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Home , Galaxy Zoo

IIA Summer School & IGM Hands-on session Instructions

Galaxy Morphology and color magnitude diagram of galaxies

Aim : To query a list of parameters from (SDSS) database and Zoo projects using SQL query and plot the color- magnitude diagram for galaxies.

Probably you are familiar with the Hertzsprung-Russell diagram for stellar classification. We can make a similar "color-magnitude" diagram for galaxies using the photometric data from the SDSS. We can also look at the morphological classification provide by the citizen project Galaxy Zoo. When you plot absolute magnitude (proxy for luminosity) and color (difference between two magnitudes), spirals and ellipticals will occupy different regions of the plot due to their difference in star formation.

The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at in New Mexico, . Details about SDSS : https://www.sdss.org

Galaxy Zoo is a crowdsourced project which invites people to assist in the morphological classification of large numbers of galaxies. It is an example of as it enlists the help of members of the public to help in scientific research Details about Galaxy Zoo : https://www.zooniverse.org/projects/ zookeeper/galaxy-zoo/about/research

SQL stands for Structured Query Language. SQL is a standard programming language specifically designed for storing, retrieving, managing or manipulating the data inside a relational database management system Primer about SQL : https://www.tutorialrepublic.com/sql-tutorial/ Exercise 1: Running an SQL query on SDSS database to generate a with different Galaxy Zoo probabilities for ellipticals, spirals clockwise, spirals anti clockwise, edge on and mergers.

(1) Run the following SQL query on this link http://skyserver.sdss.org/ dr16/en/tools/search/sql.aspx

SELECT top 10 g.objid, zns.nvote, zns.p_el as elliptical, zns.p_cw as spiralclock, zns.p_acw as spiralanticlock, zns.p_edge as edgeon, zns.p_dk as dontknow, zns.p_mg as merger, p.ra, p.dec, p.run, p.rerun, p.camcol, p.field,dbo.fPhotoTypeN(p.type) as type,p.modelMag_u as umag, p.modelMag_g as gmag, p.modelMag_r as rmag, p.modelMag_i as imag, p.modelMag_z as zmag , p.objID, s.z as redshift, pz.absMagU as absMagU, pz.absMagG as absMagG, pz.absMagR as absMagR, pz.absMagI as absMagI, pz.absMagZ as absMagZ

FROM Galaxy as g JOIN ZooNoSpec AS zns ON G.objid = zns.objid JOIN PhotoTag AS p ON G.objid = p.objid JOIN SpecObj s ON s.bestObjID = p.objID JOIN Photoz AS pz ON G.objid = pz.objid WHERE g.clean=1 and zns.nvote >= 10 and zns.p_edge > 0.7

Brief explanation of the commands :

SELECT command selects the top 10 galaxies and outputs the parameters specified after this command in to a table g.objid ….. These parameters are queried.. the usage for queried parameters when you query multiple is to point the parameter to the relevant table..for example g.objid means the objid in the galaxy (g is defined as Galaxy later) table

From command specifies from which table to query from here it is the Galaxy table

JOIN command joins two table based on the specified parameter..here galaxy and galaxy zoo tables are joined based on their objid

Further join multiple tables as we have queried parameters from these tables

WHERE ..these are the constrains on which the output will be generated...here we specify it should have a clean phiotmetry, number of votes in Galaxy zoo must be greater than 10 and the probability for a specific morphology of galaxy to be greater than 0.9..

So this will return a list containing galaxies with edge on probabilities greater than 0.9

(2) Run this query and generate a list of galaxies with probabilities greater than 0.9 for ellipticals, spirals clockwise, spirals anti clockwise, edge on and mergers. Basically you have to change the last change zns.p_edge > 0.9 to zns.p_el > 0.9 if you want to list ellipticals rather than edge ons

(3) Inspect these galaxies in the SDSS sky server page to see their actual morphology.. Inspect these for each class for at least three sources. In the SDSS sky server link, click on “search” on the left sidebar and give the objid in the relevant place and click go http://skyserver.sdss.org/dr16/en/tools/explore/Summary.aspx? Exercise 2: Plot the Galaxy color magnitude Diagram

(1) The SQL query already has relevant commands to query the magnitudes

(2) Run the query to return 100 ellipticals and 100 spirals clockwise. You have to run the query twice; once with zns.p_el >0.9 and another time with zns.p_cw >0.9 To return 100 sources, change SELECT TOP 10 to SELECT TOP 100

(3) The required parameters are g - r color and absolute R magnitude. For g-r color, the SQL returned table has parameters gmag,rmag and compute their difference. Also, absMagR is included

(4) Read/Import the above two files in your favourite plotting software, python matplotlib, gnuplot, Microsoft excel etc.

(5) Plot the absMagR vs g-r to generate the Galaxy color-magnitude diagram. Notice that spirals and ellipticals are distributed separately in this diagram Two versions of CMD are shown below Left : absMagR vs (absMagU- absMagR) Right : absMagR vs (g-r) Caveats : No exactly similar to the CMD in the literature as this is not a homogeneous sample, no dust correction applied, SDSS photometry for low redshift galaxies has some issues

Things you can explore: (1) Explore different CMDs using different choice of color and absMag (2) Increase the number of sources and see whether it has any implications (3) Include both clockwise and anti clockwise spirals

For any queries/difficulties regarding this exercise, contact the following people who will be available online during the hands-on session Vivek, Mousumi, Indrani, Sujay, Ankit