could be found for it.
• Comment: Key code for comments regarding kinematic distances. Key is at the bottom of the table. Unless otherwise specified, the shells are clearly associated with Galactic plane gas, so the kinematic distances should be relatively reliable.

Table of Expansion Velocities (Download .csv)

Contains Expansion Velocity estimates for 12 shells with Q_exp ≥ 4.0

Contains the following columns:

• Shell ID: GSHlll+bb+vvv
• Expansion Quality parameter Q_exp
• Velocities of front (V_f) and rear (V_b) walls (km/s), where possible
• Estimated Expansion velocity (km/s):
  • V_exp = (V_b - V_b)/2
• V₁ and V₂: Min / Max velocities at which object appears "shell-like", for comparison with V_f and V_b
• Lower limit on expansion velocity (km/s):
  • V_exp > (V_b - V₁)/2 or
  • V_exp > (V₂ - V_f)/2
• Comment: Key code for comments regarding expansion velocities. Key is at the bottom of the table.

Table of Derived Shell Properties (Download .csv)

Contains upper limits on age and estimated energies for shells with measurements of expansion velocity and/or physical size.

Contains the following columns:

• Shell ID: GSHlll+bb+vvv
• Age upper limit(s) t₁ and t₂ (Myr):
  • Based on expansion velocity and physical diameter(s)
• Estimated Thermal Energies E₁ and E₂ (erg):
  • Calculated for Pressure P/k = 3000 cm^-3 K
• Estimated Kinetic Energies E_K1 and E_K2 (erg):
  • Mass estimated from that initially enclosed in shell volume, assuming constant density and calculated for n_H = 1 atom / cm³
• Estimated Total Energies E_Ch1 and E_Ch2 (erg):
  • Calculated using Chevalier's (1974) formula, assuming n_H = 1 atom / cm³

Table of Shell Axes and Position Angles (Download .csv)

Contains estimates of shell axes and position angle of major axis

Contains the following columns:

• Shell ID: GSHlll+bb+vvv
• Semi-major and Semi-minor axes a and b in degrees.
• Position angle (ϕ) of major axis, measured in degrees counterclockwise from Galactic Plane