Selection of Homework Questions

   

Topic 3: Catalogs and Global Parameters

(a) Construct a single table which allows you to compare the following for RC3 and RSA :

• morphological type,   (unpack the RC3 morphology code into the normal form using the table on p15).
• luminosity class,
• total blue magnitude,
• galactic absorption,
• internal absorption,
• corrected total blue magnitude (note that in RC3 this is the weighted mean of the corrected values for B_T and m_B (the photoelectric and photographic magnitudes),
• heliocentric velocity,   (for RC3, take weighted mean of 21cm and optical values).
Write a brief summary of any significant differences between the RSA and RC3 listings and explain them as best you can.

Galaxies : NGC 976, 1097, 1433, 3900, 5074, 5548, 7371.

(b) Magnitude corrections : For NGC 976 verify that the entries in RC3 for galactic, internal, and K corrections are as described in the introduction. For galactic you can look up the E(B-V) value using the link given in Topic 3.7c.

(c) HI and M/L values : For NGC 1097 use the HI data (m₂₁) to evaluate the M_HI/L_B ratio for the galaxy, in solar units (ie M/L_B,). You will need to find out how to convert m₂₁ to an HI mass, and you need to know the sun's absolute blue magnitude M_B, = 5.48. Note : DONT use equation 78 in RC3, which is incorrect.

Using a simple Keplerian approach, use the HI linewidth and D₂₅ to calculate the galaxy Mass, and hence a global M/L_B ratio, again in solar units. Dont forget to correct the 21cm linewidth for inclination.

(2) Web Data Bases.

(a) For NGC 976 access an image of size 10 x 10 arcmin from the Digital Sky Survey (DSS --- use the web link from Topic 2 notes). Compare the images from the First Generation, the Second Red and the Second Blue surveys, and briefly summarize the differences. Make a grey scale plot from the Second Generation Blue image, as well as a finding chart for this galaxy (a line image with star positions and the galaxy position marked -- use "skyplot" found within NED).

(b) Also for NGC 976, use "SkyView" to generate images of the same region taken from the VLA NVSS survey and the 2MASS J survey. Modify the B/W lookup table so the fainter objects are visible, and make prints of each (by downloading a GIF). Now start up and become familiar with "Aladin" (probably using the Java Applet interface). Bring in the POSS-II image as well as a 2MASS image. Generate a data plane from the NED catalogs, and data plane of HST observations (using the Mission Logs). Gather the basic information on the sources in the lower window. If you are using the Java Applet you wont be able to download any information --- so just "snap" an image from the screen (using the SUN snap tool) and print this out. Now access the HST observations of Bill Sparkes (NIC3 images) and print one out.

(3) General Web Resources.

For NGC 5074 use the web to find out as much as you can about it and write up, in bullet style, your findings. You should target catalogs, multiwaveband data and literature studies. Start with the sites given in the Topic 3 notes, and be sure to include SIMBAD in your search.

(4) Exploring the SDSS database.

An exercise that helps you become familiar with the Sloan Digital Sky Survey database can be found here (this is a pdf file). Associated with this exercise, are two papers you may find useful: Richards et al 2002 ( here, 1.9Mb pdf file) and Veilleux and Osterbrock 1987 ( here, 5.3Mb pdf file).