{ "metadata": { "name": "", "signature": "sha256:933ba4e9ab345a1c546b1df304758fc01ab8f2b29cfc1f0fccfea3fb6f5f547c" }, "nbformat": 3, "nbformat_minor": 0, "worksheets": [ { "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# Selecting Galaxies from SDSS" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "We need about 10,000 galaxies from SDSS, in a narrow redshift range around z = 0.1, to match with our halos. \n", "We can grab this data from the SDSS skyserver SQL server from python, using the `mechanize` web browser, and then manipulate the catalog with `pandas`." ] }, { "cell_type": "code", "collapsed": false, "input": [ "# Querying skyserver, using code from Eduardo Martin's blog post at\n", "# http://balbuceosastropy.blogspot.com/2013/10/an-easy-way-to-make-sql-queries-from.html\n", "\n", "import pandas as pd\n", "\n", "def SDSS_select(sql):\n", " from StringIO import StringIO # To read a string like a file\n", " import mechanize\n", " url = \"http://skyserver.sdss3.org/dr10/en/tools/search/sql.aspx\"\n", " br = mechanize.Browser()\n", " br.open(url)\n", " br.select_form(name=\"sql\")\n", " br['cmd'] = sql\n", " br['format']=['csv']\n", " response = br.submit()\n", " file_like = StringIO(response.get_data())\n", " return pd.read_csv(file_like, skiprows=1)" ], "language": "python", "metadata": {}, "outputs": [], "prompt_number": 1 }, { "cell_type": "markdown", "metadata": {}, "source": [ "We want a sample of galaxies and their 5-band photometry, plus their redshifts and possibly positions." ] }, { "cell_type": "code", "collapsed": false, "input": [ "galaxies = \"SELECT top 10000 \\\n", "objid, ra, dec, z, \\\n", "dered_u AS mag_u, \\\n", "dered_g AS mag_g, \\\n", "dered_r AS mag_r, \\\n", "dered_i AS mag_i, \\\n", "dered_z AS mag_z \\\n", "FROM SpecPhoto \\\n", "WHERE \\\n", "(class = 'Galaxy')\"\n", "print galaxies" ], "language": "python", "metadata": {}, "outputs": [ { "output_type": "stream", "stream": "stdout", "text": [ "SELECT top 10000 objid, ra, dec, z, dered_u AS mag_u, dered_g AS mag_g, dered_r AS mag_r, dered_i AS mag_i, dered_z AS mag_z FROM SpecPhoto WHERE (class = 'Galaxy')\n" ] } ], "prompt_number": 2 }, { "cell_type": "markdown", "metadata": {}, "source": [ "This SQL checks out at the [SkyServer SQL box](http://skyserver.sdss3.org/dr9/en/tools/search/sql.asp), which has a syntax checking option." ] }, { "cell_type": "code", "collapsed": false, "input": [ "data = SDSS_select(galaxies)\n", "data" ], "language": "python", "metadata": {}, "outputs": [ { "html": [ "
\n", " | objid | \n", "ra | \n", "dec | \n", "z | \n", "mag_u | \n", "mag_g | \n", "mag_r | \n", "mag_i | \n", "mag_z | \n", "
---|---|---|---|---|---|---|---|---|---|
0 | \n", "1237657586562367630 | \n", "43.775040 | \n", "0.413649 | \n", "0.126386 | \n", "21.03417 | \n", "19.34688 | \n", "18.38340 | \n", "17.95347 | \n", "17.66356 | \n", "
1 | \n", "1237663239272989373 | \n", "43.653400 | \n", "0.434200 | \n", "0.547067 | \n", "24.91928 | \n", "22.78911 | \n", "20.91748 | \n", "19.79025 | \n", "19.40255 | \n", "
2 | \n", "1237663239272988917 | \n", "43.668442 | \n", "0.439617 | \n", "0.052173 | \n", "19.85831 | \n", "18.94410 | \n", "18.48233 | \n", "18.25059 | \n", "18.19678 | \n", "
3 | \n", "1237663239273185525 | \n", "43.989582 | \n", "0.599770 | \n", "0.136318 | \n", "21.39913 | \n", "19.34047 | \n", "18.32451 | \n", "17.88236 | \n", "17.55692 | \n", "
4 | \n", "1237678617437012415 | \n", "43.821293 | \n", "0.758974 | \n", "0.073327 | \n", "20.48200 | \n", "19.30610 | \n", "18.76852 | \n", "18.46322 | \n", "18.28343 | \n", "
5 | \n", "1237678617437077917 | \n", "44.007378 | \n", "0.792395 | \n", "0.193352 | \n", "20.12095 | \n", "19.38557 | \n", "18.79778 | \n", "18.46749 | \n", "18.30729 | \n", "
6 | \n", "1237663784216560179 | \n", "43.832413 | \n", "0.107809 | \n", "0.040651 | \n", "20.03710 | \n", "18.94928 | \n", "18.43859 | \n", "18.17211 | \n", "17.99428 | \n", "
7 | \n", "1237663239273185656 | \n", "44.016762 | \n", "0.455286 | \n", "0.188615 | \n", "20.57470 | \n", "19.83936 | \n", "19.31141 | \n", "19.04830 | \n", "19.05104 | \n", "
8 | \n", "1237657586562498655 | \n", "43.969959 | \n", "0.381950 | \n", "0.170142 | \n", "22.31340 | \n", "20.41215 | \n", "19.38978 | \n", "18.88227 | \n", "18.52340 | \n", "
9 | \n", "1237678617437077985 | \n", "43.899548 | \n", "0.718535 | \n", "0.151472 | \n", "20.81523 | \n", "19.50208 | \n", "18.87636 | \n", "18.46378 | \n", "18.29541 | \n", "
10 | \n", "1237663239273185751 | \n", "44.004189 | \n", "0.604719 | \n", "0.066272 | \n", "20.18939 | \n", "19.21815 | \n", "18.56936 | \n", "18.26274 | \n", "18.13155 | \n", "
11 | \n", "1237657587099304470 | \n", "43.902180 | \n", "0.665468 | \n", "0.151065 | \n", "22.01183 | \n", "20.26443 | \n", "19.21065 | \n", "18.89541 | \n", "18.60719 | \n", "
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14 | \n", "1237657586562498772 | \n", "44.025291 | \n", "0.251850 | \n", "0.106721 | \n", "20.36275 | \n", "18.93699 | \n", "18.44948 | \n", "18.15108 | \n", "18.30925 | \n", "
15 | \n", "1237663784216690940 | \n", "44.025455 | \n", "0.111749 | \n", "0.126447 | \n", "21.76604 | \n", "19.85276 | \n", "18.97080 | \n", "18.54132 | \n", "18.27745 | \n", "
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19 | \n", "1237663784216690835 | \n", "44.038860 | \n", "0.183669 | \n", "0.153760 | \n", "20.90098 | \n", "19.10948 | \n", "18.06659 | \n", "17.61707 | \n", "17.35549 | \n", "
20 | \n", "1237663784216690968 | \n", "44.141319 | \n", "0.111346 | \n", "0.358172 | \n", "22.12443 | \n", "20.23563 | \n", "18.48760 | \n", "17.85881 | \n", "17.52025 | \n", "
21 | \n", "1237678617437143893 | \n", "44.123199 | \n", "0.741500 | \n", "0.846062 | \n", "25.07072 | \n", "21.64779 | \n", "20.37119 | \n", "19.24862 | \n", "18.74790 | \n", "
22 | \n", "1237660241384833417 | \n", "44.033955 | \n", "0.593850 | \n", "0.065717 | \n", "21.58032 | \n", "20.13515 | \n", "19.42918 | \n", "19.05468 | \n", "18.82600 | \n", "
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10000 rows \u00d7 9 columns
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