Querying CosmoDC2 Mock v1 catalogs

This tutorial demonstrates how to access the CosmoDC2 Mock V1 catalogs. More information about these catalogs can be found here: https://irsa.ipac.caltech.edu/Missions/cosmodc2.html

These catalogs can be accessed through IRSA’s Virtual Ovservatory Table Access Protocol (TAP) service. See https://www.ivoa.net/documents/TAP/ for details on the protocol. This service can be accessed through Python using the PyVO library.

# Uncomment the next line to install dependencies if needed.
# !pip install numpy matplotlib pyvo

import pyvo as vo

service = vo.dal.TAPService("https://irsa.ipac.caltech.edu/TAP")

List the available DC2 tables¶

tables = service.tables
for tablename in tables.keys():
    if not "tap_schema" in tablename:
        if "dc2" in tablename:
            tables[tablename].describe()

Choose the DC2 catalog you want to work with.¶

IRSA currently offers 3 versions of the DC2 catalog.

• cosmodc2mockv1_new has been optimized to make searches with constraints on stellar mass and redshift fast.

• cosmodc2mockv1 has been optimized to make searches with spatial constraints fast.

• cosmodc2mockv1_heavy is the same as cosmodc2mockv1_new, except that it does not contain galaxies with stellar masses <= 10^7 solar masses.

If you are new to the DC2 catalog, we recommend that you start with cosmodc2mockv1_heavy

# Choose the abridged table to start with.
# Queries should be faster on smaller tables.

tablename = 'cosmodc2mockv1_heavy'

How many rows are in the chosen table?¶

With TAP, you can query catalogs with constraints specified in IVOA Astronomical Data Query Language (ADQL; https://www.ivoa.net/documents/latest/ADQL.html), which is based on SQL.

# For example, this snippet of ADQL counts the number of elements in
# the redshift column of the table we chose.
adql = f"SELECT count(redshift) FROM {tablename}"
adql

# In order to use TAP with this ADQL string using pyvo, you can do the following:
result = service.run_async(adql)
result

The above query shows that there are 597,488,849 redshifts in this table. Running count on an entire table is an expensive operation, therefore we ran it asynchronously to avoid any potential timeout issues. To learn more about synchronous versus asynchronous PyVO queries please read the relevant PyVO documentation.

What is the default maximum number of rows returned by the service?¶

This service will return a maximum of 2 billion rows by default.

service.maxrec

This default maximum can be changed, and there is no hard upper limit to what it can be changed to.

print(service.hardlimit)

List the columns in the chosen table¶

This table contains 301 columns.

columns = tables[tablename].columns
print(len(columns))

Let’s learn a bit more about them.

for col in columns:
    print(f'{f"{col.name}":30s}  {col.description}')

Create a histogram of redshifts¶

Let’s figure out what redshift range these galaxies cover. Since we found out above that it’s a large catalog, we can start with a spatial search over a small area of 0.1 deg. The ADQL that is needed for the spatial constraint is:

adql = f"SELECT redshift FROM {tablename} WHERE CONTAINS(POINT('ICRS', RAMean, DecMean), CIRCLE('ICRS',54.218205903,-37.497959343,.1))=1"
adql

Now we can use the previously-defined service to execute the query with the spatial contraint.

cone_results = service.run_sync(adql)

# Plot a histogram
import numpy as np
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt

num_bins = 20
# the histogram of the data
n, bins, patches = plt.hist(cone_results['redshift'], num_bins,
                            facecolor='blue', alpha = 0.5)
plt.xlabel('Redshift')
plt.ylabel('Number')
plt.title('Redshift Histogram CosmoDC2 Mock Catalog V1 abridged')

We can easily see form this plot that the simulated galaxies go out to z = 3.

Visualize galaxy colors at z ~ 0.5¶

Now let’s visualize the galaxy main sequence at z = 2.0. First, we’ll do a narrow redshift cut with no spatial constraint.

Let’s do it as an asynchronous search since this might take awhile, too.

service = vo.dal.TAPService("https://irsa.ipac.caltech.edu/TAP")
adql = f"SELECT Mag_true_r_sdss_z0, Mag_true_g_sdss_z0, redshift FROM {tablename} WHERE redshift > 0.5 and redshift < 0.54"
results = service.run_async(adql)

len(results['mag_true_r_sdss_z0'])

# Since this results in almost 4 million galaxies,
# we will construct a 2D histogram rather than a scatter plot.
plt.hist2d(results['mag_true_r_sdss_z0'], results['mag_true_g_sdss_z0']-results['mag_true_r_sdss_z0'],
           bins=200, cmap='plasma', cmax=500)

# Plot a colorbar with label.
cb = plt.colorbar()
cb.set_label('Number')

# Add title and labels to plot.
plt.xlabel('SDSS Mag r')
plt.ylabel('SDSS rest-frame g-r color')

# Show the plot.
plt.show()

About this notebook¶

Author: Vandana Desai (IRSA Science Lead)

Updated: 2024-07-24

Contact: the IRSA Helpdesk with questions or reporting problems.